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preliminary technical data general description the ADM1487 is an ultra-low power rs-485/rs-422 transceiver consisting of one driver and one receiver per package. quiescent operating current is typically 80a and 1a in shutdown mode. the driver and receiver both have three-state outputs. this allows multiple drivers to be connected to an rs-485/rs-422 bus, or several receiver outputs to be connected to a serial data bus. the driver will maintain a high-impedance output state even with power off, while the receiver features fail-safe operation that guarantees a logic high output if the inputs are left open-circuit. the device has slew-rate limited drivers to minimize elec- tromagnetic interference (emi) and reduce reflections caused by incorrectly terminated cables. features low power - 120a max icc with driver disabled high input impedance ? up to 256 transceivers on bus low-current (1a) shutdown mode slew rate control for error-free data transmission and low emi 10kv esd protection (human body model) on rs-485 i/o pins thermal protection of driver glitch-free driver power-up allows hot connection driver maintains high output impedance with power off wide common-mode range allows 7v ground differ- ences between devices pin-compatible with industry standard 75176 applications battery-powered rs-485/rs-422 systems level translation functional block diagram 1 2 3 4 8 7 6 5 d r ro de di v cc b a gnd ADM1487 ?1? ADM1487 a rev. prc 08/02 information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of analog devices. one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781/329-4700 www.analog.com fax: 781/326-8703 analog devices, inc., 2002 preliminary technical data ultra-low power rs-485/rs-422 transceiver with low emi and +/-10kv esd protection
ADM1487 ?2? rev. prc preliminary technical data ADM1487 specifications dc electrical characteristics (v cc = +5v 5%, t a = 0c to +70c, unless otherwise noted) parameter min typ max units test conditions/comments differential driver output voltage,v od1 5 v unloaded, i o = 0 differential driver output voltage, v od2 2.0 v figure 1, r = 50 re ), v ih 2v input low voltage (de, di, re ), v il 0.8 v input current (de, di, re ), i in1 2 a input current (a, b), i in2 0.30 ma de = 0, v cc = 0v or 5.25v, v in = 12v -0.15 ma de = 0, v cc = 0v or 5.25v, v in = ?7v differential input threshold voltage -0.2 0.2 v ?7v re = v cc driver short-circuit ourrent, i osd1 35 250 ma v out = high, ?7v
ADM1487 rev. prc ? ADM1487 specifications (continued) electrical characteristics (vcc = +5v ?%, ta = -40? to +85?, unless otherwise noted) parameter min typ max units test conditions/comments differential driver output voltage, v od1 5 v unloaded, i o = 0 differential driver output voltage, v od2 2.0 v figure 1, r = 50 (rs-422) 1.5 5 v figure 1, r = 27 (rs-485) driver common-mode 3 v figure 1, r = 27 or r = 50 output voltage, v oc differential input threshold ?0.2 0.2 v ?7v v cm 12v voltage for receiver, v th receiver input hysteresis, v th 45 mv v cm = 0v supply current, i cc 120 200 a no load, output enabled 80 120 a no load, output disabled supply current in shutdown mode, i shdn 1 10 a de = 0v, re = v cc driver input to output high, t dplh 150 1200 ns figu res 2, 3, r diff = 54 , c l1 = c l2 = 100pf driver input to output low, t dphl 150 1200 ns figu res 2, 3, r diff = 54 , c l1 = c l2 = 100pf driver output to output, t skew 100 600 ns figures 2, 3, r diff = 54 , c l1 = c l2 = 100pf driver rise or fall time, t dr , t df 150 2000 ns figu res 2, 3, r diff = 54 , c l1 = c l2 = 100pf receiver input to output high, t rplh 30 140 250 ns figures 2, 4, r diff = 54 , c l1 = c l2 = 100pf receiver input to output low, t rhl 30 140 250 ns figures 2, 4, r diff = 54 , c l1 = c l2 = 100pf differential receiver skew, t skd 13 ns figures 2, 4, r diff = 54 , |t rplh -t rphl | c l1 = c l2 = 100pf maximum data rate, f max 250 kbps switching characteristics (v cc = +5v ?%, t a = -40? to +85?, unless otherwise noted) parameter min typ max units test conditions/comments driver input to output high, t dplh 150 1200 ns figu res 2, 3, r diff = 54 , c l1 = c l2 = 100pf driver input to output, t dphl 150 1200 ns figu res 2, 3, r diff = 54 , c l1 = c l2 = 100pf driver output to output, t skew 250 600 ns figures 2, 3, r diff = 54 , c l1 = c l2 = 100pf driver rise or fall time, t dr , t df 150 1200 ns figu res 2, 3, r diff = 54 , c l1 = c l2 = 100pf driver enable to output high, t dzh 100 1500 ns figures 5, 6, c l = 100pf, s2 closed driver enable to output low, t dzl 100 1500 ns figures 5, 6, c l = 100pf, s1 closed driver disable time from low, t dlz 150 1500 ns figures 5, 6, c l = l5pf, s1 closed
