BQ76920: Maximum current sense voltage on SRN, SRP pins

Hi JMA,

The Absolute maximum is stated in section 6.1 of the datasheet, it is for each pin (SRN, SRP) with respect to VSS and not the differential voltage between them.

This part recommends VSS be connected at the battery side of the sense resistor through figures 8-1, 8-2, and 8-3 and the limited range of SRP in the recommended operating conditions table in 6.3.  "Grounding" on the battery side of the sense resistor provides that SRN and SRP are positive with discharge current since discharge current is typically much higher than charge current and the input pins have a higher positive range than negative as you indicate. Your assumptions are correct.

The intent of the author in the section 8.2.2.1 reference is not clear and may have been altered by editing.  There have been BMS devices where grounding was used on the pack side of the sense resistor, but this would limit the maximum discharge and short circuit current range due to the pin range.  I have flagged this as an area for clarification in a future revision, thanks for the input.  The point should be to make sure abs max is not violated.

The maximum short circuit current for a 1.5m ohm resistor with SRP referenced at VSS would be 3.6V/1.5mOhm or 2400A, but this is an idealized situation. Your ground may be not perfectly at the SRP reference point or you may have effects from system parasitics or include circuit clamp components.  You might see the application note bq769x0 Family Top 10 Design Considerations section 10 page 22.