Linear Technology LTC2983 User Manual

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Page 1

Multi-Sensor High Accuracy

Digital Temperature

Measurement System

FEATURES DESCRIPTION

Directly Digitize RTDs, Thermocouples, Thermistors and Diodes

Single 2.85V to 5.25V Supply

Results Reported in °C or °F

20 Flexible Inputs Allow Interchanging Sensors

Automatic Thermocouple Cold Junction Compensation

Built-In Standard and User-Programmable Coefficients for Thermocouples, RTDs and Thermistors

Configurable 2-, 3- or 4-Wire RTD Configurations

Measures Negative Thermocouple Voltages

Automatic Burn Out, Short-Circuit and Fault Detection

Buffered Inputs Allow External Protection

Simultaneous 50Hz/60Hz Rejection

Includes 15ppm/°C (Max) Reference (I-Grade)

APPLICATIONS

Direct Thermocouple Measurements

Direct RTD Measurements

Direct Thermistor Measurements

Custom Sensor Applications

The LT C®2983 measures a wide variety of temperature sensors and digitally outputs the result, in °C or °F, with

0.1°C accuracy and 0.001°C resolution. The LTC2983 can measure the temperature of virtually all standard (type B, E, J, K, N, S, R, T) or custom thermocouples, automatically compensate for cold junction temperatures and linearize the results. The device can also measure temperature with standard 2-, 3- or 4-wire RTDs, thermistors and diodes. It has 20 reconfigurable analog inputs enabling many sensor connections and configuration options. The LTC2983 includes excitation current sources and fault detection circuitry appropriate for each type of temperature sensor.

The LTC2983 allows direct interfacing to ground referenced sensors without the need for level shifters, negative supply voltages, or external amplifiers. All signals are buffered and simultaneously digitized with three high accuracy, 24-bit ∆∑ ADCs, driven by an internal 15ppm/°C (maximum) reference.

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Patents Pending

LTC2983

TYPICAL APPLICATION

Thermocouple Measurement with Automatic Cold Junction Compensation

2.85V TO 5.25V

0.1µF

SENSE

PT-100 RTD

REF

24-BIT

∆∑ ADC

24-BIT

∆∑ ADC

24-BIT

∆∑ ADC

(10ppm/°C)

FAULT DETECTION

LTC2983

LINEARIZATION/

INTERFACE

2983 TA01a

SPI

°C/°F

Typical Temperature Error Contribution

0.5

0.4

0.3

0.2

0.1

–0.1

ERROR (°C)

–0.2

–0.3

–0.4

–0.5

–200

THERMISTOR

3904 DIODE

200

TEMPERATURE (°C)

400

THERMOCOUPLE

RTD

600

800

1000

2983 TA01b

14001200

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For more information www.linear.com/LTC2983

Page 2

LTC2983

TABLE OF CONTENTS

Features ............................................................................................................................ 1

Applications Typical Application

Description......................................................................................................................... 1

Absolute Maximum Ratings Order Information Complete System Electrical Characteristics Pin Configuration ADC Electrical Characteristics Reference Electrical Characteristics Digital Inputs and Digital Outputs Typical Performance Characteristics Pin Functions Block Diagram Test Circuits Timing Diagram Overview Applications Information

Thermocouple Measurements Diode Measurements RTD Measurements Thermistor Measurements Direct ADC Measurements

Supplemental Information

Fault Protection and Anti-Aliasing 2- and 3-Cycle Conversion Modes Running Conversions Consecutively on Multiple Channels MUX Configuration Delay Global Configuration Register

Custom Thermocouples Custom RTDs Custom Thermistors Package Description Revision History Typical Application Related Parts

....................................................................................................................... 1

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..................................................................................................................... 72

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For more information www.linear.com/LTC2983

Page 3

(Notes 1, 2)

Supply Voltage (VDD) ................................... –0.3V to 6V

Analog Input Pins (CH1 to CH20, COM) Input Current (CH1 to CH20, COM)

................................. –0.3V to (VDD + 0.3V)

...................... ±15mA

Digital Inputs (CS, SDI, SCK, RESET) Digital Outputs (SDO, INTERRUPT)

........................................................ –0.3V to 2.8V

REFP

, Q2, Q3, LDO, V

Reference Short-Circuit Duration

................................ –0.3V to (VDD + 0.3V)

–0.3V to (VDD + 0.3V)

REFOUT

, V

REF_BVP

(Note 17)

..................... Indefinite

Operating Temperature Range

LTC2983C .................................................0ºC to 70ºC

LTC2983I ............................................. –40ºC to 85ºC

LTC2983H ...........................................–40ºC to 125ºC

LTC2983

PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS

TOP VIEW

REF_BYP

GND

VDDGND

CH17

CH18

CH19

VDDGND

COM

CH20

GND

LDO

RESET

SDI

SDO

SCK

INTERRUPT

REFOUT

REFP

GND

CH1 CH2 CH3 CH4 CH5 CH6 CH7 CH8 CH9

12111098765432

13 14 15 16 17 18 19 20 21 22 23 24

2526272829303132333435

CH10

CH11

CH12

CH13

CH14

48-LEAD (7mm × 7mm) PLASTIC LQFP

LX PACKAGE

= 150°C, θJA = 57°C/W

JMAX

CH15

CH16

ORDER INFORMATION

LEAD FREE FINISH TRAY PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LTC2983CLX#PBF LTC2983CLX#PBF LTC2983LX 48-Lead (7mm × 7mm) LQFP 0°C to 70°C LTC2983ILX#PBF LTC2983ILX#PBF LTC2983LX 48-Lead (7mm × 7mm) LQFP –40°C to 85°C LTC2983HLX#PBF LTC2983HLX#PBF LTC2983LX 48-Lead (7mm × 7mm) LQFP –40°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/

COMPLETE SYSTEM ELECTRICAL CHARACTERISTICS

The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.

PARAMETER CONDITIONS MIN TYP MAX UNITS

Supply Voltage Supply Current Sleep Current Input Range All Analog Input Channels Output Rate Two Conversion Cycle Mode (Notes 6, 9) Output Rate Three Conversion Cycle Mode (Notes 6, 9) Input Common Mode Rejection 50Hz/60Hz (Note 4) Input Normal Mode Rejection 60Hz (Notes 4, 7)

2.85 5.25 V

–0.05 VDD – 0.3 V

150 164 170 ms

225 246 255 ms

120 dB

15 20 mA 25 60 µA

For more information www.linear.com/LTC2983

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LTC2983

COMPLETE SYSTEM ELECTRICAL CHARACTERISTICS

The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.

PARAMETER CONDITIONS MIN TYP MAX UNITS

Input Normal Mode Rejection 50Hz (Notes 4, 8) Input Normal Mode Rejection 50Hz/60Hz (Notes 4, 6, 9) Power-On Reset Threshold 2.25 V Analog Power-Up (Note 11) Digital Initialization (Note 12)

The l denotes the specifications which apply over the full

ADC ELECTRICAL CHARACTERISTICS

operating temperature range, otherwise specifications are at TA = 25°C.

PARAMETER CONDITIONS MIN TYP MAX UNITS

≤ V

Resolution (No Missing Codes) –F Integral Nonlinearity V Offset Error Offset Error Drift (Note 4) Positive Full-Scale Error (Notes 3, 15) Positive Full-Scale Drift (Notes 3, 15) Input Leakage (Note 18)

H-Grade Negative Full-Scale Error (Notes 3, 15) Negative Full-Scale Drift (Notes 3, 15) Input Referred Noise (Note 5)

H-Grade Common Mode Input Range RTD Excitation Current (Note 16) RTD Excitation Current Matching Continuously Calibrated Thermistor Excitation Current (Note 16)

≤ + F

= 1.25V (Note 15)

IN(CM)

120 dB

75 dB

24 Bits

l l

–0.05 VDD – 0.3 V

–25 Table 30 25 %

Error within Noise Level of ADC

–37.5 Table 53 37.5 %

2 30 ppm of V

0.5 2 µV 10 20 nV/°C

0.1 0.5 ppm of V

0.8 1.5

100 ms 100 ms

100 ppm of V

2.0

REF

µV µV

REF

/°C

nA nA

REF

/°C

RMS RMS

REFERENCE ELECTRICAL CHARACTERISTICS

The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.

PARAMETER CONDITIONS MIN TYP MAX UNITS

Output Voltage V Output Voltage Temperature Coefficient I-Grade, H-Grade Output Voltage Temperature Coefficient C-Grade Line Regulation Load Regulation I

Output Voltage Noise 0.1Hz ≤ f ≤ 10Hz 4 µV

10Hz ≤ f ≤ 1kHz 4.5 µV

Output Short-Circuit Current Short V

Short V Turn-On Time 0.1% Setting, C Long Term Drift of Output Voltage (Note 13) 60 ppm/√khr Hysteresis (Note 14) ∆T = 0°C to 70°C

∆T = –40°C to 85°C

(Note 10) 2.49 2.51 V

REFOUT

OUT(SOURCE)

OUT(SINK)

= 100µA

REFOUT

= 100µA

to GND 40 mA to V

= 1µF 115 µs

LOAD

3 15 ppm/°C 3 20 ppm/°C

10 ppm/V

5 mV/mA 5 mV/mA

30 mA

30 70

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P-P

ppm ppm

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LTC2983

The l denotes the specifications which apply over the

DIGITAL INPUTS AND DIGITAL OUTPUTS

full operating temperature range, otherwise specifications are at TA = 25°C.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

External SCK Frequency Range External SCK LOW Period External SCK HIGH Period

CS↓ to SDO Valid CS↑ to SDO Hi-Z CS↓ to SCK↑

SCK↓ to SDO Valid SDO Hold After SCK↓ SDI Setup Before SCK↑ SDI HOLD After SCK↑ High Level Input Voltage CS, SDI, SCK, RESET Low Level Input Voltage CS, SDI, SCK, RESET Digital Input Current CS, SDI, SCK, RESET

Digital Input Capacitance CS, SDI, SCK, RESET 10 pF LOW Level Output Voltage (SDO, INTERRUPT) I High Level Output Voltage (SDO, INTERRUPT) I Hi-Z Output Leakage (SDO)

= –800µA

= 1.6mA

0 2 MHz 250 ns 250 ns

0 200 ns

0 200 ns 100 ns

225 ns

10 ns 100 ns 100 ns

VDD – 0.5 V

0.5 V

–10 10 µA

0.4 V

VDD – 0.5 V

–10 10 µA

Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime.

Note 2: All voltage values are with respect to GND. Note 3: Full scale ADC error. Measurements do not include reference error. Note 4: Guaranteed by design, not subject to test. Note 5: The input referred noise includes the contribution of internal

calibration operations.

Note 6: MUX configuration delay = default 1ms Note 7: Global configuration set to 60Hz rejection. Note 8: Global configuration set to 50Hz rejection. Note 9: Global configuration default 50Hz/60Hz rejection. Note 10: The exact value of V

is stored in the LTC2983 and used

REF

for all measurement calculations. Temperature coefficient is measured by dividing the maximum change in output voltage by the specified temperature range.

Note 11:

Analog power-up. Command status register inaccessible during

this time.

Note 12:

Digital initialization. Begins at the conclusion of Analog Power-

Up. Command status register is 0 × 80 at the beginning of digital initialization and 0 × 40 at the conclusion.

Note 13:

Long-term stability typically has a logarithmic characteristic and therefore, changes after 1000 hours tend to be much smaller than before that time. Total drift in the second thousand hours is normally less

than one third that of the first thousand hours with a continuing trend toward reduced drift with time. Long-term stability will also be affected by differential stresses between the IC and the board material created during board assembly.

Note 14:

Hysteresis in output voltage is created by package stress that differs depending on whether the IC was previously at a higher or lower temperature. Output voltage is always measured at 25°C, but the IC is cycled to the hot or cold temperature limit before successive measurements. Hysteresis measures the maximum output change for the averages of three hot or cold temperature cycles. For instruments that are stored at well controlled temperatures (within 20 or 30 degrees of operational temperature), it is usually not a dominant error source. Typical hysteresis is the worst-case of 25°C to cold to 25°C or 25°C to hot to 25°C, preconditioned by one thermal cycle.

Note 15:

Differential Input Range is ±V

Note 16:

RTD and thermistor measurements are made ratiometrically. As a

REF

/2.

result current source excitation variation does not affect absolute accuracy. Choose an excitation current such that largest sensor or R

SENSE

resistance value, when driven by the nominal excitation current, will drop 1V or less. The extended ADC input range will accommodate variation in excitation current and the ratiometric calculation will negate the absolute value of the excitation current.

Note 17: Do not apply voltage or current sources to these pins. They must be connected to capacitive loads only, otherwise permanent damage may occur.

Note 18: Input leakage measured with V

= –10mV and VIN = 2.5V.

For more information www.linear.com/LTC2983

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LTC2983

2983 G01

2983 G02

2983 G03

2983 G07

2983 G08

2983 G09

TYPICAL PERFORMANCE CHARACTERISTICS

Type J Thermocouple Error and RMS Noise vs Temperature

1.0

0.8

0.6

0.4

0.2

–0.2

–0.4

ERROR/RMS NOISE (°C)

–0.6

–0.8

–1.0

–400 800 1200 16004000

THERMOCOUPLE TEMPERATURE (°C)

Type R Thermocouple Error and RMS Noise vs Temperature

1.0

0.8

0.6

0.4

0.2

–0.2

–0.4

ERROR/RMS NOISE (°C)

–0.6

–0.8

–1.0

–400 800 1200 1600 20004000

THERMOCOUPLE TEMPERATURE (°C)

RMS NOISE ERROR

2983 G04

Type K Thermocouple Error and RMS Noise vs Temperature

1.0

0.8

0.6

0.4

0.2

–0.2

–0.4

ERROR/RMS NOISE (°C)

–0.6

–0.8

–1.0

–400 800 1200 16004000

THERMOCOUPLE TEMPERATURE (°C)

Type S Thermocouple Error and RMS Noise vs Temperature

1.0

0.8

0.6

0.4

0.2

–0.2

–0.4

ERROR/RMS NOISE (°C)

–0.6

–0.8

–1.0

–400 800 1200 1600 20004000

THERMOCOUPLE TEMPERATURE (°C)

RMS NOISE ERROR

2983 G05

Type N Thermocouple Error and RMS Noise vs Temperature

1.0

0.8

0.6

0.4

0.2

–0.2

–0.4

ERROR/RMS NOISE (°C)

–0.6

–0.8

–1.0

–400 800 1200 16004000

THERMOCOUPLE TEMPERATURE (°C)

Type T Thermocouple Error and RMS Noise vs Temperature

1.0

0.8

0.6

0.4

0.2

–0.2

–0.4

ERROR/RMS NOISE (°C)

–0.6

–0.8

–1.0

–400 200 400 6000–200

THERMOCOUPLE TEMPERATURE (°C)

RMS NOISE ERROR

2983 G06

Type E Thermocouple Error and RMS Noise vs Temperature

1.0

0.8

0.6

0.4

0.2

–0.2

–0.4

ERROR/RMS NOISE (°C)

–0.6

–0.8

–1.0

–400 400 800 12000

THERMOCOUPLE TEMPERATURE (°C)

RMS NOISE ERROR

Type B Thermocouple Error and RMS Noise vs Temperature

1.0

0.8

0.6

0.4

0.2

–0.2

–0.4

ERROR/RMS NOISE (°C)

–0.6

–0.8

–1.0

400 1200 1600 2000800

THERMOCOUPLE TEMPERATURE (°C)

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RMS NOISE ERROR

RTD PT-1000 Error and RMS Noise vs Temperature

1.0

0.8

0.6

0.4

0.2

–0.2

–0.4

ERROR/RMS NOISE (°C)

–0.6

–0.8

–1.0

–400 400 8000

RTD TEMPERATURE (°C)

RMS NOISE ERROR

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TYPICAL PERFORMANCE CHARACTERISTICS

LTC2983

RTD PT-200 Error and RMS Noise vs Temperature

1.0

0.8

0.6

0.4

0.2

–0.2

–0.4

ERROR/RMS NOISE (°C)

–0.6

–0.8

–1.0

–400 400 8000

RTD TEMPERATURE (°C)

RMS NOISE ERROR

2.252k Thermistor Error vs Temperature

1.0

0.8

0.6

0.4

0.2

–0.2

ERROR (°C)

–0.4

–0.6

–0.8

–1.0

–40 0–20 20 80 1006040 120 140

THERMISTOR TEMPERATURE (°C)

2983 G10

2983 G19

RTD PT-100 Error and RMS Noise vs Temperature

1.0

0.8

0.6

0.4

0.2

–0.2

–0.4

ERROR/RMS NOISE (°C)

–0.6

–0.8

–1.0

–400 0 200 400 600 800 1000–200

RTD TEMPERATURE (°C)

RMS NOISE ERROR

3k Thermistor Error vs Temperature

1.0

0.8

0.6

0.4

0.2

–0.2

ERROR (°C)

–0.4

–0.6

–0.8

–1.0

–40 0–20 20 80 1006040 120 140

THERMISTOR TEMPERATURE (°C)

2983 G11

2983 G20

RTD NI-120 RTD Error and RMS Noise vs Temperature

1.0

0.8

0.6

0.4

0.2

–0.2

–0.4

ERROR/RMS NOISE (°C)

–0.6

–0.8

–1.0

–100 0 100 200 300

RTD TEMPERATURE (°C)

RMS NOISE ERROR

5k Thermistor Error vs Temperature

1.0

0.8

0.6

0.4

0.2

–0.2

ERROR (°C)

–0.4

–0.6

–0.8

–1.0

–40 0–20 20 80 1006040 120 140

THERMISTOR TEMPERATURE (°C)

2983 G12

2983 G21

10k Thermistor Error vs Temperature

1.0

0.8

0.6

0.4

0.2

–0.2

ERROR (°C)

–0.4

–0.6

–0.8

–1.0

–40 0–20 20 80 1006040 120 140

THERMISTOR TEMPERATURE (°C)

2983 G22

30k Thermistor Error vs Temperature

1.0

0.8

0.6

0.4

0.2

–0.2

ERROR (°C)

–0.4

–0.6

–0.8

–1.0

–40 0–20 20 80 1006040 120 140

THERMISTOR TEMPERATURE (°C)

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2983 G23

YSI-400 Thermistor Error vs Temperature

1.0

0.8

0.6

0.4

0.2

–0.2

ERROR (°C)

–0.4

–0.6

–0.8

–1.0

–40 0–20 20 80 1006040 120 140

THERMISTOR TEMPERATURE (°C)

2983 G24

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LTC2983

2983 G26

2983 G16

TEMPERATURE (°C)

–50

–30

–101030507090110

130

2.4995

2.49975

2.5

2.50025

2.5005

REFOUT

2983 G28

125°C

90°C

25°C

–45°C

INPUT VOLTAGE (V)

–101234560

0.2

0.4

0.6

0.8

1.0

1.2

1.4

INPUT LEAKAGE (nA)

Temperature

2983 G18

TYPICAL PERFORMANCE CHARACTERISTICS

Diode Error and Repeatability vs Temperature

1.0

0.8

0.6

0.4

0.2

–0.2

ERROR (°C)

–0.4

–0.6

–0.8

–1.0

–40 20 80 140

(µA)

SLEEP

–50 –25 50 75250 100 125

DIODE TEMPERATURE (°C)

vs Temperature

SLEEP

VDD = 5.25V

= 4.1V

= 2.85V

LTC2983 TEMPERATURE (°C)

2983 G27

2983 G15

Offset vs Temperature Noise vs Temperature

2.0

1.5

1.0

0.5

OFFSET (µV)

–0.5

–1.0

–1.5

–2.0

–50 –25 50 75250 100 125

LTC2983 TEMPERATURE (°C)

VDD = 5.25V V

One Shot Conversion Current vs Temperature V

16.0

15.8

15.6

15.4

15.2

(mA)

15.0

IDLE

14.8

14.6

14.4

14.2

–50 50250–25 10075 125

VDD = 5.25V

= 4.1V

= 2.85V

LTC2983 TEMPERATURE (°C)

= 4.1V = 2.85V

2983 G13

1.2

1.0

)

0.8

RMS

0.6

NOISE (µV

0.4

0.2

–50 500 25–25 10075 125

LTC2983 TEMPERATURE (°C)

vs Temperature

REFOUT

VDD = 5.25V V

= 4.1V

= 2.85V

2983 G14

Channel Input Leakage Current vs Temperature

Adjacent Channel Offset Error vs Input Fault Voltage (VDD = 5V)

2.5

2.0

1.5

1.0

0.5

CH2 OFFSET ERROR (µV)

–0.5

4.95 5.055 5.1 5.2 5.255.15 5.3 5.35

For more information www.linear.com/LTC2983

CH1 FAULT VOLTAGE (V)

2983 G25

Adjacent Channel Offset Error vs Input Fault Voltage

2.5

2.0

1.5

1.0

0.5

CH2 OFFSET ERROR (µV)

–0.5

0 –0.05 –0.1 –0.2 –0.25–0.15 –0.3 –0.35

CH1 FAULT VOLTAGE (V)

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Page 9

PIN FUNCTIONS

LTC2983

GND (Pins 1, 3, 5, 7, 9, 12, 15, 44): Ground. Connect each of these pins to a common ground plane through a low impedance connection. All eight pins must be grounded for proper operation.

(Pins 2, 4, 6, 8, 45): Analog Power Supply. Tie all

five pins together and bypass as close as possible to the device, to ground with a 0.1μF capacitor.

REF_BYP

( Pin 11): Internal Reference Power. This is an

internal supply pin, do not load this pin with external circuitry. Decouple with a 0.1µF capacitor to GND.

REFOUT

REFP

(Pin 13): Reference Output Voltage. Short to

. A minimum 1μF capacitor to ground is required.

Do not load this pin with external circuitry.

