SR2.8 Datasheet

SR2.8
RailClamp
Low Capacitance TVS Diode Array
PROTECTION PRODUCTS
Description
Features
‹ ESD protection to
RailClamps are surge rated diode arrays designed to
protect high speed data interfaces. The SR series has
been specifically designed to protect sensitive components which are connected to data and transmission
lines from overvoltage caused by electrostatic discharge (ESD), electrical fast transients (EFT), and
tertiary lightning.
The unique design of the SR series devices incorporates four surge rated, low capacitance steering
diodes, and a TVS diode in a single package. The TVS
diode is constructed using Semtech’s proprietary low
voltage EPD technology for superior electrical characteristics at 2.8 volts.
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 components.
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.
‹
‹
‹
‹
‹
‹
IEC 61000-4-2 (ESD) ±15kV (air), ±8kV (contact)
IEC 61000-4-4 (EFT) 40A (5/50ns)
IEC 61000-4-5 (Lightning) 12A (8/20µs)
Array of surge rated diodes with internal
EPD TVS diode
Protects two I/O lines
Low capacitance (<10pF) for high-speed interfaces
Low leakage current (< 1µA)
Low operating voltage: 2.8V
Solid-state technology
Mechanical Characteristics
‹
‹
‹
‹
JEDEC SOT-143 package
Molding compound flammability rating: UL 94V-0
Marking : R2.8
Packaging : Tape and Reel
Applications
‹
‹
‹
‹
‹
‹
Circuit Diagram
Firewire
Sensitive Analog Inputs
Video Line Protection
Portable Electronics
Microcontroller Input Protection
WAN/LAN Equipment
Schematic & PIN Configuration
Pin 4
4
1
Pin 2
Pin 3
2
3
Pin 1
SOT-143 (Top View)
Revision 01/17/08
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SR2.8
PROTECTION PRODUCTS
Absolute Maximum Rating
R ating
Symbol
Value
Units
Peak Pulse Power (tp = 8/20µs)
Pp k
200
Watts
Peak Pulse Current (tp = 8/20µs)
IP P
14
A
Peak Forward Voltage (IF = 1A, tp=8/20µs)
VFP
1.5
V
Lead Soldering Temperature
TL
260 (10 sec.)
°C
Operating Temperature
TJ
-55 to +125
°C
TSTG
-55 to +150
°C
Storage Temperature
Electrical Characteristics
SR 2.8
Parameter
Reverse Stand-Off Voltage
Symbol
Conditions
Minimum
Typical
VRWM
Maximum
Units
2.8
V
Punch-Through Voltage
V PT
IPT = 2µA
3.0
V
Snap-Back Voltage
VSB
ISB = 50mA
2.8
V
Reverse Leakage Current
IR
VRWM = 2.8V, T=25°C
1
µA
Clamping Voltage
VC
IPP = 1A, tp = 8/20µs
5.0
V
Clamping Voltage
VC
IPP = 5A, tp = 8/20µs
8.5
V
Junction Capacitance
Cj
Between I/O pins and
Ground
VR = 0V, f = 1MHz
6
10
pF
Between I/O pins
VR = 0V, f = 1MHz
3
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2
pF
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SR2.8
PROTECTION PRODUCTS
Typical Characteristics
Non-Repetitive Peak Pulse Power vs. Pulse Time
Power Derating Curve
10
110
% of Rated Power or PI P
Peak Pulse Power - Ppk (kW)
100
1
0.1
90
80
70
60
50
40
30
20
10
0
0.01
0.1
1
10
100
0
1000
25
50
75
100
125
150
Ambient Temperature - TA (oC)
Pulse Duration - tp (µs)
Pulse Waveform
Clamping Voltage vs. Peak Pulse Current
110
W aveform
Parameters:
tr = 8µs
td = 20µs
90
20
18
Clamping Voltage - V C (V)
100
Percent of IPP
80
70
e -t
60
50
40
td = I PP /2
30
20
16
14
12
10
8
6
Waveform
Parameters:
tr = 8µs
td = 20µs
4
2
10
0
0
0
5
10
15
20
25
0
30
5
10
15
20
Peak Pulse Current - IPP (A)
T im e (µs)
Forward Voltage vs. Forward Current
10
Forward Voltage - VF (V)
9
8
7
6
5
4
3
Waveform
Parameters:
tr = 8µs
td = 20µs
2
1
0
0
5
10
15
20
25
30
35
40
45
50
Forward Current - IF (A)
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SR2.8
PROTECTION PRODUCTS
Applications Information
Device Connection Options for Protection of
Tw o High-Speed Data Lines
Data Line Pr
o t ection Using Int
ernal T V S Diode
Pro
Internal
as Reference
The SR2.8 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 negative 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:
Note that pins 4 is connected internally to the cathode
of the low voltage TVS. It is not recommended that this
pin be directly connected to a DC source greater than
the snap-back votlage (VSB) as the device can latch on
as described below.
