1 ltc148 3 ultra-low power rs485 low emi transceiver with shutdown s f ea t u re d u escriptio the ltc ? 1483 is an ultra-low power differential line trans- ceiver designed for data transmission standard rs485 applications with extended common-mode range (C 7v to 12v). it will also meet the requirements of rs422. the ltc1483 features output drivers with controlled slew rate, decreasing the emi radiated from the rs485 lines, and improving signal fidelity with misterminated lines. the cmos design offers significant power savings over its bipolar counterparts without sacrificing ruggedness against overload or esd damage. typical quiescent current is only 80 m a while operating and less than 1 m 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. i/o pins are protected against multiple esd strikes of over 10kv. the ltc1483 is fully specified over the commercial and extended industrial temperature range and is available in 8-pin dip and so packages. n low power: i cc = 120 m a max with driver disabled n i cc = 500 m a max with driver enabled, no load n 1 m a quiescent current in shutdown mode n controlled slew rate driver for reduced emi n single 5v supply n drivers/receivers have 10kv esd protection n C 7v to 12v common-mode range permits 7v ground difference between devices on the data line n thermal shutdown protection n power up/down glitch-free driver outputs permit live insertion or removal of transceiver n driver maintains high impedance in three-state or with the power off n up to 32 transceivers on the bus n pin compatible with the ltc485 n battery-powered rs485/rs422 applications n low power rs485/rs422 transceiver n level translator u s a o pp l ic at i u a o pp l ic at i ty p i ca l v cc1
gnd1 r ro1
re1
de1
di1 d v cc2
gnd2 r ro2
re2
de2
di2 d r term r term ltc1483 ?ta01 ro a C b di 1483 ta02 , ltc and lt are registered trademarks of linear technology corporation.
2 ltc14 8 3 symbol parameter conditions min typ max units v od1 differential driver output voltage (unloaded) i o = 0 l 5v v od2 differential driver output voltage (with load) r = 50 w (rs422) l 2v r = 27 w (rs485), figure 1 l 1.5 5 v d v od change in magnitude of driver differential output r = 27 w or r = 50 w , figure 1 l 0.2 v voltage for complementary output states v oc driver common-mode output voltage r = 27 w or r = 50 w , figure 1 l 3v d ? v oc ? change in magnitude of driver common-mode r = 27 w or r = 50 w , figure 1 l 0.2 v output voltage for complementary output states v ih input high voltage de, di, re l 2v v il input low voltage de, di, re l 0.8 v i in1 input current de, di, re l 2 m a i in2 input current (a, b) de = 0, v cc = 0v or 5.25v, v in = 12v l 1.0 ma de = 0, v cc = 0v or 5.25v, v in = C 7v l C 0.8 ma v th differential input threshold voltage for receiver C 7v v cm 12v l C 0.2 0.2 v d v th receiver input hysteresis v cm = 0v l 45 mv v oh receiver output high voltage i o = C 4ma, v id = 200mv l 3.5 v v ol receiver output low voltage i o = 4ma, v id = C 200mv l 0.4 v i ozr three-state (high impedance) output v cc = max, 0.4v v o 2.4v l 1 m a current at receiver r in receiver input resistance C 7v v cm 12v l 12 25 k w i cc supply current no load, output enabled l 300 500 m a no load, output disabled l 80 120 m a i shdn supply current in shutdown mode de = 0, re = v cc 110 m a i osd1 driver short-circuit current, v out = high C 7v v o 12v l 35 250 ma i osd2 driver short-circuit current, v out = low C 7v v o 12v l 35 250 ma i osr receiver short-circuit current 0v v o v cc l 785ma a u g w a w u w a r b s o lu t exi t i s wu u package / o rder i for atio order part number ltc1483cn8 ltc1483in8 ltc1483cs8 ltc1483is8 (note 1) supply voltage (v cc ) .............................................. 12v control input voltage ..................... C 0.5v to v cc + 0.5v driver input voltage ....................... C 0.5v to v cc + 0.5v driver output voltage ........................................... 14v receiver input voltage .......................................... 14v receiver output voltage ................ C 0.5v to v cc + 0.5v operating temperature range ltc1483c ........................................ 0 c t a 70 c ltc1483i .................................... C 40 c t a 85 c lead temperature (soldering, 10 sec)................. 300 c t jmax = 125 c, q ja = 130 c/ w (n8) t jmax = 125 c, q ja = 150 c/ w (s8) s8 part marking 1483 1483i consult factory for military grade parts. e lectr ic al c c hara terist ics v cc = 5v, (notes 2, 3) unless otherwise noted. 1
