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general description the max22500e/MAX22501E half-duplex esd-protected rs-485/rs-422 transceivers are optimized for high- speed (up to 100mbps) communication over long cables. these transceivers feature integrated hot-swap protection and a fail-safe receiver, ensuring a logic-high on the receiver output when input signals are shorted or open for longer than 10s (typ). the max22500e features integrated preemphasis circuitry that extends the distance and increases the data rate of reliable communication by reducing inter-symbol interference (isi) caused by long cables. the max22500e features a flexible logic interface down to 1.6v. the MAX22501E operates without preemphasis and is powered from a 3v to 5.5v supply. the max22500e is available in a 10-pin tdfn-ep package. the MAX22501E is available in a 8-pin tdfn-ep package. both transceivers operate over the -40c to +125c ambient temperature range. applications motion control encoder interfaces field bus networks industrial control systems backplane busses ordering information appears at end of data sheet. 19-100073; rev 0; 6/17 benefts and features high-speed operation over long distances ? up to 100mbps data rate ? integrated preemphasis extends cable length (max22500e) ? high receiver sensitivity ? wide receiver bandwidth ? symmetrical receiver thresholds integrated protection increases robustness ? -15v to +15v common mode range ? 15kv esd protection (human body model) ? 7kv iec 61000-4-2 air-gap esd protection ? 6kv iec 61000-4-2 contact discharge esd protection ? driver outputs are short-circuit protected flexibility for many different applications ? 3v to 5.5v supply range ? low voltage logic supply down to 1.6v (max22500e) ? low 5a (max) shutdown current ? available in 8-pin or 10-pin tdfn package ? -40c to +125c operating temperature range simplifed block diagram ro de di pset b a gnd vcc vl r d max 22500 e ro de di b a gnd vcc r d max 22501 e re shutdown re shutdown max22500e/MAX22501E 100mbps half-duplex rs-485/rs-422 transceivers for long cables evaluation kit available
tdfn8 package code t833-2 outline number 21-0137 land pattern number 90-0059 thermal resistance, single-layer board: junction to ambient ( ja ) 54c/w junction to case ( jc ) 8c/w thermal resistance, four-layer board: junction to ambient ( ja ) 41c/w junction to case ( jc ) 8c/w tdfn10 package code t1033-2 outline number 21-0137 land pattern number 90-0061 thermal resistance, single-layer board: junction to ambient ( ja ) 54c/w junction to case ( jc ) 9c/w thermal resistance, four-layer board: junction to ambient ( ja ) 41c/w junction to case ( jc ) 9c/w v cc ........................................................................ -0.3 v to +6 v re , de, di, vl .................................................... -0.3 v to +6 v ro (max22500e only) .............................. -0.3 v to (v l + 0.3) v ro (MAX22501E only) ............................. -0.3v to (v cc + 0.3)v pset ........................................................ -0.3 v to (v cc +0.3) v a, b ......................................................................... -15v to +15v short-circuit duration (ro, a, b) to gnd ................. continuous continuous power dissipation (t a = +70c) (8-pin tdfn (derate 24.4mw/c above +70c) ) .......................... 1951mw continuous power dissipation (t a = +70c) (10-pin tdfn (derate 24.4mw/c above +70c) ) .......................... 1951mw operating temperature range ........................ -40c to +125c junction temperature ..................................................... +150c storage temperature range ........................... -65c to +150c lead temperature (soldering 10sec) ............................. +300c reflow temperature ....................................................... +270oc absolute maximum ratings stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. these are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to ab solute maximum rating conditions for extended periods may affect device reliability. package thermal resistances were obtained using the method described in jedec specification jesd51-7, using a four-layer board. for detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial . for the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages . note that a +, #, or - in the package code indicates rohs status only. package drawings may show a different suffix character, but the drawing pertains to the package regardless of rohs status. package information maxim integrated 2 www.maximintegrated.com max22500e/MAX22501E 100mbps half-duplex rs-485/rs-422 transceivers for long cables
(v cc = 3v to 5.5v, v l = 1.6v to v cc (max22500e only), v l v cc , t a = t min to t max , unless otherwise noted (notes 1, 2)) parameter symbol conditions min typ max units power supply voltage v cc max22500e preemphasis disabled 3.0 5.5 v preemphasis enabled 4.5 5 5.5 MAX22501E 3.0 5.5 supply current i cc de = high, re = low, no load max22500e 12.7 16.5 ma MAX22501E 4 5.6 shutdown supply current i shdn de = low, re = high 5 a logic supply voltage v l max22500e only 1.6 v cc v logic supply current i l max22500e only, no load on ro 16.4 23 a driver differential driver output v od figure 1 , figure 2 r l = 54 1.5 v r l = 100 2.0 differential driver preemphasis ratio d pre max22500e only, preemphasis enabled, 4.5v v cc 5.5v (note 3) r l = 54 1.33 1.37 1.41 v/v r l = 100 1.33 1.37 1.41 change in magnitude of differential output voltage v od r l = 54, figure 1 (note 4) 0.2 v driver common-mode output voltage v oc r l = 54, normal mode and preemphasis, figure 1 v cc /2 3 v change in magnitude of common-mode voltage v oc r l = 100 or 54, figure 1 (note 4) 0.2 v single-ended driver output high v oh a or b output, i out = -20ma 2.2 v single-ended driver output low v ol a or b output, i out = +20ma 0.8 v differential output capacitance c od de = re = high, f = 4mhz 50 pf driver short-circuit output current |i ost | -15v v out +15v 250 ma receiver input current (a and b) i a,b de = gnd, v cc = gnd, +3.6v or 5.5v v in = +12v +1350 a v in = -7v -1100 differential input capacitance c a,b between a and b, de = gnd, f = 2mhz 50 pf common mode voltage range v cm -15 +15 v receiver differential threshold high v th_h -15v v cm +15v +50 +200 mv electrical characteristics maxim integrated 3 www.maximintegrated.com max22500e/MAX22501E 100mbps half-duplex rs-485/rs-422 transceivers for long cables
(v cc = 3v to 5.5v, v l = 1.6v to v cc (max22500e only), v l v cc , t a = t min to t max , unless otherwise noted (notes 1, 2)) parameter symbol conditions min typ max units receiver differential threshold low v th_l -15v v cm +15v -200 -50 mv receiver input hysteresis v th v cm = 0v, time from last transition is less than t d_fs 250 mv differential input fail-safe level v th_fs -15v v cm +15v -50 +50 mv logic interface ( re , ro, de, di) input voltage high v ih de, di, re max22500e 2/3xv l v MAX22501E 2/3 x v cc input voltage low v il de, di, re max22500e 1/3 x v l v MAX22501E 1/3 x v cc input current i in di and de, re (after frst transition) -2 +2 a input impedance on first transition r in_ft de, re 10 k ro output high voltage v oh re = gnd, (v a - v b ) > 200mv, i out = -1ma max22500e v l C 0.4 v MAX22501E v cc - 0.4 ro output low voltage v ol re = gnd, (v a C v b ) < -200mv, i out = +1ma 0.4 v three-state output current at receiver i ozr re = high, 0 v ro v cc -1 +1 a protection thermal shutdown threshold t sh temperature rising +160 c thermal shutdown hysteresis t sh_hys 10 c esd protection (a and b pins) human body model 15 kv iec61000-4-2 air gap discharge to gnd 7 iec61000-4-2 contact discharge to gnd 6 esd protection (all other pins) human body model 2 kv electrical characteristics (continued) maxim integrated 4 www.maximintegrated.com max22500e/MAX22501E 100mbps half-duplex rs-485/rs-422 transceivers for long cables
