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general description the MAX14938/max14939 isolated rs-485/profibus-dp transceivers provide 2750v rms (60s) of galvanic isolation between the cable side (rs-485 driver/receiver side) and the uart side of the device. isolation improves communication by breaking ground loops and reduces noise when there are large differences in ground potential between ports. these devices allow for robust communication up to 20mbps. an integrated ldo provides a simple and space-efficient architecture for providing power to the cable side of the ic. each device includes one half-duplex driver/receiver channel. the receiver is 1/4-unit load, allowing up to 128 transceivers on a common bus. integrated true fail-safe circuitry ensures a logic-high on the receiver output when inputs are shorted or open. undervoltage lockout disables the driver when cable-side or uart-side power supplies are below functional levels. the driver outputs/receiver inputs are protected from 35kv electrostatic discharge (esd) to gndb on the cable side, as specified by the human body model (hbm). the MAX14938/max14939 are available in a wide-body 16-pin soic package and operate over the -40c to +105c temperature range. benefts and features high-performance transceiver enables flexible designs ? integrated ldo for cable-side power ? compliant with rs-485 eia/tia-485 standard ? 20mbps maximum data rate ? allows up to 128 devices on the bus integrated protections ensures robust communication ? 35kv esd (hbm) on driver outputs/receiver inputs ? 2.75kv rms withstand isolation voltage for 60s (v iso ) ? 630v peak maximum repetitive peak-isolation voltage (v iorm ) ? 445v rms maximum working-isolation voltage (v iowm ) ? > 30 years lifetime at rated working voltage ? withstands 10kv surge per iec 61000-4-5 ? thermal shutdown safety regulatory approvals pending ul according to ul1577 cul according to csa bulletin 5a vde 0884-10 applications industrial automation equipment programmable logic controllers hvac power meters ordering information appears at end of data sheet. 19-8115; rev 0; 4/16 functional diagram ldo rs-485 transceiver vdda rxd re txd de a b vddb vldo gnda gndb (dem) MAX14938 max14939 (pv) sba + () MAX14938 only * max14939 only evaluation kit available MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection
v dda to gnda ...................................................... -0.3v to +6v v ddb to gndb ....................................................... -0.3v to +6v v ldo to gndb ..................................................... -0.3v to +16v txd, de, re , pv to gnda .................................... -0.3v to +6v sba , rxd to gnda ............................. -0.3v to (v dda + 0.3v) dem to gndb ...................................... -0.3v to (v ddb + 0.3v) a, b to gndb ...................................................... ..... -8v to +13v short circuit duration (rxd, sba to gnda, a, b, dem ,v ddb to gndb) .................................. continuous continuous power dissipation (t a = +70c) 16-pin w soic (derate 14.1mw/c above +70c) ......................................................... 1126.8mw operating temperature range ......................... -40c to +105c junction temperature ...................................................... +150c storage temperature range ............................ -65c to +150c lead temperature (soldering, 10s) ................................. +300c soldering temperature (reflow) ....................................... +260c junction-to-ambient thermal resistance ( ja ) .............. 71c/w junction-to-case thermal resistance ( jc ) ................... 