(Pin 14): Positive Reference Input. Tie to V

REFP

REFOUT

CH1 to CH20 (Pin 16 to Pin 35): Analog Inputs. May be programmed for single-ended, differential, or ratiometric operation. The voltage on these pins can have any value between GND – 50mV and V

– 0.3V. Unused pins can

be grounded or left floating. COM (Pin 36): Analog Input. The common negative input

for all single-ended configurations. The voltage on this pin can have any value between GND – 50mV and V

–

0.3V. This pin is typically tied to ground for temperature measurements.

INTERRUPT (Pin 37): This pin outputs a LOW when the device is busy either during start-up or while a conversion

cycle is in progress. This pin goes HIGH at the conclusion of the start-up state or conversion cycle.

SCK (Pin 38): Serial Clock Pin. Data is shifted out of the device on the falling edge of SCK and latched by the device on the rising edge.

SDO (Pin 39): Serial Data Out. During the data output state, this pin is used as the serial data output. When the chip select pin is HIGH, the SDO pin is in a high impedance state.

SDI (Pin 40): Serial Data Input. Used to program the device. Data is latched on the rising edge of SCK.

CS (Pin 41): Active Low Chip Select. A low on this pin enables the digital input/output. A HIGH on this pin places SDO in a high impedance state. A falling edge on CS marks the beginning of a SPI transaction and a rising edge marks the end.

RESET (Pin 42): Active Low Reset. While this pin is LOW, the device is forced into the reset state. Once this pin is returned HIGH, the device initiates its start-up sequence.

LDO (Pin 43): 2.5V LDO Output. Bypass with a 10µF capacitor to GND. This is an internal supply pin, do not load this pin with external circuitry.

Q3, Q2, Q1 (Pins 46, 47, 48):

External Bypass Pins for –200mV integrated Charge Pump. Tie a 10µF X7R capacitor between Q1 and Q2 close to each pin. Tie a 10µF X5R capacitor from Q3 to Ground. These are internal supply pins, do not make additional connections.

For more information www.linear.com/LTC2983

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Page 10

LTC2983

2983 BD

BLOCK DIAGRAM

CH1 TO CH20

COM

21:6 MUX

1µF

REFOUT

REFP

REF_BYP

10ppm/°C REFERENCE

ADC1

ADC2

ADC3

0.1µF

CHARGE

PUMP

LDO

ROM

RAM

PROCESSOR

LDO

INTERRUPT

SDO

SCK

SDI

RESET

10µF

EXCITATION

CURRENT SOURCES

For more information www.linear.com/LTC2983

GND

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Page 11

TEST CIRCUITS

SDO

1.69k

LOAD

= 20pF

SDO

LTC2983

1.69k

= 20pF

LOAD

TIMING DIAGRAM

SDO

SCK

Hi-Z TO V VOL TO V

VOH TO Hi-Z

SPI Timing Diagram

Hi-Z TO V VOH TO V

VOL TO Hi-Z

2983 TC01

SDI

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2983 TD01

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LTC2983

OVERVIEW

The LTC2983 measures temperature using the most common sensors (thermocouples, RTDs, thermistors, and diodes). It includes all necessary active circuitry, switches, measurement algorithms, and mathematical conversions to determine the temperature for each sensor type.

Thermocouples can measure temperatures from as low as –265°C to over 1800°C. Thermocouples generate a voltage as a function of the temperature difference between the tip (thermocouple temperature) and the electrical connection on the circuit board (cold junction temperature). In order to determine the thermocouple temperature, an accurate measurement of the cold junction temperature is required; this is known as cold junction compensation. The cold junction temperature is usually determined by placing a separate (non-thermocouple) temperature sensor at the cold junction. The LTC2983 allows diodes, RTDs, and thermistors to be used as cold junction sensors. In order to convert the voltage output from the thermocouple into a temperature result, a high order polynomial equation (up to 14th order) must be solved. The LTC2983 has these polynomials built in for virtually all standard thermocouples (J, K, N, E, R, S, T, and B). Additionally, inverse polynomials must be solved for the cold junction temperature. The LTC2983 simultaneously measures the thermocouple output and the cold junction temperature and performs all required calculations to report the thermocouple temperature in °C or °F. It directly digitizes both positive and negative voltages (down to 50mV below ground) from a single ground referenced supply, includes sensor burnout detection, and allows external protection/anti-aliasing circuits without the need of buffer circuits.

Diodes are convenient low cost sensor elements and are often used to measure cold junction temperatures in thermocouple applications. Diodes are typically used to measure temperatures from –60°C to 130°C, which is

suitable for most cold junction applications. Diodes generate an output voltage that is a function of temperature and excitation current. When the difference of two diode output voltages are taken at two different excitation current levels, the result (∆V The LTC2983 accurately generates excitation currents, measures the diode voltages, and calculates the temperature in °C or °F.

RTDs and thermistors are resistors that change value as a function of temperature. RTDs can measure temperatures over a wide temperature range, from as low as –200°C to 850°C while thermistors typically operate from –40°C to 150°C. In order to measure one of these devices a precision sense resistor is tied in series with the sensor. An excitation current is applied to the network and a ratiometric measurement is made. The value, in Ω, of the RTD/thermistor can be determined from this ratio. This resistance is used to determine the temperature of the sensor element using a table lookup (RTDs) or solving Steinhart-Hart equations (thermistors). The LTC2983 automatically generates the excitation current, simultaneously measures the sense resistor and thermistor/RTD voltage, calculates the sensor resistance and reports the result in °C. The LTC2983 can digitize most RTD types (PT-10, PT-50, PT-100, PT-200, PT-500, PT-1000, and NI-120), has built in coefficients for many curves (American, European, Japanese, and ITS-90), and accommodates 2-wire, 3-wire, and 4-wire configurations. It also includes coefficients for calculating the temperature of standard 2.252k, 3k, 5k, 10k , and 30k thermistors. It can be configured to share one sense resistor among multiple RTDs/thermistors and to rotate excitation current sources to remove parasitic thermal effects.

In addition to built-in linearization coefficients, the LTC2983 provides the means of inserting custom coefficients for both RTDs and thermistors.

) is proportional to temperature.

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LTC2983

OVERVIEW

Table 1. LTC2983 Error Contribution and Peak Noise Errors

SENSOR TYPE TEMPERATURE RANGE ERROR CONTRIBUTION PEAK-TO-PEAK NOISE

Type K Thermocouple –200°C to 0°C

Type J Thermocouple –210°C to 0°C

Type E Thermocouple –200°C to 0°C

Type N Thermocouple –200°C to 0°C

Type R Thermocouple 0°C to 1768°C ±(Temperature • 0.10% + 0.4)°C ±0.62°C Type S Thermocouple 0°C to 1768°C ±(Temperature • 0.10% + 0.4)°C ±0.62°C Type B Thermocouple 400°C to 1820°C ±(Temperature • 0.10%)°C ±0.83°C Type T Thermocouple –250°C to 0°C

External Diode (2 Reading) –40°C to 85°C ±0.25°C ±0.05°C External Diode (3 Reading) –40°C to 85°C ±0.25° Platinum RTD - PT-10, R

Platinum RTD - PT-100, R Platinum RTD - PT-500, R Platinum RTD - PT-1000, R

Thermistor, R

= 10kΩ –40°C to 85°C ±0.1°C ±0.01°C

SENSE

SENSE SENSE

SENSE

= 1kΩ

= 2kΩ = 2kΩ

= 2kΩ

0°C to 1372°C

0°C to 1200°C

0°C to 1000°C

0°C to 1300°C

0°C to 400°C

–200°C to 800°C –200°C to 800°C –200°C to 800°C –200°C to 800°C

±(Temperature • 0.23% + 0.05)°C ±(Temperature • 0.12% + 0.05)°C

±(Temperature • 0.23% + 0.05)°C ±(Temperature • 0.10% + 0.05)°C

±(Temperature • 0.18% + 0.05)°C ±(Temperature • 0.10% + 0.05)°C

±(Temperature • 0.27% + 0.08)°C ±

(Temperature • 0.10% + 0.08)°C

±(Temperature • 0.15% + 0.05)°C ±(Temperature • 0.10% + 0.05)°C

C ±0.2°C

±0.1°C ±0.1°C ±0.1°C ±0.1°C

±0.08°C

±0.07°C

±0.06°C

±0.13°C

±0.09°C

±0.05°C ±0.05°C ±0.02°C ±0.01°C

Table 1 shows the estimated system accuracy and noise associated with specific temperature sensing devices. System accuracy and peak-to-peak noise include the effects of the ADC, internal amplifiers, excitation current sources, and integrated reference for I-grade parts. Accuracy and noise are the worst-case errors calculated from the guaranteed maximum ADC and reference specifications. Peak-to-peak noise values are calculated at 0°C (except type B was calculated at 400°C) and diode measurements use AVG = ON mode.

Thermocouple errors do not include the errors associated with the cold junction measurement. Errors associated with a specific cold junction sensor within the operating temperature range can be combined with the errors for a given thermocouple for total temperature measurement accuracy.

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LTC2983

OVERVIEW

Memory Map

The LTC2983 channel assignment, configuration, conversion start, and results are all accessible via the RAM (see Table 2A). Table 2B details the valid SPI instruction bytes for accessing memory. The channel conversion results are mapped into memory locations 0x010 to 0x05F and can be read using the SPI interface as shown in Figure 1. A read is initiated by sending the read instruction byte = 0x03

Table 2A. Memory Map

LTC2983 MEMORY MAP

SEGMENT START

Command Status Register 0x000 0x000 1 See Table 6, Initiate Conversion, Sleep Command

Reserved 0x001 0x00F 15

Temperature Result Memory

20 Words - 80 Bytes

Reserved 0x060 0x0EF 144

Global Configuration Register 0x0F0 0x0F0 1

Reserved 0x0F1 0x0F3 3

Measure Multiple Channels Bit Mask 0x0F4 0x0F7 4 See Tables 65, 66, Run Multiple Conversions

Reserved 0x0F8 0x0F8 1 Reserved 0x0F9 0x0FE 6

Mux Configuration Delay 0x0FF 0x0FF 1 See MUX Configuration Delay Section of Data Sheet

Reserved 0x100 0x1FF 256

Channel Assignment Data 0x200 0x24F 80 See Tables 3, 4, Channel Assignment

Custom Sensor Table Data 0x250 0x3CF 384

Reserved 0x3D0 0x3FF 48

ADDRESS

0x010 0x05F 80 See Tables 8 to 10, Read Result

END

ADDRESS

followed by the address and then data. Channel assignment data resides in memory locations 0x200 to 0x24F and can be programmed via the SPI interface as shown in Figure 2. A write is initiated by sending the write instruction byte = 0x02 followed by the address and then data. Conversions are initiated by writing the conversion control byte (see Table 6) into memory location 0x000 (command status register).

SIZE

(BYTES)

DESCRIPTION

Table 2B. SPI Instruction Byte

INSTRUCTION SPI INSTRUCTION BYTE DESCRIPTION

Read 0b00000011 See Figure 1

Write 0b00000010 See Figure 2

No Opp 0bXXXXXX0X

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OVERVIEW

LTC2983

SCK

RECEIVER SAMPLES

DATA ON RISING EDGE

SDI I7 I6 I5 I4 I3 I2 I1 I0

SDO

SCK

RECEIVER SAMPLES

DATA ON RISING EDGE

SDI I7 I6 I5 I4 I3 I2 I1 I0

TRANSMITTER TRANSITIONS DATA ON FALLING EDGE

0 0 0 0 0 0 1 1

SPI INSTRUCTION BYTE

READ = 0x03

TRANSMITTER TRANSITIONS DATA ON FALLING EDGE

0 0 0 0 0 0 1 0

SPI INSTRUCTION BYTE

WRITE = 0x02

0 0 0 0 A11 A10 A9 A8

16-BIT ADDRESS FIELD

USER MEMORY READ TRANSACTION

Figure 1. Memory Read Operation

0 0 0 0 A11 A10 A9 A8

16-BIT ADDRESS FIELD

USER MEMORY WRITE TRANSACTION

A7 A6 A5 A4 A3 A2 A1 A0

D7 D6 D5 D4 D3 D2 D1 D0

FIRST DATA BYTE

D7 D6 D5 D4 D3 D2 D1 D0

FIRST DATA BYTE

• • •

SUBSEQUENT DATA BYTES MAY FOLLOW

• • •

SUBSEQUENT DATA BYTES MAY FOLLOW

2983 F01

2983 F02

Figure 2. Memory Write Operation

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LTC2983

(OPTIONAL)

APPLICATIONS INFORMATION

The LTC2983 combines high accuracy with ease of use. The basic operation is simple and is composed of five states (see Figure 3).

POWER-UP,

SLEEP

OR RESET

START-UP

≈ 200ms(MAX)

CHANNEL ASSIGNMENT

INITIATE CONVERSION

CONVERSION

STATUS CHECK

COMPLETE?

READ RESULTS

Figure 3. Basic Operation

YES

2983 F03

applicable). The user is locked out of RAM access while in the state (except for reading status location 0x000). The end of conversion is indicated by both the INTERRUPT pin going HIGH and a status register START bit going LOW and DONE bit going HIGH.

5. Read Results. In this state, the user has access to

RAM and can read the completed conversion results and fault status bits. It is also possible for the user to modify/append the channel assignment data during the read results state.

Conversion State Details State 1: Start-Up

The start-up state automatically occurs when power is applied to the LTC2983. If the power drops below a threshold of ≈2.6V and then returns to the normal operating voltage (2.85V to 5.25V), the LTC2983 resets and enters the powerup state. Note that the LTC2983 also enters the start-up state at the conclusion of the sleep state. The start-up state can also be entered at any time during normal operation by pulsing the RESET pin low.

Conversion States Overview

1. Start-Up. After power is applied to the LTC2983

>2.6V), there is a 200ms wake up period. During

this time, the LDO, charge pump, ADCs, and reference are powered up and the internal RAM is initialized. Once start-up is complete, the INTERRUPT pin goes HIGH and the command status register will return a value of 0x40 (Start bit=0, Done bit=1) when read.

2. Channel Assignment. The device automatically enters the channel assignment state after start-up is complete. While in this state, the user writes sensor specific data for each input channel into RAM. The assignment data contains information about the sensor type, pointers to cold junction sensors or sense resistors, and sensor specific parameters.

3. Initiate Conversion. A conversion is initiated by writing a measurement command into RAM memory location 0x000. This command is a pointer to the channel in which the conversion will be performed.

4. Conversion. A new conversion begins automatically following an Initiate Conversion command. In this state, the ADC is running a conversion on the specified channel and associated cold junction or R

SENSE

channel (if

In the first phase of the start-up state all critical analog circuits are powered up. This includes the LDO, reference, charge pump and ADCs. During this first phase, the command status register will be inaccessible to the user. This phase takes a maximum of 100mS to complete. Once this phase completes, the command status register will be accessible and return a value of 0x80 until the LTC2983 is completely initialized. Once the LTC2983 is initialized and ready to use, the interrupt pin will go high and the command status register will return a read value of 0x40 (Start bit=0, Done bit=1). At this point the LTC2983 is fully initialized and is ready to perform a conversion.

State 2: Channel Assignment

The LTC2983 RAM can be programmed with up to 20 sets of 32-bit (4-byte) channel assignment data. These reside sequentially in RAM with a one-to-one correspondence to each of the 20 analog input channels (see Table 3). Channels that are not used should have their channel assignment data set to all zeros (default at START-UP).

The channel assignment data contains all the necessary information associated with the specific sensor tied to that channel (see Table 4). The first five bits determine the sensor type (see Table 5). Associated with each sensor are sensor

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APPLICATIONS INFORMATION

Table 3. Channel Assignment Memory Map

CHANNEL ASSIGNMENT

NUMBER

CH1 0x200 0x201 0x202 0x203 4 CH2 0x204 0x205 0x206 0x207 4 CH3 0x208 0x209 0x20A 0x20B 4 CH4 0x20C 0x20D 0x20E 0x20F 4 CH5 0x210 0x211 0x212 0x213 4 CH6 0x214 0x215 0x216 0x217 4 CH7 0x218 0x219 0x21A 0x21B 4 CH8 0x21C 0x21D 0x21E 0x21F 4

CH9 0x220 0x221 0x222 0x223 4 CH10 0x224 0x225 0x226 0x227 4 CH11 0x228 0x229 0x22A 0x22B 4 CH12 0x22C 0x22D 0x22E 0x22F 4 CH13 0x230 0x231 0x232 0x233 4 CH14 0x234 0x235 0x236 0x237 4 CH15 0x238 0x239 0x23A 0x23B 4 CH16 0x23C 0x23D 0x23E 0x23F 4 CH17 0x240 0x241 0x242 0x243 4 CH18 0x244 0x245 0x246 0x247 4 CH19 0x248 0x249 0x24A 0x24B 4 CH20 0x24C 0x24D 0x24E 0x24F 4

CONFIGURATION

DATA START

ADDRESS

CONFIGURATION

ADDRESS + 1

DATA

CONFIGURATION

DATA

ADDRESS + 2

CONFIGURATION

DATA END

ADDRESS + 3

LTC2983

SIZE (BYTES)

Table 4. Channel Assignment Data

SENSOR TYPE SENSOR SPECIFIC CONFIGURATION

Channel

Assignment

Memory Location

31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

Unassigned

(Default)

Thermocouple Type = 1 to 9 Cold Junction Channel

RTD Type = 10 to 18 R

Thermistor Type = 19 to 27 R

Diode Type = 28 SGL=1

Sense Resistor Type = 29 Sense Resistor Value (17, 10) Up to 131,072Ω with 1/1024Ω Resolution

Direct ADC Type = 30 SGL=1

Reserved Type = 31 Not Used

Configuration Data

Start Address

Type = 0 Channel Disabled

Assignment [4:0]

Channel Assignment

SENSE

DIFF=0

[4:0]

Channel Assignment

[4:0]

2 to 3

Avg onCurrent

Reading

[1:0]

Configuration Data

Start Address + 1

SGL=1

DIFF=0

SGL=1 DIFF=0

Ideality Factor (2, 20) Value from 0 to 4 with 1/1048576 Resolution All Zeros Use Factory Set Default in ROM

Check

2, 3, 4 Wire Excitation

OC Current

Excitation

Mode

[1:0]

Mode

Excitation Current

0 0 0 0 0 0 Custom

Excitation

Current [3:0]

[3:0]

Not Used

Configuration Data

Start Address + 2

Address [5:0]

Curve

:0]

0 0 0 Custom

Custom

Address [5:0]

Configuration Data

Start Address + 3

Custom

Length - 1 [5:0]

Custom

Length - 1 [5:0]

Custom

Length - 1 [5:0]

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APPLICATIONS INFORMATION

Table 5. Sensor Type Selection

31 30 29 28 27 SENSOR TYPE

0 0 0 0 0 Unassigned 0 0 0 0 1 Type J Thermocouple 0 0 0 1 0 Type K Thermocouple 0 0 0 1 1 Type E Thermocouple 0 0 1 0 0 Type N Thermocouple 0 0 1 0 1 Type R Thermocouple 0 0 1 1 0 Type S Thermocouple 0 0 1 1 1 Type T Thermocouple 0 1 0 0 0 Type B Thermocouple 0 1 0 0 1 Custom Thermocouple 0 1 0 1 0 RTD PT-10 0 1 0 1 1 RTD PT-50 0 1 1 0 0 RTD PT-100 0 1 1 0 1 RTD PT-200 0 1 1 1 0 RTD PT-500 0 1 1 1 1 RTD PT-1000 1 0 0 0 0 RTD 1000 (0.00375) 1 0 0 0 1 RTD NI-120 1 0 0 1 0 RTD Custom 1 0 0 1 1 Thermistor 44004/44033 2.252kΩ at 25°C

0 1 0 0 Thermistor 44005/44030 3kΩ at 25°C

1 1 0 1 0 1 Thermistor 44007/44034 5kΩ at 25°C 1 0 1 1 0 Thermistor 44006/44031 10kΩ at 25°C 1 0 1 1 1 Thermistor 44008/44032 30kΩ at 25°C 1 1 0 0 0 Thermistor YSI 400 2.252kΩ at 25°C 1 1 0 0 1 Thermistor Spectrum 1003k 1kΩ 1 1 0 1 0 Thermistor Custom Steinhart-Hart 1 1 0 1 1 Thermistor Custom Table 1 1 1 0 0 Diode 1 1 1 0 1 Sense Resistor 1 1 1 1 0 Direct ADC 1 1 1 1 1 Reserved

specific configurations. These include pointers to cold junction or sense resistor channels, pointers to memory locations of custom linearization data, sense resistor values and diode ideality factors. Also included in this data are, if applicable, the excitation current level, single-ended/differential input mode, as well as sensor specific controls. Separate detailed operation sections for thermocouples, RTDs, diodes, thermistors, and sense resistors describe the assignment data associated with each sensor type in more detail. The LTC2983 demonstration

software includes a utility for checking configuration data and generating annotated C-code for programming the channel assignment data.

State 3: Initiate Conversion

Once the channel assignment is complete, the device is ready to begin a conversion. A conversion is initiated by writing Start (B7=1) and Done (B6=0) followed by the desired input channel (B4 – B0) into RAM memory location 0x000 (see Tables 6 and 7). It is possible to initiate a measurement cycle on multiple channels by setting the channel selection bits (B4 to B0) to 00000; see the Running Conversions Consecutively on Multiple Channels section of the data sheet.

