MAXIM MAX31855 Technical data

19-5793; Rev 2; 2/12

MAX31855

Cold-Junction Compensated

Thermocouple-to-Digital Converter

General Description

The MAX31855 performs cold-junction compensation and digitizes the signal from a K-, J-, N-, T-, S-, R-, or E-type thermocouple. The data is output in a signed 14-bit, SPI-compatible, read-only format. This converter resolves temperatures to 0.25NC, allows readings as high as +1800NC and as low as -270NC, and exhibits thermocouple accuracy of ±2NC for temperatures ranging from

-200NC to +700NC for K-type thermocouples. For full range accuracies and other thermocouple types, see the

Thermal Characteristics specifications.

Applications

Industrial

Appliances

HVAC

Automotive

Features

S Cold-Junction Compensation

S 14-Bit, 0.25NC Resolution

S Versions Available for K-, J-, N-, T-, S-, R-, and

E-Type Thermocouples (see Table 1)

S Simple SPI-Compatible Interface (Read-Only)

S Detects Thermocouple Shorts to GND or V

S Detects Open Thermocouple

Ordering Information appears at end of data sheet.

For related parts and recommended products to use with this part, refer to: www.maxim-ic.com/MAX31855.related

Typical Application Circuit

0.1µF

MAX31855

GND

T+

T-

�� Maxim Integrated Products 1

SCK

MICROCONTROLLER

MISO

SCK

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

MAX31855

Cold-Junction Compensated

Thermocouple-to-Digital Converter

ABSOLUTE MAXIMUM RATINGS

Supply Voltage Range (VCC to GND) .................. -0.3V to +4.0V

All Other Pins ............................................ -0.3V to (VCC + 0.3V)

Continuous Power Dissipation (TA = +70NC)

SO (derate 5.9mW/NC above +70NC) .......................470.6mW

ESD Protection (All Pins, Human Body Model) ...................±2kV

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

PACKAGE THERMAL CHARACTERISTICS (Note 1)

Junction-to-Ambient Thermal Resistance (BJA) ........170NC/W

Junction-to-Case Thermal Resistance (BJC) ...............40NC/W

Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-

layer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.

RECOMMENDED OPERATING CONDITIONS

(TA = -40NC to +125NC, unless otherwise noted.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Power-Supply Voltage V Input Logic 0 V

Input Logic 1 V

(Note 2) 3.0 3.3 3.6 V

Operating Temperature Range ........................ -40NC to +125NC

Junction Temperature .....................................................+150NC

Storage Temperature Range .......................... -65NC to +150NC

Lead Temperature (soldering, 10s) ................................+300NC

Soldering Temperature (reflow) .....................................+260NC

-0.3 +0.8 V

2.1

VCC +

0.3

DC ELECTRICAL CHARACTERISTICS

(3.0V P VCC P 3.6V, TA = -40NC to +125NC, unless otherwise noted.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Power-Supply Current I

Thermocouple Input Bias Current

Power-Supply Rejection -0.3

Power-On Reset Voltage Threshold

Power-On Reset Voltage Hysteresis

Output High Voltage V

Output Low Voltage V

�� Maxim Integrated Products 2

POR

TA = -40NC to +125NC, 100mV across the thermocouple inputs

(Note 3) 2 2.5 V

= -1.6mA

OUT

= 1.6mA 0.4 V

OUT

-100 +100 nA

VCC -

0.4

900 1500

NC/V

0.2 V

Cold-Junction Compensated

Thermocouple-to-Digital Converter

THERMAL CHARACTERISTICS

(3.0V P VCC P 3.6V, TA = -40NC to +125NC, unless otherwise noted.) (Note 4)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

MAX31855K Thermocouple Temperature Gain and Offset Error (41.276FV/NC nominal sensitivity) (Note 4)

MAX31855J Thermocouple Temperature Gain and Offset Error (57.953FV/NC nominal sensitivity) (Note 4)

MAX31855N Thermocouple Temperature Gain and Offset Error (36.256FV/NC nominal sensitivity) (Note 4)

MAX31855T Thermocouple Temperature Gain and Offset Error (52.18FV/NC nominal sensitivity) (Note 4)

MAX31855E Thermocouple Temperature Gain and Offset Error (76.373FV/NC nominal sensitivity) (Note 4)

MAX31855R Thermocouple Temperature Gain and Offset Error (10.506FV/NC nominal sensitivity) (Note 4)

MAX31855S Thermocouple Temperature Gain and Offset Error (9.587FV/NC nominal sensitivity) (Note 4)

THERMOCOUPLE

TA = -20NC to +85NC (Note 3)

