Detailed Description

The MAX1452 provides amplification, calibration, and

temperature compensation to enable an overall perfor-

mance approaching the inherent repeatability of the

sensor. The fully analog signal-path introduces no

quantization noise in the output signal while enabling

digitally controlled trimming with the integrated 16-bit

DACs. Offset and span can be calibrated to within

±0.02% of span.

The MAX1452 architecture includes a programmable

sensor excitation, a 16-step programmable-gain ampli-

fier (PGA), a 768-byte (6144 bits) internal EEPROM, four

16-bit DACs, an uncommitted op amp, and an on-chip

temperature sensor.The MAX1452 also provides a

unique temperature compensation strategy for offset

TC and FSOTC that was developed to provide a

remarkable degree of flexibility while minimizing testing

costs.

The customer can select from one to 114 temperature

points to compensate their sensor. This allows the lati-

tude to compensate a sensor with a simple first order

linear correction or match an unusual temperature

curve. Programming up to 114 independent 16-bit EEP-

ROM locations corrects performance in 1.5°C tempera-

ture increments over a range of -40°C to +125°C. For

sensors that exhibit a characteristic temperature perfor-

mance, a select number of calibration points can be

used with a number of preset values that define the

temperature curve. In cases where the sensor is at a

different temperature than the ASIC, the MAX1452 uses

the sensor bridge itself to provide additional tempera-

ture correction.

The single pin, serial Digital Input-Output (DIO) commu-

nication architecture and the ability to timeshare its

activity with the sensor’s output signal enables output

sensing and calibration programming on a single line

by parallel connecting OUT and DIO. The MAX1452

provides a Secure-Lock feature that allows the cus-

tomer to prevent modification of sensor coefficients and

the 52-byte user definable EEPROM data after the sen-

sor has been calibrated. The Secure-Lock feature also

provides a hardware override to enable factory rework

and recalibration by assertion of logic high on the

UNLOCK pin.

The MAX1452 allows complete calibration and sensor

verification to be performed at a single test station.

Once calibration coefficients have been stored in the

ASIC, the customer can choose to retest in order to ver-

ify performance as part of a regular QA audit or to gen-

erate final test data on individual sensors.

The MAX1452’s low current consumption and the inte-

grated uncommitted op amp enables a 4–20mA output

signal format in a sensor that is completely powered

from a 2-wire current loop. Frequency response can be

user-adjusted to values lower than the 3.2kHz band-

width by using the uncommitted op amp and simple

passive components.

tion path for the sensor signal. It also uses an analog

architecture for first-order temperature correction. A

digitally controlled analog path is then used for nonlin-

ear temperature correction. Calibration and correction

is achieved by varying the offset and gain of a pro-

grammable-gain-amplifier (PGA) and by varying the

sensor bridge excitation current or voltage. The PGA

Low-Cost Precision Sensor

Signal Conditioner

6

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Pin Description (continued)

PIN

NAME

FUNCTION

Positive Supply Voltage for EEPROM. Connect a 0.1

10

UNLOCK

Secure-Lock Disable. Allows communication to the device.

11

DIO

Digital Input Output. DIO allows communication with the device.

12

CLK1M

1MHz Clock Output. The clock can be shut off by a configuration bit.

13

AMPOUT

Uncommitted Amplifier Output

14

AMP-

Uncommitted Amplifier Negative Input

15

AMP+

Uncommitted Amplifier Positive Input

16

FSOTC

Full Span TC Buffered Output