LTC2984 datasheet(66/78 Pages) AD

66 / 78 page

LTC2984

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the reported temperature is a linear extrapolation using a

slope determined by points P8 and P9 (the final two table

entries in Table 72). Voltage readings below point P1 are

also reported as soft faults. The temperature reported is

the extrapolation between point P1 and P0, where P0 is

typically the sensor output voltage at 0 Kelvin. If P0 is

above 0 Kelvin, then all sensor output voltages below P0

(in mV) will report 0 Kelvin.

CUSTOM THERMOCOUPLES

Table 72. Thermocouple Example mV vs Kelvin (K) Data Memory Map

POINT

SENSOR OUTPUT

VOLTAGE (mV)

TEMPERATURE

KELVIN

START

ADDRESS

STOP

ADDRESS

BYTE 0

BYTE 1

BYTE 2

BYTE 3

BYTE 4

BYTE 5

–50.22

0x250

0x255

–30.2

99.1

0x256

0x25B

–5.3

135.4

0x25C

0x261

273.15

0x262

0x267

40.2

361.2

0x268

0x26D

mV Data

Temperature Data

55.3

522.1

0x26E

0x273

(see Table 73)

(see Table 74)

88.3

720.3

0x274

0x279

132.2

811.2

0x27A

0x27F

188.7

922.5

0x280

0x285

460.4

1000

0x286

0x28B

Table 73. Example Thermocouple Output Voltage Values (mV)

BYTE 0

BYTE 1

BYTE 2

B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5

B2 B1 B0

mV Sign 28

20 2–1 2–2 2–3 2–4 2–5 2–6 2–7 2–8 2–9 2–10 2–11 2–12 2–13 2–14

–50.22 1

–30.2 1

–5.3 1

0 0

40.2 0

55.3 0

88.3 0

132.2 0

188.7 0

460.4 0

In order to program the LTC2984 with the custom ther-

mocouple table, both the mV data and the Kelvin data are

convertedto24-bitbinaryvalues(representedastwo3-byte

tableentries).Sincemostthermocouplesgeneratenegative

output voltages, the mV values input to the LTC2984 are

2’s compliment. The sensor output voltage (units=mV),

follows the convention shown in Table 73, where the first

bit is the sign, the next nine are the integer part and the

remaining 14 bits are the fractional part.

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