THERMOCOUPLE

TA = -20NC to +85NC (Note 3)

THERMOCOUPLE

TA = -40NC to +125NC (Note 3)

THERMOCOUPLE

TA = -20NC to +85NC (Note 3)

THERMOCOUPLE

TA = -40NC to +125NC (Note 3)

THERMOCOUPLE

TA = -20NC to +85NC (Note 3)

THERMOCOUPLE

TA = -20NC to +85NC (Note 3)

THERMOCOUPLE

TA = -40NC to +125NC (Note 3)

THERMOCOUPLE

TA = -20NC to +85NC (Note 3)

THERMOCOUPLE

TA = -40NC to +125NC (Note 3)

THERMOCOUPLE

TA = -20NC to +85NC (Note 3)

THERMOCOUPLE

TA = -20NC to +85NC (Note 3)

THERMOCOUPLE

TA = -40NC to +125NC (Note 3)

THERMOCOUPLE

TA = -20NC to +85NC (Note 3)

THERMOCOUPLE

TA = -20NC to +85NC (Note 3)

THERMOCOUPLE

TA = -40NC to +125NC (Note 3)

THERMOCOUPLE

TA = -20NC to +85NC (Note 3)

THERMOCOUPLE

TA = -20NC to +85NC (Note 3)

THERMOCOUPLE

TA = -40NC to +125NC (Note 3)

= -200NC to +700NC,

= +700NC to +1350NC,

= -270NC to +1372NC,

= -210NC to +750NC,

= -210NC to +1200NC,

= -200NC to +700NC,

= +700NC to +1300NC,

= -270NC to +1300NC,

= -270NC to +400NC,

= -200NC to +700NC,

= +700NC to +1000NC,

= -270NC to +1000NC,

= -50NC to +700NC,

= +700NC to +1768NC,

= -50NC to +1768NC,

= -50NC to +700NC,

= +700NC to +1768NC,

= -50NC to +1768NC,

MAX31855

-2 +2

-4 +4

-6 +6

-2 +2

-4 +4

-2 +2

-4 +4

-6 +6

-2 +2

-4 +4

-2 +2

-3 +3

-5 +5

-2 +2

-4 +4

-6 +6

-2 +2

-4 +4

-6 +6

�� Maxim Integrated Products 3

MAX31855

Cold-Junction Compensated

Thermocouple-to-Digital Converter

THERMAL CHARACTERISTICS (continued)

(3.0V P VCC P 3.6V, TA = -40NC to +125NC, unless otherwise noted.) (Note 4)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Thermocouple Temperature Data Resolution

Internal Cold-Junction Temperature Error

Cold-Junction Temperature Data Resolution

Temperature Conversion Time (Thermocouple, Cold Junction, Fault Detection)

Thermocouple Conversion Power-Up Time

CONV

CONV_PU

TA = -20NC to +85NC (Note 3) TA = -40NC to +125NC (Note 3)

TA = -40NC to +125NC

(Note 5) 70 100 ms

(Note 6) 200 ms

-2 +2

-3 +3

SERIAL-INTERFACE TIMING CHARACTERISTICS

(See Figure 1 and Figure 2.)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Input Leakage Current I Input Capacitance C Serial-Clock Frequency f SCK Pulse-High Width t SCK Pulse-Low Width t SCK Rise and Fall Time 200 ns CS Fall to SCK Rise SCK to CS Hold

CS Fall to Output Enable CS Rise to Output Disable

SCK Fall to Output Data Valid t CS Inactive Time

Note 2: All voltages are referenced to GND. Currents entering the IC are specified positive, and currents exiting the IC are negative. Note 3: Guaranteed by design; not production tested. Note 4: Not including cold-junction temperature error or thermocouple nonlinearity. Note 5: Specification is 100% tested at TA = +25NC. Specification limits over temperature (TA = T

design and characterization; not production tested.

Note 6: Because the thermocouple temperature conversions begin at V

temperature conversion may not produce an accurate result. Therefore, the t greater than V

Note 7: For all pins except T+ and T- (see the Thermocouple Input Bias Current parameter in the DC Electrical Characteristics

table).

to guarantee a valid thermocouple temperature conversion result.

CCMIN

LEAK

SCL

CSS

(Note 7) -1 +1 µA

100 ns 100 ns

(Note 3) 200 ns

, depending on VCC slew rates, the first thermocouple

POR

CONV_PU

specification is required after VCC is

MIN

0.25

0.0625

8 pF

to T

) are guaranteed by

MAX

5 MHz

100 ns

40 ns 40 ns

�� Maxim Integrated Products 4

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