Other Parts Discussed in Thread: CSD16406Q3
I have the following circuit in a prototype board:
At this point, I have verified that all footprints and layout are correct, all connections are good. However, when I plug in the battery, the two FETs in Q7 do not turn on and no return path is established. I have also gotten to the point that both U10 and U11 are removed to totally isolate just the BQ29700 function. Still will not turn on the FETs. One thing I did find is that the dual FET chosen for Q7 actually has 1k gate resistors built into the package. I am wondering if this is causing sufficient turn-on delay that the chip sees a high voltage between GND and BAT_RTN terminals and thinks there is a fault condition. However it doesn't try to recover.
One other thing - I tied a 100k resistor between GND and BAT_RTN. With this in place, it will turn on after ~1sec delay, but then it is stable. I can see the proper voltages at the gates of both FETs and I can then remove the 100k resistor and it stays on. It just needs some sort of kick-start to get it stabilized. Anyone encounter this before? Could it be the 1k gate resistors? The part - MTM78E2B0LBF - is specifically designed for this application, so I don't understand the behavior.
Thanks,
Jamie