BQ78350 + BQ76920 confusion

Hi Luke,

What you are seeing in the BQ Studio software is the precision that the BQ78350 and BQ76920 allow.

If you look in the TRM (SLUUBD3B Revised in May 2016), the stored value is U1 (unsigned byte).

The reason some protections don't need such granularity is because large voltage drops do not occur instantaneously (except for extreme cases like short circuits and possibly short overloads). The COV (over-voltage) and CUV (under-voltage) protections are implemented for normal charge or discharge of the battery where the changes occur gradually. These "slow" protections are handled by the BQ78350.

For some cases, the time to transfer data from the BQ76920 to the BQ78350 would be too long (think short circuit for example), so they're handled by the AFE.

As mentioned above, critical protections (short circuit, overload) are handled by the BQ76920 directly. These settings are configured in stored in the BQ76920 (but configured from the BQ78350) and have preset values. The BQ76920 will measure the voltage difference across the sense resistor and determine the current passing through it. The easiest way to determine the values needed for the configuration for the two registers is to make a spreadsheet with these values to determine the matching current.

As for the configuration question, the BQ78350 once configured will update the register settings in the BQ76920. The COV and CUV are configured in seconds and mV. You might have to reset your BQ78350 for the changes to take effect. There is a Reset command that you can send.
The critical protections are configured in BQ Studio through the AOLD and ASCD sections of the Protection registers. As can be seen in the screenshot you uploaded, you should have a Threshold and Delay register for each. These are the preset values that I was talking about earlier.
Look in these sections in the TRM for the meaning of each bit:
3.6.1 Overload in Discharge Protection
3.6.2 Short Circuit in Discharge Protection

Side note:
I found BQ Studio to be a little buggy, so once I change a value in BQ Studio, I click on Write to Data Memory a few times, then click on the Write All (in the top right corner). And then move the focus to another "register" and read the memory just to make sure it was configured properly. That's just me that has become paranoid because I thought I configured something, and debugged for a long time until I realized that the register was not updated properly.

Hope this helps