Asymmetrical TVS Diode for Extended Common-Mode

SM712
Asymmetrical TVS Diode for
Extended Common-Mode RS-485
PROTECTION PRODUCTS
Description
Features
The SM712 transient voltage suppressor (TVS) diode is
designed for asymmetrical (12V to -7V ) protection in
multi-point data transmission standard RS-485 applications. The SM712 may be used to protect devices
from transient voltages resulting from electrostatic
discharge (ESD), electrical fast transients (EFT), and
lightning.
‹ 400 watts peak pulse power (tp = 8/20µs)
‹ Transient protection for asymmetrical data lines to
‹
‹
‹
‹
The SM712 features 400 Watts (tp = 8/20µs) of
power handling capability to accommodate the higher
transient voltage levels which may be expected in
extended common mode applications. This provides
higher equipment reliability and eliminates the “guess
work” required when using zener diodes that are not
rated to handle such transient conditions.
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)
Protects two +12V to -7V lines
Low capacitance
Low clamping voltage
Solid-state silicon avalanche technology
Mechanical Characteristics
‹
‹
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‹
The SM712 replaces four discrete components by
integrating two 12V and two 7V TVS diodes in a single
package. The integrated design aids in reducing
voltage over-shoot associated with trace inductance.
The low clamping voltage of the SM712 minimizes the
stress on the protected transceiver. The SOT23
package allows flexibility in the design of “crowded”
circuit boards.
JEDEC SOT23 package
Molding compound flammability rating: UL 94V-0
Marking : 712
Packaging : Tape and Reel per EIA 481
Applications
‹ Protection of RS-485 transceivers with extended
‹
‹
‹
‹
Circuit Diagram
common-mode range
Security systems
Automatic Teller Machines
HFC systems
Networks
Schematic & PIN Configuration
SOT23 (Top View)
Revision 11/17/04
1
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SM712
PROTECTION PRODUCTS
Absolute Maximum Rating
R ating
Symbol
Value
Units
Peak Pulse Power (tp = 8/20µs)
Pp k
400
Watts
Peak Pulse Current (tp = 8/20µs)
IP P
17
A
Lead Soldering Temp erature
TL
260 (10 sec.)
°C
Op erating Temp erature
TJ
-55 to +125
°C
TSTG
-55 to +150
°C
Storage Temp erature
Electrical Characteristics
SM712
Pins 1 to 3 and
2 to 3
(12V T VS)
Parameter
MI N
Symbol
Conditions
Reverse Stand-Off Voltage
VRWM
Pin 3 to 1 or Pin 2 to 1
Reverse Breakdown Voltage
V BR
IPT = 1mA
Reverse Leakage Current
IR
VR = VRWM
1
20
µA
Clamp ing Voltage
VC
IPP = 5A,
tp = 8/20µs
20
10
V
Clamp ing Voltage
VC
IPP = 17A,
tp = 8/20µs
26
12
V
Junction Cap acitance
Cj
VR = 0V, f = 1MHz
75
75
pF
MAX
2
MI N
T YP
12
13.3
VR = VRWM, f = 1MHz
 2004 Semtech Corp.
T YP
Pins 3 to 1 and
3 to 2
(7V T VS)
MAX
Units
7
V
7.5
45
V
45
pF
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SM712
PROTECTION PRODUCTS
Typical Characteristics
Non-Repetitive Peak Pulse Power vs. Pulse Time
Power Derating Curve
10
110
% of Rated Power or IPP
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
Pulse Waveform
80
Percent of IPP
150
175
22
Clamping Voltage - VC (V)
90
-t
60
50
40
125
24
W aveform
Parameters:
tr = 8µs
td = 20µs
100
e
100
Clamping Voltage vs. Peak Pulse Current
110
70
75
Ambient Temperature - TA (oC)
Pulse Duration - tp (µs)
td = I PP /2
30
20
20
18
Pin 1 to 3 and 2 to 3
16
14
12
10
Pin 3 to 1 and 3 to
8
6
Waveform
Parameters:
tr = 8µs
td = 20µs
4
2
10
0
0
0
5
10
15
20
25
0
30
2
4
6
8
10
12
14
16
Peak Pulse Current - IPP (A)
T im e (µs)
Capacitance vs. Reverse Voltage
80
Capacitance - Cj (pF)
70
60
50
40
30
20
10
f = 1MHz
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
Reverse Voltage - VR (V)
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SM712
PROTECTION PRODUCTS
Applications Information
RS-485 Common Mode Voltages
Device Connection for Protection of Two RS-485 Data
Lines
EIA RS-485 specifies a ±7V ground difference between
devices on the bus. This permits the bus voltage to
range from +12V (5V + 7V) to -7V (0 - 7V).
