I have designed a LCC/DCC command station using a Pocket Beagle 2 and was wondering about powering the processor board for a short time on battery power, in order to have time to do a clean shutdown when the main power source is removed. I am powering the processor board off the Vin pin on the “cape”. But this won’t keep the battery charged. Is there a possible way arounf this?
Your observation matches the official documentation. In the battery-charging schematic (PocketBeagle 2 Design and Specifications in the official BeagleBoard docs) the BQ21040 charger’s IN pin is tied to the USB_5V rail, while the LM73100 power path switches the system between VIN_5V, USB_5V and VBAT - so VIN_5V (pin P1.01) powers the board but does not feed the charger. The same doc says the charger operates from USB VBUS or a cape header pin, and the pinout table lists VIN.USB on cape pin P1.07; the most consistent reading is that P1.07 feeds that same USB_5V rail, so moving your 5 V input there should also charge the battery - but I have not seen the full schematic sheet, so treat that as a hypothesis to verify first. Keep to the documented 5 V / 1 A input spec, and note the charge current is programmed to 540 mA (ISET) per the schematic. Your clean-shutdown plan itself works as designed: when both external rails drop, the LM73100 falls back to VBAT.
Your observation matches the official documentation. In the battery-charging
schematic (PocketBeagle 2 Design and Specifications in the official
BeagleBoard docs) the BQ21040 charger’s IN pin is tied to the USB_5V rail,
while the LM73100 power path switches the system between VIN_5V, USB_5V and
VBAT - so VIN_5V (pin P1.01) powers the board but does not feed the charger.
The same doc says the charger operates from USB VBUS or a cape header pin,
and the pinout table lists VIN.USB on cape pin P1.07; the most consistent
reading is that P1.07 feeds that same USB_5V rail, so moving your 5 V input
there should also charge the battery - but I have not seen the full
schematic sheet, so treat that as a hypothesis to verify first. Keep to the
documented 5 V / 1 A input spec, and note the charge current is programmed
to 540 mA (ISET) per the schematic. Your clean-shutdown plan itself works as
designed: when both external rails drop, the LM73100 falls back to VBAT.
VIN.USB on cape pin P1.07 is the power for USB1, the host USB interface, not
USB0, the device USB interface. This is not a system power rail.
Thanks for the correction - you’re right to push back on that one. I flagged the P1.07 route as a hypothesis precisely because the docs don’t tie VIN.USB into the LM73100 power path, and your reading (USB1 host supply, not a system rail) fits that gap. The practical takeaway stands: power the board and charge the battery through the documented USB input, and don’t rely on P1.07 for either.