We're trying to get a BQ24650 and BQ28550 working nicely together, but are having some difficulties with the BQ28550 not automatically reconnecting the battery when a charger is inserted.
The BQ24650 is currently taking a 5V USB input (we intend to use this with a PV panel), and if we momentarily short the BQ28550's charge control FETs (i.e. connect battery return to system ground) the system comes completely up and we're seeing the charge current that we expect.
Our problem arises when the battery is first connected to the BQ28550 or we encounter and over-discharge event. Once either of these events are encountered, both charging and discharging of the batteries becomes permanently disabled (until the FETs are shorted as mentioned above). We'd expect that reinserting the 5V source into the BQ24650 should cause the BQ28550 to reconnect the batteries to the system, but it never does. The only way to reawaken our system and/or enable charging of the batteries is to short the FETs.
Looking at figure 5, the fact that both charging and discharging is disabled leads me to believe that the problem is that BQ28550 is not recognizing the attaching of the charger. I don't know if this is due in part to BQ24650 and BQ28550 not playing nice with each other, but the BQ28550 datasheet and technical user's manual provides absolutely no information on how the presence of an charger is detected.
I've attached the fuel gauge schematic we are using, and would appreciate any help available.
Thanks,
-F