LTC1535Isolated RS485 TransceiverFEATURESssssssDESCRIPTIO®sssssUAPPLICATIOSsssssUL Rated Isolated RS485: 2500VRMSUL Recognized File #E151738Eliminates Ground Loops250kBd Maximum Data RateSelf-Powered with 420kHz ConverterHalf- or Full-DuplexFail-Safe Output High for Open orShorted Receiver InputsShort-Circuit Current LimitSlow Slew Rate Control68kΩ Input Impedance Allows Up to 128 NodesThermal Shutdown8kV ESD Protection On Driver Outputs andReceiver InputsAvailable in 28-Lead SW PackageThe LTC®1535 is an isolated RS485 full-duplex differentialline transceiver. Isolated RS485 is ideal for systems wherethe ground loop is broken to allow for much larger com-mon mode voltage ranges. An internal capacitive isolationbarrier provides 2500VRMS of isolation between the linetransceiver and the logic level interface. The powered sidecontains a 420kHz push-pull converter to power the iso-lated RS485 transceiver. Internal full-duplex communica-tion occurs through the capacitive isolation barrier. Thetransceiver meets RS485 and RS422 requirements.The driver and receiver feature three-state outputs, withthe driver maintaining high impedance over the entirecommon mode range. The drivers have short-circuit cur-rent limits in both directions and a slow slew rate select tominimize EMI or reflections. The 68kΩ receiver inputallows up to 128 node connections. A fail-safe featuredefaults to a high output state when the receiver inputs areopen or shorted., LTC and LT are registered trademarks of Linear Technology Corporation.Isolated RS485 Receiver/DriverRS485 with Large Common Mode VoltageBreaking RS485 Ground LoopsMultiple Unterminated Line TapsTYPICAL APPLICATIO**CTX02-146591/2 BAT54C+10µF22VCC10µF1LOGIC COMMON1FLOATING RS485 COMMON2**TRANSFORMERCOOPER (561) 241-7876REDEDI27262541REDEDIGNDRO28RO3ST2420kHz1/2 BAT54C211GND2+1VCCST1VCC2RDU14ABRO2161517TWISTED-PAIRCABLEYZSLO131218 1535 TA01U1535fa1
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LTC1535ABSOLUTE AXIU RATIGS(Note 1)WUPACKAGE/ORDER IFORATIOTOP VIEWVCC1ST12ST23GND428RO27RE26DE25DIUVCC to GND................................................................6VVCC2 to GND2............................................................8VControl Input Voltage to GND......–0.3V to (VCC + 0.3V)Driver Input Voltage to GND........–0.3V to (VCC + 0.3V)Driver Output Voltage(Driver Disabled) to GND2..............(VCC2 – 13V) to 13VDriver Output Voltage(Driver Enabled) to GND2...............(VCC2 – 13V) to 10VReceiver Input Voltage to GND2............................±14VReceiver Output Voltage..............–0.3V to (VCC + 0.3V)Operating Temperature RangeLTC1535C........................................0°C ≤ TA ≤ 70°CLTC1535I.....................................–40°C ≤ TA ≤ 85°CStorage Temperature Range.................–65°C to 150°CLead Temperature (Soldering, 10 sec)..................300°CELECTRICAL CHARACTERISTICSSYMBOLVCCVCC2ICCICC2VOD1VOD2VOCIOSD1PARAMETERVCC Supply RangeVCC2 Supply RangeVCC Supply CurrentVCC2 Supply CurrentDifferential Driver OutputDifferential Driver OutputDriver Output Common Mode VoltageDriver Short-Circuit CurrentVOUT = HIGHVOUT = LOWLogic Input High VoltageLogic Input Low VoltageInput Current (A, B)Receiver Input ThresholdReceiver Input HysteresisReceiver Input ImpedanceThe q denotes the specifications which apply over the full operatingtemperature range, otherwise specifications are at TA = 25°C. VCC = 5V, VCC2 = 5V unless otherwise noted.CONDITIONSqqVIHVILIINVTH∆VTHRIN2
