P2 boards with USB-C for power
Rayman
Posts: 15,111
Seems learned something new about USB-C power today...
Already knew that 5.1k pull-downs on the CC pins auto negotiate 500mA (when connected to USB2) or 900mA (when connected to USB3).
Thinking this means don't really need an FTDI chip to negotiate this with the host and then enable with a mosfet. Seems that is an old thing that one doesn't need anymore. The p2 platform2 board still includes these things, but maybe should be removed in future...
But, what seeing now is that if you connect the CC pins to P2 pins and run ADC on them, you can determine if you are allowed to draw either 1.5 A or 3.0 A.
Think that is what is being described here:
https://www.st.com/resource/en/application_note/an5225-introduction-to-usb-typec-power-delivery-for-stm32-mcus-and-mpus-stmicroelectronics.pdf
There is also the BCD (battery charge detection) optional output from FT231X. This is another way to tell that you can draw 1 A, described here:
https://ftdichip.com/wp-content/uploads/2020/08/AN_175_Battery-Charger-Detection-over-USB-with-FT-X-Devices.pdf
Comments
I've never tried to read up on any version of USB power capabilities. So, ignoring PD negotiations, it looks like the sink device (UFP) doesn't specify what it needs. One just buys a source device (DFP) that can deliver it.
Like you say, just put the 5k1 pull-down resistors on there and it's advertised as a sink.
It'd be quite easy to make a tester for displaying a source's advertised non-PD 5V rating.