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# About the temperature threshold accuracy on TMP709

Other Parts Discussed in Thread: TMP709, LM26, LM57

Hello,

Regarding to the temperature threshold accuracy on TMP709, I have some question.

(1)Can we program the TMP709 temperature threshold by an external 1% resistor at TA>0°C (less than 0°C)?

If so, could please tell me the resistor value at set point -20° C?

And about the operating temperature range (0°C >TA≥-40°C) in datasheet,

It means that it does not guarantee as the accuracy. My understanding is correct?

(2) How much threshold accuracy does it have from 0°C to 60°C?

(TA = +60°C to +100°C -> +-0.5°C typ, +-3°C max),

Will the accuracy become +-0.5 ° C (typ) in the range from 0 ° C to 125 ° C?

Or will we refer figure.4(TEMPERATURE ERROR vs TRIP TEMPERATURE) on page 5 in datasheet?

Regards,

Tao_2199

• Hi Tao,

Thank you for reaching out to us! Someone will get back to you shortly.

Aaron
• Hi Tao,

1) Use a 115kOhm resistor to set the trip point to -20C. The equation to get this value is from Equation 1 of the datasheet. The TMP709 can functionally operate between -40C and 0C but the accuracy specs are not valid for that temperature range.

2) The TMP709 was trimmed to trip at the temperature range from 60C to 100C. Any other temperature range will yield a large temperature trip accuracy. For example, at 0C the trip accuracy is +/-6C.

If you would like to trip at -20C, the TMP709 is not the correct temperature switch IC for doing this. I recommend using the LM26 or the LM57 temperature switch IC instead.

-Michael Wong