general description the max3250 is a 3.0v to 5.5v powered, ?0v isolated eia/tia-232 and v.28/v.24 communications interface with high data-rate capabilities. the max3250 is a dual die part that operates with up to ?0v difference between the rs-232 side and the logic side (isocom to gnd). this makes the device ideal for operation in noisy conditions with high common-mode voltages. this feature prevents damage to the device if rs-232 lines are inadvertently short-circuited to a +24v or ?8v power bus. the max3250 is powered by a single 3v to 5.5v supply on the logic side. power is transferred from the logic side to the isolated side by ?00v external capacitors. the max3250 has two receivers (rx) and two drivers (tx) and is guaranteed to run at data rates of 250kbps while maintaining rs-232 output levels. the trans- ceivers have a proprietary low-dropout transmitter out- put stage, delivering true rs-232 performance from a 3v to 5.5v supply with a dual charge pump. the device features a fault open-drain output to signal an exces- sive isolated-side voltage condition on any of the rs- 232 inputs. this output can drive an alarm led or can be monitored by the processor to prevent operation under these conditions. the receiver outputs are high impedance in shutdown, allowing multiple interfaces (irda, rs-232, rs-485) to be connected to the same uart. the max3250 is available in a space-saving 28-pin ssop package. applications industrial control programmable logic controller point-of-sale equipment pc-to-router connections diagnostic ports telecom equipment features 50v isolation 20 a supply current in shutdown 250kbps guaranteed data rate fault output high-impedance transmitter and receiver outputs in shutdown space-saving ssop package inductorless/transformerless design simplifies emi compliance low-cost replacement for opto-isolated transceivers meets eia/tia-232 specifications down to 3.0v max3250 50v isolated, 3.0v to 5.5v, 250kbps, 2 tx/2 rx, rs-232 transceiver ________________________________________________________________ maxim integrated products 1 ordering information 19-2443; rev 3; 9/11 for pricing delivery, and ordering information please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. typical operating circuit appears at end of data sheet. part temp range pin-package max3250cai+ 0 c to +70 c 28 ssop max3250eai+ -40 c to +85 c 28 ssop 28 27 26 25 24 23 22 21 20 19 18 17 16 15 1 2 3 4 5 6 7 8 9 10 11 12 13 14 v cc c2- gnd fault shdn n.c. isocom n.c. c2+ isovcc r1in r2in t1out t2out v- c4- c4+ c3- v+ c3+ c1+ n.c. n.c. t2in t1in r2out r1out c1- ssop top view max3250 + pin configuration + denotes a lead(pb)-free/rohs-compliant package.
max3250 50v isolated, 3.0v to 5.5v, 250kbps, 2 tx/2 rx, rs-232 transceiver 2 _______________________________________________________________________________________ absolute maximum ratings stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. (all voltages referenced to gnd, unless otherwise noted.) v cc ...........................................................................-0.3v to +6v isocom...............................................................................?0v isovcc to isocom.................................................-0.3v to +6v v+ to isocom (note 1)............................................-0.3v to +7v v- to isocom (note 1)............................................+0.3v to -7v v+ + |v-| (note 1) ...................................................................13v input voltages t_in, shdn ...........................................................-0.3v to +6v r_in to isocom...............................................................?5v output voltages t_out to isocom ........................................................?3.2v r_out .....................................................-0.3v to (v cc + 0.3v) fault ....................................................................-0.3v to +6v c1-, c2- ......................................................