LTC2984 datasheet(75/78 Pages) AD

75 / 78 page

LTC2984

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For more information www.linear.com/LTC2984

CUSTOM THERMISTORS

A custom thermistor tied to CH5, with a sense resistor on

CH3/4, is programmed with the channel assignment data

shown in Table 87 (refer to Figure 27 for a similar format).

In this case the custom data begins at memory location

0x26E (starting address is 30). The starting address

(offset from 0x250) is entered in the custom thermistor

data pointer field of the channel assignment data. The data

length (set to 0) is always six 32-bit floating point words.

Table 87. Custom Steinhart-Hart Channel Assignment Data

CONFIGURATION

FIELD

DESCRIPTION # BITS

BINARY

DATA

MEMORY

ADDRESS 210

MEMORY

ADDRESS 211

MEMORY

ADDRESS 212

MEMORY

ADDRESS 213

(1) Thermistor Type

Custom

Steinhart-Hart

11010 1 1 0 1 0

(2) Sense Resistor

Channel Pointer

CH4

00100

0 0 1 0 0

(3) Sensor

Configuration

Single-Ended

100

1 0 0

(4) Excitation Current

1µA

0011

0 0 1 1

Not Used

Set These Bits

to 0

0 0 0

(5) Custom Thermistor

Data Pointer

Start Address

= 30

011110

0 1 1 1 1 0

(5) Custom Steinhart-

Hart Length Always

Set to 0

Fixed at Six

32-Bit Words

000000

0 0 0 0 0 0

Universal Sensor Hardware

TheLTC2984canbeconfiguredasauniversaltemperature

measurement device. Up to four sets of universal inputs

can be applied to a single LTC2984. Each of these sets can

directly digitize a 3-wire RTD, 4-Wire RTD, Thermistor, or

thermocouple without changing any on board hardware

(see Figure 45). Each sensor can share the same four ADC

inputsandprotection/filteringcircuitryareconfiguredusing

software changes (new channel assignment data) only.

One sense resistor and cold junction sensor are shared

among all four banks of sensors.

TheLTC2984includesmanyflexible,softwareconfigurable

inputmodes.Inordertosharefourcommoninputsamong

all four sensor types each sensor requires specific con-

figuration bits (see Table 88). 3-Wire RTDs are configured

with shared RSENSE, 4-Wire RTDs and thermistors are

configured as shared and/or rotated, thermocouples are

configured differential with internal ground, and diodes

are configured as single-ended.

Table 88. Sensor Configuration for Universal Hookup

SENSOR TYPE

CONFIGURATION

OPTIONS

CONFIGURATION

BITS

SEE TABLE

3-Wire RTD

B18 = 1, B19 = 0

Table 32

4-Wire RTD

B18 = 1, B19 = 0

Table 32

4-Wire RTD

Rotate

B18 = 0, B19 = 1

Table 32

Thermistor

B19 = 0, B20 = 1

Table 56

Thermistor

Rotate

B19 = 1, B20 = 0

Table 56

Thermocouple

Single-Ended

B21 = 1

Table 18

Diode

Single-Ended

B26 = 1

Table 21

LTC2984 Datasheet(PDF) 75 Page - Analog Devices

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