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ltc488/ltc489 1 4889fb typical application description quad rs485 line receiver the ltc ? 488 and ltc489 are low power differential bus/ line receivers designed for multipoint data transmission standard rs485 applications with extended common mode range (12v to C7v). they also meet the require- ments of rs422. the cmos design offers signi? cant power savings over its bipolar counterpart without sacri? cing ruggedness against overload or esd damage. the receiver features three-state outputs, with the receiver output maintaining high impedance over the entire com- mon mode range. the receiver has a fail-safe feature which guarantees a high output state when the inputs are left open. both ac and dc speci? cations are guaranteed 4.75v to 5.25v supply voltage range. l , lt, ltc and ltm are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. features applications n low power: i cc = 7ma typ n designed for rs485 or rs422 applications n single 5v supply n C7v to 12v bus common mode range permits 7v ground difference between devices on the bus n 60mv typical input hysteresis n receiver maintains high impedance in three-state or with the power off n 28ns typical receiver propagation delay n pin compatible with the sn75173 (ltc488) n pin compatible with the sn75175 (ltc489) n low power rs485/rs422 receivers n level translator 120 4000 ft 24 gauge twisted pair di receiver 1/4 ltc488 120 driver 1/4 ltc486 ro en en 1 2 4 12 3 en en 120 4000 ft 24 gauge twisted pair di receiver 1/4 ltc489 120 driver 1/4 ltc487 ro en12 1 2 4 3 en12 4889 ta01
ltc488/ltc489 2 4889fb ltc488 ltc488 1 2 3 4 5 6 7 8 top view n package 16-lead plastic dip 16 15 14 13 12 11 10 9 b1 a1 ro1 en ro2 a2 b2 gnd v cc b4 a4 ro4 en ro3 a3 b3 r r r r t jmax = 150c, ja = 70c/w 1 2 3 4 5 6 7 8 top view sw package 16-lead plastic (wide) so 16 15 14 13 12 11 10 9 b1 a1 ro1 en ro2 a2 b2 gnd v cc b4 a4 ro4 en ro3 a3 b3 r r r r t jmax = 150c, ja = 90c/w ltc489 ltc489 1 2 3 4 5 6 7 8 top view n package 16-lead plastic dip 16 15 14 13 12 11 10 9 b1 a1 ro1 en12 ro2 a2 b2 gnd v cc b4 a4 ro4 en34 ro3 a3 b3 r r r r t jmax = 150c, ja = 70c/w 1 2 3 4 5 6 7 8 top view sw package 16-lead plastic (wide) so 16 15 14 13 12 11 10 9 b1 a1 ro1 en12 ro2 a2 b2 gnd v cc b4 a4 ro4 en34 ro3 a3 b3 r r r r t jmax = 150c, ja = 90c/w absolute maximum ratings supply voltage (v cc ) ................................................12v control input currents .......................... C25ma to 25ma control input voltages ..................C0.5v to (v cc + 0.5v) receiver input voltages ..........................................14v receiver output voltages ..............C0.5v to (v cc + 0.5v) (note 1) pin configuration operating temperature range ltc488c/ltc489c ................................... 0c to 70c ltc488i/ltc489i .................................. C40c to 85c storage temperature range ................... C65c to 150c lead temperature (soldering, 10 sec) .................. 300c
ltc488/ltc489 3 4889fb dc electrical characteristics note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. the l denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. v cc = 5v (notes 2, 3), unless otherwise noted. order information lead free finish tape and reel part marking package description temperature range ltc488cn#pbf ltc488cn#trpbf ltc488cn 16-lead plastic dip 0c to 70c ltc488csw#pbf ltc488csw#trpbf ltc488csw 16-lead plastic so 0c to 70c ltc488in#pbf ltc488in#trpbf ltc488in 16-lead plastic dip C40c to 85c ltc488isw#pbf ltc488isw#trpbf ltc488isw 16-lead plastic so C40c to 85c ltc489cn#pbf ltc489cn#trpbf ltc489cn 16-lead plastic dip 0c to 70c ltc489csw#pbf ltc489csw#trpbf ltc489csw 16-lead plastic so 0c to 70c ltc489in#pbf ltc489in#trpbf ltc489in 16-lead plastic dip C40c to 85c ltc489isw#pbf ltc489isw#trpbf ltc489isw 16-lead plastic so C40c to 85c consult ltc marketing for parts speci? ed with wider operating temperature ranges. consult ltc marketing for information on non-standard lead based ? nish parts. