19-1405; Rev 0; 10/98 General Description The MAX3291/MAX3292 high-speed RS-485/RS-422 transceivers feature driver preemphasis circuitry, which extends the distance and increases the data rate of reli- able communication by reducing intersymbol interfer- ence (ISI) caused by long cables. The MAX3291 is programmable for data rates of 5Mbps to 10Mbps, while the MAX3292 is programmable for data rates up to 10Mbps by using a single external resistor. The MAX3291/MAX3292 are full-duplex devices that operate from a single +5V supply and offer a low-cur- rent shutdown mode that reduces supply current to 100nA. They feature driver output short-circuit current limiting and a fail-safe receiver input that guarantees a logic-high output if the input is open circuit. A 1/4-unit- load receiver input impedance allows up to 128 trans- ceivers on the bus. Applications Long-Distance, High-Speed RS-485/RS-422 Communications Telecommunications Industrial-Control Local Area Networks MA AXILM RS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication Features @ Preemphasis Increases the Distance and Data Rate of Reliable RS-485/RS-422 Communication Data Rate Optimized for 5Mbps to 10Mbps (MAX3291) Programmable up to 10Mbps (MAX3292) ---.hU OHmhCU OH 100nA Low-Current Shutdown Mode Allow Up to 128 Transceivers on the Bus -7V to +12V Common-Mode Input Voltage Range Pin-Compatible with 75180, MAX489, MAX491 MAX3080, MAX3083, MAX3086, MAX1482 Ordering Information PART TEMP. RANGE PIN-PACKAGE MAX3291CSD 0C to +70C 14S0 MAX3291 CPD 0C to +70C 14 Plastic DIP MAX3291ESD -40C to +85C 14S0 MAX3291EPD -40C to +85C 14 Plastic DIP MAX3292CSD 0C to +70C 14S0 MAX3292CPD 0C to +70C 14 Plastic DIP MAX3292ESD -40C to +85C 14S0 MAX3292EPD -40C to +85C 14 Plastic DIP Typical Operating Circuit and Functional Diagram Reser* Peser* fed oom offend SEM PEE | Cpser" = PEE | Cpser* = (PSET) | 1 Voc| 14 (PSE) | 4 Voc} 14 13 (Veco) L2 (eco) A]12_ R=Zo R=Zo 9] Y 2 RO <1 TW OCC eww 10 1 > DI By ti Z ; me + DE ne LS PE 5 Z|10 _ R=Z R=Z 1148 p14 PW OC TM, 12 Le Yo A MAXIM MAXIM (_) ARE FOR MAXS292 MAX3201 MAX3201 MAX3292 ONLY MAXI292 MAX3292 Zp = THE CHARACTERISTIC IMPEDANCE OF THECABLE 7(6) | GND 7(6) | GND Pin Configuration appears at end of data sheet. MAXIMA Maxim Integrated Products 1 For free samples & the latest literature: http:/1vwww.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 1-800-835-8769. COCEXVW/LECEXVWNMAX3291/MAX3292 RS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication ABSOLUTE MAXIMUM RATINGS Supply Voltage (VCC, VCCD) oicetesti ieee nsesieneaseenees +6V Operating Temperature Ranges Control Input Voltage (RE, DE, PEE, MAX829_C Danie ceecccecesssessceeceseesessssssaeeeeneeeesseees 0C to +70C PSET, DI) woes eee eeeee nse enenee -0.3V to (Vcc + 0.3V) MAX329_E Duce eee nee eeeeee nee w- 40C to +85C Driver Output Voltage (Y, Z) ..ceeeeeeee eee -7.5V to +12.5V Storage Temperature Range..........00 ..-65C to +160C Receiver Input Voltage (A, B)....... eee -7.5V to +12.5V Lead Temperature (soldering, 10S@C) ....... cece +300C Receiver Output Voltage (RO)... -0.3V to (Vcc + 0.3V) Continuous Power Dissipation (Ta = +70C) 14-Pin SO (derate 8.7mMW/C above +70C)......c eee 695mW 14-Pin Plastic DIP (derate 10.0mW/C above +70C) ..800mW 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 absolute maximum rating conditions for extended periods may affect device reliability. DC ELECTRICAL CHARACTERISTICS (Typical Operating Circuit, Vcc = +5V 45%, RpseT = 0 (MAX3292), Vcc = VecD (MAX3292), TA = TMIN to TMAX, unless otherwise noted. Typical values are at Vcc = +5V and Ta = +25C.) (Note 