USB power delivery hack

A project log for Silly hardware wishlist

Too simple for a project page & which may never happen.

lion-mclionheadlion mclionhead 12/17/2023 at 03:240 Comments

The lion kingdom has 2 USB  power supplies capable of arbitrary voltages.  For just 1 application, it's not economical to buy an off self power delivery chip when a dedicated power supply is the same price.  It would be economical to make the application circuit negotiate the voltage on its own.  So far, there are no open source implementations of the protocol. 

The only search terms which work are "usb c power delivery breakout".  Anything else causes the goog to spit out garbage.

What little information there is has people trying to reverse engineer it instead of bothering to decipher the spec.  It seems to be a 1 megbaud RS232 signal on the CC wire.  The high voltage is 1.2V.  The 2 sides pull the wire low to communicate in both directions.  The application circuit would always depend on its own voltage regulator & the configured USB voltage would be for powering a load.  It wouldn't be capable of eliminating the voltage regulator.

Another guy got a bit farther with a $1300 Lecroy.

Lions noticed the crown of test equipment going from Tektronics to Rigol & now Lecroy.  The guy graduated in 2008, worked for Jeri Ellison at CastAR,  went on to all the top tier companies, started working with USB 3/C right when it 1st came out in 2016.  Every generation starts out at whatever the latest thing is & that becomes their ground zero.  There's no such thing as paying your dues with USB 1.

The current best price of $10 for 5 chips would only be affordable if there were at least 2 applications.  Then the cost per power supply would be $5.  The mane applications now would be powering 12V LED tapes, a 12V audio amplifier & 12V audio recorder.  Those might be all that's needed to justify an off the shelf solution.

The starting point for an implementation would be to sniff an existing circuit.  The general idea is no matter what, USB power delivery needs a high speed front end to access the 1.2V 1 megbaud serial signals.  There might be a way to use a complimentary BJT circuit to boost the 1.2V to 3.3 but no-one is doing it.