IPP
ISB
EPD TVS Characteristics
These devices are constructed using Semtech’s
proprietary EPD technology. By utilizing the EPD technology, the SR2.8 can effectively operate at 2.8V while
maintaining excellent electrical characteristics.
IPT
VBRR
IR
VRWM
VSB VPT VC
IBRR
The EPD TVS employs a complex nppn structure in
contrast to the pn structure normally found in traditional 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 (VRWM). During an ESD
event, the device will begin to conduct and will enter a
low impedance state when the punch through voltage
(VPT) is exceeded. Unlike a conventional device, the low
voltage TVS will exhibit a slight negative resistance
characteristic as it conducts current. This characteristic aids in lowering the clamping voltage of the device,
but must be considered in applications where DC
voltages are present.
Figure 1 - EPD TVS IV Characteristic Curve
characteristics due to its structure. This point is
defined on the curve by the snap-back voltage (VSB)
and snap-back current (ISB). To return to a nonconducting state, the current through the device must
fall below the ISB (approximately <50mA) and the
voltage must fall below the VSB (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.
When the TVS is conducting current, it will exhibit a
slight “snap-back” or negative resistance
 2008 Semtech Corp.
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SR2.8
PROTECTION PRODUCTS
Applications Information (continued)
Board Layout Considerations for ESD Protection
Board layout plays an important role in the suppression
of extremely fast rise-time ESD transients. Recall that
the voltage developed across an inductive load is
proportional to the time rate of change of current
PIN
Descriptions
through the load (V = L di/dt). The total clamping
voltage seen by the protected load will be the sum of
the TVS clamping voltage and the voltage due to the
parasitic inductance (VC(TOT) = VC + L di/dt) . Parasitic
inductance in the protection path can result in significant voltage overshoot, reducing the effectiveness of
the suppression circuit. An ESD induced transient for
example reaches a peak in approximately 1ns. For a
30A pulse (per IEC 61000-4-2 Level 4), 1nH of series
inductance will increase the effective clamping voltage
by 30V
(V = 1x10-9 (30/1x10-9)). For maximum effectiveness,
the following board layout guidelines are recommended:
z
z
z
Minimize the path length between the SR3.3 and
the protected line.
Place the SR2.8 near the connector to restrict
transient coupling in nearby traces.
Minimize the path length (inductance) between the
RJ45 connector and the SR2.8.
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 compared 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.
 2008 Semtech Corp.
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SR2.8
PROTECTION PRODUCTS
Outline Drawing - SOT-143
D
A
e
H
e/2
DIM
4
3
GAUGE
PLANE
SEATING
PLANE
B
C
1
c
0.25
L
L1
E
E1
0
DETAIL A
2
bxN
e1
bbb
A2
C A B
A
SEE DETAIL A
SIDE VIEW
4X
A
A1
A2
b
b1
c
D
E
E1
e
e1
L
L1
N
0
aaa
bbb
ccc
DIMENSIONS
INCHES
MILLIMETERS
MIN NOM MAX MIN NOM MAX
.035
-
1.22
.048 0.80
0.15
.006 0.013
.042 0.75 0.90 1.07
.020 0.30
0.51
.037 0.76
0.94
.008 0.08
0.20
.114 .120 2.80 2.90 3.04
.093 .104 2.10 2.37 2.64
.051 .055 1.20 1.30 1.40
.075
1.92 BSC
.008
0.20 BSC
.015 .020 .024 0.40 0.50 0.60
(.021)
(0.54)
4
4
0°
8°
0°
8°
.006
0.15
.008
0.20
.004
0.10
.031
.000
.029
.011
.029
.003
.110
.082
.047
ccc C
SEATING PLANE
A1
b1
aaa
C
C A B
NOTES:
1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
2. DATUMS -A- AND -B-
TO BE DETERMINED AT DATUM PLANE -H-
3. DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS
OR GATE BURRS.
4. REFERENCE JEDEC STD TO-253, VARIATION D.
Land Pattern - SOT-143
X1
X1
Y
DIM
Z
C
E1
G
E2
Y
X2
C
E1
E2
G
X1
X2
Y
Z
DIMENSIONS
INCHES
MILLIMETERS
(.087)
.076
.068
.031
.039
.047
.055
.141
(2.20)
1.92
1.72
0.80
1.00
1.20
1.40
3.60
X1
NOTES:
1. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY
CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR
COMPANY'S MANUFACTURING GUIDELINES ARE MET.
2. REFERENCE IPC-SM-782A.
 2008 Semtech Corp.
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SR2.8
PROTECTION PRODUCTS
Marking Codes
Part Number
Marking
Code
SR2.8
R2.8
Ordering Information
Par t
Number
Lead Finish
Qty per
Reel
R eel Size
SR2.8.TC
SnPb
3,000
7 Inch
SR2.8.TCT
Pb Free
3,000
7 Inch
Contact Information
Semtech Corporation
Protection Products Division
200 Flynn Road, Camarillo, CA 93012
Phone: (805)498-2111 FAX (805)498-3804
 2008 Semtech Corp.
7
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