(v cc = 3v to 5.5v, v l = 1.6v to v cc (max22500e only), v l v cc , t a = t min to t max , unless otherwise noted (notes 1, 2)) parameter symbol conditions min typ max units driver (note 5) driver propagation delay t dplh r l = 54, c l = 50pf, figures 3 , 4 20 ns t dphl r l = 54, c l = 50pf, figures 3 , 4 20 differential driver output skew t dskew |t dplh C t dphl |, r l = 54, c l = 50pf, figures 3 , 4 (note 6) MAX22501E 1.2 ns max22500e, v l = v cc , v cc 3v 1.2 max22500e, v l v cc 1.6 driver differential output rise and fall time t hl , t lh r l = 54, c l = 50pf, figure 4 (note 6) 3 ns data rate dr 100 mbps driver enable to output high t dzh r l = 500, c l = 50pf, figures 5 , 6 30 ns driver enable to output low t dzl r l = 500, c l = 50pf, figures 5 , 6 30 ns driver disable time from low t dlz r l = 500, c l = 50pf, figures 5 , 6 30 ns driver disable time from high t dhz r l = 500, c l = 50pf, figures 5 , 6 30 ns driver enable from shutdown to output high t dzh(shdn) r l = 1k, c l = 15pf, figures 5 , 6 100 s driver enable from shutdown to output low t dzl(shdn) r l = 1k, c l = 15pf, figures 5 , 6 100 s time to shutdown t shdn (notes 7, 8) 50 800 ns driver preemphasis interval t pre max22500e only, 4.5v v cc 5.5v, r l = 100, figure 2 r pset = 4k 10 13 16 ns r pset = 400k 0.8 1 1.2 s receiver (note 5) delay to fail-safe operation t d_fs 10 s receiver propagation delay t rplh ,t rphl c l = 15pf, figure 7 , figure 8 20 ns receiver output skew t rskew |t rphl - t rplh |, c l = 15pf, figures 7 , 8 (note 6) 2.5 ns data rate dr 100 mbps receiver enable to output high t rzh r l = 1k, c l = 15pf, figure 9 30 ns receiver enable to output low t rzl r l = 1k, c l = 15pf, figure 9 30 ns receiver disable time from low t rlz r l = 1k, c l = 15pf, figure 9 30 ns receiver disable time from high t rhz r l = 1k, c l = 15pf, figure 9 30 ns electrical characteristics - switching maxim integrated 5 www.maximintegrated.com max22500e/MAX22501E 100mbps half-duplex rs-485/rs-422 transceivers for long cables
note 1: all devices are 100% production tested at t a = +25c. specifications for all temperature limits are guaranteed by design. note 2: all currents into the device are positive; all currents out of the device are negative. all voltages are referenced to device ground, unless otherwise noted. note 3: v odp is the differential voltage between a and b during the preemphasis interval on the max22500e, and is the differential voltage when preemphasis is disabled. v odp = d pre x v od . note 4: v od and v oc are the changes in v od and v oc , respectively, when the di input changes state. note 5: capacitive load includes test probe and fixture capacitance. note 6: not production tested. guaranteed by design. note 7: shutdown is enabled by driving re high and de low. the device is guaranteed to have entered shutdown after t shdn has elapsed. note 8: the timing parameter refers to the driver or receiver enable delay, when the device has exited the initial hot-swap protect state and is in normal operating mode. (v cc = 3v to 5.5v, v l = 1.6v to v cc (max22500e only), v l v cc , t a = t min to t max , unless otherwise noted (notes 1, 2)) parameter symbol conditions min typ max units receiver enable from shutdown to output high t rzh(shdn) r l =1k, c l =15pf, figure 9 100 s receiver enable from shutdown to output low t rzl(shdn) r l =1k, c l =15pf, figure 9 100 s time to shutdown t shdn (notes 7, 8) 50 800 ns figure 1: driver dc test load figure 2: driver preemphasis timing electrical characteristics - switching (continued) test circuits/diagrams v oc b a v od v odp r l 2 r l 2 t pre v od v odp a or b b or a 50 % max 22500 e only , preemphasis enabled v odp = d pre x v od maxim integrated 6 www.maximintegrated.com max22500e/MAX22501E 100mbps half-duplex rs-485/rs-422 transceivers for long cables
