Hey Guys,
The problem of using a LiIon battery to allow BeageBone boards to orderly shutdown is object of several posts here.
In my particular case I just want to use the battery power to allow shutdown and disconnect the battery from the power path at the end of power down sequence to work around the problem of VSYS being kept with 4,1 V causing VDD_3V3A to set to around 0,8V.
As I don't intend to run on battery nor on USB, I came up with this solution and I would like to have your thoughts in why it didn't work ....
The whole idea is to connect the battery in the USB input of the PMIC (instead of BAT terminal) allowing battery power to be connected/disconnected using power path control bit D4 in the Power Path Control Register (PPATH). With this I can change the shutdown routine of the OS to disconnect the battery power from VSYS just at the end of the power off cycle, before issuing the POWER_EN Signal.
As the battery still needs to be charged, my idea is to connect BAT SENSE to the battery (+) and connect BAT to BAT SENSE via a low Vf diode in order to prevent the battery from supplying the original power path. It should work because the charging cycle tests the battery presence sending a small current to it and sensing the voltage (via BAT SENSE I suppose). Naturally TS is supposed to be connect do a 10K resistor to ground.
However, it didn't work! PMIC just didn't turn on when AC input is connect to a suitable 5V power supply.
Below is the circuit:
Does someone can explain why it doesn't work?
Best regards