PROTECTION PRODUCTS
Description
RailClamps are surge rated diode arrays designed to
protect high speed data interfaces. The SR series has
been specifically designed to protect sensitive compo-
nents which are connected to data and transmission
lines from overvoltage caused by electrostatic dis-
charge
(ESD),
electrical fast transients
(EFT),
and
lightning.
The unique design of the SRDA series devices incorpo-
rates surge rated, low capacitance steering diodes and
a TVS diode in a single package. During transient
conditions, the steering diodes direct the transient to
either the positive side of the power supply line or to
ground. The internal TVS diode prevents over-voltage
on the power line, protecting any downstream compo-
nents.
The low capacitance array configuration allows the user
to protect six high-speed data or transmission lines.
The low inductance construction minimizes voltage
overshoot during high current surges.
RailClamp
Low Capacitance TVS Diode Array
Features
Transient protection for high-speed data lines to
IEC 61000-4-2 (ESD) ±15kV (air), ±8kV (contact)
IEC 61000-4-4 (EFT) 40A (5/50ns)
IEC 61000-4-5 (Lightning) 24A (8/20µs)
Array of surge rated diodes with internal TVS diode
Protects six I/O lines and power supply line
Low capacitance (<15pF) for high-speed interfaces
Low operating & clamping voltages
Solid-state technology
SRDA3.3-6 and SRDA05-6
Mechanical Characteristics
JEDEC SO-8 package
UL 497B listed
Molding compound flammability rating: UL 94V-0
Marking : Part number, date code, logo
Packaging : Tube or Tape and Reel
Applications
USB Power & Data Line Protection
T1/E1 secondary IC Side Protection
Token Ring
HDSL, SDSL secondary IC Side Protection
Video Line Protection
Microcontroller Input Protection
Base stations
I
2
C Bus Protection
Circuit Diagram
Schematic and PIN Configuration
I/O 1
1
I/O 2
2
+V
REF
3
I/O 3
4
8
GND
I/O 6
I/O 5
I/O 4
7
6
5
S0-8 (Top View)
Revision 01/15/08
www.semtech.com
1
SRDA3.3-6 and SRDA05-6
PROTECTION PRODUCTS
Applications Information
Device Connection Options for Protection of Six High-
Speed Lines
The SRDA TVS is designed to protect four data lines
from transient overvoltages by clamping them to a
fixed reference. When the voltage on the protected
line exceeds the reference voltage (plus diode V
F
) the
steering diodes are forward biased, conducting the
transient current away from the sensitive circuitry.
Data lines are connected at pins 1, 2, 4, 5, 6 and 7.
The negative reference is connected at pin 8. These
pins should be connected directly to a ground plane on
the board for best results. The path length is kept as
short as possible to minimize parasitic inductance.
The positive reference is connected at pins 2 and 3.
In the case of the SRDA3.3-6, pins 2 and 3 are
connected internally to the cathode of the low voltage
TVS. It is not recommended that these pins be directly
connected to a DC source greater than the snap-back
votlage (V
SB
) as the device can latch on as described
below.
EPD TVS Characteristics
These devices are constructed using Semtech’s
proprietary EPD technology. By utilizing the EPD tech-
nology, the SRDA3.3-6 can effectively operate at 3.3V
while maintaining excellent electrical characteristics.
V
BRR
I
SB
Data Line Protection Using Internal TVS Diode as
Reference
EPD TVS IV Characteristic Curve
I
PP
I
PT
I
R
V
RWM
V V V
C
SB
PT
The EPD TVS employs a complex nppn structure in
contrast to the pn structure normally found in tradi-
tional silicon-avalanche TVS diodes. Since the EPD
TVS devices use a 4-layer structure, they exhibit a
slightly different IV characteristic curve when compared
to conventional devices. During normal operation, the
device represents a high-impedance to the circuit up to
the device working voltage (V
RWM
). During an ESD
event, the device will begin to conduct and will enter a
low impedance state when the punch through voltage
(V
PT
) is exceeded. Unlike a conventional device, the low
voltage TVS will exhibit a slight negative resistance
characteristic as it conducts current. This characteris-
tic aids in lowering the clamping voltage of the device,
but must be considered in applications where DC
voltages are present.
When the TVS is conducting current, it will exhibit a
slight “snap-back” or negative resistance characteris-
tics due to its structure. This point is defined on the
2008 Semtech Corp.
5
I
BRR
curve by the snap-back voltage (V
SB
) and snap-back
current (I
SB
). To return to a non-conducting state, the
current through the device must fall below the I
SB
(approximately <50mA) and the voltage must fall below
the V
SB
(normally 2.8 volts for a 3.3V device). If a 3.3V
TVS is connected to 3.3V DC source, it will never fall
below the snap-back voltage of 2.8V and will therefore
stay in a conducting state.
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