-0.3v to (v cc + 0.3v) c1+, c2+, c3+, c3-, c4+, c4- to isocom .....................................-0.3v to (isovcc + 0.3v) t_out current ..............30ma (continuous), 50ma (peak, 10?) r_in current..................30ma (continuous), 50ma (peak, 10?) isocom current ...........30ma (continuous), 50ma (peak, 10?) short-circuit duration t_out to isocom .................continuous continuous power dissipation (t a = +70?) 28-pin ssop (derate 15mw/? above +70 ?) .......1201.2mw operating temperature ranges max3250cai .....................................................0? to +70? max3250eai...................................................-40? to +85? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) .................................+300? soldering temperature (reflow) .......................................+260? electrical characteristics (v cc = 3.0v to 5.5v, see typical operating circuit and table 1 for capacitor values, isocom = gnd, t a = t min to t max , unless oth- erwise noted. typical values are at v cc = 3.3v and t a = +25?.) (note 2) parameter conditions min typ max units dc characteristics supply current shdn = v cc , no load 15 35 ma shdn = gnd, v isocom = gnd 20 45 supply current shutdown shdn = gnd, v isocom = 50v 350 ? maximum ground differential | v gnd - v isocom | 50 v isolation resistance between gnd and isocom 60 k ? logic inputs input logic low t_in, shdn 0.8 v v cc = 3.3v 2.0 input logic high t_in, shdn v cc = 5.0v 2.4 v transmitter input hysteresis 0.5 v input leakage current t_in, shdn -1 0.01 +1 ? receiver outputs output leakage current shdn = gnd -10 0.05 +10 ? output-voltage low i out = 1.6ma 0.4 v output-voltage high i out = -1.0ma v cc - 0.6 v cc - 0.1 v fault output output-voltage low (open drain) i out = 5ma 0.4 v output leakage current fault not asserted 1 ? fault trip level | v gnd - v isocom | 55 v note 1: v+ and v- can have a maximum magnitude of 7v, but their absolute difference cannot exceed 13v.
max3250 50v isolated, 3.0v to 5.5v, 250kbps, 2 tx/2 rx, rs-232 transceiver _______________________________________________________________________________________ 3 electrical characteristics (continued) (v cc = 3.0v to 5.5v, see typical operating circuit and table 1 for capacitor values, isocom = gnd, t a = t min to t max , unless oth- erwise noted. typical values are at v cc = 3.3v and t a = +25?.) (note 2) parameter conditions min typ max units receiver inputs (relative to isocom) input-voltage range -25 +25 v v cc = 3.3v 1.2 0.6 input threshold low t a = +25? v cc = 5.0v 1.3 0.8 v v cc = 3.3v 2.4 1.6 input threshold high t a = +25? v cc = 5.0v 2.4 1.7 v input hysteresis 0.5 v input resistance t a = +25? 3 5 7 k ? transmitter outputs (relative to isocom) output-voltage swing all transmitter outputs loaded with 3k ? to isocom, t a = +25? 5.0 5.4 v output resistance isovcc = v+ = v- = 0v, v t_out = 2v 300 10m ? output short-circuit current -60 +60 ma output leakage current v cc = 0 or 3v to 5.5v, v t_out = 12v, shdn = gnd -25 +25 ? timing characteristics (v cc = 3.0v to 5.5v, see typical operating circuit and table 1 for capacitor values, isocom = gnd, t a = t min to t max , unless oth- erwise noted. typical values are at v cc = 3.3v and t a = +25?.) parameter conditions min typ max units maximum data rate r l = 3k ? , c l = 1000pf to isocom, one transmitter, t a = +25? 250 kbps receiver propagation delay r_in to r_out, c l = 150pf to gnd 0.4 ? receiver skew | t phl - t plh | 100 ns transmitter skew | t phl - t plh | (note 3) 120 ns c l = 150pf to 1000pf to isocom 630 transition-region slew rate v cc = 3.3v, t a = +25?, r l = 3k ? to 7k ? to isocom, measured from +3v to -3v or -3v to +3v c l = 150pf to 2500pf to isocom 430 v/? fault propagation delay 0.3 ? time to shutdown 0.5 ? v isocom = gnd 300 time to exit shutdown v isocom = 50v 350 ? 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: transmitter skew is measured at the transmitter zero crosspoints.
