LTC2402 datasheet(27/32 Pages) LINER

27 / 32 page

LTC2401/LTC2402

APPLICATIO S I FOR ATIO

at VIN = VB = FSSET, see Figure 29. Similarly, the offset

errors due to RP2 are removed by the ground sense input

ZSSET. The absolute zero output of the ADC (data out =

000000HEX) occurs at VIN = VA= ZSSET. Parasitic resistors

RP3 to RP5 have negligible errors due to the 1nA (typ)

leakage current at pins FSSET, ZSSET and VIN. The wide

dynamic input range (– 300mV to 5.3V) and low noise

(0.6ppm RMS) enable the LTC2401 or the LTC2402 to

directly digitize the output of the bridge sensor.

The LTC2402 is ideal for applications requiring continu-

ous monitoring of two input sensors. As shown in

Figure 30, the LTC2402 can monitor both a thermocouple

temperature probe and a cold junction temperature sen-

sor. Absolute temperature measurements can be

performed with a variety of thermocouples using digital

cold junction compensation.

The selection between CH0 and CH1 is automatic. Initially,

after power-up, a conversion is performed on CH0. For

each subsequent conversion, the input channel selection

is alternated. Embedded within the serial data output is a

status bit indicating which channel corresponds to the

conversion result. If the conversion was performed on

CH0, this bit (Bit 30) is LOW and is HIGH if the conversion

was performed on CH1 (see Figure 31).

Figure 29. Transfer Curve with Zero-Scale and Full-Scale Set

Figure 30. Isolated Temperature Measurement

00000H

12.5%

UNDER

RANGE

FFFFFH

ZSSET

FSSET

VIN

24012 F29

12.5%

EXTENDED

RANGE

VCC

FSSET

ZSSET

SCK

CH1

SDO

GND

THERMOCOUPLE

COLD JUNCTION

ISOLATION

BARRIER

PROCESSOR

CH0

–

110

12k

THERMISTOR

100

Ω

2.7V TO 5.5V

LTC2402

24012 F30

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