Linear Technology LTC2983 - Thermistor Measurements

LTC2983
43
2983fc
For more information www.linear.com/LTC2983
Table 50. Thermistor Channel Assignment Word
(1) THERMISTOR
TYPE
(2) SENSE RESISTOR
CHANNEL POINTER
(3) SENSOR
CONFIGURATION
(4) EXCITATION
CURRENT
(5) CUSTOM THERMISTOR
DATA POINTER
TABLE 51 TABLE 27 TABLE 52 TABLE 53 TABLES 76, 77, 78, 80, 81
Measurement Class 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Thermistor Type = 19 to 27 R
SENSE
Channel
Pointer [4:0]
SGL = 1
DIFF = 0
Excitation
Mode
Excitation Current
[3:0]
Not Used
0 0 0
Custom Address
[5:0]
Custom Length – 1
[5:0]
Table 51. Thermistor Type: 1/T=A+B•ln(R)+C•ln(R)
2
+ D•ln(R)
3
+ E•ln(R)
4
+ F•ln(R)
5
B31 B30 B29 B28 B27 THERMISTOR TYPE A B C D E F
1 0 0 1 1 Thermistor 44004/44033
2.252kΩ at 25°C
1.46800E-03 2.38300E-04 0 1.00700E-07 0 0
1 0 1 0 0 Thermistor 44005/44030
3kΩ at 25°C
1.40300E-03 2.37300E-04 0 9.82700E-08 0 0
1 0 1 0 1 Thermistor 44007/44034
5kΩ at 25°C
1.28500E-03 2.36200E-04 0 9.28500E-08 0 0
1 0 1 1 0 Thermistor 44006/44031
10kΩ at 25°C
1.03200E-03 2.38700E-04 0 1.58000E-07 0 0
1 0 1 1 1 Thermistor 44008/44032
30kΩ at 25°C
9.37600E-04 2.20800E-04 0 1.27600E-07 0 0
1 1 0 0 0 Thermistor YSI-400
2.252kΩ at 25°
C
1.47134E-03 2.37624E-04 0 1.05034E-07 0 0
1 1 0 0 1 Spectrum 1003k 1kΩ
at 25°C
1.445904E-3 2.68399E-04 0 1.64066E-07 0 0
1 1 0 1 0 Thermistor Custom
Steinhart-Hart
user input user input user input user input user input user input
1 1 0 1 1 Thermistor Custom Table not used not used not used not used not used not used
THERMISTOR MEASUREMENTS
Channel Assignment – Thermistor
For each thermistor tied to the LTC2983, a 32-bit channel
assignment word is programmed into a memory location
corresponding to the channel the sensor is tied to (see
Table 50). This data includes (1) thermistor type, (2)
sense resistor channel pointer, (3) sensor configuration,
(4) excitation current, (5) Steinhart-Hart address pointer
or custom table address pointer.
APPLICATIONS INFORMATION
(1) Thermistor Type
The thermistor type is determined by the first five input
bits (B31 to B27) as shown in Table 51. Linearization coef-
ficients based on Steinhart-Hart equation for commonly
used Thermistor types 44004/44033, 44005/44030,
44006/44031, 44007/44034, 44008/44032 and YSI-400
are built into the device. If other custom thermistors are
used, Thermistor Custom Steinhart-Hart or Thermis-
tor Custom Table (temperature vs resistance) can be
selected. In this case, user specific data can be stored
in the on-chip RAM starting at the address defined in
Thermistor Custom Steinhart-Hart or Thermistor Custom
Table address pointers.