ADM1487 ?4? rev. prc preliminary technical data ADM1487 specifications (continued) switching characteristics (v cc = +5v 5%, t a = -40c to +85c, unless otherwise noted) parameter min typ max units test conditions/comments driver disable time from high, t dhz 150 1500 ns f igures 5, 6, c l = l5pf, s2 closed receiver input to output, t rplh 30 140 250 ns figures.2, 4, r diff = 54 , c l1 = c l2 = 100pf receiver input to output low, t rphl 30 140 250 ns figures.2, 4, r diff = 54 , c l1 = c l2 = 100pf differentialreceiverskew, t skd 13 ns figures.2, 4, r diff = 54 , |t plh -t phl | c l1 = c l2 = 100pf receiver enable to output low, t rzl 20 50 ns figures 7, 8, c rl = l5pf, s1 closed receiver enable to output high, t rzh 20 50 ns figures 7, 8, c rl = l5pf, s2 closed receiver disable from low, t rlz 20 50 ns figures 7, 8, c rl = l5pf, s1 closed receiver disable from high, t rhz 20 50 ns figures 7, 8, c rl = l5pf, s2 closed maximum data rate, f max 250 kbps time to shutdown, t shdn 50 200 600 ns de = 0, re = low to high transition driver enable from shutdown to 2000 ns figures 5, 6, c l = 100pf, s2 closed output high, t dzh(shdn) driver enable from shutdown to 2000 ns figures 5, 6, c l = 100pf, s1 closed output low, t dzl(shdn) receiver enable from shutdown to 2000 ns figures 7, 8, c l = l5pf, s2 closed output high, t rzh(shdn) receiver enable from shutdown to 2000 ns figures 7, 8, c l = l5pf, s1 closed output low, t rzl(shdn) notes 1 absolute maximum ratings are those beyond which the safety of the device cannot be guaranfeed. 2 all currents into device pins are positive; all currents out ot device pins are negative. all voltages are referenced to device ground unless otherwise specified. 3 all typicals are given for vcc = 5v and tp = 25c. 4 the ADM1487 is not tested and is not quality-assurance sampled at -40c and at 85c. these specifications are guaranteed by des ign, correlation, andlor inference from 0c, 25c and/or 70c tests. absolute maximum ratings supply voltage (vcc) . . . . . . . . . . . . . . . . . . . . . . . . . . 12v control input voltage . . . . . . . . . . . ?0.5v to vcc + 0.5v driver input voltage . . . . . . . . . . . ?0.5v to vcc + 0.5v driver output voltage . . . . . . . . . . . . . . . . . . . . . . . . 14v receiver inputvoltage . . . . . . . . . . . . . . . . . . . . . . . . 14v receiver output voltage . . . . . . . . . ?0.5v to vcc + 0.5v operating temperature range . . . . . . 0c t a 70c lead temperature (soldering, 10 sec) . . . . . . . . . 300c *stresses above those listed under ?absolute maximum ratings? may cause permanent damage to the device. this is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. thermal characteristics 8-pin plastic dip package pin configuration ordering information model temperature range package option ADM1487jn 0c to +70c 8 pin plastic dip ADM1487jr 0c to +70c 8 pin so ADM1487an ?40c to +85c 8 pin plastic dip ADM1487ar ?40c to +85c 8 pin so ADM1487 top view (not to scale) ro de di v cc b a gnd 1 2 3 4 8 7 6 5
ADM1487 rev. prc e5e r r v od v oc a a figure 1. driver dc load test circuit r diff v od2 c l1 c l2 3v de di ro d r 15pf a b a b figure 2. driver/receiver timing test circuit di b a v 0 /2 v 0 t df v diff v 0 -v 0 0v 90% 10% t dr 90% 10% t skew = |t dplh -t dphl | 3v 0v 1.5v t dplh t d phl v diff = v a - v b
# # figure 3. driver propagation delays
# # figure 4. receiver propagation delays ADM1487 test circuits and timing v cc s1 s2 test point c rl 15pf 500 v output under test figure 5. test load for driver enable/disable time test 3v 0v de a, b a, b v ol t dzl(shdn) , t dzl t dlz output normally low output normally high 1.5v 2.3v v ol + 0.5v v oh - 0.5v v ol t dzh(shdn) , t dzh t dhz 2.3 v
# # 5v v oh figure 6. driver enable and disable times ro test point v cc 1k v 1k v s1 s2 c rl 15pf figure 7. test load for receiver enable/disable time test output normally low output normally high 1.5 v 0.5v 0.5v 1.5 v 5v 1.5 v 5v
# # figure 8. receiver enable and disable delay times
ADM1487 ?6? rev. prc preliminary technical data ADM1487 typical performance characteristics a w a i t i n g d a t a tpc1. no-load supply current vs. tem- perature a w a i t i n g d a t a tpc2. o utput current vs. receiver out- put high voltage a w a i t i n g d a t a tpc3. output current vs. receiver out- put low voltage a w a i t i n g d a t a tpc4. receiver output high voltage vs. temperature a w a i t i n g d a t a tpc5. receiver