ltc1480 1 1480fa output current (ma) 0 0 output voltage (v) 0.5 1.0 1.5 2.0 2.5 60 70 80 1480 ta02 10 20 30 40 50 90 3.0 3.5 v cc = 3.3v t a = 25 c applicatio s u descriptio u features typical applicatio u , ltc and lt are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. true rs485 from a single 3.3v supply low power: i cc = 500 a max with driver disabled i cc = 600 a max with driver enabled, no load 1 a quiescent in shutdown mode ?v to 12v common mode range permits 7v ground difference between devices on the data line thermal shutdown protection power up/down glitch-free driver outputs permit live insertion or removal of transceiver driver maintains high impedance in three-state or with the power off up to 32 transceivers on the bus 50ns typical driver propagation delays with 10ns skew pin compatible with the ltc485 available in 8-lead dip and so packages 3.3v ultralow power rs485 transceiver the ltc 1480 is an ultralow power differential line trans- ceiver which provides full rs485 compatibility while oper- ating from a single 3.3v supply. it is designed for data transmission standard rs485 applications with extended common mode range (12v to ?v). it also meets the requirements of rs422 and features high speed operation up to 2.5mb/s. the cmos design offers significant power savings without sacrificing ruggedness against overload or esd damage. typical quiescent current is only 300 a while operating and 1 a in shutdown. the driver and receiver feature three-state outputs, with the driver outputs maintaining high impedance over the entire common mode range. excessive power dissipation caused by bus contention or faults is prevented by a thermal shutdown circuit which forces the driver outputs into a high impedance state. the receiver has a fail-safe feature which guarantees a high output state when the inputs are left open. the ltc1480 is fully specified over the commercial and extended industrial temperature range. the ltc1480 is available in 8-pin so and dip packages. battery-powered rs485/rs422 applications low power rs485/rs422 transceiver level translator driver differential output voltage vs output current 3.3v rs485 network ro re de 1480 ta01 ltc1480 ltc1480 a a b b a b 120 ? 120 ? shield shield r 3.3v ro re de ltc1480 r 3.3v 3.3v r d ro re de di d di di d
ltc1480 2 1480fa the denotes the specifications which apply over the full operating temperature range. v cc = 3.3v (notes 2, 3). electrical characteristics 1 2 3 4 8 7 6 5 top view v cc b a gnd n8 package 8-lead pdip s8 package 8-lead plastic so r d ro re de di supply voltage (v cc ) ................................................ 7v control input voltage ..................... 0.3v to v cc + 0.3v driver input voltage ....................... 0.3v to v cc + 0.3v driver output voltage ........................................... 14v receiver input voltage .......................................... 14v receiver output voltage ................ 0.3v to v cc + 0.3v operating temperature range ltc1480c ....................................... 0 c t a 70 c ltc1480i .................................... 40 c t a 85 c storage temperature range ................. 65 c to 150 c lead temperature (soldering, 10 sec).................. 300 c absolute axi u rati gs w ww u package/order i for atio uu w (note 1) t jmax = 125 c, ja = 130 c/ w (n8) t jmax = 125 c, ja = 150 c/ w (s8) order part number s8 part marking consult ltc marketing for parts specified with wider operating temperature ranges. ltc1480cn8 ltc1480in8 ltc1480cs8 ltc1480is8 1480 1480i order options tape and reel: add #tr lead free: add #pbf lead free tape and reel: add #trpbf lead free part marking: http://www.linear.com/leadfree/ symbol parameter conditions min typ max units v od1 differential driver output voltage (unloaded) i o = 0v 3.3 v v od2 differential driver output voltage (with load) r = 27 ? (rs485) (figure 1) 1.5 3.3 v r = 50 ? (rs422) 2.0 v ? v od change in magnitude of driver differential output r = 27 ? or r = 50 ? (figure 1) 0.2 v voltage for complementary output states v oc driver common mode output voltage r = 27 ? or r = 50 ? (figure 1) 2v ? ? v oc ? change in magnitude of driver common mode r = 27 ? or r = 50 ? (figure 1) 0.2 v output voltage for complementary output states v ih input high voltage de, di, re 2v v il input low voltage de, di, re 0.8 v i in1 input current de, di, re 2 a i in2 input current (a, b) de = 0, v cc = 0v or 3.6v, v in = 12v 1.0 ma de = 0, v cc = 0v or 3.6v, v in = 7v 0.8 ma v th differential input threshold voltage for receiver 7v v cm 12v 0.2 0.2 v ? v th receiver input hysteresis v cm = 0v 70 mv v oh receiver output high voltage i o = 4ma, v id = 200mv 2v v ol receiver output low voltage i o = 4ma, v id = 200mv 0.4 v i ozr three-state (high impedance) output v cc = max, 0.4v v o 2.4v 1 a current at receiver r in receiver input resistance 7v v cm 12v 12 k ? i cc supply current no load, output enabled 400 600 a no load, output disabled 300 500 a i shdn supply current in shutdown mode de = 0, re = v cc 110 a