figure 3: driver timing test circuit figure 4: driver propagation delays figure 5: driver enable and disable times (t dzh , t dhz ) b a v od v odp r l c l de v cc di b a v od v l or v cc 0 vo - vo 0 50 % 50 % t dplh t dphl v od 10 % 90 % 90 % 10 % t lh t hl f = 1 mhz , t lh = 3 ns , t hl = 3 ns v od = ( v a - v b ) t dskew = | t dplh - t dphl | a b di c l r l out generator gnd or vcc 50 de out 0 v 0 v vl or vcc 50 % 50 % voh t dzh , t dzh ( shdn ) t dhz 0 . 25 v maxim integrated 7 www.maximintegrated.com max22500e/MAX22501E 100mbps half-duplex rs-485/rs-422 transceivers for long cables
figure 7: receiver propagation delay test circuit figure 8: receiver propagation delays figure 6: driver enable and disable times (t dzl , t dlz ) ate v id a b r a b v oh ro v ol + 1 v - 1 v t rphl t rplh 50% 50% t rskew = |t rphl C t rphl | a b di c l r l out generator gnd or v cc 50 de out 0 v vl or vcc 50 % 50 % v ol t dzl , t dzl ( shdn ) t dlz 0 . 25 v v cc vl or vcc maxim integrated 8 www.maximintegrated.com max22500e/MAX22501E 100mbps half-duplex rs-485/rs-422 transceivers for long cables
figure 9: receiver enable and disable times re ro 0 v 0 v vl or vcc 50 % v oh t rzh , t rzh ( shdn ) s 1 open s 2 closed s 3 = + 1 . 5 v re ro 0 v v ol vl or vcc 50 % v oh t rzl , t rzl ( shdn ) s 1 closed s 2 open s 3 = - 1 . 5 v c l 15 pf generator 50 + 1 . 5 v - 1 . 5 v vl or vcc s 1 s 2 s 3 v io r ro r l 1 k re ro 0 v 0 v vl or vcc 50 % v oh t rhz s 1 open s 2 closed s 3 = + 1 . 5 v re ro 0 v v ol vl or vcc 50 % vl or vcc t rlz s 1 closed s 2 open s 3 = - 1 . 5 v 0 . 25 v 0 . 25 v 50 % 50 % maxim integrated 9 www.maximintegrated.com max22500e/MAX22501E 100mbps half-duplex rs-485/rs-422 transceivers for long cables
v cc = 5v, v l = v cc (max22500e only), 60 termination between a and b, t a = 25c, unless otherwise noted. typical operating characteristics 0 2 5 5 0 7 5 1 0 0 1 2 5 1 5 0 0 . 1 1 1 0 1 0 0 i c c ( m a ) d a t a r a t e ( m bp s ) m a x 22500 e s u pp l y curr e n t vs . d a t a r a t e ( p r ee m p ha s i s e nab l e d ) t o c 0 1 n o l o a d 5 4 l o a d s q u a r e w ave o n d i ( 50 % du t y c y c l e ) pse t r es i s t o r a d j u s t e d f o r ea ch d a t a r a t e 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0 10 20 30 40 50 v ol (v) sink current (ma) ro output voltage low vs. load current toc04 (v a - v b ) < - 200mv v cc = 5v v cc = 3.3v 0 . 0 0 . 5 1 . 0 1 . 5 2 . 0 2 . 5 3 . 0 3 . 5 4 . 0 4 . 5 - 4 0 - 2 5 - 1 0 5 2 0 3 5 5 0 6 5 8 0 9 5 1 1 0 1 2 5 v o d ( v ) t e m pe r a t ur e ( o c ) d i ffe r e n t i a l dr i ve r o u t p u t v o lt a g e vs . t e m pe r a t ur e t o c 0 7 v c c = 5 v v c c = 3 . 3 v r l = 5 4 0 2 5 5 0 7 5 1 0 0 1 2 5 1 5 0 0 . 0 1 0 . 1 1 1 0 1 0 0 i cc ( m a ) d a t a r a t e ( m bp s ) m a x 22500 e s u pp l y curr e n t vs . d a t a r a t e ( p r ee m p ha s i s d i s ab l e d ) t o c 0 2 v c c = 5 v , n o l o a d v c c = 5 v , 5 4 l o a d v c c = 3 . 3 v , n o l o a d v c c = 3 . 3 v , 5 4 l o a d s q u a r e w ave o n d i ( 50 % du t y c y c l e ) 2.5 3.0 3.5 4.0 4.5 5.0 5.5 -50 -40 -30 -20 -10 0 v oh (v) source current (ma) ro output voltage high vs. load current toc05 v cc = 3.3v v cc = 5v (v a - v b ) > +200mv 0 2 5 5 0 7 5 1 0 0 1 2 5 1 5 0 0 . 0 1 0 . 1 1 1 0 1 0 0 i c c ( m a ) d a t a r a t e ( m bp s ) m a x 22501 e s u pp l y curr e n t vs . d a t a r a t e t o c 0 3 v c c = 5 v , n o l o a d v c c = 5 v , 5 4 l o a d v c c = 3 . 3 v , n o l o a d v c c = 3 . 3 v , 5 4 l o a d s q u a r e w ave o n d i ( 50 % du t y c y c l e ) 0 1 2 3 4 5 6 0 25 50 75 100 v od (v) load current (ma) differential driver output voltage vs. load current toc06 v cc = 5v v cc = 3.3v maxim integrated 10 www.maximintegrated.com max22500e/MAX22501E 100mbps half-duplex rs-485/rs-422 transceivers for long cables