UWWWORDER PARTNUMBERLTC1535CSWLTC1535ISWGND211Z12Y13VCC214SW PACKAGE28-LEAD PLASTIC SO18SLO17RO216A15BTJMAX = 125°C, θJA = 125°C/WConsult LTC Marketing for parts specified with wider operating temperature ranges.MIN4.54.5TYPMAX5.57.5UNITSVVmAmAmAVVVTransformer Not Driven (Note 10)R = 27Ω, Figure 2No LoadNo LoadR = 50Ω (RS422) (Note 2), VCC2 = 4.5VR = 27Ω(RS485), Figure 2, VCC2 = 4.5VDC Level, R = 50Ω, Figure 2Driver Enabled (DE = 1)–7V ≤ VCM ≤ 10V–7V ≤ VCM ≤ 10VDE, DI, RESLODE, DI, RESLO(Note 3)–7V ≤ VCM ≤ 12V, (Note 4)–7V ≤ VCM ≤ 12V0°C ≤ TA ≤ 0°C–40°C ≤ TA ≤ 85°CVIN = 12VVIN = –7Vqqqqqqqqqqqqqqqqqqq1363721.52.0606024287312522.51001001.72.21.71.80.810.25–0.203.0150150VmAmAVVVVmAmAmVmVmVkΩ1535fa–20010550–90303068–107070100元器件交易网www.cecb2b.com
LTC1535The q denotes the specifications which apply over the full operatingtemperature range, otherwise specifications are at TA = 25°C. VCC = 5V, VCC2 = 5V unless otherwise noted.SYMBOLVIOCVOHVOLIOZVOH2VOL2fSWRSWHRSWLIRELIREHVUVLVUVHVISOPARAMETERReceiver Input Open Circuit VoltageRO Output High VoltageRO Output Low VoltageDriver Output LeakageRO2 Output High VoltageRO2 Output Low VoltageDC Converter FrequencyDC Converter Impedance HighDC Converter Impedance LowRE Output Low CurrentRE Output High CurrentUndervoltage Low ThresholdUndervoltage High ThresholdIsolation VoltageRE Sink Current, Fault = 0RE Source Current, Fault = 1RE Fault = 1, (Note 5)RE Fault = 0, (Note 5)1 Minute, (Note 6)1 SecondIRO = –4mA, VCC = 4.5VIRO = 4mA, VCC = 4.5VDriver Disabled (DE = 0)IRO2 = –4mA, VCC = 4.5VIRO2 = 4mA, VCC = 4.5VqqqqqqqqqqqELECTRICAL CHARACTERISTICSCONDITIONSMIN3.7TYP3.44.00.41MAXUNITSVV0.8VµAV3.72903.90.442042.50.859065–801304.254.40VkHzΩΩµAµAVVVRMSVRMS–40803.704.0525003000–501004.004.20The q denotes the specifications which apply over the full operatingtemperature range, otherwise specifications are at TA = 25°C. VCC = 5V, VCC2 = 5V, R = 27Ω (RS485) unless otherwise noted.SYMBOLtSJfMAXtPLHtPHLtr, tftZHtZLtLZtHZtPLHtPHLtPLHtPHLtr, tftLZtHZtSTARTtTOFPARAMETERData Sample JitterMax Baud RateDriver Input to OutputDriver Input to OutputDriver Rise or Fall TimeDriver Enable to OutputDriver Enable to OutputDriver Disable to OutputDriver Disable to OutputReceiver Input to ROReceiver Input to ROReceiver Input to RO2Receiver Input to RO2Receiver Rise or Fall TimeReceiver Disable to OutputReceiver Disable to OutputInitial Start-Up TimeData Time-Out FaultST1, ST2 Duty CycleCONDITIONSFigure 8, (Note 7)Jitter = 10% Max, SLO = 1, (Note 8)DE = 1, SLO = 1, Figure 4, Figure 6DE = 1, SLO = 0, Figure 4, Figure 6DE = 1, SLO = 1, Figure 4, Figure 6DE = 1, SLO = 0, Figure 4, Figure 6DE = 1, SLO = 1, Figure 4, Figure 6DE = 1, SLO = 0, VCC = VCC2 = 4.5VDI = 1, SLO = 1, Figure 5, Figure 7DI = 0, SLO = 1, Figure 5, Figure 7DI = 0, SLO = 1, Figure 