Calling Analog Experts - WEMOs LiPo Shield Help

[McGovernR]

Hello EEVblog community,

Glad to be here. I have a question regarding some circuitry on the WEMOs Battery Shield. Below is a screen shot of the circuitry. Vbus is connected to the board's charging input (USB) and +5V supplies 5VDC to the Wemos D1 mini AND is connected to the output of the charging chip.

I'd like to understand fundamentally what is happening with this circuitry. To me, it looks like some sort of protection circuitry, but why use a matched PNP transistor pair with a FET.

Link to complete circuit:
https://wiki.wemos.cc/_media/products:d1_mini_shields:sch_battery_v1.2.0.pdf

[danadak]

Explanation over here - https://www.eevblog.com/forum/projects/power-injection-protection-on-vdd-output/


Regards, Dana.