Hi to all, I have some doubts about USB bus layout for USB to serial interface.
I have to re-design board using TUSB3410, board was born for different chip so I can't change PCB dimensions.
Board is TUSB3410 then about 2" track length, then connector to main PCB, then 2" to 4 port USB hub.
1) taking a look to TI application notes (I don't remember which one), it's said I have to keep 3W distance from USB line (+ or -) to other signal lines. 5W from clock lines. (W is track width for USB).
Is not clear if I must keep 3W distance from EVERYTHING (so also from ground layer) or only from signals.
2) I'm working with USB 2.0, so I don't need EXTREME speed: nominal USB bus impedence si 90 Ohm, usual tolerance is 15%.
I know I'll get reflections if impedance doesn't match, but is this so important for USB 2.0? I mean, for a 4" (ok, it would be slightly shorter) bus length, for USB to serial line for 115200 maximum bitrate, can I use bigger tolerance?
Thanks.
