protection products 1 www.semtech.com protection products srda3.3-6 and srda05-6 railclamp ? ? ? ? ? low capacitance tvs diode array description features circuit diagram schematic and pin configuration revision 02/03/03 railclamps are surge rated diode arrays designed to protect high speed data interfaces. the sr series has been specifically designed to protect sensitive compo- nents which are connected to data and transmission lines from overvoltage caused by electrostatic dis- charge (esd) , electrical fast transients (eft) , and lightning. the unique design of the srda series devices incorpo- rates 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 compo- nents. 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. applications mechanical characteristics ? usb power & data line protection ? t1/e1 secondary ic side protection ? token ring ? hdsl, sdsl secondary ic side protection ? video line protection ? microcontroller input protection ? base stations ? i 2 c bus protection ? 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 six i/o lines and power supply line ? low capacitance (<15pf) for high-speed interfaces ? low operating & clamping voltages ? solid-state technology ? 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 s0-8 (top view) i/o 1 i/o 2 i/o 3 i/o 4 i/o 5 i/o 6 +v ref gnd 1 2 3 4 5 6 7 8
2 ? 2003 semtech corp. www.semtech.com protection products protection products srda3.3-6 and srda05-6 absolute maximum rating electrical characteristics g n i t a rl o b m y se u l a vs t i n u t ( r e w o p e s l u p k a e p p ) s 0 2 / 8 =p k p 0 0 5s t t a w i ( e g a t l o v d r a w r o f k a e p f ) s 0 2 / 8 = p t , a 1 =v p f 5 . 1v e r u t a r e p m e t g n i r e d l o s d a e lt l ) . c e s 0 1 ( 0 6 2c e r u t a r e p m e t g n i t a r e p ot j 5 2 1 + o t 5 5 -c e r u t a r e p m e t e g a r o t st g t s 0 5 1 + o t 5 5 -c 6 - 3 . 3 a d r s r e t e m a r a pl o b m y ss n o i t i d n o cm u m i n i ml a c i p y tm u m i x a ms t i n u e g a t l o v f f o - d n a t s e s r e v e rv m w r 3 . 3v e g a t l o v h g u o r h t - h c n u pv t p i t p a 2 =5 . 3v e g a t l o v k c a b - p a n sv b s i b s a m 0 5 =8 . 2v t n e r r u c e g a k a e l e s r e v e ri r v m w r c 5 2 = t , v 3 . 3 =1a e g a t l o v g n i p m a l cv c i p p s 0 2 / 8 = p t , a 1 =3 . 5v e g a t l o v g n i p m a l cv c i p p s 0 2 / 8 = p t , a 0 1 =0 1v e g a t l o v g n i p m a l cv c i p p s 0 2 / 8 = p t , a 5 2 =5 1v t n e r r u c e s l u p k a e pi p p t p s 0 2 / 8 =5 2a e c n a t i c a p a c n o i t c n u jc j d n a s n i p o / i n e e w t e b d n u o r g v r z h m 1 = f , v 0 = 85 1f p s n i p o / i n e e w t e b v r z h m 1 = f , v 0 = 4f p note: (1) the srda3.3-6 is constructed using semtech?s propri- etary epd process technology. see applications section for more information.
3 ? 2003 semtech corp. www.semtech.com protection products protection products srda3.3-6 and srda05-6 6 - 5 0 a d r s r e t e m a r a pl o b m y ss n o i t i d n o cm u m i n i ml a c i p y tm u m i x a ms t i n u e g a t l o v f f o - d n a t s e s r e v e rv m w r 5v e g a t l o v n w o d k a e r b e s r e v e rv r b i t a m 1 =6 v t n e r r u c e g a k a e l e s r e v e ri r v m w r c 5 2 = t , v 5 =0 1a e g a t l o v g n i p m a l cv c i p p t , a 1 = p s 0 2 / 8 =8 . 9v e g a t l o v g n i p m a l cv c i p p t , a 0 1 = p s 0 2 / 8 =2 1v e g a t l o v g n i p m a l cv c i p p t , a 5 2 = p s 0 2 / 8 =0 2v t n e r r u c e s l u p k a e pi p p t p s 0 2 / 8 =5 2a e c n a t i c a p a c n o i t c n u jc j d n a s n i p o / i n e e w t e b d n u o r g v r z h m 1 = f , v 0 = 85 1f p s n i p o / i n e e w t e b v r z h m 1 = f , v 0 = 4f p electrical characteristics (continued)
4 ? 2003 semtech corp. www.semtech.com protection products protection products srda3.3-6 and srda05-6 typical characteristics non-repetitive peak pulse power vs. pulse time power derating curve 0.01 0.1 1 10 0.1 1 10 100 1000 pulse duration - t p (s) peak pulse power - p pk (kw) 0 10 20 30 40 50 60 70 80 90 100 110 0 25 50 75 100 125 150 ambient temperature - t a ( o c) % of rated power or i pp 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 (s) percent of i pp e -t td = i pp /2 waveform parameters: tr = 8s td = 20s pulse waveform variation of capacitance vs. reverse voltage forward voltage vs. forward current -14 -12 -10 -8 -6 -4 -2 0 0123456 reverse voltage - v r (v) % change in capacitance 0 1 2 3 4 5 6 7 8 9 10 0 5 10 15 20 25 30 35 40 45 50 forward current - i f (a) forward voltage - v f (v) waveform parameters: tr = 8 s td = 20 s 0 2 4 6 8 10 12 14 16 0 5 10 15 20 25 30 peak pulse current - i pp (a) clamping voltage - v c (v) srda05-6 srda3.3-6 waveform parameters: tr = 8s td = 20s
