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1 ltc1688/LTC1689 100mbps rs485 hot swapable quad drivers n ultrahigh speed: 100mbps n guaranteed propagation delay: 8ns 4ns over temperature n 50mbps operation with v dd = 3v n low channel-to-channel skew: 500ps typ n low t plh /t phl skew: 500ps typ n hot swap tm capable n driver outputs maintain high impedance in three-state or with power off n short-circuit protected: 3ma typ output current for an indefinite short n thermal shutdown protected n single 5v or 3v supply n pin compatible with ltc486/ltc487 the ltc ? 1688/LTC1689 are ultrahigh speed, differential bus/line drivers that can operate at data rates up to 100mbps. propagation delay is guaranteed at 8ns 4ns over the full operating temperature range. these devices operate over the full rs485 common mode range (C 7v to 12v), and also meet rs422 requirements. the driver outputs are hot swap capable, maintaining backplane data integrity during board insertion and removal. the drivers feature three-state outputs, maintain- ing high impedance over the entire common mode range (C 7v to 12v). outputs also remain high impedance during power-up and with the power off. a short-circuit feature detects bus contention and substantially reduces driver output current. thermal shutdown circuitry protects the parts from excessive power dissipation. the ltc1688 allows all four drivers to be enabled together, while the LTC1689 allows two drivers at a time to be enabled. the ltc1688/LTC1689 operate from a single 5v or 3v supply and draw only 9ma of supply current. n high speed rs485 twisted-pair drivers n high speed backplane drivers n complementary clock drivers n sts-1/oc-1 data drivers n scsi drivers hot swap is a trademark of linear technology corporation. , ltc and lt are registered trademarks of linear technology corporation. 20ns pulse across 100 feet of category 5 utp 20ns/div 2v/div 2v/div 2v/div 5v/div 1688/89 ta02 driver input driver outputs receiver input receiver output cable delay 1688/89 ta01 receiver 1/4 ltc1688 100 w 100 w 1/4 ltc1518 100 ft category 5 utp driver 50mbps rs485 data connection descriptio u features applicatio s u typical applicatio u
2 ltc1688/LTC1689 wu u package / o rder i for atio a u g w a w u w a r b s o lu t exi t i s (note 1) supply voltage (v dd ) ................................................ 7v enable input voltages ................. C 0.5v to (v dd + 0.5v) enable input currents ..................... C 100ma to 100ma driver input voltages .................. C 0.5v to (v dd + 0.5v) driver output voltages ................. (C 12v + v dd ) to 12v driver input currents ...................... C 100ma to 100ma short-circuit duration (v out : C 7v to 10v) ...... indefinite operating temperature range ltc1688c/LTC1689c ............................. 0 c to 70 c ltc1688i/LTC1689i .......................... C 40 c to 85 c storage temperature range ................ C 65 c to 150 c lead temperature (soldering, 10 sec)................. 300 c dc electrical characteristics symbol parameter conditions min typ max units v dd = 5v, per driver, t a = 25 c, unless otherwise noted (note 2) v od1 differential driver output (unloaded) i out = 0 l v dd v v od2 differential driver output (with load) r = 50 w (rs422) l 2v r = 25 w (rs485), figure 1 l 1.5 3.0 v d v od change in magnitude of driver differential r = 25 w or 50 w , figure 1 l 0.2 v output voltage for complementary output states v oc driver common mode output voltage r = 25 w or 50 w , figure 1 l 23v d? v oc ? change in magnitude of driver common r = 25 w or 50 w , figure 1 l 0.2 v mode output voltage for complementary output states v ih input high voltage en, enb, en12, en34, di l 2v v il input low voltage en, enb, en12, en34, di l 0.8 v i in1 input current en, enb, en12, en34, di l 1 m a i oz three-state (high impedance) v out = C 7v to 12v l 2 200 m a output current i dd supply current of entire device no load, digital input pins = 0v or v dd l 918 ma i osd1 driver short-circuit current, v out = high v out = C 7v to 10v l 20 ma i osd2 driver short-circuit current, v out = low v out = C 7v to 10v l 20 ma v dd = 3v, per driver, t a = 25 c, unless otherwise noted (note 2) v od1 differential driver output (unloaded) i out = 0 l v dd v v od2 differential driver output (with load) r = 50 w (rs422) 1.5 v r = 25 w (rs485), figure 1 l 0.65 2.0 v d v od change in magnitude of driver differential r = 25 w or 50 w , figure 1 0.1 v output voltage for complementary output states v oc driver common mode output voltage r = 25 w or 50 w , figure 1 1.3 v order part number ltc1688cs LTC1689cs ltc1688is LTC1689is top view s package 16-lead plastic so *LTC1689 only 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 di1 do1a do1b en (en12*) do2b do2a di2 gnd v dd di4 do4a do4b enb (en34*) do3b do3a di3 t jmax = 150 c, q ja = 90 c/ w the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. consult factory for parts specified with wider operating temperature ranges.
