Typical Nonratiometric

Operating Circuit

(12VDC < VPWR < 40VDC)

Nonratiometric output configuration enables the sensor

power to vary over a wide range. A high performance

voltage reference, such as the MAX6105, is incorporat-

ed in the circuit to provide a stable supply and refer-

ence for MAX1452 operation. A typical example is

when wide ranges of input voltage are to be expected

and the system A/D or readout device does not enable

ratiometric operation.

Typical 2-Wire, Loop Powered,

4–20mA Operating Circuit

Process Control systems benefit from a 4–20mA current

loop output format for noise immunity, long cable runs,

and 2-wire sensor operation. The loop voltages can

range from 12VDC to 40VDC and are inherently nonra-

tiometric. The low current consumption of the MAX1452

allows it to operate from loop power with a simple

4–20mA drive circuit efficiently generated using the

integrated uncommitted op amp (Figure 4).

Internal Calibration Registers (ICRs)

The MAX1452 has five 16-bit internal calibration regis-

ters that are loaded from EEPROM, or loaded from the

serial digital interface.

Data can be loaded into the internal calibration regis-

ters under three different circumstances.

Normal Operation, Power-On Initialization Sequence

•

The MAX1452 has been calibrated, the Secure-

Lock byte is set (CL[7:0] = FFhex) and UNLOCK is

low.

•

Power is applied to the device.

•

The power-on reset functions have completed.

•

Registers CONFIG, OTCDAC, and FSOTCDAC are

refreshed from EEPROM.

•

Registers ODAC, and FSODAC are refreshed from

the temperature indexed EEPROM locations.

Normal Operation, Continuous Refresh

•

The MAX1452 has been calibrated, the Secure-

Lock byte has been set (CL[7:0] = FFhex) and

UNLOCK is low.

•

Power is applied to the device.

•

The power-on reset functions have completed.

•

The temperature index timer reaches a 1ms time

period.

Low-Cost Precision Sensor

Signal Conditioner

_______________________________________________________________________________________

9

MAX1452

VPWR

+12V TO +40V

OUT

GND

RSTC

RISRC

0.1

µF 0.1µF

0.1

µF

0.1

µF

INM

INP

7

9

2

16

1

8

3

BDR

OUT

5

6

4

FSOTC

ISRC

SENSOR

MAX6105

5V

GND

1

3

IN

2

1k

Ω

G

S

D

2N4392

Figure 3. Basic Nonratiometric Output Configuration