Maxim MAX1457CWI, MAX1457CCJ, MAX1457C-D Datasheet

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________________General Description

The MAX1457 is a highly integrated analog-sensor signal processor optimized for piezoresistive sensor calibration and compensation. It includes a programmable current source for sensor excitation, a 3-bit programmable-gain amplifier (PGA), a 12-bit ADC, five 16-bit DACs, and an uncommitted op amp. Achieving a total error factor within 0.1% of the sensor’s repeatability errors, the MAX1457 compensates offset, full-span output (FSO), offset TC, FSO TC, and full-span output nonlinearity of silicon piezoresistive sensors.

The MAX1457 calibrates and compensates first-order temperature errors by adjusting the offset and span of the input signal via digital-to-analog converters (DACs), thereby eliminating quantization noise. If needed, residual higher-order errors are then compensated using linear interpolation of the first-order coefficients stored in a look-up table (in external EEPROM).

The MAX1457 integrates three traditional sensormanufacturing operations into one automated process:

• Pretest: Data acquisition of sensor performance under the control of a host test computer.

• Calibration and Compensation: Computation and storage (in an external EEPROM) of calibration and compensation

coefficients determined from transducer pretest data.

• Final Test: Verification of transducer calibration and compensation, without removal from a pretest socket.

Analog outputs are provided for both pressure and temperature. A general-purpose, uncommitted op amp is also included on-chip to increase the overall circuit gain, or to facilitate the implementation of a 2-wire, 4–20mA transmitter. The serial interface is compatible with MicroWire™ and SPI™, and directly connects to an external EEPROM. Additionally, built-in testability features of the MAX1457 facilitate manufacturing and calibration of multiple sensor modules, thus lowering manufacturing cost.

Although optimized for use with piezoresistive sensors, the MAX1457 may also be used with other resistive sensor types (i.e., accelerometers and strain gauges) with the addition of a few external components.

_______________________Customization

Maxim can customize the MAX1457 for unique requirements. With a dedicated cell library of more than 90 sensor-specific functional blocks, Maxim can quickly provide customized MAX1457 solutions. Contact Maxim for additional information.

____________________________Features

♦ High Accuracy (within ±0.1% of sensor’s

repeatable errors)

♦ Compensates Offset, Offset TC, FSO, FSO TC,

Temperature/Pressure Nonlinearity

♦ Rail-to-Rail

Analog Output for Calibrated, Temperature-Compensated Pressure Measurements

♦ Programmable Sensor Excitation Current ♦ SPI/MicroWire-Compatible Serial Interface ♦ Fast Signal-Path Settling Time (<1ms) ♦ Accepts Sensor Outputs from 5mV/V to 30mV/V ♦ Pin-Compatible with MCA7707

MAX1457

0.1%-Accurate Signal Conditioner

for Piezoresistive Sensor Compensation

________________________________________________________________

Maxim Integrated Products

MAX1457

BIAS

GENERATOR

OSCILLATOR

16-BIT DAC - OFFSET TC

16-BIT DAC - OFFSET

16-BIT DAC - FSO

16-BIT DAC - FSO TC

16-BIT DAC - FSO LINEARITY

FSOTCDAC OTCDAC OFSTDAC FSODAC

LINDAC

LINOUT

FSOTCOUT

VBBUF

BDRIVE

A = 1

AMPOUT

VOUT

NBIAS

FADJ FOUT

SERIAL

EEPROM

INTERFACE

AGND

PGA

MCS

ECS

ECLK

EDI

EDO

LINDACREF

AMP+

AMP-

BDRIVE

ISRC

INM

INP

12-BIT ADC

19-1342; Rev 1; 8/98

PART

MAX1457CWI MAX1457CCJ 0°C to +70°C

0°C to +70°C

TEMP. RANGE PIN-PACKAGE

28 Wide SO 32 TQFP

EVALUATION KIT

AVAILABLE

_______________Ordering Information

Ordering Information continued at end of data sheet.

Note:

Contact the factory for customized solutions.

Dice are tested at TA= +25°C.

Pin Configurations appear at end of data sheet.

MAX1457C/D 0°C to +70°C Dice*

Rail-to-Rail is a registered trademark of Nippon Motorola, Ltd. SPI is a trademark of Motorola, Inc. MicroWire is a trademark of National Semiconductor Corp.

Functional Diagram

MAX1457

0.1%-Accurate Signal Conditioner for Piezoresistive Sensor Compensation

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VDD= +5V, VSS= 0V, TA= +25°C, unless otherwise noted.)

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.