max3250 50v isolated, 3.0v to 5.5v, 250kbps, 2 tx/2 rx, rs-232 transceiver 4 _______________________________________________________________________________________ typical operating characteristics (v cc = 3.3v, 250kbps data rate, see typical operating circuit and table 1 for capacitor values, all transmitters loaded with 3k ? and c l to isocom, t a = +25?, unless otherwise noted.) max3250 toc05 temperature ( c) supply current ( a) 60 35 10 -15 -200 -100 0 100 200 300 400 -300 -40 85 shutdown current vs. temperature isocom = -50v isocom = 0v isocom = +50v time to exit shutdown v isocom = 0v tout 5v/div max3250 toc04 100 s/div shdn 5v/div max3250 toc03 load capacitance (pf) supply current (ma) 4000 3000 2000 1000 10 20 30 40 50 60 70 80 90 0 0 5000 t1 transmitting at 250kbps t2 transmitting at 20kbps operating supply current vs. load capacitance 250kbps 120kbps 20kbps max3250 toc02 load capacitance (pf) slew rate (v/ s) 4000 3000 2000 1000 5 10 15 20 25 30 0 0 5000 slew rate vs. load capacitance -slew +slew for data rates up to 250kbps max3250 toc01 load capacitance (pf) transmitter output voltage (v) 4000 3000 2000 1000 -4 -2 0 2 4 6 8 -6 0 5000 transmitter output voltage vs. load capacitance v out+ v out- t1 transmitting at 250kbps t2 transmitting at 20kbps common-mode fault response isocom 50v/div max3250 toc07 fault 5v/div 4ms/div peak ground offset voltage vs. frequency max3250 toc06 frequency (hz) peak ground offset ( v) 300 100 200 400 500 10 20 30 40 50 60 0 0600 v cc = 3.3v v cc = 5v
max3250 50v isolated, 3.0v to 5.5v, 250kbps, 2 tx/2 rx, rs-232 transceiver _______________________________________________________________________________________ 5 pin description pin name function 1 c1- negative terminal of the power isolation capacitor. connect a 100v capacitor from c1- to c1+. see table 1 for values. 2 r1out ttl/cmos receiver output 3 r2out ttl/cmos receiver output 4 t1in ttl/cmos transmitter input 5 t2in ttl/cmos transmitter input 6, 22, 23 n.c. no connection. not internally connected. 7 n.c. no connection. leave unconnected or connect to isocom. 8 c1+ positive terminal of the power isolation capacitor. connect a 100v capacitor from c1+ to c1-. see table 1 for values. 9 c3+ positive terminal of the voltage-doubler charge-pump capacitor. connect a 0.1? capacitor from c3+ to c3-. 10 v+ +5.5v generated by the charge pump, referenced to isocom. bypass v+ to isocom with a 0.47? capacitor. 11 c3- negative terminal of the voltage-doubler charge-pump capacitor. connect a 0.1? capacitor from c3- to c3+. 12 c4+ positive terminal of the inverting charge-pump capacitor. connect a 0.47? capacitor from c4+ to c4-. 13 c4- negative terminal of the inverting charge-pump capacitor. connect a 0.47? capacitor from c4- to c4+. 14 v- -5.5v generated by the charge pump, referenced to isocom. bypass v- to isocom with a 0.47? capacitor. 15 isocom isolated ground 16 t2out rs-232 transmitter output 17 t1out rs-232 transmitter output 18 r2in rs-232 receiver input 19 r1in rs-232 receiver input 20 isovcc internally generated isolated power-supply voltage, referenced to isocom. bypass isovcc to isocom with a 2.2? capacitor. 21 c2+ positive terminal of the power isolation capacitor. connect a 100v capacitor from c2+ to c2-. see table 1 for values. 24 shdn shutdown control. drive shdn low to enter low-power shutdown mode. drive shdn high or connect to v cc for normal operation. 25 fault overvoltage indicator. active low, open drain. 26 gnd ground 27 c2- negative terminal of the power isolation capacitor. connect a 100v capacitor from c2- to c2+. see table 1 for values. 28 v cc 3.0v to 5.5v supply voltage. bypass v cc to gnd with a 1? capacitor.