Table 6. Command Status Register

B7 B6 B5 B4 B3 B2 B1 B0

Start = 1 Done = 0 0 Channel Selection 1 to 20 Start Conversion

1 0 0 1 0 1 1 1 Initiate Sleep

Table 7. Input Channel Mapping

B7 B6 B5 B4 B3 B2 B1 B0 CHANNEL SELECTED

1 0 0 0 0 0 0 0 Multiple Channels 1 0 0 0 0 0 0 1 CH1 1 0 0 0 0 0 1 0 CH2 1 0 0 0 0 0 1 1 CH3 1 0 0 0 0 1 0 0 CH4 1 0 0 0 0 1 0 1 CH5 1 0 0 0 0 1 1 0 CH6 1 0 0 0 0 1 1 1 CH7 1 0 0 0 1 0 0 0 CH8 1 0 0 0 1 0 0 1 CH9 1 0 0 0 1 0 1 0 CH10 1 0 0 0 1 0 1 1 CH11 1 0 0 0 1 1 0 0 0 1 1 0 1 CH13 1 0 0 0 1 1 1 0 CH14 1 0 0 0 1 1 1 1 CH15 1 0 0 1 0 0 0 0 CH16 1 0 0 1 0 0 0 1 CH17 1 0 0 1 0 0 1 0 CH18 1 0 0 1 0 0 1 1 CH19 1 0 0 1 0 1 0 0 CH20 1 0 0 1 0 1 1 1 Sleep

All Other Combinations Reserved

1 0 0 CH12

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APPLICATIONS INFORMATION

LTC2983

Bits B4 to B0 determine which input channel the conversion is performed upon and are simply the binary equivalent of the channel number (see Table 7).

Bit B5 should be set to 0. Bits B7 and B6 serve as start/done bits. In order to start

a conversion, these bits must be set to “10” (B7=1 and B6=0). When the conversion begins, the INTERRUPT pin goes LOW. Once the conversion is complete, bits B7 and B6 will toggle to “01” (B7=0 and B6=1) (Address = 0x000) and the INTERRUPT pin will go HIGH, indicating the conversion is complete and the result is available.

State 4: Conversion

The measurement cycle starts after the initiate conversion command is written into RAM location 0x000 (Table 6). The LTC2983 simultaneously measures the selected input sensor, sense resistors (RTDs and thermistors), and cold junction temperatures if applicable (thermocouples).

Once the conversion is started, the user is locked out of the RAM, with the exception of reading status data stored in RAM memory location 0x000.

Once the conversion is started the INTERRUPT pin goes low. Depending on the sensor configuration, two or three 82ms cycles are required per temperature result. These correspond to conversion rates of 167ms and 251ms, respectively. Details describing these modes are described in the 2- and 3-cycle Conversion Modes section of the data sheet.

The end of conversion can be monitored either through the interrupt pin (LOW to HIGH transition), or by reading the command status register in RAM memory location 0x000 (start bit, B7, toggles from 1 to 0 and DONE bit, B6, toggles from 0 to 1).

State 5: Read Results

Once the conversion is complete, the conversion results can be read from RAM memory locations corresponding to the input channel (see Table 8).

The conversion result is 32 bits long and contains both the sensor temperature (D23 to D0) and sensor fault data (D31 to D24) (see Tables 9A and 9B).

Table 8. Conversion Result Memory Map

CONVERSION

CHANNEL

CH1 0x010 0x013 4 CH2 0x014 0x017 4 CH3 0x018 0x01B 4 CH4 0x01C 0x01F 4 CH5 0x020 0x023 4 CH6 0x024 0x027 4 CH7 0x028 0x02B 4

CH8 0x02C 0x02F 4

CH9 0x030 0x033 4 CH10 0x034 0x037 4 CH11 0x038 0x03B 4 CH12 0x03C 0x03F 4 CH13 0x040 0x043 4 CH14 0x044 0x047 4 CH15 0x048 0x04B 4 CH16 0x04C 0x04F 4 CH17 0x050 0x053 4 CH18 0x054 0x057 4 CH19 0x058 0x05B 4 CH20 0x05C 0x05F 4

START

ADDRESS

END ADDRESS SIZE (BYTES)

The result is reported in °C for all temperature sensors with a range of –273.16°C to 8192°C and 1/1024°C resolution or in °F with a range of –459.67°F to 8192°F with 1/1024°F resolution. Included with the conversion result are seven sensor fault bits and a valid bit. These bits are set to a 1 if there was a problem associated with the corresponding conversion result (see Table 10). Two types of errors are reported: hard errors and soft errors. Hard errors indicate the reading is invalid and the resulting temperature reported is –999°C or °F. Soft errors indicate operation beyond the normal temperature range of the sensor or the input range of the ADC. In this case, the calculated temperature is reported but the accuracy may be compromised. Details relating to each fault type are sensor specific and are described in detail in the sensor specific sections of this data sheet. Bit D24 is the valid bit and will be set to a 1 for valid data.

Once the data read is complete, the device is ready for a new initiate conversion command. In cases where new channel configuration data is required, the user has access to the RAM in order to modify existing channel assignment data.

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LTC2983

APPLICATIONS INFORMATION

Table 9A. Example Data Output Words (°C)

START ADDRESS START ADDRESS + 1 START ADDRESS + 2 START ADDRESS + 3

D31 D30 D29 D28 D27 D26 D25 D24 D23 D22 D21 D20 D19 D18 D17 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4D3 D2 D1 D0

Fault Data SIGN MSB LSB

Temperature Sensor

8191.999°C 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1024°C 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

1°C 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0

1/1024°C 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1

0°C 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0

–1/1024°C 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

–1°C 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0

–273.15°C 1 1 1 1 1 1 0 1 1 1 0 1 1 1 0 1 1 0 1 1 0 0 1 1 1

Hard

Fault

ADC Hard Fault

CJ Hard Fault

Soft

Fault

Sensor

Over

Range

Fault

Sensor

Under

Range

Fault

ADC

Out

Range

Fault

Valid

If 1

4096°C

1°C 1/1024°C

(END ADDRESS)

0 0 0 0 0 0 0 0 0 0

Table 9B. Example Data Output Words (°F)

START ADDRESS START ADDRESS + 1 START ADDRESS + 2 START ADDRESS + 3

D31 D30 D29 D28 D27 D26 D25 D24 D23 D22 D21 D20 D19 D18 D17 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0

Fault Data SIGN MSB LSB

Temperature Sensor

8191.999°F 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1024°F 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

1°F 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0

1/1024°F 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1

0°F 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0

–1/1024°F 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

–1°F 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0

–459.67°F 1 1 1 1 1 1 0 0 0 1 1 0 1 0 0 0 1 0 1 0 1 0 0 1 0

Hard

Fault

ADC Hard Fault

CJ Hard Fault

Soft

Fault

Sensor

Over

Range

Fault

Sensor

Under

Range

Fault

ADC

Out

Range

Fault

Valid

If 1

4096°F

1°F 1/1024°F

(END ADDRESS)

0 0 0 0 0 0 0 0 0 0

Table 10. Sensor Fault Reporting

BIT FAULT ERROR TYPE DESCRIPTION OUTPUT RESULT

D31 Sensor Hard Fault Hard Bad Sensor Reading –999°C or °F D30 Hard ADC-Out-of-Range Hard Bad ADC Reading (Could Be Large External Noise Event) –999°C or °F D29 CJ Hard Fault Hard Cold Junction Sensor Has a Hard Fault Error –999°C or °F D28 CJ Soft Fault Soft Cold Junction Sensor Result Is Beyond Normal Range Suspect Reading D27 Sensor Over Range Soft Sensor Reading Is Above Normal Range Suspect Reading D26 Sensor Under Range Soft Sensor Reading Is Below Normal Range Suspect Reading D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond ±1.125 • V D24 Valid NA Result Valid (Should Be 1) Discard Results if 0 Suspect Reading

/2 Suspect Reading

REF

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APPLICATIONS INFORMATION

THERMOCOUPLE MEASUREMENTS

Table 11. Thermocouple Channel Assignment Word

(1) THERMOCOUPLE

TYPE

TABLES 4, 12 TABLE 13 TABLE 14 TABLES 67 TO 69

Measurement Type 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Thermocouple Types 1 to 9 Cold Junction

(2) COLD JUNCTION

CHANNEL POINTER

Channel Assignment

[4:0]

(3) SENSOR

CONFIGURATION

SGL=1 DIFF=0

Check

Current

[1:0]

(4) CUSTOM THERMOCOUPLE

DATA POINTER

0 0 0 0 0 0 Custom Address

[5:0]

Custom Length –1

[5:0]

Channel Assignment – Thermocouples

For each thermocouple tied to the LTC2983, a 32-bit channel assignment word is programmed into a memory location corresponding to the channel the sensor is tied to (see Table 11). This word includes (1) thermocouple type, (2) cold junction channel pointer, (3) sensor configuration, and (4) custom thermocouple data pointer.

(1) Thermocouple Type

The thermocouple type is determined by the first five input bits B31 to B27 as shown in Table 12. Standard NIST coefficients for types J,K,E,N,R,S,T and B thermocouples are stored in the device ROM. If custom thermocouples are used, the custom thermocouple sensor type can be selected. In this case, user-specific data can be stored in the on-chip RAM starting at the address defined in the custom thermocouple data pointer.

(2) Cold Junction Channel Pointer

The cold junction compensation can be a diode, RTD, or thermistor. The cold junction channel pointer tells the LTC2983 which channel (1 to 20) the cold junction

Table 12. Thermocouple Type

(1) THERMOCOUPLE TYPE

B31 B30 B29 B28 B27 THERMOCOUPLE TYPES

0 0 0 0 1 Type J Thermocouple 0 0 0 1 0 Type K Thermocouple 0 0 0 1 1 Type E Thermocouple 0 0 1 0 0 Type N Thermocouple 0 0 1 0 1 Type R Thermocouple 0 0 1 1 0 Type S Thermocouple 0 0 1 1 1 Type T Thermocouple 0 1 0 0 0 Type B Thermocouple 0 1 0 0 1 Custom Thermocouple

sensor is assigned to (see Table 13). When a conversion is performed on a channel tied to a thermocouple, the cold junction sensor is simultaneously and automatically measured. The final output data uses the embedded coefficients stored in ROM to automatically compensate the cold junction temperature and output the thermocouple sensor temperature.

Table 13. Cold Junction Channel Pointer

(2) COLD JUNCTION CHANNEL POINTER

B26 B25 B24 B23 B22 COLD JUNCTION CHANNEL

0 0 0 0 0 No Cold Junction

0 0 0 0 1 CH1 0 0 0 1 0 CH2 0 0 0 1 1 CH3 0 0 1 0 0 CH4 0 0 1 0 1 CH5 0 0 1 1 0 CH6 0 0 1 1 1 CH7 0 1 0 0 0 CH8 0 1 0 0 1 CH9 0 1 0 1 0 CH10 0 1 0 1 1 CH11 0 1 1 0 0 CH12 0 1 1 0 1 CH13 0 1 1 1 0 CH14 0 1 1 1 1 CH15 1 0 0 0 0 CH16 1 1 0 0 1 0 CH18 1 0 0 1 1 CH19 1 0 1 0 0 CH20

0 0 0 1 CH17

All Other Combinations Invalid

Compensation, 0°C Used for Calculations

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(3) Sensor Configuration

The sensor configuration field (see Table 14) is used to select single-ended (B21=1) or differential (B21=0) input and allows selection of open circuit current if internal open-circuit detect is enabled (bit B20). Single-ended readings are measured relative to the COM pin and differential are measured between the selected CH

and adjacent CH

(see Figure 4).

TC-1

If open-circuit detection is enabled, B20=1, then the user can select the pulsed current value applied during opencircuit detect using bits B18 and B19 . The user determines the value of the open circuit current based on the size of the external protection resistor and filter capacitor (typically 10µA). This network needs to settle within 50ms to 1µV or less. The duration of the current pulse is approximately 8ms and occurs 50ms before the normal conversion cycle.

Thermocouple channel assignments follow the general convention shown in Figure 4. The thermocouple positive terminal ties to CH

(where TC is the selected channel

number) for both the single-ended and differential modes of operation. For single-ended measurements the thermocouple negative terminal and the COM pin are grounded. The thermocouple negative terminal is tied to CH

TC-1

for differential measurements. This node can either be grounded or tied to a bias voltage.

(4) Custom Thermocouple Data Pointer

See Custom Thermocouples section near the end of this data sheet for more information.

SINGLE-ENDED

DIFFERENTIAL

COM

0.1µF

TC-1

–

CHANNEL

ASSIGNMENT

CHANNEL

ASSIGNMENT

(1≤ TC ≤ 20)

= CH

= CHTC (2≤ TC ≤ 20)

Figure 4. Thermocouple Channel Assignment Convention

Table 14. Sensor Configuration

(3) SENSOR CONFIGURATION

SGL OC

CHECK

B21 B20 B19 B18

0 0 X X Differential External 0 1 0 0 Differential 10µA 0 1 0 1 Differential 100µA 0 1 1 0 Differential 500µA 0 1 1 1 Differential 1mA 1 0 X X Single-Ended External 1 1 0 0 Single-Ended 10µA 1 1 0 1 Single-Ended 100µA 1 1 1 0 Single-Ended 500µA 1 1 1 1 Single-Ended 1mA

OC CURRENT SINGLE-ENDED/

DIFFERENTIAL

OPEN-CIRCUIT

CURRENT

2983 F04

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LTC2983

Fault Reporting – Thermocouple

Each sensor type has a unique fault reporting mechanism indicated in the upper byte of the data output word. Table 15 shows faults reported in the measurement of thermocouples.

Bit D31 indicates the thermocouple sensor is open (broken or not plugged in), the cold junction sensor has a hard fault, or the ADC is out of range. This is indicated by a reading well beyond the normal operating range. Bit D30 indicates a bad ADC reading. This can be a result of either a broken (open) sensor or an excessive noise event (ESD or static discharge into the sensor path). Either of these are a hard error and –999°C or °F is reported. In the case of an excessive noise event, the device should recover and the following conversions will be valid if the noise event was a random, infrequent event. Bit D29 indicates a hard fault occurred at the cold junction sensor and –999°C or °F is reported. Refer to the specific sensor (diode, themistor, or RTD) used for cold junction compensation. Bit D28 indicates a soft fault occurred at the cold junction

sensor. A valid temperature is reported, but the accuracy may be compromised since the cold junction sensor is operating outside its normal temperature range. Bits D27 and D26 indicate over or under temperature limits have been exceeded for specific thermocouple types, as defined in Table 16. Bit D25 indicates the absolute voltage measured by the ADC is beyond its normal operating range. This fault reflects a reading that is well beyond the normal range of a thermocouple.

Table 16. Thermocouple Temperature Limits

THERMOCOUPLE TYPE LOW TEMP LIMIT °C HIGH TEMP LIMIT °C

J-Type –210 1200 K-Type –265 1372 E-Type –265 1000 N-Type –265 1300

R-type –50 1768 S-Type –50 1768

T-Type –265 400 B-Type 40 1820

Custom Lowest Table Entry Highest Table Entry

Table 15. Thermocouple Fault Reporting

BIT FAULT ERROR TYPE DESCRIPTION OUTPUT RESULT

D31 Sensor Hard Fault Hard Open Circuit or Hard ADC or Hard CJ –999°C or °F D30 Hard ADC-Out-of-Range Hard Bad ADC Reading (Could Be Large External Noise Event) –999°C or °F D29 CJ Hard Fault Hard Cold Junction Sensor Has a Hard Fault Error –999°C or °F D28 CJ Soft Fault Soft Cold Junction Sensor Result Is Beyond Normal Range Suspect Reading D27 Sensor Over Range Soft Thermocouple Reading Greater Than High Limit Suspect Reading D26 Sensor Under Range Soft Thermocouple Reading Less Than Low Limit Suspect Reading D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond ±1.125 • V D24 Valid NA Result Valid (Should Be 1) Discard Results if 0 Valid Reading

/2 Suspect Reading

REF

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DIODE MEASUREMENTS

Table 17. Diode Channel Assignment Word

(1) SENSOR TYPE (2) SENSOR

TABLE 18 TABLE 19 TABLE 20

Measurement Class 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Diode Type = 28 SGL=1

CONFIGURATION

DIFF=0

2 or 3

Readings

(3) EXCITATION

CURRENT

Avg onCurrent [1:0] Non-Ideality Factor (2, 20) Value from 0 to 4 with 1/1048576 Resolution

All Zeros Uses a Factory Set Default of 1.003

(4) DIODE IDEALITY FACTOR VALUE

Channel Assignment – Diode

For each diode tied to the LTC2983, a 32-bit channel assignment word is programmed into a memory location corresponding to the channel the sensor is tied to (see Table 17). This word includes (1) diode sensor selection, (2) sensor configuration, (3) excitation current, and (4) diode ideality factor.

1) Sensor Type

The diode is selected by the first five input bits B31 to B27 (see Table 18).

Table 18. Diode Sensor Selection

(1) SENSOR TYPE

B31 B30 B29 B28 B27 SENSOR TYPE

1 1 1 0 0 Diode

(2) Sensor Configuration

The sensor configuration field (bits B26 to B24) is used to define various diode measurement properties. Configuration bit B26 is set high for single-ended (measurement relative to COM) and low for differential.

Bit B25 sets the measurement algorithm. If B25 is low, two conversion cycles (one at 1I and one at 8I current excitation) are used to measure the diode. This is used in applications where parasitic resistance between the LTC2983 and the diode is small. Parasitic resistance effects can be removed by setting bit B25 high, enabling three conversion cycles (one at 1I, one at 4I and one at 8I).

Table 20. Programming Diode Ideality Factor

B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0

Example h 2

1.25 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

1.003 (Default) 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

1.006 0 1 0 0 0 0 0 0 0 1 1 0 0 0 1 0 0 1 0 0 1 1

1202–12–22–32–42–52–62–72–82–92–102–112–122–132–142–152–162–172–182–192–20

Bit B24 enables a running average of the diode temperature reading. This reduces the noise when the diode is used as a cold junction temperature element on an isothermal block where temperatures change slowly.

The algorithm used for diode averaging is a simple recursive running average. The new value is equal to the average of the current reading plus the previous value.

NEW VALUE=

CURRENT READING

PREVIOUS VALUE

If the current reading is 2°C above or below the previous value, the new value is reset to the current reading.

(3) Excitation Current

The next field in the channel assignment word (B23 to B22) controls the magnitude of the excitation current applied to the diode (see Table 19). In the two conversion cycle mode, the device performs the first conversion at a current equal to 8x the excitation current 1I. The second conversion occurs at 1I. Alternatively, in the three conversion cycle mode the first conversion excitation current is 8I, the second is 4I and the 3rd is 1I.

Table 19. Diode Excitation Current Selection

(3) EXCITATION CURRENT

B23 B22 1I 4I 8I

0 0 10µA 40µA 80µA 0 1 20µA 80µA 160µA 1 0 40µA 160µA 320µA 1 1 80µA 320µA 640µA

(4) DIODE IDEALITY FACTOR VALUE

0 0

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LTC2983

(4) Diode Ideality Factor

The last field in the channel assignment word (B21 to B0) sets the diode ideality factor within the range 0 to 4 with

–20

1/1048576 (2

) resolution. The top two bits (B21 to B20) are the integer part and bits B19 to B0 are the fractional part of the ideality factor (see Table 20).

Diode channel assignments follow the general convention shown in Figure 5. The anode ties to CH

(where D is

the selected channel number) for both the single-ended and differential modes of operation, and the cathode is grounded. For differential diode measurements, the cathode is also tied to CH

D-1

Fault Reporting - Diode

Each sensor type has unique fault reporting mechanism indicated in the upper byte of the data output word. Table 21 shows faults reported in the measurement of diodes.

Bit D31 indicates the diode is open, shorted, not plugged in, wired backwards, or the ADC reading is bad. Any of these are hard faults and –999°C or °F is reported. Bit D30 indicates a bad ADC reading. This can be a result of either a broken (open) sensor or an excessive noise event (ESD or static discharge into the sensor path). This is a

hard error and –999°C or °F is reported. In the case of an excessive noise event, the device should recover and the following conversions will be valid if the noise event was a random, infrequent event. Bits D29 and D28 are not used for diodes. Bits D27 and D26 indicate over or under temperature limits (defined as T > 130°C or T < –60°C). The calculated temperature is reported, but the accuracy may be compromised. Bit D25 indicates the absolute voltage measured by the ADC is beyond its normal operating range. If a diode is used as the cold junction element, any hard or soft error is flagged in the corresponding thermocouple result (bits D28 and D29 in Table 15).

CHANNEL

= CH

(1≤ D ≤ 20)

= CH

(2≤ D ≤ 20)

2983 F05

ASSIGNMENT

SINGLE-ENDED

DIFFERENTIAL

Figure 5. Diode Channel Assignment Convention

COM

D-1

CHANNEL

ASSIGNMENT

Table 21. Diode Fault Reporting

BIT FAULT ERROR TYPE DESCRIPTION OUTPUT RESULT

D31 Sensor Hard Fault Hard Open, Short, Reversed, or Hard ADC –999°C or °F D30 Hard ADC-Out-of-Range Hard Bad ADC Reading (Could Be Large External Noise Event) –999°C or °F D29 Not Used for Diodes N/A Always 0 D28 Not Used for Diodes N/A Always 0 D27 Sensor Over Range Soft T > 130°C Suspect Reading D26 Sensor Under Range Soft T < –60°C Suspect Reading D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond ±1.125 • V D24 Valid NA Result Valid (Should Be 1) Discard Results if 0 Valid Reading

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/2 Suspect Reading

REF

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Example: Single-Ended Type K and Differential Type T Thermocouples with Shared Diode Cold Junction Compensation

Figure 6 shows a typical temperature measurement system where two thermocouples share a single cold junction diode. In this example, a Type K thermocouple is tied to CH1 and a Type T thermocouple is tied to CH3 and CH4. They both share a single cold junction diode with ideality factor of

h=1.003 tied to CH2. Channel as-

signment data for both thermocouples and the diode are

TYPE K THERMOCOUPLE ASSIGNED TO CH1 (CH CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x200 TO 0x203 RESULT MEMORY LOCATIONS 0x010 TO 0x013

DIODE COLD JUNCTION ASSIGNED TO CH CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x204 TO 0x207 RESULT MEMORY LOCATIONS 0x014 TO 0x017

TYPE K

CH1

0.1µF

CH2

η = 1.003

shown in Tables 22 to 24. Thermocouple #1 (Type K) sensor type and configuration data are assigned to CH1. 32-bits of binary configuration data are mapped directly into memory locations 0x200 to 0x203 (see Table 22). The cold junction diode sensor type and configuration data are assigned to CH2. 32-bits of binary configuration data are mapped directly into memory locations 0x204 to 0x207 (see Table 23). Thermocouple #2 (Type T) sensor type and configuration data are assigned to CH4. 32-bits of binary configuration data are mapped directly

)

TC=1

(CH

)

D=2

TYPE T

CH3

TYPE T THERMOCOUPLE JUNCTION ASSIGNED TO CH4 (CH CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x20C TO 0x20F RESULT MEMORY LOCATIONS 0x01C TO 0x01F

0.1µF

CH4

COM

Figure 6. Dual Thermocouple with Diode Cold Junction Example

2983 F06

TC=4

)

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APPLICATIONS INFORMATION

LTC2983

into memory locations 0x20C to 0x20F (see Table24). A conversion is initiated on CH1 by writing 10000001 into memory location 0x000. Both the Type K thermocouple and the diode are measured simultaneously. The LTC2983 calculates the cold junction compensation and determines the temperature of the Type K thermocouple. Once the

conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01000001. Similarly, a conversion can be initiated on CH4 by writing 10000100 into memory location 0x000. The results (in °C) can be read from memory locations 0x010 to 0x013 for CH1 and 0x01C to

0x01F for CH4.

