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1 ltc1686/ltc1687 52mbps precision delay rs485 fail-safe transceivers descriptio n u n precision propagation delay over temperature: receiver/driver: 18.5ns 3.5ns n high data rate: 52mbps n low t plh /t phl skew: receiver/driver: 500ps typ n C7v to 12v rs485 input common mode range n guaranteed fail-safe operation over the entire common mode range n high input resistance: 3 22k, even when unpowered n short-circuit protected n thermal shutdown protected n driver maintains high impedance in three-state or with power off n single 5v supply n pin compatible with ltc490/ltc491 n 45db cmrr at 26mhz features the ltc ? 1686/ltc1687 are high speed, precision delay, full-duplex rs485 transceivers that can operate at data rates as high as 52mbps. the devices also meet the requirements of rs422. a unique architecture provides very stable propagation delays and low skew over a wide common mode and ambient temperature range. the driver and receiver feature three-state outputs, with disabled driver outputs maintaining high impedance over the entire common mode range. a short-circuit feature detects shorted outputs and substantially reduces driver output current. a similar feature also protects the receiver output from short circuits. thermal shutdown circuitry protects from excessive power dissipation. the receiver has a fail-safe feature that guarantees a high output state when the inputs are shorted or are left floating. the ltc1686/ltc1687 rs485 transceivers guarantee receiver fail-safe operation over the entire common mode range (C 7v to 12v). receiver input resistance remains 3 22k when the device is unpowered or disabled. the ltc1686/ltc1687 operate from a single 5v supply and draw only 7ma of supply current. applicatio n s u n high speed rs485/rs422 full duplex transceivers n level translator n backplane transceiver n sts-1/oc-1 data transceiver n signal repeaters , ltc and lt are registered trademarks of linear technology corporation. 10mbps data pulse 400 feet category 5 utp 1686/87 ta02 driver input receiver input receiver output 100ns/div 1v/div 2v/div 5v/div cable delay ltc1686/87 ?ta01 100 w 100 w 100 w 100 w ltc1686 ltc1686 r d r d 3 2 7 8 6 5 400 ft of category 5 utp receiver driver receiver driver typical applicatio n u
2 ltc1686/ltc1687 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 ) .............................................. 10v control input currents .................... C 100ma to 100ma control input voltages .................. C 0.5v to v dd + 0.5v driver input voltages .................... C 0.5v to v dd + 0.5v driver output voltages ................................. + 12v/C 7v receiver input voltages ................................ + 12v/C 7v receiver output voltages ............. C 0.5v to v dd + 0.5v receiver input differential ...................................... 10v driver short-circuit duration (v out : C 7v to 10v) ..................................... indefinite receiver short-circuit duration (v out : 0v to v dd ) ........................................ indefinite operating temperature range ltc1686c/ltc1687c ............................. 0 c to 70 c ltc1686i/ltc1687i .......................... C 40 c to 85 c storage temperature range ................ C 65 c to 150 c lead temperature (soldering, 10 sec)................. 