BQ76925: Cell Input protection diodes

Hi JP,

The zeners shown in the BQ76930 schematic are to protect the gate of the external balance FETs.  They can be necessary on any system where the battery voltage can exceed the Vgs limit of the FET.  

Some users will protect the inputs to the BMS board with zeners on the cells.  These typically need to be a large device since they must take the transients from the cells.  Other users will limit the voltage at the IC pins where a smaller device can be used because of the input resistor to limit current and the capacitor to absorb some of the transient. There are always tradeoffs.  At the IC pins the zeners need to allow at least 1.5X the normal cell voltage for balancing operation while conducting before the abs max of the pins. Some users will use a larger input resistor for lower current into the part and better filtering without large capacitors and add external balancing. And some users are cost sensitive and will increase the input resistance and may control connection and switching carefully to avoid transients to keep the component count low.  You have many approaches depending on your needs.