v cc = 5v, v l = v cc (max22500e only), 60 termination between a and b, t a = 25c, unless otherwise noted. typical operating characteristics (continued) 0 2 4 6 8 1 0 1 2 1 4 1 6 1 8 2 0 - 4 0 - 2 5 - 1 0 5 2 0 3 5 5 0 6 5 8 0 9 5 1 1 0 1 2 5 dr i ve r p r o p a g a t i o n d e l a y ( n s ) t e m pe r a t ur e ( o c ) dr i ve r p r o p a g a t i o n d e l a y vs . t e m pe r a t ur e t o c 1 0 v c c = 5 v , t d pl h v c c = 3 . 3 v , t d p h l v c c = 3 . 3 v , t d pl h v c c = 5 v , t d p h l r l = 5 4 c l = 50 p f 0 . 0 0 . 5 1 . 0 1 . 5 2 . 0 2 . 5 3 . 0 3 . 5 4 . 0 4 . 5 5 . 0 - 4 0 - 2 5 - 1 0 5 2 0 3 5 5 0 6 5 8 0 9 5 1 1 0 1 2 5 t d ske w ( n s ) t e m pe r a t ur e ( o c ) dr i ve r p r o p a g a t i o n d e l a y s k e w vs . t e m pe r a t ur e t o c 1 1 v c c = 5 v v c c = 3 . 3 v r l = 5 4 c l = 50 p f 0 2 4 6 8 10 12 14 16 18 20 -40 -25 -10 5 20 35 50 65 80 95 110 125 receiver propagation delay (ns) temperature (oc) receiver propagation delay vs. temperature toc12 v cc = 5v, t rplh v cc = 3.3v, t rphl v cc = 3.3v, t rplh v cc = 5v, t rphl c l = 15pf dr i ve r p r e m p ha s i s ( m a x 22500 e ) d i 5 v / d i v v a - v b 2 v / d i v t o c 1 3 20n s / d i v 0 1 0 1 1 0 1 0 0 1 r l = 5 4 , c l = 10 p f , r se t = 8 k 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0 25 50 75 100 125 150 driver output voltage low (v) sink current (ma) driver output voltage low vs. load current toc08 v cc = 5v v cc = 3.3v di = gnd 2.0 2.5 3.0 3.5 4.0 4.5 5.0 -150 -125 -100 -75 -50 -25 0 driver output voltage high (v) source current (ma) driver output voltage high vs. load current toc09 v cc = 5v v cc = 3.3v di = v cc maxim integrated 11 www.maximintegrated.com max22500e/MAX22501E 100mbps half-duplex rs-485/rs-422 transceivers for long cables
pin name function max22500e MAX22501E 1 - v l logic supply input. v l defnes the interface logic levels on de, di and ro. apply a voltage between 1.6v to 5.5v to v l . bypass v l to ground with a 0.1f capacitor as close to the device as possible. 2 1 ro receiver output. see the receiving function table for more information. 3 3 de driver output enable. force de high to enable driver. pull de low to three-state the driver output. 4 2 re receiver enable. pull re high to disable and the receiver and tri-state ro. the device is in low-power shutdown when re = high and de = low. 5 4 di driver input. see the transmitting function table for more information. 6 - pset preemphasis select control input. connect a resistor from pset to gnd to select the preemphasis duration. see the layout recommendations in the applications information section for more information. to disable preemphasis, connect pset to gnd or v cc . 7 5 gnd ground 8 6 a noninverting receiver input/driver output 9 7 b inverting receiver input/driver output 10 8 v cc supply input. bypass v cc to ground with a 0.1f ceramic capacitor as close to the device as possible. pin confguration max 22500 e + ep tdfn - ep 3 m m x 3 m m top view 10 v cc 9 b 8 a 7 gnd 6 pset di 5 re 4 de 3 ro 2 v l 1 + max 22501 e top view 8 v cc 7 b 6 a 5 gnd 4 di 3 de 2 re 1 ro tdfn - ep 3 m m x 3 m m pin description maxim integrated 12 www.maximintegrated.com max22500e/MAX22501E 100mbps half-duplex rs-485/rs-422 transceivers for long cables