300 c symbol parameter conditions min typ max units v od1 differential driver output (unloaded) i out = 0 l v dd v v od2 differential driver output (with load) r = 50 w (rs422) 2.0 v r = 27 w (rs485), figure 1 l 1.5 v dd v d v od change in magnitude of driver differential r = 27 w or 50 w , figure 1 l 0.2 v output voltage for complementary output states v oc driver common mode output voltage r = 27 w or 50 w , v dd = 5v, figure 1 l 23v d? v oc ? change in magnitude of driver common r = 27 w or 50 w , figure 1 l 0.2 v mode output voltage for complementary output states v ih input high voltage d, de, re l 2v v il input low voltage d, de, re l 0.8 v i in1 input current d, de, re l C1 1 m a i in2 input current (a, b) v a , v b = 12v, v dd = 0v or 5.25v l 500 m a v a , v b = C 7v, v dd = 0v or 5.25v l C 500 m a v th differential input threshold voltage C 7v v cm 12v l C 0.3 0.3 v for receiver d v th receiver input hysteresis v cm = 0v 25 mv v oh receiver output high voltage i out = C 4ma, v id = 300mv l 3.5 4.8 v consult factory for industrial and military grade parts. v dd = 5v 5% unless otherwise noted (notes 2, 3). dc electrical characteristics t jmax = 125 c, q ja = 150 c/ w wu u package / o rder i for atio ltc1687cs ltc1687is t jmax = 125 c, q ja = 90 c/ w order part number 14 13 12 11 10 9 8 7 6 5 4 3 2 1 top view s package 14-lead plastic so nc y nc z b nc v dd d gnd gnd r re de a r d order part number ltc1686cs8 ltc1686is8 s8 part marking s8 package 8-lead plastic so 1 2 3 4 8 7 6 5 top view v dd r d gnd a b z y r d 1686 1686i
3 ltc1686/ltc1687 dc electrical characteristics v dd = 5v 5% unless otherwise noted (notes 2, 3). symbol parameter conditions min typ max units v ol receiver output low voltage i out = 4ma, v id = C 300mv l 0.4 v i ozr three-state (high impedance) output 0.4v v out 2.4v l C1 1 m a current at receiver i ozd three-state (high impedance) output v out = C 7v to 12v l C 200 200 m a current at driver c load receiver and driver output load capacitance (note 4) l 500 pf i dd supply current no load, pins d, de, re = 0v or v dd l 712 ma i osd1 driver short-circuit current, v out = high v out = C 7v or 10v (note 5) l 20 ma i osd2 driver short-circuit current, v out = low v out = C 7v or 10v (note 5) l 20 ma i osr receiver short-circuit current v out = 0v or v dd (note 5) l 20 ma r in input resistance C 7v v cm 12v l 22 k w c in input capacitance a, b, d, de, re inputs (note 4) 3 pf open-circuit input voltage v dd = 5v (note 4), figure 5 l 3.2 3.3 3.4 v fail-safe time to detect fail-safe condition 2 m s time cmrr receiver input common mode v cm = 2.5v, f = 26mhz 45 db rejection ratio symbol parameter conditions min typ max units t plh , t phl driver input-to-output propagation delay r diff = 54 w , figures 3, 5 ltc1686c/ltc1687c l 15 18.5 22 ns c l1 = c l2 = 100pf ltc1686i/ltc1687i l 13 18.5 25 ns t skew driver output a-to-output b skew r diff = 54 w , c l1 = c l2 = 100pf, 500 ps figures 3, 5 t r , t f driver rise/fall time r diff = 54 w , c l1 = c l2 = 100pf, 3.5 ns figures 3, 5 t zh driver enable to output high c l = 100pf, s2 closed, figures 4, 6 l 25 50 ns t zl driver enable to output low c l = 100pf, s1 closed, figures 4, 6 l 25 50 ns t lz driver disable from low c l = 15pf, s1 closed, figures 4, 6 l 25 50 ns t hz driver disable from high c l = 15pf, s2 closed, figures 4, 6 l 25 50 ns t plh , t phl receiver input-to-output propagation delay c l = 15pf, figures 3, 7 ltc1686c/ltc1687c l 15 18.5 22 ns ltc1686i/ltc1687i l 13 18.5 25 ns t sqd receiver skew ? t plh C t phl ? c l = 15pf, figures 3, 7 500 ps t zl receiver enable to output low c l = 15pf, s1 closed, figures 2, 8 l 25 50 ns t zh receiver enable to output high c l = 15pf, s2 closed, figures 2, 8 l 25 50 ns t lz receiver disable from low c l = 15pf, s1 closed, figures 2, 8 l 25 50 ns t hz receiver disable from high c l = 15pf, s2 closed, figures 2, 8 l 25 50 ns maximum receiver input (note 4) l 2000 ns rise/fall times t pkg-pkg package-to-package skew c l = 15pf, same temperature (note 4) 1.5 ns switchi n g characteristics u v dd = 5v, unless otherwise noted (notes 2, 3).
