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MAX1452

Low-Cost Precision Sensor Signal Conditioner

Maxim Integrated 

MAX1452

Low-Cost Precision Sensor

Signal Conditioner

VDD

VDD

IRO

DAC

MAX1452

BIAS

GENERATOR

OSCILLATOR

CLK1M

TEST

INP

∑

PGA

OUT

INM

ISRC

BDR

VDDF

DIO

UNLOCK

AMP+

AMP-

CURRENT

SOURCE

TEMP

SENSOR

8-BIT ADC

INTERNAL

EEPROM

6144 BITS

416 BITS

FOR USER VDD

ANAMUX

A=1

FSOTC

176

TEMPERATURE

LOOK UP

POINTS FOR

OFFSET AND

SPAN.

BDR OP-AMP

AMPOUT

VSS

Figure 1. Functional Diagram

or voltage. The PGA 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

234V/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 following

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 number

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 tem-

perature 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 resolu-

tion 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 offset 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 maximum 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 temperature 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

output the coefficient value at index 00hex. The maximum

indexing value is AFhex, which is the highest lookup table

entry. All temperatures higher than approximately 184°C

output the highest lookup table index value. No indexing

wraparound 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 resolution approach-

ing 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 corresponding to approximately

-69°C. All temperatures below this value output the coef-

ficient value at index 00hex. The maximum indexing

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

All temperatures higher than approximately 184°C output

the highest lookup table index value. No indexing wrap-

around errors are produced.

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