On the BQ25120A the chip disable (/CD) input pin is used to disable the device and has dual functionality based on if the adapter (VIN) is present.
- Battery Only Mode: When operating on battery only mode the /CD pin is used to place the device either in High Impedance mode (/CD = Low) or Active Battery mode (/CD = High).
- >>High Impedance Mode: The lowest quiescent current while operating from the battery. SYS is powered by battery, the MR input and LSCTRL are active. Other circuits are in a low power or sleep stage.
- >>Active Battery Mode: Normal operation from battery. SYS is powered by battery, and other circuits are active.
- Adapter Present: When the adapter (VIN) is present the /CD controls the charging operation where driving /CD high will disable charge.
For connecting to the microcontroller (MCU): The /CD pin is internally pulled down on the device. If left un connected, the device will be operating on High Impedance Mode without VIN and charge will be enable with the adapter present. The charge could be disable/enable via I2C by setting /CE = 0 on the Fast Charge Control Register (0x03). You should connect the /CD to the MCU if you would like to enter active battery mode or if you would like to control charge current with the /CD pin, instead of with the I2C command.