5, Figure 7DI = 1, SLO = 1, Figure 5, Figure 7RE = 0, Figure 3, Figure 8RE = 0, Figure 3, Figure 8RE = 0, Figure 3, Figure 8RE = 0, Figure 3, Figure 8RE = 0, Figure 3, Figure 8Figure 3, Figure 9Figure 3, Figure 9(Note 9)(Note 9)0°C ≤ TA ≤ 70°C–40°C ≤ TA ≤ 85°CqqqqqqqqqqqqqqqqUSWITCHIG CHARACTERISTICSMIN250TYP25041060013006001300MAX2858551560855156010010001400140013001300855855UNITSnskBdnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsnsns15020500100010007007006006003030203030120012005657%%1535fa
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LTC1535ELECTRICAL CHARACTERISTICSNote 1: Absolute Maximum Ratings are those values beyond which thelife of a device may be impaired.Note 2: RS422 50Ω specification based on RS485 27Ω test.Note 3: IIN is tested at VCC2 = 5V, guaranteed by design fromGND2 ≤ VCC2 ≤ 5.25V.Note 4: Input fault conditions on the RS485 receiver are detected with afixed receiver offset. The offset is such that an input short or open willresult in a high data output.Note 5: The low voltage detect faults when VCC2 or VCC drops below VUVLand reenables when greater than VUVH. The fault can be monitoredthrough the weak driver output on RE.Note 6: Value derived from 1 second test.Note 7: The input signals are internally sampled and encoded. The internalsample rate determines the data output jitter since the internal sampling isasynchronous with respect to the external data. Nominally, a 4MHzinternal sample rate gives 250ns of sampling uncertainty in the inputsignals.Note 8: The maximum baud rate is 250kBd with 10% sampling jitter.Lower baud rates have lower jitter.Note 9: Start-up time is the time for communication to recover after a faultcondition. Data time-out is the time a fault is indicated on RE after datacommunication has stopped.Note 10. ICC measured with no load, ST1 and ST2 floating.TYPICAL PERFOR A CE CHARACTERISTICSVCC Supply Current vsTemperature130120110VCC = 5VCOOPERCTX02-14659TRANSFORMERRL = 54Ω9080VCC2 = 6V6.0VCC2 = 5VVCC2 CURRENT (mA)VCC CURRENT (mA)1009080706050–50–2506050403020fDI = fMAXSLO = 0VRL = 54Ω0VCC2 VOLTAGE (V)RL = 120ΩRL = OPEN255075100125150TEMPERATURE (°C)1535 G01Maximum Baud Rate vsTemperature5006560400fMAX (kHz)TIME (ns)555045403530300TIME (ns)200VCC = VCC2 = 4.5VSLO = VCC2RL = 54Ω0255075100125150TEMPERATURE (°C)1535 G04100–50–254
UWVCC2 Supply Current vsTemperature6.5VCC2 Supply Voltage vsTemperaturefDI = 250kHzSLO = 0VRL = OPEN, VCC = 5V70RL = 54Ω, VCC = 5V5.5RL = 54Ω, VCC = 4.5V5.0COOPERCTX02-14659TRANSFORMERVCC2 = 4.5V10–50–25255075100125150TEMPERATURE (°C)1535 G024.5–50–250255075100125150TEMPERATURE (°C)1535 G03Driver Differential Output Rise/Fall Time vs Temperature800VCC2 = 5V, 4.5VSLO = VCC2RL = 54Ω700600500400300Driver Differential Output Rise/Fall Time vs TemperatureSLO = 0VRL = 54ΩVCC2 = 5VVCC2 = 4.5V25–50–250255075100125150TEMPERATURE (°C)1535 G05200–50–250255075100125150TEMPERATURE (°C)1535 G061535fa元器件交易网www.cecb2b.com