Supply Voltage, VDDto VSS......................................-0.3V to +6V

All other pins....................................(V

- 0.3V) to (VDD+ 0.3V)

Continuous Power Dissipation (T

= +70°C)

28-Pin Wide SO (derate 12.50mW/°C above +70°C) ..........1W

32-Pin TQFP (derate 11.1mW/°C above +70°C)...........889mW

Operating Temperature Ranges

MAX1457C_ _ ......................................................0°C to +70°C

MAX1457A_ _ .................................................-40°C to +125°C

Storage Temperature Range.............................-65°C to +150°C

Lead Temperature (soldering, 10sec).............................+300°C

Reference voltage = 5.000V

BIAS

= 400kΩ, f

CLK

= 100kHz (Note 1)

Gain = 54, DC to 10Hz, sensor impedance = 5kΩ, full-span output = 4V

OUT

= (VSS+ 0.25V) to (VDD- 0.25V)

(Note 5)

(Note 4)

5kΩ load to VSSor V

From VSSto V

CLK

= 100kHz, to 63% of final value

(Notes 2, 3)

CONDITIONS

µV200DAC Voltage Resolution

VVSS+ 1.3 VDD- 1.3V

ISRC

Current-Source Reference Input Voltage Range

VVSS+ 1.3 VDD- 1.3V

Bridge Voltage Swing

mA0.1 0.5 2.0I

Bridge Current Range

%FSO0.0025Output Noise

-1.0 1.0

(sink) (source)

Output Current Range

VSS+ 0.02 VDD- 0.02

Output Voltage Swing

ppm/°C±50Differential Signal Gain Tempco

V/V54 to 306Differential Signal Gain Range

mA2.0 2.6I

Supply Current

V4.5 5 5.5V

Supply Voltage

mV/V5 to 30

Input-Referred Adjustable Full-Span Output Range

mV±100

Input-Referred Adjustable Offset Range

dB90CMRRCommon-Mode Rejection Ratio

ms1Output Step-Response Time

MΩ

Input Impedance

µV/°C±0.5Input-Referred Offset Tempco

0.01Amplifier Gain Nonlinearity

UNITSMIN TYP MAXSYMBOLPARAMETER

Output filter capacitor = 0.1µF, f

CLK

= 100kHz LSB2Differential Nonlinearity

Bits16DAC Resolution

VSS+ 0.25 VDD- 0.25

TA= T

MIN

to T

MAX

V/V49 54 60Minimum Differential Signal Gain

GENERAL CHARACTERISTICS

ANALOG INPUT (PGA)

ANALOG OUTPUT (PGA)

DIGITAL-TO-ANALOG CONVERTERS

CURRENT SOURCE

No load

MAX1457

0.1%-Accurate Signal Conditioner

for Piezoresistive Sensor Compensation

_______________________________________________________________________________________ 3

Note 1: Circuit of Figure 5 with current source turned off. This value is adjustable through a bias resistor and represents the IC cur-

rent consumption. This excludes the 93C66 EEPROM average current, which is approximately 13µA at a refresh rate of 3Hz (f

CLK

= 100kHz).

Note 2: Temperature errors for the entire range are compensated together with the sensor errors. Note 3: The sensor and the MAX1457 must always be at the same temperature during calibration and use. Note 4: This is the maximum allowable sensor offset at minimum gain (54V/V). Note 5: This is the sensor’s sensitivity normalized to its drive voltage, assuming a desired full-span output of 4V and a bridge volt-

age of 2.5V. Lower sensitivities can be accommodated by using the auxiliary op amp. Higher sensitivities can be accommodated by operating at lower bridge voltages.

ELECTRICAL CHARACTERISTICS (continued)

(VDD= +5V, VSS= 0V, TA= +25°C, unless otherwise noted.)

VBR= 2.5V to 3.5V, f

CLK

= 100kHz

OUT

= (VSS+ 0.25V) to (VDD- 0.25V)

(VIN- V

OUT

) at VIN= 2.5V,

BIAS

= 400kΩ (no load)

5kΩ load to VSSor V

BIAS

= 400kΩ, VIN= 2.5V (no load)

BIAS

= 400kΩ, VIN= 2.5V,

OUT

= 2.5V ±20mV

CLK

= 100kHz

BIAS

= 400kΩ

BIAS

= 400kΩ (no load)

CONDITIONS

-1.0 1.0

(sink) (source)