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3
4 8
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top view v cc
b
a
gnd n8 package
8-lead pdip s8 package
8-lead plastic so r d ro
re
de
di
3 ltc148 3 v cc = 5v, (notes 2, 3) unless otherwise noted. switchi g characteristics u 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 = 5v and t a = 25 c. the l denotes specifications which apply over the full operating temperature range. note 1: absolute maximum ratings are those beyond which the safety of the device cannot be guaranteed. supply current vs temperature receiver ? t plh C t phl ? vs temperature temperature ( c) ?0
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0 25 75 1483 g02 ?5 0 50 100 125 ? t plh ?t phl ? (ns) driver differential output voltage vs output current output voltage (v) 0 70
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0 3 1483 g03 12 45 output current (ma) t a = 25 c typical perfor m a n ce characteristics uw temperature ( c) ?0 supply current ( m a) 50 350
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0 1483 g01 0 25 25 75 125 175 150 100 driver enabled driver disabled thermal shutdown
with driver enabled ltc1483 symbol parameter conditions min typ max units t plh driver input to output r diff = 54 w , c l1 = c l2 = 100pf, l 150 1200 ns t phl driver input to output l 150 1200 ns t skew driver output to output l 100 600 ns t r , t f driver rise or fall time l 150 1200 ns t zh driver enable to output high c l = 100pf (figures 4, 6), s2 closed l 100 1500 ns t zl driver enable to output low c l = 100pf (figures 4, 6), s1 closed l 100 1500 ns t lz driver disable time from low c l = 15pf (figures 4, 6), s1 closed l 150 1500 ns t hz driver disable time from high c l = 15pf (figures 4, 6), s2 closed l 150 1500 ns t plh receiver input to output r diff = 54 w , c l1 = c l2 = 100pf, l 30 140 200 ns t phl receiver input to output l 30 140 200 ns t skd ? t plh C t phl ? differential receiver skew l 13 ns t zl receiver enable to output low c rl = 15pf (figures 2, 8), s1 closed l 20 50 ns t zh receiver enable to output high c rl = 15pf (figures 2, 8), s2 closed l 20 50 ns t lz receiver disable from low c rl = 15pf (figures 2, 8), s1 closed l 20 50 ns t hz receiver disable from high c rl = 15pf (figures 2, 8), s2 closed l 20 50 ns f max maximum data rate l 250 kbits/s t shdn time to shutdown de = 0, re = l 50 200 600 ns t zh(shdn) driver enable from shutdown to output high c l = 100pf (figures 4, 6), s2 closed l 2000 ns t zl(shdn) driver enable from shutdown to output low c l = 100pf (figures 4, 6), s1 closed l 2000 ns t zh(shdn) receiver enable from shutdown to output high c l = 15pf (figures 2, 8), s2 closed l 3500 ns t zl(shdn) receiver enable from shutdown to output low c l = 15pf (figures 2, 8), s1 closed l 3500 ns (figures 3, 5) (figures 3, 7)
4 ltc14 8 3 typical perfor m a n ce characteristics uw driver differential output voltage vs temperature temperature ( c) ?0 differential voltage (v) 2.5
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2.0
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1.5
0 50 75 1483 g04 ?5 25 100 125 r l = 54 w driver output high voltage vs output current output voltage (v) 0 output current (ma) 2 4 5 0
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?0 1483 g06 13 t a = 25 c pi n fu n ctio n s uuu 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. 4.75v < v cc < 5.25v. ro (pin 1): receiver output. if the receiver output is enabled (re low), then if a > b by 200mv, 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 m a) shutdown state. fu ctio tables uu ltc1483 transmitting inputs outputs re de di b a x1101 x1010 00xzz 1 0 x z* z* *shutdown mode for ltc1483 ltc1483 receiving inputs outputs re de a C b ro 00 3 0.2v 1 00 C 0.2v 0 0 0 inputs open 1 10 x z* *shutdown mode for ltc1483 output voltage 0