inputs outputs re de di a b x 1 1 1 0 x 1 0 0 1 0 0 x high impedance high impedance 1 0 x shutdown. a and b are high impedance x = dont care inputs outputs re de (v a - v b ) time from last a-b transition ro 0 x +200mv always 1 0 x -200mv < (v a - v b ) < +200mv < t d_fs indeterminate ro is latched to previous value 0 x -50mv < (v a - v b ) < +50mv > t d_fs 1 0 x -200mv always 0 0 x open/shorted > t d_fs 1 1 1 x x high impedance 1 0 x x shutdown. ro is high impedance ro de di pset b a re gnd vcc vl r d max 22500 e 3 . 3 v 5 v microcontroller 120 ro de di b a re gnd vcc r d max 22501 e 3 . 3 v 120 3 . 3 v microcontroller functional tables transmitting function table receiving function table half-duplex application circuit functional diagrams maxim integrated 13 www.maximintegrated.com max22500e/MAX22501E 100mbps half-duplex rs-485/rs-422 transceivers for long cables
detailed description the max22500e/MAX22501E esd-protected rs-485/ rs-422 transceivers are optimized for high-speed, half- duplex communications over long cables. both transceivers feature integrated hot-swap functionality to eliminate false transitions on the driver during power-up or during a hot- plug event. these transceivers also feature fail-safe receiver inputs, guaranteeing a logic-high on the receiver output when inputs are shorted or open for longer than 10s (typ). receiver threshold voltages the max22500e and MAX22501E receivers feature large threshold hysteresis of 250mv (typ) for increased differential noise rejection. additionally, the receivers feature symmetrical threshold voltages. symmetric thresholds have the advantage that recovered data at the ro output does not have duty cycle distortion. typically, fail-safe receivers, which have unipolar (non-symmetric) thresholds, show some duty cycle distortion at high signal attenuation due to long cable lengths. preemphasis (max22500e only) the max22500e features integrated driver preemphasis circuitry, which strongly improves signal integrity at high data rates over long distances by reducing inter-symbol interference (isi) caused by long cables. preemphasis is set by connecting a resistor (r pset ) between pset and ground. long cables attenuate the high-frequency content of transmitted signals due to the cable's limited bandwidth. this causes signal/pulse distortion at the receiving end, resulting in isi. isi causes jitter in data and clock recovery circuits. isi can be visualized by considering the following cases: if a series of ones (1's) is transmitted, followed by a zero (0), the transmission-line voltage has risen to a high value by the end of the string of ones. it takes longer for the signal to move toward the '0' state because the starting voltage on the line is so far from the zero crossing. similarly, if a data pattern has a string of zeros followed by a one and then another zero, the one-to-zero transition starts from a voltage that is much closer to the zero-crossing (v a - v b = 0) and it takes much less time for the signal to reach the zero crossing. preemphasis reduces isi by boosting the differential signal amplitude at every transition edge, counteracting the high frequency attenuation of the cable. when the di input changes from a logic-low to a logic-high, the differential output (v a - v b ) is driven high to v odp . at the end of the preemphasis interval, the differential voltage returns to a lower level (v od ). the preemphasis differential high voltage (v odp ) is typically 1.37 the v od voltage. if di switches back to a logic-low state before the preemphasis interval ends, the differential output switches directly from the 'strong' v odp high to a 'strong' low (-v odp ). driver behavior is similar when the di input changes from a logic-high to a logic-low. when this occurs, the differential output is pulled low to -v odp until the end of the preemphasis interval, at which point v a - v b = -v odp . setting the preemphasis interval connect a resistor (r pset ) between pset and gnd to set the preemphasis time interval on the max22500e. an optimum preemphasis interval ranges from 1 to 1.5 unit intervals (bit time). use the following equation to calculate the resistance needed on pset to achieve a 1.2 preemphasis interval: r pset = 400x10 9 /dr