23c/w (note 1) dc electrical characteristics (v dda C v gnda = 1.71v to 5.5v, v ddb C v gndb = 4.5v to 5.5v, t a = t min to t max , unless otherwise noted. typical values are at v dda C v gnda = 3.3v, v ddb C v gndb = 5v, v gnda = v gndb , and t a = +25c.) (notes 2, 3) parameter symbol conditions min typ max units power supply voltage v dda 1.71 5.5 v v ddb 4.5 5.5 supply current i dda v dda = 5v, de = high, re = txd = low, rxd unconnected, no load 4 6.6 ma i ddb de = high, re = txd = low, rxd unconnected, no bus load, v ddb = 5v 7.6 12.5 undervoltage-lockout threshold v uvloa v dda rising 1.50 1.58 1.65 v v uvlob v ddb rising 2.55 2.7 2.85 undervoltage-lockout threshold hysteresis v uvhysta 50 mv v uvhystb 200 ldo ldo supply voltage v ldo relative to gndb, ldo is on (note 4) 4.68 14 v ldo supply current i ldo de = high, txd = low, no bus load, v ldo = 5v 7.7 12.9 ma ldo output voltage v ddb 4.5 5 5.5 v ldo current limit 300 ma load regulation v ldo = 5.68v, i load = 20ma to 40ma 0.19 1.7 mv/ma line regulation v ldo = 5.68v to 14v, i load = 20ma 0.12 4.5 mv/v maxim integrated 2 note 1: 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 . 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 characteristics MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection www.maximintegrated.com
dc electrical characteristics (continued) (v dda C v gnda = 1.71v to 5.5v, v ddb C v gndb = 4.5v to 5.5v, t a = t min to t max , unless otherwise noted. typical values are at v dda C v gnda = 3.3v, v ddb C v gndb = 5v, v gnda = v gndb , and t a = +25c.) (notes 2, 3) parameter symbol conditions min typ max units dropout voltage v ldo = 4.68v, i ddb = 120ma 100 180 mv load capacitance nominal value (note 8) 1 10 f logic interface (txd, rxd, de, re, sba , pv, dem) input high voltage v ih re , txd, de, pv to gnda 2.25v < v dda < 5.5v 0.7 x v dda v 1.71v < v dda < 1.89v 0.78 x v dda input low voltage v il re , txd, de, pv to gnda 2.25v < v dda < 5.5v 0.8 v 1.71v < v dda < 1.89v 0.6 input hysteresis v hys re , txd, de, pv to gnda 220 mv input capacitance c in re , txd, de, pv, f sw = 1mhz 2 pf input pull-up current i pu txd, pv -10 -4.5 -1.5 a input pull-down current i pd de, re 1.5 4.5 10 a sba pull-up resistance r sba max14939 only 3 5 8 k output voltage high v oh rxd to gnda, i out = -4ma v dda -0.4 v MAX14938 only, dem to gndb, i out = -4ma v ddb -0.4 output voltage low v ol rxd to gnda, i out = 4ma 0.40 v MAX14938 only, dem to gndb, i out = 4ma 0.40 max14939 only, sba to gnda, i out = 4ma 0.45 short-circuit output pullup current i sh_pu 0v v rxd v dda , re = low -42 ma MAX14938 only, 0v v dem v ddb , de = high, pv = high -42 short-circuit output pulldown current i sh_pd 0v v rxd v dda , re = low +40 ma MAX14938 only, 0v v dem v ddb , de = low, pv = high +40 max14939 only, 0v v v dda , side b is powered and working +60 three-state output current i oz 0v v rxd v dda , re = high -1 +1 a maxim integrated 3 MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection www.maximintegrated.com
dc electrical characteristics (continued) (v dda C v gnda = 1.71v to 5.5v, v ddb C v gndb = 4.5v to 5.5v, t a = t min to t max , unless otherwise noted. typical values are at v dda C v gnda = 3.3v, v ddb C v gndb = 5v, v gnda = v gndb , and t a = +25c.) (notes 2, 3) parameter symbol conditions min typ max units driver differential driver output |v od | r l = 54, txd = high or low, figure 1a 2.1 v r l = 100, txd = high or low, figure 1a 2.9 -7v v cm +12v, figure 1b 1.5 5 differential driver peak-to-peak output v odpp figure 2 (note 5) 4.0 6.8 v change in magnitude of differential driver output voltage v od r l = 54 (note 6) -0.2 +0.2 v driver common mode output voltage v oc r l = 54, figure 1a 1.8 3 v change in magnitude of common-mode voltage v oc r l = 54, figure 1a (note 6) -0.2 +0.2 v driver short-circuit output current i osd gndb v out +12v, output low (note 7) +250 ma -7v v out v ddb , output high (note 7) -250 driver short-circuit foldback output current i osdf (v ddb C 1v) v out +12v, output low (note 7, 8) +15 ma -7v v out +1v, output high (note 7, 8) -15 receiver input current (a and b) i a , i b de = low, v ddb = gndb or 5.5v v in = +12v +250 a v in = -7v -200 receiver differential threshold voltage v th -7v v cm +12v -200 -125 -50 mv receiver input hysteresis v th v cm = 0v 15 mv receiver input resistance r in -7v v cm +12v, de = low 48 k differential input capacitance c a,b measured between a and b, de = re = low at 6mhz 8 pf maxim integrated 4 MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection www.maximintegrated.com