ltc1480 3 1480fa temperature ( c) ?0 1.9 2.0 2.2 20 60 1480 g03 1.8 1.7 ?0 0 40 80 100 1.6 1.5 2.1 differential voltage (v) r l = 100 ? r l = 54 ? v cc = 3.3v output voltage (v) 0 output current (ma) 50 100 150 1.5 2.5 1480 g02 0 ?0 0.5 1.0 2.0 3.0 3.5 100 150 v cc = 3.3v t a = 25 c temperature ( c) ?5 200 supply current ( a) 225 275 300 325 75 425 1480 g01 250 25 175 125 ?0 50 0 150 100 350 375 400 driver disabled thermal shutdown with driver enabled v cc = 3.3v the denotes the specifications which apply over the full operating temperature range. v cc = 3.3v (notes 2, 3). typical perfor a ce characteristics uw note 1: absolute maximum ratings are those beyond which the safety of the device cannot be guaranteed. note 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. note 3: all typicals are given for v cc = 3.3v and t a = 25 c. driver output low/high voltage vs output current supply current vs temperature driver differential output voltage vs temperature switchi g characteristics u symbol parameter conditions min typ max units i osd1 driver short-circuit current, v out = high 7v v o 12v 35 250 ma i osd2 driver short-circuit current, v out = low 7v v o 12v 35 250 ma i osr receiver short-circuit current 0v v o v cc 785ma t plh driver input to output r diff = 54 ? , c l1 = c l2 = 100pf, 25 50 80 ns (figures 3, 5) t phl driver input to output 25 50 80 ns t skew driver output to output 10 20 ns t r , t f driver rise or fall time 51540ns t zh driver enable to output high c l = 100pf (figures 4, 6), s2 closed 70 120 ns t zl driver enable to output low c l = 100pf (figures 4, 6), s1 closed 70 120 ns t lz driver disable time from low c l = 15pf (figures 4, 6), s1 closed 70 120 ns t hz driver disable time from high c l = 15pf (figures 4, 6), s2 closed 70 120 ns t plh receiver input to output r diff = 54 ? , c l1 = c l2 = 100pf, 30 140 200 ns (figures 3, 7) t phl receiver input to output 30 140 200 ns t skd ? t plh ?t phl ? differential receiver skew 13 ns t zl receiver enable to output low c rl = 15pf (figures 2, 8), s1 closed 50 80 ns t zh receiver enable to output high c rl = 15pf (figures 2, 8), s2 closed 50 80 ns t lz receiver disable from low c rl = 15pf (figures 2, 8), s1 closed 50 80 ns t hz receiver disable from high c rl = 15pf (figures 2, 8), s2 closed 50 80 ns f max maximum data rate 2.5 mbits/s t shdn time to shutdown de = 0, re = 50 200 600 ns t zh(shdn) driver enable from shutdown to output high c l = 100pf (figures 4, 6), s2 closed 70 120 ns t zl(shdn) driver enable from shutdown to output low c l = 100pf (figures 4, 6), s1 closed 70 120 ns t zh(shdn) receiver enable from shutdown to output high c l = 15pf (figures 2, 8), s2 closed 4500 ns t zl(shdn) receiver enable from shutdown to output low c l = 15pf (figures 2, 8), s1 closed 4500 ns
ltc1480 4 1480fa temperature ( c) ?0 2.0 output voltage (v) 2.4 3.0 0 40 60 1480 g09 2.2 2.8 2.6 ?0 20 80 100 v cc = 3.3v i o = 8ma temperature ( c) ?0 output voltage (v) 0.4 0.5 0.6 20 60 1480 g08 0.3 0.2 ?0 0 40 80 100 0.1 0 v cc = 3.3v i o = 8ma pi fu ctio s uu u temperature ( c) ?0 time (ns) 12 10 8 6 4 2 0 20 60 1480 g07 ?0 0 40 80 100 v cc = 3.3v output voltage (v) 3.30 output current (ma) ? ?0 ?2 1.30 1480 g06 ? ? 0 2.80 2.30 1.80 ? ?6 ?4 3.05 2.55 2.05 1.55 v cc = 3.3v t a = 25 c output voltage (v) 0 output current (ma) 15 20 25 1.6 1480 g05 10 5 0 0.2 0.4 0.6 1.0 1.4 1.8 0.8 1.2 2.0 v cc = 3.3v t a = 25 c temperature ( c) ?0 time (ns) 6.5 20 1480 g04 5.0 4.0 ?0 0 40 3.5 3.0 7.0 6.0 5.5 4.5 60 80 100 v cc = 3.3v typical perfor m a n ce characteristics u w high, the driver outputs will be fed back to the receiver and the receive output will correspond to the driver input. di (pin 4): driver input. if the driver outputs are enabled (de high) then a low on di forces the outputs a low and b high. a high on di with the driver outputs enabled will force a high and b low. gnd (pin 5): ground. a (pin 6): driver output/receiver input. b (pin 7): driver output/receiver input. v cc (pin 8): positive supply. 