Temperature sensor LPC54618

raluralu · ‎09-21-2020

I am looking for documentation on how to convert ADC readout into temperetaure.
UM10912 chapter 45.3 refers to Data Sheet where one should find a way to calibrate sensor.

DataSheet for LPC546XX chapter 7.22 is missing some technical details to conduct temperature calibration and conversion from adc to temperature.

Can someone help me on approach to measure temperature using internal sensor?

frank_m · ‎09-21-2020

There is a diagram in the datasheet, specifying the temp. sensor voltage across the temperature range. (Fig.42 at page 142).

The datasheet further says:

The temperature sensor transducer uses an intrinsic pn-junction diode reference and outputs a CTAT voltage (Complement To Absolute Temperature). The output voltage varies inversely with device temperature with an absolute accuracy of better than ±5 °C over the full temperature range (-40 °C to +105 °C). The temperature sensor is only approximately linear with a slight curvature. The output voltage is measured over different ranges of temperatures and fit with linear-least-square lines.

Such p-n voltages use to differ, I suppose the given diagram is an average. So, it seems you need to calibrate it yourself (record the voltage at two or more temperatures). Or check the SDK examples, perhaps there is one for the sensor (check the ADC section).

I use such internal sensors rarely, the junction temperature inside the MCU package is of limited value (auto-heating).

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raluralu · ‎09-21-2020

@frank_m thank you for your help. So far I was able to autocalibarte adc, and to read out digital value form adc connected on temperature sensor. Value on adc from temp sensor is around 630 adc counts (not sure if correct yet). How to make conversion of this digital adc readout in terms of temperature value? What particular section in manuals did you had in mind?

frank_m · ‎09-21-2020

There is a diagram in the datasheet, specifying the temp. sensor voltage across the temperature range. (Fig.42 at page 142).

The datasheet further says:

The temperature sensor transducer uses an intrinsic pn-junction diode reference and outputs a CTAT voltage (Complement To Absolute Temperature). The output voltage varies inversely with device temperature with an absolute accuracy of better than ±5 °C over the full temperature range (-40 °C to +105 °C). The temperature sensor is only approximately linear with a slight curvature. The output voltage is measured over different ranges of temperatures and fit with linear-least-square lines.

Such p-n voltages use to differ, I suppose the given diagram is an average. So, it seems you need to calibrate it yourself (record the voltage at two or more temperatures). Or check the SDK examples, perhaps there is one for the sensor (check the ADC section).

I use such internal sensors rarely, the junction temperature inside the MCU package is of limited value (auto-heating).

frank_m · ‎09-21-2020

The user manual (UM10912) has two sections (44 and 45), dealing with ADC configuration and temperature sensor.

The characteristics of the sensor are described in the datasheet.