dc electrical characteristics (continued) (v dda C v gnda = 1.71v to 5.5v, v ddb C v gndb = 4.5v to 5.5v, t a = t min to t max , unless otherwise noted. typical values are at v dda C v gnda = 3.3v, v ddb C v gndb = 5v, v gnda = v gndb , and t a = +25c.) (notes 2, 3) switching electrical characteristics (v dda C v gnda = 1.71v to 5.5v, v ddb C v gndb = 4.5v to 5.5v, t a = t min to t max , unless otherwise noted. typical values are at v dda C v gnda = 3.3v, v ddb C v gndb = 5v, v gnda = v gndb , and t a = +25c.) (note 8) parameter symbol conditions min typ max units protection thermal-shutdown threshold t shdn temperature rising +160 c thermal-shutdown hysteresis t hyst 15 c esd protection (a and b pins to gndb) human body model 35 kv iec 61000-4-2 air gap discharge 12 iec 61000-4-2 contact discharge 10 esd protection (all other pins) human body model 4 kv parameter symbol conditions min typ max units dynamic common mode transient immunity cmti (note 9) 35 kv/s glitch rejection txd, de, rxd 10 17 29 ns driver driver propagation delay t dplh, t dphl r l = 54, c l = 50pf, figure 3 and figure 4 68 ns differential driver output skew |t dplh C t dphl | t dskew r l = 54, c l = 50pf, figure 3 and figure 4 6 ns driver differential output rise or fall time t lh , t hl r l = 54, c l = 50pf, figure 3 and figure 4 15 ns maximum data rate dr max 20 mbps driver enable to output high t dzh r l = 500, c l = 50pf, figure 5 88 ns maxim integrated 5 MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection www.maximintegrated.com
switching electrical characteristics (continued) (v dda C v gnda = 1.71v to 5.5v, v ddb C v gndb = 4.5v to 5.5v, t a = t min to t max , unless otherwise noted. typical values are at v dda C v gnda = 3.3v, v ddb C v gndb = 5v, v gnda = v gndb , and t a = +25c.) (note 8) note 2: all devices are 100% production tested at t a = +25c. specifications over temperature are guaranteed by design. note 3: all currents into the device are positive. all currents out of the device are negative. all voltages are referenced to their respective ground (gnda or gndb), unless otherwise noted. note 4: v ldo max indicates voltage capability of the circuit. power dissipation requirements may limit v ldo max to a lower value. note 5: v odpp is the difference in v od when txd is high and when txd is low. note 6: v od and v oc are the changes in v od and v oc , respectively, when the txd input changes state. note 7: the short circuit output current applies to the peak current just prior to foldback current limiting. note 8: not production tested. guaranteed by design. note 9: cmti is the maximum sustainable common-mode voltage slew rate while maintaining the correct output states. cmti applies to both rising and falling common-mode voltage edges. tested with the transient generator connected between gnda and gndb. v cm = 1kv. note 10: capacitive load includes test probe and fixture capacitance. parameter symbol conditions min typ max units driver enable to output low t dzl r l = 500, c l = 50pf, figure 6 88 ns driver disable time from low t dlz r l = 500, c l = 50pf, figure 6 80 ns driver disable time from high t dhz r l = 500, c l = 50pf, figure 5 80 ns receiver receiver propagation delay t rplh, t rphl c l = 15pf, figure 7 and 8 (note 10) 68 ns receiver output skew |t rplh - t rphl | t rskew c l = 15pf, figure 7 and 8 (note 10) 6 ns maximum data rate dr max 20 mbps receiver enable to output high t rzh r l = 1k, c l = 15pf, s2 closed, figure 9 20 ns receiver enable to output low t rzl r l = 1k, c l = 15pf, s1 closed, figure 9 30 ns receiver disable time from low t rlz r l = 1k, c l = 15pf, s1 closed, figure 9 20 ns receiver disable time from high t rhz r l = 1k, c l = 15pf, s2 closed, figure 9 20 ns maxim integrated 6 MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection www.maximintegrated.com