4 ltc1686/ltc1687 the l denotes specifications which apply over the full operating temperature range. 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: all typicals are given for v dd = 5v, t a = 25 c. note 4: guaranteed by design, but not tested. note 5: short-circuit current does not represent output drive capability. when the output detects a short-circuit condition, output drive current is significantly reduced (from hundreds of ma to 20ma max) until the short is removed. typical perfor m a n ce characteristics uw frequency (hz) 10 42.0 common mode rejection ratio (db) 42.5 43.5 44.0 44.5 46.5 1686/87 g01 43.0 1k 100k 1m 45.0 45.5 46.0 t a = 25 c receiver input cmrr temperature ( c) ?5 supply current (ma) 53 54 55 50 100 1686/87 g03 52 51 50 025 75 56 57 58 both driver and receiver enabled and loaded 25mbps data rate data rate (mbps) 1 50 60 70 40 30 1686/87 g02 40 30 10 20 50 20 10 0 supply current (ma) both driver and receiver enabled and loaded t a = 25 c supply current vs data rate supply current vs temperature receiver propagation delay vs load capacitance receiver propagation delay vs common mode load capacitance (pf) 5 0 propagation delay (ns) 5 10 15 20 30 15 25 35 55 1686/87 g04 105 205 25 t a = 25 c receiver common mode (v) ? 0 propagation delay (ns) 5 15 20 25 ? 2 412 1686/87 g05 10 ? 0 6 8 10 t a = 25 c receiver propagation delay vs input overdrive receiver input overdrive (v) 0.3 0.5 0 receiver propagation delay (ns) 10 25 0.7 1.25 1.5 1686/87 g06 5 20 15 1.0 2.0 2.5 t a = 25 c minimum input pulse width v dd = 5v 5% (note 4) ltc1686c/ltc1687c l 17 19.2 ns ltc1686i/ltc1687i l 20 25 ns maximum data rate v dd = 5v 5% (note 4) ltc1686c/ltc1687c l 52 60 mbps ltc1686i/ltc1687i l 40 50 mbps maximum input frequency v dd = 5v 5% (note 4) ltc1686c/ltc1687c l 26 30 mhz ltc1686i/ltc1687i l 20 25 mhz switchi n g characteristics u v dd = 5v, unless otherwise noted (notes 2, 3). symbol parameter conditions min typ max units
5 ltc1686/ltc1687 typical perfor m a n ce characteristics uw receiver propagation delay vs temperature temperature ( c) 50 ?5 0 propagation delay (ns) 10 25 0 50 75 1686/87 g09 5 20 15 25 100 125 driver propagation delay vs temperature temperature ( c) ?0 0 propagation delay (ns) 5 10 15 20 25 0 20 40 60 1686/87 g07 80 100 receiver maximum data rate vs input overdrive receiver input differential (v) 0.3 40 50 70 0.6 1.0 1686/87 g10 30 20 0.4 0.5 0.7 1.5 2.5 10 0 60 data rate (mbps) t a = 25 c driver propagation delay vs driver input voltage driver input voltage (v) 2.5 propagation delay (ns) 15 20 25 4.5 1686/87 g08 10 5 0 3.0 3.5 4.0 5.0 t lh v dd = 5v input threshold = 1.5v t a = 25 c t hl driver propagation delay vs capacitive load load capacitance (pf) 5 16.0 propagation delay (ns) 16.5 17.0 17.5 18.0 19.0 15 25 50 75 1686/87 g11 100 150 18.5 t a = 25 c pi n fu n ctio n s uuu ltc1686 v dd (pin 1): positive supply, 5v to 5%. bypass with 0.1 m f ceramic capacitor. r (pin 2): receiver output. if a 3 b by 300mv, then r will be high. if a b by 300mv, then r will be low. d (pin 3): driver input. controls the states of the y and z outputs. do not float. gnd (pin 4): ground. y (pin 5): noninverting driver output. z (pin 6): inverting driver output. b (pin 7): inverting receiver input. a (pin 8): noninverting receiver input. ltc1687 nc (pins 1, 8, 13): no connection. r (pin 2): receiver output. if a 3 b by 300mv, then r will be high. if a b by 300mv, then r will be low. re (pin 3): receiver enable. re = low enables the receiver. re = high forces receiver output into high impedance state. do not float.
