The NTC thermistor implementation assumes a constant pull-up voltage
and that the ADC channel is measured against a reference voltage so that
the absolute voltage across the NTC can be calculated. Based on the
relationship of `pullup-uv` and this absolute NTC voltage, the resistance
of the NTC is calculated.
There are applications where the "pullup-uv" is not constant, but VDD.
Most ADCs support relative measurements against VDD. If `pullup-uv` is not
defined, the implementation assumes now that the ADC channel is configured
to use VDD as a reference and therefore no millivolt conversion is
required.
Signed-off-by: Stefan Schwendeler <Stefan.Schwendeler@husqvarnagroup.com>
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