Implementing USB-C PD PHY directly into micro-controller

Question

I want to explore more USB-C PD, in particular Programmable Power Supply (PPS), to supply my projects with power. There are some good projects¹ using some standard communication (e.g. SPI or I2C) to communicate to as dedicated IC (e.g. STUSB4500, FUSB302, or AP33772), that then communicates via the CC pins to the PSU (USB-C PD PHY).

However, that means extra cost and extra space for the dedicated communication chip. I guess that's ok for most applications, but I'm curious; from reading a presentation explaining the details of the USB-C PHY layer I would think that it should be rather doable to implement the same logic directly into any better micro-controller (like an ESP32). I say that because the link speed is spec'ed at 300kbps at low impedance at 1.125V (shiftable to and from 3.3V e.g. with PCA9306) via two pins. Sure, then a lot of processing is happening on the logical data to the physical, but that should not be "too hard"^TM to implement, right? Or am I missing any good reason/complication not to do that?

¹ To name a few:

1. SparkFun Power Delivery Board - USB-C (Qwiic) (STUSB4500)
2. Mike Rakin's Board + Github (STUSB4500)
3. Ryan Ma's "PD Micro" board + Github (FUSB302)
4. Reclaimer Lab's USB-C Power Delivery PHY Breakout Board or USB-C Explorer board (both FUSB302)
5. AP33772 Validation Platform Setup (AP33772)

Addition: Apparently there are a few micro-controllers with built-in capabilities (thanks @Justme), like the STM32G071. There is even an official discovery kit (STM32G071B-DISCO) and wiki entry.

Answer 1

I've done that with the benefits as you state. This is purely anecdotal, but hey, one data point :)

Most notably: I can buy the MCUs without PD PHY functionality, but the applicable ones (for my use) with PD PHY are vaporware in practice. Furthermore, I need the rather specialized peripheral set on the microcontroller I already use, so switching to a different uC is not possible. Even further, PD is just a tiny bit of the overall device functionality in my case, so choosing an MCU based on that is a bit of a stretch.

There are stand-alone USB PD interface chips with SPI or I2C MCU interface, but they don't quite do what I need. So if you can use those - definitely don't overlook them.

The PD PHY discrete hardware is about a dollar's worth of discrete mosfets and resistors and such. Looks scary on the schematic, but occupies a dozen or two mm^2 on the board (using tiniest parts possible). Sure, doing discrete designs takes some effort, but these days industry-strength SPICE is free-as-in-beer, so that's a good start.

And if we can't buy discrete small signal mosfets anymore, the world is ending, so no need to worry about USB PD, as I usually say.

Level shifter ICs are a wonderful thing if they do what you need for the price you can afford and with a shipping date that works for you. I often go with discrete parts because they are always available, and I'm comfortable enough putting them together. It's probably a rare sight nowadays to see a mostly digital product with dozens of discrete BJTs/mosfets in it, but this strategy has worked for me. It may not work for you - keep that in mind, and I'm far from suggesting it as some magic bullet. It's a tradeoff, with factors different for everyone.