LTC1535TYPICAL PERFOR A CE CHARACTERISTICSSwitcher Frequency vsTemperature600VCC = 5VVCC2 = 6VOUTPUT VOLTAGE (V)OUTPUT VOLTAGE (V)500FREQUENCY (kHz)3VCC2 = 5V2VCC2 = 4.5V1SLO = VCC2RL = 54Ω200–50–250255075100125150TEMPERATURE (°C)1535 G07400300Receiver Output High Voltage vsTemperature4.5VCC = 5VOUTPUT VOLTAGE (V)I = 8mA4OUTPUT VOLTAGE (V)4.0VCC = 4.5V3.553OUTPUT VOLTAGE (V)3.0–50–250255075100125150TEMPERATURE (°C)1535 G10Driver Output Low Voltage vsOutput Current5TA = 25°C4OUTPUT VOLTAGE (V)OUTPUT VOLTAGE (V)VCC = 6V3VCC = 5VVCC = 4.5V45OUTPUT VOLTAGE (V)2100102030405060708090100110OUTPUT CURRENT (mA)1535 G13UWDriver Differential Output Voltagevs Temperature41.00.90.80.70.60.50.40.30.20.1Receiver Output Low Voltage vsTemperatureI = 8mAVCC = 4.5VVCC = 5V0–50–250255075100125150TEMPERATURE (°C)1535 G080–50–250255075100125150TEMPERATURE (°C)1535 G09Driver Differential Output Voltagevs Output Current5VCC = 5.5VVCC = 5VTA = 25°C4Driver Output High Voltage vsOutput CurrentTA = 25°C3VCC = 4.5V2VCC = 5VVCC = 5.5V2VCC = 4.5V110010203040506070OUTPUT CURRENT (mA)809000102030405060708090100110OUTPUT CURRENT (mA)1535 G121535 G11Driver Differential Output Voltagevs VCC2 Supply Voltage5.0TA = 25°CRL = 60ΩReceiver Output Voltage vs LoadCurrentTA = 25°CVCC = 5VOUTPUT HIGH, SOURCING4.04.531.0OUTPUT LOW, SINKING0.5214.555.566.57VCC2 SUPPLY VOLTAGE (V)7.51535 G14001234567LOAD CURRENT (mA)891535 G151535fa5
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LTC1535PI FUCTIOSPOWER SIDEVCC (Pin 1): 5V Supply. Bypass to GND with 10µF capaci-tor.ST1 (Pin 2): DC Converter Output 1 to DC Transformer.ST2 (Pin 3): DC Converter Output 2 to DC Transformer.GND (Pin 4): Ground.DI (Pin 25): Transmit Data TTL Input to the Isolated SideRS485 Driver. Do not float.DE (Pin 26): Transmit Enable TTL Input to the IsolatedSide RS485 Driver. A high level enables the driver. Do notfloat.RE (Pin 27): Receive Data Output Enable TTL Input. A lowlevel enables the receiver. This pin also provides a faultoutput signal. (See Figure 11.)RO (Pin 28): Receive Data TTL Output.ISOLATED SIDEGND2 (Pin 11): Isolated Side Power Ground.Z (Pin 12): Differential Driver Inverting Output.Y (Pin 13): Differential Driver Noninverting Output.VCC2 (Pin 14): 5V to 7.5V Supply from DC Transformer.Bypass to GND2 with 10µF capacitor.B (Pin 15): Differential Receiver Inverting Input.A (Pin 16): Differential Receiver Noninverting Input.RO2 (Pin 17): Isolated Side Receiver TTL Output. Thisoutput is always enabled and is unaffected by RE.SLO (Pin 18): Slow Slew Rate Control of RS485 Driver. Alow level forces the driver outputs into slow slew ratemode.BLOCK DIAGRA128VCCRO27RE2625DEDI4GND6
WUUUPOWER SIDE1ISOLATED SIDE1.3+2ST13ST2420kHz11GND214VCC212.75k63.5kA27.25k16DECODEENCODER12.75k27.25k63.5kRO2Y17131218B15FAULTENCODEENDECODEDZSLO100kVCC21535 BDENFAULT1535fa元器件交易网www.cecb2b.com
LTC1535TEST CIRCUITS ILOAD**CTX02-146591/2 BAT54CIEXTVCC2+10µF2IVCC21/2 BAT54C2VCC10µF1ROfRO =MAXBAUDRATE27262541LOGIC COMMON1FLOATING RS485 COMMON2REDEDIGND28RO3ST2420kHz211GND214VCC2+1VCCST1ARBRO2161517YZC150pF2SLOW SLEWRATE JUMPER22RLC250pFYDZSLO131218 1535 F01**TRANSFORMERCOOPER (561) 241-7876Figure 1. Self-Oscillation at Maximum Data Rate(Test Configuration for the First Six Typical Performance Characteristics Curves)YRVODRZ1535 F02RECEIVEROUTPUTTEST POINTS11kVCCVOCCRL1kS21535 F03Figure 2. Driver DC Test LoadFigure 3. Receiver Timing Test Load3VDEYDIZR1535 F04RCL1S1OUTPUTUNDER TEST500ΩCLS21535 F05VCCCL2Figure 4. Driver Timing Test CircuitFigure 5. Driver Timing Test Load1535fa7
