While doing the port protection schematics changes I noticed some changes that could also make sense to already include in BP7 Rev0:
- change the USB termination resistors to the 27R recommended by RapPi
- change the GIGANTIC SOT-23 MMBT7002K fets to more appropriate SOT-523
- you already have a lot of 4.7µF caps in 0402. My default instead is 10µF in 0402 (Samsung CL05A106MQ5NUNC / C15525). So when you copied my reset/bootloader circuit you added one more BOM line. I think this isn’t necessary. So I suggest to change it to 4.7µF / 560k instead. The values have to be tested with your capacitors because voltage derating plays a big factor here. The 560k are eyeballed, we could use this revision to fine-tune.
I implemented all of the changes above in my pull request for the port protection stuff, so you could copy from there.
Alternatives:
- An alternative could of course be that you change all your 4.7µF caps to CL05A106MQ5NUNC. They will probably have more capacitance left at the target voltage, but depends on actual part no you use.
- You also have some 2.2µF caps in 0402. I don’t know what the point of these is in comparison to also using 4.7µF or 10µF.
- I now use the 10µF everywhere I have used 100nF for decoupling in the past and the voltage isn’t too high (<= 5V).