Table 22. Thermocouple #1 Channel Assignment (Type K, Cold Junction CH2, Single-Ended, 10µA Open-Circuit Detect)

CONFIGURATION FIELD

(1) Thermocouple Type

(2) Cold Junction Channel Pointer

(3) Sensor Configuration

Not Used Set These Bits to 0 6 000000 0 0 0 0 0 0 (4) Custom

Thermocouple Data Pointer

DESCRIPTION # BITS BINARY DATA MEMORY

Type K 5 00010 0 0 0 1 0

Single-Ended,

10µA Open-Circuit

Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0

5 00010 0 0 0 1 0

4 1100 1 1 0 0

ADDRESS 0x200

MEMORY

ADDRESS 0x201

MEMORY

ADDRESS 0x202

MEMORY

ADDRESS 0x203

Table 23. Diode Channel Assignment (Single-Ended 3-Reading, Averaging On, 20µA/80µA Excitation, Ideality Factor = 1.003))

CONFIGURATION FIELD

(1) Sensor Type Diode 5 11100 1 1 1 0 0 (2) Sensor

Configuration

(3) Excitation Current

(4) Ideality Factor 1.003 22 0100000000110001001001 0 1 0 0 0 0 0 0 0 0 1 1 0 0 0 1 0 0 1 0 0 1

DESCRIPTION # BITS BINARY DATA MEMORY

Single-Ended,

3-Reading, Average On

20µA, 80µA,

160µA

3 111 1 1 1

2 01 0 1

ADDRESS 0x204

MEMORY

ADDRESS 0x205

MEMORY

ADDRESS 0x206

MEMORY

ADDRESS 0x207

Table 24. Thermocouple #2 Channel Assignment (Type T, Cold Junction CH2, Differential, 100µA Open-Circuit Detect)

CONFIGURATION FIELD

(1) Thermocouple Type

(2) Cold Junction Channel Pointer

(3) Sensor Configuration

Not Used Set These Bits

(4) Custom Thermocouple Data Pointer

DESCRIPTION #

Type T 5 00111 0 0 1 1 1

Differential,

100µA Open-

Circuit Current

to 0

Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0

BITS

BINARY DATA MEMORY

5 00010 0 0 0 1 0

4 0101 0 1 0 1

6 000000 0 0 0 0 0 0

ADDRESS 0x20C

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MEMORY

ADDRESS 0x20D

MEMORY

ADDRESS 0x20E

MEMORY

ADDRESS 0x20F

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RTD MEASUREMENTS

Table 25. RTD Channel Assignment Word

(1) RTD TYPE (2) SENSE RESISTOR

TABLE 26 TABLE 27 TABLE 28 TABLE 29 TABLE 30 TABLES 72 TO 74

Measurement Class 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 RTD Type = 10 to 18 R

CHANNEL POINTER

Channel

SENSE

Assignment [4:0]

(3) SENSOR

CONFIGURATION

2, 3, 4

Wire

Excitation

Mode

(4) EXCITATION

CURRENT

Excitation

Current [3:0]

(5) RTD

CURVE

Curve

[1:0]

(6) CUSTOM RTD DATA POINTER

Custom Address

[5:0]

Custom Length – 1

[5:0]

Channel Assignment – RTD

For each RTD tied to the LTC2983, a 32-bit channel assignment word is programmed into a memory location corresponding to the channel the sensor is tied to (see Table

25). This word includes (1) RTD type, (2) sense resistor channel pointer, (3) sensor configuration, (4) excitation current, (5) RTD curve, and (6) custom RTD data pointer.

(1) RTD Type

The RTD type is determined by the first five input bits B31 to B27 as shown in Table 26. Linearization coefficients for RTD types PT-10, PT-50, PT-100, PT-200, PT-500, PT-1000, and NI-120 with selectable common curves (α = 0.003850, α = 0.003911, α = 0.003916, and α = 0.003926) are built into the device. If custom RTDs are used, RTD Custom can be selected. In this case, user specific data can be stored in the on-chip RAM starting at the address defined by the custom RTD data pointers.

Table 26. RTD Type

(1) RTD TYPE

B31 B30 B29 B28 B27 RTD TYPE

0 1 0 1 0 RTD PT-10 0 1 0 1 1 RTD PT-50 0 1 1 0 0 RTD PT-100 0 1 1 0 1 RTD PT-200 0 1 1 1 0 RTD PT-500 0 1 1 1 1 RTD PT-1000 1 0 0 0 0 RTD 1000 (α=0.00375) 1 0 0 0 1 RTD NI-120 1 0 0 1 0 RTD Custom

(2) Sense Resistor Channel Pointer

RTD measurements are performed ratiometrically relative to a known R

resistor. The sense resistor channel

SENSE

pointer field indicates the differential channel the sense resistor is tied to for the RTD (see Table 27). Sense resistors are always measured differentially.

Table 27. Sense Resistor Channel Pointer

(2) SENSE RESISTOR CHANNEL POINTER

B26 B25 B24 B23 B22 SENSE RESISTOR CHANNEL

0 0 0 0 0 Invalid 0 0 0 0 1 Invalid 0 0 0 1 0 CH2-CH1 0 0 0 1 1 CH3-CH2 0 0 1 0 0 CH4-CH3 0 0 1 0 1 CH5-CH4 0 0 1 1 0 CH6-CH5 0 0 1 1 1 CH7-CH6 0 1 0 0 0 CH8-CH7 0 1 0 0 1 CH9-CH8 0 1 0 1 0 CH10-CH9 0 1 0 1 1 CH11-CH10 0 1 1 0 0 CH12-CH11 0 1 1 0 1 CH13-CH12 0 1 1 1 0 C 0 1 1 1 1 CH15 -CH14 1 0 0 0 0 CH16-CH15 1 0 0 0 1 CH17-CH16 1 0 0 1 0 CH18-CH17 1 0 0 1 1 CH19-CH18 1 0 1 0 0 CH20-CH19

All Other Combinations Invalid

H14-CH13

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(3) Sensor Configuration

The sensor configuration field is used to define various RTD properties. Configuration bits B20 and B21 determine if the RTD is a 2, 3, or 4 wire type (see Table 28).

sensor using a high impedance Kelvin sensing. 4-wire measurements with Kelvin R

SENSE

tions where sense resistor wiring parasitics can lead to errors; this is especially useful for low resistance PT-10 type RTDs. In this case, both the RTD and sense resistor

The simplest configuration is the 2-wire configuration.

have Kelvin sensing connections.

While this setup is simple, parasitic errors due to IR drops in the leads result in systematic temperature errors. The 3-wire configuration cancels RTD lead resistance errors (if the lines are equal resistance) by applying two matched current sources to the RTD, one per lead. Mismatches in the two current sources are removed through transparent background calibration. 4-wire RTDs remove unbalanced

The next sensor configuration bits (B18 and B19) determine the excitation current mode. These bits are used to enable R

sharing, where one sense resistor is used

SENSE

for multiple 2-, 3-, and/or 4-wire RTDS. In this case, the RTD ground connection is internal and each RTD points to the same R

SENSE

channel.

RTD lead resistance by measuring directly across the

Table 28. RTD Sensor Configuration Selection

(3) SENSE

CONFIGURATION

NUMBER

OF WIRES

B21 B20 B19 B18

0 0 0 0 2-Wire External No No 5 0 0 0 1 2-Wire Internal No Yes 9 0 1 0 0 3-Wire External No No 5 • 0 1 0 1 3-Wire Internal No Yes 9 • 0 1 1 X Reserved 1 0 0 0 4-Wire External No No 4 • • 1 0 0 1 4-Wire Internal No Yes 1 0 1 0 4-Wire Internal Yes Yes 6 • • • 1 0 1 1 Reserved 1 1 0 0 4-Wire,

1 1 0 1 4-Wire,

1 1 1 0 4-Wire,

1 1 1 1 Reserved

EXCITATION

MODE

NUMBER

OF WIRES

Kelvin

SENSE

Kelvin

SENSE

Kelvin

SENSE

MEASUREMENT MODE BENEFITS

GROUND

CONNECTION

External No No 4 • • •

Internal No Yes 5 • • •

Internal Yes Yes 5 • • • •

CURRENT

SOURCE

ROTATION

SENSE

RESISTOR

SHARING

RTDs

POSSIBLE

PER

DEVICE

CANCELS RTD

MATCHED

LEAD

RESISTANCE

6 • •

CANCELS RTD

MISMATCH

LEAD

RESISTANCE

THERMOCOUPLE

are useful in applica-

CANCELS

PARASITIC

EFFECTS

CANCELS

SENSE

LEAD

RESISTANCE

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Bits B18 and B19 are also used to enable excitation current rotation to automatically remove parasitic thermocouple effects. Parasitic thermocouple effects may arise from the physical connected between the RTD and the measurement instrument. This mode is available for all 4-wire configurations using internal current source excitation.

(4) Excitation Current

The next field in the channel assignment word (B17 to B14) controls the magnitude of the excitation current applied to the RTD (see Table 29). The current selected is the total current flowing through the RTD independent of the wiring configuration. The R

current is 2x the

SENSE

sensor excitation current for 3-wire RTDs. In order to prevent soft or hard faults, select a current

such that the maximum voltage drop across the sensor or sense resistor is nominally 1.0V. For example, if R

SENSE

is 10kΩ and the RTD is a PT-100, select an excitation current of 100µA for 2-wire and 4-wire RTDs and select 50µA for a 3-wire RTD. Alternatively, using a 1kΩ sense resistor with a PT-100 RTD allows 500µA excitation for any wiring configuration.

Table 29. Total Excitation Current for All RTD Wire Types

(4) EXCITATION CURRENT

B17 B16 B15 B14 CURRENT

0 0 0 0 Reserved 0 0 0 1 5μA 0 0 1 0 10μA 0 0 1 1 25μA 0 1 0 0 50μA 0 1 0 1 100µA 0 1 1 0 250µA 0 1 1 1 500µA 1 0 0 0 1mA

(5) RTD Curve

Bits B13 and B12 set the RTD curve used and the corresponding Callendar-Van Dusen constants (shown in Table 30).

(6) Custom RTD Data Pointer

In the case where an RTD not listed in Table 30 is used, a custom RTD table may be entered into the LTC2983.

See Custom RTD section near the end of this data sheet for more information.

Table 30. RTD Curves: RT = R0 • (1 + a • T + b • T2 + (T – 100°C) • c • T3) for T < 0°C, RT = R0 • (1 + a • T + b • T2) for T > 0°C

(5) CURVE

B13 B12 CURVE ALPHA a b c

0 0 European Standard 0.00385 3.908300E-03 –5.775000E-07 –4.183000E-12 0 1 American 0.003911 3.969200E-03 –5.849500E-07 –4.232500E-12 1 0 Japanese 0.003916 3.973900E-03 –5.870000E-07 –4.400000E-12 1 1 ITS-90 0.003926 3.984800E-03 –5.870000E-07 –4.000000E-12 X X RTD1000-375 0.00375 3.810200E-03 –6.018880E-07 –6.000000E-12 X X *NI-120 N/A N/A N/A N/A

*NI-120 uses table based data.

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LTC2983

Fault Reporting – RTD

Each sensor type has unique fault reporting mechanism indicated in the most significant byte of the data output word. Table 31 shows faults reported in the measurement of RTDs.

Bit D31 indicates the RTD or R

is open, shorted, or not

SENSE

plugged in. This is a hard fault and –999°C or °F is reported. Bit D30 indicates a bad ADC reading. This can be a result of either a broken (open) sensor or an excessive noise event (ESD or static discharge into the sensor path). This

Table 31. RTD Fault Reporting

BIT FAULT ERROR TYPE DESCRIPTION OUTPUT RESULT

D31 Sensor Hard Fault Hard Open or Short RTD or R D30 Hard ADC-Out-of-Range Hard Bad ADC Reading (Could Be Large External Noise Event) –999°C or °F D29 Not Used for RTDs N/A Always 0 Valid Reading D28 Not Used for RTDs N/A Always 0 Valid Reading D27 Sensor Over Range Soft T > High Temp Limit (See Table 32) Suspect Reading D26 Sensor Under Range Soft T < Low Temp Limit (See Table 32) Suspect Reading D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond ±1.125 • V D24 Valid N/A Result Valid (Should Be 1) Discard Results if 0 Valid Reading

is a hard error and –999°C or °F is reported. In the case of an excessive noise event, the device should recover and the following conversions will be valid if the noise was a random infrequent event. Bits D29 and D28 are not used for RTDs. Bits D27 and D26 indicate over or under temperature limits (see Table 32). The calculated temperature is reported, but the accuracy may be compromised. Bit D25 indicates the absolute voltage measured by the ADC is beyond its normal operating range. If an RTD is used as the cold junction element, any hard or soft error is also flagged in the thermocouple result.

SENSE

/2 Suspect Reading

REF

–999°C or °F

Table 32. Voltage and Resistance Ranges

RTD TYPE MIN Ω MAX Ω LOW TEMP LIMIT °C HIGH TEMP LIMIT °C

PT-10 1.95 34.5 –200 850

PT-50 9.75 172.5 –200 850 PT-100 19.5 345 –200 850 PT-200 39 690 –200 850 PT-500 97.5 1725 –200 850

PT-1000 195 3450 –200 850

NI-120 66.6 380.3 –80 260

Custom Table Lowest Table Entry Highest Table Entry Lowest Table Entry Highest Table Entry

2983fc

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LTC2983

APPLICATIONS INFORMATION

Sense Resistor

Table 33. Sense Resistor Channel Assignment Word

(1) SENSOR TYPE (2) SENSE RESISTOR VALUE (Ω)

FIGURE 36 FIGURE 40

Measurement Class 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Sense Resistor Type = 29 Sense Resistor Value (17, 10) Up to ≈ 131,072Ω with 1/1024Ω Resolution

Channel Assignment

For each sense resistor tied to the LTC2983, a 32-bit channel assignment word is programmed into a memory location corresponding to the channel the sensor is tied to (see Table 33). This word includes (1) sense resistor selection and (2) sense resistor value.

(1) Sensor Type

The sense resistor is selected by setting the first 5 input bits, B31 to B27, to 11101 (see Table 34).

Table 34. Sense Resistor Selection

(1) SENSOR TYPE

B31 B30 B29 B28 B27 SENSOR TYPE

1 1 1 0 1 Sense Resistor

(2) Sense Resistor Value

The last field in the channel assignment word (B26 to B0) sets the value of the sense resistor within the range 0 to 131,072Ω with 1/1024Ω precision (see Table 35). The top 17 bits (B26 to B10) create the integer and bits B9 to B0 create the fraction of the sense resistor value.

Example: 2-Wire RTD

The simplest RTD configuration is the 2-wire configuration, 2-wire RTDs follow the general convention shown in Figure 7. They require only two connections per RTD and

can be tied directly to 2-lead RTD elements. The disadvantages of this topology are errors due to parasitic lead resistance. If sharing is not selected (1 R then CH

should be grounded. The ground connection

RTD

should be removed if sharing is enabled (1 R

SENSE

per RTD),

for

SENSE

multiple RTDs).

2ND TERMINAL TIES TO SENSE RESISTOR (CH CH

EXCITATION

CURRENT

FLOW

RTD-1

RTD

OPTIONAL GND, REMOVE FOR R

CHANNEL

ASSIGNMENT

= CH

RTD

SENSE

Figure 7. 2-Wire RTD Channel Assignment Convention

(2≤ RTD ≤ 20)

SHARING

RSENSE

2983 F07

)

Sense resistor channel assignments follow the general convention shown in Figure 8. The sense resistor is tied between CH

RSENSE

and CH

RSENSE-1

, where CH

RSENSE

is tied to the 2nd terminal of the RTD. Channel assignment data (see Table 33) is mapped into a memory location corresponding to CH

EXCITATION

CURRENT

FLOW

SENSE

RSENSE

RSENSE-1

RSENSE

Figure 8. Sense Resistor Channel Assignment Convention for 2-Wire RTDs

CHANNEL

ASSIGNMENT

= CH

(2≤ RSENSE ≤ 20)

RSENSE

2983 F08

Table 35. Example Sense Resistor Values

B26 B25 B24 B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0 Example R 2 10,000.2Ω 0 0 0 1 0 0 1 1 1 0 0 0 1 0 0 0 0 0 0 1 1 0 0 1 1 0 1

99.99521kΩ 1 1 0 0 0 0 1 1 0 1

1.0023kΩ 0 0 0 0 0 0 0 1 1 1 1 1 0 1 0 1 0 0 1 0 0 1 1 0 0 1 1

16215214213212211210292827262524232221202–12–22–32–42–52–62–72–82–92–10

(2) SENSE RESISTOR VALUE (Ω)

0 0 1 1 0 1 1 0 0 1 1 0 1 0 1 1 1

2983fc

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APPLICATIONS INFORMATION

LTC2983

Example: 2-Wire RTDs with Shared R

SENSE

Figure 9 shows a typical temperature measurement system using multiple 2-wire RTDs. In this example, a PT-1000 RTD ties to CH17 and CH18 and an NI-120 RTD ties to CH19 and CH20. Using this configuration, the LTC2983 can digitize up to nine 2-wire RTDs with a single sense resistor.

RTD #1 sensor type and configuration data are assigned to CH

. 32 bits of binary configuration data are

mapped directly into memory locations 0x244 to 0x247 (see Table 36). RTD #2 sensor type and configuration data are assigned to CH

. 32-bits of binary configuration data

are mapped directly into memory locations 0x24C to 0x24F

2-WIRE PT-1000

SENSE

5001.5Ω

0.01µF

(see Table 37). The sense resistor is assigned to CH16. The user-programmable value of this resistor is 5001.5Ω. 32bits of binary configuration data are mapped directly into memory locations 0x23C to 0x23F (see Table 38).

A conversion is initiated on CH

by writing 10010010 into

memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01010010. The resulting temperature in °C can be read from memory locations 0x054 to 0x057 (corresponding to CH and read from CH

SENSE RESISTOR ASSIGNED TO CH16 (CH CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x23C TO 0x23F

RTD #1 ASSIGNED TO CH CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x244 TO 0x247 RESULT MEMORY LOCATIONS 0x054 TO 0x057

). A conversion can be initiated

in a similar fashion.

)

RSENSE=16

(CH

RTD=18

)

2-WIRE NI-120

0.01µF

Figure 9. Shared 2-Wire RTD Example

Table 36. Channel Assignment Data for 2-Wire RTD #1 (PT-1000, R α = 0.003916 Curve)

CONFIGURATION FIELD

(1) RTD TYPE PT-1000 5 01111 0 1 1 1 1 (2) Sense Resistor

Channel Pointer (3) Sensor

Configuration (4) Excitation

Current (5) Curve Japanese,

(6) Custom RTD Data Pointer

DESCRIPTION # BITS BINARY DATA MEMORY

2-Wire with

Shared R

SENSE

10µA 4 0010 0 0 1 0

α = 0.003916

Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0

5 10000 1 0 0 0 0

4 0001 0 0 0 1

2 10 1 0

ADDRESS 0x244

RTD #2 ASSIGNED TO CH CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x24C TO 0x24F RESULT MEMORY LOCATIONS 0x05C TO 0x05F

on CH16, 2-Wire, Shared R

SENSE

MEMORY

ADDRESS 0x245

(CH

)

RTD=20

SENSE

MEMORY

ADDRESS 0x246

2983 F09

, 10µA Excitation Current,

MEMORY

ADDRESS 0x247

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APPLICATIONS INFORMATION

Table 37. Channel Assignment Data for 2-Wire RTD #2 (NI-120, R

CONFIGURATION FIELD

(1) RTD TYPE NI-120 5 10001 1 0 0 0 1 (2) Sense Resistor

Channel Pointer (3) Sensor

Configuration (4) Excitation

Current (5) Curve European

(6) Custom RTD Data Pointer

DESCRIPTION # BITS BINARY DATA MEMORY

2-Wire with

Shared R

SENSE

100µA 4 0101 0 1 0 1

α = 0.00385

Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0

5 10000 1 0 0 0 0

4 0001 0 0 0 1

2 00 0 0

ADDRESS 0x24C

on CH16, 2-Wire, Shared R

SENSE

Table 38. Channel Assignment Data for Sense Resistor (Value = 5001.5Ω)

CONFIGURATION FIELD

(1) Sensor Type Sense Resistor 5 11101 1 1 1 0 1 (2) Sense

Resistor Value

DESCRIPTION # BITS BINARY DATA MEMORY

ADDRESS 0x23C

5001.5Ω 27 000010011100010011000000000 0 0 0 0 1 0 0 1 1 1 0 0 0 1 0 0 1 1 0 0 0 0 0 0 0 0 0

Example: 3-Wire RTD

MEMORY

ADDRESS 0x24D

MEMORY

ADDRESS 0x23D

, 100µA Excitation Current)

SENSE

MEMORY

ADDRESS 0x24E

MEMORY

ADDRESS 0x23E

MEMORY

ADDRESS 0x24F

MEMORY

ADDRESS 0x23F

3-wire RTD channel assignments follow the general convention shown in Figure 10. Terminals 1 and 2 tie to the input/excitation current sources and terminal 3 connects to the sense resistor. Channel assignment data is mapped to memory locations corresponding to CH

RSENSE

3RD TERMINAL TIES TO SENSE RESISTOR

EXCITATION

CURRENT

FLOW

Figure 10. 3-Wire RTD Channel Assignment Convention

RTD-1

RTD

CHANNEL

ASSIGNMENT

= CH

RTD

(2≤ RTD ≤ 20)

RTD

2983 F10

Sense resistor channel assignments follow the general convention shown in Figure 11. The sense resistor is tied between CH

RSENSE

and CH

RSENSE-1

tied to the 3rd terminal of the RTD and CH to ground (or left floating for R

, where CH

RSENSE-1

sharing). Channel

SENSE

RSENSE

is tied

assignment data (see Table 33) is mapped into the memory

CHANNEL

= CH

SENSE

(2≤ RSENSE ≤ 20)

RSENSE

SHARING)

2983 F11

location corresponding to CH

(OPTIONAL GND, REMOVE FOR R

RSENSE-1

2x EXCITATION

CURRENT

FLOW

SENSE

RSENSE

ASSIGNMENT

Figure 11. 3-Wire Sense Resistor Channel Assignment Convention for 3-Wire RTDs

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LTC2983

Figure 12 shows a typical temperature measurement system using a 3-wire RTD. In this example, a 3-wire RTD’s terminals tie to CH ties to CH

and CH6. The sense resistor and RTD connect

together at CH

, CH8, and CH7. The sense resistor

The 3-wire RTD reduces the errors associated with parasitic lead resistance by applying excitation current to each RTD input. This first order cancellation removes matched lead resistance errors. This cancellation does not remove

3-WIRE PT-200

SENSE

12,150.39Ω

0.01µF

errors due to thermocouple effects or mismatched lead resistances. The RTD sensor type and configuration data are assigned to CH

. 32 bits of binary configuration data

are mapped directly into memory locations 0x220 to 0x223 (see Table 39). The sense resistor is assigned to CH

. The

user-programmable value of this resistor is 12150.39Ω. 32 bits of binary configuration data are mapped directly into memory locations 0x218 to 0x21B (see Table 40).