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LTC1535UWWSWITCHI G TI E WAVEFOR S 3VDI0VtPLHZVOYVO0V–VO80%20%trtSJ80%20%tSJtf 1535 F061.5Vtr ≤ 10ns, tf ≤ 10nstPHL1.5VVDIFF = V(Y) – V(Z)Figure 6. Driver Propagation Delays3VDE0V5VY, ZVOLVOHY, Z0VtZH tSJ2.3V2.3VtZL tLZOUTPUT NORMALLY LOW0.5V1.5Vtr ≤ 10ns, tf ≤ 10ns1.5VOUTPUT NORMALLY HIGHtHZtSJ0.5V1535 F07Figure 7. Driver Enable and Disable TimestSJVOHROVOLtPHLVOD2A – B–VOD20V1.5VOUTPUTtr ≤ 10ns, tf ≤ 10nsINPUTtPLH0V1.5VtSJ1535 F08Figure 8. Receiver Propagation Delays3VRE0V5VRO1.5VtSJRO0VtZHtSJ1.5VOUTPUT NORMALLY HIGHtHZtSJ1.5Vtr ≤ 10ns, tf ≤ 10ns tZLtLZOUTPUT NORMALLY LOWtSJ0.5V1535 F091.5V0.5VFigure 9. Receiver Enable and Disable Times1535fa8
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LTC1535APPLICATIOS IFORATIOIsolation Barrier and Sampled CommunicationThe LTC1535 uses the SW-28 isolated lead frame packageto provide capacitive isolation barrier between the logicinterface and the RS485 driver/receiver pair. The barrierprovides 2500VRMS of isolation. Communication betweenthe two sides uses the isolation capacitors in a multiplexedway to communicate full-duplex data across this barrier(see Figure 20 and Block Diagram). The data is sampledand encoded before transmitting across the isolationbarrier, which will add sampling jitter and delay to thesignals (see Figures 13 and 14). The sampling jitter isapproximately 250ns with a nominal delay of 600ns. At250kBd rate, this represents 6.2% total jitter. The nominalDE signal to the driver output delay is 875ns ±125ns,which is longer due to the encoding. Communicationstart-up time is approximately 1µs to 2µs. A time-out faultwill occur if communication from the isolated side fails.Faults can be monitored on the RE pin.The maximum baud rate can be determined by connectingin self-oscillation mode as shown in Figure 1. In thisconfiguration, with SLO = VCC2, the oscillation frequencyis set by the internal sample rate. With SLO = 0V, thefrequency is reduced by the slower output rise and falltimes.**CTX02-146591/2 BAT54C221114VCC2GND2VCC2 (V)1/2 BAT54C2VCC10µF141LOGIC COMMON1FLOATING RS485 COMMON2GND3ST2420kHz+1VCCST1UPush-Pull DC/DC ConverterThe powered side contains a full-bridge open-loop driver,optimized for use with a single primary and center-tappedsecondary transformer. Figure 10 shows the DC/DC con-verter in a configuration that can deliver up to 100mA ofcurrent to the isolated side using a Cooper CTX02-14659transformer.Because the DC/DC converter is open-loop, care in choos-ing low impedance parts is important for good regulation.Care must also be taken to not exceed the VCC2 recom-mended maximum voltage of 7.5V when there is very lightloading. The isolated side contains a low voltage detectcircuit to ensure that communication across the barrierwill only occur when there is sufficient isolated supplyvoltage. If the output of the DC/DC converter is over-loaded, the supply voltage will trip the low voltage detec-tion at 4.2V. For higher voltage stand-off, the CooperCTX02-14608 transformer may be used.ILOADIEXTWUUVCC2 vs ILOAD+10µFIVCC286VCC = 5.5V4VCC = 5VVCC = 4.5V200 1535 F1050100TOTAL LOAD CURRENT, ILOAD (mA)150**TRANSFORMERCOOPER (561) 241-78761535 F10aFigure 101535fa9