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel speci? cations, go to: http://www.linear.com/tapeandreel/ symbol parameter conditions min typ max units v inh input high voltage en, en , en12, en34 l 2.0 v v inl input low voltage en, en , en12, en34 l 0.8 v i in1 input current en, en , en12, en34 l 2 a i in2 input current (a, b) v cc = 0v or 5.25v, v in = 12v v cc = 0v or 5.25v, v in = C 7v l l 1.0 C0.8 ma ma v th differential input threshold voltage for receiver C7v v cm 12v l C0.2 0.2 v v th receiver input hysteresis v cm = 0v 60 mv v oh receiver output high voltage i o = C4ma, v id = 0.2v l 3.5 v v ol receiver output low voltage i o = 4ma, v id = C0.2v l 0.4 v i ozr three-state output current at receiver v cc = max 0.4v v o 2.4v l 1 a i cc supply current no load, digital pins = gnd or v cc l 710 ma r in receiver input resistance C7v v cm 12v, v cc = 0v l 12 k i osr receiver short-circuit current 0v v o v cc l 785ma t plh receiver input to output c l = 15pf (figures 1, 3) l 12 28 55 ns t phl receiver input to output c l = 15pf (figures 1, 3) l 12 28 55 ns t skd | t plh C t phl | differential receiver skew c l = 15pf (figures 1, 3) 4 ns note 2: all currents into device pins are positive; all currents out of device pins are negative. all voltages are referenced to device ground unless otherwise speci? ed. note 3: all typicals are given for v cc = 5v and t a = 25c. the l denotes the speci? cations which apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. v cc = 5v 5% (notes 2, 3), unless otherwise noted. symbol parameter conditions min typ max units t zl receiver enable to output low c l = 15pf (figures 2, 4) s1 closed l 30 60 ns t zh receiver enable to output high c l = 15pf (figures 2, 4) s2 closed l 30 60 ns t lz receiver disable from low c l = 15pf (figures 2, 4) s1 closed l 30 60 ns t hz receiver disable from high c l = 15pf (figures 2, 4) s2 closed l 30 60 ns
ltc488/ltc489 4 4889fb typical performance characteristics receiver output low voltage vs output current at t a = 25c ttl input threshold vs temperature receiver | t plh C t phl | vs temperature supply current vs temperature receiver output low voltage vs temperature at i = 8ma receiver output high voltage vs temperature at i = 8ma receiver output high voltage vs output current at t a = 25c temperature (c) C50 0 output voltage (v) 0.1 0.3 0.4 0.5 50 0.9 4889 g01 0.2 C25 125 0.6 0.7 0.8 0 25 75 100 temperature (c) C50 3.0 output voltage (v) 3.8 50 4889 g02 3.4 C25 125 4.2 4.6 0 25 75 100 4.8 4.4 4.0 3.6 3.2 output voltage (v) 5 0 output current (ma) C8 4889 g03 C4 43 C12 C16 2 C2 C6 C10 C14 C18 output voltage (v) 0 0 output current (ma) 16 1.0 4889 g04 8 0.5 1.5 24 32 2.0 4 12 20 28 36 temperature (c) C50 1.55 input threshold voltage (v) 1.59 50 8889 g05 1.57 C25 125 1.61 1.63 0 25 75 100 temperature (c) C50 1 time (ns) 3 50 4889 g06 2 C25 125 4 5 0 25 75 100 temperature (c) C50 5.4 supply current (ma) 6.2 50 4889 g07 5.8 C25 125 6.6 7.0 0 25 75 100
