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| PROTECTION PRODUCTS Description 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 ESD (electrostatic discharge), EFT (electrical fast transients), and lightning. The unique design of the SRDA series devices incorporates 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. RailClampO 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) 24A (8/20s) Array of surge rated diodes with internal TVS diode Protects four I/O lines & power supply line Low capacitance (<15pF) for high-speed interfaces Low operating & clamping voltages Solid-state technology SRDA3.3-4 THRU SRDA12-4 u u u u u u u u u u u u u u u u u u 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 USB Power & Data Line Protection T1/E1 secondary IC Side Protection T3/E3 secondary IC Side Protection HDSL, IDSL secondary IC Side Protection Video Line Protection Microcontroller Input Protection Base stations I2C Bus Protection Circuit Diagram Schematic & PIN Configuration I/O REF1 1 8 REF 2 REF 1 I/O 1 I/O 2 I/O 3 I/O 4 2 7 I/O REF 1 3 6 I/O REF2 I/O 4 5 REF 2 S0-8 (Top View) Revision 9/2000 1 www.semtech.com SRDA3.3-4 THRU SRDA12-4 PROTECTION PRODUCTS Absolute Maximum Rating R ating Peak Pulse Pow er (tp = 8/20s) Peak Pulse Current (tp = 8/20s) Peak Forw ard Voltage (IF = 1A, tp =8/20s) Lead Soldering Temp erature Op erating Temp erature Storage Temp erature Symbo l Pp k I PP V FP TL TJ TSTG Value 500 25 1.5 260 (10 sec.) -55 to +125 -55 to +150 Units Watts A V C C C Electrical Characteristics SR DA3.3-41 Par ame te r Reverse Stand -Off Voltage Punch -Th rough Voltage Snap -Back Voltage Reverse Leakage Current Clamp ing Voltage Clamp ing Voltage Clamp ing Voltage Junction Cap acitance Symbo l VRWM V PT VSB IR VC VC VC Cj IPT = 2 A ISB = 50mA V RWM = 3.3V, T=25C IPP = 1A , tp = 8/20 s IPP = 10A , tp = 8/20 s IPP = 25A , tp = 8/20 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 8 3.5 2.8 1 5.3 10 15 15 Co nd itio ns Minimum Typ ical Maximum 3.3 Units V V V A V V V pF 4 pF Note: (1) The SRDA3.3-4 is constructed using Semtechs proprietary EPD process technology. See applications section for more information. a 2000 Semtech Corp. 2 www.semtech.com SRDA3.3-4 THRU SRDA12-4 PROTECTION PRODUCTS Electrical Characteristics (continued) SR DA05-4 Par ame te r Reverse Stand-Off Voltage Reverse Breakdow n Voltage Reverse Leakage Current Clamp ing Voltage Clamp ing Voltage Clamp ing Voltage Junction Cap acitance Symbo l VRWM V BR IR VC VC VC Cj It = 1mA VRWM = 5V, T=25C IPP = 1A, tp = 8/20s IPP = 10A, tp = 8/20s IPP = 25A, tp = 8/20s Betw een I/O p ins and Gnd V R = 0V, f = 1MHz Betw een I/O p ins V R = 0V, f = 1MHz 8 6 10 9.8 12 20 15 Co nd itio ns Minimum Typ ical Maximum 5 Units V V A V V V pF 4 pF SR DA12-4 Par ame te r Reverse Stand-Off Voltage Reverse Breakdow n Voltage Reverse Leakage Current Clamp ing Voltage Clamp ing Voltage Clamp ing Voltage Junction Cap acitance Symbo l VRWM V BR IR VC VC VC Cj It = 1mA VRWM = 12V, T=25C IPP = 1A, tp = 8/20s IPP = 10A, tp = 8/20s IPP = 20A, tp = 8/20s Betw een I/O p ins and Gnd V R = 0V, f = 1MHz Betw een I/O p ins V R = 0V, f = 1MHz 8 13.3 1 17 20 25 15 Co nd itio ns Minimum Typ ical Maximum 12 Units V V A V V V pF 4 pF a 2000 Semtech Corp. 3 www.semtech.com SRDA3.3-4 THRU SRDA12-4 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 IPP 90 80 70 60 50 40 30 20 10 1 0.1 0.01 0.1 1 10 Pulse Duration - tp (s) 100 1000 0 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 Waveform Parameters: tr = 8s td = 20s 22 20 Clamping Voltage - VC (V) 18 16 14 12 10 8 6 4 2 0 0 5 10 15 20 25 30 35 Peak Pulse Current - IPP (A) Waveform Parameters: tr = 8s td = 20s SRDA3.3-4 SRDA05-4 SRDA12-4 Variation of Capacitance vs. Reverse Voltage 0 -2 % Change in Capacitance -4 -6 -8 -10 -12 1 -14 0 1 2 3 Reverse Voltage (V) 4 5 6 0 0 I/O to GND f = 1MHz Forward Voltage - V F (V) 10 9 8 7 6 5 4 3 2 Forward Voltage vs. Forward Current Waveform Parameters: tr = 8s td = 20s 5 10 15 20 25 30 35 40 45 50 Forward Current - IF (A) a 2000 Semtech Corp. 4 www.semtech.com SRDA3.3-4 THRU SRDA12-4 PROTECTION PRODUCTS Applications Information Device Connection Options for Protection of Four High-Speed Lines The SRDA TVS is designed to protect four data lines from transient overvoltages 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 1, 4, 6 and 7. The negative reference 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 inductance. The positive reference is connected at pins 2 and 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 (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 SRDA can be isolated from the power supply by adding a series resistor between pins 2 & 3 and VCC. A value of 10kW 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, pins 2 & 3 are 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 V drop of the diode. F For negative events, the bottom diode will be biased when the voltage exceeds the V of the diode. At first F 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 a 2000 Semtech Corp. 5 www.semtech.com SRDA3.3-4 THRU SRDA12-4 PROTECTION PRODUCTS Applications Information (continued) approximation, the clamping voltage due to the characteristics of the protection diodes is given by: V =V +V C CC C F F (for positive duration pulses) PIN -V V = Descriptions (for negative duration pulses) 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: V = V + V + L di C CC F P ESD /dt (for positive duration pulses) (for negative duration pulses) V = -V - L di C F G ESD /dt Figure 1 - Rail-To-Rail Protection Topology (First Approximation) ESD current reaches a peak amplitude of 30A in 1ns for a level 4 ESD contact discharge per IEC 61000-4-2. Therefore, the voltage overshoot due to 1nH of series inductance is: V = L di P ESD /dt = 1X10-9 (30 / 1X10-9) = 30V Example: Consider a V = 5V, a typical V of 30V (at 30A) for the CC F 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: V = 5V + 30V + (10nH X 30V/nH) = 335V C 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 the high V of the discrete diode. It is not uncommon F for the V of discrete diodes to exceed the damage F 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 RailClamps integrated TVS diode helps to mitigate the effects of parasitic inductance in the power supply connection. During an ESD event, Figure 2 - The Effects of Parasitic Inductance When Using Discrete Components to Implement Rail-To-Rail Protection Figure 3 - Rail-To-Rail Protection Using RailClamp TVS Arrays a 2000 Semtech Corp. 6 www.semtech.com SRDA3.3-4 THRU SRDA12-4 PROTECTION PRODUCTS Applications Information (continued) 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: V =V C F(RailClamp) technology, the SRDA3.3-4 can effectively operate at 3.3V while maintaining excellent electrical characteristics. The IV characteristic curve of the EPD device is shown in Figure 4. The device represents a high impedance to the circuit up to the working voltage (VRWM). During a transient event, the device will begin to conduct as it is biased in the reverse direction. When the punchthrough voltage (VPT) is exceeded, the device enters a low impedance state, diverting the transient current away from the protected circuit. When the device is conducting current, it will exhibit a slight snap-back or negative resistance characteristic due to its structure. This must be considered when connecting the device to a power supply rail. To return to a non-conducting state, the current through the device must fall below the snap-back current (approximately < 50mA) to allow it to travel back through the negative resistance region. If this is a concern, a 10kW current limiting resistor can be placed between the supply rail and the positive reference pins (2 & 3) to prevent device latchup. RailClamp is a registered trademark of Semtech corporation ,PP +V TVS This is given in the data sheet as the rated clamping voltage of the device. For an SRDA05-4 the typical clamping voltage is <16V at I =30A. The diodes PP internal to the RailClamp are low capacitance, fast switching devices that are rated to handle high transient currents and maintain excellent forward voltage characteristics. Using the RailClamp does not negate the need for good board layout. All other inductive paths must be considered. The connection between the positive supply and the SRDA and from the ground plane to the SRDA must be kept as short as possible. The path between the SRDA and the protected line must also be minimized. The protected lines should be routed directly to the SRDA. Placement of the SRDA on the PC board is also critical for effective ESD protection. The device should be placed as close as possible to the input connector. The reason for this is twofold. First, inductance resists change in current flow. If a significant inductance exists between the connector and the TVS, the ESD current will be directed elsewhere (lower resistance path) in the system. Second, the effects of radiated emissions and transient coupling can cause upset to other areas of the board even if there is no direct path to the connector. By placing the TVS close to the connector it will divert the ESD current immediately and absorb the ESD energy before it can be coupled into nearby traces. (Reference Semtech application note SI99-01 for further information on board layout) SRDA3.3-4 EPD TVS Characteristics The internal TVS of the SRDA3.3-4 is constructed using Semtechs proprietary EPD technology. The structure of the EPD TVS is vastly different from the traditional pn-junction devices that are internal to the SRDA05-4 and SRDA12-4 devices. At voltages below 5V, high leakage current and junction capacitance render conventional avalanche technology impractical for most applications. However, by utilizing the EPD a 2000 Semtech Corp. 7 ,6% ,37 9%55 ,5 9 5:0 9 9 9& 6% 37 ,%55 Figure 4 - EPD TVS IV Characteristic Curve www.semtech.com SRDA3.3-4 THRU SRDA12-4 PROTECTION PRODUCTS Typical Applications Universal Serial Bus ESD Protection T1/E1 Interface Protection a 2000 Semtech Corp. 8 www.semtech.com SRDA3.3-4 THRU SRDA12-4 PROTECTION PRODUCTS Outline Drawing - SO-8 Notes: (1) Controlling dimension: Inch (unless otherwise specified). Land Pattern - SO-8 a 2000 Semtech Corp. 9 www.semtech.com SRDA3.3-4 THRU SRDA12-4 PROTECTION PRODUCTS Ordering Information Par t Numbe r SRDA 3.3-4.TB SRDA 3.3-4.TE SRDA 05-4.TB SRDA 05-4.TE SRDA 12-4.TB SRDA 12-4.TE Wo r king Vo ltage 3.3V 3.3V 5V 5V 12V 12V Qty p e r Reel 500 2500 500 2500 500 2500 R e e l Size 7 Inch 13 Inch 7 Inch 13 Inch 7 Inch 13 Inch Note: (1) No suffix indicates tube pack. Contact Information Semtech Corporation Protection Products Division 652 Mitchell Rd., Newbury Park, CA 91320 Phone: (805)498-2111 FAX (805)498-3804 a 2000 Semtech Corp. 10 www.semtech.com |
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