USBUFxxW6
Technical information
2.1
Application example
Figure 3.
Downstream port
Host/Hub USB por transceivert
Implementation of ST solutions for USB ports
USBDF01W5
Rt
D+ in
Ct Rd
D+ out
USBUF01W6
D2
Gnd
D1
Upstream port
D+
Peripheral transceiver
D+
D+
CABLE
D+
Ct
Rt
Ct
Rt
3.3 V
Rp
Gnd
Gnd
Ct Rd
D- in
Rt
D- out
D-
D-
D-
D3
3.3V
D4
D-
FULL SPEED CONNECTION
Downstream port
Host/Hub USB por transceivert
USBDF01W5
Rt
D+ in
Ct Rd
D+ out
USBUF01W6
D2
Gnd
D1
Upstream port
D+
Peripheral transceiver
D+
D+
CABLE
D+
Ct
Rt
Ct
Rt
3.3 V
Rp
Gnd
Gnd
Ct Rd
D- in
Rt
D- out
D-
D-
D-
D3
3.3V
D4
D-
LOW SPEED CONNECTION
2.2
EMI filtering
Current FCC regulations requires that class B computing devices meet specified maximum
levels for both radiated and conducted EMI.
●
●
Radiated EMI covers the frequency range from 30 MHz to 1 GHz.
Conducted EMI covers the 450 kHz to 30 MHz range.
For the types of devices utilizing the USB, the most difficult test to pass is usually the
radiated EMI test. For this reason the USBUFxxW6 device is aiming to minimize radiated
EMI.
The differential signal (D+ and D-) of the USB does not contribute significantly to radiated or
conducted EMI because the magnetic field of both conductors cancels each other.
The inside of the PC environment is very noisy and designers must minimize noise coupling
from the different sources. D+ and D-must not be routed near high speed lines (clocks
spikes).
Induced common mode noise can be minimized by running pairs of USB signals parallel to
each other and running grounded guard trace on each side of the signal pair from the USB
controller to the USBUF device. If possible, locate the USBUF device physically near the
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STMICROELECTRONICS [ STMICROELECTRONICS ]