ltc488/ltc489 5 4889fb pin functions b 1 (pin 1): receiver 1 input. a1 (pin 2): receiver 1 input. ro1 (pin 3): receiver 1 output. if the receiver output is enabled, then if a > b by 200mv, ro1 will be high. if a < b by 200mv, then ro1 will be low. en (pin 4) ltc488: receiver output enabled. see function table for details. en12 (pin 4) ltc489: receiver 1, receiver 2 output enabled. see function table for details. ro2 (pin 5): receiver 2 output. refer to ro1. a2 (pin 6): receiver 2 input. b2 (pin 7): receiver 2 input. gnd (pin 8): ground connection. b3 (pin 9): receiver 3 input. a3 (pin 10): receiver 3 input. ro3 (pin 11): receiver 3 output. refer to ro1. en (pin 12) ltc488: receiver output disabled. see func- tion table for details. en34 (pin 12) ltc489: receiver 3, receiver 4 output enabled. see function table for details. ro4 (pin 13): receiver 4 output. refer to ro1. a4 (pin 14): receiver 4 input. b4 (pin 15): receiver 4 input. v cc (pin 16): positive supply; 4.75v v cc 5.25v. function tables ltc488 differential enables output a C b en en ro v id 0.2v h x x l h h C0.2v < v id < 0.2v h x x l ? ? v id 0.2v h x x l l l xlhz ltc489 differential enables output a C b en12 or en34 ro v id 0.2v h h C0.2v < v id < 0.2v h ? v id 0.2v h l xlz h: high level l: low level x: irrelevant ?: indeterminate z: high impedance (off)
ltc488/ltc489 6 4889fb test circuits switching time waveforms figure 1. receiver timing test circuit note: the input pulse is supplied by a generator having the following characteristics: f = 1mhz, duty cycle = 50%, t r < 10ns, t f 10ns, z out = 50 figure 2. receiver enable and disable timing test circuit d 4889 f01 driver receiver c l ro a b 54 100pf 100pf 1k 4889 f02 c l s1 s2 1k v cc receiver output 0v Cv od2 t phl f = 1mhz; t r 10ns; t f 10ns 0v t plh v od2 input a, b v oh 1.5v 1.5v v ol ro input 4889 f03 f = 1mhz; t r 10ns; t f 10ns 1.5v ro 4889 f04 0v 3v 1.5v t zl v ol v oh 1.5v t lz 0.5v 0.5v t hz output normally low output normally high 0v 5v 1.5v t zh ro en or en12 figure 3. receiver propagation delays figure 4. receiver enable and disable times
ltc488/ltc489 7 4889fb typical application a typical connection of the ltc488/ltc489 is shown in figure 5. two twisted-pair wires connect up to 32 driver/ receiver pairs for half-duplex data transmission. there are no restrictions on where the chips are connected to the wires, and it isnt necessary to have the chips connected at the ends. however, the wires must be terminated only at the ends with a resistor equal to their characteristic impedance, typically 120. the input impedance of a receiver is typically 20k to gnd, or 0.5 unit rs485 load, so in practice 50 to 60 transceivers can be connected to the same wires. the optional shields around the twisted- pair help reduce unwanted noise, and are connected to gnd at one end. cables and data rate the transmission line of choice for rs485 applications is a twisted-pair. there are coaxial cables (twinaxial) made for this purpose that contain straight-pairs, but these are less ? exible, more bulky, and more costly than twisted-pairs. many cable manufacturers offer a broad range of 120 cables designed for rs485 applications. losses in a transmission line are a complex combination of dc conductor loss, ac losses (skin effect), leakage, and ac losses in the dielectric. in good polyethylene cable such as the belden 9841, the conductor losses and dielectric losses are of the same order of magnitude, leading to relatively low overall loss (figure 6). when using low loss cables, figure 7 can be used as a guideline for choosing the maximum line length for a given applications information figure 5. typical connection figure 7. cable length vs data rate figure 6. attenuation vs frequency for belden 9841 120 120 3 rx 2 1 4889 f05 dx 1 3 shield rx en dx 1/4 ltc486 12 shield 4 12 3 2 dx dx 1/4 ltc486 1 en 1/4 ltc488 or 1/4 ltc489 rx 3 1 2 4 rx 1/4 ltc488 or 1/4 ltc489 en en frequency (mhz) 0.1 0.1 loss per 100 ft (db) 1 10 1 10 100 4889 f06 data rate (bps) 10k 10 cable length (ft) 100 1k 10k 100k 1m 10m 4889 f07 2.5m