6 ltc1686/ltc1687 de (pin 4): driver enable. de = high enables the driver. de = low will force the driver output into a high impedance state. do not float. d (pin 5): driver input. controls the states of the y and z outputs when de = high. do not float. gnd (pins 6, 7): ground. y (pin 9): noninverting driver output. pi n fu n ctio n s uuu z (pin 10): inverting driver output. b (pin 11): inverting receiver input. a (pin 12): noninverting receiver input. v dd (pin 14): positive supply, 5v to 5%. bypass with 0.1 m f ceramic capacitor. receiving inputs output re de a C b r 0x 3 300mv 1 0x C 300mv 0 0 x inputs open 1 0 x inputs shorted together 1 a = b = C 7v to 12v 1 x x hi- z fu ctio tables u u transmitting inputs line outputs re de d condition z y x 1 1 no fault 0 1 x 1 0 no fault 1 0 x 0 x x hi- z hi- z x 1 x fault 10ma current source (ltc1687) test circuits v od y z r r v oc 1686/87 ?f01 figure 1. driver dc test load receiver output c l 15pf 1k s1 s2 test point v dd 1k 1686/87 f02 figure 2. driver dc test load output under test c l s1 s2 v dd 500 w 1686/87 f04 figure 3. driver/receiver timing test circuit figure 4. driver timing test load #2 3v de y z d r diff c l1 c l2 r 15pf a b re 1686/87 f03
7 ltc1686/ltc1687 switchi g ti e wavefor s uw w figure 5. driver propagation delays d 3v 1.5v t plh t r t skew 1/2 v o 90% 10% 0v z y v o ? o 0v 90% 1.5v t phl t skew 1/2 v o f = 1mhz, t r 3ns, t f 3ns 10% t f v diff = v(y) ?v(z) 1686/87 f05 v o 1.5v t zl 2.5v 2.5v t zh 1.5v t lz 0.5v 0.5v t hz f = 1mhz, t r 3ns, t f 3ns output normally low output normally high 3v 0v de 5v v ol v oh 0v y, z y, z 1686/87 f06 figure 6. driver enable and disable times 2.5v t phl f = 1mhz, t r 3ns, t f 3ns r ? od2 a ?b 0v 2.5v t plh output input v od2 v ol v oh 1686/87 f07 figure 7. receiver propagation delays 1.5v t zl 2.5v 2.5v t zh 1.5v t lz 0.5v 0.5v t hz f = 1mhz, t r 3ns, t f 3ns output normally low output normally high 3v 0v re 5v 0v r r 1686/87 f08 figure 8. receiver enable and disable times
8 ltc1686/ltc1687 equivale t i put networks u u figure 9. input thevenin equivalent a b 1686/87 f09 3 22k 3.3v 3 22k 3.3v re = 0 or 1, v dd = 5v v dd = 0v a b 3 22k 3 22k applicatio n s i n for m atio n wu u u theory of operation unlike typical cmos transceivers whose propagation delay can vary by as much as 500% from package to package and show significant temperature drift, the ltc1686/ltc1687 employ a novel architecture that pro- duces a tightly controlled and temperature compensated propagation delay. the differential timing skew is also minimized between rising and falling output edges of the receiver output and the complementary driver outputs. the precision timing features of the ltc1686/ltc1687 reduce overall system timing constraints by providing a narrow 3.5ns window during which valid data appears at the receiver/driver output. the driver and receiver will have propagation delays that typically match to within 1ns. in clocked data systems, the low skew minimizes duty cycle distortion of the clock signal. the ltc1686/ltc1687 can be used at data rates of 52mbps with less than 5% duty cycle distortion (depending on cable length). when a clock signal is used to retime parallel data, the maximum recom- mended data transmission rate is 26mbps to avoid timing errors due to clock distortion. fail-safe features the ltc1686/ltc1687 have a fail-safe feature that guar- antees the receiver output to be in a logic high state when the inputs are either shorted or left open (note that when inputs are left open, large external leakage currents might override the fail-safe circuitry). in order to maintain good high frequency performance, it is necessary to slow down the transient response of the fail-safe feature. when a line fault is