Power management - adding rp2040 to JDM-055

[MCorgano]

I have a bit of an odd question. What I'm trying to do is replace the JDS board entirely with a small usb C rp2040 board, that has a 5v pin and ground common with the usb port on the board. For getting power into the controller, 5v+gnd -> into the flex cable to the controller is trivial, and charging works. The issue is I also want to power this board FROM the controller. I need 5v (or VBat would work) ~100ma peak for my use case, so and the usual power rail for the LED's won't be enough voltage and likely enough current

The second option would be connecting it to the battery pins directly, and powering it from there. The 4.3v-3.8v would be enough, however then I can't use it to charge the battery (or can I?). That means I either have it connected to somewhere the battery can power (with like a mosfet switched by the 3v3 rail switched by the PMIC, so it doesn't drain the battery), OR have it connected to usb external power and charge the controller, but how would I do both?

How would I connect the Rp2040 board to the controller so I can charge it AND switch it to take in power from the controller when the usb is unplugged so the rp board still functions?

[MCorgano]

I've been going through a couple ideas in my head

One is modify the rp2040 board to decouple the usb port from the rest of the board.
https://www.waveshare.com/w/upload/4/4c/RP2040_Zero.pdf
Thinking of breaking the connection of the 3v3 regulator between it and the main chip, and then powering the main chip from a 3v rail inside the controller. Right now most the points im tapping into are on the ribbon going to the JDS board, I was wondering if I could pull from the power line for the LED to instead power the rp2040. Effectively
USB port -> 5V+ground only -> JDS ribbon -> controller, charges battery, does the PMIC stuff to generate 3v -> Back out to JDS ribbon -> 3v in on the rp2040

My main concern with this is I don't want to overwhelm and fry the PMIC. When I measure the current of the entire rp2040 chip AND led's running on a usb power meter, it peaks around 110ma. For this setup im looking to just power the rp2040 which i'm thinking should be fine. This disables my ability to power / program the rp2040 zero board outside the controller, but in theory it should work in terms of running off the controller and programming via usb as long as the controller is on right?

Edit: The LED line is 4.2v or vBat not 3v. I would instead need to cut the connection between usb -> 3v regulator and feed the power in there instead. still should be possible to solder. The rp2040 while running my code used 32ma of current


However, that doesn't help with the LED's that want 5v in for power. They can run fine on VBat just a little dimmer, but I need to make sure this line is switched so that idle power draw doesn't drain the battery on the controller.


If someone who has more experience with adding things / drawing power from a JDM-055 controller could sanity check this idea to make sure there isn't any glaring issues, that would be fantastic.