ESP-WROOM-32 - 3.3v rail voltage excursion

[MakerMan]

I have a few of these ESP-WROOM-32 devices (38 pin).

I am powering the following from the 3.3V supply which should not, I think, cause any issues in terms of supply capability.
- BME280
- 1115 ADC
- 9808 temperature sensor

The 3.3V rail has parallel 0.1u and 10u capacitors to ground.

The ESP-WROOM-32 is powered from the USB connection. I have tested while powering from both computers and good quality USB power adaptors.

I am monitoring the 3.3V rail using one of the channels on the 1115 ADC and this is a fairly typical voltage vs time graph.



It is interesting to note that unless this is a measurement anomaly, the 3.3V rail drops momentarily, sometimes below 3.1V.

While this doesn't seem to cause any issues, I was wondering whether this is common ...?

[ESP_Sprite]

Hard to say without knowing how you measure, but it's a known thing that WiFi power usage is pretty spikey. Depending on the layout of your circuit (long wires, thin tracks, marginal LDO, ...) that can pull down the power by a fair bit.

[MakerMan]

For measurement, I take the 3.3V rail to a voltage divider, just so that this is moved away from the top end of the ADC range a little.
The calculations back-out the impact of the voltage divider to give the 3.3V rail voltage, which seems to average about 3.265V with these three external boards powered.

There are no very thin or very long tracks ...

I have now powered up another ESP-WROOM-32 with no connections other than to take it's 3.3V output to an ADC connected to another ESP-WROOM-32. I'll let this run for a few hours and then compare the chart, but I can immediately see that with no boards connected the rail is at 3.28V. It's still clearly got voltage excursions though. I'll post the graph later for comparison.

[MakerMan]

This is a graph of an ESP-WROOM-32 3.3V rail monitored by an ADC connected to another ESP32, so that the device under test has no load, or capacitors added. This appears to show that the voltage excursions are present even when not powering other devices although they are much lower in magnitude.