Can't startup with 5v battery pack through USB-C and Teensy 4


Well-known member
I could use some guidance here.
I designed a board that uses a Teensy 4 powered by a usb-c connector through a power switch.

If I power with a wall charger, my board startups fine after turning on the board's power switch.

When I connect with a typical 5volt battery pack through a usb-a to usb-c cable I get some problems
The usb-a connector is plugged into the battery output and the usb-c cable into the power input
of my board.

On my board I pull down CC1 and CC2 to ground with 5.1K resistors as requested in spec.

If a battery pack has been sitting, and I plug the battery into the board, then turn on the board's power switch, the battery pack is happy and turns on.

However, if I power down (don't unplug the battery), wait for a while for the battery pack to go back to sleep, then turn on the power switch on my board, the battery pack is NOT happy and will not turn on.

The battery appears to determine the presence of the CC1 and CC2 path to ground, and decides whether it will turn on.

I connected CC1 and CC2 to output pins and set them low on power up. No change.

Any ideas ?
Last edited:
I was going to hook up a switch and tied the ends of the 5.1K resistors connected to CC1 and CC2
together. This seems to work on the batteries I tested with usb-a outputs (although I have no idea why).
I have one battery pack that outputs usb-a and usb-c. It works with usb-a but not with usb-c output.