Portenta ADC Problem

Official Hardware Portenta Family Portenta H7
4

The ADC AREF design is flawed.

I ran this loop:

  while (true) {
    for ( int i = 0; i < 50000; i++) {
      analogRead(A0);
    }
    delay(2000);
  }

I measured the AREF pin which is connected directly to VREF+ on the STM32H747XIH6. The voltage drops well over 0.1 volt when the ADC is active which explains over a 1000 count change which is close to the jump on the graph.

Guess connecting AREF to an external reference would fix it.

I am done with Portenta, too many problems.

Edit: I did one more test. I looked at regulation of the 3V3 power.

The 3V3 is not very well regulated. It's about 2.99 V average but fluctuates a lot when running the ADC test program. The USB is supplying an average of 4.96 V at 0.04A.

The voltage rises a lot in the delay call, the CPU must sleep in a low power mode. The USB current drops to almost zero during delay.

The power management chip is really complex.

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