ESP32 goes into unknown state

[dovov97815]

We have developed battery operated product using ESP32-WROOM-32E.
when device goes into deep sleep around 8-10uA current are flow normally.

During Testing of product we face an issue which is described as below.
During deep sleep of ESP32-WROOM-32E we removed battery from device so now slowly- slowly voltage gets down on ESP32-WROOM-32E VCC-GND pin.

Case 1:
Voltage Down Start from 3.3V and when it reached to 1.4V - 1.5V, we again plug battery into device and now voltage on ESP32 VCC-GND pin is 3.3V .
then we press Button on GPIO32 which is our external wake-up source and ESP32-WROOM-32E wake-up start working completely.


Case 2:
Voltage Down Start from 3.3V and when it reached to 1.2V - 1.3V, we again plug battery into device and now voltage on ESP32 VCC-GND pin is 3.3V.
but in these condition ESP32 didn't boot again and also not react on button press on GPIO32 external wake-up. its goes into unknown condition.
its only react now when we restart it.

[boarchuz]

ESP32 datasheet, section 2.3:

• In scenarios where ESP32 is powered on and off repeatedly by switching the power rails, while there is a large capacitor on the VDD33 rail and CHIP_PU and VDD33 are connected, simply switching off the CHIP_PU power rail and immediately switching it back on may cause an incomplete power discharge cycle and failure to reset the chip adequately.
An additional discharge circuit may be required to accelerate the discharge of the large capacitor on rail VDD33, which will ensure proper power-on-reset when the ESP32 is powered up again.
• When a battery is used as the power supply for the ESP32 series of chips and modules, a supply voltage supervisor is recommended, so that a boot failure due to low voltage is avoided. Users are recommended to pull CHIP_PU low if the power supply for ESP32 is below 2.3 V.