ASSIGNED TO CH7 (CH

SENSE

CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x218 TO 0x21B

3-WIRE RTD ASSIGNED TO CH

CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x220 TO 0x223 RESULT MEMORY LOCATIONS 0x030 TO 0x033

SENSE=7

(CH

RTD=9

2983 F12

)

Figure 12. 3-Wire RTD Example

Table 39. Channel Assignment Data for 3-Wire RTD (PT-200, R

CONFIGURATION FIELD

(1) RTD TYPE PT-200 5 01101 0 1 1 0 1 (2) Sense

Resistor Channel Pointer

(3) Sensor Configuration

(4) Excitation Current

(5) Curve American,

(6) Custom RTD Data Pointer

DESCRIPTION # BITS BINARY DATA MEMORY

3-Wire 4 0100 0 1 0 0

50µA 4 0100 0 1 0 0

α = 0.003911

Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0

5 00111 0 0 1 1 1

2 01 0 1

ADDRESS 0x220

on CH7, 3-Wire, 50µA Excitation Current, α = 0.003911 Curve)

SENSE

Table 40. Channel Assignment Data for Sense Resistor (Value = 12150.39Ω)

CONFIGURATION FIELD

(1) Sensor Type Sense Resistor 5 11101 1 1 1 0 1 (2) Sense Resistor

Value

DESCRIPTION # BITS BINARY DATA MEMORY

ADDRESS 0x218

12150.39Ω 27 000101111011101100110001111 0 0 0 1 0 1 1 1 1 0 1 1 1 0 1 1 0 0 1 1 0 0 0 1 1 1 0

MEMORY

ADDRESS 0x221

MEMORY

ADDRESS 0x219

MEMORY

ADDRESS 0x222

MEMORY

ADDRESS 0x21A

MEMORY

ADDRESS 0x223

MEMORY

ADDRESS 0x21B

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2983fc

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LTC2983

APPLICATIONS INFORMATION

A conversion is initiated on CH9 by writing 10001001 into memory location 0x000 . Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01001001. The resulting temperature in °C can be read from memory locations 0x030 to 0x033 (corresponding to CH

Example: Standard 4-Wire RTD (No Rotation or R

SENSE

Sharing)

Standard 4-wire RTD channel assignments follow the general convention shown in Figure 13. Terminal 1 is tied to ground, terminals 2 and 3 (Kelvin sensed signal) tie to CH

RTD

and CH

, and the 4th terminal ties to the

RTD-1

sense resistor. Channel assignment data (see Table 25) is mapped to memory locations corresponding to CH

EXCITATION

CURRENT

FLOW

RSENSE

4TH TERMINAL TIES TO SENSE RESISTOR (CH

RTD-1

RTD

CHANNEL

ASSIGNMENT

= CH

(2≤ RTD ≤ 20)

RTD

RSENSE

)

Sense resistor channel assignments follow the general convention shown in Figure 14. The sense resistor is tied between CH

RSENSE

and CH

SENSE-1

, where CH

RSENSE

is tied to the 4th terminal of the RTD. Channel assignment data (see Table 33) is mapped into a memory location corresponding to CH

EXCITATION

CURRENT

FLOW

SENSE

RSENSE-1

RSENSE

Figure 14. Sense Resistor Channel Assignment Convention for 4-Wire RTDs

CHANNEL

ASSIGNMENT

= CH

(2≤ RSENSE ≤ 20)

RSENSE

2983 F14

Figure 13. 4-Wire RTD Channel Assignment Convention

2983 F13

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APPLICATIONS INFORMATION

LTC2983

Figure 15 shows a typical temperature measurement system using a 4-wire RTD. In this example, a 4-wire RTD’s terminals tie to GND, CH sense resistor ties to CH

tor and RTD share a common connection at CH

, CH12, and CH11. The

and CH10. The sense resis-

. The

RTD sensor type and configuration data are assigned to

. 32 bits of binary configuration data are mapped

directly into memory locations 0x230 to 0x233 (see Table 41). The sense resistor is assigned to CH

. The

user programmable value of this resistor is 5000.2Ω.

4-WIRE PT-1000

SENSE

5000.2Ω

0.01µF

32 bits of binary configuration data are mapped directly into memory locations 0x228 to 0x22B (see Table 42).

A conversion is initiated on CH

by writing 10001101

into the data byte at memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01001101. The resulting temperature in °C can be read from memory locations 0x040 to 0x043 (corresponding to CH

SENSE RESISTOR ASSIGNED TO CH11 (CH

CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x228 TO 0x22B

RTD ASSIGNED TO CH CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x230 TO 0x233 RESULT MEMORY LOCATIONS 0x040 TO 0x043

(CH

RTD=13

)

SENSE=11

2983 F15

)

Figure 15. Standard 4-Wire RTD Example

Table 41. Channel Assignment Data for 4-Wire RTD (PT-1000, R

on CH11, Standard 4-Wire, 25µA Excitation Current,

SENSE

α = 0.00385 Curve)

CONFIGURATION FIELD

(1) RTD TYPE PT-1000 5 01111 0 1 1 1 1 (2) Sense

Resistor Channel Pointer

(3) Sensor Configuration

(4) Excitation Current

(5) Curve European,

(6) Custom RTD Data Pointer

DESCRIPTION # BITS BINARY DATA MEMORY

4-Wire,

No Rotate,

No Share

25µA 4 0011 0 0 1 1

α=0.00385

Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0

5 01011 0 1 0 1 1

4 1000 1 0 0 0

2 00 0 0

ADDRESS 0x230

Table 42. Channel Assignment Data for Sense Resistor (Value = 5000.2Ω)

CONFIGURATION FIELD

(1) Sensor Type Sense Resistor 5 11101 1 1 1 0 1 (2) Sense

Resistor Value

DESCRIPTION # BITS BINARY DATA MEMORY

ADDRESS 0x228

5000.2Ω 27 000010011100010000011001100 0 0 0 0 1 0 0 1 1 1 0 0 0 1 0 0 0 0 0 1 1 0 0 1 1 0 0

MEMORY

ADDRESS 0x231

MEMORY

ADDRESS 0x229

MEMORY

ADDRESS 0x232

MEMORY

ADDRESS 0x22A

MEMORY

ADDRESS 0x233

MEMORY

ADDRESS 0x22B

2983fc

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LTC2983

APPLICATIONS INFORMATION

Example: 4-Wire RTD with Rotation

One method to improve the accuracy of an RTD over the standard 4-wire implementation is by rotating the excitation current source. Parasitic thermocouple effects are automatically removed through autorotation. In order to perform autorotation, the 1st terminal of the RTD ties to CH

instead of GND, as in the standard case. This

RTD+1

allows the LTC2983 to automatically change the direction of the current source without the need for additional external components.

4-wire RTD with rotation channel assignments follow the general convention shown in Figure 16. Terminal 1 is tied to CH tie to CH

EXCITATION

RTD

CURRENT

FLOW

, terminals 2 and 3 (Kelvin sensed signal)

RTD+1

and CH

RSENSE

, and the 4th terminal ties to the

RTD-1

4TH TERMINAL TIES TO SENSE RESISTOR

RTD–1

RTD

RTD+1

CHANNEL

ASSIGNMENT

= CH

(2≤ RTD ≤ 19)

RTD

2983 F16

sense resistor. Channel assignment data (see Table25) is mapped to memory locations corresponding to CH

RTD

Sense resistor channel assignments follow the general convention shown in Figure 17. The sense resistor is tied between CH tied to the 4

and CH

RSENSE th

terminal of the RTD. Channel assignment

RSENSE-1

, where CH

RSENSE

data is mapped into a memory location corresponding to

RSENSE

FLOW

RSENSE-1

SENSE

RSENSE

CHANNEL

ASSIGNMENT

= CH

(2≤ RSENSE ≤ 20)

RSENSE

2983 F17

EXCITATION

CURRENT

Figure 17. Sense Resistor Channel Assignment Convention for 4-Wire RTDs with Rotation

Figure 16. 4-Wire RTD Channel Assignment Convention

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APPLICATIONS INFORMATION

LTC2983

Figure 18 shows a typical temperature measurement system using a rotating 4-wire RTD. In this example a 4-wire RTD’s terminals tie to CH and CH

. The sense resistor is tied to CH6 and CH5.

The sense resistor and RTD connect together at CH

, CH16, CH15,

The RTD sensor type and configuration data are assigned to CH

. 32 bits of binary configuration data are

mapped directly into memory locations 0x23C to 0x23F

(see Table 43). The sense resistor is assigned to CH

0.01µF

PT-100

SENSE

10.0102k

The user programmable value of this resistor is 10.0102kΩ. 32 bits of binary configuration data are mapped directly into memory locations 0x214 to 0x217 (see Table 44).

A conversion is initiated on CH

by writing 10010000 into

memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01010000. The resulting temperature in °C can be read from memory locations 0x04C to 0x04F (corresponding to CH

SENSE RESISTOR ASSIGNED TO CH6 (CH CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x214 TO 0x217

RTD ASSIGNED TO CH

CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x23C TO 0x23F RESULT MEMORY LOCATIONS 0x04C TO 0x04F

)

SENSE=6

(CH

RTD=16

)

2983 F18

Figure 18. Rotating 4-Wire RTD Example

Table 43. Channel Assignment Data for Rotating 4-Wire RTD (PT-100, R

SENSE

α = 0.003911 Curve)

CONFIGURATION FIELD

(1) RTD TYPE PT-100 5 01100 0 1 1 0 0 (2) Sense

Resistor Channel Pointer

(3) Sensor Configuration

(4) Excitation Current

(5) Curve American,

(6) Custom RTD Data Pointer

DESCRIPTION # BITS BINARY DATA MEMORY

4-Wire with

Rotation

100µA 4 0101 0 1 0 1

α=0.003911 Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0

5 00110 0 0 1 1 0

4 1010 1 0 1 0

2 01 0 1

ADDRESS 0x23C

Table 44. Channel Assignment Data for Sense Resistor (Value = 10.0102kΩ)

CONFIGURATION FIELD

(1) Sensor Type Sense Resistor 5 11101 1 1 1 0 1 (2) Sense Resistor

Value

DESCRIPTION # BITS BINARY DATA MEMORY

ADDRESS 0x214

10.0102kΩ 27 000100111000110100011001100 0 0 0 1 0 0 1 1 1 0 0 0 1 1 0 1 0 0 0 1 1 0 0 1 1 0 0

on CH6, Rotating 4-Wire, 100µA Excitation Current,

MEMORY

ADDRESS 0x23D

MEMORY

ADDRESS 0x215

MEMORY

ADDRESS 0x23E

MEMORY

ADDRESS 0x216

MEMORY

ADDRESS 0x23F

MEMORY

ADDRESS 0x217

2983fc

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LTC2983

APPLICATIONS INFORMATION

Example: Multiple 4-Wire RTDs with Shared R

SENSE

Figure 19 shows a typical temperature measurement system using two 4-wire RTDs with a shared R

SENSE

. The LTC2983 can support up to six 4-wire RTDs with a single sense resistor. In this example, the first 4-wire RTD’s terminals tie to CH the 2nd ties to CH resistor ties to CH

, CH19, CH18, and CH6. The sense

and CH6. The sense resistor and both

, CH16, CH15, and CH6 and

RTDs connect together at CH6. This channel assignment convention is identical to that of the rotating RTD. This

0.01µF

4-WIRE PT-100

4-WIRE PT-500

SENSE

10k

topology supports both rotated and non-rotated RTD excitations. Channel assignment data for each sensor is shown in Tables 45 to 47.

A conversion is initiated on CH

by writing 10010000 into

SENSE RESISTOR ASSIGNED TO CH6 (CH CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x214 TO 0x217

RTD #1 ASSIGNED TO CH CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x23C TO 0x23F RESULT MEMORY LOCATIONS 0x04C TO 0x04F

RTD #2 ASSIGNED TO CH19 (CH CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x248 TO 0x24B RESULT MEMORY LOCATIONS 0x058 TO 0x05B

(CH

). A conversion can be initiated

in a similar fashion.

)

SENSE=6

)

RTD=16

)

RTD=19

0.01µF

Figure 19. Shared R

Table 45. Channel Assignment Data for 4-Wire RTD #1 (PT-100, R Current, α = 0.003926 Curve)

CONFIGURATION FIELD

(1) RTD TYPE PT-100 5 01100 0 1 1 0 0 (2) Sense

Resistor Channel Pointer

(3) Sensor Configuration

(4) Excitation Current

(5) Curve ITS-90,

(6) Custom RTD Data Pointer

DESCRIPTION # BITS BINARY DATA MEMORY

ADDRESS 0x23C

4-Wire

5 00110 0 0 1 1 0

4 1010 1 0 1 0

Rotated

100µA 4 0101 0 1 0 1

2 11 1 1

α=0.003926

Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0

4-Wire RTD Example

SENSE

on CH6, 4-Wire, Shared R

SENSE

MEMORY

ADDRESS 0x23D

2983 F19

, Rotated 100µA Excitation

SENSE

MEMORY

ADDRESS 0x23E

MEMORY

ADDRESS 0x23F

2983fc

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LTC2983

Table 46. Channel Assignment Data for 4-Wire RTD #2 (PT-500, R

on CH6, 4-Wire, Rotated 50µA Excitation Current,

SENSE

α = 0.003911 Curve)

CONFIGURATION FIELD

(1) RTD TYPE PT-500 5 01110 0 1 1 1 0 (2) Sense

Resistor Channel Pointer

(3) Sensor Configuration

(4) Excitation Current

(5) Curve American,

(6) Custom RTD Data Pointer

DESCRIPTION # BITS BINARY DATA MEMORY

4-Wire

Shared,

No Rotation

50µA 4 0100 0 1 0 0

α=0.003911

Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0

5 00110 0 0 1 1 0

4 1001 1 0 0 1

2 01 0 1

ADDRESS 0x248

Table 47. Channel Assignment Data for Sense Resistor (Value = 10.000kΩ)

CONFIGURATION FIELD

(1) Sensor Type Sense Resistor 5 11101 1 1 1 0 1 (2) Sense

Resistor Value

DESCRIPTION # BITS BINARY DATA MEMORY

ADDRESS 0x214

10.000kΩ 27 000100111000100000000000000 0 0 0 1 0 0 1 1 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0

MEMORY

ADDRESS 0x249

MEMORY

ADDRESS 0x215

MEMORY

ADDRESS 0x24A

MEMORY

ADDRESS 0x216

MEMORY

ADDRESS 0x24B

MEMORY

ADDRESS 0x217

Example: 4-Wire RTD with Kelvin R

SENSE

It is possible to cancel the parasitic lead resistance in the sense resistors by configuring the 4-wire RTD with a 4-wire (Kelvin connected) sense resistor. This is useful when using a PT-10 or PT-50 with a small valued R

SENSE

or when the sense resistor is remotely located or in applications requiring extreme precision.

RSENSE–2

RSENSE–1

EXCITATION

CURRENT

Figure 20. Sense Resistor with Kelvin Connections Channel Assignment Convention

FLOW

SENSE

TIES TO RTD TERMINAL 4

RSENSE

The 4-wire RTD channel assignments follow the general conventions previously defined (Figures 14 and 16) for a standard 4-wire RTD. The sense resistor follows the convention shown in Figure 20.

CHANNEL

ASSIGNMENT

= CH

(3≤ RSENSE ≤ 20)

RSENSE

2983 F20

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2983fc

Page 42

LTC2983

APPLICATIONS INFORMATION

Figure 21 shows a typical temperature measurement system using a 4-wire RTD with a Kelvin connected R example, the 4-wire RTD’s terminals tie to CH

. In this

SENSE

, CH16, CH15, and CH6. The sense resistor ties to CH6, CH5, and CH4 and excitation current is applied to CH

and CH17. The sense

resistor’s nominal value is 1kΩ in order to accommodate a 1mA excitation current. The sense resistor and RTD connect together at CH

. This topology supports both rotated, shared

and standard 4-wire RTD topologies. If rotated or shared

SENSE

4-WIRE PT-10

0.01µF

configuration are not used then terminal 1 of the RTD is tied to ground instead of CH

, freeing up one input channel. Channel

assignment data is shown in Tables 48 and 49. A conversion is initiated on CH

by writing 10010000

into memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01010000 (see Table 6). The resulting temperature in °C can be read from memory locations 0x04C to 0x04F (corresponding to CH

SENSE RESISTOR ASSIGNED TO CH6 (CH CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x214 TO 0x217

RTD ASSIGNED TO CH16 (CH CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x23C TO 0x23F RESULTS MEMORY LOCATIONS 0x04C TO 0x04F

RTD=16

)

SENSE=6

)

0.01µF

2983 F21

Figure 21. Sense Resistor with Kelvin Connections Example

Table 48. Channel Assignment Data for 4-Wire RTD with Kelvin Connected R

SENSE

(PT-10, R

on CH6, 4-Wire, Kelvin R

SENSE

Rotated 1mA Excitation Current, α = 0.003916 Curve)

CONFIGURATION FIELD

(1) RTD TYPE PT-10 5 01010 0 1 0 1 0 (2) Sense Resistor

Channel Pointer (3) Sensor

Configuration (4) Excitation Current 1mA 4 1000 1 0 0 0 (5) Curve Japanese, α=0.003916 2 10 1 0 (6) Custom RTD

Data Pointer

DESCRIPTION # BITS BINARY DATA MEMORY

ADDRESS 0x23C

4-Wire Kelvin R

SENSE

5 00110 0 0 1 1 0

4 1110 1 1 1 0

MEMORY

ADDRESS 0x23D

MEMORY

ADDRESS 0x23E

and Rotation

Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0

Table 49. Channel Assignment Data for Sense Resistor (Value = 1000Ω)

CONFIGURATION FIELD

(1) Sensor Type Sense Resistor 5 11101 1 1 1 0 1 (2) Sense

Resistor Value

DESCRIPTION # BITS BINARY DATA MEMORY

ADDRESS 0x214

MEMORY

ADDRESS 0x215

MEMORY

ADDRESS 0x216

1000Ω 27 000000011111010000000000000 0 0 0 0 0 0 0 1 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0

with

SENSE

MEMORY

ADDRESS 0x23F

MEMORY

ADDRESS 0x217

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LTC2983

THERMISTOR MEASUREMENTS

Channel Assignment – Thermistor

(1) Thermistor Type

The thermistor type is determined by the first five input bits (B31 to B27) as shown in Table 51. Linearization coef-

For each thermistor tied to the LTC2983, a 32-bit channel assignment word is programmed into a memory location corresponding to the channel the sensor is tied to (see Table 50). This data includes (1) thermistor type, (2) sense resistor channel pointer, (3) sensor configuration, (4) excitation current, (5) Steinhart-Hart address pointer or custom table address pointer.

ficients based on Steinhart-Hart equation for commonly used Thermistor types 44004/44033, 44005/44030, 44006/44031, 44007/44034, 44008/44032 and YSI-400 are built into the device. If other custom thermistors are used, Thermistor Custom Steinhart-Hart or Thermistor Custom Table (temperature vs resistance) can be selected. In this case, user specific data can be stored in the on-chip RAM starting at the address defined in Thermistor Custom Steinhart-Hart or Thermistor Custom Table address pointers.

