USB-C power supply schematic

[oli1]

Hey,

I'm designing an stm32mpu1 board and I have the Discovery Kit (DK) as a reference design.In the DK I see the following schematic for the USB-C power supply (CN7):

I am not quite sure what the point of the MOSFETS is.

For the other USB-C (CN6) I see MOSFETS AND Bipolar transistors:

Can someone explain what they are for? I'm trying to decide weather I need them in my design or not. Until now I always just connected the power supply to my PMIC and all I ever needed was some ESDs for protection and decoupling/bulk caps.

[AScha.3 · Accepted solution]

Hi,

the mosfets are for connecting the board 5V supply to the USB 5V  - or not .

>I need them in my design or not

Depends on : what you want to do with the USB :

- you have a powered cpu/board and want just plug in a USB memory stick, so only host -> connect 5V to the usb .

- you have a powered cpu/board, but want host and device (= connect to a PC on this plug also), 

so you need some switches (the 2 mosfets ) to switch on 5V power to plug, to get a connected usbstick to work;

but if you switch to device mode, to connect a PC, you dont want to get a short between your onboard 5V and the 4..5V coming from PC, so you have to switch off the mosfets .

So..it depends, on what you want to do, whether you need switches controlled by your software and can decide, to power the USB, or not.

[oli1]

God dammit thats makes a lot of sense. Thanks man!