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LTC1535APPLICATIOS IFORATIODriver Output and Slow Slew Rate ControlThe LTC1535 uses a proprietary driver output stage thatallows a common mode voltage range that extends be-yond the power supplies. Thus, the high impedance stateis maintained over the full RS485 common mode range.The output stage provides 100mA of short-circuit currentlimiting in both the positive and negative directions. Thus,even under short-circuit conditions, the supply voltagefrom the open-loop DC converter will remain high enoughfor proper communication across the isolation barrier.The driver output will be disabled in the event of a thermalshutdown and a fault condition will be indicated throughthe RE weak output.The CMOS level SLO pin selects slow or fast slew rates onthe RS485 driver output (see Figures 15, 16, 17, 18 fortypical waveforms). The SLO input has an internal 100kpull-up resistor. When SLO is low, the driver outputs areslew rate limited to reduce high frequency edges. Leftopen or tied high, SLO defaults to fast edges. The partdraws more current during slow slew rate edges.REPOLLDEFAULTBUFFERPOLLFAULTFAULT INDICATED WHEN RE IS THREE-STATED1535 F11Figure 11. Detecting Fault Conditions10
UMonitoring Faults on REThe RE pin can be used to monitor the following faultconditions: low supply voltages, thermal shutdown or atime-out fault when there is no data communication acrossthe barrier. During a fault, the receiver output, RO, defaultsto a high state (see Table 2). Open circuit or short-circuitconditions on the twisted pair do not cause a fault indica-tion. However, the RS485 receiver defaults to a highoutput state when the receiver input is open or short-circuited.The RE pin has a weak current drive output mode forindicating fault conditions. This fault state can be polledusing a bidirectional microcontroller I/O line or by usingthe circuit in Figure 11, where the control to RE is three-stated and the fault condition read back from the RE pin.The weak drive has 100µA pull-up current to indicate afault and 50µA pull-down current for no fault. This allowsthe RE pin to be polled without disabling RE on nonfaultconditions.Both sides contain a low voltage detect circuit. A voltageless than 4.2V on the isolated side disablescommunication.VCCVCCRORELTC1535DIFAULTGND1535faWUU元器件交易网www.cecb2b.com
LTC1535APPLICATIOS IFORATIOTable 1. List of Transformers Designed for LTC1535DCISOLATIONVOLTAGEPHONE(1 Second)NUMBER500V500V1.25kV500V100V500V(561) 241-7876(0 89) 636-2 80 00(800) 888-7724(605) 886-4385(33) 3 84 35 04 0403-3667-3320(775) 852-01403.75kVAC(561) 241-7876MANUFACTURERCooperCooperEpcos AG (Germany)B78304-A1477-A3(USA)MidcomPulse FEE (France)Sumida (Japan)Transpower31160R P1597S-167-5779TTI7780-SMTable 2. Fault Mode BehaviorFUNCTION (PINS)DC/DC Converter (2, 3)RO (28)RE = 0VRE = VCCRE = FloatingRO2 (17)Driver OutputsY and Z (13,12)Communication AcrossIsolation BarrierFault Indicator on RE (27)VCC > VUVHVCC2 > VUVHOnActiveHi-ZActiveActiveActiveActiveLowVCC < VUVLVCC2 > VUVHOnForced HighHi-ZHi-ZActiveHi-ZDisabledHighVCC > VUVHVCC2 < VUVLOnForced HighHi-ZHi-ZActiveHi-ZDisabledHighVCC < VUVLVCC2 > VUVLOnForced HighHi-ZHi-ZActiveHi-ZDisabledHighTHERMALSHUTDOWNOffForced HighHi-ZHi-ZActiveHi-ZDisabledHighTable 3. Driver Function TableINPUTSREXXXDE110DI10XA10ZOUTPUTSB01ZNote: Z = high impedance, X = don’t careUPARTNUMBERCTX02-14659CTX02-14608WUUTable 4. Receiver Function TableINPUTSRE00001111DEXXXXXXXXA–B≥ VTH(MAX)≤ VTH(MIN)Inputs OpenInputs Shorted≥ VTH(MAX)≤ VTH(MIN)Inputs OpenInputs ShortedRO1011ZZZZOUTPUTSRO210111011Note: Z = high impedance, X = don’t care1535fa
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LTC1535APPLICATIOS IFORATIOHigh Voltage ConsiderationsThe LTC1535 eliminates ground loops on data communi-cation lines. However, such isolation can bring potentiallydangerous voltages onto the circuit board. An examplewould be accidental faulting to 117V AC at some point onthe cable which is then conducted to the PC board.Figure␣12 shows how to detect and warn the user orinstaller that a voltage fault condition exists on the twistedpair or its shield. A small (3.2mm) glow lamp is connectedbetween GND2 (the isolated ground) and the equipment’ssafety “earth” ground. If a potential of more than 75V ACis present on the twisted pair or shield, B1 will light,indicating a wiring fault. Resistors R3 and R4 are used toballast the current in B1. Two resistors are necessarybecause they can only stand off 200V each, as well as forpower dissipation. As shown, the circuit can withstand adirect fault to a 440V 3∅ system.Other problems introduced by floating the twisted pairinclude the collection of static charge on the twisted pair,its shield and the attached circuitry. Resistors R1 and R2LTC1535BGND22Z2EQUIPMENT SAFETY GROUNDEARTH GROUNDFLOATING RS485 COMMON2Figure 12. Detecting Wiring Faults1535fa12
Uprovide a path to shunt static charge safely to ground.Again, two resisitors are necessary to withstand highvoltage faults. Electrostatic spikes, electromagneticallyinduced transients and radio frequency pickup are shuntedby addition capacitor C1.Receiver Inputs Fail-SafeThe LTC1535 features an input common mode rangecovering the entire RS485 specified range of –7V to 12V.Differential signals of greater than ±200mV within thespecified input common mode range will be converted toTTL compatible signals at the receiver outputs, RO andRO2. A small amount of input hyteresis is included tominimize the effects of noise on the line signals. If thereceiver inputs are floating or shorted, a designed-inreceiver offset guarantees a fail-safe logic high at thereceiver outputs. If a fail-safe logic low is desired, connectas shown in Figure 19.AYTWISTED-PAIRNETWORK2R1*470kR2*470kC1***10nFR3**100kR4**100kB1CN2R (JKL)*IRC WCR1206**IRC WCR1210***PANASONIC ECQ-U2A103MV1535 F12WUU元器件交易网www.cecb2b.com
