1www.semtech.com
PROTECTION PRODUCTS
SR05
RailClamp
Low Capacitance TVS Diode Array
Description Features
Circuit Diagram Schematic & PIN Configuration
Revision 02/18/05
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 SR series devices incorpo-
rates four 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 two high-speed data or transmission lines.
The low inductance construction minimizes voltage
overshoot during high current surges. Applications
Mechanical Characteristics
USB Power & Data Line Protection
Ethernet 10BaseT
I2C Bus Protection
Video Line Protection
T1/E1 secondary IC Side Protection
Portable Electronics
Microcontroller Input Protection
WAN/LAN Equipment
ISDN S/T Interface
ESD protection 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 two I/O lines
Low capacitance (<10pF) for high-speed interfaces
Low clamping voltage
Low operating voltage: 5.0V
Solid-state silicon-avalanche technology
JEDEC SOT-143 package
UL 497B listed
Molding compound flammability rating: UL 94V-0
Marking : R05
Packaging : Tape and Reel per EIA 481
Pin 4
Pin 2 Pin 3
Pin 1
SOT-143 (Top View)
1
23
4
2 2005 Semtech Corp. www.semtech.com
PROTECTION PRODUCTS
SR05
Absolute Maximum Rating
Electrical Characteristics
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3 2005 Semtech Corp. www.semtech.com
PROTECTION PRODUCTS
SR05
Typical Characteristics
Non-Repetitive Peak Pulse Power vs. Pulse Time Power Derating Curve
0.01
0.1
1
10
0.1 1 10 100 1000
Pulse Duration - tp (µs)
Peak Pulse Power - PPk (kW)
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
Clamping Voltage vs. Peak Pulse Current
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
0
2
4
6
8
10
12
14
16
18
0 5 10 15 20 25
Peak Pulse Current - IPP (A)
Clamping Voltage - VC (V)
Waveform
Parameters:
tr = 8µs
td = 20µs
4 2005 Semtech Corp. www.semtech.com
PROTECTION PRODUCTS
SR05
Device Connection Options for Protection of Two
High-Speed Data Lines
The SR05 TVS 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
pin 4 directly to the positive supply rail (VCC). In this
configuration the data lines are referenced to the
supply voltage. The internal TVS diode prevents
over-voltage on the supply rail.
2. The SR05 can be isolated from the power supply by
adding a series resistor between pin 4 and VCC. A
value of 10kΩ is recommended. The internal TVS
and steering diodes remain biased, providing the
advantage of lower capacitance.
3. In applications where no positive supply reference
is available, or complete supply isolation is desired,
the internal TVS may be used as the reference. In
this case, pin 4 is not connected. 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).
ESD Protection With RailClamps
RailClamps are optimized for ESD protection using the
rail-to-rail topology. Along with good board layout,
these devices virtually eliminate the disadvantages of
using discrete components to implement this topology.
Consider the situation shown in Figure 1 where dis-
crete diodes or diode arrays are configured for rail-to-
rail protection on a high speed line. During positive
duration ESD events, the top diode will be forward
biased when the voltage on the protected line exceeds
the reference voltage plus the VF drop of the diode.
Data Line and Power Supply Protection Using Vcc as
reference
Data Line Protection with Bias and Power Supply
Isolation Resistor
Data Line Protection Using Internal TVS Diode as
Reference
Applications Information
5 2005 Semtech Corp. www.semtech.com
PROTECTION PRODUCTS
SR05
PIN Descriptions
For negative events, the bottom diode will be biased
when the voltage exceeds the VF of the diode. At first
approximation, the clamping voltage due to the charac-
teristics of the protection diodes is given by:
VC = VCC + VF(for positive duration pulses)
VC = -VF(for negative duration pulses)
However, for fast rise time transient events, the
effects of parasitic inductance must also be consid-
ered as shown in Figure 2. Therefore, the actual
clamping voltage seen by the protected circuit will be:
VC = VCC + VF + LP diESD/dt (for positive duration pulses)
VC = -VF - LG diESD/dt (for negative duration pulses)
ESD current reaches a peak amplitude of 30A in 1ns
for a level 4 ESD contact discharge per IEC 61000-4-2.
