Low-voltage shut-down compatible with deep sleep in a battery-operated ESP32

Question

I'm designing a battery-operated device driven by an S2 mini board, which is based on an ESP32-S2 microcontroller. In order to save battery the board wakes up every 15 mn, does its thing, and then goes into deep sleep for another 15 mn. I'd like to implement some sort of low-voltage shut-down system to avoid over-draining the batteries.

I can do something like that in software, using the board's ADC to read battery levels, but some small current will continue flowing due to the resistors used to read the battery level, along with the LDO regulator's quiescent current (I'm using a HT733).

Is there a way to block all current out of the batterr once its voltage is below a certain threshold? Could I do something like this with a well-chosen p MOSFET? Or am I just better off with the software option?

Answer 1

If you are using a Li-ion or a Li-pol battery, there are "overcharge/over-discharge" ICs like S-8200A that you can use:

One MOSFET is for overcharge protection and the other is for over-discharge protection.

If you insist on using an ADC from the processor, you can use an N-MOSFET for the divider circuit (between the ground and the resistor) and turn on the MOSFET once you want to measure the battery voltage and turn it off to cut off the resistors from the ground. Once the battery is below the threshold and you turn off the MOSFET, there will be no current drawn via the divider resistors. It will add some error in measurement but can be calibrated in the code to compensate for the error.

Answer 2

I just use (in the case of lipo) two 50k resistors, connected to the lipo directly and ground. In the dividing part a connection to the esp32. Current used is like 30-40uA, and bypasses the LDO. I can imagine for some cases it’s too much.. but for a case where every 15 min an esp is used to measure it’s peanuts and even for a empty lion would take months to drain critically. Connected to an rtc gpio you could use the ulp to measure in deepsleep and go into hibernation if critical.