output low voltage vs. temperature a w a i t i n g d a t a tpc6. shutdown current vs. temperature pin function description pin mnemonic description 1 r o receiver output. when re is low and a - b (more positive than) 200mv, ro will be high. when re is low and a - b (more negative than) ?200mv, ro will be low. 2 re receiver output enable. take re low to enable ro; ro is high impedance when re is high. take re high and de low to enter low-power shutdown mode. 3 d e driver output enable. take de high to enable driver outputs. these outputs are high impedance when de is low. take re high and de low to enter low-power shutdown mode. 4 d i driver input. with de high, a low on di forces non-inverting output low and inverting output high. similarly, a high on di forces non-inverting output high and inverting output low. 5 gnd ground 6 a non-inverting receiver input and non-inverting driver output 7 b inverting receiver input and inverting driver output 8v cc positive supply 4.75v =v cc =5.25v
ADM1487 rev. prc e7e transmitting inputs outputs re de di z y x11 0 1 x10 1 0 0 0 x high-z high-z 1 0 x shutdown* x = don?t care circuit description the ADM1487 is a differential input, differential output transceiver designed rs-485/rs-422 serial data communi- cations over twisted-pair cables. it is a half-duplex device intended for alternate transmission and reception of data over a single twisted-pair cable, and the driver outputs and receiver inputs are internally linked and brought out to a single pair of pins. its principal features include ultra-low power operation, a controlled slew-rate driver that minimizes electromagnetic interference (emi) and signals reflections due to incor- rectly terminated lines, and high input impedance that al- lows up to 256 receivers to be connected to a bus. three-state bus connection the ADM1487 has a driver enable pin (de) that enables the driver outputs when taken high or puts the driver out- puts into a high-impedance state when taken low. this al- lows several driver outputs to be connected to an rs-422/ rs-485 bus. similarly, the device has a (active-low) receiver enable pin ( re ). taking this low enables the receiver, while tak- ing it high puts the receiver outputs into a high-impedance state. this allows several receiver outputs to be connected to a serial data bus. the input impedance of the device is 96k , which is 8 times higher than the standard rs-485 load of 12k . a standard driver can driver 32 standard loads, so up to 256 ADM1487 receivers, or a combination of ADM1487 and other devices up to 32 unit loads, may be connected to an rs-422/rs485 bus driven by a single driver. low power operation the ADM1487 draws very little supply current (typically 80a) when the driver outputs are disabled or unloaded. this will increase by up to 72a if the driver outputs are enabled (but unloaded) and applying the maximum output swing of 5v across the receiver input resistors. however, in practical applications with the device driving and rs-485/rs422 cable or bus, the current drain is dominated by the current sourced into the line termination resistors and any other devices on the bus. with a half-ter- mination (120 load) between the driver outputs, the load current can be in excess of 13ma as the drivers force a minimum of 1.5v across the line, and can be greater than 25ma with a fully terminated 60 line attached. device truth tables shutdown mode if re is taken high while de is taken low, the device will enter a low-power shutdown mode, in which the supply current is typically 1a. if the driver outputs are active immediately before shut- down (de high), the supply current will not drop to 1 until the driver outputs have settled to their three-state mode, which can take up to 2.6s worst-case. if de is al- ready low and shutdown is entered by taking re high, the supply current will drop to 1a very quickly. when re is taken low and/or de is takem high, the de- vice will wake up within 3.5s. if shutdown mode is not used, the fact that de is active- high and re is active-low offers a convenient way of switching the device between transmit and receive, by ty- ing de and re together. this is useful, for example, in applications using half duplex operation and where several receiver outputs are connected to a serial bus. the device is guaranteed not to enter shutdown mode if de and re are driven in this way. if de is low and re is high for less than 50ns the device will not enter shutdown. if de is low and re is high for greater than 600ns, the device is guaranteed to enter