BQ76920: BQ76920+BQ76200 application

Hi Dustin,
High side MOSFETs allow the use of the PACK- as a reference for simple communication busses such as SMB, I2C, UART, or RS4xx. Different busses tolerate different amounts of offset in the reference vs the signals. When the high side power signal is the only positive potential out of the battery most of the concern for leakage in a battery is avoided. Some disadvantages of high side if using P-channel FETs are the continuous power for the drive circuit, the higher RDSON, and lower selection compared to N-channel. If using N-channel the disadvantage is the need for a voltage above the battery voltage and level translation for the gate voltage, this means needing the capability of a driver such as the bq76200.
Low side MOSFETs break the PACK- signal, so it can't be used for reference for a simple communication bus. Referencing a low side communication bus to low side protected PACK- will usually result in a path to allow continued discharge or charge through the communication lines. If the BATT- reference is brought out of the battery for a communication reference the system design must be certain this is safe for the application and meets all applicable regulations. Advantages of low side protection are its simplicity for FET control, and the availability of N-channel FETs with good performance. Disadvantages of low side protection are the complexity of the system if communication is needed out of the battery since an isolated communication bus is likely needed.