_______________Detailed Description

The MAX1458 provides an analog amplification path for

the sensor signal. Calibration and temperature com-

pensation are achieved by varying the offset and gain

of a programmable-gain amplifier (PGA) and by varying

the sensor bridge current. The PGA uses a switched-

capacitor CMOS technology, with an input-referred

coarse offset trimming range of approximately ±63mV

(9mV steps). An additional output-referred fine offset

trim is provided by the Offset DAC (approximately

2.8mV steps). The PGA provides eight gain values from

+41V/V to +230V/V. The bridge current source is pro-

grammable from 0.1mA to 2mA.

The MAX1458 uses four 12-bit DACs and one 3-bit

DAC, with calibration coefficients stored by the user in

an internal 128-bit EEPROM. This memory contains the

following information as 12-bit-wide words:

• Configuration register

• Offset calibration coefficient

• Offset temperature error compensation coefficient

• FSO (full-span output) calibration coefficient

• FSO temperature error compensation coefficient

• 24 user-defined bits for customer programming of

manufacturing data (e.g., serial number and date)

Figure 1 shows a typical pressure-sensor output and

defines the offset, full-scale, and full-span output values

as a function of voltage.

1%-Accurate, Digitally Trimmed

Sensor Signal Conditioner

4

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NAME

FUNCTION

1

SCLK

tor. Data is clocked in on the rising edge of the clock. The maximum SCLK frequency is 10kHz.

2

CS

Chip-Select Input. The MAX1458 is selected when this pin is high. When low, OUT and DIO become high

PIN

3, 11

I.C.

Internally Connected. Leave unconnected.

4

TEMP

Temperature Sensor Output. An internal temperature sensor (a 100k

Ω, 4600ppm/°C TC resistor) which can

provide a temperature-dependent voltage.

8

Negative Power-Supply Input

7

WE

Dual-Function Input Pin. Used to enable EEPROM erase/write operations. Also used to set the DAC refresh-

Enable (WE) section.

6

DIO

resistor. High impedance when CS is low.

5

FSOTC

Buffered FSOTC DAC Output. An internal 75k

14

INP

Positive Sensor Input. Input impedance >1M

Ω. Rail-to-rail input range.

13

BDRIVE

Sensor Excitation Current Output. This current source drives the bridge.

12

INM

Negative Sensor Input. Input impedance >1M

Ω. Rail-to-rail input range.

10

OUT

PGA Output Voltage

9

ISRC

Current-Source Reference. An internal 75k

Pin Description

16

LIMIT

Voltage Limit Input. This pin sets the maximum voltage at OUT. If left unconnected, the output voltage will be

15