where dr is the data rate and 1mbps dr 100mbps. preemphasis only minimally degrades the jitter on the eye diagram when using short cables, making it reasonable to permanently enable preemphasis on systems where cable lengths may vary or change. figure 10 and figure 11 are eye diagrams taken at 100mbps over a 10m cat-5e cable. note that the eye varies only slightly as preemphasis is enabled or disabled. figure 12 and figure 13 show the driver eye diagrams over a long cable length. the max22500e was used as the driver and the eye diagrams were taken at the receiv - er input after a length of 100m cat-5e cable. figure 12 shows the signal at the receiver when the driver preem - phasis is disabled. figure 13 shows the receiver signal when preemphasis is enabled. fail-safe functionality the max22500e/MAX22501E feature fail-safe receiver inputs, guaranteeing a logic-high on the receiver output (ro) when the receiver inputs are shorted or open for longer than 10s (typ). when the differential receiver input voltage is greater than -50mv [(v a - v b ) -50mv] for more than 10s (typ), ro is logic-high. for example, in the case of a terminated bus with all transmitters disabled, the receivers differential input voltage is pulled to 0v by the termination resistor, so (v a - v b = 0v) > -50mv and ro is guaranteed to be a logic-high after 10s (typ). driver single-ended operation the a and b outputs on the max22500e/MAX22501E can be used in the standard differential operating mode or as single-ended outputs. because the driver outputs swing rail-to-rail, they can also be used as individual standard ttl logic outputs. maxim integrated 14 www.maximintegrated.com max22500e/MAX22501E 100mbps half-duplex rs-485/rs-422 transceivers for long cables
figure 11: eye diagram, 100mbps over 10m cat-5e cable, preemphasis enabled figure 10: eye diagram, 100mbps over 10m cat-5e cable, preemphasis disabled figure 13: eye diagram, 50mbps over 100m cat-5e cable, preemphasis enabled figure 12: eye diagram, 50mbps over 100m cat-5e cable, preemphasis disabled e y e d i a g r a m p r e e m p h a s i s e n a b l e d v a - v b 1 v / d i v 2 . 5 n s / d i v 1 0 0 m b p s , 1 0 m c a t - 5 e c a b l e p r e e m p h a s i s e n a b l e d e y e d i a g r a m p r e e m p h a s i s d i s a b l e d v a - v b 1 v / d i v 2 . 5 n s / d i v 1 0 0 m b p s , 1 0 m c a t - 5 e c a b l e p r e e m p h a s i s d i s a b l e d e y e d i a g r a m p r e e m p h a s i s d i s a b l e d v a - v b 7 0 0 m v / d i v 5 n s / d i v 5 0 m b p s , 1 0 0 m c a t - 5 e c a b l e p r e e m p h a s i s d i s a b l e d e y e d i a g r a m p r e e m p h a s i s e n a b l e d v a - v b 7 0 0 m v / d i v 5 n s / d i v 5 0 m b p s , 1 0 0 m c a t - 5 e c a b l e p r e e m p h a s i s e n a b l e d maxim integrated 15 www.maximintegrated.com max22500e/MAX22501E 100mbps half-duplex rs-485/rs-422 transceivers for long cables
hot-swap capability the de and re enable inputs feature hot-swap functionality. at each input there are two nmos devices, m1 and m2 ( figure 14 ). when v cc ramps from zero, an internal 10ms timer turns on m2 and sets the sr latch, which also turns on m1. transistors m2 (a 500a current sink) and m1 (a 100a current sink) pull de to gnd through a 5k resistor. m2 is designed to pull de to the disabled state against an external parasitic capacitance up to 100pf that can drive de high. after 10s, the timer deactivates m2 while m1 remains on, holding de low against three-state leakages that can drive de high. m1 remains on until an external source overcomes the required input current. at this time, the sr latch resets and m1 turns off. when m1 turns off, de reverts to a standard, high-impedance cmos input. whenever v cc drops below 1v, the hot-swap input is reset. there is a complimentary circuit for re that uses two pmos devices to pull re to v