3 ltc1688/LTC1689 symbol parameter conditions min typ max units d? v oc ? change in magnitude of driver common r = 25 w or 50 w , figure 1 0.1 v mode output voltage for complementary output states v ih input high voltage en, enb, en12, en34, di l 1.4 v v il input low voltage en, enb, en12, en34, di l 0.5 v i in1 input current en, enb, en12, en34, di (note 3) l 1 m a i oz three-state (high impedance) v out = C 7v to 10v (note 3) l 1 200 m a output current i dd supply current of entire device no load, digital input pins = 0v or v dd 5ma i osd1 driver short-circuit current, v out = high v out = C 7v to 8v (note 3) l 20 ma i osd2 driver short-circuit current, v out = low v out = C 7v to 8v (note 3) l 20 ma note 1: absolute maximum ratings are those values beyond which the life of a device may be impaired. note 2: all currents into the device pins are positive; all currents out of the device pins are negative. note 3: guaranteed by design or correlation, but not tested. switchi n g characteristics u symbol parameter conditions min typ max units v dd = 5v, t a = 25 c, unless otherwise noted (note 2) t plh , t phl driver input-to-output propagation delay r diff = 50 w , c l1 = c l2 = 25pf, l 4812 ns figures 2, 4 t skew driver output-to-output skew r diff = 50 w , c l1 = c l2 = 25pf, 500 ps figures 2, 4 t r , t f driver rise/fall time r diff = 50 w , c l1 = c l2 = 25pf, 2 ns figures 2, 4 t zh driver enable to output high c l = 25pf, s2 closed, figures 3, 5 l 10 35 ns t zl driver enable to output low c l = 25pf, s1 closed, figures 3, 5 l 10 35 ns t lz driver disable from low c l = 15pf, s1 closed, figures 3, 5 l 25 65 ns t hz driver disable from high c l = 15pf, s2 closed, figures 3, 5 l 25 65 ns c l(max) maximum output capacitive load (note 3) l 200 pf maximum data rate (note 3) l 100 mbps maximum driver input rise/fall time (note 3) l 500 ns v dd = 3v, t a = 25 c, unless otherwise noted (note 2) t plh , t phl driver input-to-output propagation delay r diff = 50 w , c l1 = c l2 = 25pf, 11 ns figures 2, 4 t skew driver output-to-output skew r diff = 50 w , c l1 = c l2 = 25pf, 1 ns figures 2, 4 t r , t f driver rise/fall time r diff = 50 w , c l1 = c l2 = 25pf, 4 ns figures 2, 4 t zh driver enable to output high c l = 25pf, s2 closed, figures 3, 5 25 ns t zl driver enable to output low c l = 25pf, s1 closed, figures 3, 5 25 ns t lz driver disable from low c l = 15pf, s1 closed, figures 3, 5 50 ns t hz driver disable from high c l = 15pf, s2 closed, figures 3, 5 50 ns c l(max) maximum output capacitive load (note 3) l 200 pf maximum data rate 50 mbps maximum driver input rise/fall time (note 3) l 500 ns dc electrical characteristics the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c. the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t a = 25 c.
