ADC The sampling value is smaller than the actual value

[xiang san]

Hi ,

    I have a question ,according to the official configuration and example, the ADC sampling voltage value is smaller than the actual voltage value. For example, the actual voltage is 4.2V, the sampling value is only 3.8V after conversion according to the full voltage of 3.3V, and only 3V after conversion according to 3.3V. What's the problem?I can confirm that the reference voltage is 3.3V.

    

[Karl Ylvisaker]

Hello,

For example, the actual voltage is 4.2V, the sampling value is only 3.8V after conversion

Please be advised that the absolute maximum ratings applies to all I/O pins of the nRF52840, including the AIN pins.
If you exceed these ratings you may damage the chip. If you have exposed the chip to 4.2 V directly on one of the I/O pins the chip may already be damaged.
Could you detail how you connected the AIN pin to the 4.2 V signal in order to measure it?

If you intend to measure voltages at this level, such as in the case of a Lithium Ion battery, please see this blogpost on the subject for the recommended way to proceed.

can confirm that the reference voltage is 3.3V.

Please elaborate on how you have confirmed the reference voltage. Please also elaborate on what SAADC configuration you were using when you were performing your tests.

Best regards,
Karl