detected, the output will go high typically in 2 m s. note that the ltc1686/ltc1687 guarantee receiver fail- safe performance over the entire (C 7v to 12v) common mode range! when the inputs are accidentally shorted (by cutting through a cable, for example), the short circuit fail-safe feature will guarantee a high output logic level. note also that if the line driver is removed and the ground terminated resistors are left in place, the receiver will see this as a short and output a logic high. both of these fail-safe features will keep the receiver from outputting false data pulses under line fault conditions. thermal shutdown and short-circuit protection prevent latchup damage to the ltc1686/ltc1687 during fault conditions. output short-circuit protection the ltc1686/ltc1687 employ voltage sensing short- circuit protection at the output terminals of both the driver and receiver. for a given input polarity, this circuitry determines what the correct output level should be. if the output level is different from the expected, it shuts off the big output devices. for example, if the driver input is >2v, it expects the a output to be >3.25v and the b output to be <1.75v. if the a output is subsequently shorted to a voltage below v dd /2, this circuitry shuts off the big output devices and turns on a smaller device in its place
9 ltc1686/ltc1687 (the converse applies for the b output). the outputs then appear as 10ma current sources. note that under normal operation, the output drivers can sink/source >50ma. a time-out period of about 50ns is used in order to maintain normal high frequency operation, even under heavy ca- pacitive loads. if the cable is shorted at a large distance from the device outputs, it is possible for the short to go unnoticed at the driver outputs due to parasitic cable resistance. addition- ally, when the cable is shorted, it no longer appears as a simple transmission line impedance, and the parasitic ls and cs might give rise to ringing and even oscillation. all these conditions disappear once the device comes out of short-circuit mode. for cables with the typical rs485 termination (no dc bias on the cable, such as figure 10), the ltc1686/ltc1687 will automatically come out of short-circuit mode once the physical short has been removed. cable termination the recommended cable termination for the ltc1686/ ltc1687 is a single resistor across the two wires at each end of the twisted-pair line (see figure 10). the ltc1687 can also be used with cable terminations with a dc bias (such as fast-20 and fast-40 differential scsi termina- tors). when using a biased termination with the ltc1687, however, the de pin must be held low for at least 200ns after the part has been powered up. this ensures proper start-up into the dc load of the biased termination. fur- thermore, when the ltc1687 output is shorted, the de pin applicatio n s i n for m atio n wu u u should be pulsed low for at least 200ns after the short has been removed. since the ltc1686 driver is always enabled, the ltc1686 should only be used with single resistor termination, as shown in figure 10. high speed twisted-pair transmission data rates up to 52mbps can be transmitted over 100 feet of category 5 twisted pair. figure 10 shows the ltc1687 receiving differential data from another ltc1687 trans- ceiver. figure 11a shows a 26mhz (52mbps) square wave propagated over 100 feet of category 5 utp. figure 11b shows a more stringent case of propagating a 20ns pulse over 100 feet of category 5 utp. figure 12 shows a 2mhz (4mbps) square wave propagated over 1000 feet of category 5 unshielded twisted pair. note that the ltc1686/ ltc1687 can still perform reliably at this distance and speed. very inexpensive unshielded telephone grade