ltc488/ltc489 8 4889fb data rate. with lower quality pvc cables, the dielectric loss factor can be 1000 times worse. pvc twisted-pairs have terrible losses at high data rates (> 100kbps), and greatly reduce the maximum cable length. at low data rates how- ever, they are acceptable and much more economical. cable termination the proper termination of the cable is very important. if the cable is not terminated with its characteristic imped- ance, distorted waveforms will result. in severe cases, distorted (false) data and nulls will occur. a quick look at the output of the driver will tell how well the cable is terminated. it is best to look at a driver connected to the end of the cable, since this eliminates the possibility of getting re? ections from two directions. simply look at the driver output while transmitting square wave data. if the cable is terminated properly, the waveform will look like a square wave (figure 8). if the cable is loaded excessively (47), the signal initially sees the surge impedance of the cable and jumps to an initial amplitude. the signal travels down the cable and is re? ected back out of phase because of the mistermination. when the re? ected signal returns to the driver, the ampli- tude will be lowered. the width of the pedestal is equal to twice the electrical length of the cable (about 1.5ns/foot). if the cable is lightly loaded (470), the signal re? ects in phase and increases the amplitude at the drive output. an input frequency of 30khz is adequate for tests out to 4000 ft. of cable. ac cable termination cable termination resistors are necessary to prevent un- wanted re? ections, but they consume power. the typical differential output voltage of the driver is 2v when the cable is terminated with two 120 resistors, causing 33ma of dc current to ? ow in the cable when no data is being sent. this dc current is about 60 times greater than the supply current of the ltc488/ltc489. one way to eliminate the unwanted current is by ac coupling the termination resistors as shown in figure 9. the coupling capacitor must allow high frequency energy to ? ow to the termination, but block dc and low frequen- cies. the dividing line between high and low frequency depends on the length of the cable. the coupling capaci- tor must pass frequencies above the point where the line represents an electrical one-tenth wavelength. the value of the coupling capacitor should therefore be set at 16.3pf per foot of cable length for 120 cables. with the coupling capacitors in place, power is consumed only on the signal edges, and not when the driver output is idling at a 1 or 0 state. a 100nf capacitor is adequate for lines up to 4000 feet in length. be aware that the power savings start to decrease once the data rate surpasses 1/(120)(c). applications information figure 8. termination effects figure 9. ac-coupled termination 4889 f08 dx probe here rt = 120 rt = 47 rt = 470 rt rx receiver driver 488/9 f09 c = line length (ft)(16.3pf) 120 c rx receiver
ltc488/ltc489 9 4889fb applications information 4889 f10 110 rx 130 130 110 5v rx receiver 1.5k 120 5v 1.5k rx 120 5v c 100k receiver receiver 4889 f11 120 driver y z receiver open-circuit fail-safe some data encoding schemes require that the output of the receiver maintains a known state (usually a logic 1) when the data is ? nished transmitting and all drivers on the line are forced in three-state. the receiver of the ltc488/ltc489 has a fail-safe feature which guarantees the output to be in a logic 1 state when the receiver inputs are left ? oating (open-circuit). when the input is terminated with 120 and the receiver output must be forced to a known state, the circuits of figure 10 can be used. the termination resistors are used to generate a dc bias which forces the receiver output to a known state, in this case a logic 0. the ? rst