PROTECTION PRODUCTS
Description
RailClamps are surge rated diode arrays designed to
protect high speed data interfaces. The SRDA70-4 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 unique design of the SRDA70-4 integrates eight
surge rated, low capacitance steering diodes in a low
profile SO-8 package. During transient conditions, the
steering diodes direct the transient to either the
positive side of the power supply line or to ground. The
SRDA70-4 may be used as a stand alone device or in
conjunction with TVS diodes for enhanced protection.
The low capacitance array configuration allows the user
to protect four high speed data or I/O lines. The low
inductance construction minimizes voltage overshoot
during high current surges.
RailClamp
Ò
Low Capacitance TVS Diode Array
Features
u
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 diodes
Protects four I/O lines
Low capacitance for high-speed interfaces
High surge capability
Low forward voltage characteristics
Solid-state silicon avalanche technology
SRDA70-4
u
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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 per EIA 481
Applications
Latch-Up Protection
Microcontroller Input Protection
Token Ring
I
2
C Bus Protection
Video Line Protection
Set Top Box I/O
LAN/WAN Equipment
Circuit Diagram
Schematic & PIN Configuration
REF 1
I/O 1
REF 1
I/O 1
I/O 2
I/O 3
I/O 4
REF 2
I/O 4
I/O 3
REF 2
REF 1
I/O 2
REF 2
SO-8 (Top View)
Revision 9/2000
1
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SRDA70-4
PROTECTION PRODUCTS
Absolute Maximum Rating
R ating
Peak Pulse Current (tp = 8/20µ s)
Rectifier Rep etitive Peak Reverse Voltage
Th ermal Resistance, Junction to A mb ient
Th ermal Resistance, Junction to Case
Lead Sold ering Temp erature
Op erating Temp erature
Storage Temp erature
Symbo l
I
PP
V
RRM
q
JA
q
JC
T
L
T
J
T
STG
Value
24
70
163
38.8
260 (10 sec.)
-55 to +125
-55 to +150
Units
A
V
°C /W
°C /W
°C
°C
°C
Electrical Characteristics
SR DA70-4
Par ame te r
Rectifier Rep etitive Peak reverse
Voltage
Reverse Breakd ow n Voltage
Reverse Leakage Current
Forw ard Voltage
Forw ard Voltage
Junction Cap acitance
Symbo l
V
RRM
V
BR
I
R
V
F
V
F
C
j
I
t
= 50µ A
V
RWM
= 70V, T=25°C
I
PP
= 1A , tp = 8/20µ s
I
PP
= 10A , tp = 8/20µ s
Betw een I/O p ins and
Gnd
V
R
= 0V, f = 1MHz
Betw een I/O p ins
V
R
= 0V, f = 1MHz
4
85
5
1.3
3.3
15
Co nd itio ns
Minimum
Typ ical
Maximum
70
Units
V
V
µA
V
V
pF
pF
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SRDA70-4
PROTECTION PRODUCTS
Typical Characteristics
Non-Repetitive Peak Pulse Power vs. Pulse Time
10
110
100
Power Derating Curve
Peak Pulse Power - P
PP
(kW)
% of Rated Power or I
PP
90
80
70
60
50
40
30
20
10
1
0.1
0.01
0.1
1
10
Pulse Duration - tp (µs)
100
1000
0
0
25
50
75
100
125
150
Ambient Temperature - T
A
(
o
C)
Pulse Waveform
110
100
90
80
Percent of I
PP
70
60
50
40
30
20
10
0
0
5
10
15
Time (µs)
20
25
30
td = I
PP
/2
e
-t
Variation of Capacitance vs. Reverse Voltage
0
Waveform
Parameters:
tr = 8µs
td = 20µs
-2
% Change in Capacitance
-4
-6
-8
-10
-12
-14
-16
0
1
2
3
Reverse Voltage (V)
4
5
6
I/O to GND
f = 1MHz
Foward Voltage vs. Forward Current
10
9
Forward Voltage - V
F
(V)
8
7
6
5
4
3
2
1
0
0
5
10
15
20
25
30
35
40
45
50
Forward Current - I
F
(A)
Waveform
Parameters:
tr = 8µs
td = 20µs
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SRDA70-4
PROTECTION PRODUCTS
Applications Information
Device Connection Options for Protection of Four
High-Speed Data Lines
The SRDA70-4 TVS is designed to protect four 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 V
F
) the
steering diodes are forward biased, conducting the
transient current away from the sensitive circuitry.
Data lines are connected at pins 1, 4, 6 and 7. The
negative reference (REF2) is connected at pins 5 & 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 induc-
tance.
The positive reference (REF1) is connected at pins 2 &
3. The options for connecting the positive reference
are as follows:
1. To protect data lines and the power line, connect
pins 2 & 3 directly to the positive supply rail (V
CC
).
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. The SRDA70-4 can be isolated from the power
supply by adding a series resistor between pins 2 &
3 and V
CC
. A value of 10kW is recommended. The
internal 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,
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).
I/O Protection
Microcontroller Protection
SRDA70-4
ã
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SRDA70-4
PROTECTION PRODUCTS
Outline Drawing - SO-8
Land Pattern - SO-8
ã
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