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0 3 1483 g05 12 4 output current (ma) t a = 25 c driver output low voltage vs output current
5 ltc148 3 test circuits switchi g ti e wavefor s uw w 3v de a b di r diff c l1 c l2 ro 15pf a b re ltc1483 ?f03 figure 3. driver/ receiver timing test circuit figure 4. driver timing test load output
under test c l s1 s2 v cc 500 w ltc1483 ?f04 v od a b r r v oc ltc1483 ?f01 receiver
output c rl
1k s1 s2 test point v cc 1k ltc1483 ?f02 figure 1. driver dc test load figure 2. receiver timing test load figure 6. driver enable and disable times 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 5v v ol v oh 0v a, b a, b ltc1483 ?f06 t r 10ns, t f 10ns figure 5. driver propagation delays di 3v 1.5v t plh t r t skew 1/2 v o v o 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) ltc1483 ?f05
6 ltc14 8 3 switchi g ti e wavefor s uw w 1.5v t phl ro ? od2 a ?b 0v 0v 1.5v t plh output input v od2 v ol v oh ltc1483 ?f07 t r 10ns, t f 10ns figure 7. receiver propagation delays 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 5v 0v ro ro ltc1483 ?f08 t r 10ns, t f 10ns figure 8. receiver enable and disable times applicatio s i for atio uu w u basic theory of operation traditionally rs485 transceivers have been designed us- ing bipolar technology because the common-mode range of the device must extend beyond the supplies and the device must be immune to esd damage and latch-up. unfortunately, most bipolar devices draw a large amount of supply current, which is unacceptable for the numerous applications that require low power consumption. the ltc1483 is a cmos rs485/rs422 transceiver which features ultra-low power consumption without sacrificing esd and latch-up immunity. the ltc1483 uses a proprietary driver output stage, which allows a common-mode range that extends beyond the power supplies while virtually eliminating latch-up and providing excellent esd protection. figure 9 shows the ltc1483 output stage while figure 10 shows a conven- tional cmos output stage. when the conventional cmos output stage of figure 10 enters a high impedance state, both the p-channel (p1) and the n-channel (n1) are turned off. if the output is then driven above v cc or below ground, the p+/n -well diode (d1) or the n+/p-substrate diode (d2) respectively will turn on and clamp the output to the supply. thus, the output stage is no longer in a high impedance state and is not able to meet the rs485 common-mode range require- ment. in addition, the large amount of current flowing through either diode will induce the well-known cmos latch-up condition, which could destroy the device. logic v cc sd3 p1 d1 output sd4 d2 n1 ltc1483 ?f09 figure 9. ltc1483 output stage logic v cc p1 d1 output d2 n1 ltc1483 ?f10 figure 10. conventional cmos output stage
7 ltc148 3 applicatio s i for atio uu w u the ltc1483 output stage of figure 9 eliminates these problems by adding two schottky diodes, sd3 and sd4. the schottky diodes are fabricated by a proprietary modi- fication to the standard n-well cmos process. when the output stage is operating normally, the schottky diodes are forward biased and have a small voltage drop across them. when the output is in the high impedance state and is driven above v cc or below ground, the parasitic diode d1 or d2 still turns on, but sd3 or sd4 will reverse bias and prevent current from flowing into the n-well or the sub- strate. thus the high impedance state is maintained even with the output voltage beyond the supplies. with no minority carrier current flowing into the n-well or sub- strate, latch-up is virtually eliminated under power-up or power-down conditions. the ltc1483 output stage will maintain a high impedance state until the breakdown of the