Linear Technology LTC2983 - Page 60

LTC2983
60
2983fc
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a slope determined by points P8 and P9 (the final two
table entries). 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 typi-
cally 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
In order to program the LTC2983 with the custom ther-
mocouple table, both the mV data and the Kelvin data are
converted to 24-bit binary values (represented as two 3-byte
table entries). Since most thermocouples generate negative
output voltages, the mV values input to the LTC2983 are
2’s compliment. The sensor output voltage (units=mV),
follows the convention shown in Table 69, where the first
bit is the sign, the next nine are the integer part and the
remaining 14 bits are the fractional part.
Table 68. 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
P0 –50.22 0 0x250 0x255
P1 –30.2 99.1 0x256 0x25B
P2 –5.3 135.4 0x25C 0x261
P3 0 273.15 0x262 0x267
P4 40.2 361.2 0x268 0x26D mV Data Temperature Data
P5 55.3 522.1 0x26E 0x273 (see Table 69) (see Table 70)
P6 88.3 720.3 0x274 0x279
P7 132.2 811.2 0x27A 0x27F
P8 188.7 922.5 0x280 0x285
P9 460.4 1000 0x286 0x28B
Table 69. 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 B4 B3 B2 B1 B0
mV Sign 2
8
2
7
2
6
2
5
2
4
2
3
2
2
2
1
2
0
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 1 1 1 0 0 1 1 0 1 1 1 0 0 0 1 1 1 1 0 1 1 0 0
–30.2 1 1 1 1 1 0 0 0 0 1 1 1 0 0 1 1
0 0 1 1 0 1 0 0
–5.3 1 1 1 1 1 1 1 0 1 0 1 0 1 1 0 0 1 1 0 0 1 1 0 1
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
40.2 0 0 0 0 1 0 1 0 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0
55.3 0 0 0 0 1 1 0 1 1 1 0 1 0 0 1 1 0 0 1 1 0 0 1 1
88.3 0 0 0 1 0 1 1 0 0 0 0 1 0 0 1 1 0 0 1 1 0 0 1 1
132.2 0 0 1 0 0 0 0 1 0 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0
188.7 0 0 1 0 1 1 1 1 0 0 1 0 1 1 0 0 1 1 0 0 1 1 0 0
460.4 0 1 1 1 0 0 1 1 0 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1