shutdown. receiver inputs the ADM1487 receiver has an input common-mode range covering the entire rs-485 range of ?7v to 12v. internal 96k input resistors from each line terminal to ground provide a 1/8 unit load to the rs485 bus. differential signals greater than 200mv within the speci- fied input common-mode range are converted to a ttl- compatible logic signal at the receiver output. a small amount of input hysteresis is included to minimize the ef- fects of noise on the line signals. if the line is terminated or the receiver inputs are shorted together, the receiver output will retain the last valid line signal due to the 45mv of hysteresis incorporated in the receiver circuit. if the receiver inputs are left floating (unterminated), an in- ternal pull-up of 10a at the a input will force the re- ceiver output to a guranteed high output state. driver output stage the rs-485 specification requires that a transceiver with- stand common-mode voltages of up to 12v above or ?7v below system ground at the rs-485 line connections. in addition, the transceiver must be protected against both esd and latch-up. this precludes the use of conventional receiving inputs output re de a-b ro 0x 0.2v 1 0x -0.2v 0 0 x open/shorted 1 1 0 x shutdown* *in shutdown mode, driver and receiver outputs high impedance
ADM1487 ?8? rev. prc preliminary technical data cmos outout stages, which include parasitic diodes from their driver outputs to each supply rail and can latch up when these diodes conduct. v cc parasitic diode d p parasitic diode d p schottky reverse-biased when output > v cc +v d schottky reverse-biased when output < gnd - v d figure 9. ADM1487 driver output stage the ADM1487 output includes schottky diodes in series with the positive supply to the drain of the p-channel output device and in series with the drain of the n-channel output device. these diodes prevent the p-channel's parasitic diode from conducting when the output voltage exceeds v cc and prevent the n-channel's parasitic diode from conducting when the output voltage falls below ground. slew rate control the driver output stage of the ADM1487 has a controlled slew rate to minmize signal reflections on incorrectly termi- nated lines and to reduce electromagnetic interference (emi). current limit and thermal shutdown the ADM1487 incorporates two protection mechanisms to guard the drivers against short-circuits, bus contention or other fault conditions. the first is a current-limited output stage that protects the driver against short-circuits over the entire common-mode voltage range by limiting the output current to about 70ma. under extreme fault condtions where the current limit is not effective, a thermal shutdown circuit puts the driver outputs into a high-impedance state if the die temperature exceeds 150c, and does not turn them back on until the temperature has fallen to 130c. enhanced esd protection all analog devices parts incorporate protection against electrostatic discharge (esd) to protect the devices dur- ing handling, assembly and normal operation. in addition, the ADM1487 has enhanced esd protection up to 10kv on the a and b i/o pins to protect against severe opera- tional conditions such as line transients, connection and disconnection. application information figure 10 shows a typical application of the ADM1487. this is a half-duplex rs-485/rs-422 network. up to 254 additional ADM1487s can be connected along the cable (termination resistors are only required at each end). figure 10. typical half-duplex rs-485/rs-422 network outline dimensions dimensions shown in inches and (mm). 8-pin plastic dual-in-line package (n-8) 8 14 5 0.430 (10.92) 0.348 (8.84) 0.280 (7.11) 0.240 (6.10) pin 1 seating plane 0.022 (0.558) 0.014 (0.356) 0.060 (1.52) 0.015 (0.38) 0.210 (5.33) max 0.130 (3.30) min 0.070 (1.77) 0.045 (1.15) 0.100 (2.54) bsc 0.160 (4.06) 0.115 (2.93) 0.325 (8.25) 0.300 (7.62) 0.015 (0.381) 0.008 (0.204) 0.195 (4.95) 0.115 (2.93) 8-pin so package (r-8) 85 4 1 0.1968 (5.00) 0.1890 (4.80) 0.1574 (4.00) 0.1497 (3.80) 0.2440 (6.20) 0.2284 (5.80) pin 1 seating plane 0.0098 (0.25) 0.0040 (0.10) 0.0192 (0.49) 0.0138 (0.35) 0.102 (2.59) 0.094 (2.39) 0.0500 (1.27) bsc 0.0098 (0.25) 0.0075 (0.19) 0.0500 (1.27) 0.0160 (0.41) 8 0 0.0196 (0.50) 0.0099 (0.25) x 45 100n di d r 5 6 7 8 4 3 2 1 ADM1487 de ro 100n +5v (v cc ) +5v (v cc ) r t r t data in (di) receiver output (ro) 1 2 3 4 8 7 6 5 d r receiver enable ( driver enable (de) ADM1487 cable terminated at ends additional ADM1487s a b a b a b

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