Therefore, the voltage overshoot due to 1nH of series
inductance is:
V = LP diESD/dt = 1X10-9 (30 / 1X10-9) = 30V
Example:
Consider a VCC = 5V, a typical VF of 30V (at 30A) for the
steering diode and a series trace inductance of 10nH.
The clamping voltage seen by the protected IC for a
positive 8kV (30A) ESD pulse will be:
VC = 5V + 30V + (10nH X 30V/nH) = 335V
This does not take into account that the ESD current is
directed into the supply rail, potentially damaging any
components that are attached to that rail. Also note
that it is not uncommon for the VF of discrete diodes to
exceed the damage threshold of the protected IC. This
is due to the relatively small junction area of typical
discrete components. It is also possible that the
power dissipation capability of the discrete diode will
be exceeded, thus destroying the device.
The RailClamp is designed to overcome the inherent
disadvantages of using discrete signal diodes for ESD
suppression. The RailClamp’s integrated TVS diode
helps to mitigate the effects of parasitic inductance in
Figure 1 - “Rail-Figure 1 - “Rail-
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Figure 2 - The Effects of Parasitic InductanceFigure 2 - The Effects of Parasitic Inductance
Figure 2 - The Effects of Parasitic InductanceFigure 2 - The Effects of Parasitic Inductance
Figure 2 - The Effects of Parasitic Inductance
When Using Discrete Components to ImplementWhen Using Discrete Components to Implement
When Using Discrete Components to ImplementWhen Using Discrete Components to Implement
When Using Discrete Components to Implement
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Applications Information (continued)
6 2005 Semtech Corp. www.semtech.com
PROTECTION PRODUCTS
SR05
Applications Information (continued)
the power supply connection. During an ESD event,
the current will be directed through the integrated TVS
diode to ground. The total clamping voltage seen by
the protected IC due to this path will be:
VC = VF(RailClamp) + VTVS
This is given in the data sheet as the rated clamping
voltage of the device. For a SR05 the typical clamping
voltage is <16V at IPP=30A. The diodes internal to the
RailClamp are low capacitance, fast switching devices
that are rated to handle transient currents and main-
tain excellent forward voltage characteristics.
Universal Serial Bus ESD Protection
The figure below illustrates how to use the SR05 to
protect one upstream USB port and the SRDA05-4 to
protect two downstream 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 pro-
tected controller chip. The 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.
Reference Semtech application note SI96-18 for
further information.
Matte Tin Lead Finish
Matte tin has become the industry standard lead-free
replacement for SnPb lead finishes. A matte tin finish
is composed of 100% tin solder with large grains.
Since the solder volume on the leads is small com-
pared to the solder paste volume that is placed on the
land pattern of the PCB, the reflow profile will be
determined by the requirements of the solder paste.
Therefore, these devices are compatible with both
lead-free and SnPb assembly techniques. In addition,
unlike other lead-free compositions, matte tin does not
have any added alloys that can cause degradation of
the solder joint.
7 2005 Semtech Corp. www.semtech.com
PROTECTION PRODUCTS
SR05
ISDN S/T Interface Protection
Universal Serial Bus ESD Protection
Typical Applications
8 2005 Semtech Corp. www.semtech.com
PROTECTION PRODUCTS
SR05
Land Pattern - SOT-143
Outline Drawing - SOT-143
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DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS
3.
1.
DATUMS AND TO BE DETERMINED AT DATUM PLANE
REFERENCE JEDEC STD TO-253, VARIATION D.4.
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NOTES:
1. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY
CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR
COMPANY'S MANUFACTURING GUIDELINES ARE MET.
DIM
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MILLIMETERSINCHES
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DIMENSIONS
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9 2005 Semtech Corp. www.semtech.com
PROTECTION PRODUCTS
SR05
Contact Information
Semtech Corporation
Protection Products Division
200 Flynn Road, Camarillo, CA 93012
Phone: (805)498-2111 FAX (805)498-3804
Marking Codes
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Ordering Information
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