1) PARAMETER | SYMBOL | CONDITIONS | MIN TYP MAX | UNITS DRIVER . . . . R= 272 1.5 5.0 Differential Driver Output VoD Figure 1 No load (Note 2) 525 Vv jo load (Note . Differential Driver Output with Preemphasis Vopp | R= 27 2.4 V Differential Driver DPER | Figure 1, R = 272 (Note 3) 165 20 235 Vv Preemphasis Ratio Change in Magnitude of AV, Differential Output Voltage AVooe Figure 1, R = 272 (Note 4) 0.2 Vv (Normal and Preemphasis) Driver Common-Mode Output Voltage (Normal and Voc Figure 1, R= 27Q Vec/2 3 Vv Preemphasis) Change in Magnitude of Common-Moade Voltage AVoc Figure 1, R= 27Q (Note 5) 0.3 Vv (Normal and Preemphasis) Change in Magnitude of Common-Mode Output Voltage (Normal to AVNP Figure 1, R= 27Q 50 mV Preemphasis) . DE, DI, RE 2.4 Input High Voltage VIH PEE 375 Vv Input Low Voltage VIL DE, DI, RE, PEE 0.8 Vv Input Current IIN DE, DI, RE +2 pA PEE Input Current (MAX3291) IPEE -15 -30 -45 HA PSET Input Current (MAX3292) IPSET VpseET = Voc 70 110 HA Output Leakage (Y and Z) lo Voon al NI D or 5.25V a 7 = = = HA Driver Short-Circuit Output losp_| -7V< VouT< +12V (Note 6) +30 +250 mA Current 2 MA AXIAARS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication DC ELECTRICAL CHARACTERISTICS (continued) (Typical Operating Circuit, Voc = +5V 5%, RPSET = 0 (MAX3292), Vcc = Vocb (MAX3292), Ta = TMIN to TMAX, unless otherwise noted. Typical values are at Vcc = +5V and Ta = +25C.) (Note 1) PARAMETER | SYMBOL | CONDITIONS | MIN TYP MAX | UNITS RECEIVER DE = GND, VIN = +12V 250 Input Current (A and B) lA, B Voc = GND or 5.25V Vin = Vv 150 pA Receiver Differential Threshold Voltage VTH -7V < Vom $+12V -200 200 mV Receiver Input Hysteresis AVTH VA=VB=0 35 mV Receiver Output High Voltage VOH lo = -4mA, Va - VB = VTH 3.5 Vv Receiver Output Low Voltage VoL lo = 4mA, VA - VB = -VTH 0.4 Vv Three-State Output Current at < < + Receiver lozR 0<Vo<Vcc 0.1 +1 HA Receiver Input Resistance RIN -7V < Vom $+12V 48 kQ Receiver Output Short-Circuit < < + + Current losR_ | 0< VRO< Voc 415 +95 mA SUPPLY CURRENT No-Load Supply Current loc + lccp| RE = GND, DE= Vcc 2.0 3.0 mA Supply Current in Shutdown RE = Vcc, DE = GND, W = Vz = 0 to Vec or Mode ISHDN floating 1 10 HA COCEXVW/LECEXVWN SWITCHING CHARACTERISTICS (Typical Operating Circuit, Vcc = +5V 45%, RPsET = 0 (MAX3292), Vcc = Vecb (MAX3292), Ta = +25C, unless otherwise noted. Typical values are at Vcc = +5V and Ta = +25C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX | UNITS . . tDPLH Figures 3 and 5, RplFF = 54Q 44 65 Driver Propagation Dela , , ns Peg Y tpPHL | CL1 = CL2 = SOpF 44 65 Driver Differential Output tHL Figures 3 and 5, RpiFF = 54, 42 ns Rise or Fall Time tLH CL1 = Clo = SOpF MAX3291/MAX3292, Figures 3 and 10, Reset = 0 80 100 120 ns Driver Preemphasis Interval tPRE RDIFF = 54Q, Ci1 = Cle = 50pF MAX3292, Reger = 523kQ 0.75 1 1.25 ys Preemphasis Voltage Level to tPTND Figures 3 and 10, RpIFF = 54Q, 30 ns Normal Voltage Level Delay CL1 = Clo = SOpF Differential Driver Output Figures 3 and 5, RDIFF = 542, Skew ItppLH - toPHL| "OSKEW | Cry = Clo = 50pF i. Maximum Data Rate fMAX 10 Mbps MAXIMA 3MAX3291/MAX3292 RS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication SWITCHING CHARACTERISTICS (continued) (Typical Operating Circuit, Vcc = +5V +5%, Reset = 0 (MAX3292), Voc = Vecb (MAX3292), Ta = +25C, unless otherwise noted. Typical values are at Vcc = +5V and TA = +25C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX | UNITS Driver Enable to Output High tDZH Gon 100 6, S2 closed, RL = 500Q, 72 405 ns Driver Enable to Output Low tDZL Coe t00pr 6, S1 closed, RL = 500Q, 55 405 ns Driver