Good Afternoon,
I am looking at a problem with BQ77910A monitoring 8 cells. The device uses CHG & DSG pins to switch N channel FETs that drive the power P channel high side DSG & CHG FETS.
When I force an OC in discharge the alarm shows on the bq77910 eval software, so I know my sense resistor settings and config are correct. However the DSG and CHG pins remain high so DSG and CHG FETS remain on.
Thinking that the device may have failed, I simulated a shorted thermistor. That alarm is reported but surprisingly the DSG and CHG pins go low and so the DSG & CHG FETs are switched off; as would be expected. Can you help please?
Thanks,
Martin
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Addendum
I have further ascertained that the DSG and CHG pins are oscillating (pulsing low). It begins at the desired trip current. The duty increases as the overcurrent is increased. The problem is that the DSG & CHG FETs never remain off.
The circuit is the same as Texas app circuit 910A-Pch.sch.