USB Type C PD Minimum Requirement

Question

I have been wanting to veer away from older USB connectors and start using USB Type-C receptacles in future designs but the standard is quite confusing as a hobbyist.

Searching the internet I see that you can use 5.1k ohm pull-down resistors on the CC pins and this will allow the standard 5V (some places say 100 mA, while others say 150 mA or 1.5A).

Since I can't find any solid (at least for me) answer, I will ask the question here...will the schematic below ensure that only 5V is provided if the user connects the device to a USB-C PD compliant PSU? Will this design allow use of both USB-A to USB-C and USB-C to USB-C cables?

My main concern is it could randomly jump to 12V, 18V, or 20V and fry the circuitry.

^{simulate this circuit – Schematic created using CircuitLab}

Answer 1

No USB power source gives anything else than 5V until negotiated for more.

Your schematic cannot negotiate anything related to PD via CC pins so it will always get 5V like any normal USB device.

Of course negotiation through USB pins is also possible but if your MCU can not or will not negotiate anything about supply voltage like QuickCharge or similar, then it also won't get anything else than the standard 5V.

Yes this schematic will work with both Type-C to Type-C cables and Type-A to Type-C cables. Actually Type-A to Type-C cables will forcibly give you 5V even without the CC being connected, because that's how Type-A works.

But like you said yourself, you don't know how much current is available. Your device cannot know that via PD. Your device has to draw 1 Unit Load before the host asks your device via USB enumeration process how much current it needs, and then it will let your device to draw that amount or go to sleep because what you requested is not available.

And since your device is not a USB3 device, you cannot draw 150mA. If your device is USB2 or it is plugged to USB2 host it must draw max 100mA.