LTC2983
69
2983fc
For more information www.linear.com/LTC2983
A custom thermistor tied to CH5, with a sense resistor on
CH3/4, is programmed with the channel assignment data
shown in Table 83 (refer to Figure 24 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.
Universal Sensor Hardware
The LTC2983 can be configured as a universal temperature
measurement device. Up to four sets of universal inputs
can be applied to a single LTC2983. 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 42). Each sensor can share the same four ADC
inputs and protection/filtering circuitry are configured us-
ing software changes (new channel assignment data) only.
One sense resistor and cold junction sensor are shared
among all four banks of sensors.
CUSTOM THERMISTORS
The LTC2983 includes many flexible, software configurable
input modes. In order to share four common inputs among
all four sensor types each sensor requires specific con-
figuration bits (see Table 84). 3-Wire RTDs are configured
with shared R
SENSE
, 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 83. 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
5 11010 1 1 0 1 0
(2) Sense Resistor
Channel Pointer
CH
4
5 00100 0 0 1 0 0
(3) Sensor
Configuration
Single-Ended 3 100 1 0 0
(4) Excitation Current 1µA 4 0011 0 0 1 1
Not Used Set These Bits
to 0
3 00 0 0 0
(5) Custom Thermistor
Data Pointer
Start Address
= 30
6 011110 0 1 1 1 1 0
(5) Custom Steinhart-
Hart Length Always
Set to 0
Fixed at Six
32-Bit Words
6 000000 0 0 0 0 0 0
Table 84. Sensor Configuration for Universal Hookup
SENSOR TYPE CONFIGURATION
OPTIONS
CONFIGURATION
BITS
SEE TABLE
3-WIRE RTD Share B18 = 1, B19 = 0 Table 28
4-WIRE RTD Share B18 = 1, B19 = 0 Table 28
4-WIRE RTD Rotate B18 = 0, B19 = 1 Table 28
Thermistor Share B19 = 0, B20 = 1 Table 52
Thermistor Rotate B19 = 1, B20 = 0 Table 52
Thermocouple Single-Ended B21 = 1 Table 14
Diode Single-Ended B26 = 1 Table 17
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