n-channel or p-channel is reached when going positive or negative respectively. the output will be clamped to either v cc or ground by a zener voltage plus a schottky diode drop, but this voltage is well beyond the rs485 operating range. an esd cell protects output against multiple 10kv human body model esd strikes. because the esd injected current in the n-well or substrate consists of majority carriers, latch-up is pre- vented by careful layout techniques. slew rate the ltc1483 is designed for systems that are sensitive to electromagnetic radiation. the part features a slew rate limited driver that reduces high frequency electromag- netic emissions, while improving signal fidelity by reduc- ing reflections due to misterminated cables. figures 11 and 12 show the spectrum of the signal at the driver output for a standard slew rate rs485 driver and the slew rate limited ltc1483. the ltc1483 shows significant reduc- tion of the high frequency harmonics. because the driver is slew rate limited, the maximum operating frequency is limited to 250kbits/s. low power operation the ltc1483 is designed to operate with a quiescent current of 120 m a max. with the driver in three-state i cc will 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 circuits as described herein will not infringe on existing patent rights. 05 4 3 frequency (mhz) 2 1 20
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log magnitude (dbv rms ) drop to this 120 m a level. with the driver enabled there will be additional current drawn by the internal 12k resistor. under normal operating conditions this additional current is overshadowed by the current drawn by the external bus impedance. figure 12. slew rate limited ltc1483 driver output spectrum transmitting at 150khz figure 11. typical rs485 driver output spectrum transmitting at 150khz
8 ltc14 8 3 ? linear technology corporation 1994 lt/gp 1094 10k ? printed in the usa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7487 (408) 432-1900 l fax : (408) 434-0507 l telex : 499-3977 applicatio s i for atio uu w u 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 ltc1483 will enter shutdown mode when re is high and de is low. in shutdown the ltc1483 typically draws only 1 m 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. toggling either re or de will wake the ltc1483 back up within 3.5 m s. if the slow slew rate driver was active immediately prior to shutdown, the supply current will not drop to 1 m a until the driver outputs have reached a steady state; this can take as long as 2.6 m s under worst case conditions. if the driver was disabled prior to shutdown the supply current will drop to 1 m a immediately. related parts part number description comments ltc485 5v low power rs485 interface transceiver low power ltc1480 3.3v ultra-low power rs485 transceiver worlds first 3v powered 485 transceiver with low power consumption ltc1481 5v ultra-low power rs485 transceiver with shutdown lowest power ltc1485 5v differential bus transceiver highest speed ltc1487 5v ultra-low power rs485 with low emi shutdown high input impendance/low emi/lowest power and high input impendance dimension in inches (millimeters) unless otherwise noted. package descriptio n u n package 8-lead plastic dip n8 0695 0.005
(0.127)
min 0.100 0.010
(2.540 0.254) 0.065
(1.651)
typ 0.045 ?0.065
(1.143 ?1.651) 0.130 0.005
(3.302 0.127) 0.015
(0.380)
min 0.018 0.003
(0.457 0.076) 0.125
(3.175)
min
12 3 4 87 6 5 0.255 0.015*
(6.477 0.381)
0.400*
(10.160)
max 0.009 ?0.015
(0.229 ?0.381) 0.300 ?0.325
(7.620 ?8.255) 0.325 +0.025
0.015 +0.635
0.381 8.255 () *these dimensions do not include mold flash or protrusions.
mold flash or protrusions shall not exceed 0.010 inch (0.254mm) 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) 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) so8 0695 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)
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
*
** s package 8-lead plastic soic
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