LTC2984 datasheet(68/78 Pages) AD

68 / 78 page

LTC2984

2984fb

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In addition to digitizing standard RTDs, the LTC2984

can also digitize custom RTDs (RTD type=0b10010, see

Table 30). Custom sensor data (minimum of three, maxi-

mum of 64 pairs) reside sequentially in memory and are

arrangedinblocksofsixbytesofmonotonicallyincreasing

tabular data Ω vs temperature (see Table 76).

Table 76. Custom RTD/Thermistor Tabular Data Format

ADDRESS

BYTE 0 BYTE 1 BYTE 2 BYTE 3 BYTE 4 BYTE 5

0x250 + 6* Start Address

Table Entry #1 (Ω)

Table Entry #1 (Kelvin)

0x250 + 6* Start Address + 6

Table Entry #2 (Ω)

Table Entry #2 (Kelvin)

0x250 + 6* Start Address + 12 Table Entry #3 (Ω)

Table Entry #3 (Kelvin)

•

Max Address = 0x3CA

Table Entry #64 (Ω)

Table Entry #64 (Kelvin)

CUSTOM RTDS

Figure 42. Custom RTD Example (Ω vs Kelvin )

2984 F42

NOTE:

P0 SHOULD BE THE

EXTRAPOLATION

POINT TO 0

RESISTANCE ()

RESISTANCE < p1

SOFT FAULT

CONDITION

RESISTANCE > p9

SOFT FAULT

CONDITION

Custom RTD Example

Inthisexample,asimplifiedRTDcurveisimplemented(see

Figure 42). Points P1 to P9 represent the normal operating

rangeofthecustomRTD.Resistancereadingsabovepoint

P9 result in a soft fault and the reported temperature is

a linear extrapolation using a slope determined by points

P8 and P9 (the final two table entries). Resistance read-

ings below point P1 are also reported as soft faults. The

temperature reported is the extrapolation between point

P1 and P0, where P0 is the sensor output temperature

at 0Ω (This point should be 0Ω for proper interpolation

below point P1).

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