utilizes a switched capacitor CMOS technology, with an

input referred offset trimming range of more than

±150mV with an approximate 3µV resolution (16 bits).

The PGA provides gain values from 39V/V to 240V/V in

16 steps.

The MAX1452 uses four 16-bit DACs with calibration

coefficients stored by the user in an internal 768 x 8

EEPROM (6144 bits). This memory contains the follow-

ing information, as 16-bit wide words:

•

Configuration Register

•

Offset Calibration Coefficient Table

•

Offset Temperature Coefficient Register

•

FSO (Full-Span Output) Calibration Table

•

FSO Temperature Error Correction Coefficient

Register

•

52 bytes (416 bits) uncommitted for customer pro-

gramming of manufacturing data (e.g., serial num-

ber and date)

Offset Correction

Initial offset correction is accomplished at the input

stage of the signal gain amplifiers by a coarse offset

setting. Final offset correction occurs through the use of

a temperature indexed lookup table with 176 16-bit

entries. The on-chip temperature sensor provides a

unique 16-bit offset trim value from the table with an

indexing resolution of approximately 1.5°C from -40°C

to +125°C. Every millisecond, the on-chip temperature

sensor provides indexing into the offset lookup table in

EEPROM and the resulting value transferred to the off-

set DAC register. The resulting voltage is fed into a

summing junction at the PGA output, compensating the

sensor offset with a resolution of ±76µV (±0.0019%

FSO). If the offset TC DAC is set to zero then the maxi-

mum temperature error is equivalent to one degree of

temperature drift of the sensor, given the Offset DAC

has corrected the sensor at every 1.5°C. The tempera-

ture indexing boundaries are outside of the specified

Absolute Maximum Ratings. The minimum indexing

value is 00hex corresponding to approximately -69°C.

All temperatures below this value will output the coeffi-

cient value at index 00hex. The maximum indexing

value is AFhex, which is the highest lookup table entry.

All temperatures higher than approximately 184°C will

output the highest lookup table index value. No index-

ing wrap-around errors are produced.

FSO Correction

Two functional blocks control the FSO gain calibration.

First, a coarse gain is set by digitally selecting the gain

of the PGA. Second, FSO DAC sets the sensor bridge

current or voltage with the digital input obtained from a

temperature-indexed reference to the FSO lookup table

in EEPROM. FSO correction occurs through the use of

a temperature indexed lookup table with 176 16-bit

entries. The on-chip temperature sensor provides a

unique FSO trim from the table with an indexing resolu-

tion approaching one 16-bit value at every 1.5°C from

-40°C to +125°C. The temperature indexing boundaries

are outside of the specified Absolute Maximum

Ratings. The minimum indexing value is 00hex corre-

sponding to approximately -69°C. All temperatures

below this value will output the coefficient value at

index 00hex. The maximum indexing value is AFhex,

which is the highest lookup table entry. All tempera-

tures higher than approximately 184°C will output the

highest lookup table index value. No indexing wrap-

around errors are produced.

Linear and Nonlinear Temperature

Compensation

Writing 16-bit calibration coefficients into the offset TC

and FSOTC registers compensates first-order tempera-

Low-Cost Precision Sensor

Signal Conditioner

_______________________________________________________________________________________

7

MAX1452

BIAS

GENERATOR

OSCILLATOR

ANAMUX

FSOTC

176

TEMPERATURE

LOOK UP

POINTS FOR

OFFSET AND

SPAN.

OP-AMP

A = 1

AMPOUT

OUT

CLK1M

TEST

INTERNAL

EEPROM

6144 BITS

416 BITS

FOR USER

BDR

PGA

VDDF

BDR

DIO

UNLOCK

AMP+

AMP-

INP

ISRC

INM

8-BIT ADC

TEMP

SENSOR

IRO

DAC

CURRENT

SOURCE

∑

Figure 1. Functional Diagram