Hi all.
I’ve got a very strange problem with several WiFi LoRa 32 V3.2 boards.
My application puts the ESP32 into deep sleep to wake up on a timer event.
The board is powered by lithium battery (fully charged, 4,2V) via the JST header.
The USB-C port is not connected.
If the deep sleep lasts only a couple of minutes or up to around one hour everything works fine. The ESP32 comes up with reset reason ESP_RST_DEEPSLEEP.
But, if the deep sleep lasts more than around one hour the ESP32 wakes ups in time but the reset reason is ESP_RST_POWERON as if someone pushed the RST button.
In this case I can see some kind of strange ripple on the CHIP_PU (Reset) line. This starts exactly when the ESP wakes up by the timer and causes the ESP to reset because of the voltage drop on the reset pin.
Blue line is CHIP_PU (Reset), red is Vdd 3V3 to prove a stable supply.
Even if the ESP does not reset - when the deep sleep lasted less than around an hour, there is a voltage drop on the reset line. But only a short one and not as deep. So the ESP does not reset.
What causes this ripple?
If I power the board via USB everything works fine.
Is this strange behaviour a side effect of the unpowered circuitry to reset / upload via DTR / RTS lines?
What can I do to circumvent this problem?
