Battery Management
!PAY ATTENTION! Always use a battery with a protection circuit! And pay attention to the polarity of the battery. The wrong polarity may destroy the ESP32 Touchdown or your battery!
To make the most of all the wireless features of the ESP32, I have included the ability to run the ESP32 TouchDown of a battery. The ESP32 TouchDown uses a MCP73831 battery management IC for charging. The battery itself is connected via a MOSFET to the 3.3V regulator. This allows for the ESP32 TouchDown to charge the battery, but also switch between USB and battery power near instantly. Quick enough to keep the ESP32 TouchDown running.
The charge current is pretty low as not to stress the battery to much and keep the overall current draw down. The charge current is determined by the Rprog resistor. I have chosen a 3.3K resistor, which means a charge current of around 300mA. This can be calculated according to the datasheet with the following formula:
When there is no battery present, the CHARGE LED will flash. I myself find this quite annoying, so I have added the option to disable the charge LED. You can do this by de-soldering the jumper next to the battery connector:
The On/Off switch does not disable battery charging. This means that even when the ESP32 TouchDown is off, the battery can be charged.