1 ltc14 81 ultra-low power rs485 transceiver with shutdown s f ea t u re d u escriptio the ltc ? 1481 is an ultra-low power differential line trans- ceiver designed for data transmission standard rs485 applications. it will also meet the requirements of rs422. 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. the ltc1481 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 drivers/receivers have 10kv esd protection n 1 m a quiescent current in shutdown mode n high speed: up to 2.5mbits/s data rate n single 5v supply 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 30ns typical driver propagation delays with 5ns skew 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 temperature (?) ?0 supply current ( m a) 50 350
300
250
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150
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50
0 1481 ta02 0 25 25 75 125 175 150 100 driver enabled driver disabled thermal shutdown
with driver enabled v cc1
gnd1 r ro1
re1
de1
di1 d v cc2
gnd2 r ro2
re2
de2
di2 d rt rt ltc1481 ?ta01 supply current vs temperature , ltc and lt are registered trademarks of linear technology corporation.
2 ltc14 81 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 2.0 v 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 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 ltc1481cn8 ltc1481in8 ltc1481cs8 ltc1481is8 (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 ltc1481c ........................................ 0 c t a 70 c ltc1481i .................................... 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 1481 1481i 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
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
3 ltc14 81 v cc = 5v (notes 2, 3) unless otherwise noted. switchi g characteristics u symbol parameter conditions min typ max units t plh driver input to output r diff = 54 w , c l1 = c l2 = 100pf, l 10 30 60 ns t phl driver input to output l 10 30 60 ns t skew driver output to output l 510ns t r , t f driver rise or fall time l 31540ns t zh driver enable to output high c l = 100pf (figures 4, 6), s2 closed l 40 70 ns t zl driver enable to output low c l = 100pf (figures 4, 6), s1 closed l 40 70 ns t lz driver disable time from low c l = 15pf (figures 4, 6), s1 closed l 40 70 ns t hz driver disable time from high c l = 15pf (figures 4, 6), s2 closed l 40 70 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 2.5 mbits/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 40 100 ns t zl(shdn) driver enable from shutdown to output low c l = 100pf (figures 4, 6), s1 closed l 40 100 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) 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. typical perfor m a n ce characteristics uw 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. output voltage (v) 0 70
60
50
40
30
20
10
0 3 1481 g01 12 45 output current (ma) t a = 25? driver differential output voltage vs output current temperature (?) ?0 differential voltage (v) 2.5
2.4
2.3
2.2
2.1
2.0
1.9
1.8
1.7
1.6
1.5 0 50 75 1481 g02 ?5 25 100 125 r l = 54 w driver differential output voltage vs temperature driver output low voltage vs output current output voltage (v) 1 0
70
60
50
40
30
20
10
0 4 1481 g03 23 output current (ma) t a = 25?
4 ltc14 81 typical perfor m a n ce characteristics uw driver output high voltage vs output current output voltage (v) 0 output current (ma) 4 5 0
10
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50
60
70
80
?0 1481 g04 12 3 t a = 25? temperature (?) ?0
3.0
2.5
2.0
1.5
1.0
0.5
0 25 75 1481 g05 ?5 0 50 100 125 time (ns) temperature (?) ?0
14
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6
4
2
0 25 75 1481 g05 ?5 0 50 100 125 time (ns) driver skew vs temperature receiver ? t plh C t phl ? vs temperature fu ctio tables uu ltc1481 transmitting inputs outputs re de di b a x1101 x1010 00xzz 1 0 x z* z* *shutdown mode for ltc1481 ltc1481 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 ltc1481 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. pi n fu n ctio n s uuu 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.
5 ltc14 81 test circuits 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 ltc1481 ?f06 f = 1mhz, 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 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) ltc1481 ?f05 switchi g ti e wavefor s uw w output
under test c l s1 s2 v cc 500 w ltc1481 ?f04 3v de a b di r diff c l1 c l2 ro 15pf a b re ltc1481 ?f03 v od a b r r v oc ltc1481 ?f01 receiver
output c rl
1k s1 s2 test point v cc 1k ltc1481 ?f02 figure 2. receiver timing test load figure 4. driver timing test load figure 1. driver dc test load figure 3. driver/receiver timing test circuit
6 ltc14 81 switchi g ti e wavefor s uw w 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 ltc1481 ?f08 f = 1mhz, t r 10ns, t f 10ns applicatio s i for atio uu w u basic theory of operation traditionally, rs485 transceivers have been designed using 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 ltc1481 is a cmos rs485/rs422 transceiver which features ultra-low power consumption without sacrificing esd and latch-up immunity. the ltc1481 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 ltc1481 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. the ltc1481 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. 1.5v t phl ro ? od2 a ?b 0v 0v 1.5v t plh output input v od2 v ol v oh ltc1481 ?f07 f = 1mhz, t r 10ns, t f 10ns figure 7. receiver propagation delays figure 8. receiver enable and disable times
7 ltc14 81 applicatio s i for atio uu w u low power operation the ltc1481 is designed to operate with a quiescent current of 120 m a max. with the driver in three-state,i cc will drop to this 120 m a level. with the driver enabled there will be additional current drawn by the internal 12k resis- tor. under normal operating conditions this additional current is overshadowed by the current drawn by the external bus impedance. 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 ltc1481 will enter shutdown mode when re is high and de is low. in shutdown the ltc1481 typically draws only 1 m a of supply current. in order to guarantee that the part goes into shutdown, de must be low and re must be high 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 ltc1481 back up within 3.5 m s. 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 ltc1481 propagation delay. the receiver delay times are: ? t plh C t phl ? = 13ns typ, v cc = 5v the drivers skew times are: skew = 5ns typ, v cc = 5v 10ns max, v cc = 5v, t a = C 40 c to 85 c 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. d r receiver
out r
54 w 100pf 100pf ttl in
t r , t f < 6ns ltc1481 ?f11 figure 11. receiver propagation delay test circuit logic v cc sd3 p1 d1 output sd4 d2 n1 ltc1481 ?f09 esd logic v cc p1 d1 output d2 n1 ltc1481 ?f10 figure 9. ltc1481 output stage figure 10. conventional cmos output stage the ltc1481 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. because the esd injected current in the n-well or substrate consists of majority carriers, latch-up is prevented by careful layout techniques. an esd cell protects output against multiple 10kv human body model esd strikes.
8 ltc14 81 ? linear technology corporation 1994 lt/gp 0894 10k ? printed in usa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7487 (408) 432-1900 l fax : (408) 434-0507 l telex : 499-3977 package descriptio n u n8 package 8-lead plastic dip s8 package 8-lead plastic soic dimensions in inches (millimeters) unless otherwise noted. n8 0694 0.045 ?0.015
(1.143 ?0.381) 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 protursions 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 0294 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 *these dimensions do not include mold flash or protrusions.
mold flash or protrusions shall not exceed 0.006 inch (0.15mm).
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