Adafruit Pro Trinket LiPoly/LiIon Backpack on Particle Photo

[JinjiroSan]

Hello,
I have couple of Pro Trinkets and Pro Trinket LiPoly/LiIon Backpacks which work perfectly together. Now, I also have a Particle Photon which I would love to use the same backpack on.
Operations should ideally be the same so when usb power is applied to the Photon, the backpack should charge the LiPo. No usb power should switch to LiPo power.

Is this possible?

[adafruit_support_rick]

No reason why you can't do that. Obviously, the pinouts don't match. But you can solder wires to connect the backpack. 5V to VIN, G to GND, and BAT to VBAT.

[JinjiroSan]

Thx for the quick reply. Not to sure if this will work though.

If I'm reading the photon docs correctly, the VBAT can't be used to power the board (it's only to supply power to the internal RTC, backup registers and SRAM when 3V3 is not present).

I thought about connecting the BAT to the Photon 3V3 (as it is bi-directional depending on USB/VIN power) but it seems the max voltage is 3.6 and I measured the backpack BAT on 3.920V.

[adafruit_support_rick]

Oops! You're right. Yeah - that's not going to work. You have to pass the battery voltage to VIN. But VIN is also where you'd get the 5V for charging.

[JinjiroSan]

Yeah, don't know how to work around this. I probably can't connect both the VIN and the BAT to the same 5V so it's either getting the power from the LiPo or charging the LiPo, correct?

Any other options I can look at that are similarly small in size?

I could probably use a Powerboost 1000C but that's a bit big compared to the Photon and complete package size I'm going for.

[adafruit_support_rick]

This is pretty much the same thing - same charging circuit. The difference is that it has the microUSB jack.
https://www.adafruit.com/product/1904
So, you would plug the USB into the charger instead of into the photon. Connect the BAT pin to VIN.