The BQ25968 uses an I²C compatible interface to program and read many parameters. I²C is a 2-wire serial interface developed by NXP (formerly Philips Seminconductor, see I²C BUS Specification, Version 5, October 2012). The BUS consists of a data line (SDA) and a clock line (SCL) with pull-up structures. When the BUS is idle, both SDA and SCL lines are pulled high. All the I²C compatible devices connect to the I²C BUS through open drain I/O terminals, SDA and SCL. A master device, usually a microcontroller or digital signal processor, controls the BUS. The master is responsible for generating the SCL signal and device addresses. The master also generates specific conditions that indicate the START and STOP of data transfer. A slave device receives and/or transmits data on the BUS under control of the master device.

The BQ25968 device works as a slave and supports the following data transfer modes, as defined in the I²C BUS™ Specification: Standard Mode (100 kbps) and Fast Mode (400 kbps). The interface adds flexibility to the battery management solution, enabling most functions to be programmed to new values depending on the instantaneous application requirements. The I²C circuitry is powered from the battery in Active Battery Mode. The battery voltage must stay above VBATUVLO when no VIN is present to maintain proper operation.

The data transfer protocol for standard and fast modes is exactly the same; therefore, they are referred to as the F/S-Mode in this document. The BQ25968 device only supports 7-bit addressing. The device 7-bit address is determined by the ADDR pin on the device.

To avoid I²C hang-ups, a timer (TI2CRESET) runs during I²C transactions. If the transaction takes longer than TI2CRESET, any additional commands are ignored and the I²C engine is reset. The timeout is reset with START and repeated START conditions and stops when a valid STOP condition is sent.