In BQ40Z60' typical application schematic (figure 8 of SLUSAW3D) the charger portion output connects to VSYS node, designed to power the system.
Under over-discharged battery condition the battery may disconnect from VSYS following SUV protection trip, which powers the system off (a few other conditions also lead to disconnection from VSYS.)
Next, after DC power application, the charger produces charging current to the battery (it may also choose a lower pre-charging current.) This powers up VSYS node and the system may switch on.
Since the battery can't supplement the charger until SUV protection is recovered, VSYS voltage may sag in case of the charger power deficiency. This may lead to uncontrollable system on and off switching.
My idea is to remove the charger portion output to CHG FET and DSG FET midpoint. The charger power then will not be visible to the system before DSG FET is enabled.
The only drawback I can see is that the system can't be supplied by the unbacked charger any more, which only occurs under fault conditions.
Perhaps I overlook some important matters? Can the experts share their opinions?
Regards,
Sergey
