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STM32L471 ADC offset 0.1V?

michael.m
Associate II

The CPU is powered using 1.8V both on VDD as well as VDDA (4.7uH coil as well as 1n/100n/1u capacitors in power path).

When I measure the Vbat pin (100n cap supporting) in the range 2V-3.6V using the ADC I always measure about 0.1V less than the voltage as measured by my lab equipment.

Where does this offset originate from? I find nothing in AN2834 that would correspond to such a high error (it is like 228 LSB)

3 REPLIES 3
michael.m
Associate II

sorry, due to the 1/3 scaling the error is only 76 LSB at the input level

Uwe Bonnes
Principal II

With VDDA 1.8 Volt you can not measure 2 to 3.6 Volt. So probably you have a resistive divider that you don't tell to us. Maybe RIN of the ADC and the divider interact noticably?

Did you perform calibration?

Note, that depending on the battery's capacity and internal resistance, the VBAT measurement divider can be a significant load.

JW