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I've been looking into how to create my own pcb with a USB-C connector which breaks out into pins (VCC, D+, D- and GND) to then connect this to a Raspberry Pi Pico microcontroller but I have a few questions:

  1. There are many different USB-C connectors, how do I know which to get?
  2. Do I need to limit the power from the USB-C connector pcb to the Pico so it doesn't damage the Pico with 5v power? Do I need to add resistors to lower the voltage to 3.3v?
  3. The Pico I'm working with is a clone with its own USB-C connector - should I use a cable to connect the breakout pins to the USB-C port on the Pico or should I connect them to individual pins on the Pico? If so, should I use 3v3, vsys or vbus for the vcc line?
  4. Apparently I also need to add a 5.1k resistor to each of the CC lines to indicate that the USB-C breakout pcb is an upstream facing port - if someone could confirm this is appropriate for my project that would be really helpful please.

Schematic Start

USB-C Pico

USB-C connectors

Level shifter

https://randomnerdtutorials.com/how-to-level-shift-5v-to-3-3v/

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  • \$\begingroup\$ "many types of USB-C connectors" I think you are mixing up USB 3.0 and USB-C. USB-C is a physical connector, there is only one type which is the one with rounded edges. USB 3.0, on the other hand, is an advancement of USB which has three differential pairs rather than the traditional two with USB 2.0 and down. Additionally, if the Pico clone you are using already has a USB-C connector, why must you need another? \$\endgroup\$
    – lemon
    Commented May 7 at 7:48
  • \$\begingroup\$ @lemon thank you for the reply - Apologies I should have specified that the different USB-C connectors I am confused about seem to have different numbers of pins and the shapes of the reverse side are different (I've added a new picture to the original post). I'm making an enclosed device that will have the Pico inside and a separate USB-C mount that will be flush to the edge of the device so the user can easily insert/remove a USB-C cable when using, so essentially they won't be able to plug it into the Pico directly \$\endgroup\$
    – cAYK
    Commented May 7 at 8:02
  • \$\begingroup\$ USB-C can support the negotiation of higher voltages than the normal 5v to support fast chargers but not for less than 5v as you appear to require. You must use a voltage regulator (linear, LDO, buck etc.) to reduce the voltage to 3v3 for your Pico. Resistors will not do this. Find and understand a schematic of a 3v3 device which uses USB-C to see how it works. \$\endgroup\$
    – 6v6gt
    Commented May 7 at 8:04
  • \$\begingroup\$ @6v6gt thank you for the reply - I had a look into 3v3 devices that use USB-C and came across a schematic that uses 2k and 1k resistors (added link/photo to original post) - could I use this as a workaround? I understand using a voltage regulator is best practice but the circuit I'm building is not high speed and is very basic with just a few switches that go to GPIO pins so I'd like to make the pcb as simple as possible. I've looked into the voltage regulator LM1117 and it looks like two extra capacitors would need to be added \$\endgroup\$
    – cAYK
    Commented May 7 at 8:32
  • \$\begingroup\$ @cAYK That circuit which you have shown is a level shifter for changing a 5volt signal voltage of a few milliamps to 3v3. It is wholly unsuitable for providing power for a microcontroller. \$\endgroup\$
    – 6v6gt
    Commented May 7 at 9:41

1 Answer 1

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  1. You seem to know what electrical connections you need. Then select any connector with at least those electrical connections that you feel works for you, e.g. SMD or through hole, mid-mount, current rating, etc.

  2. Based on the question, what you ask is not what you need to know. You don't need to limit power or current. Yes you need to drop 5V to 3.3V. Resistors are completely wrong idea to do this. You use a voltage regulator like everyone else and your existing Pico with USB connector.

  3. You have not defined what VCC you mean. USB VBUS input is 5V, VSYS is likely separate 5V input, and 3.3V is regulated from VBUS or VSYS source. If you have 5V output, send it to VSYS input. If you have 3.3V output, send it to 3.3V input.

  4. Yes this is true.

However, if you already have a board with Type-C connector, there is little benefit of adding extra Type-C breakout.

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  • \$\begingroup\$ Thank you very much for the answers - I just wanted to clarify regarding question 3, does that mean I could connect the breakout 5v VCC pin from the USB-C power source to the VSYS pin on the Pico as it can handle 5v? So I wouldn't need to add a voltage regulator to the USB-C pcb? Also just to clarify regarding your last point: I'm making an enclosed device that will have the Pico inside and a separate USB-C mount that will be flush to the edge of the device so the user can easily insert/remove a USB-C cable when using, so essentially they won't be able to plug it into the Pico directly \$\endgroup\$
    – cAYK
    Commented May 7 at 8:21
  • \$\begingroup\$ @cAYK I believe the manual of your board will have instructions how to power it. If it accepts 5V then you don't need to convert 5V to 3V3. It does not matter from where the 5V comes. I may come from 5V output of the breakout board. But please note, you only talk about powering it. That is fine. But you have no data connection then if you need it. \$\endgroup\$
    – Justme
    Commented May 7 at 8:31

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