4 ltc1688/LTC1689 typical perfor m a n ce characteristics uw propagation delay vs temperature temperature ( c) 14 12 10 8 6 4 2 0 propagation delay (ns) 1688/89 g01 0 20 40 60 80 100 v di = 0v to 3v r diff = 50 c l = 25pf v dd = 3v v dd = 5v supply current vs data rate data rate (mbps) 250 200 150 100 50 0 supply current (ma) 1688/89 g03 0 20 40 60 80 100 120 v dd = 5v r diff = 50 , per driver c l = 25pf, per driver t a = 25 c 4 drivers switching 1 driver switching load capacitance (pf) 14 12 10 8 6 4 2 0 propagation delay (ns) 1688/89 g02 0 10 20 30 40 50 60 v di = 0v to 3v r diff = 50 t a = 25 c v dd = 3v v dd = 5v propagation delay vs load capacitance temperature ( c) output current ( a) 1688/89 g04 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 0 20 40 60 80 100 v dd = 5v v out = 12v v out = 7v temperature ( c) 2.5 2.0 1.5 1.0 0.5 0 v od2 1688/89 g05 0 20 40 60 80 100 r diff = 50 v dd = 5v v dd = 3v temperature ( c) 180 160 140 120 100 80 60 40 20 0 i dd (ma) 1688/89 g06 0 20 40 60 80 100 v dd = 5v r diff = 50 , per driver 0.1mbps 1 driver loaded 4 drivers loaded three-state output current i dd vs temperature v od2 vs temperature
5 ltc1688/LTC1689 pi n fu n ctio n s uuu di1 (pin 1): driver 1 input. do not float. do1a (pin 2): driver 1 noninverting output. do1b (pin 3): driver 1 inverting output. en (pin 4, ltc1688): high true enable pin, enables all four drivers. a low on pin 4 and a high on pin 12 will put all driver outputs into a high impedance state. see function tables for details. do not float. en12 (pin 4, LTC1689): enables drivers 1 and 2. a low on pin 4 will put the outputs of drivers 1 and 2 into a high impedance state. see function tables for details. do not float. do2b (pin 5): driver 2 inverting output. do2a (pin 6): driver 2 noninverting output. di2 (pin 7): driver 2 input. do not float. gnd (pin 8): ground connection. a good ground plane is recommended for all applications. di3 (pin 9): driver 3 input. do not float. do3a (pin 10): driver 3 noninverting output. do3b (pin 11): driver 3 inverting output. enb (pin 12, ltc1688): low true enable pin, enables all four drivers. a low on pin 4 and a high on pin 12 will put all driver outputs into a high impedance state. see function tables for details. do not float. en34 (pin 12, LTC1689): enables drivers 3 and 4. a low on pin 12 will put the outputs of drivers 3 and 4 into a high impedance state. see function tables for details. do not float. do4b (pin 13): driver 4 inverting output. do4a (pin 14): driver 4 noninverting output. di4 (pin 15): driver 4 input. do not float. v dd (pin 16): power supply input. this pin should be bypassed with a 0.1 m f ceramic capacitor as close to the pin as possible. recommended: v dd = 3v to 5.25v. fu ctio tables u u ltc1688 inputs outputs di en enb outa outb hh x h l lh x l h hx l h l lx l l h x l h hi-z hi-z LTC1689 inputs outputs di en12/en34 outa outb hhhl lhlh x l hi-z hi-z 1688/89 tc03 output under test c l s1 500 dd v w s2 1688/89 tc01 a b r r od v oc v figure 1. driver dc test load figure 3. driver timing test load driver 1688/89 tc02 enb (en34) di a b en (en12) r diff c l1 c l2 figure 2. driver timing test circuit test circuits
6 ltc1688/LTC1689 applicatio n s i n for m atio n wu u u the ltc1688/LTC1689 family of rs485 quad differential drivers employs a novel architecture and fabrication pro- cess that allows ultra high speed operation (100mbps) and hot swap capability while maintaining the ruggedness of rs485 operation (three-state outputs can float from C 7v to 12v with a single 5v supply). unlike typical cmos drivers whose propagation delay can vary as much as 500%, the propagation delay of the ltc1688/LTC1689 drivers will only vary by 50% (a narrow 4ns window). this performance is achieved by designing the input stage of each driver to have minimum propagation delay shift over temperature and from part to part. the ltc1688/LTC1689 have an esd rating of 6kv human body model. 