LTC2995 datasheet(52/90 Pages) AD

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LTM2985

Rev. 0

For more information www.analog.com

THERMISTOR MEASUREMENTS

Channel Assignment – Thermistor

For each thermistor tied to the LTM2985, a 32-bit channel

assignment word is programmed into a memory location

corresponding to the channel the sensor is tied to (see

Table 54). 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.

(1) Thermistor Type

The thermistor type is determined by the first five input

bits (B31 to B27) as shown in Table 55. Linearization

coefficients based on Steinhart-Hart equation for com-

APPLICATIONS INFORMATION

Table 54. Thermistor Channel Assignment Word

(1) THERMISTOR

TYPE

(2) SENSE RESISTOR

CHANNEL POINTER

(3) SENSOR

CONFIGURATION

(4) EXCITATION

CURRENT

(5) CUSTOM THERMISTOR

DATA POINTER

TABLE 55

TABLE 31

TABLE 56

TABLE 57

TABLES 96, 97, 98, 100, 101

Measurement Class 31 30 29 28 27 26 25 24 23 22

18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

Thermistor

Type = 19 to 27

RSENSE 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 55. 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

Thermistor 44004/44033

2.252kΩ at 25°C

1.46800E-03 2.38300E-04

1.00700E-07

Thermistor 44005/44030

3kΩ at 25°C

1.40300E-03 2.37300E-04

9.82700E-08

Thermistor 44007/44034

5kΩ at 25°C

1.28500E-03 2.36200E-04

9.28500E-08

Thermistor 44006/44031

10kΩ at 25°C

1.03200E-03 2.38700E-04

1.58000E-07

Thermistor 44008/44032

30kΩ at 25°C

9.37600E-04 2.20800E-04

1.27600E-07

Thermistor YSI-400

2.252kΩ at 25°C

1.47134E-03 2.37624E-04

1.05034E-07

Spectrum 1003k 1kΩ

at 25°C

1.445904E-3 2.68399E-04

1.64066E-07

Thermistor Custom

Steinhart-Hart

user input

Thermistor Custom Table

not used

monlyusedThermistortypes44004/44033,44005/44030,

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 Thermistor

CustomTable(temperaturevsresistance)canbeselected.

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 ad-

dress pointers.

(2) Sense Resistor Channel Pointer

Thermistor measurements are performed ratiometrically

relative to a known RSENSE resistor. The sense resistor

channel pointer field indicates the differential channel

the sense resistor is tied to for the current thermistor

(see Table 31).

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