max3250 50v isolated, 3.0v to 5.5v, 250kbps, 2 tx/2 rx, rs-232 transceiver 6 _______________________________________________________________________________________ detailed description the max3250 is a 3.0v to 5.5v powered, ?0v isolated eia/tia-232 and v.28/v.24 communications interface with high data-rate capabilities. the max3250 is a dual die part that operates with up to ?0v difference between the rs-232 side and the logic side (isocom to gnd). this makes the device ideal for operation in noisy conditions with high common-mode voltages. this feature prevents damage to the device if rs-232 lines are inadvertently short-circuited to a +24v or ?8v power bus. the max3250 typically draws 15ma of supply current when unloaded. supply current drops to 20? when the device is placed in shutdown mode. the max3250 has two receivers and two drivers and is guaranteed to operate at data rates up to 250kbps. the device features a fault open-drain output to signal an excessive isolated-side voltage condition on any of the rs-232 inputs. this output can drive an alarm led or can be monitored by the processor to prevent operation under these conditions. the receiver outputs are high impedance in shutdown, allowing multiple interfaces (irda, rs-232, rs-485) to be connected to the same uart (figure 1). the max3250 is a low-cost replacement for opto-isolated transceivers. isolated power supply the max3250 drives a high-frequency square wave into c1 and a complementary square wave into c2. these power controller fault shdn gnd c1- c2- c1+ c2+ isocom tout2 rin2 isovcc c3+ c3- c4+ c4- v+ v- tin1 rout1 rout2 tin2 tout1 rin1 rs-232 charge pump v cc max3250 fault detector osc figure 1. functional diagram
max3250 50v isolated, 3.0v to 5.5v, 250kbps, 2 tx/2 rx, rs-232 transceiver _______________________________________________________________________________________ 7 ac waveforms are rectified on the isolated side of the dual die to power its internal circuitry (isovcc). capacitor c6 filters the output of the rectifier. see the typical operating circuit . the power controller works in a dual power mode. power is maximum when the isolated power supply is below its regulation point. power is reduced when the isolated power supply is above its regulation point. dual charge-pump voltage converter the rs-232 drivers are powered from a regulated dual charge pump that provides output voltages of +5.5v (dou- bling charge pump) and -5.5v (inverting charge pump) relative to isocom over the 3.0v to 5.5v v cc range. the charge pumps are powered from isovcc and operate in a discontinuous mode. if the output voltages are less than 5.5v, the charge pumps are enabled. if the output voltages exceed 5.5v, the charge pumps are disabled. each charge pump requires a flying capacitor (c3, c4) and a reservoir capacitor (c7, c8) to generate the v+ and v- supplies. rs-232 transmitters the transmitters are inverting level translators that convert ttl/cmos-logic levels to ?.0v eia/tia-232-compliant levels. they guarantee a 250kbps data rate with worst- case loads of 3k ? in parallel with 1000pf to isocom. in shutdown, the transmitters are disabled and the outputs are forced into a high-impedance state. when powered off or shut down, the outputs can be driven up to ?2v relative to isocom. the transmitter inputs do not have pullup resistors. all unused inputs should be connected to v cc or gnd. rs-232 receivers the receivers convert rs-232 signals to cmos-logic output levels. the receivers?outputs are forced into a high-impedance state when the device is in shutdown. this allows a single uart to multiplex between differ- ent protocols. low-power shutdown mode shutdown mode is obtained by driving shdn low. in shutdown, the devices typically draw only 20? of sup- ply current and no power is transferred across the iso- lation capacitors. the charge pumps are disabled, and the receiver outputs and transmitter outputs are high impedance. when exiting shutdown the charge pumps and transmitter outputs are fully operational in typically 500? (figure 3). connect shdn to v cc if the shut- down mode is not used. applications information power isolation capacitors the values for capacitors c1 and c2 are important for proper operation of the device. these capacitors should be 0.047? for 4.5v to 5.5v operation, and 0.47? for 3.0v to 3.6v operation. smaller values result in insufficient supply voltage on the isolated side. larger values are not allowed. capacitor c9 provides an ac feedback path for proper controller operation. connect c9 from isocom to gnd. the values for c1, c2, and c9 determine the maximum frequency and amplitude of the voltage difference between the local and isolated ground. table 1 shows proper capacitance values. load current per transmitter (ma) transmitter output voltage (v) 7 6 4 5 2 3 1 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 -6 08 v cc = 3.0v v out+ v out- t1 t2 v cc v out1+ v out2- figure 2. transmitter output voltage vs. load current per transmitter 100 s/div 2v/div t2out v cc = 3.3v shdn 5v/div t1out figure 3. transmitter outputs when exiting shutdown or powering up