Disable Time from Low tDLZ Center 6, S1 closed, RL = 5002, 53 100 ns Driver Disable Time from High tDHZ Center 6, S2 closed, RL = 500, HW 400 ns tRPLH i = = 49 85 Receiver Propagation Delay rjaures 7and 9, CL = SOpF, Vip = 2V, ns tRPHL CM = 0 52 85 Receiver Output Skew . ltapLy - tae tRSKEW Figures 7 and 9, CL = 100pF 3 ns Receiver Enable to Output Figures 2 and 8, RL = 1kQ, CL = 100pF, Low tRZL $1 closed 3 43 55 ns Receiver Enable to Output Figures 2 and 8, RL = 1kQ, CL = 100pF, High 'RZH | 82 closed 8 48 8s ns Receiver Disable Time from Figures 2 and 8, RL = 1kQ, CL = 15pF, Low tALZ $1 closed 25 45 ns Receiver Disable Time from Figures 2 and 8, RL = 1kQ, CL = 15pF, High 'RHZ | 82 closed 25 45 ns Time to Shutdown tSHDN Figures 4 and 11 (Note 7) 50 160 500 ns Driver Enable from Shutdown Figures 2 and 6, RL = 500Q, CL = 100pF, to Output High 'DZH(SHDN) S2 closed 6000 8750 ns Driver Enable from Shutdown Figures 2 and 6, RL = 500Q, CL = 100pF, to Output Low tDZL(SHDN) | 4 closed 6000 8750 ns Receiver Enable from Figures 2 and 8, RL = 1kQ, CL = 100pF, Shutdown to Output High 'RZH(SHDN) S2 closed 850 1800 ns Receiver Enable from Figures 2 and 8, RL = 1kQ, CL = 100pF, Shutdown to Output Low 'RZL(SHDN) $1 closed 30 1500 ns Note 1: ground unless otherwise noted. Guaranteed by design. DPER is defined as (VopP/ Vop). Note 2: Note 3: Note 4: Note 5: Note 6: current limiting. Note 7: All currents into the device are positive; all currents out of the device are negative. All voltages are referenced to device AVopp and AVoc are the changes in Vpp and Voc, respectively, when the DI input changes. This specification reflects constant operating conditions. When operating conditions shift, the maximum value may be momentarily exceeded. AVopp and AVoc are the changes in Vop and Voc, respectively, when the DI input changes state. Maximum current level applies to peak current just prior to foldback-current limiting; minimum current level applies during Shutdown is enabled by bringing RE high and DE low. If the enable inputs are in this state for less than 50ns, the device is guaranteed not to enter shutdown. If the enable inputs are in this state for at least 500ns, the device is guaranteed to have entered shutdown. Time to shutdown for the device (tsHDN) is measured by monitoring RO as in Figure 4. MAXUMRS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication (Vcc = +5V, TA = +25C, unless otherwise noted.) 45 40 3.5 3.0 25 2.0 15 1.0 DRIVER DIFFERENTIAL OUTPUT VOLTAGE (V) 05 0 TYPICAL PREEMPHASIS WAVEFORM PREEM PHASIS INTERVAL vs. Reser (Cpser = 0. 1,1F) MAX3291/2-02 Pepe (kQ2) 0 100 200 300 400 500 600 700 800900 1000 5 2500 5 2250 3 % 2000 z@ 1750 fe : Hi 4500 : : Zz Vy - Vz [tHe +] 2Vi wh 1250 i: w ov 1000 = fH 750 * 500 250 0 100ns/div DRIVER DIFFERENTIAL QUTPUT VOLTAGE vs. RoirF $ 4.25 STRONG g 5 = 400 @ 375 @ 3 S 350 5 325 2 300 2 275 IE 2.50 a 2.25 2.00 10 20 30 40 50 60 70 80 90 100 -40 RoirF () DRIVER PROPAGATION DELAY vs. TEMPERATURE 50.0 Cy =Cio = 50pF 4I5 # 450 > a 425 a S 400 & 5 37.5 2 350 325 30.0 40-20 0 20 40 60 80 TEMPERATURE (C) ROIFF = -20 MAX3291/2-07 100 Reger (kQ2) DRIVER DIFFERENTIAL OUTPUT VOLTAGE vs. TEMPERATURE 540 0 STRONG NORMAL (Vop) 20 40 60 TEMPERATURE (C) 80 52. ow oS Q QR PROPAGATION DELAY (ns) on a Q 100 1200 1000 800 600 400 200 YY 0 | 60.0 57.5 55.0 40.0 Typical Operating Characteristics Rere AND tpre vs. tgaup MAX3291/92 toc 03 0 500 1000 1500 2000 tpaup (ns) RECEIVER PROPAGATION DELAY vs. 5 -40 -20 0 TEMPERATURE C. = 50pF MAX3291/2-06 20 40 60 80) 100 TEMPERATURE (C) Va- VB 20ns/div MAX3291/2-08 2.5V/ div 5V/ div Note A: Dotted