twisted pair is shown in figure 13. despite the noticeable loss at the receiver input, the ltc1686/ltc1687 can still transfer at 30mbps over 100 feet of telephone grade utp. note that under all these conditions, the ltc1686/ltc1687 can pass through a single data pulse equal to the inverse of the data rate (e.g., 20ns for 50mbps data rate). transmission over long distances 1mbps over 4000 feet category 5 utp the ltc1685/ltc1686/ltc1687 family of high speed transceivers is capable of 1mbps transmission over 4000 feet of category 5 utp. high quality cable provides lower figure 10 ltc1686/87 ?f10 100 w 100 w 100 w 100 w ltc1687 r d r d 5 2 11 12 10 9 4 de 3 re de re category 5 utp receiver ltc1687 driver receiver driver
10 ltc1686/ltc1687 applicatio n s i n for m atio n wu u u 1686/87 f11a driver input receiver output 10ns/div 2v/div 2v/div figure 11a. 100 feet of category 5 utp: 50mbps dc and ac attenuation over long distances. figure 14a shows a 1 m s pulse propagated down 4000 feet of category 5 utp. notice the significant attenuation at the receiver input and the clean pulse at the receiver output. the dc attenuation is due to the parasitic resistance of the cable. figure 14b shows a 1mbps square wave over the same 4000 feet of cable. 1686/87 f12 driver input receiver output 100ns/div 2v/div 2v/div figure 12. 1000 feet of category 5 utp: 4mbps 1686/87 f13 driver input differential receiver input receiver output 20ns/div 2v/div 2v/div 2v/div 1685 f11b receiver input driver input receiver output 20ns/div 2v/div 5v/div 2v/div cable delay figure 11b. 100 feet of category 5 utp: 20ns pulse figure 13. 100 feet of telephone grade utp: 30mbps 1685 f14a receiver input driver input receiver output 1 m s/div 1v/div 5v/div 2v/div cable delay figure 14a. 4000 feet of category 5 utp 1 m s pulse 1685 f14b driver input receiver output 1 m s/div 5v/div 2v/div figure 14b. 4000 feet of category 5 utp 1mbps square wave 1.6mbps over 8000 feet (1.5 miles) category 5 utp using repeaters the ltc1686/ltc1687 can be used as repeaters to extend the effective length of a high speed twisted-pair line. figure 15a shows a three repeater configuration using 2000 feet segments of category 5 utp. figure 15b shows the
11 ltc1686/ltc1687 applicatio n s i n for m atio n wu u u figure 15a. 1.6mbps, 8000 feet (1.5 miles) using three repeaters 2v/div 5v/div 2v/div 5v/div driver 1 input receiver 5 output driver 1 input receiver 5 output 1686/87 f15b 2 m s/div delay of 8000 ft of cable goes above or below the rails. it is advisable to terminate the pc traces when approaching maximum speeds. since the ltc1686/ltc1687 are not intended to drive parallel terminated cables with characteristic impedances much less than that of twisted pair, both ends of the pc trace must be series terminated with the characteristic imped- ance of the trace. for best results, the signal should be routed differentially. the true and complement outputs of the ltc1686/ltc1687 should be routed on adjacent lay- ers of the pc board. the two traces should be routed very symmetrically, minimizing and equalizing parasitics to nearby signal and power/ground layers. for single-ended transmission, route the series terminated single-ended trace over an adjacent ground plane. then set the (by- passed) negative input of the receiver to roughly 2.5v. note that single-ended operation might not reach maxi- mum speeds. layout considerations a ground plane is recommended when using high fre- quency devices like the ltc1686/ltc1687. a 0.1 m f ce- ramic bypass capacitor less than 0.25 inch away from the v dd pin is also recommended. propagation of a 600ns pulse through the network of figure 15a. the bottom two traces show a 1.6mbps square wave. notice that the duty cycle does not