SparkFun Power Delivery Board - USB-C (Qwiic) Ground Issues

Components & Accessories Power
1

Hi,

I have a SparkFun Power Delivery Board - USB-C (Qwiic) which uses the STUSB4500 chip. Why does the circuit stop working when I connect a probe to ground? Or just touch a wire to ground? Is it because this board only uses the minimum implementation and doesn’t have MOSFET T4 as in the STUSB4500 datasheet?

I noticed that if I plug the probe before and insert the cable, it works fine. But if I attempt to do it while it’s connected, and there is a bit of movement (shake/bounce), it stops. I’m using this board connected to another PCB that has an audio socket, and everytime I plug a cable the power stops, this is really annoying. Could someone clarify what’s happening? :smiley:

Thanks,

Kines

2

Yes, it uses the minimum implementation https://cdn.sparkfun.com/assets/9/2/6/8 … ematic.pdf

I’d guess that it is triggering the power negotiation step whenever it detects a jolt to the system when it detects instability…the setup works when you have the probe in-place beforehand because it is stabilizing with the probe in place, effectively grounding or bypassing some noise or interference. You could probably work around this by using separate ground, or separating the power sources altogether

3

Thanks for your reply. I tried to separate the ground with an inductor and a 10ohm resistor, but this doesn’t fix the issue, and a separate power source defeats the whole purpose of using this USB PD board.

Do you think if I make a custom PCB with the full circuit (including MOSFET T4) instead of the minimum implementation this will work correctly?

If anyone has the official evaluation board (STEVAL-ISC005V1) to tell me that would be great.

Thanks,

Ian

4

Are you sure the audio negatives are ground? Some amplifiers have balanced outs and won’t work right if the neg is grounded.

5

Hi, this has nothing to do with differential audio or the audio connections. The moment any ground is touched and vibrates it will stop the PD controller, so any cable that goes in any sort of connector will do that.

6

What is the other end of the cable connected to?

Is this a purely mechanical issue (ie, tapping the board with a non-conductive item like a bic pen) or is it specifically connecting something to ground (where?)

7

It’s not purely mechanical. Tapping ground with a pen or finger won’t do anything, but tapping it with a wire (with no end) or any other conductive metal (scissors) will stop the power delivery.