LTC1535APPLICATIOS IFORATIODIY–ZFigure 13. Driver Propagation Delaywith Sample Jitter. SLO = VCC21535 F13.tifZY1535 F15.tifFigure 15. Driver Output.R = 27Ω, VCC2 = 5V, SLO = VCC2Y–Z1535 F17.tifFigure 17. Driver Differential Output.R = 27Ω, VCC2 = 5V, SLO = VCC2UDIY–ZWUUFigure 14. Driver Propagation Delaywith Sample Jitter. SLO = 0V1535 F14.tifZY1535 F16.tifFigure 16. Driver Output.R = 27Ω, VCC2 = 5V, SLO = 0VY–Z1535 F18.tifFigure 18. Driver Differential Output.R = 27Ω, VCC2 = 5V, SLO = 0V1535fa
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LTC1535TYPICAL APPLICATIOS3VDEYDIZR1535 F04ROREDEDI(20a) NoninvertingFigure 20. Configuring Receiver for TTL Level Input. Y and Z Outputs Are TTL Compatible with No Modification2VCC10µF1RO28RO+1VCCST1RE1VCCDI27262541REDEDIGNDDYZSLOLOGIC COMMON114
URCL1CL2Figure 19. Fail-Safe Logic “0”LTC1535ABYZTTL INPUT30kROREDEDILTC1535ABYZTTL INPUT30k1535 TA05(20b) InvertingFull-Duplex Connection**CTX02-146591/2 BAT54C+10µF21/2 BAT54C3ST2420kHz211GND214VCC2ARBRO216120Ω151713120Ω1218 1535 TA02FLOATING RS485 COMMON2**TRANSFORMERCOOPER (561) 241-78761535fa元器件交易网www.cecb2b.com
LTC1535PACKAGE DESCRIPTIOSW Package28-Lead Plastic Small Outline Isolation Barrier (Wide .300 Inch)(Reference LTC DWG # 05-08-1690) .291 – .299**(7.391 – 7.595).005(0.127)RAD MIN.010 – .029× 45°(0.254 – 0.737).009 – .013(0.229 – 0.330)NOTE 1.016 – .050(0.406 – 1.270)NOTE:INCHES1. DIMENSIONS IN (MILLIMETERS)2. PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS THE PART MAY BE SUPPLIED WITH OR WITHOUT ANY OF THE OPTIONS.*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED .006\" (0.152mm) PER SIDE**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED .010\" (0.254mm) PER SIDEInformation furnished by Linear Technology Corporation is believed to be accurate and reliable.However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.U .697 – .712*(17.70 – 18.08)2827262518171615NOTE 1.394 – .419(10.007 – 10.643)123411121314.093 – .104(2.362 – 2.642).037 – .045(0.940 – 1.143)0° – 8° TYP.050(1.270)BSC.014 – .019(0.356 – 0.482)TYP.004 – 0.012(0.102 – 0.305)SW28 (ISO) 05021535fa15
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LTC1535TYPICAL APPLICATIO“SDO”“SCK”LOGIC 5VROST1REDEDIVCC110µF110VTANT+ISOLATION1BARRIERRELATED PARTSPART NUMBERLT1424-5LTC1485LTC1531LT1785/LT1791LTC1690DESCRIPTIONIsolated Flyback Switching RegulatorHigh Speed RS485 TransceiverSelf-Powered Isolated Comparator±60V Fault Protected RS485 Transceiver, Half/Full-DuplexFull-Duplex RS485 TransceiverCOMMENTS±5% Accurate with No Optoisolator Required10Mbps, Pin Compatible with LTC4852.5V Isolated Reference, 3000VRMS Isolation±15kV ESD Protection, Industry Standard Pinout±15kV ESD Protection, Fail-Safe Receiver16
Linear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507 q www.linear.comUComplete, Isolated 24-Bit Data Acquisition System1/2 BAT54CLT1761-5INSHDNGNDOUT10µFBYP+T110µF16VTANT1µF+10µF10VTANT21/2 BAT54CST2LTC1535G1G2VCC2ABYZ+210µF10VTANTLTC2402FOSCKSDOCSGNDVCCFSSETCH1CH0ZSSET10µFCERAMIC21k1212= LOGIC COMMON= FLOATING COMMON221535 TA03T1 = COOPER CTX02-146591535fa LT/TP 1103 1K REV A • PRINTED IN USA
© LINEAR TECHNOLOGY CORPORATION 1999
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