line represents region in which preemphasis may not work in systems with excessive power-supply noise. See Preemphasis at Low Data Rates. MAAXIAA COCEXVW/LECEXVWNRS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication DI W- Vz MAX3291/MAX3292 3.00 275 = 250 2.25 2.00 1.75 1.50 1.25 1.00 0.75 0.50 0.25 0 NO-LOAD SUPPLY CURRENT ( DRIVER PROPAGATION DELAY 20ns/div NO-LOAD SUPPLY CURRENT vs. TEMPERATURE 40 -20 0 2 60 TEMPERATURE (C) MAX3291/2-12 80 100 0.30 Q nD on 0.20 0.15 0.10 OUTPUT LOW VOLTAGE (V) 0.05 0 70 60 50 40 30 20 OUTPUT SINK CURRENT (mA) 10 0 vs. TEMPERATURE RECEIVER OUTPUT LOW VOLTAGE Ipo=8mA "| _ MAX3291/2-10. _ LT -40 20 0 20 40 60 TEMPERATURE (C) 80 OUTPUT SINK CURRENT vs. RECEIVER OUTPUT LOW VOLTAGE 100 0 05 10 1.5 20 25 30 35 40 45 5.0 OUTPUT LOW VOLTAGE (V) 4.60 4.55 fF RR SF hh wD oa fo OUTPUT HIGH VOLTAGE ( BR 30 25 20 OUTPUT SOURCE CURRENT (mA) a Typical Operating Characteristics (continued) (Vcc = +5V, TA = +25C, unless otherwise noted.) RECEIVER OUTPUT HIGH VOLTAGE vs. TEMPERATURE Ipo=8mA MAX3291/2-14 40 -20 0 2 40 60 80 = 100 TEMPERATURE (C) OUTPUT SOURCE CURRENT vs. RECEIVER OUTPUT HIGH VOLTAGE || N NY \ 0 05 10 15 20 25 30 35 40 45 50 OUTPUT HIGH VOLTAGE (V) MAXUMRS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication Pin Description PIN NAME FUNCTION MAX3291 | MAX3292 Preemphasis Enable Input. To enable preemphasis, leave PEE unconnected, connect to 1 _ PEE Voc, or drive high. To enable strong-level-drive only mode, connect PEE to GND or drive low. Preemphasis Set Input. Sets the preemphasis interval. Connect a resistor (RPSET) in paral- _ 1 PSET lel with a capacitor (CpseET) from PSET to Vcc to set the preemphasis interval. See Typical Operating Circuit. 2 2 RO Receiver Output. When RE is low and if A - B > 200mV, RO is high; if A - B < -200mV, RO is low. 3 3 RE Receiver Output Enable. Drive RE low to enable RO; RO is high impedance when RE is high. Drive RE high and DE low to enter low-power shutdown mode. 4 4 DE Driver Output Enable. Drive DE high to enable the driver outputs. These outputs are high impedance when DE is low. Drive RE high and DE low to enter low-power shutdown mode. Driver Input. With DE high, a low on DI forces the noninverting output low and the inverting 5 5 DI output high. Similarly, a high on DI forces the noninverting output high and the inverting output low. 6, 8, 13 8 N.C. No Connection. Not internally connected. 7 6,7 GND Ground 9 9 Y Noninverting Driver Output 10 10 Z Inverting Driver Output 11 11 B Inverting Receiver Input 12 12 A Noninverting Receiver Input _ 13 Vecb Connect to Vcc 14 14 Voc Positive Supply: +4.75V < Vcc < +5.25V Y Von OUTPUT. Voor UNDERTEST [yp <* * 4 $2 COCEXVW/LECEXVWN Figure 1. Driver DC Test Load Figure 2. Driver or Receiver Enable/Disable Timing Test Load MA AXIAMA 7MAX3291/MAX3292 RS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication 5V t<tsHpN t> tSHDN DE _ | > > RE OD ' ' | tRZH(SHDN) <I RO ' ' I ~ DE=LOW Figure 3. Driver Timing Test Circuit Figure 4. Shutdown Timing Diagram 5V DI 1.5V 1.5V oe YS 0 : Nm 1.5V 0 <4 VeH a v7 em) At tpzshpn), tz. tp.z 0 DIFFERENTIAL 23V OUTPUT NORMALLY LOW Vo." + 0.5V Yn Voir =Vy- Vz YZ QUTPUT NORMALLY HIGH Volpe 0 DIFFERENTIAL 80% 2.3V Vou" - 0.5V 0 \ VPL >| tozysupn), tozH toyz | tLH tskew =| tPLH- tPHL | | Yn- 2v | =Voo | Yp- Zp | = Voop *NOTE: Vou AND Vo_ ARETHE OUTPUT LEVELS IN FIGURE 2 WITH $2 AND $1 CLOSED, RESPECTIVELY. Figure 5. Driver Propagation Delays Figure 6. Driver Enable and Disable Times Vou PO A HV 0 DIFFERENTIAL B -1V trskew =| tRPLH- tRPHL | RE 4.5V 15V 0 KAY > tRZL(SHDN), tRZL {Az | ~< Voc rs