PROTECTION PRODUCTS
4. Low leakage current for minimal power consump-
tion.
5. Ability to remain undamaged by repetitive ESD
strikes
6. Capacity to handle ESD currents as high as 30A.
7. Minimum package size
2
www.semtech.com
SI96-18
Surging
Ideas
TVS Diode Application Note
Figure 2 - Upstream & Downstream USB Port Protection
USB Protection Topology
Each USB port consists of four lines. Two lines (D+ &
D-) are used for bidirectional data transfer, and two
lines are reserved for bus voltage and ground. Both
USB power and data line connections are vulnerable to
ESD strikes. Most protection techniques typically
utilize multiple discrete devices, but this is not advis-
able. Interconnections between discrete components
increases the parasitic inductance in the conduction
path of the transient current, thus reducing the overall
effectiveness of the protection circuit. The Semtech
RailClamp
series provides an easily implemented,
cost effective solution for protecting multiple high-
speed lines and the power supply line. The RailClamp
devices are integrated arrays of low capacitance, surge
rated steering diodes and a TVS diode in a single
package. The devices are designed to exceed the ESD
requirements of IEC 61000-4-2.
Figures 1 and 2 illustrate how to use the SR05 to
protect one USB port and the SRDA05-4 to protect
two USB ports. When the voltage on the data lines
exceed the bus voltage (plus one diode drop), the
internal rectifiers are forward biased conducting the
transient current away from the protected controller
chip. The integrated TVS diode directs the surge to
ground. The TVS diode also acts to suppress ESD
strikes directly on the voltage bus. Thus, both power
and data pins are protected with a single device. The
SR05 adds a maximum loading capacitance of 10pF
and the SRDA05-4 adds a maximum loading capaci-
tance of 15pF per line.
With proper design and layout, the USB port can be
protected to >15kV (Human Body Model per IEC
61000-4-2).
References & Further Information
z
Universal Serial Bus Specification, Revision 1.0,
January 15, 1996
USB Implementers Forum Web Site: www.usb.org
z
RailClamp is a registered trademark of Semtech Corporation