MIC2551A_11 Datasheet, PDF (9/11 Pages) Micrel Semiconductor – USB Transceiver

MIC2551A
PCB Layout Recommendations
Although the USB standard and applications are not based in
an impedance controlled environment, a properly designed
PCB layout is recommended for optimal transceiver perfor-
mance. The suggested PCB layout hints are as follows:
• Match signal line traces (VP/VM, D+, D–) to
40ps, approximately ¹/₃ inch if possible. FR-4
PCB material propagation is about 150ps/inch,
so to minimize skew try to keep VP/VM, D+/D–
traces as short as possible.
• For every signal line trace width (w), separate
the signal lines by 1.5 – 2 widths. Place all other
traces at >2 widths from all signal line traces.
• Maintain the same number of vias on each
differential trace, keeping traces approximately
at same separation distance along the line.
• Control signal line impedances to ±10%.
• Keep R_S as close to the IC as possible, with
equal distance between R_S and the IC for both
D+ and D–.
Micrel, Inc.
November 2008
9
M9999-112008