The battery stack monitor uses the LTC6813-1 IC from Analog. With a 16-bit ADC, multiplexer and precision voltage reference, the LTC6813 can monitor up to 18 series connected cells of various chemistries with a pack voltage from 16 to 90 volts.
The LTC6813 is a slave device and is unable to perform any decisions. An ESP32 host-processor is used to interrogate the voltage of each cell over the SPI interface, and based on internally programmed thresholds, turn on the associated MOSFET switch for cell balancing. The ESP32 also provides a BLE or WiFi interface for cell monitoring.
The LTC6813’s general purpose IO pins are connected to individual MOSFET switches and can be used to connect/disconnect loads and/or chargers to the battery pack based on state of charge (SoC).
A watchdog timer open-drain output pin is driven low when the LTC6813 has received no valid command for 2 seconds. This is connected to the microcontroller to provide extra safety.