safety regulatory approvals (pending) insulation characteristics note 11: v iorm , v iowm , and v iso are defined by the iec 60747-5-5 standard. note 12: product is qualifi ed at v iso for 60 seconds. 100% production tested at 120% of v iso for 1 second. ul the MAX14938/max14939 is certifed under ul1577. for more details, see file e351759. rate up to 2750vrms isolation voltage for basic insulation. cul pending vde pending tuv pending parameter symbol conditions value units partial discharge test voltage v pr method b1 = v iorm x 1.875 (t = 1s, partial discharge < 5pc) 1182 v p maximum repetitive peak withstand voltage v iorm (note 11) 630 v p maximum working isolation voltage v iowm (note 11) 445 v rms maximum transient isolation voltage v iotm t = 1s 4600 v p maximum withstand isolation voltage v iso t = 60s, f = 60hz (note 11, 12) 2750 v rms maximum surge isolation voltage v iosm iec 61000-4-5, 1.2/50s 10 kv insulation resistance r s t a = +150c, v io = 500v >10 9 barrier capacitance input to output cio 2 pf creepage distance cpg wide so 8 mm clearance distance clr wide so 8 mm internal clearance distance through insulation 0.015 mm comparitive tracking resistance index cti material group ii (iec 60112) 575 climatic category 40/125/21 pollution degree (din vde 0110, table 1) 2 maxim integrated 7 MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection www.maximintegrated.com
figure 1. driver dc test load figure 2. v odpp swing under profibus equivalent load test r l 2 r l 2 v oc v od y z (a) 37 5 v cm y z (b) 37 5 + - 60 v od r l c l v od txd gnda a b 50% 50% gnda txd b a 20% 80% 20% 80% 0 v o -v o v diff t dskew = |t dplh - t dphl | v diff = v a - v b v dda f = 1mhz, t lh p 3ns, t hl p 3ns 1/2 v o t dplh t lh t hl t dphl v o 1/2 v o gndb txd a b gnda v ddb v dda 195i 110i v od 195i figure 3. driver timing test circuit figure 4. driver propagation delays maxim integrated 8 MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection www.maximintegrated.com
figure 5. driver enable and disable times (t dhz , t dzh ) figure 6. driver enable and disable times (t dzl , t dlz ) gnda gndb 250mv 50% t dzh t dhz de v dda v oh 50% out r l = 500i 50i out s1 a b d txd gnda or v dda gnda gndb generator de c l 50pf r l = 500i c l = 50pf 50i gndb gnda out gnda 250mv 50% t dzl t dlz de s1 a b d txd gnda or v dda v ddb v dda 50% out v ddb v ol generator de figure 7. receiver propagation delay test circuit v id b a receiver output ate r maxim integrated 9 MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection www.maximintegrated.com
figure 8. receiver propagation delays a b v oh v ol rxd t rphl t rskew = |t rphl - t rplh | f = 1mhz, t lh p 3ns, t hl p 3ns t rplh -1v 1v 2 v dda 2 v dda figure 9. receiver enable and disable times generator 50i r l 1ki c l 15pf r -1.5v +1.5v rxd s1 v dda gnda gndb gnda s2 s3 v id re re rxd re rxd re re rxd rxd gnda t rhz t rlz 0.25v 0.25v 50% 50% gnda gnda 2 s1 open s2 closed s3 = +1.5v s1 open s2 closed s3 = +1.5v s1 closed s2 open s3 = -1.5v s1 closed s2 open s3 = -1.5v v oh gnda gnda v oh v dda v dda v dda 50% 50% v dda t rzl v ol gnda v dda v dda v dda v ol t rzh 2 v dda maxim integrated 10 MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection www.maximintegrated.com
