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參數資料
| 型號： | ELECTROSTATIC |
| 英文描述： | Single Synchronous Buck Pulse-Width Modulation (PWM) Controller; Temperature Range: 0°C to 70°C; Package: 14-SOIC |
| 中文描述： | 靜電放電（ESD）的以太網收發(fā)器（73K號保護） |
| 文件頁數： | 1/1頁 |
| 文件大?。?/td> | 73K |
| 代理商： | ELECTROSTATIC |
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www.semtech.com
PROTECTION PRODUCTS
SI97-01
Surging Ideas
TVS Diode Application Note
Revision 9/2000
Electrostatic Discharge (ESD) Protection for Ethernet
Transceivers
This application note illustrates how to implement ESD
protection for Ethernet transceivers. The protection
technique shown may be used to aid in meeting the
test requirements of IEC 61000-4-2. This type of
protection may be used to prevent damage to trans-
ceivers which interface the Ethernet coaxial LAN to the
DTE or PC.
IEC 61000-4-2 defines ESD immunity requirements for
equipment which is shipped into the European Commu-
nity. The standard defines test voltages as high as
15kV for air discharge (8 kV contact discharge) and
induced current as high as 30A. The test procedure
requires that equipment be able to withstand ten
pulses in both positive and negative polarity.
An electrostatic discharge to the shield of the coaxial
connector causes an electromagnetic wave to propa-
gate across the transceiver board interface to the
circuit board. The wave travel along the metal traces
which connect the shield to the PC board ground plane.
The effects of circuit board trace inductance can result
in voltage potentials greater than 1.5kV at the CDS
pin. Voltage overstress of this magnitude can cause
dielectric breakdown of the transceiver chip. Also, the
current impulse flowing in the conductors will result in
Figure 1 - Ethernet Transceiver with ESD Protection
electromagnetic coupling of transients to surrounding
components on the board.
A typical Ethernet transceiver circuit with transient
protection is shown in Figure 1. TVS1 and TVS2 are
transient voltage suppression (TVS) diodes designed to
shunt the transient current away from the protected
Ethernet transceiver. The voltage across the input pins
is reduced to the clamping voltage of the TVS diode,
protecting the IC from damage. The TVS devices are
chosen such that the working voltage is greater than
the normal circuit operating voltage of 9V. Semtechs
SM12 is a 300W device rated to handle the transient
energy associated with ESD impulses and low level
lightning induced voltages. The SM12 provides bidirec-
tional protection in a SOT23 package, minimizing
board space requirements. The devices are placed as
follows: 1) BNC shield to common ground plane; 2)
CDS pin to -V
EE bus.; 3) If the HBE function is used, an
additional device should be placed from HBE pin to -
V
EE.
A 330W damping resistor is shown at the input of the
RXI pin to limit inrush current which may be induced
into the line. Finally, good circuit board layout tech-
niques should be used to further reduce the effects of
ESD induced transients.
8392
Component
Part Description
TVS1 & TVS2
SM12 300W TVS Diode
R1
330W 1/2 Watt
R2
1MW 1/2 Watt
C1
.01mF 750V
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