The QwiicBus hookup guide includes this statement when discussing powering the differential bus (VCC1) at 5v:
It is also strongly recommended to OPEN the 0-1 jumper on the primary / first EndPoint to isolate VCC (VDDA) from VCC1 (VDDB) but leave the 0-1 jumper on the terminating EndPoint CLOSED .
But does not seem to explain why VCC ought to be isolated from VCC1. Shouldn’t the PCA9615 be just fine operating at 5v VCC if the controller is a 5v device?
Is it just a concern about presenting 5v on the “3.3v” Qwiic connector and header?
The recommendation to isolate VCC (VDDA) from VCC1 (VDDB) in the QwiicBus setup when powering the differential bus at 5V is mainly to avoid power conflicts. if the two sides of the PCA9615 bus (controller side and bus side) are supplied by different voltage levels, voltage mismatch or overcurrent flow may happen.
But if the controller or other device connected to the Endpoint is a 5v system, there is no conflict with a 5v differential, correct?
Most Qwiic devices are 3.3 volt only and 5 volts can damage or destroy them. As long as EVERY device on the bus is 5 volt tolerate you can use 5 volts and be OK. Just be aware you can easily plug in a Qwiic enabled board that’s not 5 volt tolerant and there’s a good chance that board will be damaged if you accidentally plug it in.
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That makes sense; but then the recommendation to close the 0-1 jumper on the terminating EndPoint creates that very same risk.