(v dda C v gnda = 3.3v, v ddb C v gndb = 5v, v gnda = v gndb , and t a = +25c, unless otherwise noted.) 0 5 10 15 20 25 30 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 source current (ma) output high voltage (v) receiver output current vs output high voltage toc04 0 1 2 3 4 5 6 7 8 -45 -30 -15 0 15 30 45 60 75 90 105 i dda (ma) temperature ( c) v dda supply current vs. temperature toc01 no load no switching -140 -120 -100 -80 -60 -40 -20 0 20 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 output current (ma) output high voltage (v) driver output current vs output high voltage toc07 0 2 4 6 8 10 12 14 -45 -30 -15 0 15 30 45 60 75 90 105 i ddb (ma) temperature ( c) v ddb supply current vs. temperature toc02 no load no switching 0 5 10 15 20 25 30 -45 -30 -15 0 15 30 45 60 75 90 105 propagation delay (ns) temperature ( c) transmitter propagation delay vs. temperature toc08 r l = 54 ? c l = 50pf t pdhl t pdlh 0 5 10 15 20 25 30 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 sink current (ma) output low voltage (v) receiver output current vs output low voltage toc03 0 5 10 15 20 25 30 35 40 45 50 -45 -30 -15 0 15 30 45 60 75 90 105 propagation delay (ns) temperature ( c) receiver propagation delay vs. temperature toc09 t rphl t rplh c l = 15pf 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 -45 -30 -15 0 15 30 45 60 75 90 105 vod (v) temperature ( c) differential output voltage vs. temperature toc05 no load 120? load 54? load 0 20 40 60 80 100 120 140 0 1 2 3 4 5 6 7 8 9 10 11 12 output current (ma) output low voltage (v) driver output current vs output low voltage toc6 maxim integrated 11 7slfdo2shudwljkdudfwhulvwlfv www.maximintegrated.com MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection
(v dda C v gnda = 3.3v, v ddb C v gndb = 5v, v gnda = v gndb , and t a = +25c, unless otherwise noted.) receiver propagation delay rxd 2v/div 0v b 1v/div a 1v/div toc12 10ns/div c l = 15pf 0 10 20 30 40 50 60 70 80 -45 -30 -15 0 15 30 45 60 75 90 105 enable/disable delay (ns) temperature ( c) driver enable/disable delay vs. temperature toc10 t dzh t dzl t dhz t dlz 0 10 20 30 40 50 60 70 80 0 5 10 15 20 i ddb (ma) data rate (mbps) v ddb supply current vs. data rate toc14 no load 54? load 120? load driver propagation delay txd 2v/div 0v a 1v/div b 1v/div toc11 10ns/div r l = 54 ? c l = 50pf 0 1 2 3 4 5 6 7 8 0 5 10 15 20 i dda (ma) data rate (mbps) v dda supply current vs. data rate toc13 maxim integrated 12 7slfdo2shudwljkdudfwhulvwlfvfrwlxhg www.maximintegrated.com MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection
pin name reference function MAX14938 max14939 1 1 v dda gnda uart/logic-side power input. bypass v dda to gnda with both 0.1f and 1f capacitors as close to the device as possible. 2, 8 2, 8 gnda - uart/logic-side ground. gnda is the ground reference for digital signals. 3 3 rxd gnda receiver data output. drive re low to enable rxd. with re low, rxd is high when (v a C v b ) > -50mv and is low when (v a C v b ) < -200mv. rxd is high when v ddb is less than v uvlob . rxd is high impedance when re is high. 4 4 re gnda receiver output enable. driver re low or connect to gnda to enable rxd. drive re high to disable rxd. rxd is high-impedance when re is high. re has an internal 4.5a pull-down to gnda. 5 5 de gnda driver output enable. drive de high to enable bus driver outputs a and b. drive de low or connect to gnda to disable a and b. a and b are high impedance when de is low. de has an internal 4.5a pull-down to gnda. 6 6 txd gnda driver input. with de high, a low on txd forces the noninverting output (a) low and the inverting output (b) high. similarly, a high on txd forces the noninvert - ing output high and the inverting output low. txd has an internal 4.5a pull-up to v dda . n.c. b re 1 2 16 15 v ddb gndb gnda rxd v dda wide soic 3 4 14 13 v ldo n.c. sba 5 12 a de txd 6 7 11 10 gndb gnda 8 9 max14939 + n.c. b re 1 2 16 15 v ddb gndb gnda rxd v dda top view 3 4 14 13 v ldo dem pv 5 12 a de txd 6 7 11 10 gndb gnda 8 9 MAX14938 + maxim integrated 13 pin confguration pin description MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection www.maximintegrated.com
