FEDEVEL
Platform forum

Nick.T , 05-27-2025, 04:22 PM

@Phil Hi Phill,
I am currently creating my version of the board for the course and want to use USB PD to power the board instead of a barrel Jack. Seem straightforward enough

I had a question about the VCC is being tied to the USB MicroB and the barrel jacks via the diodes. Doesn't this mean that if the barrel jack is not connect and the usb cable is plugged in the board will try to power up from the microB USB which may not provide enough current (limited to 500mA or 1A or the like) Wouldn't this present a problem and perhaps the efuse should be prevented from switching on when only the microB USB is connected or similar or did you not encounter a problem with this?

Robert Feranec , 05-28-2025, 05:57 AM

This is how we did the USB power switching, page 28: https://www.imx6rex.com/wp-content/uploads/2016/01/Schematic-OpenRex-V1I1-Production.pdf

Robert Feranec , 05-28-2025, 05:59 AM

actually it was a tricky circuit, we had to design a couple of small test boards to make it work the way as we wanted

QDrives , 05-28-2025, 03:14 PM

Not a way I would do it... Why did you have Q1?

Nick.T , 05-31-2025, 07:56 AM

thanks for the reply Robert,
I will have a look at your implmentation but maybe the USB-C connector / PD tigger IC provides a nice presence detection that can be used to control the e-fuse

Robert Feranec , 06-02-2025, 05:40 AM

only one could be active, no back flow allowed

QDrives , 06-02-2025, 01:42 PM

Yes, but Q1 does not prevent "back flow". It can completely prevent 'forward flow'.

Robert Feranec , 06-03-2025, 07:17 AM

I had a closer look, you are right I was wrong. If only Q1 would be used then Vin would flow to the USB connector through the diode. That is why the guy designing the circuit also added Q2