Table 50. Thermistor Channel Assignment Word

(1) THERMISTOR

TYPE

TABLE 51 TABLE 27 TABLE 52 TABLE 53 TABLES 76, 77, 78, 80, 81

Measurement Class 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Thermistor Type = 19 to 27 R

Table 51. Thermistor Type: 1/T=A+B•ln(R)+C•ln(R)2 + D•ln(R)3 + E•ln(R)4 + F•ln(R)

B31 B30 B29 B28 B27 THERMISTOR TYPE A B C D E F

1 0 0 1 1 Thermistor 44004/44033

1 0 1 0 0 Thermistor 44005/44030

1 0 1 0 1 Thermistor 44007/44034

1 0 1 1 0 Thermistor 44006/44031

1 0 1 1 1 Thermistor 44008/44032

1 1 0 0 0 Thermistor YSI-400

1 1 0 0 1 Spectrum 1003k 1kΩ

1 1 0 1 0 Thermistor Custom

1 1 0 1 1 Thermistor Custom Table not used not used not used not used not used not used

(2) SENSE RESISTOR

CHANNEL POINTER

SENSE

Pointer [4:0]

2.252kΩ at 25°C

3kΩ at 25°C

5kΩ at 25°C

10kΩ at 25°C

30kΩ at 25°C

2.252kΩ at 25°

at 25°C

Steinhart-Hart

Channel

(3) SENSOR

CONFIGURATION

SGL = 1 DIFF = 0

1.46800E-03 2.38300E-04 0 1.00700E-07 0 0

1.40300E-03 2.37300E-04 0 9.82700E-08 0 0

1.28500E-03 2.36200E-04 0 9.28500E-08 0 0

1.03200E-03 2.38700E-04 0 1.58000E-07 0 0

9.37600E-04 2.20800E-04 0 1.27600E-07 0 0

1.47134E-03 2.37624E-04 0 1.05034E-07 0 0

1.445904E-3 2.68399E-04 0 1.64066E-07 0 0

user input user input user input user input user input user input

Excitation

Mode

(4) EXCITATION

CURRENT

Excitation Current

[3:0]

Not Used 0 0 0

(5) CUSTOM THERMISTOR

DATA POINTER

Custom Address

[5:0]

Custom Length – 1

[5:0]

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APPLICATIONS INFORMATION

(2) Sense Resistor Channel Pointer

Thermistor measurements are performed ratiometrically relative to a known R

resistor. The sense resistor

SENSE

channel pointer field indicates the differential channel the sense resistor is tied to for the current thermistor (see Table 27).

(3) Sensor Configuration

The sensor configuration field is used to define various thermistor properties. Configuration bit B21 is set high for single-ended (measurement relative to COM) and low for differential (see Table 52).

The next sensor configuration bits (B19 and B20) determine the excitation current mode. These bits are used to enable R

sharing, where one sense resistor is used

SENSE

for multiple thermistors. In this case, the thermistor ground connection is internal and each thermistor points to the same R

SENSE

channel.

Bits B19 and B20 are also used to enable excitation current rotation to automatically remove parasitic thermocouple effects. Parasitic thermocouple effects may arise from the physical connection between the thermistor and the measurement instrument. This mode is available for differential thermistor configurations using internal current source excitation.

Table 52. Sensor Configuration Data

(3) SENSOR

CONFIGURATION

SGL EXCITATION

MODE

B21 B20 B19

0 0 0 Differential No No 0 0 1 Differential Yes Yes 0 1 0 Differential Yes No 0 1 1 Reserved 1 0 0 Single-Ended No No 1 0 1 Reserved

1 1 0 Reserved

1 1 1 Reserved

SINGLE-ENDED/

DIFFERENTIAL

SHARE R

SENSE

ROTATE

(4) Excitation Current

The next field in the channel assignment word (B18 to B15) controls the magnitude of the excitation current applied to the thermistor (see Table 53). In order to prevent hard or soft faults, select a current such that the maximum voltage drop across the sensor or sense resistor is nominally

1.0V. The LTC2983 has no special requirements related to the ratio between the voltage drop across the sense resistor and the sensor. Consequently, it is possible to have a sense resistor several orders of magnitude smaller than the maximum sensor value. For optimal performance over the full thermistor temperature range, auto ranged current can be selected. In this case, the LTC2983 conversion is performed in three cycles (instead of the standard two cycles) (see Table 64). The first cycle determines the optimal excitation current for the sensor resistance value and R

value. The following two cycles use that cur-

SENSE

rent to measure the thermistor temperature.

Table 53. Excitation Current for Thermistors

(4) EXCITATION CURRENT

B18 B17 B16 B15 CURRENT

0 0 0 0 Reserved 0 0 0 1 250nA 0 0 1 0 500nA 0 0 1 1 1µA 0 1 0 0 5μA 0 1 0 1 10μA 0 1 1 0 25μA 0 1 1 1 50μA 1 0 0 0 100µA 1 0 0 1 250µA 1 0 1 0 500µA 1 0 1 1 1mA 1 1 0 0 Auto Range* 1 1 0 1 Invalid 1 1 1 0 Invalid 1 1 1 1 Reserved

*Auto Range not allowed for custom sensors

(5) Steinhart-Hart Address/Custom Table Address

See Custom Thermistors section near the end of this data sheet for more information.

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LTC2983

Fault Reporting – Thermistor

Each sensor type has unique fault reporting mechanism indicated in the upper byte of the data output word. Table 54 shows faults reported during the measurement of thermistors.

This is a hard error and –999°C is output. In the case of an excessive noise event, the device should recover and the following conversions will be valid if the noise event was a random infrequent event. Bits D29 and D28 are not used for thermistors. Bits D27 and D26 indicate the reading is over or under temperature limits (see Table 55). The

Bit D31 indicates the thermistor or R or not plugged in. This is a hard fault and –999°C is reported. Bit D30 indicates a bad ADC reading. This could be a result of either a broken (open) sensor or an excessive noise event (ESD or static discharge into the sensor path).

Table 54. Thermistor Fault Reporting

BIT FAULT ERROR TYPE DESCRIPTION OUTPUT RESULT

D31 Sensor Hard Fault Hard Open or Short Thermistor or R D30 Hard ADC-Out-of-Range Hard Bad ADC Reading (Could Be Large External Noise Event) –999°C D29 Not Used for Thermistors N/A Always 0 Valid Reading D28 Not Used for Thermistors N/A Always 0 Valid Reading D27 Sensor Over Range* Soft T > High Temp Limit Suspect Reading D26 Sensor Under Range* Soft T < Low Temp Limit Suspect Reading D25 ADC Out-of-Range Soft ADC Absolute Input Voltage Is Beyond ±1.125 • V D24 Valid N/A Result Valid (Should Be 1) Discard Results if 0 Valid Reading *Do not apply to custom Steinhart-Hart sensor type. Custom table thermistor over/under range is determined by the resistor table values, see custom

thermistor table example for details.

is open, shorted,

SENSE

calculated temperature is reported, but the accuracy may be compromised. Bit D25 indicates the absolute voltage measured by the ADC is beyond its normal operating range. If a thermistor is used as the cold junction element, any hard or soft error is flagged in the thermocouple result.

SENSE

/2 Suspect Reading

REF

–999°C

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2983 F23

APPLICATIONS INFORMATION

Table 55. Thermistor Temperature/Resistance Range

THERMISTOR TYPE MIN (Ω) MAX (Ω) LOW Temp Limit (°C) HIGH Temp Limit (°C)

Thermistor 44004/44033 2.252kΩ at 25°C 41.9 75.79k –40 150 Thermistor 44005/44030 3kΩ at 25°C 55.6 101.0k –40 150 Thermistor 44007/44034 5kΩ at 25°C 92.7 168.3k –40 150 Thermistor 44006/44031 10kΩ at 25°C 237.0 239.8k –40 150 Thermistor 44008/44032 30kΩ at 25°C 550.2 884.6k –40 150 Thermistor YSI 400 2.252kΩ at 25°C 6.4 1.66M –80 250 Spectrum 1003K 1kΩ at 25°C 51.1 39.51k –50 125 Thermistor Custom Steinhart-Hart N/A N/A N/A N/A

Thermistor Custom Table Second Table Entry Last Table Entry

Example: Single-Ended Thermistor

The simplest thermistor configuration is the single-ended configuration. Thermistors using this configuration share a common ground (COM) between all sensors and are each tied to a unique sense resistor (R

SENSE

sharing is not allowed for single-ended thermistors). Single-ended thermistors follow the convention shown in Figure 22. Terminal 1 ties to ground (COM) and terminal 2 ties to CH

and the sense resistor. Channel assignment

THERM

data (see Table 50) is mapped to memory locations corresponding to CH

EXCITATION

CURRENT

FLOW

Figure 22. Single-Ended Thermistor Channel Assignment Convention

THERM

2ND TERMINAL TIES TO SENSE RESISTOR (CH

COM

THERM

CHANNEL

ASSIGNMENT

= CH

RSENSE

(1 ≤ THERM ≤ 20)

THERM

)

2983 F22

Sense resistor channel assignments follow the general convention shown in Figure 23. The sense resistor is tied between CH

RSENSE

and CH

RSENSE-1

, where CH

RSENSE

is tied to the 2nd terminal of the thermistor. Channel assignment data (see Table 33) is mapped into the memory location corresponding to CH

EXCITATION

CURRENT

FLOW

SENSE

RSENSE

RSENSE-1

RSENSE

Figure 23. Sense Resistor Channel Assignment Convention

CHANNEL

ASSIGNMENT

= CH

(2≤ RSENSE ≤ 20)

RSENSE

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LTC2983

Figure 24 shows a typical temperature measurement system using a single-ended thermistor. In this example a 10kΩ (44031 type) thermistor is tied to a 10.1kΩ sense resistor. The thermistor is assigned channel CH5 (memory locations 0x210 to 0x213) and the sense resistor to CH4 (memory locations 0x20C to 0x20F). Channel assignment data are shown in Tables 56 and 57.

COM

SENSE

10.1k

TYPE 44031

100pF

Figure 24. Single-Ended Thermistor Example

A conversion is initiated on CH

by writing 10000101 into

memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01000101. The resulting temperature in °C can be read from memory locations 0x020 to 0x023 (corresponding to CH

SENSE RESISTOR ASSIGNED TO CH4 (CH CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x20C TO 0x20F

THERMISTOR ASSIGNED TO CH5 (CH CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x210 TO 0x213 RESULT MEMORY LOCATIONS 0x020 TO 0x023

SENSE=4

THERM=5

)

2983 F24

Table 56. Channel Assignment Data for Single-Ended Thermistor (44006/44031 10kΩ at 25°C Type Thermistor, Single-Ended Configuration, R

CONFIGURATION FIELD

(1) Thermistor Type

(2) Sense Resistor Channel Pointer

(3) Sensor Configuration

(4) Excitation Current

Not Used Set These Bits

(5) Custom RTD Data Pointer

on CH4, 1µA Excitation Current)

SENSE

DESCRIPTION # BITS BINARY DATA MEMORY

44006/44031

10kΩ at 25°C

Single-Ended 3 100 1 0 0

1µA 4 0011 0 0 1 1

to 0

Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0

5 10110 1 0 1 1 0

5 00100 0 0 1 0 0

3 000 0 0 0

ADDRESS 0x210

MEMORY

ADDRESS 0x211

MEMORY

ADDRESS 0x212

MEMORY

ADDRESS 0x213

Table 57. Channel Assignment Data for Sense Resistor (Value = 10.1kΩ)

CONFIGURATION FIELD

(1) Sensor Type Sense Resistor 5 11101 1 1 1 0 1 (2) Sense

Resistor Value

DESCRIPTION # BITS BINARY DATA MEMORY

ADDRESS 0x20C

10.1kΩ 27 000100111011101000000000000 0 0 0 1 0 0 1 1 1 0 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0

MEMORY

ADDRESS 0x20D

MEMORY

ADDRESS 0x20E

MEMORY

ADDRESS 0x20F

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2983 F26

APPLICATIONS INFORMATION

Example: Differential Thermistor

The differential thermistor configuration allows separate ground sensing for each sensor. In this standard differential configuration, one sense resistor is used for each thermistor. Differential thermistors follow the convention shown in Figure 25. Terminal 1 ties to CH shorted to ground and terminal 2 ties CH

THERM-1

THERM

and is

to and the sense resistor. Channel assignment data (see Table 50) is mapped to memory locations corresponding to CH

2ND TERMINAL TIES TO SENSE RESISTOR

EXCITATION

CURRENT

FLOW

Figure 25. Differential Thermistor Channel Assignment Convention

THERM–1

THERM

1ST TERMINAL TIES TO GND

CHANNEL

ASSIGNMENT

= CH

(2 ≤ THERM ≤ 20)

THERM

2983 F25

Sense resistor channel assignments follow the general convention shown in Figure 26. The sense resistor is tied between CH

RSENSE

and CH

RSENSE-1

, where CH

RSENSE

is tied to the 2nd terminal of the thermistor. Channel assignment data (see Table 33) is mapped into a memory location corresponding to CH

RSENSE-1

EXCITATION

CURRENT

FLOW

SENSE

RSENSE

CHANNEL

ASSIGNMENT

Figure 26. Sense Resistor Channel Assignment Convention

= CH

(2 ≤ RSENSE ≤ 20)

RSENSE

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LTC2983

Figure 27 shows a typical temperature measurement system using a differential thermistor. In this example a 30kΩ (44032 type) thermistor is tied to a 9.99kΩ sense resistor. The thermistor is assigned channel CH13 (memory locations 0x230 to 0x233) and the sense resistor to CH11 (memory locations 0x228 to 0x22B). Channel assignment data is shown in Tables 58 and 59).

TYPE 44032

SENSE

9.99k

100pF

Figure 27. Differential Thermistor Example

A conversion is initiated on CH

by writing 10001101 into

memory location 0x000. Once the conversion is complete, the INTERRUPT pin goes HIGH and memory location 0x000 becomes 01001101. The resulting temperature in °C can be read from memory locations 0x040 to 0x043 (Corresponding to CH

SENSE RESISTOR ASSIGNED TO CH11 (CH CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x228 TO 0x22B

THERMISTOR ASSIGNED TO CH5 (CH CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x230 TO 0x233 RESULT MEMORY LOCATIONS 0x040 TO 0x043

THERM=13

SENSE=11

)

2983 F27

)

Table 58. Channel Assignment Data for Differential Thermistor (44008/44032 30kΩ at 25°C Type Thermistor, Differential Configuration, R

CONFIGURATION FIELD

(1) Thermistor Type

(2) Sense Resistor Channel Pointer

(3) Sensor Configuration

(4) Excitation Current

Not Used Set These Bits

(5) Custom RTD Data Pointer

on CH11, Auto Range Excitation)

SENSE

DESCRIPTION # BITS BINARY DATA MEMORY

44008/44032 30kΩ at 25°C

Differential,

No Share, No Rotate

Auto Range 4 1100 1 1 0 0

to 0

Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0

5 10111 1 0 1 1 1

5 01011 0 1 0 1 1

3 000 0 0 0

2 000 0 0 0

ADDRESS 0x230

MEMORY

ADDRESS 0x231

MEMORY

ADDRESS 0x232

ADDRESS 0x233

Table 59. Channel Assignment Data for Sense Resistor (Value = 9.99kΩ)

CONFIGURATION FIELD

(1) Sensor Type Sense

(2) Sense Resistor Value

DESCRIPTION # BITS BINARY DATA MEMORY

ADDRESS 0x228

5 11101 1 1 1 0 1

Resistor

9.99kΩ 27 000100111000001100000000000 0 0 0 1 0 0 1 1 1 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0

MEMORY

ADDRESS 0x229

MEMORY

ADDRESS 0x22A

ADDRESS 0x22B

MEMORY

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APPLICATIONS INFORMATION

Example: Shared/Rotated Differential Thermistor

The differential thermistor configuration allows separate internal ground sensing for each sensor. In this configuration, one sense resistor can be used for multiple thermistors. Differential thermistors follow the convention shown in Figure 28. Terminal 1 ties to CH ties to CH

THERM-1

and the sense resistor. Channel assign-

and terminal 2

THERM

ment data (see Table 50) is mapped to memory locations corresponding to CH

2ND TERMINAL TIES TO SENSE RESISTOR

EXCITATION

CURRENT

FLOW

Figure 28. Thermistor with Shared R Assignment Convention

THERM

THERM–1

THERM

ASSIGNMENT

CHANNEL

= CH

SENSE

(2 ≤ THERM ≤ 20)

THERM

Channel

2983 F28

Sense resistor channel assignments follow the general convention shown in Figure 29. The sense resistor is tied between CH

RSENSE

and CH

RSENSE-1

, where CH

SENSE

is tied to the 2nd terminal of the thermistor. Channel assignment data (see Table 33) is mapped into a memory location corresponding to CH

THERM

Figure 30 shows a typical temperature measurement system using a shared sense resistor and one rotated/ one non-rotated differential thermistors. In this example

RSENSE-1

EXCITATION

CURRENT

SENSE

FLOW

RSENSE

CHANNEL

ASSIGNMENT

= CH

(2 ≤ RSENSE ≤ 20)

RSENSE

Figure 29. Sense Resistor Channel Assignment Convention for Thermistors

2983 F29

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LTC2983

a 30kΩ (44032 Type) thermistor is tied to a 10.0kΩ sense resistor and configured as rotated/shared. The second thermistor a 2.25kΩ (44004 Type) is configured as a non-rotated/shared. Channel assignment data are shown in Tables 60 to 62.

TYPE 44032

TYPE 44033

SENSE

100pF

10k

100pF

A conversion is initiated on CH

by writing 10010010 into

). A conversion can be initiated

and read from CH20 in a similar fashion.

SENSE RESISTOR ASSIGNED TO CH16 (CH CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x23C TO 0x23F

THERMISTOR #1 ASSIGNED TO CH18 (CH CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x244 TO 0x247 RESULT MEMORY LOCATIONS 0x054 TO 0x057

THERMISTOR #2 ASSIGNED TO CH20 (CH CHANNEL ASSIGNMENT MEMORY LOCATIONS 0x24C TO 0x24F RESULT MEMORY LOCATIONS 0x05C TO 0x05F

SENSE=16

THERM=18

THERM=20

2983 F30

)

Figure 30. Rotated and Shared Thermistor Example

Table 60. Channel Assignment Data Differential Thermistor (44008/44032 30kΩ at 25°C Type Thermistor, Differential Configuration with Sharing and Rotation, R

CONFIGURATION FIELD

(1) Thermistor Type

(2) Sense Resistor Channel Pointer

(3) Sensor Configuration

(4) Excitation Current

Not Used Set These Bits

(5) Custom RTD Data Pointer

DESCRIPTION # BITS BINARY DATA MEMORY

44008/44032 30kΩ at 25°C

Differential,

Rotate and

Shared

250nA

Excitation

Current

Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0

on CH16, 250nA Excitation Current)

SENSE

5 10111 1 0 1 1 1

5 10000 1 0 0 0 0

3 001 0 0 1

4 0001 0 0 0 1

3 000 0 0 0

to 0

ADDRESS 0x244

MEMORY

ADDRESS 0x245

MEMORY

ADDRESS 0x246

MEMORY

ADDRESS 0x247

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Table 61. Channel Assignment Data Differential Thermistor (44004/44033 2.252kΩ at 25°C Type Thermistor, Differential Configuration with Sharing and No Rotation, R

Configuration Field

(1) Thermistor Type

(2) Sense Resistor Channel Pointer

(3) Sensor Configuration

(4) Excitation Current

Not Used Set These

(5) Custom RTD Data Pointer

Description # Bits Binary Data MEMORY

44004/44033

2.252kΩ at 25°C

Differential,

No Rotate

and Shared

10µA

Excitation

Current

Bits to 0

Not Custom 12 000000000000 0 0 0 0 0 0 0 0 0 0 0 0

5 10011 1 0 0 1 1

5 10000 1 0 0 0 0

3 010 0 1 0

4 0101 0 1 0 1

3 000 0 0 0

on CH16, 10µA Excitation Current)

SENSE

ADDRESS 0x24C

MEMORY

ADDRESS 0x24D

MEMORY

ADDRESS 0x24E

ADDRESS 0x24F

MEMORY

Table 62. Channel Assignment Data for Sense Resistor (Value = 10.0kΩ)

Configuration Field

(1) Sensor Type Sense Resistor 5 11101 1 1 1 0 1 (2) Sense

Resistor Value

Description # Bits Binary Data MEMORY

ADDRESS 0x23C

10.0kΩ 27 000100111000100000000000000 0 0 0 1 0 0 1 1 1 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0

MEMORY

ADDRESS 0x23D

MEMORY

ADDRESS 0x23E

MEMORY

ADDRESS 0x23F

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LTC2983

Typical Application Thermocouple Measurements

The LTC2983 includes 20 fully configurable analog input channels. Each input channel can be configured to accept any sensor type. Figure 31 shows a typical application digitizing multiple thermocouples. Each thermocouple requires a cold junction sensor and each cold junction sensor can be shared amongst multiple thermocouples.

CH1 V

CH2

CH3

CH4

CH5

CH6

CH7

CH8

CH9

CH10

CH11

SENSE

CH12

4-WIRE

RTD

CH13

CH14

CH15

CH16

For example, the thermocouple tied to CH1 can use the diode tied to CH2 as a cold junction sensor. However, any thermocouple (CH1, CH3, CH5, CH6, CH9, CH10, or CH16) can use any diode (CH2, CH4, or CH7), RTD (CH13, CH14), or Thermistor (CH19, CH20) as its cold junction compensation. The LTC2983 simultaneously measures both the thermocouple and cold junction sensor and outputs the results in °C or °F.

