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PROTECTION PRODUCTS Description
RailClamps are surge rated diode arrays designed to protect high speed data interfaces. The SR12 has been specifically designed to protect sensitive components which are connected to data and transmission lines from overvoltages caused by ESD (electrostatic discharge), EFT (electrical fast transients), and lightning. The unique design of the SR12 incorporates 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 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.
RailClamp Low Capacitance TVS Diode Array
Features
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) 0.5kV, 12A (8/20s) Array of surge rated diodes with internal TVS Diode Protects two I/O lines Operating Voltage: 12 volts Low capacitance (5pF typical) for high-speed interfaces Low clamping voltage Solid-state silicon-avalanche technology
SR12
Mechanical Characteristics
JEDEC SOT-143 package UL 497B listed Molding compound flammability rating: UL 94V-0 Marking : R12 Packaging : Tape and Reel per EIA 481 RoHS/WEEE Compliant
Applications
ADSL Industrial Electronics RS-422 Interfaces Portable Electronics Microcontroller Input Protection WAN/LAN Equipment
Circuit Diagram
Pin 4
Schematic & PIN Configuration
1
Pin 2 Pin 3
4
2
Pin 1
3
SOT-143 (Top View)
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SR12
PROTECTION PRODUCTS Absolute Maximum Rating
Rating Peak Pulse Power (tp = 8/20s) Peak Pulse Current (tp = 8/20s) Peak Forward Voltage (IF = 1A, tp=8/20s) Lead Soldering Temperature Operating Temperature Storage Temperature Symbol Ppk IPP VFP TL TJ TSTG Value 500 16 1.5 260 (10 sec.) -55 to +125 -55 to +150 Units Watts A V C C C
Electrical Characteristics
SR12 Parameter Reverse Stand-Of f Voltage Reverse Breakdown Voltage Reverse Leakage Current Clamping Voltage Clamping Voltage Junction Capacitance Symbol VRWM VBR IR VC VC Cj It = 1mA VRWM =12V, T=25C IPP = 5A, tp = 8/20s IPP = 16A, tp = 8/20s Between I/O pins and Ground VR = 0V, f = 1MHz Between I/O pins VR = 0V, f = 1MHz 5 13.3 1 24 31 10 Conditions Minimum Typical Maximum 12 Units V V A V V pF
3
pF
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SR12
PROTECTION PRODUCTS Typical Characteristics
Non-Repetitive Peak Pulse Power vs. Pulse Time
10 (kW)
110 100 % of Rated Power or PP I 90 80 70 60 50 40 30 20 10 0
Power Derating Curve
PP
Peak Pulse Power - P
1
0.1
0.01 0.1 1 10 Pulse Duration - tp (s) 100 1000
0
25
50
75
100
125
150
Ambient Temperature - TA (oC)
Pulse Waveform
110 100 90 80 Percent of IPP 70 60 50 40 30 20 10 0 0 5 10 15 Time (s) 20 25 30 td = IPP/2 e
-t
Clamping Voltage vs. Peak Pulse Current
33
Waveform Parameters: tr = 8s td = 20s
30 (V) Clamping Voltage - V
C
27 24 21 18 15 12 9 6 3 0 0 4 8 12 16 20 Peak Pulse Current - IR (A) Waveform Parameters: tr = 8s td = 20s
Forward 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 - IF (A) Waveform Parameters: tr = 8s td = 20s
% Change in Capacitance 0 -2 -4 -6 -8 -10 -12 -14 -16 0
Capacitance vs. Reverse Voltage
1
2
3
4
5
6
Reverse Voltage - VR (V)
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SR12
PROTECTION PRODUCTS Applications Information
Device Connection Options for Protection of Two High-Speed Data Lines The SR12 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: 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 SR12 can be isolated from the power supply by adding a series resistor between pin 4 and VCC. A value of 10k 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 discrete diodes or diode arrays are configured for rail-torail 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
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SR12
PROTECTION PRODUCTS Applications Information (continued)
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 characteristics of the protection diodes is given by: VC = VCC + VF (for positive duration pulses) PIN Descriptions (for negative duration pulses) VC = -VF However, for fast rise time transient events, the effects of parasitic inductance must also be considered 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 1000-4-2. 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 2 - The Effects of Parasitic Inductance When Using Discrete Components to Implement Pro Rail-T Rail- To-Rail Pr o t ection "Rail-T Pro Topology Figure 1 - "Rail-To-Rail" Pr o t ection Topology (First Approximation)
Rail-T Pro Figure 3 - Rail- To-Rail Pr o t ection Using RailClamp Arrays RailClam p T V S Arra ys
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SR12
PROTECTION PRODUCTS 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 SR12 the typical clamping voltage is <30V at IPP=16A. The diodes internal to the RailClamp are low capacitance, fast switching devices that are rated to handle transient currents and maintain excellent forward voltage characteristics. 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.
Typical Applications
ADSL Interface Protection
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SR12
PROTECTION PRODUCTS Outline Drawing - SOT-143
D e e/2 4 3
B A H
DIM SEATING PLANE
C
GAUGE PLANE 0.25 L L1 DETAIL A
0
c
DIMENSIONS INCHES MILLIMETERS MIN NOM MAX MIN NOM MAX
.031 .000 .029 .011 .029 .003 .110 .082 .047 .048 0.80 1.22 .006 0.013 0.15 .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 .035 -
E1
E
1 e1
2 bxN bbb CAB SIDE VIEW SEE DETAIL A
A A1 A2 b b1 c D E E1 e e1 L L1 N 0 aaa bbb ccc
A2
A
4X
ccc C
SEATING PLANE b1 aaa CAB A1
C
NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). 2. DATUMS -A- AND -BTO BE DETERMINED AT DATUM PLANE -H3. 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 G E1 E2
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
Y
X2
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.
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SR12
PROTECTION PRODUCTS Marking Codes
Part Number SR12 Marking Code R12
Ordering Information
Par t Number SR12.TC SR12.TCT Lead Finish SnPb Pb Free Qty per Reel 3,000 3,000 R eel Size 7 Inch 7 Inch
Contact Information
Semtech Corporation Protection Products Division 200 Flynn Rd., Camarillo, CA 93012 Phone: (805)498-2111 FAX (805)498-3804
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