USB-C power problem

[crgarcia]

Full project documentation/layout/schematics/etc: link

I had this design that worked fine with Micro USB (full schematics)



I now replaced it with an USB-C (full schematic)




When I connect an USB-C, the voltage drops almost to 2 volts (sorry for the img quality, rigol software stopped working)



The current seems to fluctuate between 20mA and 40mA (measured with a multimeter)

If I connect an external bench power supply to the 5V line, then it works fine, and current reaches around 80mA.

I am a bit lost on how to troubleshoot this...
Do you know what could be wrong?
Any ideas on what I can try out?

Thank you!

[NiHaoMike]

Connect shield and ground just as it was done for the micro USB. I also assume you ruled out a defective connector or defective cable?

[crgarcia]

Thank you very much evb149 and NiHaoMike!!

I found the problem:
The guilty one is the 50 Ohm resistor I added to the VBus (5V+) to limit inrush current. I placed it there because I have too much capacitance (> USB documented limitations)

Now I replaced the resistor by a 0Ohms and now everything works.

Thanks!

[pigrew]

Thank you very much evb149 and NiHaoMike!!

I found the problem:
The guilty one is the 50 Ohm resistor I added to the VBus (5V+) to limit inrush current. I placed it there because I have too much capacitance (> USB documented limitations)

Now I replaced the resistor by a 0Ohms and now everything works.

Thanks!

Yep... it gotta be between 1 and 10 uF.

My solution is usually putting a "soft-start" load switch (permanently turned on), which often has a side-benefit of integrating overcurrent protection.

[jbb]

You can also get switch ICs with over voltage protection, which is helpful.

One thing to keep an eye on is cable plugging - the cable has a little inductance and can form a resonant network with input caps. This can turn a 5V input into an 8V peak or more.
TVS diodes are of limited use there - you need around a 6V device, and it seems they can be relied on to reliably clamp at approximately 1.5x rating, ie 9V.

There are dire rumours around of non-compliant “USB” wall chargers that simply spit out 20V all the time.