cc . driver output protection two mechanisms prevent excessive output current and power dissipation caused by faults or by bus contention. the first, a current limit on the output stage provides immediate protection against short circuits over the whole common-mode voltage range. the second, a thermal-shutdown circuit, forces the driver outputs into a high-impedance state if the die temperature exceeds +160c (typ). low-power shutdown mode the max22500e/MAX22501E feature a low-power shutdown mode to reduce supply current when the transceiver is not needed. pull the re input high and the de input low to put the device in low-power shutdown mode. if the inputs are in this state for at least 800ns, the parts are guaranteed to enter shutdown. the max22500e/ MAX22501E draw 5a (max) of supply current when the device is in shutdown. the re and de inputs can be driven simultaneously. the max22500e/MAX22501E are guaranteed not to enter shutdown if re is high and de is low for less than 50ns. applications information layout recommendations ensure that the preemphasis set resistor (r pset ) is located close to the pset and gnd pins in order to minimize interference by other signals. minimize the trace length to the pset resistor. additionally, place a ground plane under r pset and surround it with ground connections/ traces to minimize interference from the a and b switching signals. see figure 15 . network topology the max22500e/MAX22501E transceivers are designed for high-speed bidirectional rs-485/rs-422 data communications. multidrop networks can cause impedance discontinuities which affect signal integrity. maxim recom - mends using a point-to-point network topology ( figure 16 ), instead of a multidrop topology, when communicating with high data rates. terminate the transmission line at both ends with the cables characteristic impedance to reduce reflections. figure 14: simplified structure of the driver enable (de) pin 10 s vcc timer 5 k 100 a 500 a timer de de ( hot - swap ) maxim integrated 16 www.maximintegrated.com max22500e/MAX22501E 100mbps half-duplex rs-485/rs-422 transceivers for long cables
figure 15. sample pset resistor placement figure 16: point-to-point half-duplex communication for high speeds ro de di pset b a re gnd vcc vl r d max 22500 e ro b a gnd r d di 3 . 3 v 5 v microcontroller re de pset max 22500 e vcc 5 v 0 . 1 f 0 . 1 f maxim integrated 17 www.maximintegrated.com max22500e/MAX22501E 100mbps half-duplex rs-485/rs-422 transceivers for long cables
part preemphasis logic supply pin-package pin-pitch package code max22500eatb+ y y tdfn10-ep* 5mm t1033+2 max22500eatb+t y y tdfn10-ep* 5mm t1033+2 MAX22501Eata+ n n tdfn8-ep* 6.5mm t833+2 MAX22501Eata+t n n tdfn8-ep* 6.5mm t833+2 + denotes a lead (pb)-free/rohs-compliant package. * ep = exposed pad ordering information maxim integrated 18 www.maximintegrated.com max22500e/MAX22501E 100mbps half-duplex rs-485/rs-422 transceivers for long cables
revision number revision date description pages changed 0 6/17 initial release revision history ? 2017 maxim integrated products, inc. 19 maxim integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim integrated product. no circuit patent licenses are implied. maxim integrated reserves the right to change the circuitry and specifcations without notice at any time. the parametric values (min and max limits) shown in the electrical characteristics table are guaranteed. other parametric values quoted in this data sheet are provided for guidance. maxim integrated and the maxim integrated logo are trademarks of maxim integrated products, inc. max22500e/MAX22501E 100mbps half-duplex rs-485/rs-422 transceivers for long cables for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim integrateds website at www.maximintegrated.com.

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