pin name reference function MAX14938 max14939 7 - pv gnda power valid input. hold pv low to disable the driver while the supplies stabilize. pull pv high when power is stable to enable the driver. pv has an internal 4.5a pull-up to v dda . 7 sba gnda side b active indicator output. sba asserts low when side b is powered and working. sba has an internal 5k pull-up resistor to v dda . 9, 15 9, 15 gndb cable-side ground. gndb is the ground reference for the internal ldo, the dem output, and the profbus/rs-485 bus signals. 10 - dem gndb driver enable monitor output. dem is high when the transmitter is enabled. see the function tables for more information. 14 10, 14 n.c. no connection. not internally connected. 11 11 v ldo gndb ldo power input. connect a minimum voltage of 4.68v to v ldo to power the cable-side of the transceiver. bypass v ldo to gndb with both 0.1f and 1f capacitors as close to the device as possible. to disable the internal ldo, leave v ldo unconnected or connect to gndb. 12 12 a gndb noninverting receiver input and noninverting driver output 13 13 b gndb inverting receiver input and inverting driver output 16 16 v ddb gndb cable-side power input/isolated ldo power output. bypass v ddb to gndb with both 0.1f and 1f capacitor as close to the device as possible. v ddb is the output of the internal ldo when power is applied to v ldo . when the internal ldo is not used (v ldo is unconnected or connected to gndb), v ddb is the positive supply input for the cable-side of the ic. maxim integrated 14 pin description (continued) MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection www.maximintegrated.com
* note: drive de low to disable the transmitter outputs. drive de high to enable the transmitter outputs. de has an internal pull-down to gnda. ** MAX14938 only, x = dont care *note: drive re high to disable the receiver output. drive re low to enable to receiver output. re has an internal pulldown to gnda. x = dont care function tables transmitting inputs outputs v dda v ddb de txd pv** a b dem** v uvloa v uvlob 1 1 1 1 0 1 v uvloa v uvlob 1 0 1 0 1 1 v uvloa v uvlob 0 x x high-z high-z 0 < v uvloa v uvlob x x x high-z high-z 0 v uvloa < v uvlob x x x high-z high-z 0 < v uvloa < v uvlob x x x high-z high-z 0 receiving inputs outputs v dda v ddb re (v a - v b ) rxd v uvloa v uvlob 0 > -50mv 1 v uvloa v uvlob 0 < -200mv 0 v uvloa v uvlob 0 open/short 1 v uvloa v uvlob 1 x high-z < v uvloa v uvlob x x high-z v uvloa < v uvlob 0 x 1 < v uvloa < v uvlob x x high-z sba v dda v ddb sba < v uvloa < v uvlob high < v uvloa v uvlob high v uvloa < v uvlob high v uvloa v uvlob low maxim integrated 15 MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection www.maximintegrated.com
detailed description the MAX14938/max14939 isolated profibus-dp/ rs-485 transceivers provide 2750v rms (60s) of galvan- ic isolation between the profibus-dp/rs-485 cable - side of the transceiver and the uart side. these devices allow fast (20mbps) communication across an isolation barrier when a large potential exists between grounds on each side of the barrier. isolation data isolation is achieved using high-voltage capacitors that allow data transmission between the uart side and the profibus/rs-485 cable side of the transceiver. integrated ldo the MAX14938/max14939 include an internal low-drop - out regulator with a set 5v (typ) output that is used to power the cable-side of the ic. the output of the ldo is v ddb . in addition to powering the transceiver, v ddb can source up to 10ma, allowing external termination resistors to be powered without the need for an external regulator. the ldo has a 300ma (typ) current limit. if the ldo is unused, connect v ldo to gndb and apply +5v directly to v ddb . true fail-safe the MAX14938/max14939 guarantee a logic-high on the receiver output when the receiver inputs are shorted or open, or when connected to a terminated transmis - sion line with all drivers disabled. the receiver