Other Parts Discussed in Thread: BQSTUDIO
Tool/software:
I have a question about the bq76905 monitor. I found that the Settings, Configuration, FET Options, FET_EN settings bit must be set for the part to start working, i.e. for CHG and DSG fets to be enabled in autonomous mode. The default value for FET_EN is 0. So, there's a chicken and egg problem. I can't talk to the 76905 without having a common ground reference, and the bit must be set to connect the grounds via the CHG and DSG fets. Does TI have a recommended method of setting this bit? I see that OTP is an option at the factory but that requires high volumes. We could externally program the part after power is applied (battery cells attached), but if the part ever lost power we would need to re-enable that bit. That means an RMA for us.
I included excerpts below from the bqstudio tool showing the FET_EN bit, the technical ref manual, and the EVM user manual.
The EVM gets around this with a net tie (NT1 on schematic) to Vss so that the bq76905 remains powered and has a common reference. But that effectively bypasses the fet protections, right? I need a way to temporarily enable the protection fets to be able to interface with the part.
