PROTECTION PRODUCTS
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PROTECTION PRODUCTS
SM712
Asymmetrical TVS Diode for
Extended Common-Mode RS-485
Description Features
Circuit Diagram Schematic & PIN Configuration
Revision 11/17/04
The SM712 transient voltage suppressor (TVS) diode is
designed for asymmetrical (12V to -7V ) protection in
multi-point data transmission standard RS-485 applica-
tions. The SM712 may be used to protect devices
from transient voltages resulting from electrostatic
discharge (ESD), electrical fast transients (EFT), and
lightning.
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.
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.
Applications
Mechanical Characteristics
Protection of RS-485 transceivers with extended
common-mode range
Security systems
Automatic Teller Machines
HFC systems
Networks
400 watts peak pulse power (tp = 8/20µs)
Transient protection for asymmetrical 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) 12A (8/20µs)
Protects two +12V to -7V lines
Low capacitance
Low clamping voltage
Solid-state silicon avalanche technology
JEDEC SOT23 package
Molding compound flammability rating: UL 94V-0
Marking : 712
Packaging : Tape and Reel per EIA 481
SOT23 (Top View)
22004 Semtech Corp. www.semtech.com
PROTECTION PRODUCTS
PROTECTION PRODUCTS
SM712
Absolute Maximum Rating
Electrical Characteristics
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32004 Semtech Corp. www.semtech.com
PROTECTION PRODUCTS
SM712
Typical Characteristics
Non-Repetitive Peak Pulse Power vs. Pulse Time Power Derating Curve
Pulse Waveform 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
Capacitance vs. Reverse Voltage
0
10
20
30
40
50
60
70
80
90
100
110
0 25 50 75 100 125 150 175
Ambient Temperature - TA (oC)
% of Rated Power or I
PP
0.01
0.1
1
10
0.1 1 10 100 1000
Pulse Duration - tp (µs)
Peak Pulse Power - Ppk (kW)
0
2
4
6
8
10
12
14
16
18
20
22
24
0246810121416
Peak Pulse Current - IPP (A)
Clamping Voltage - VC (V)
Pin 1 to 3 and 2 to 3
Pin 3 to 1 and 3 to
Waveform
Parameters:
tr = 8µs
td = 20µs
0
10
20
30
40
50
60
70
80
012345678910111213
Reverse Voltage - VR (V)
Capacitance - Cj (pF)
f = 1MHz
42004 Semtech Corp. www.semtech.com
PROTECTION PRODUCTS
PROTECTION PRODUCTS
SM712
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 volt-
ages 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.
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:
zPlace the SM712 near the input terminals or
connectors to restrict electromagnetic coupling.
zMinimize the path length between the SM712 and
the protected line. This minimizes voltage over-
shoot due to parasitic inductance of board traces.
zUse ground planes whenever possible.
zLong, single trace ground conductors should be
avoided. The ground pin (Pin 3) should be con-
nected directly to a ground plane on the circuit
board for best results.
zMinimize all conductive loops including power and
ground loops.
zNever run critical signals near board edges.
RS-485 Protection Circuit
Applications Information
52004 Semtech Corp. www.semtech.com
PROTECTION PRODUCTS
SM712
Land Pattern - SOT23
Outline Drawing - SOT23
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e1
D
E1 E
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A1
A2
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A
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B
C
SEATING PLANE
aaa C
1.401.20
N3 3
0-8°0°8°0° -
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bbb .008 0.20
aaa .004 0.10
INCHES
.114
L1
E
D
b
e
c
.012
.003
.082
A1
DIM
A
MIN
.000
.035
0.51
0.18
2.64
0.30
0.08
2.10
.022
-
.075
-
.093
.020
.007
.104
(0.55)
1.90 BSC
-
-
2.37
2.90
MILLIMETERS
MAX
0.10
1.12
MIN
DIMENSIONS
0.01
MAXNOM
-
-.004
.044
NOM
0.89
-
-
3.042.80.110 .120
e1 .037 0.95 BSC
L .015 .020 0.500.40.024 0.60
A2 .035 .037 0.950.88.040 1.02
E1 .051 1.30
SEE DETAIL A
SIDE VIEW
DATUMS AND TO BE DETERMINED AT DATUM PLANE
-A- -B-
2.
CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
NOTES:
OR GATE BURRS.
DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS
3.
1.
-H-
H
DETAIL A
0.25
C
SEATING
PLANE
GAUGE
PLANE 0c
L
L1
REFERENCE IPC-SM-782A.
2.
E .037 0.95
Y
Y
G
ZC
E
X
E1
E1 .075 1.90
NOTES:
1. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY
CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR
COMPANY'S MANUFACTURING GUIDELINES ARE MET.
DIM
Y
Z
G
X
C
MILLIMETERSINCHES
(2.20)
.055
.141
.039
.031
(.087)
1.40
3.60
1.00
0.80
DIMENSIONS
62004 Semtech Corp. www.semtech.com
PROTECTION PRODUCTS
PROTECTION PRODUCTS
SM712
Contact Information
Semtech Corporation
Protection Products Division
200 Flynn Road, Camarillo, CA 93012
Phone: (805)498-2111 FAX (805)498-3804
Ordering Information
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