LTC2995 datasheet(84/90 Pages) AD

84 / 90 page

LTM2985

Rev. 0

For more information www.analog.com

CUSTOM THERMISTORS

Figure 60. Custom NTC Thermistor Example (Ω vs Kelvin)

Figure 61. Custom PTC Thermistor Example (Ω vs Kelvin)

2985 F60

NOTE:

P0 SHOULD BE THE

EXTRAPOLATION

POINT TO 0

RESISTANCE ()

RESISTANCE < p1

SENSOR UNDER-RANGE

SOFT FAULT CONDITION

RESISTANCE > p9

SENSOR OVER-RANGE

SOFT FAULT CONDITION

2985 F61

NOTE:

P0 SHOULD BE THE

EXTRAPOLATION

POINT TO 0

RESISTANCE ()

RESISTANCE < p1

SENSOR UNDER-RANGE

SOFT FAULT CONDITION

RESISTANCE > p9

SENSOR OVER-RANGE

SOFT FAULT CONDITION

In addition to digitizing standard thermistors, the

LTM2985canalsodigitizecustomthermistors(thermistor

type=0b11011, see Table 55). Custom sensor data (mini-

mum of three, maximum of 64 pairs) reside sequentially

in memory and are arranged in blocks of six bytes of

monotonically increasing tabular data Ω vs temperature

(see Table 91).

Custom Thermistor Table Example

Inthisexample,asimplifiedthermistorNTC(negativetem-

peraturecoefficient)curveisimplemented(seeFigure 60).

Points P1 to P9 represent the normal operating range of

the custom thermistor. Resistance readings above point

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 must be 0Ω for proper interpolation

below point P1).

In addition to NTC type thermistors, it is also possible to

implement PTC (positive temperature coefficient) type

thermistors (see Figure 61). In both cases, table entries

start at the minimum resistance and end at the maximum

resistance value.

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