protection products 1 www.semtech.com protection products sm712 asymmetrical tvs diode for extended common-mode rs-485 description features circuit diagram schematic & pin configuration revision 01/29/03 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 = 8/20s) 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 (t p = 8/20s) ? 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 (8/20s) ? 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)
2 ? 2003 semtech corp. www.semtech.com protection products protection products sm712 absolute maximum rating electrical characteristics 2 1 7 m s d n a 3 o t 1 s n i p 3 o t 2 ) s v t v 2 1 ( d n a 1 o t 3 s n i p 2 o t 3 ) s v t v 7 ( r e t e m a r a pl o b m y ss n o i t i d n o cn i mp y tx a mn i mp y tx 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 1 o t 2 n i p r o 1 o t 3 n i p2 17v 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 p a m 1 =3 . 3 15 . 7v t n e r r u c e g a k a e l e s r e v e ri r v = r v m w r 10 2 a e g a t l o v g n i p m a l cv c i p p , a 5 = s 0 2 / 8 = p t 0 20 1v e g a t l o v g n i p m a l cv c i p p , a 7 1 = s 0 2 / 8 = p t 6 22 1v e c n a t i c a p a c n o i t c n u jc j v r z h m 1 = f , v 0 =5 75 7f p v r v = m w r z h m 1 = f ,5 45 4f p 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 4s t t a w t ( t n e r r u c e s l u p k a e p p ) s 0 2 / 8 =i p p 7 1a 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
3 ? 2003 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 (s) percent of i pp e -t td = i pp /2 waveform parameters: tr = 8s td = 20s 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 - t a ( o c) % of rated power or i pp 0.01 0.1 1 10 0.1 1 10 100 1000 pulse duration - t p (s) peak pulse power - p pk (kw) 0 2 4 6 8 10 12 14 16 18 20 22 24 0246810121416 peak pulse current - i pp (a) clamping voltage - v c (v) pin 1 to 3 & 2 to 3 pin 3 to 1 & 3 to 2 waveform parameters: tr = 8s td = 20s 0 10 20 30 40 50 60 70 80 012345678910111213 reverse voltage - v r (v) capacitance - c j (pf) f = 1mhz
4 ? 2003 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 & 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: z place the sm712 near the input terminals or connectors to restrict electromagnetic coupling. z minimize the path length between the sm712 and the protected line. this minimizes voltage over- shoot due to parasitic inductance of board traces. z use ground planes whenever possible. z long, 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. z minimize all conductive loops including power and ground loops. z never run critical signals near board edges. rs-485 protection circuit applications information
5 ? 2003 semtech corp. www.semtech.com protection products sm712 land pattern - sot23 note 1 : grid placement courtyard is 8 x 8 elements (4mm x 4mm) in accordance with the international grid detailed in iec publication 97. outline drawing - sot23
6 ? 2003 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 r e b m u n t r a pl e e r r e p y t qe z i s l e e r c t . 2 1 7 m s0 0 0 , 3h c n i 7 g t . 2 1 7 m s0 0 0 , 0 1h c n i 3 1
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