The BQ2416xx uses an I²C-compatible interface to program charge parameters. I²C is a 2-wire serial interface developed by Philips Semiconductor (see I²C-Bus Specification, Version 2.1, January 2000). The bus consists of a data line (SDA) and a clock line (SCL) with pullup structures. When the bus is idle, both SDA and SCL lines are pulled high. All I²C-compatible devices connect to the I²C bus through open drain I/O pins, SDA and SCL. A host device, usually a microcontroller or a digital signal processor, controls the bus. The host is responsible for generating the SCL signal and device addresses. The host also generates specific conditions that indicate the START and STOP of data transfer. A target device receives and/or transmits data on the bus under control of the host device.

The BQ2416xx device works as a target 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 charging solution, enabling most functions to be programmed to new values depending on the instantaneous application requirements. Register contents remain intact as long as battery voltage remains above 2.5 V (typical). The I²C circuitry is powered from VBUS when a supply is connected. If the VBUS supply is not connected, the I²C circuitry is powered from the battery through BAT. The battery voltage must stay above 2.5 V with no input connected in order 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 BQ2416xx devices only support 7-bit addressing. The device 7-bit address is defined as ‘1101011’ (6Bh).