LTC2984 datasheet(55/78 Pages) AD

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LTC2984

2984fb

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Example: Differential Thermistor

The differential thermistor configuration allows separate

ground sensing for each sensor. In this standard differ-

ential configuration, one sense resistor is used for each

thermistor. Differential thermistors follow the convention

shown in Figure 28. Terminal 1 ties to CHTHERM and is

shorted to ground and terminal 2 ties CHTHERM-1 to and

thesenseresistor.Channelassignmentdata(seeTable54)

ismappedtomemorylocationscorrespondingtoCHTHERM.

APPLICATIONS INFORMATION

Sense resistor channel assignments follow the general

convention shown in Figure 29. The sense resistor is tied

betweenCHRSENSEandCHRSENSE-1,whereCHRSENSEistied

to the 2nd terminal of the thermistor. Channel assignment

data (see Table 37) is mapped into a memory location cor-

responding to CHRSENSE.

Figure 28. Differential Thermistor Channel Assignment

Convention

2984 F28

CHTHERM

CHTHERM–1

EXCITATION

CURRENT

FLOW

= CHTHERM (2 ≤ THERM ≤ 20)

2ND TERMINAL TIES TO SENSE RESISTOR

1ST TERMINAL TIES TO GND

CHANNEL

ASSIGNMENT

Figure 30 shows a typical temperature measurement

system using a differential thermistor. In this example a

30kΩ (44032 type) thermistor is tied to a 9.99kΩ sense

resistor.ThethermistorisassignedchannelCH13(memory

locations 0x230 to 0x233) and the sense resistor to CH11

(memory locations 0x228 to 0x22B). Channel assignment

data is shown in Tables 62 and 63).

A conversion is initiated on CH13bywriting10001101into

memory location 0x000. Once the conversion is complete,

the INTERRUPT pin goes HIGH and memory location

0x000 becomes 01001101. The resulting temperature in

°C can be read from memory locations 0x040 to 0x043

(Corresponding to CH13).

Figure 29. Sense Resistor Channel Assignment Convention

2984 F29

CHRSENSE-1

CHRSENSE

RSENSE

EXCITATION

CURRENT

FLOW

= CHRSENSE (2 ≤ RSENSE ≤ 20)

CHANNEL

ASSIGNMENT

Figure 30. Differential Thermistor Example

2984 F30

SENSE RESISTOR ASSIGNED TO CH11 (CHSENSE=11)

CH10

CHANNEL ASSIGNMENT

MEMORY LOCATIONS 0x228 TO 0x22B

CH11

CH12

CH13

THERMISTOR ASSIGNED TO CH5 (CHTHERM=13)

CHANNEL ASSIGNMENT

MEMORY LOCATIONS 0x230 TO 0x233

RESULT MEMORY LOCATIONS 0x040 TO 0x043

RSENSE

9.99k

100pF

TYPE 44032

100pF

LTC2984 Datasheet(PDF) 55 Page - Analog Devices

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