Hello,

This is a schematic that I have been irritating another forum way too much about. I want to spare the sanity of the people over there and ask this one single question here. No PCB routed yet - just working on schematic.

Project background: I am creating a simple timer. I will be using this timer daily, but I will be the only one using it. Hence, it is a hobbyist project. Circuit needs to be reliable enough for daily use but doesn't have to go overkill.

What I am asking about: I am basically changing the schematic below:


to include a USB-C power input. USB-C will be used for power only - no data.

Here is what I have come up with for adding USB-C:

NOTE 1: I know that this schematic is very bad if I were to connect both J1 and J2 to power at the same time. However - J1 is only intended as I backup if I (as a beginner) f*** up the USB-C part of the circuit. I guarantee that these two will NEVER be connected to power at the same time.

NOTE 2: Just as a disclaimer, I have changed some resistors on BTN_INPUT_MULTIPLEXING between the first and second image. R12 is wrongly placed in the first image (marked Rev 0.2). I also changed the labels of the resistors on that part of the circuit. But that shouldn't matter for the USB-C part

My questions:

- Have I gotten the USB-C circuit correct? Of course in general. But particularly, I am concerned about:
- Will PWR_SWITCH work with USB-C? I see no reason why it shouldn't, but I have never worked with USB-C before so I wanted to be sure.
- After some advice from people online (but without accounting for USB-C) I added a 4.7uF decoupling cap intended to be close to the power input. You can see it as C3 on the board. Does adding USB-C change anything regarding this? I.e. should I reconsider or change my caps. I know the spec allows for caps (up to a certain value, which I am not exceeding).
- Now that freakin shield connection. Am I safe with what I am doing right now? As I said there is no data transfer, USB is only used for power. There are a million different suggestions for how to wire it online. Spec says it should be connected to GND. Some recommends a cap and resistor in parallel - I would imagine it is a bit overkill for a hobbyist project. This hobbyist-geared tutorial: https://dubiouscreations.com/2021/04/06/designing-with-usb-c-lessons-learned/ does not even use a resistor (just connecting it to GND directly). The 1M resistor idea is from this tutorial: https://www.pcbway.com/blog/PCB_Design_Tutorial/How_to_add_USB_C_to_your_projects.html.

 

You've got the required resistors to the CC pins – that's often overlooked and without them, a USB-C PD power supply won't supply any voltage. That's perfect.

The schematic symbol doesn't show all of the Vbus and ground pins – make sure all Vbus pins and all power ground pins are connected (no, not to each other ). For your application, all the shell connections don't matter. Connect to ground or leave floating – either way is ok.

To prevent any problems if power is connected to the USB and the other power input connector, I'd install a Schotkey (however it's spelled) diode between Vbus and the rest of the circuit. This will prevent any possibility of the other power supply feeding back into the USB C source, which could be an expensive piece of equipment. The small voltage drop won't hurt anything. For maximum protection, you could also add a diode in series with the other power input.

I'd add an LED + resistor or two to port pins. They come in handy when troubleshooting (says the guy who recently forgot to include any LEDs on a complex micro broad )

 

You've got the required resistors to the CC pins – that's often overlooked and without them, a USB-C PD power supply won't supply any voltage. That's perfect.

The schematic symbol doesn't show all of the Vbus and ground pins – make sure all Vbus pins and all power ground pins are connected (no, not to each other ). For your application, all the shell connections don't matter. Connect to ground or leave floating – either way is ok.

To prevent any problems if power is connected to the USB and the other power input connector, I'd install a Schotkey (however it's spelled) diode between Vbus and the rest of the circuit. This will prevent any possibility of the other power supply feeding back into the USB C source, which could be an expensive piece of equipment. The small voltage drop won't hurt anything. For maximum protection, you could also add a diode in series with the other power input.

I'd add an LED + resistor or two to port pins. They come in handy when troubleshooting (says the guy who recently forgot to include any LEDs on a complex micro broad )

Thanks a lot!

Do you happen to have any input regarding the following two points (mentioned in OP):

- Will PWR_SWITCH work with USB-C? I see no reason why it shouldn't, but I have never worked with USB-C before so I wanted to be sure.
- After some advice from people online (but without accounting for USB-C) I added a 4.7uF decoupling cap intended to be close to the power input. You can see it as C3 on the board. Does adding USB-C change anything regarding this? I.e. should I reconsider or change my caps. I know the spec allows for caps (up to a certain value, which I am not exceeding).

 

You have to identify VCC and GND with Power Flags if this Kicad?