5 ? 2003 semtech corp. www.semtech.com protection products protection products srda3.3-6 and srda05-6 device connection options for protection of six 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 v f ) the steering diodes are forward biased, conducting the transient current away from the sensitive circuitry. data lines are connected at pins 1, 2, 4, 5, 6 and 7. the negative reference is connected at pin 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 pin 3 directly to the positive supply rail (v cc ). 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 pin 3 and v cc . 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 3 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 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 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 dis- crete diodes or diode arrays are configured for rail-to- rail 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 f drop of the diode. for negative events, the bottom diode will be biased when the voltage exceeds the v f of the diode. at first applications information
6 ? 2003 semtech corp. www.semtech.com protection products protection products srda3.3-6 and srda05-6 pin descriptions figure 1 - ?rail-to-rail? protection topology (first approximation) 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 applications information (continued) approximation, the clamping voltage due to the charac- teristics of the protection diodes is given by: v c = v cc + v f (for positive duration pulses) v c = -v f (for negative duration pulses) however, for fast rise time transient events, the effects of parasitic inductance must also be consid- ered as shown in figure 2. therefore, the actual clamping voltage seen by the protected circuit will be: v c = v cc + v f + l p di esd /dt (for positive duration pulses) v c = -v f - l g di esd /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 = l p di esd /dt = 1x10 -9 (30 / 1x10 -9 ) = 30v example: consider a v cc = 5v, a typical v f 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: v c = 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 the high v f of the discrete diode. it is not uncommon for the v f of discrete diodes to exceed the damage threshold of the protected ic. this is due to the relatively small junction area of typical discrete compo- nents. 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 the power supply connection. during an esd event,
7 ? 2003 semtech corp. www.semtech.com protection products protection products srda3.3-6 and srda05-6 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 c = v f(railclamp) + v tvs this is given in the data sheet as the rated clamping voltage of the device. for an srda05-6 the typical clamping voltage is <16v at i pp =30a. the diodes internal to the railclamp are low capacitance, fast switching devices that are rated to handle high tran- sient 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 consid- ered. 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 mini- mized. 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 signifi- cant 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 immedi- ately 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) the epd technology, the srda3.3-6 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 (v rwm ). during a transient event, the device will begin to conduct as it is biased in the reverse direction. when the punch- through voltage (v pt ) 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 pin to prevent device latch-up. railclamp is a registered trademark of semtech corporation i pp i sb i pt i r v rwm v v pt v c v brr i brr sb figure 4 - epd tvs iv characteristic curve srda3.3-6 epd tvs characteristics the internal tvs of the srda3.3-4 is constructed using semtech?s proprietary epd technology. the structure of the epd tvs is vastly different from the traditional pn-junction devices that are internal to the srda05-6. at voltages below 5v, high leakage current and junction capacitance render conventional avalanche technology impractical for most applications. however, by utilizing
8 ? 2003 semtech corp. www.semtech.com protection products protection products srda3.3-6 and srda05-6 video line protection typical applications
9 ? 2003 semtech corp. www.semtech.com protection products protection products srda3.3-6 and srda05-6 notes: (1) controlling dimension: inch (unless otherwise specified). outline drawing - so-8 land pattern - so-8
10 ? 2003 semtech corp. www.semtech.com protection products protection products srda3.3-6 and srda05-6 contact information semtech corporation protection products division 200 flynn road, camarillo, ca 93012 phone: (805)498-2111 fax (805)498-3804 ordering information r e b m u n t r a p g n i k r o w e g a t l o v r e p y t q l e e r e z i s l e e r b t . 6 - 3 . 3 a d r sv 3 . 30 0 5h c n i 7 e t . 6 - 3 . 3 a d r sv 3 . 30 0 5 2h c n i 3 1 b t . 6 - 5 0 a d r sv 50 0 5h c n i 7 e t . 6 - 5 0 a d r sv 50 0 5 2h c n i 3 1 note: (1) no suffix indicates tube pack.
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