50mbps with 3v operation the ltc1688/LTC1689 are designed to operate with a 3v power supply and still achieve 50mbps operation (see electrical characteristics table for 3v dc and ac specifica- 1688/89 f04 b a di v o v o ? o 1/2 v o 3v 0v t skew 1.5v t plh 1.5v t phl 1/2 v o v diff = v(a) ?v(b) 90% 10% t f 90% 10% t skew t r f = 1mhz; t r < 3ns; t f < 3ns figure 4. driver propagation delays 1688/89 f05 a, b en 3v 0v f = 1mhz; t r 3ns; t f 3ns v ol v oh 1.5v 1.5v 5v output normally low t zl 1/2 v dd 1/2 v dd t lz 0.5v a, b 0v t zh output normally high t hz 0.5v figure 5. driver enable and disable times switchi g ti e wavefor s uw w figure 6. 3v high speed data transmission 20ns/div 2v/div 2v/div 5v/div 1688/89 f06 LTC1689 output receiver output far end of cable tions). figure 6 shows waveforms of an LTC1689 driving a receiver using 100 feet of category 5 utp. both parts are operating at 3v supply.
7 ltc1688/LTC1689 applicatio n s i n for m atio n wu u u hot swap capability with the ltc1688/LTC1689 outputs disabled but con- nected to the transmission line, the user can turn on/off the power to the ltc1688/LTC1689 without inducing a differ- ential signal on the transmission line. due to capacitive coupling, however, there can be a small amount of com- mon mode charge injected into both disabled outputs, which is not seen as a differential signal (see figure 7). the disabled outputs can be hooked/unhooked to a transmis- sion line without disturbing the existing data. output short-circuit protection in addition to 100mbps operation and hot swap capability, the ltc1688/LTC1689 employ voltage sensing short- circuit protection that reduces short-circuit current by over an order of magnitude. for a given input polarity, this circuitry determines what the correct output level should be. if the output level is different from the expected, the circuitry shuts off the big output devices. much smaller devices are instead turned on, thus producing a much smaller short-circuit output current (3ma typical). for example, if the driver input is > 2v, it expects the a output to be > 3.25v and the b output to be less than 1.75v. if the a output is subsequently shorted to a voltage below v dd /2, this circuitry shuts off the big outputs and turns on 3ma current sources instead (the converse applies to the b output). note that these 3ma current sources are active only during a short-circuit fault. during normal operation, the regular output drivers can sink/source > 50ma. a time-out period of about 50ns is required before a short- circuit fault is detected. this circuitry might falsely detect a short under excess output capacitive load (> 200pf). additionally, a short might go undetected if there is too much resistance (user inserted or cable parasitic) between the physical short and the actual driver output. for cables with the recommended rs485 termination (no dc bias on the cable, see figure 8), the ltc1688/LTC1689 will automatically come out of short-circuit mode once the physical short has been removed. to prevent permanent damage to the part, the maximum allowable short is 10v (not 12v). note that during a short, the voltage right at the pin should not ring to a voltage higher than 12v. instability could surface if the short is made with long leads (parasitic inductance). once the short is removed, the instability will disappear. figure 7. common mode charge injection during hot swapping a output b output
