HW/Doc: Problems with input power muxing using Schottky ORing diodes?
Created by: jks-prv
Thanks for recently adding the rev A1 design files, especially the schematic.
Are you guys sure about using Schottky ORing diodes (D81,82) for input multiplexing between the USB-C and cape power-in sources? There are a couple problems I can see.
Depending on current draw by the AI you might be exceeding the power dissipation of the diodes. Their Pd is spec'd at 850 mW and you'll hit that by putting only ~1.5A through them (half of what the USB-C input is capable of). The BBB avoided this of course by using low-loss FET muxing inside the PMIC.
I ran some simulations of your Q15 PFET + B360A diode circuit and over the USB-C 5V power adapter voltage supply range spec of 4.75 - 5.5V you're not going to meet the VDD Vmin input spec on your USB-C CCL (TUSB322I U22). It's short about 0.2V depending on the Vf of the diodes. Simulation results with AI drawing ~2A.
If it's late in the game to be making changes you might at least want to see if you can spec a better Schottky with lower Vf (e.g. SSB44). A much better solution would be to use something like a TPS2120 in place of the diodes.