1www.semtech.com
PROTECTION PRODUCTS
SR70
RailClamp
Low Capacitance TVS Diode Array
Description Features
Circuit Diagram Schematic & PIN Configuration
Revision 04/18/03
RailClamps are surge rated diode arrays designed to
protect high speed data interfaces. The SR70 has
been specifically designed to protect sensitive compo-
nents which are connected to data and transmission
lines from over-voltages caused by ESD (electrostatic
discharge), EFT (electrical fast transients), and light-
ning. The SR70 has been optimized for use on ADSL
and other high-speed interfaces.
The unique design of the SR70 integrates four surge
rated, low capacitance steering diodes in a low profile
SOT-143 package. It has a typical capacitance of only
5pF and may be used to protect two high-speed lines
without sacrificing signal integrity. The SR70 is de-
signed to replace “standard” rectifiers that are not
rated for the high energy surges that are normally
expected in telecommunications applications.
During transient conditions, the steering diodes direct
the transient to either the positive side of the power
supply line or to ground. The maximum clamping
voltage seen by the protected circuit will be one diode
drop (VF) above the supply (reference) voltage. The
SR70 may be used as a stand alone device or in
conjunction with TVS diodes for enhanced protection.
Applications
Mechanical Characteristics
ADSL Lines
I2C Bus Protection
Video Line Protection
T1/E1 secondary IC Side Protection
Portable Electronics
Microcontroller Input Protection
WAN/LAN Equipment
ISDN S/T Interface
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) 1kV, 24A (8/20µs)
Array of surge rated, low capacitance diodes
Protects two I/O lines
Low capacitance (5pF typical) for high-speed
interfaces
Low clamping voltage
Solid-state silicon-avalanche technology
JEDEC SOT-143 package
UL 497B listed
Molding compound flammability rating: UL 94V-0
Marking : R70
Packaging : Tape and Reel per EIA 481
Pin 4
Pin 2 Pin 3
Pin 1
SOT-143 (Top View)
1
23
4
2 2003 Semtech Corp. www.semtech.com
PROTECTION PRODUCTS
SR70
Absolute Maximum Rating
Electrical Characteristics (T=25oC)
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3 2003 Semtech Corp. www.semtech.com
PROTECTION PRODUCTS
SR70
Typical Characteristics
Non-Repetitive Peak Pulse Power vs. Pulse Time Power Derating Curve
0
10
20
30
40
50
60
70
80
90
100
110
0 25 50 75 100 125 150
Ambient Temperature - TA (oC)
% of Rated Power or I
PP
0
10
20
30
40
50
60
70
80
90
100
110
0 5 10 15 20 25 30
Time (µs)
Percent of IPP
e-t
td = IPP/2
Waveform
Parameters:
tr = 8µs
td = 20µs
Pulse Waveform
Forward Voltage vs. Forward Current
Capacitance vs. Reverse Voltage
0
1
2
3
4
5
6
7
8
9
10
0 5 10 15 20 25 30 35 40 45 50
Forward Current - IF (A)
Forward Voltage - V F (V)
Waveform
Parameters:
tr = 8µs
td = 20µs
-16
-14
-12
-10
-8
-6
-4
-2
0
0123456
Reverse Voltage - VR (V)
% Change in Capacitance
I/O to GND
f = 1MHz
0.01
0.1
1
10
0.1 1 10 100 1000
Pulse Duration - tp (µs)
Peak Pulse Power - PPk (kW)
4 2003 Semtech Corp. www.semtech.com
PROTECTION PRODUCTS
SR70
Device Connection Options for Protection of Two
High-Speed Data Lines
The SR70 is designed to protect two data lines from
transient over-voltages by clamping them to a fixed
reference. When the voltage on the protected line
exceeds the reference voltage (plus diode VF) the
steering diodes are forward biased, conducting the
transient current away from the sensitive circuitry.
Data lines are connected at pins 2 and 3. The nega-
tive reference (REF1) is connected at pin 1. This pin
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 (REF2) is connected at pin 4.
The options for connecting the positive reference are
as follows:
1. To protect data lines and the power line, connect
pins 2 and 3 directly to the positive supply rail (VCC).
In this configuration the data lines are referenced
to the supply voltage. An external TVS diode may
be added between the supply rail and ground in
order to prevent over-voltage on the supply rail.
2. In applications where no positive supply reference
is available, or complete supply isolation is desired,
an external TVS diode may be used as the refer-
ence. The steering diodes will begin to conduct
when the voltage on the protected line exceeds the
working voltage of the TVS (plus one diode drop).
SR70 Pin Configuration
Applications Information
Data Line and Power Supply Protection Using Vcc as
reference
1
23
4
5 2003 Semtech Corp. www.semtech.com
PROTECTION PRODUCTS
SR70
Land Pattern
Notes:
(1) Controlling dimension: Inch (unless otherwise specified).
(2) Dimension A and B do not include mold protrusions. Mold protrusions are .006” max.
Outline Drawing
6 2003 Semtech Corp. www.semtech.com
PROTECTION PRODUCTS
SR70
Contact Information
Semtech Corporation
Protection Products Division
200 Flynn Rd., Camarillo, CA 93012
Phone: (805)498-2111 FAX (805)498-3804
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Marking Codes
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Ordering Information
R70
SR70 Marking (Top View)