8 ltc1688/LTC1689 cable termination the recommended cable termination for use with the ltc1688/LTC1689 is a single resistor across the two ends of a transmission cable (see figure 8). when pc traces are used as the transmission line, its characteristic imped- ance should be chosen close to 100 w in order to better match the specified timing characteristics of the ltc1688/ LTC1689. category 5 unshielded twisted pair can be used over short distances at the maximum data rates (100mbps). for point-to-point configurations (see figure 9), a single resistor across the cable at the receiver end is sufficient. a single resistor termination lowers power consumption and increases the differential output signal. see enable pins section for cable terminations with a dc bias. applicatio n s i n for m atio n wu u u enable pins for cable terminations with a dc bias (such as high voltage differential scsi, see figure 10), the driver out- puts must be disabled for at least 200ns after power-up. this ensures that the driver outputs do not disturb the cable upon power-up. it also ensures the correct output start-up conditions. when there is an output short fault condition and the cable has a dc biased termination, such as figure 10, the driver outputs must be disabled for at least 200ns after the short has been removed. recall that for transmission lines that have the recommended rs485 single resistor termination (figures 8 and 9), the ltc1688/ LTC1689 will come out of a short-circuit fault condition automatically without having to disable the outputs. 1688/89 f10 1/4 ltc1518 150 w 330 w de di 330 w 1/4 ltc1688 term power 150 w 330 w 330 w term power 1/4 ltc1518 figure 10. dc-biased termination (recommended for scsi applications only) figure 8. multipoint transmission figure 9. point-to-point transmission 1688/89 f08 1/4 ltc1518 1/4 ltc1519 100 w 100 w 1/4 ltc1688 1688/89 f09 1/4 ltc1518 100 w 1/4 LTC1689
9 ltc1688/LTC1689 applicatio n s i n for m atio n wu u u high speed twisted-pair transmission data rates up to 100mbps can be transmitted over short distances using category 5 utp (unshielded twisted pair). the cable distance will determine the maximum data rate. figures 11 and 12 show an 8ns pulse propagating over 25 feet of category 5 utp. notice how the cable attenuates the signal. lucent technologies brf2a and brs2a receivers are recommended for these ultrahigh speed applications. high speed backplane transmission the ltc1688/LTC1689 can be used in backplane point-to- point and multipoint applications. at high data rates, signals should be routed differentially and pc traces should be terminated (see figure 13). note that the rs485 specification calls for characteristic impedances near 100 w ; therefore, pc trace transmission lines should be designed with an impedance close to 100 w . if trace impedance is much less than 100 w , and the trace is double terminated, the part will experience excess heating. the propagation delay could then fall outside the specified window. the lt1720 dual ultrafast tm comparator is a good choice for high data rate backplane applications. figure 12. 100mbps differential data connection figure 11. 8ns pulse over 25 feet category 5 utp 10ns/div 2v/div 2v/div 2v/div 5v/div 1688/89 f11 driver input driver output receiver input receiver output 1688/89 f12 receiver 1/4 ltc1688 100 100 + 25 ft category 5 utp driver figure 13. 100mbps backplane transmission backplane receiver 1/4 ltc1688 1/2 lt1720 100 1688/89 f13 driver transmission line ultrafast is a trademark of linear technology corporation.
10 ltc1688/LTC1689 applicatio n s i n for m atio n wu u u layout considerations a ground plane is recommended when using high fre- quency devices like the ltc1688/LTC1689. a 0.1 m f ceramic bypass capacitor less than 0.25 inch away from the v dd pin is also recommended. special care should be taken to route the differential outputs very symmetrically in order to obtain the same parasitic capacitances and thus maintain good propagation delay skew. parasitic capacitance from each input to its corresponding outputs should also be minimized. any excess capaci- tance could result in slower operation or even instability. channel output pairs should be kept away from other output pairs to avoid parasitic coupling. data rate vs cable length cable length and quality limit the maximum data rate in a twisted pair system. category 5 unshielded twisted pair is a good choice for high speed data transmission, as it exhibits superior bandwidth over other cables of similar cost. driver and receiver