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I'm a newbie trying to figure out how to power a DIY project using USB-C PD.

I'm building a project using about 120 RGB LEDS (consuming 60mA at 5V) and a Raspberry Pi 4 (max 3A at 5V). So I would expect a max load of 7.2A for the LEDs + 3A = 10.2A.

I'd like to power both using the same USB-C port.

I have a 60W USB-C PD charger which would provide me with 3A at 20V and I had the intention to use this as an input for a step-down DC-DC converter (XW-12-5-50W) that would output 10A at 5V.

Is there a way I can get 20V 3A out of my charger via a USB-C PD module? I have a ZY12PDN USB-C PD module but I think the max output is 3A, so it might not be the right option.

Thanks

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  • \$\begingroup\$ what does that module's datasheet say? \$\endgroup\$
    – Marcus Müller
    Commented Oct 20, 2020 at 12:11
  • \$\begingroup\$ (Is there a way?) - there is always a way but it may not be practical for you or cheap enough or particularly suited for what you want. \$\endgroup\$
    – Andy aka
    Commented Oct 20, 2020 at 12:14
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    \$\begingroup\$ You need a suitable chip to implement the negotiation. Realistically, simplify your life and just buy a high current 5v supply, rather than have the dual challenges of needing to buy a PD negotiation solution and then a very high current DC-DC converter. \$\endgroup\$
    – Chris Stratton
    Commented Oct 20, 2020 at 13:20

1 Answer 1

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I stumbled upon this question as well today. I will respond to this question in more general terms and then specifically for your setup.

There are some limitations in regards to how much power you can draw from USB-C with PD.

You can find part of the official specification here, or the full specification here, but I will summarize it as follows:

1. USB-C PD upper power/voltage/current limits

The maximum power you can draw from USB-C PD is 100W (20V/5A). This means that your 60W application is well within the limit of what USB-C PD can offer.

This limit is imposed by the voltage and current allowed to be used with USB-C PD which is 20V and 5A. Keep in mind that these limits are not interdependent. That means you can't use 10V at 6A (60W), because the current exceeds the 5A limit. The same applies to voltage. USB-C PD will not deliver 15W with the 30V/.5A configuration because it is not within the spec.

2. USB-C PD power profiles

When you power a USB-C load, it is up to the receiving device to communicate the power requirements by using the USB PD protocol. The chipset in ZY12PDN offers you a wide range of power profiles:

  • Red; Selectable mode, 5V present
  • Yellow: 9V
  • Green: 12V
  • Ice/Teal: 15V
  • Blue: 20V

You should be able to choose between those by pressing the button.

Please refer to the English Instructions in this article.

3. USB-C Cable

As outlined by this answer (and referenced to the USB-C documentation in the same answer) the cable use can limit the amount of power you can transmit. You will generally look for an EMCA enabled cable (see photo) if you want to exceed 60W. enter image description here

To wrap up, 3A at 20V is sufficient for your purpose. However, there is nothing to limit this module to 3A, which means it could provide up to 100W (20V/5A), as long as your AC/DC wall transformer allows it.

I use the terms RX and TX as "receiver (the device to be charged) and transmitter (the device that offers the power)"

Because there seem to exist custom solutions from microchip giants such as Texas Instruments, I am using a less strict language when not talking about the USB-C PD per se.

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