Electronics > Projects, Designs, and Technical Stuff
USB C PD
artag:
I'm designing a product that needs up to 15W. I'd like to use USB C PD at higher than 5V to keep the current low. I can do this with existing PD triggers or perhaps with a processor but there seem too many options.
If I ask for 12V and get it, I can run a DC-DC converter to provide 5V at the load point. This seems like a good architecture.
But what should I do if the PD negotiation only lets me have 5V. Should I refuse to start ? Or accept 5V and a resulting voltage drop at 3A ? This might mean upconverting.
It seems as though, in order for it to 'just work' for the user, I'd have to have a buck/boost converter taking the highest voltage it can get from the power supply, and trying to make up (perhaps with reduced functionality) if I can get only a low voltage.
How is it expected to negotiate and work (from the user's point of view, not technically) to make best use of the options available ? Or have they screwed up and provided every conceivable option but no reasonable strategy ?
OM222O:
USB PD is non trivial and takes a lot of coding + special negotiating ICs (if you don't wanna run out of ram on your MCU). If you can use just a buck converter and turn for example 20v down to 5 (which is very easy to do) then you're set. But if you want it to be able to actually accept charge AND charge other devices then you need PD.
jbb:
I’m not an expert on the standard, but I think you’re allowed to not operate if you don’t get enough power.
If you want to be formal, I think you’re not meant to go above 5V until you go past 15W. So you can define your product as needing 16W :-)
However, you need to consider your use case. One thing I haven’t been able to get good data on is “how much power can this USB C port on my laptop output?” So if you need USB Comms and >15W power you might run the risk of the device not working with many USB C sources.
On converters... do you really need 5V inside? That would be buck boost converter country. If you could get it to work at 4V that might work with buck only...
It’s handy how the USB power spec leaves just enough room to charge a LiIon cell.
w169:
Look at page 11 of this document:
https://www.st.com/resource/en/application_note/dm00536349-usb-typec-power-delivery-using-stm32xx-series-mcus-and-stm32xxx-series-mpus-stmicroelectronics.pdf
If your device is programmed to request any PDO (Power Delivery Output) from the Source, you should get it!
Then you've to carefully place protections on your hardware to avoid its destruction.
For example if you select the right R1/R2 on this component (https://www.st.com/resource/en/datasheet/tcpp01-m12.pdf), it should do the job.
R1/R2 will actually set the voltage limit of your application and trigger the internal over voltage protection when exceeded (p:12).
mgwalker95:
Are you trying to design a PD source, a PD sink or a DPR(dual role port both a source and a sink)?
If you are designing a PD sink look into the STUSB4500. Here is a sparkfun breakout board for it: https://www.sparkfun.com/products/15801
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