bandwidth affects the maximum data rate only over distances of less than 100', even for the best cables. the ltc1688/LTC1689 rs485 drivers and ltc1518/ltc1519 52mbps rs485 receivers are the fast- est in the industry. the ltc1688/LTC1689 drivers can reach speeds over 100mbps, with a rise and fall time of just 2ns. at speeds in excess of 52mbps, the non-rs485 lucent technologies brf2a receiver is recommended. detailed information on data rate vs cable length is pro- vided by the cable manufacturer. they characterize their cables for bit rate and 0% to 50% rise time vs cable length, allowing a rapid comparison of various cable types. the following oscilloscope waveforms illustrate how a cable attenuates the signal and slows its rise time at different lengths. also shown are the driver input and receiver output. 1688/89 f14 receiver 1/4 ltc1688 1/4 LTC1689 100 w 100 w category 5 cable under test driver figure 14. test circuit for cable speed evaluation 2 s/div 1688/89 f15 2v/div driver input receiver input receiver output cable delay figure 15. 4000 feet, 0.5mbps, ltc1518 receiver 2 s/div 1688/89 f16 2v/div driver input receiver input receiver output cable delay figure 17. 1000 feet, 2mbps, ltc1518 receiver figure 16. 4000 feet, 1mbps, ltc1518 receiver 500ns/div 1688/89 f17 2v/div driver input receiver input receiver output cable delay
11 ltc1688/LTC1689 information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. figure 19. 1000 feet, 1mbps, ltc1518 receiver figure 18. 1000 feet, 5mbps, ltc1518 receiver applicatio n s i n for m atio n wu u u figure 21. 200 feet, 33mbps, ltc1518 receiver figure 20. 200 feet, 20mbps, ltc1518 receiver figure 23. 25 feet, 100mbps, brf2a receiver figure 22. 100 feet, 50mbps, ltc1518 receiver 500ns/div 1688/89 f18 2v/div driver input receiver input receiver output cable delay 1 s/div 1688/89 f19 2v/div driver input receiver input receiver output cable delay 100ns/div 1688/89 f20 2v/div driver input receiver input receiver output cable delay 50ns/div 1688/89 f21 2v/div driver input receiver output cable delay receiver input 50ns/div 1688/89 f22 2v/div driver input receiver input receiver output cable delay 10ns/div 1688/89 f23 2v/div driver input receiver output cable delay receiver input
12 ltc1688/LTC1689 ? linear technology corporation 1999 16889fs sn16889 lt/tp 1099 4k ? printed in the usa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 l fax: (408) 434-0507 l www.linear-tech.com part number description comments ltc486/ltc487 low power quad rs485 drivers 110 m a typ supply current, 10mbps, C 7v to 12v common mode range lt ? 1394 7ns ultrafast single supply comparator 6ma typ supply current, ground sensing on single supply ltc1518/ltc1519 high speed, precision quad rs485 receivers 52mbps, pin compatible with ltc488/ltc489 ltc1520 high speed, precision quad differential line receiver single supply, 18ns propagation delay, 100mv threshold ltc1685 high speed, precision rs485 transceiver 52mbps, pin compatible with ltc485 ltc1686/ltc1687 high speed, precision rs485 full-duplex transceivers 52mbps, pin compatible with ltc490/ltc491 lt1720 dual 4.5ns ultrafast single supply comparator 4ma per comparator, optimized for 3v or 5v operation related parts package descriptio n u dimensions in inches (millimeters) unless otherwise noted. s package 16-lead plastic small outline (narrow 0.150) (ltc dwg # 05-08-1610) 0.016 ?0.050 (0.406 ?1.270) 0.010 ?0.020 (0.254 ?0.508) 45 0 ?8 typ 0.008 ?0.010 (0.203 ?0.254) 1 2 3 4 5 6 7 8 0.150 ?0.157** (3.810 ?3.988) 16 15 14 13 0.386 ?0.394* (9.804 ?10.008) 0.228 ?0.244 (5.791 ?6.197) 12 11 10 9 s16 1098 0.053 ?0.069 (1.346 ?1.752) 0.014 ?0.019 (0.355 ?0.483) typ 0.004 ?0.010 (0.101 ?0.254) 0.050 (1.270) bsc dimension does not include mold flash. mold flash shall not exceed 0.006" (0.152mm) per side dimension does not include interlead flash. interlead flash shall not exceed 0.010" (0.254mm) per side * **

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