MIC2551A-2.5
Configuration Mode
Normal
Disconnect (D+/D-
sharing)
VBUS/VTRM
Connected
Open
VIF
Connected
Connected
Notes
Normal supply configuration and operation.
Micrel, Inc.
VP/VM are HIGH outputs, RCV is LOW.
With OE# = 0 and SUS = 1, data lines may be driven with external
devices up to 3.6V.
With D+, D- floating, I
IF
draws less than 1µA.
VP/VM are HIGH outputs, RCV is LOW.
With D+, D- floating, I
IF
draws less than 1µA.
Logic controlled input pins are Hi-Z. No communication is possible
until interface voltage is restored.
Inoperative
Disconnect
Disable Mode
Unpowered
Ground
Connected
Connected
Connected
Open
Ground
Table 1. Power Supply Configuration
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 one-third 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 dif-
ferential 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–.
March 2010
9
M9999-030810
MICREL [ MICREL SEMICONDUCTOR ]
