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 not?
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