threshold is fixed between -50mv and -200mv. if the differential receiver input voltage (v a C v b ) is greater than or equal to -50mv, rxd is logic-high. in the case of a terminated bus with all transmitters disabled, the receivers differen - tial input voltage is pulled to zero by the termination resis - tors. due to the receiver thresholds of the MAX14938/ max14939, this results in a logic-high at rxd. driver output protection two mechanisms prevent excessive output current and power dissipation caused by faults or bus contention. the first, a foldback mode current limit on the output stage, provides immediate protection against short circuits over the entire 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). thermal shutdown the MAX14938/max14939 are protected from overtemperature damage by integrated thermal shutdown circuitry. when the junction temperature (t j ) exceeds +160c (typ), the driver outputs go high- impedance. the device resumes normal operation when t j falls below +145c (typ). applications information 128 transceivers on the bus the standard rs-485 receiver input impedance is one unit load. a standard driver can drive up to 32 unit-loads. the MAX14938/max14939 transceivers have a ?-unit load receiver, which allows up to 128 transceivers, connected in parallel, on one communication line. connect any com - bination of these devices, and/or other rs-485 devices, for a maximum of 32 unit-loads to the line. typical application the MAX14938/max14939 transceivers are designed for bidirectional data communications on multipoint bus transmission lines. figure 10 and figure 11 show typical network application circuits. to minimize reflections, the bus should be terminated at both ends in its characteristics impedance, and stub lengths off the main line should be kept as short as possible. maxim integrated 16 MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection www.maximintegrated.com
figure 10. typical isolated half-duplex rs-485 application rxd re txd de rs-485 transceiver a b rxd re txd de rs-485 transceiver a b rs-485 transceiver a b rxdretxd de rs-485 transceiver a b 120? 120? integrated isolation barrier MAX14938 max14939 rxdretxd de figure 11. typical isolated profibus application profibus a line profibus b line rxd re txd de rs-485 transceiver a b MAX14938 max14939 220? 390? 390? v ldo v ddb v dda 1 1 2 2 2 1f 1f 2 1f ldo 1 0.1f 2 0.1f 1f rxd re txd de rs-485 transceiver a b 220? 390? 390? v ddb v dda 3 3 3 4 4 1f v ldo 1f 3 MAX14938 max14939 3 0.1f 0.1f 4 ldo 2 0.1f 3 0.1f maxim integrated 17 MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection www.maximintegrated.com
profbus termination these devices are designed for driving profibus-dp terminated networks. the driver maintains 2.1v (min) when driving a worst-case loading condition of two standard 220 termination resistors with 390 pullups/ pulldowns. layout considerations it is recommended to design an isolation, or keep-out, channel underneath the isolator that is free from ground and signal planes. any galvanic or metallic connection between the cable-side and uart-side will defeat the isolation. ensure that the decoupling capacitors between v dda and gnda and between v ldo , v ddb , and gndb are located as close as possible to the ic to minimize inductance. route important signal lines close to the ground plane to minimize possible external influences. on the cable-side of the MAX14938/max14939, it is good practice to have the bus connectors and termination resistor as close as possible to the a and b pins. extended esd protection esd protection structures are incorporated on all pins to protect against electrostatic discharge encountered during handling and assembly. the driver outputs and receiver inputs of the MAX14938/max14939 have extra protection against static electricity to both the uart-side and cable-side ground references. the esd structures