2.85V TO 5.25V

2, 4, 6, 8, 45

REFOUT

REFP

REF_BYP

LDO

RESET

SDI

SDO

SCK

INTERRUPT

GND

1, 3, 5, 7, 9, 12, 15, 44

0.1µF

10µF

1µF

10µF

(OPTIONAL, DRIVE LOW TO RESET)

SPI INTERFACE

CH17

SENSE

CH18

CH19

CH20

COM

2983 F31

Figure 31. Typical Thermocouple Application

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Typical Application RTD and Thermistor Measurements

The LTC2983 includes 20 fully configurable analog input channels. Each input channel can be configured to accept any sensor type. Figure 32 shows a typical application digitizing multiple RTDs and thermistors. Each RTD/ thermistor requires a sense resistor which can be shared with multiple sensors. RTDs can be configured as 2, 3, or 4-wire topologies. For example, a single sense resistor

CH1

SENSE

CH2

4-WIRE

RTD

2-WIRE

RTD

3-WIRE

RTD

3-WIRE

RTD

SENSE

4-WIRE

RTD

CH3

CH4

CH5

CH6

CH7

CH8

CH9

CH10

CH11

CH12

CH13

CH14

CH15

CH16

CH17

CH18

CH19

CH20

COM

(CH1, CH2) is shared between a 4-wire RTD (CH4, CH3), a 2-wire RTD (CH7, CH6), two 3-wire RTDs (CH9, CH8 and CH11, CH10) and a thermistor (CH13, CH12). This can be mixed with diode sensors (CH15) and thermocouples (CH14). Sense resistors (CH17, CH16) can also be dedicated to specific sensors, in this case a 4-wire RTD (CH19, CH18). Current is applied through both the sense resistor and RTD/Thermistor, the resulting voltages are simultaneously measured and the results are output in °C or °F.

2.85V TO 5.25V

2, 4, 6, 8, 45

REFOUT

REFP

REF_BYP

LDO

RESET

SDI

SDO

SCK

INTERRUPT

GND

2983 F32

1, 3, 5, 7, 9, 12, 15, 44

0.1µF

10µF

1µF

10µF

(OPTIONAL, DRIVE LOW TO RESET)

SPI INTERFACE

Figure 32. Typical RTD/Thermistor Application

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SUPPLEMENTAL INFORMATION

LTC2983

24-BIT ∆∑ ADC

–

24-BIT ∆∑ ADC

–

SINGLE-ENDED

DIFFERENTIAL

ADC

COM

ADC

ADC-1

Figure 33. Direct ADC Channel Assignment Conventions

Direct ADC Measurements

In addition to measuring temperature sensors, the LTC2983 can perform direct voltage measurements. Any channel can be configured to perform direct single-ended or differential measurements. Direct ADC channel assignments follow the general convention shown in Figure 33. The 32-bit channel assignment word is programmed into a memory location corresponding to the input channel. The channel assignment word is 0xF000 0000 for differ-

CHANNEL ASSIGNMENT

= CH

(1 ≤ ADC ≤ 20)

ADC

(2 ≤ ADC ≤ 20)

ADC

2983 F33

ential readings and 0xF400 0000 for single-ended. The positive input channel ties to CH

for both single-ended

ADC

and differential modes. For single-ended measurements the ADC negative input is COM while for differential measurements it is CH

. For single ended measurements,

ADC-1

COM can be driven with any voltage above GND–50mV and below V

DD

–0.3V.

The direct ADC results are available in memory at a location corresponding to the conversion channel.

Table 63. Direct ADC Output Format

START ADDRESS START ADDRESS + 1 START ADDRESS + 2 START ADDRESS + 3

D31 D30 D29 D28 D27 D26 D25 D24 D23 D22 D21 D20 D19 D18 D17 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0

Fault Data SIGN MSB LSB

NA NA Soft

Volts Sensor

REF

1.75 • V

1.125 •

–1.125 • V

/2 1 1 0 0 1 0 1 1 0 1 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

REF

/2 0 0 0 0 1 0 1 1 0 0 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

REF

/2 0 0 0 0 0 0 0 1 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

REF

/2220 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1

REF

0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

–V

REF

–V

/2 0 0 0 0 0 0 0 1 1 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

REF

–1.75 • V

REF

< –V

REF

Range

Hard

Fault

1 1 0 0 1 0 1 CLAMPED to Factory Programmed Value

0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

0 0 0 0 0 1 1 1 1 1 0 1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 1 1 1 1 0 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 1 1 1 CLAMPED to Factory Programmed Value

Above

Soft

Below

Soft

Range

Valid

Always

1 ± 2V 1V 0.5V 0.25V ...

Integer Fraction

of V

REF

of –V

REF

(END ADDRESS)

0 0 0 0 0 0

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LTC2983

SUPPLEMENTAL INFORMATION

The data is represented as a 32-bit word (see Table 63) where the eight most significant bits are fault bits and the bottom 24 are the ADC reading in volts. For direct ADC readings hard fault errors do not clamp the digital output. Readings beyond ±1.125 • V

/2 exceed the normal ac-

REF

curacy range of the LTC2983 and flag a soft error; these results should be discarded. Readings beyond ±1.75 •

–5

INL ERROR (ppm)

–10

–15

–20

–1.5 –0.5 0 0.5 1 1.5–1

DIFFERENTIAL INPUT VOLTAGE (V)

90°C 25°C –45°C

2983 F34

/2 exceed the usable range of the LTC2983; these

REF

result in a hard fault and should be discarded. Figures 34 to 36 show typical integral nonlinearity varia-

tion at various supply voltages and temperatures for a differential input voltage (±V

/2) and V

REF

/2 common

REF

mode input voltage.

–5

INL ERROR (ppm)

–10

–15

–20

–1.5 –0.5 0 0.5 1 1.5–1

DIFFERENTIAL INPUT VOLTAGE (V)

90°C 25°C –45°C

2983 F35

Figure 34. Integral Nonlinearity as a Function of Temperature at VDD = 5.25V

–5

INL ERROR (ppm)

–10

–15

–20

–1.5 –0.5 0 0.5 1 1.5–1

DIFFERENTIAL INPUT VOLTAGE (V)

Figure 36. Integral Nonlinearity as a Function of Temperature at VDD = 2.85V

Figure 35. Integral Nonlinearity as a Function of Temperature at VDD = 3.3V

90°C 25°C –45°C

2983 F36

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SUPPLEMENTAL INFORMATION

LTC2983

Fault Protection and Anti-Aliasing

The LTC2983 analog input channels draw a maximum of 1nA DC. As a result, it is possible to add anti-aliasing and fault protection circuitry directly to the input of the LTC2983. The most common input circuitry is a low pass filter with 1k to 10k resistance (limited by excitation current for RTDs and thermistors) and a capacitor with 100pF-0.1µf capacitance. This circuit can be placed directly between the thermocouples and 4-wire RTDs and the LTC2983. In the case of 3-wire RTDs, mismatch errors between the protection resistors can degrade the performance. Thermistors requiring input projection should be tied to the LTC2983 through a Kelvin type connection in order to avoid errors due to the fault protection resistors.

2- and 3-Cycle Conversion Modes

The LTC2983 performs multiple internal conversions in order to determine the sensor temperature. Normally, two internal conversion cycles are required for each temperature result providing a maximum output time of 167.2ms. The LTC2983 uses these two cycles to automatically remove offset/offset drift errors, reduce 1/f noise, autocalibrate matched internal current sources, and provide simultaneous 50/60Hz noise rejection.

In addition to performing two conversion cycles per result, the LTC2983 also offers several unique features by utilizing a 3rd conversion cycle. In this case, the maximum output time is 251ms and all the benefits of the 2-cycle modes are present (see Table 64).

One feature utilizing the three conversion cycle mode is the internal open circuit detect mode. Typically, thermocouple open circuit detection is performed by adding a high resistance pull-up between the thermocouple and V

. This method can be used with the LTC2983 while operating in the two conversion cycle mode (OC=0). This external pull-up can interact with the input protection circuitry and lead to temperature measurement errors and increased noise. These problems are eliminated by selecting the internal open circuit detection mode (OC=1). In this case, a current is pulsed for 8ms and allowed to settle during one conversion cycle. This is followed by the normal two

conversion cycle measurement of the thermocouple. If the thermocouple is broken, the current pulse will result in an open circuit fault.

A second feature taking advantage of the 3rd conversion cycle is thermistor excitation current auto ranging. Since a thermistor’s resistance varies many orders of magnitude, the performance in the low resistance regions are compromised by the small currents required by the high resistance regions of operation. The auto ranging mode applies a test current during the first conversion cycle in order to determine the optimum current for the resistance state of the thermistor. It then uses that current to perform the thermistor measurement using the normal 2-cycle measurement. If a 3-cycle thermistor measurement is used as the cold junction sensor for a 2-cycle thermocouple measurement, the thermocouple conversion result is ready after three cycles.

A third feature requiring a 3rd conversion cycle is the three current diode measurement. In this mode, three ratioed currents are applied to the external diode in order to cancel parasitic lead resistance effects. This is useful in applications where the diode is remotely located and significant, unknown parasitic lead resistance requires cancellation. If a 3-cycle diode or thermistor measurement is used as the cold junction sensor for a 2-cycle thermocouple measurement, the thermocouple conversion result is ready after three cycles.

Table 64. 2- and 3-Cycles Conversion Modes

TYPE OF SENSOR CONFIGURATION NUMBER OF

Thermocouple OC = 0 2 167.2ms RTD All 2 167.2ms Thermistor Non-Autorange

Current Diode Two Readings 2 167.2ms Thermocouple OC = 1 3 251ms Thermocouple OC = 0, 3-Cycle

Cold Junction

Thermistor Autorange

Current Diode Three Readings 3 251ms

CONVERSION

CYCLES

2 167.2ms

3 251ms

MAXIMUM OUTPUT

TIME

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Running Conversions Consecutively on Multiple Channels

Generally, during the Initiate Conversion state, a conversion measurement is started on a single input channel determined by the channel number (bits B[4:0] = 00001 to 10100) written into memory location 0x000. Multiple consecutive conversions can be initiated by writing bits B[4:0]=00000 into memory location 0. Conversions will be initiated on each channel selected in the mask register (see Table 65).

For example, using the mask data shown in Table 66, after 1000000 is written into memory location 0, conversions are initiated consecutively on CH20, CH19, CH16, and CH1. Once the conversions begin, the INTERRUPT pin goes LOW and remains LOW until all conversions are complete. If the mask register is set for a channel that has no assignment data, that conversion step is skipped. All the results are stored in the conversion result memory locations and can be read at the conclusion of the measurement cycle.

Entering/Exiting Sleep Mode

The LTC2983 can be placed into sleep mode by writing 0x97 to memory location 0x000. On the rising edge of CS following the memory write (see Figure 2) the device enters the low power sleep state. It remains in this state until CS is brought low or RESET is asserted. Once one of these two signals is asserted, the LTC2983 begins its start-up cycle as described in State 1: Start-Up section of this data sheet.

MUX Configuration Delay

The LTC2983 performs 2 or 3 internal conversion cycles per temperature result. Each conversion cycle is performed with different excitation and input multiplexer configurations. Prior to each conversion, these excitation circuits and input switch configurations are changed and an internal

1ms (typical) delay ensures settling prior to the

conversion cycle in most cases.

Table 65. Multiple Conversion Mask Register

MEMORY LOCATION B7 B6 B5 B4 B3 B2 B1 B0

0x0F4 Reserved 0x0F5 CH20 CH19 CH18 CH17 0x0F6 CH16 CH15 CH14 CH13 CH12 CH11 CH10 CH9 0x0F7 CH8 CH7 CH6 CH5 CH4 CH3 CH2 CH1

Table 66. Example Mask Register Select CH20, CH19, CH16, and CH1

MEMORY LOCATION B7 B6 B5 B4 B3 B2 B1 B0

0x0F4 Reserved 0x0F5 1 1 0 0 0x0F6 1 0 0 0 0 0 0 0 0x0F7 0 0 0 0 0 0 0 1

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SUPPLEMENTAL INFORMATION

2983 F37

LTC2983

If excessive RC time constants are present in external sensor circuits (large bypass capacitors used for thermistors or RTDs) it is possible to increase the settling time between current source excitation and MUX switching. The extra delay is determined by the value written into the MUX configuration delay register (memory location 0x0FF). The value written into this memory location is multiplied by 100µs; therefore the maximum extra MUX delay is 25.5ms (i.e. 0x0FF = 255 • 100µs).

Global Configuration Register

The LTC2983 includes a global configuration register (memory location 0x0F0, see Figure 37). This register is used to set the notch frequency of the digital filter and temperature results format (°C or °F). The default setting is simultaneous 50/60Hz rejection (75dB rejection with 1ms MUX delay). If higher 60Hz rejection is required (120dB rejection), write 0x01 into memory location 0x0F0; if higher 50Hz rejection is required (120dB rejection) write 0x02 into memory location 0x0F0.

The default temperature units reported by the LTC2983 are °C. The reported temperature can also be output in °F by setting bit 3 of memory location 0x0F0 to 1. All other global configuration bits should be set to 0.

MEMORY LOCATION 0x0F0 0 0 0 0 0

Figure 37. Global Configuration Register

0 = °C 1 = °F

}

00 50/60Hz REJECTION 01 60Hz REJECTION 10 50Hz REJECTION 11 RESERVED

Reference Considerations

The mechanical stress of soldering the LTC2983 to a PC board can cause the output voltage reference to shift and temperature coefficient to change. These two changes are not correlated. For example, the voltage may shift but the temperature coefficient may not. To reduce the effects of stress-related shifts, mount the reference near the short edge of the PC board or in a corner.

CUSTOM THERMOCOUPLES

In addition to digitizing standard thermocouples, the LTC2983 can also digitize user-programmable, custom thermocouples (thermocouple type=0b01001, see Table

12). Custom sensor data (minimum of three, maximum of 64 pairs) reside sequentially in memory and are arranged in blocks of six bytes of monotonically increasing tabular data as mV vs temperature (see Table 67).

Table 67. Custom Thermocouple Tabular Data Format

ADDRESS BYTE 0 BYTE 1 BYTE 2 BYTE 3 BYTE 4 BYTE 5

0x250 + 6* Start Address Table Entry #1 (mV) Table Entry #1 (Kelvin) 0x250 + 6* Start Address + 6 Table Entry #2 (mV) Table Entry #2 (Kelvin) 0x250 + 6* Start Address + 12 Table Entry #3 (mV) Table Entry #3 (Kelvin)

• • •

Max Address = 0x3CA Table Entry #64 (mV) Table Entry #64 (Kelvin)

Custom Thermocouple Example

In this example, a simplified thermocouple curve is implemented (see Figure 38). Points P1 to P9 represent the normal operating range of the custom thermocouple. Voltage readings above point P9 result in a soft fault and the reported temperature is a linear extrapolation using

TEMPERATURE (K)

VOLTAGE < p1 SOFT FAULT CONDITION

(0mV, 273.15K)

NOTE: P0 SHOULD BE THE EXTRAPOLATION POINT TO 0K

(0mV, 0K)

Figure 38. Custom Thermocouple Example (mV vs Kelvin)

VOLTAGE > p9 SOFT FAULT CONDITION

VOLTAGE (mV)

2983 F38

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CUSTOM THERMOCOUPLES

a slope determined by points P8 and P9 (the final two table entries). Voltage readings below point P1 are also reported as soft faults. The temperature reported is the extrapolation between point P1 and P0, where P0 is typically the sensor output voltage at 0 Kelvin. If P0 is above 0 Kelvin, then all sensor output voltages below P0 (in mV) will report 0 Kelvin.

In order to program the LTC2983 with the custom thermocouple table, both the mV data and the Kelvin data are converted to 24-bit binary values (represented as two 3-byte table entries). Since most thermocouples generate negative output voltages, the mV values input to the LTC2983 are 2’s compliment. The sensor output voltage (units=mV), follows the convention shown in Table 69, where the first bit is the sign, the next nine are the integer part and the remaining 14 bits are the fractional part.

Table 68. Thermocouple Example mV vs Kelvin (K) Data Memory Map

POINT SENSOR OUTPUT

VOLTAGE (mV)

P0 –50.22 0 0x250 0x255 P1 –30.2 99.1 0x256 0x25B P2 –5.3 135.4 0x25C 0x261 P3 0 273.15 0x262 0x267 P4 40.2 361.2 0x268 0x26D mV Data Temperature Data P5 55.3 522.1 0x26E 0x273 (see Table 69) (see Table 70) P6 88.3 720.3 0x274 0x279 P7 132.2 811.2 0x27A 0x27F P8 188.7 922.5 0x280 0x285 P9 460.4 1000 0x286 0x28B

TEMPERATURE

KELVIN

START

ADDRESS

STOP

ADDRESS

BYTE 0 BYTE 1 BYTE 2 BYTE 3 BYTE 4 BYTE 5

Table 69. Example Thermocouple Output Voltage Values (mV)

BYTE 0 BYTE 1 BYTE 2

B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0

mV Sign 2

–50.22 1 1 1 1 0 0 1 1 0 1 1 1 0 0 0 1 1 1 1 0 1 1 0 0

–30.2 1 1 1 1 1 0 0 0 0 1 1 1 0 0 1 1

–5.3 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 0 1 1 0 0 1 1 0 1

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

40.2 0 0 0 0 1 0 1 0 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0

55.3 0 0 0 0 1 1 0 1 1 1 0 1 0 0 1 1 0 0 1 1 0 0 1 1

88.3 0 0 0 1 0 1 1 0 0 0 0 1 0 0 1 1 0 0 1 1 0 0 1 1

132.2 0 0 1 0 0 0 0 1 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0

188.7 0 0 1 0 1 1 1 1 0 0 1 0 1 1 0 0 1 1 0 0 1 1 0 0

460.4 0 1 1 1 0 0 1 1 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1

827262524232221202–12–22–32–42–52–62–72–82–92–102–112–122–132–14

0 0 1 1 0 1 0 0

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CUSTOM THERMOCOUPLES

LTC2983

In order to simplify the temperature field, temperature values are input in Kelvin as an unsigned value, but the final temperatures reported by the LTC2983 are reported in °C or °F. The sensor temperature (Kelvin), follows the convention shown in Table 70, where the first 14 bits are the integer part and the remaining 10 bits are the fractional part.

In this example, a custom thermocouple tied to CH1, with a cold junction sensor on CH2, is programmed with the

Table 70. Example Thermocouple Temperature Values

BYTE 3 BYTE 4 BYTE 5

B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0

Temperature 2

273.15 0 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 1 0 0 1 1 0 0 1

13212211210292827262524232221202–12–22–32–42–52–62–72–82–92–10

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

99.1 0 0 0 0 0 0 0 1 1 0 0 0 1 1 0 0 0 1 1 0 0

135.4 0 0 0 0 0 0 1 0 0 0 0 1 1 1 0 1 1 0 0 1 1 0 0 1

361.2 0 0 0 0 0 1 0 1 1 0 1 0 0 1 0 0 1 1 0 0 1 1 0 0

522.1 0 0 0 0 1 0 0 0 0 0 1 0 1 0 0 0 0 1 1 0 0 1 1 0

720.3 0 0 0 0 1 0 1 1 0 1 0 0 0 0 0 1 0 0 1 1 0 0 1 1

811.2 0 0 0 0 1

922.5 0 0 0 0 1 1 1 0 0 1 1 0 1 0 1 0 0 0 0 0 0 0 0 0 1000 0 0 0 0 1 1 1 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0

1 0 0 1 0 1 0 1 1 0 0 1 1 0 0 1 1 0 0

channel assignment data shown in Table 71 (refer to Figure 6 for similar format). In this case the custom data begins at memory location 0x250 (starting address is 0). The starting address (offset from 0x250) is entered in the custom thermocouple data pointer field of the channel assignment data. The table data length –1 (9 in this example) is entered into the custom thermocouple data length field of the thermocouple channel assignment word. Refer to Table 68 where the number of six byte entries is 10.

1 1 0

Table 71. Custom Thermocouple Channel Assignment Data

CONFIGURATION FIELD

(1) Thermocouple Type

(2) Cold Junction Channel Pointer

(3) Sensor Configuration

Not Used Set These Bits to 0 6 000000 0 0 0 0 0 0 (4) Custom

Thermocouple Data Pointer

Custom Thermocouple Data Length-1

DESCRIPTION # BITS BINARY

Type Custom 5 01001 0 1 0 0 1

Single-Ended,

10µA Open Circuit

Start Address = 0

(Start at 0x250)

Data Length –1

= 9

(10 Paired Entries)

5 00010 0 0 0 1 0

4 1100 1 1 0 0

6 000000 0 0 0 0 0 0

6 001010 0 0 1 0 0 1

DATA

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MEMORY

ADDRESS 200

ADDRESS 201

MEMORY

ADDRESS 202

MEMORY

ADDRESS 203

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CUSTOM RTDS

In addition to digitizing standard RTDs, the LTC2983 can also digitize custom RTDs (RTD type=0b10010, see Table26). Custom sensor data (minimum of three, maximum of 64 pairs) reside sequentially in memory and are arranged in blocks of six bytes of monotonically increasing tabular data Ω vs temperature (see Table 72).

Table 72. Custom RTD/Thermistor Tabular Data Format

ADDRESS BYTE 0 BYTE 1 BYTE 2 BYTE 3 BYTE 4 BYTE 5

0x250 + 6* Start Address Table Entry #1 (Ω) Table Entry #1 (Kelvin) 0x250 + 6* Start Address + 6 Table Entry #2 (Ω) Table Entry #2 (Kelvin) 0x250 + 6* Start Address + 12 Table Entry #3 (Ω) Table Entry #3 (Kelvin)

• • •

Max Address = 0x3CA Table Entry #64 (Ω) Table Entry #64 (Kelvin)

Custom RTD Example

In this example, a simplified RTD curve is implemented (see Figure 39). Points P1 to P9 represent the normal operating range of the custom RTD. Resistance readings above point P9 result in a soft fault and the reported temperature is a linear extrapolation using a slope determined by points P8 and P9 (the final two table entries). Resistance readings below point P1 are also reported as soft faults. The temperature reported is the extrapolation between point P1 and P0, where P0 is the sensor output temperature at 0Ω (This point should be 0Ω for proper interpolation below point p1).

RESISTANCE < p1 SOFT FAULT CONDITION

TEMPERATURE (K)

NOTE: P0 SHOULD BE THE EXTRAPOLATION POINT TO 0Ω

RESISTANCE > p9 SOFT FAULT CONDITION

RESISTANCE (Ω)

2983 F39

Figure 39. Custom RTD Example (Ω vs Kelvin )

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CUSTOM RTDS

LTC2983

Custom RTD table data is formatted in Ω (sensor output resistance) vs Kelvin (see Table 73). Each table entry pair spans six bytes. The first set of data can begin at any memory location greater than or equal to 0x250 and end at or below 0x3CF.