3.0v < v cc < 3.6v. ro (pin 1): receiver output. if the receiver output is enabled (re low) and a > b by 200mv, then ro will be high. if a < b by 200mv, then ro will be low. re (pin 2): receiver output enable. a low enables the receiver output, ro. a high input forces the receiver output into a high impedance state. de (pin 3): driver outputs enable. a high on de enables the driver output. a, b and the chip will function as a line driver. a low input will force the driver outputs into a high impedance state and the chip will function as a line receiver. if re is high and de is low, the part will enter a low power (1 a) shutdown state. if re is low and de is receiver output low voltage vs output current receiver output high voltage vs output current driver skew vs temperature receiver ? ? ? ? ? t plh ?t phl ? ? ? ? ? vs temperature receiver output low voltage vs temperature receiver output high voltage vs temperature
ltc1480 5 1480fa di 3v 1.5v t plh t r t skew 1/2 v o v o f = 1mhz, t r 10ns, t f 10ns 90% 10% 0v b a v o ? o 0v 90% 1.5v t phl t skew 1/2 v o 10% t f v diff = v(a) ?v(b) 1480 f05 switchi g ti e wavefor s uw w output under test c l s1 s2 v cc 500 ? 1480 f04 3v de a b di r diff c l1 c l2 ro 15pf a b re 1480 f03 ltc1480 receiver ltc1480 driver receiver output c rl 1k s1 s2 test point v cc 1k 1480 f02 v od a b r r v oc 1480 f01 test circuits fu ctio tables uu ltc1480 transmitting inputs outputs re de di b a x1101 x1010 00xzz 1 0 x z* z* *shutdown mode ltc1480 receiving inputs outputs re de a ?b ro 00 0.2v 1 00 0.2v 0 0 0 inputs open 1 10 x z* *shutdown mode figure 2. receiver timing test load figure 1. driver dc test load figure 5. driver propagation delays figure 4. driver timing test load figure 3. driver/receiver timing test circuit
ltc1480 6 1480fa logic v cc sd3 p1 d1 output sd4 d2 n1 1480 f10 p1 logic v cc p1 d1 output d2 n1 1480 f09 1.5v t zl(shdn) , t zl t zh(shdn) , t zh 1.5v 1.5v 1.5v t lz 0.5v 0.5v t hz output normally low output normally high 3v 0v re 3.3v v ol v oh 0v ro ro 1480 f08 f = 1mhz, t r 10ns, t f 10ns 1.5v t phl ro ? od2 a ?b 0v 0v 1.5v t plh output input v od2 v ol v oh 1480 f07 f = 1mhz, t r 10ns, t f 10ns 1.5v 2.3v 2.3v t zh(shdn) , t zh t zl(shdn) , t zl 1.5v t lz 0.5v 0.5v t hz output normally low output normally high 3v 0v de 3.3v v ol v oh 0v a, b a, b 1480 f06 f = 1mhz, t r 10ns, t f 10ns applicatio s i for atio wu u u switchi g ti e wavefor s uw w cmos output driver the ltc1480 transceiver provides full rs485 compatibility while operating from a single 3.3v supply. the rs485 specification requires that a transceiver withstand common mode voltages of up to 12v or ?v at the rs485 line connections. additionally, the transceiver must be immune to both esd and latch-up. this rules out traditional cmos drivers, which include parasitic diodes from their driver outputs to each supply rail (figure 9). the ltc1480 uses a proprietary process enhancement which adds a pair of schottky diodes to the output stage (figure 10), preventing figure 9. conventional cmos output stage figure 10. ltc1480 output stage figure 6. driver enable and disable times figure 7. receiver propagation delays figure 8. receiver enable and disable times
ltc1480 7 1480fa driver outputs enabled but unterminated, quiescent cur- rent will rise as one of the two outputs sources current into the internal receiver input resistance. with the minimum receiver input resistance of 12k and the maximum output swing of 3.3v, the quiescent current will rise by a maxi- mum of 275 a. typical quiescent current rise with the driver enabled is about 100 a. the quiescent current rises significantly if the driver is enabled when it is externally terminated. with 1/2 termina- tion load (120 ? between the driver outputs) the quiescent current will jump to at least 13ma as the drivers force a minimum of 1.5v across the termination resistance. with a fully terminated 60 ? line attached, the current will rise to greater than 25ma with the driver enabled, completely overshadowing the extra 100 a drawn by internal receiver inputs. shutdown mode both the receiver output (ro) and the driver outputs (a, b) can be placed in three-state mode by bringing re high and de low respectively. in addition, the ltc1480 will enter shutdown mode when re is high and de is low. in shutdown the ltc1480 typically draws only 1 a of supply current. in order to guarantee that the part goes into shutdown, re must be high and de must be low for at least 600ns simultaneously. if this time duration is