RO 1.5V OUTPUT NORMALLY LOW Vo. +0.5V OUTPUT NORMALLY HIGH RO 15V Vou - 0.5V > {RZH(SHDN); 'RZH = tRHZ >) Figure 7. Receiver Propagation Delays Figure 8. Receiver Enable and Disable Times MAXUMRS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication 0 DIFFERENTIAL al ATE Vip R RO v A Figure 9. Receiver Propagation Delay Test Circuit Figure 10. Preemphasis Timing Voc @ Fe 1k = MAXIM MAX3291 MAX3292 RO DI DE iL Figure 11. Time-to-Shutdown Test Circuit Function Tables COCEXVW/LECEXVWN TRANSMITTING RECEIVING INPUTS OUTPUTS INPUTS OUTPUT RE DE DI Z Y RE DE AB RO x 1 1 4 0 X >0.2V 1 x 1 , ; Fs 0 X < -0.2V 0 0 0 X High-Z High-Z x Open : ' 1 1 X High-Z 0 x SHUTOOWN 1 0 x | High ang X = Dont care Z = High impedance SHUTDOWN = Low-power shutdown; driver and receiver outputs are high impedance. MA AXIAMAMAX3291/MAX3292 RS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication Detailed Description The MAX3291/MAX3292 high-speed RS-485/RS-422 transceivers feature driver preemphasis circuitry, which extends the distance and increases the data rate of reliable communication by reducing intersymbol inter- ference (ISI) caused by long cables. The MAX3291 is programmable for data rates of 5Mbps to 10Mbps, while the MAX3292 is programmable for data rates up to 10Mbps by using a single external resistor. The MAX3291/MAX3292 are full-duplex devices that operate from a single +5V supply and offer a low-cur- rent shutdown mode that reduces supply current to 100nA. They feature driver output short-circuit current limiting and a fail-safe receiver input that guarantees a logic-high output if the input is open circuit. A 1/4-unit- load receiver input impedance allows up to 128 trans- ceivers on the bus. Inter-symbol interference (ISI) causes significant prob- lems for UARTs if the total RS-485/RS-422 signal jitter becomes 10% or more of the baud period. ISI is caused by the effect of the cables RC time constant on different bit patterns. If a series of ones is transmitted, followed by a zero, the transmission-line voltage rises to a high value at the end of the string of ones (signal 1 in Figure 12). As the signal moves towards the zero state, it takes longer to reach the zero-crossing, because its starting voltage is farther from the zero crossing. On the other hand, if the 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 (VA - VB = 0) and it takes much less time for the signal to reach the zero- crossing (signal 2 in Figure 12). In other words, the propagation delay depends upon the previous bit pat- tern. This is inter-symbol interference (ISI). Preemphasis reduces ISI by increasing the signal amplitude at every transition edge for about one baud period, counteracting the effects of the cable (see the section Setting the Preemphasis Interval. Figure 13 shows a typical preemphasis waveform optimized for data rates between 5Mbps and 10Mbps. When DI changes from a logic low to a logic high, the differential output switches to a strong high. At the end of the pre- emphasis interval, the strong high returns to a normal high level. Both levels meet RS-485/RS-422 specifica- tions, and the strong levels are typically 1.9 times larger than the normal levels. If DI switches back to a logic low before the end of the preemphasis interval, the dif- ferential output switches directly from the strong high to the strong low. Similarly, this explanation applies when DI transitions from high to low. 10 SIGNAL 1 I BAUD PERIOD > Va- VB 6 SIGNAL 2 Figure 12. Inter-Symbol Interference among Two Data Patterns: Signal 1 = 11111110, Signal 2 = 00000010 W- Vz 2.5Vidiv pf 5V/div 100ns