The SM712 is designed to protect two RS-485 data
lines in extended common mode applications. The
SM712 may be used to protect devices from transient
voltages resulting from ESD, EFT, and lightning. The
device is designed with asymmetrical operating voltages for optimum protection. The TVS diodes at pins 1
and 2 have a working voltage of 12 volts. These pins
are connected to the differential data line pairs. The
TVS diodes at pin 3 have a working voltage of 7 volts.
Pin 3 is connected to ground. The internal TVS diodes
of the SM712 will protect the transceiver input from
positive transient voltage spikes greater than 12V and
negative spikes greater than 7V.
RS-485 Protection Circuit
A series current limiting resistor may be added in
applications requiring enhanced surge immunity.
Circuit Board Layout Recommendations.
Good circuit board layout is critical for the suppression
of fast rise-time transients such as ESD. The following
guidelines are recommended:
z
z
z
z
z
z
Place the SM712 near the input terminals or
connectors to restrict electromagnetic coupling.
Minimize the path length between the SM712 and
the protected line. This minimizes voltage overshoot due to parasitic inductance of board traces.
Use ground planes whenever possible.
Long, single trace ground conductors should be
avoided. The ground pin (Pin 3) should be connected directly to a ground plane on the circuit
board for best results.
Minimize all conductive loops including power and
ground loops.
Never run critical signals near board edges.
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SM712
PROTECTION PRODUCTS
Outline Drawing - SOT23
D
A
DIM
e1
A
A1
A2
b
c
D
E
E1
e
e1
L
L1
N
0
aaa
bbb
H
3
B
E1
GAUGE
PLANE
SEATING
PLANE
E
0
c
0.25
C
L
L1
DETAIL A
1
2
bxN
bbb
e
A2
A
.035
.000
.035
.012
.003
.110
.082
.047
.015
0°
.037
.114
.093
.051
.075
.037
.020
.022
3
.004
.008
.044
.004
.040
.020
.007
.120
.104
.055
.024
8°
0.89
1.12
0.01
0.10
0.88 0.95 1.02
0.30
0.51
0.08
0.18
2.80 2.90 3.04
2.10 2.37 2.64
1.20 1.30 1.40
1.90 BSC
0.95 BSC
0.40 0.50 0.60
(0.55)
3
0°
8°
0.10
0.20
C A B
3X
aaa C
SEE DETAIL A
SIDE VIEW
SEATING PLANE
A1
DIMENSIONS
INCHES
MILLIMETERS
MIN NOM MAX MIN NOM MAX
C
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.
Land Pattern - SOT23
X
Y
DIM
Z
G
Y
C
C
E
E1
G
X
Y
Z
DIMENSIONS
INCHES
MILLIMETERS
(.087)
.037
.075
.031
.039
.055
.141
(2.20)
0.95
1.90
0.80
1.00
1.40
3.60
E
E1
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.
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SM712
PROTECTION PRODUCTS
Ordering Information
Part Number
Lead Finish
Qty per
Reel
R eel Size
SM712.TC
PbSn
3,000
7 Inch
SM712.TCT
Pb-Free
Matte Sn
3,000
7 Inch
Contact Information for Semtech International AG
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Korea Branch
Tel: 886-2-2748-3380
Fax: 886-2-2748-3390
Semtech Sw itz erland GmbH
Japan Branch
Tel: 81-3-6408-0950
Fax: 81-3-6408-0951
Tel: 82-2-527-4377
Fax: 82-2-527-4376
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Tel: 44-1794-527-600
Fax: 44-1794-527-601
Tel: 86-21-6391-0830
Fax: 86-21-6391-0831
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Tel: 33-(0)169-28-22-00
Fax: 33-(0)169-28-12-98
Semtech International AG is a wholly-owned subsidiary of
Semtech Corporation, which has its headquarters in the U.S.A.
Semtech Germany GmbH
Tel: 49-(0)8161-140-123
Fax: 49-(0)8161-140-124
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