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PROTECTION PRODUCTS
EClamp2122S
Applications Information
Figure 1 - EClamFigure 1 - EClam
Figure 1 - EClamFigure 1 - EClam
Figure 1 - EClam
p2p2
p2p2
p2
122S Cir122S Cir
122S Cir122S Cir
122S Cir
cuit Diagramcuit Diagram
cuit Diagramcuit Diagram
cuit Diagram
C1
C1
C2
C2
Device Connection
The EClamp2122S is designed to provide termination,
EMI filtering and ESD protection for two USB I/O lines.
The equivalent circuit diagram is shown in Figure 1.
The device is connected as follows:
z USB data lines are routed through the
EClamp2122S for easy implementation and opti-
mum pc board layout. Pin 1 is connected to the
voltage supply line. The input of the D+ line is
routed into pin 2 and out of pin 5. The input of the
D- line is connected at pin 3 and the output at pin
4. Pin 6 is connected to ground. The ground
connection should be made directly to the ground
plane for best results. The path length is kept as
short as possible to reduce the effects of parasitic
inductance in the board traces.
USB Port Design with EClamp2122S
The Universal Serial Bus (USB) specification requires
termination and filtering components for proper opera-
tion. In addition, an open USB socket is vulnerable to
hazardous ESD discharges in excess of 15kV. These
discharges can occur on the data lines or the voltage
bus. The EClamp2122S is an easily implemented
solution designed to meet the termination & EMI filter
requirements of the USB specification revision 1.1. It
also provides ESD protection to IEC 61000-4-2.
USB line termination is achieved with series resistors
on both the D+ and D- lines. These resistors preserve
signal integrity by matching the cable impedance to
that of the differential driver. 15kΩ pull-down resis-
tors are used to identify a downstream port. Capaci-
tors are used to bypass high frequency energy to
ground and for edge rate control of the USB signals.
Integrated TVS diodes provide ESD protection of both
(D+ & D-) data lines and the voltage bus (V
BUS
).
General layout guidelines are given below:
z Avoid running D+ & D- signal line traces near high
speed clock lines or similar signal lines.
z Avoid running critical signal lines near board edges.
z Place the EClamp2122S near the USB connector
to restrict transient coupling.
z Minimize the path length between the USB connec-
tor and the EClamp2122S.