In order to program the LTC2983 with the custom RTD table, both the resistance data and the Kelvin data are

resistance (units=Ω) follows the convention shown in Table 74, where the first 13 bits are the integer part and the remaining 11 bits are the fractional part.

converted to 24-bit binary values. The sensor output

Table 73. RTD Example Resistance vs Kelvin Data Memory Map

POINT SENSOR OUTPUT

RESISTANCE (Ω)

P0 0 112.3 0x28C 0x291 P1 80 200.56 0x292 0x297 P2 150 273.16 0x298 0x29D P3 257.36 377.25 0x29E 0x2A3 P4 339.22 489.66 0x2A4 0x2A9 Resistance Data Temperature Data P5 388.26 595.22 0x2AA 0x2AF P6 512.99 697.87 0x2B0 0x2B5 P7 662.3 765.14 0x2B6 0x2BB P8 743.5 801.22 0x2BC 0x2C1 P9 2001.89 900.5 0x2C2 0x2C7

TEMPERATURE

(K)

START

ADDRESS

STOP

ADDRESS

BYTE 1 BYTE 2 BYTE 3 BYTE 1 BYTE 2 BYTE 3

Table 74. Example RTD Resistance Values

BYTE 1 BYTE 2 BYTE 3

B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0

Resistance 2

257.36 0 0 0 0 1 0 0 0 0 0 0 0 1 0 1 0 1 1 1 0 0 0 0 1

339.22 0 0 0 0 1 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 0 1 0

388.26 0 0 0 0 1 1 0 0 0 0 1 0 0 0 1 0 0 0 0 1 0 1 0 0

512.99 0 0 0 1 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 0 1 0 1 1

662.3 0 0 0 1

743.5 0 0 0 1 0 1 1 1 0 0 1 1 1 1 0 0 0 0 0 0 0 0 0 0

2001.89 0 0 1 1 1 1 1 0 1 0 0 0 1 1 1 1 0 0 0 1 1 1 1 0

12211210292827262524232221202–12–22–32–42–52–62–72–82–92–102–11

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

80 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0

150 0 0 0 0 0 1 0 0 1 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0

0 1 0 0 1 0 1 1 0 0 1 0 0 1 1 0 0 1 1 0

0 0 0 0

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CUSTOM RTDS

convention shown in Table 75, where the first 14 bits are the integer part and the remaining 10 bits are the fractional part.

In this example, a custom RTD tied to CH12/13, with a sense resistor on CH10/11, is programmed with the channel assignment data shown in Table 76 (refer to Figure 15 for a similar format). In this case, the custom data begins

at memory location 0x28C (starting address is 10). The starting address (offset from 0x250) is entered in the custom RTD data pointer field of the channel assignment data. The table data length –1 (9 in this case) is entered into the custom RTD data length field of the channel assignment word. Refer to Table 72 where the total number of paired entries is 10.

Table 75. Example RTD Temperature Values

BYTE 1 BYTE 2 BYTE 3

B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0

Temperature 2

112.3 0 0 0 0 0 0 0 1 1 1 0 0 0 0 0 1 0 0 1 1 0 0 1 1

200.56 0 0 0 0 0 0 1 1 0 0 1 0 0 0 1 0 0 0 1 1 1

273.16 0 0 0 0 0 0 1 0 0 1 0 0 0 1 0 0 1 0 1 0 0 0 1 1

377.25 0 0 0 0 0 0 1 1 1 1 1 0 0 1 0 1 0 0 0 0 0 0 0 0

489.66 0 0 0 0 0 0 0 1 1 0 1 0 0 1 1 0 1 0 1 0 0 0 1 1

595.22 0 0 0 0 1 0 0 1 0 1 0 0 1 1 0 0 1 1 1 0 0 0 0 1

697.87 0 0 0 0 1 0 1 0 1 1 1 0 0 1 1 1 0 1 1 1 1 0 1 0

765.14 0 0 0 0 1

801.22 0 0 0 0 1 0 1 0 1 0 0 0 0 1 0 0 1 1 1 0 0 0 0 1

900.5 0 0 0 0 1 1 1 0 0 0 0 1 0 0 1 0 0 0 0 0 0 0 0 0

13212211210292827262524232221202–12–22–32–42–52–62–72–82–92–10

1 0 1 1 1 1 1 0 1 0 0 1 0 0 0 1 1 1 1

1 0 1

Table 76. Custom RTD Channel Assignment Data

CONFIGURATION FIELD

(1) RTD Type Custom 5 10010 1 0 0 1 0 (2) Sense Resistor

Channel Pointer (3) Sensor

Configuration (4) Excitation Current 25µA 4 0011 0 0 1 1 (5) Curve Not Used for

(6) Custom RTD Data Pointer

(6) Custom RTD Data Length-1

DESCRIPTION # BITS BINARY

4-Wire, No

Rotate, No Share

Custom

Start Address

= 10

Data Length –1

= 9

10 Paired Entries

DATA

5 01011 0 1 0 1 1

4 1000 1 0 0 0

2 00 0 0

6 001010 0 0 1 0 1 0

6 001001 0 0 1 0 0 1

MEMORY

ADDRESS 230

MEMORY

ADDRESS 231

MEMORY

ADDRESS 232

MEMORY

ADDRESS 233

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LTC2983

In addition to digitizing standard thermistors, the LTC2983 can also digitize custom thermistors (thermistor type=0b11011, see Table 51). Custom sensor data (minimum of three, maximum of 64 pairs) reside sequentially in memory and are arranged in blocks of six bytes of monotonically increasing tabular data Ω vs temperature (see Table 72).

Custom Thermistor Table Example

In this example, a simplified thermistor NTC (negative temperature coefficient) curve is implemented (see Figure 40). Points P1 to P9 represent the normal operating range of the custom thermistor. Resistance readings above point

RESISTANCE > p9 SENSOR OVER-RANGE SOFT FAULT CONDITION

TEMPERATURE (K)

RESISTANCE < p1 SENSOR UNDER-RANGE SOFT FAULT CONDITION

NOTE: P0 SHOULD BE THE EXTRAPOLATION POINT TO 0Ω

P9 result in a soft fault and the reported temperature is a linear extrapolation using a slope determined by points P8 and P9 (the final two table entries). Resistance readings below point P1 are also reported as soft faults. The temperature reported is the extrapolation between point P1 and P0, where P0 is the sensor output temperature at 0Ω (This point must be 0Ω for proper interpolation below point p1).

In addition to NTC type thermistors, it is also possible to implement PTC (positive temperature coefficient) type thermistors (see Figure 41). In both cases, table entries start at the minimum resistance and end at the maximum resistance value.

RESISTANCE < p1 SENSOR UNDER-RANGE

TEMPERATURE (K)

SOFT FAULT CONDITION

RESISTANCE (Ω)

Figure 40. Custom NTC Thermistor Example (Ω vs Kelvin)

2983 F40

NOTE: P0 SHOULD BE THE EXTRAPOLATION POINT TO 0Ω

RESISTANCE > p9 SENSOR OVER-RANGE SOFT FAULT CONDITION

RESISTANCE (Ω)

Figure 41. Custom PTC Thermistor Example (Ω vs Kelvin)

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LTC2983

CUSTOM THERMISTORS

Custom thermistor table data is formatted in Ω (sensor output resistance) vs Kelvin (see Table 77). Each table entry pair spans six bytes. The first set of data can begin at any memory location greater than or equal to 0x250 and end below 0x3CF.

In order to program the LTC2983 with the custom thermistor table, both the resistance data and the Kelvin data are converted to 24-bit binary values. The sensor output resistance (units=Ω) follows the convention shown in

Table 77. NTC Thermistor Example Resistance vs Kelvin Data Memory Map

POINT SENSOR OUTPUT

RESISTANCE(Ω)

P0 0 457.5 0x2C8 0x2CD P1 80 400.2 0x2CE 0x2D3 P2 184 372.3 0x2D4 0x2D9 P3 423.2 320.1 0x2DA 0x2DF P4 973.36 290.55 0x2E0 0x2E5 Resistance Data Temperature Data P5 2238.728 249.32 0x2E6 0x2EB P6 5149.0744 240.3 0x2EC 0x2F1 P7 26775.18688 230 0x2F2 0x2F7 P8 139230.9718 215.3 0x2F8 0x2FD P9 724001.0532 200 0x2FE 0x303

TEMPERATURE

(K)

START

ADDRESS

STOP

ADDRESS

Table 78, where the first 20 bits are the integer part and the remaining four bits are the fractional part.

In order to simplify the temperature field, temperature values are input in Kelvin as an unsigned value, but the final temperatures reported by the LTC2983 are reported in °C or °F. The sensor temperature (Kelvin) follows the convention shown in Table 79, where the first 14 bits are the integer part and the remaining 10 bits are the fractional part.

BYTE 1 BYTE 2 BYTE 3 BYTE 1 BYTE 2 BYTE 3

Table 78. Example Thermistor Resistance Values

BYTE 1 BYTE 2 BYTE 3

B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0

Resistance 2

973.36 0 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 1 1 0 1 0 1 0 1

2238.728 0 0 0 0 0 0 0 0 1 0 0 0 1 0 1 1 1 1 1 0 1 0 1 1

5149.074 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 1 1 1 0 1 0 0 0 1

26775.19 0 0 0 0 0 1 1 0 1 0 0 139231 0 0 1 0 0 0 0 1 1 1 1 1 1 1 0 1 1 1 1 1 0 0 0 0

724001.1 1 0 1 1 0 0 0 0 1 1 0 0 0 0 1 0 0 0 0 1 0 0 0 1

19218217216215214213212211210292827262524232221202–12–22–32–4

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

80 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0

184 0 0

423.2 0 0 0 0 0 0 0 0 0 0 0 1 1 0 1 0 0 1 1 1 0 0 1 1

0 0 0 0 0 0 0 0 0 0 1 0 1 1 1 0 0 0 0 0 0 0

0 1 0 0 1 0 1 1 1 0 0 1 1

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CUSTOM THERMISTORS

LTC2983

In this example, a custom thermistor tied to CH5, with a sense resistor on CH3/4, is programmed with the channel assignment data shown in Table 80 (refer to Figure 24 for similar format). In this case the custom data begins at memory location 0x2C8 (starting address is 20). The

starting address (offset from 0x250) is entered in the custom thermistor data pointer field of the channel assignment data. The table data length –1 (9 in this case) is entered into the custom thermistor data length field of the thermistor channel assignment word.

Table 79. Example Thermistor Temperature Values

BYTE 1 BYTE 2 BYTE 3

B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0

Temperature 2

457.5 0 0 0 0 0 1 1 1 0 0 1 0 0 1 1 0 0 0 0 0 0 0 0 0

400.2 0 0 0 0 0 1 1 0 0 1 0 0 0 0 0 0 1 1 0 0 1

372.3 0 0 0 0 0 1 0 1 1 1 0 1 0 0 0 1 0 0 1 1 0 0 1 1

320.1 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 1 1 0 0 1 1 0

290.55 0 0 0 0 0 1 0 0 1 0 0 0 1 0 1 0 0 0 1 1 0 0 1 1

249.32 0 0 0 0 0 0 1 1 1 1 1 0 0 1 0 1 0 1 0 0 0 1 1 1

240.3 0 0 0 0 0 0 1 1 1 1 0 0 0 0 0 1 0 0 1 1 0 0 1 1

215.3 0 0 0 0 0 0 1 1 0 1 0 1 1 1 0 1 0 0 1 1 0 0 1 1

13212211210292827262524232221202–12–22–32–42–52–62–72–82–92–10

230 0 0 0 0 0

200 0 0 0 0 0 0 1 1 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0

0 1 1 1 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0

1 0 0

Table 80. Custom Thermistor Channel Assignment Data

CONFIGURATION FIELD

(1) Thermistor Type Custom Table 5 11011 1 1 0 1 1 (2) Sense Resistor

Channel Pointer (3) Sensor

Configuration (4) Excitation Current 1µA 4 0011 0 0 1 1 Not Used Set These Bits

(5) Custom Thermistor Data Pointer

(5) Custom Thermistor Length-1

DESCRIPTION # BITS BINARY

Single-Ended 3 100 1 0 0

to 0

Start Address

= 20

Length –1 = 9 6 001001 0 0 1 0 0 1

DATA

5 00100 0 0 1 0 0

3 00 0 0 0

6 010100 0 1 0 1 0 0

MEMORY

ADDRESS 210

MEMORY

ADDRESS 211

MEMORY

ADDRESS 212

MEMORY

ADDRESS 213

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LTC2983

+F •ln(R)

CUSTOM THERMISTORS

In addition to custom table driven thermistors, it is also possible to directly input Steinhart-Hart coefficients into the LTC2983 (thermistor type 11010, see Table 51). Steinhart-Hart coefficients are commonly specified

Steinhart-Hart data is stored sequentially in any memory location greater than or equal to 0x250 and below 0x3CF. Each coefficient is represented by a standard, single-

precision, IEEE754 32-bit value (see Table 81). parameters provided by thermistor manufacturers. The Steinhart-Hart equation is:

= A+B •ln(R)+C•ln(R)2+D •ln(R)3+E •ln(R)

Table 81. Steinhart-Hart Custom Thermistor Data Format

ADDRESS COEFFICIENT VALUE

0x250 + 4 *Start Address A 32-Bit Single-Precision Floating Point Format 0x250 + 4 *Start Address + 4 B 32-Bit Single-Precision Floating Point Format 0x250 + 4 *Start Address + 8 C 32-Bit Single-Precision Floating Point Format 0x250 + 4 *Start Address + 12 D 32-Bit Single-Precision Floating Point Format 0x250 + 4 *Start Address + 16 E 32-Bit Single-Precision Floating Point Format 0x250 + 4 *Start Address + 20 F 32-Bit Single-Precision Floating Point Format

Example Custom Steinhart-Hart Thermistor

In this example a Steinhart-Hart equation is entered into

memory starting at location 0x300 (see Table 82).

Table 82. Custom Steinhart-Hart Data Example

COEFFICIENT VALUE START

ADDRESS

A 1.45E-03 0x300 0 0 1 1 1 0 1 0 1 0 1 1 1 1 1 0 0 0 0 0 1 1 0 1 1 1 1 0 1 1 0 1 B 2.68E-04 0x304 0 0 1 1 1 0 0 1 1 0 0 0 1 1 0 0 1 0 0 0 0 0 1 0 0 1 0 1 1 0 1 0 C 0 0x308 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 D 1.64E-07 0x30C 0 0 1 1 0 1 0 0 0 E 0 0x310 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 F 0 0x314 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

SIGN EXPONENT MANTISSA

MSB LSB MSB LSB

0 1 1 0 0 0 0 0 0 0 1 0 1 1 1 1 1 1 1 1 0 1 0

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CUSTOM THERMISTORS

Table 83. Custom Steinhart-Hart Channel Assignment Data

CONFIGURATION FIELD

(1) Thermistor Type Custom

(2) Sense Resistor Channel Pointer

(3) Sensor Configuration

(4) Excitation Current 1µA 4 0011 0 0 1 1 Not Used Set These Bits

(5) Custom Thermistor Data Pointer

(5) Custom SteinhartHart Length Always Set to 0

DESCRIPTION # BITS BINARY

Steinhart-Hart

Single-Ended 3 100 1 0 0

to 0

Start Address

= 30

Fixed at Six

32-Bit Words

DATA

5 11010 1 1 0 1 0

5 00100 0 0 1 0 0

3 00 0 0 0

6 011110 0 1 1 1 1 0

6 000000 0 0 0 0 0 0

MEMORY

ADDRESS 210

MEMORY

ADDRESS 211

MEMORY

ADDRESS 212

LTC2983

MEMORY

ADDRESS 213

A custom thermistor tied to CH5, with a sense resistor on CH3/4, is programmed with the channel assignment data shown in Table 83 (refer to Figure 24 for a similar format). In this case the custom data begins at memory location 0x26E (starting address is 30). The starting address (offset from 0x250) is entered in the custom thermistor data pointer field of the channel assignment data. The data length (set to 0) is always six 32-bit floating point words.

Universal Sensor Hardware

The LTC2983 can be configured as a universal temperature measurement device. Up to four sets of universal inputs can be applied to a single LTC2983. Each of these sets can directly digitize a 3-wire RTD, 4-Wire RTD, Thermistor, or thermocouple without changing any on board hardware (see Figure 42). Each sensor can share the same four ADC inputs and protection/filtering circuitry are configured using software changes (new channel assignment data) only. One sense resistor and cold junction sensor are shared among all four banks of sensors.

The LTC2983 includes many flexible, software configurable

input modes. In order to share four common inputs among

all four sensor types each sensor requires specific con-

figuration bits (see Table 84). 3-Wire RTDs are configured

with shared R

, 4-Wire RTDs and thermistors are

SENSE

configured as shared and/or rotated, thermocouples are

configured differential with internal ground, and diodes

are configured as single-ended.

Table 84. Sensor Configuration for Universal Hookup

SENSOR TYPE CONFIGURATION

OPTIONS

3-WIRE RTD Share B18 = 1, B19 = 0 Table 28 4-WIRE RTD Share B18 = 1, B19 = 0 Table 28 4-WIRE RTD Rotate B18 = 0, B19 = 1 Table 28

Thermistor Share B19 = 0, B20 = 1 Table 52 Thermistor Rotate B19 = 1, B20 = 0 Table 52

Thermocouple Single-Ended B21 = 1 Table 14

Diode Single-Ended B26 = 1 Table 17

CONFIGURATION

BITS

SEE TABLE

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LTC2983

PACKAGE DESCRIPTION

Please refer to http://www.linear.com/product/LTC2938#packaging for the most recent package drawings.

LX Package

48-Lead Plastic LQFP (7mm × 7mm)

(Reference LTC DWG # 05-08-1760 Rev A)

0.50 BSC

0.20 – 0.30

1.30 MIN

7.15 – 7.25

5.50 REF

1 2

PACKAGE OUTLINE

RECOMMENDED SOLDER PAD LAYOUT

APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED

11° – 13°

R0.08 – 0.20

GAUGE PLANE

0° – 7°

0.25

5.50 REF

7.15 – 7.25

1 2

C0.30 – 0.50

9.00 BSC

7.00 BSC

SEE NOTE: 4

A A

7.00 BSC

1.35 – 1.45

9.00 BSC

1.60

MAX

11° – 13°

1.00 REF

0.45 – 0.75

NOTE:

1. PACKAGE DIMENSIONS CONFORM TO JEDEC #MS-026 PACKAGE OUTLINE

2. DIMENSIONS ARE IN MILLIMETERS

3. DIMENSIONS OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.25mm ON ANY SIDE, IF PRESENT

4. PIN-1 INDENTIFIER IS A MOLDED INDENTATION, 0.50mm DIAMETER

5. DRAWING IS NOT TO SCALE

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

SECTION A – A

For more information www.linear.com/LTC2983

COMPONENT

PIN “A1”

TRAY PIN 1

BEVEL

0.50 BSC

0.17 – 0.27

XXYY

LTCXXXX

LX-ES

Q_ _ _ _ _ _

PACKAGE IN TRAY LOADING ORIENTATION

0.05 – 0.150.09 – 0.20

LX48 LQFP 0113 REV A

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LTC2983

REVISION HISTORY

REV DATE DESCRIPTION PAGE NUMBER

A 07/15 Removed Tape and Reel options

Added Absolute Maximum Ratings for Q Changed reference Output Voltage Temperature Coefficient Changed Error Contribution for thermocouples Changed filter capacitor values in Figures 9, 12, 15, 18, 19, 21

B 09/15 Revised Table 2A. Memory Map

Revised the following tables so that all bytes contain eight bits: Table 69, 70, 74, 75, 78, 79

C 01/16 Added H-Grade option 3, 4

, Q2, Q3, LDO, V

REFOUT

, V

REF_BYP

3 3 4

33, 35, 37, 39,

40, 42

60, 61, 63, 64,

66, 67

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LTC2983

2983 F42

TYPICAL APPLICATION

THERMOCOUPLE

THERMISTOR

SHARE WITH ALL

FOUR SETS OF SENSORS

3-WIRE RTD 4-WIRE RTD

THREE MORE SETS

OF UNIVERSAL

SENSOR INPUTS

(OPTIONAL DRIVE

LOW TO RESET)

SPI INTERFACE

CH1

SENSE

17 48

CH2

CH3

LTC2983

CH4

CH5

CH6

CH7 TO CH2022 TO 35

COM

RESET

SDI

SDO

SCK

INTERRUPT

REFOUT

REF_BYP

2, 4, 6, 8, 45

REFP

LDO

1, 3, 5, 7, 9, 12, 15, 44

GND

2.85V TO 5.25V

0.1µF

10µF

1µF

10µF

Figure 42. Universal Inputs Allow Common Hardware Sharing for Thermocouples, Diodes, Thermistors, 3-Wire RTDs, and 4-Wire RTDs

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Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507

Temperature Measurement System with EEPROM

C Temperature, Voltage and

Current Monitor

C Voltage, Current, Temperature

Monitor

Monitor with Alert Outputs

C Coulomb Counter Monitors Charge, Current, Voltage and Temperature with 1% Accuracy. Works with Any

Pin/Software Compatible Version of LTC2983 with Integrated EEPROM

Remote and Internal Temperatures, 14-Bit Voltages and Current, Internal 10ppm/°C Reference

Monitors Temperature and Two Voltages, Adjustable Thresholds, Open Drain Alert Outputs, Temperature to Voltage Output with Integrated 1.8V Reference, ±1°C (Max) Accuracy

Voltage Output with Integrated 1.8V Reference, ±1°C (Max) Accuracy

Battery Chemistry and Capacity

For more information www.linear.com/LTC2983

●

www.linear.com/LTC2983

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LT 0116 REV C• PRINTED IN USA

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