max3250 50v isolated, 3.0v to 5.5v, 250kbps, 2 tx/2 rx, rs-232 transceiver 8 _______________________________________________________________________________________ to achieve full isolation capability, c1, c2, and c9 should be rated for 100v or higher operation and be x7r or x5r type or metalized film dielectric. y5v and z5u dielectrics should be avoided as their voltage and tem- perature coefficients make their power-transfer capabili- ties insufficient. charge-pump and bypass capacitors capacitors c3?8 should be x7r or x5r type dielec- tric. their voltage rating needs to be 10v or higher. layout information because the max3250 is intended for systems requir- ing ?0v isolation, some consideration in component placement is necessary. a 20mil air gap should isolate the logic side and the isolated rs-232 side, across the n.c. pins (pin num- bers 6, 7, 22, and 23) of the max3250. the only com- ponents that cross this air gap should be c1, c2, and c9, which should all have a minimum 100v rating. all capacitors should be located as close to the max3250 as possible. maximum voltage between isocom and logic gnd high values of applied isolation voltage and frequency can cause ripple on isovcc, v+, v-, and in extreme cases on v cc . therefore, it is recommended that the isolation-voltage and frequency be limited to the values shown in the typical operating characteristics . insert a 1k ? 1/4w resistor in series with any isolation test voltage when testing for maximum values of applied isolation voltage. exceeding the maximum lim- its of voltage and frequency (see the typical operating characteristics ) could trigger a holding current in the internal esd-protection device if the ?0v isolation limit is exceeded. this resistor should not be used in normal application. transmitter outputs when exiting shutdown figure 3 shows two transmitter outputs when exiting shutdown mode. as they become active, the two trans- mitter outputs are shown going to opposite rs-232 lev- els (one transmitter input is high, the other is low). each transmitter is loaded with 3k ? in parallel with 2500pf. the transmitter outputs display no ringing or undesir- able transients as they come out of shutdown. note that the transmitters are enabled only when the magnitude of v- exceeds approximately -3v. v cc (v) c1, c2 ( f) c3 (?) c4, c7, c8 (?) c5 (?) c6 (?) c9 (nf) 3.0 to 3.6 0.47 0.1 0.47 1 2.2 10 4.5 to 5.5 0.047 0.1 0.47 1 2.2 10 table 1. required capacitor values
max3250 50v isolated, 3.0v to 5.5v, 250kbps, 2 tx/2 rx, rs-232 transceiver _______________________________________________________________________________________ 9 chip information process: bicmos rin1 tout1 gnd v cc isocom v- isovcc v+ rin2 tout2 tin1 rout1 tin2 rout2 c1- c1+ c2- c2+ c4+ c4- c3+ c3- cable v cc c5 1 f c1 0.47 f gnd offset remote ground max3250 fault shdn micro c2 0.47 f c9 10nf 50v c6 2.2 f c8 0.47 f c7 0.47 f c4 0.47 f c3 0.1 f remote micro remote xcvr typical operating circuit package information for the latest package outline information and land patterns (footprints), go to www.maxim-ic.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. 28 ssop a28m+3 21-0056 90-0095
max3250 50v isolated, 3.0v to 5.5v, 250kbps, 2 tx/2 rx, rs-232 transceiver maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications 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 guidanc e. 10 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2011 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. revision history revision number revision date description pages changed 0 4/02 initial release 1 2/03 updated design 2 1/08 updated ec table 3 3 9/11 added lead-free packaging information; corrected pin names, power dissipation, and soldering temperature in absolute maximum ratings ; updated capacitor values in data sheet. 1, 2, 3, 5?
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