less than 50ns the part will not enter shutdown mode. propagation delay many digital encoding schemes are dependent upon the difference in the propagation delay times of the driver and receiver. figure 11 shows the test circuit for the ltc1480 propagation delay. the receiver delay times are: ? t plh ?t phl ? = 13ns typ, v cc = 3.3v the driver? skew times are: t skew = 10ns typ, v cc = 3.3v 20ns max, v cc = 3.3v, t a = 40 c to 85 c applicatio s i for atio wu u u 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. current from flowing when the common mode voltage exceeds the supply rails. latch-up at the output drivers is virtually eliminated and the driver is prevented from loading the line under rs485 specified fault conditions. when two or more drivers are connected to the same transmission line, a potential condition exists whereby more than two drivers are simultaneously active. if one or more drivers is sourcing current while another driver is sinking current, excessive power dissipation may occur within either the sourcing or sinking element. this condi- tion is defined as driver contention, since multiple drivers are competing for one transmission line. the ltc1480 provides a current limiting scheme to prevent driver contention failure. when driver contention occurs, the current drawn is limited to about 70ma preventing exces- sive power dissipation within the drivers. the ltc1480 has a thermal shutdown feature which protects the part from excessive power dissipation. under extreme fault conditions, up to 250ma can flow through the part causing rapid internal temperature rise. the thermal shutdown circuit will disable the driver outputs when the internal temperature reaches 150 c and turns them back on when the temperature cools to 130 c. this cycle will repeat as necessary until the fault condition is removed. receiver inputs the ltc1480 features an input common mode range covering the entire rs485 specified range of ?v to 12v. differential signals of greater than 200mv within the specified input common mode range will be converted to a ttl compatible signal at the receiver output. a small amount of input hysteresis is included to minimize the effects of noise on the line signals. if the receiver inputs are floating (unterminated) an internal pull-up of 10 a at the a input will force the receiver output to a known high state. low power operation the ltc1480 draws very little supply current whenever the driver outputs are disabled. in shutdown mode the quiescent current is typically less than 1 a. with the receiver active and the driver outputs disabled, the ltc1480 will typically draw 300 a quiescent current. with the
ltc1480 8 1480fa .016 ?.050 (0.406 ?1.270) .010 ?.020 (0.254 ?0.508) 45 0 ?8 typ .008 ?.010 (0.203 ?0.254) so8 0303 .053 ?.069 (1.346 ?1.752) .014 ?.019 (0.355 ?0.483) typ .004 ?.010 (0.101 ?0.254) .050 (1.270) bsc 1 2 3 4 .150 ?.157 (3.810 ?3.988) note 3 8 7 6 5 .189 ?.197 (4.801 ?5.004) note 3 .228 ?.244 (5.791 ?6.197) .245 min .160 .005 recommended solder pad layout .045 .005 .050 bsc .030 .005 typ inches (millimeters) note: 1. dimensions in 2. drawing not to scale 3. these dimensions do not include mold flash or protrusions. mold flash or protrusions shall not exceed .006" (0.15mm) n8 1002 .065 (1.651) typ .045 ?.065 (1.143 ?1.651) .130 .005 (3.302 0.127) .020 (0.508) min .018 .003 (0.457 0.076) .120 (3.048) min 12 3 4 87 6 5 .255 .015* (6.477 0.381) .400* (10.160) max .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 .100 (2.54) bsc *these dimensions do not include mold flash or protrusions. mold flash or protrusions shall not exceed .010 inch (0.254mm) part number description comments ltc485 5v low power rs485 interface transceiver low power ltc1481 5v ultralow power rs485 transceiver with shutdown lowest power ltc1483 5v ultralow power rs485 low emi transceiver with shutdown low emi/lowest power ltc1485 5v differential bus transceiver high speed, 10mbps ltc1487 5v ultralow power rs485 with low emi, shutdown high input impedance/low emi/lowest power and high input impedance related parts s8 package 8-lead plastic small outline (narrow .150 inch) (reference ltc dwg # 05-08-1610) n8 package 8-lead pdip (narrow .300 inch) (reference ltc dwg # 05-08-1510) package descriptio u d r receiver out r 100 ? 100pf 100pf ttl in t r , t f < 6ns 1480 f11 br applicatio s i for atio wu u u linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 1995 lt/lt 0605 rev a ? printed in usa figure 11. receiver propagation delay test circuit
|