Figure 13. Typical Preemphasis Waveform with a 100ns Preemphasis Interval Applications Information Data Rate vs. Cable Length In general, preemphasis allows either double the dis- tance for a fixed data rate or double the data rate for a fixed existing cable distance over existing RS-485 transceivers that do not feature preemphasis. Figure 14 shows that the MAX3291/MAX3292 transmits approxi- mately twice as far at the same data rate or twice as fast at the same cable length as a conventional RS-485 transceiver without preemphasis for 10% jitter. MAXUMRS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication Setting the Preemphasis Interval The MAX3291 has an internal fixed preemphasis interval of 100ns. Use the MAX3291 for existing designs requiring industry-standard 75180 pin-compatibility at data rates of 5Mbps to 10Mbps. The MAX3292 has a resistor-programmable preemphasis interval for more flexibility. For data rates less than 1Mbps use the following equation to calculate RPser (the pre- emphasis setting resistor): RPset = 580 (tBAuUD - 100) where tBAUD = one baud period in ns. For example, a baud rate of 500kbps produces a baud period of 2us (2us = 2000ns). Rpset = 580 (tpaup - 100) RPseET = 580 (2000 - 100) = 1.1MQ For data rates of 1Mbps to 10Mbps use the following equation to calculate Reset: RpPset = 580 (tBAUD - 100)(tBAUD / 1000) where tBAUD = one baud period inns. For example, a baud rate of 1Mbps produces a baud period of 1s (1s = 1000ns). RPsET = 580 (1000 - 100)(1000 / 1000) = 522kQ (closest standard value is 523kQ) Set the preemphasis interval by connecting the RPSET resistor from PSET to Vcc. Use a 0.1pF bypass capaci- tor (CpseT) from PSET to Vcc. If PSET is connected directly to Vcc (RPsET = 0) , the preemphasis interval reverts to the nominal 100ns value. 10,000 24-GAUGE TWISTED PAIR 10%. TER PREEMPHASIS 485 DRIVER LIMIT 1000 485 DRIVER LIMIT CABLE LENGTH (FEET) PREEMPHASIS REQUIRED FOR ERROR- FREE TRANSMISSION 100 04 1 10 DATA RATE (Mbps) Eye Diagrams One simple method to quickly determine your circuit configuration is to view an eye diagram. An eye dia- gram is a scope photo (voltage vs. time) showing the transitions of a pseudo-random bit string displaying at least one bit interval. Use an eye diagram to quickly calculate the total jitter of a circuit configuration. Jitter is the total time variation at the zero-volt differential cross- ing, and percent jitter is expressed as a percentage of one baud period, tpaup. Figures 15 and 16 show typi- cal eye diagrams for a non-preemphasis device and the MAX3291/MAX3292. ISI and jitter are often used interchangeably; however they are not exactly the same thing. ISI usually makes up the majority of the jit- ter, but asymmetrical high and low driver output voltage levels and time skews of non-ideal transceivers (driver and receiver) also contribute to jitter. Figure 15. Eye Diagram of a Typical RS-485 Transceiver Without Preemphasis, while Driving 1000 feet of Cable at 5Mbps Figure 14. Preemphasis Driver Performance Compared to a Conventional Driver Without Preemphasis at 10% Jitter MA AXIAMA Figure 16. Eye Diagram of the MAX3292 with a Preemphasis Interval of 175ns, while Driving 1000 feet of Cable at 5Mbps 11 COCEXVW/LECEXVWNMAX3291/MAX3292 RS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication % Jitter = (total jitter / taauD) - 100 When the total amount of time skew becomes 10% or more of the baud period, the data error rate can increase sharply. 