Output Current Range

VSS+ 0.02 VDD- 0.02

Output Voltage Swing

mV-20 20

Offset Voltage (as unity-gain follower)

dB60A

Open-Loop Gain

VVSS+ 1.3 VDD- 1.2CMR

Input Common-Mode Voltage Range

LSB2ADC Differential Nonlinearity

mV-20 20V

OFS

Offset Voltage

µA-50 50Current Drive

ms160Conversion Time

Bits12ADC Resolution

VVSS+ 1.3 VDD- 1.3Voltage Swing

UNITSMIN TYP MAXSYMBOLPARAMETER

VSS+ 0.25 VDD- 0.25

ANALOG-TO-DIGITAL CONVERTER

UNCOMMITTED OP AMP

OUTPUTS (LINDAC, FSOTCDAC)

No load

MAX1457

0.1%-Accurate Signal Conditioner for Piezoresistive Sensor Compensation

4 _______________________________________________________________________________________

______________________________________________________________Pin Description

1 28

Positive Sensor Input. Input impedance >1MΩ. Rail-to-rail input range.

2 29

Negative Sensor Input. Input impedance >1MΩ. Rail-to-rail input range. 3 30 Positive Input of General-Purpose Operational Amplifier 4 31 Negative Input of General-Purpose Operational Amplifier

—

4, 16,

22, 32

Not internally connected.

7 3

PGA Output Voltage. Connect a 0.1µF capacitor from VOUT to VSS. High impedance when

MCS is low.

6 2 Sensor Excitation Current. This pin drives a nominal 0.5mA through the sensor.

5 1 Output of General-Purpose Operational Amplifier. High impedance when MCS is low.

12 9 Reference Input to FSO Linearity DAC. Normally tied to VOUT.

11 8

Buffered FSO Linearity DAC Output. Use a resistor (R

LIN

) greater than 100kΩ, from LINOUT to ISRC to correct second order FSO nonlinearity errors. Leave unconnected if not correcting second order FSO nonlinearity errors.

10 7 Buffered Bridge Voltage (the voltage at BDRIVE). Leave unconnected if unused.

9 6

Buffered FSO TC DAC Output. Tie to ISRC with a resistor (R

STC

≥ 50kΩ).

8 5

Current-Source Reference. Connect a 50kΩ resistor from ISRC to VSS.

INP

INM

AMP+

AMP-

N.C.

VOUT

BDRIVE

AMPOUT

LINDACREF

LINOUT

VBBUF

FSOTCOUT

ISRC

13 10 FSO Linearity DAC Output Voltage. Connect 0.1µF capacitor from LINDAC to VSS.LINDAC 14 11 Negative Power Supply InputV

15 12 OFFSET TC DAC Output Voltage. Connect a 0.1µF capacitor from OTCDAC to VSS.OTCDAC 16 13 FSO DAC Output Voltage. Connect a 0.1µF capacitor from FSODAC to VSS.FSODAC 17 14 FSO TC DAC Output Voltage. Connect a 0.1µF capacitor from FSOTCDAC to VSS.FSOTCDAC 18 15 OFFSET DAC Output Voltage. Connect a 0.1µF capacitor from OFSTDAC to VSS.OFSTDAC

19 17

Serial Input (data from EEPROM), active high. CMOS logic-level input pin through which the MAX1457’s internal registers are updated with EEPROM coefficients. Disabled when MCS is low.

EDO

20 18

Serial Output (data to EEPROM), active high. CMOS logic-level output pin through which the MAX1457 gives external commands to the EEPROM. Temperature-compensation data is available through this pin. Becomes high impedance when MCS is low.

EDI

21 19 CMOS Logic-Level Clock Output for external EEPROM. High impedance when MCS is low.ECLK 22 20

Chip-Select Output for external EEPROM. CMOS logic-level output pin through which the MAX1457 enables/disables EEPROM operation. High impedance when MCS is low.

ECS 23 21 Frequency Output. Internal oscillator output signal. Normally left open.FOUT 24 23

Frequency Adjust. Connect to VSSwith a 1.5MΩ resistor (R

OSC

) to set internal oscillator fre-

quency to 100kHz. Connect a 0.1µF bypass capacitor from FADJ to V

FADJ

FUNCTIONNAME

25 24

Master Chip Select. The MAX1457 is selected when MCS is high. Leave unconnected for normal operation (internally pulled up to VDDwith 1MΩ resistor). External 5kΩ pull-up may be required in noisy environments.

MCS

26 25

Bias Setting Pin. Connect to VDDwith a 400kΩ resistor (R

BIAS

). Connect a 0.1µF bypass

capacitor from NBIAS to V

NBIAS

27 26 Mid-Supply Reference for Analog Circuitry. Connect a 0.1µF capacitor from VSSto AGND.AGND 28 27 Positive Power-Supply Input. Connect a 0.1µF capacitor from VDDto VSS.V

TQFPSO

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