method consumes about 208mw and the second about 8mw. the lowest power solution is to use an ac termination with a pullup resistor. simply swap the receiver inputs for data protocols ending in logic 1. fault protection all of ltcs rs485 products are protected against esd tran- sients up to 2kv using the human body model (100pf, 1.5k). however, some applications need more protection. the best protection method is to connect a bidirectional transzorb ? from each line side pin to ground (figure 11). a transzorb is a silicon transient voltage suppressor that has exceptional surge handling capabilities, fast response time, and low series resistance. they are available from general instruments, gsi, and come in a variety of break- down voltages and prices. be sure to pick a breakdown voltage higher than the common mode voltage required for your application (typically 12v). also, dont forget to check how much the added parasitic capacitance will load down the bus. figure 11. esd protection with transzorbs figure 10. forcing 0 when all drivers are off
ltc488/ltc489 10 4889fb package description n package 16-lead pdip (narrow .300 inch) (reference ltc dwg # 05-08-1510) n16 1002 .255 .015* (6.477 0.381) .770* (19.558) max 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 .020 (0.508) min .120 (3.048) min .130 .005 (3.302 0.127) .065 (1.651) typ .045 ?.065 (1.143 ?1.651) .018 .003 (0.457 0.076) .008 ?.015 (0.203 ?0.381) .300 ?.325 (7.620 ?8.255) .325 +.035 ?015 +0.889 0.381 8.255 () note: 1. dimensions are inches millimeters *these dimensions do not include mold flash or protrusions. mold flash or protrusions shall not exceed .010 inch (0.254mm) .100 (2.54) bsc
ltc488/ltc489 11 4889fb 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 representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. package description sw package 16-lead plastic small outline (wide .300 inch) (reference ltc dwg # 05-08-1620) s16 (wide) 0502 note 3 .398 ?.413 (10.109 ?10.490) note 4 16 15 14 13 12 11 10 9 1 n 23 4 5 6 78 n/2 .394 ?.419 (10.007 ?10.643) .037 ?.045 (0.940 ?1.143) .004 ?.012 (0.102 ?0.305) .093 ?.104 (2.362 ?2.642) .050 (1.270) bsc .014 ?.019 (0.356 ?0.482) typ 0 ?8 typ note 3 .009 ?.013 (0.229 ?0.330) .005 (0.127) rad min .016 ?.050 (0.406 ?1.270) .291 ?.299 (7.391 ?7.595) note 4 45 .010 ?.029 (0.254 ?0.737) inches (millimeters) note: 1. dimensions in 2. drawing not to scale 3. pin 1 ident, notch on top and cavities on the bottom of packages are the manufacturing options. the part may be supplied with or without any of the options 4. these dimensions do not include mold flash or protrusions. mold flash or protrusions shall not exceed .006" (0.15mm) .420 min .325 .005 recommended solder pad layout .045 .005 n 1 2 3 n/2 .050 bsc .030 .005 typ
ltc488/ltc489 12 4889fb linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 1992 lt 0309 rev b ? printed in usa related parts typical application rs232 receiver part number description comments ltc485 low power rs485 transceiver low power, half-duplex ltc490 low power rs485 full-duplex transceiver full-duplex in so-8 ltc1480 3v, ultralow power rs485 transceiver 1a shutdown mode ltc1481 3v, ultralow power rs485 transceiver lowest power on 5v supply ltc1483 ultralow power rs485 low emi transceiver low emi/low power with shutdown ltc1485 fast rs485 transceiver 10mbps operation ltc1487 ultralow power rs485 with low emi and high input impedance up to 256 nodes on a bus ltc1685 high speed rs485 transceiver 52mbps, pin compatible with ltc485 ltc1686/ltc1687 high speed rs485 full-duplex transceiver 52mbps, pin compatible ltc490/ltc491 4889 ta02 rs232 in 5.6k rx receiver 1/4 ltc488 or 1/4 ltc489

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