notice- ably degrade. for the case of the single pulse, however, there is a slight degradation of the pulse width. by slowing down the data rate slightly to 1mbps, one can obtain minimal pulse width degradation as the signal traverses through the repeater network. figure 16 shows that the output pulse (bottom trace) is nearly the same width to the input pulse (top trace). the middle three traces of figure 16 show the signal at the end of each of the first three 2000 feet sections of category 5 utp. notice how the ltc1687 repeaters are able to regenerate the signal with little loss. this implies that we can cascade more repeater networks and potentially achieve 1mbps operation at total distances of over 10,000 feet! a higher data rate can be achieved if the repeaters are spaced closer together. high speed backplane transmission the ltc1686/ltc1687 can also be used in backplane point-to-point transceiver applications, where the user wants to assure operation even when the common mode 2v/div 1v/div 1v/div 1v/div 5v/div driver 1 input receiver 2 input receiver 3 input receiver 4 input receiver 5 output 1686/87 f16 2 m s/div figure 15b. 1.6mbps pulse and square wave signals over 8000 feet category 5 utp using three repeaters figure 16. intermediate signals of a 1 m s pulse 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. ltc1687 ltc1687 repeater 2000 ft 2000 ft 2000 ft 2000 ft 1686/87 f15a ltc1687 repeater ltc1687 repeater ltc1687 d r5 r4 d r3 d r2 d1 r
12 ltc1686/ltc1687 ? linear technology corporation 1997 16867fs, sn16867 lt/tp 1197 4k ? printed in the usa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 l (408) 432-1900 fax: (408) 434-0507 l telex: 499-3977 l www.linear-tech.com long traces bounded by a v dd and/or gnd planes can add substantial parasitic capacitance. parasitic capacitances on the receiver/driver outputs can also unduly slow down both the propagation delay and the rise/fall times. applicatio n s i n for m atio n wu u u the receiver inputs are high bandwidth and high imped- ance. if they are left floating, any capacitive coupling from any other signal can cause a glitch at the receiver output. thus, if the receiver is not being used, it is advisable to always ground at least one of the two receiver input pins. package descriptio n u dimensions in inches (millimeters) unless otherwise noted. s8 package 8-lead plastic small outline (narrow 0.150) (ltc dwg # 05-08-1610) part number description comments ltc490 low power rs485 full-duplex transceiver i cc = 300 m a (typ), so-8 package ltc491 low power rs485 full-duplex transceiver i cc = 300 m a (typ), 14-lead so package ltc1518 high speed quad rs485 receiver 52mbps, pin compatible with ltc488 ltc1519 high speed quad rs485 receiver 52mbps, pin compatible with ltc489 ltc1520 high speed quad differential receiver 52mbps, 100mv threshold, rail-to-rail common mode ltc1685 high speed rs485 transceiver 52mbps, pin compatible with ltc485 related parts so8 0996 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) 0.053 ?0.069 (1.346 ?1.752) 0.014 ?0.019 (0.355 ?0.483) 0.004 ?0.010 (0.101 ?0.254) 0.050 (1.270) typ 1 2 3 4 0.150 ?0.157** (3.810 ?3.988) 8 7 6 5 0.189 ?0.197* (4.801 ?5.004) 0.228 ?0.244 (5.791 ?6.197) 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 * ** s package 14-lead plastic small outline (narrow 0.150) (ltc dwg # 05-08-1610) s14 0695 1 2 3 4 0.150 ?0.157** (3.810 ?3.988) 14 13 0.337 ?0.344* (8.560 ?8.738) 0.228 ?0.244 (5.791 ?6.197) 12 11 10 9 5 6 7 8 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) 0.053 ?0.069 (1.346 ?1.752) 0.014 ?0.019 (0.355 ?0.483) 0.004 ?0.010 (0.101 ?0.254) 0.050 (1.270) typ 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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