Question
We want to use ADuM4160 in an isolated USB HUB but have the following problem:
we need to isolate only 2 USB ports of SMSC USB2514B USB Hub (attached).
However, USB line pairs USBDNx-Dx from the hub are mirrored compared with the
inputs of ADuM4160, so we either cross the traces or must connect under the
device from inside (at the isolation trench).
Questions :
1. Is this a known problem ?
2. Is there a way to operate ADuM4160 in the opposite direction, ie connecting
downstream from the hub to downstream of ADUM4160 and setting the proper
direction using a particular configuration?
Answer
If I understand correctly, you don't like the ordering of D+ and D- because you
cannot make them match the D+/D- in the SMSC part without crossing one line
over the other. This is something that we have noticed a long time ago and will
reverse the order of these pins on the next rev of silicon.
The part cannot be turned around because you always need to match an upstream
and downstream port. The pull-ups are only on the Upstream side and the pull
downs are only on the Downstream side.
If you want to avoid punching vias through the PCB, then I would suggest that
you use one of the series resistors to do the hop. Run one line straight
between the pads of the 24ohm series resistor and use the installed resistor to
hop the trace. You might need a big resistor, but it keeps the traces on the
top.