withstand high-esd events during normal operation and when powered down. after an esd event, the devices keep working without latch-up or damage. bypass v dda to gnda and bypass v ddb and v ldo to gndb with 0.1f and 1f capacitors to ensure maxi - mum esd protection. esd protection can be tested in various ways. the transmitter outputs and receiver inputs of the MAX14938/ max14939 are characterized for protection to the cable- side ground (gndb) to the following limits: 35kv hbm 12kv using the air-gap discharge method specifed in iec 61000-4-2 10kv using the contact discharge method speci - fed in iec 61000-4-2 esd test conditions esd performance depends on a variety of conditions. contact maxim for a reliability report that documents test setup, test methodology, and test results. human body model (hbm) figure 12 shows the hbm test model, while figure 13 shows the current waveform it generates when discharged in a low-impedance state. this model consists of a 100pf capacitor charged to the esd voltage of interest, which is then discharged into the test device through a 1.5k? resistor. iec 61000-4-2 the iec 61000-4-2 standard covers esd testing and performance of finished equipment. however, it does not specifically refer to integrated circuits. the MAX14938/ max14939 help in designing equipment to meet iec 61000-4-2 without the need for additional esd protection components. the major difference between tests done using the hbm and iec 61000-4-2 is higher peak current in iec 61000- 4-2 because series resistance is lower in the iec 61000- 4-2 model. hence, the esd withstand voltage measured to iec 61000-4-2 is generally lower than that measured using the hbm. figure 14 shows the iec 61000-4-2 model and figure 15 shows the current waveform for iec 61000-4-2 esd contact discharge test. maxim integrated 18 MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection www.maximintegrated.com
figure 12. human body esd test model figure 13. human body current waveform charge-current- limit resistor discharge resistance storage capacitor c s 100pf r c 1m r d 1500 high- voltage dc source device under test i p 100% 90% 36.8% t rl time t dl current waveform peak-to-peak ringing (not drawn to scale) i r 10% 0 0 amps figure 14. iec 61000-4-2 esd test model figure 15. iec 61000-4-2 esd generator current waveform charge-current- limit resistor discharge resistance storage capacitor c s 150pf r c 50m to 100m r d 330 high- voltage dc source device under test t r = 0.7ns to 1ns 30ns 60ns t 100% 90% 10% i peak i maxim integrated 19 MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection www.maximintegrated.com
ldo rs-485 transceiver v dda rxd txd de a b v ddb v ldo gnda (dem) gndb MAX14938 max14939 re isolation barrier c () MAX14938 only * max14939 only sba* (pv) typical application circuit maxim integrated 20 MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection www.maximintegrated.com
package information 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 type package code outline no. land pattern no. 16 soic w16m+9 21-0042 90-0107 ordering information/selector guide part dem pv sba temp range pin-package MAX14938gwe+ -40c to +105c 16 soic (w) MAX14938gwe+t -40c to +105c 16 soic (w) max14939gwe+ -40c to +105c 16 soic (w) max14939gwe+t -40c to +105c 16 soic (w) +denotes lead(pb)-free/rohs-compliant package. t = tape & reel maxim integrated 21 chip information process: bicmos MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection www.maximintegrated.com
revision history revision number revision date description pages changed 0 4/16 initial release ? 2015 maxim integrated products, inc. g 22 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. MAX14938/max14939 2.75kv rms isolated 20mbps half-duplex profibus/ rs-485 transceivers with 35kv esd protection 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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