128 Transceivers on the Bus The standard RS-485 receiver input impedance is 12kQ (one unit load), and the standard driver can drive up to 32 unit loads. The MAX3291/MAX3292 transceivers have a 1/4-unit-load receiver input impedance (48kQ), allow- ing up to 128 transceivers to be connected in parallel on one communication line. Any combination of these devices and/or other RS-485 transceivers with a total of 32 unit-loads or less can be connected to the line. Low -Power Shutdown Mode Initiate low-power shutdown mode by bringing RE high and DE low. In shutdown the MAX3291/MAX3292 typi- cally draw only 1pA of supply current. Simultaneously driving RE and DE is allowed; the parts are guaranteed not to enter shutdown if RE is high and DE is low for less than 80ns. If the inputs are in this state for at least 300ns, the parts are guaranteed to enter shutdown. Enable times tzH and tzL in the Switching Characteris- tics tables correspond to when the part is not in the low- power shutdown state. Enable times tZH(SHDN) and 1ZL(SHDN) assume the parts are shut down. It takes dri- vers and receivers longer to activate from the low- power shutdown mode (tZH(SHDN), tZL(SHDN)) than from the driver/receiver disable mode (tZH, tZL). Line Repeater For line lengths greater than what one MAX3291/ MAX3292 can drive, use the repeater application shown in Figure 17. Figure 18 shows the system differential voltage for the MAX3292 driving 4000 feet of 26AWG twisted-pair wire into two 120Q termination loads. Line Termination The MAX3291/MAX3292 are targeted for applications requiring the best combination of long cable length and lowest bit-error rate. In order to achieve this combina- tion, the cable system must be set up with care. There are three basic steps: 1) The cable should only have two ends (no tree configu- ration with long branches), which are terminated with a simple resistor termination whose value is the cables characteristic impedance (Zo). Avoid termina- tions anywhere else along the cable. This ensures that there are no reflections at the end of the cable, and that all transmitters (whether they are located at the ends of the cable or somewhere along the length) see the same impedance, equal to Zo /2. 2) Make all branches or stubs short enough so that twice the propagation delay along the stub (down and back) is significantly less than one baud period (around 15% or less). This ensures that the reflec- tions from the end of the stub (which are unavoid- able, since the stubs are not terminated) settle in much less than a baud period. If the application requires a branch much longer than this, use a repeater (see the Line Repeater section). MAXIMA MAX3291 MAX3292 A R DATA IN IAS Oo m7 Z Y hy DI 5V/div RECEVER INPUT Var Vg [oof ceehes toe | 1Wdiv 5Vidiv 2usidiv TYPICAL OPERATING CIRCUIT, Reger = 1MQ Figure 17. Line-Repeater Application 12 Figure 18. MAX3292 System Differential Voltage Driving 4000 Feet, Using Two 120Q Termination Resistors MAXUMRS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication 3) Don't overload the cable with too many receivers. Even though the MAX3291/MAX3292 receives pre- sent only 1/4-unit load, placing 128 receivers on the cable will attenuate the signal if soaced out along the cable and, in addition, cause reflections if clumped in one spot. The MAX3291/MAX3292 suc- cessfully drive the cables to correct RS-485/RS-422 levels with 128 receivers, but the preemphasis effect is significantly diminished. The MAX3291/ MAX3292 are centered for a load imped- ance of 54Q, which corresponds to the parallel combina- tion of the cable impedance and termination resistors. If your cable impedance deviates somewhat from this value, you still get the preemphasis effect (although the ideal preemphasis time, tpRE, May need adjustment). However, if your cable impedance is significantly differ- ent, the preemphasis ratio DPER changes, resulting in significantly less preemphasis. Determine the preempha- sis ratio versus load by referring to the Driver Differential Output Voltage vs. RDIFF graph in the Typical Operating Characteristics. Read the strong and normal levels from the graph (remember that the horizontal units are half your cable impedance) and divide the two numbers to get DPER (DPER = VSTRONG / VNORMAL = VopP/ Vop). Figures 19 and 20 show typical network application cir- cuits with proper termination. Preemphasis at Low Data Rates (MAX3292) At low data rates (<iMsps), preemphasis operation is not guaranteed because it is highly dependent on the system power-supply noise. Minimize this noise by increasing bypass capacitance and using a power supply with a fast transient response. DI Ald MAXIM NOTE: REAND DEON. MAX3291 MAX3292 DI DE RO RE Figure 19. Typical Half-Duplex RS-485 Network AL (( . Y Ro 4 R Rane ) Raho D DI RFA al ( ( oe B ) Z DE Le Z (( B * RE nH p Ran cc Re Ao R RO Y 7 )) A y Zz 8 A y ZB A R R MAXIM D D MAX3291 MAX3292 | rotl | a | DI DE RE DI DE Figure 20. Typical Full-Duplex RS-485 Network MA AXIAMA 13 COCEXVW/LECEXVWNMAX3291/MAX3292 RS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication Pin Configuration TOP VIEW MAXIM MAX3291 MAX3292 PEE(PSEN [1 | 0 [| F [3 | be [4] oi [5 | N.c. (eND) [6 | = eno [7] 14] Voc 113] N.C. (Voc) 2] A tt] B 10] z ia | Y le | Ne. so/DIP () ARE FOR THE MAX3292 ONLY. 14 TRANSISTOR COUNT: 2280 SUBSTRATE CONNECTED TO GND Chip Information MAXUMRS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication MA AXIAMA H BOG Hd N Ho H HE a 0-8 AIA + 4 $A leh pele fh LG Lae INCHES [MILLIMETERS INCHES MILLIMETERS MIN | MAX | MIN | MAX MIN | MAX | MIN | MAX |.N_[MSO12 A{0.053 | 0.069] 1.35] 1.75 D/0.189 {0.197 | 4.80}5.00 |8 | A Alj 0.004 | 0.010 | 0.10 [0.25 D|0.337| 0.344] 8.55}8.75|14] B B{0.014 {0.019 | 0.35/0.49 D|0.386|0.394] 9.80}10.00}16] C C{0.007 |0.010 | 0.19 |0.2e5 e 0.050 1.27 NOTES: E {0.150 |0.157 | 3.80] 4.00 1. Dae DO NOT INCLUDE MOLD FLASH H[0.22e8|0.244|5.80/620) * Th exceeD Sm coed h {0.010 |0.020 | 0.e5| 0.50 3. LEADS oo BE COPLANAR WITHIN L {0,016 |0,050 | 0.40 | 1.27 4. CONTROLLING DIMENSION: MILLIMETER 5. MEETS JEDEC MS012-xx AS SHOWN IN ABOVE TABLE 6. N = NUMBER OF PINS SVIAXIZVI)Packace FAMILY OUTLINE: UIC Js0"( 14 [21-9041 A Package Information e es 15 COCEXVW/LECEXVWNMAX3291/MAX3292 RS-485/RS-422 Transceivers with Preemphasis for High-Speed, Long-Distance Communication Package Information (continued) # POIPN EPS E > + aA 0-15 i fe eB* 4 | i | exis, one INCHES | MILLIMETERS MIN | MAX | MIN | MAX A|--- |0.200 | --- [5.08 : : A1/0.015 |--- |0.38 | --- ZT 7 Ae|0.1e5 (0175 |3.18 14.45 745 (0.7 A3/0.055 [0.080 {1.40 [2.03 D (0.885 /0,.915 22.48 2 B/0.016 0022|041 056 D/1.015 [1045 |25.78]e B1 {0.045 |0.065 |1.14 1.65 14 \ \ C (0.008 |0.01e |0.2c0 {0.30 . . 4.54 D1 /0.005 |0.080 {0.13 2.03 E {0.300 |0.325|7.6e |8.2e6 NOTES: E1 [0.240 [0.310 [6.10 |7.87 3, MOLD FLASH U& PRUTRUSINS- NAT e 0,100 -- 2.D4 -- TO EXCEED 15mm .0067) : N N I: MI eAla.300 |--- [7.62 |---| # werrs bepee MeonISKx AS SHINS leB] --- 0,400 --- 10.16 IN ABOVE TABLE L [0.415 [0.150 [292 [3.81 2: SMILIAR TO JEDEC MO-OSGAB ZVLAI AI) packace FAMILY QUTLINE: PDIP a0] 21-0043 A Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 16 Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 1998 Maxim Integrated Products Printed USA MAXIMA is a registered trademark of Maxim Integrated Products.