ADC reference not connected

[giuseppescarpi]

Hello, fellows engineers.

On an RT1051-based board, I forgot to connect the ADC reference (pin N14, VDDA_ADC).

The strange fact is that the ADC seems to work more or less correctly, as if there were an internal connection to VCC.

Do you have any idea about this? Is there any settings that allows the ADC to work even if there is no external reference?

Thanks

G.

[jeremyzhou]

Hi,
Thank you for your interest in NXP Semiconductor products and for the opportunity to serve you.
The VDDA_ADC_3P3 must be powered.

Hope this is clear.
Have a great day,
TIC

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[giuseppescarpi]

Hi TIC,

Thank you for your reply, the datasheet is very clear.

Nonetheless, on this board with VDDA_ADC disconnected we see that the peripheral works as expected, it is only not very precise (the measurement is repeatable, but scaled down). I suspect that the peripheral gets back-supplied.

We may even think to connect another ADC pin as a sort of "external reference"... I reckon this sounds horrible from an engineering point of view, but I would like to have a better understanding.

Thanks

Giuseppe