LTC1535 Isolated RS485 Transceiver Features n Description UL Rated Isolated RS485: 2500VRMS UL Recognized File #E151738 Eliminates Ground Loops 250kBd Maximum Data Rate Self-Powered with 420kHz Converter Half- or Full-Duplex Fail-Safe Output High for Open or Shorted Receiver Inputs Short-Circuit Current Limit Slow Slew Rate Control 68k Input Impedance Allows Up to 128 Nodes Thermal Shutdown 8kV ESD Protection On Driver Outputs and Receiver Inputs Available in 28-Lead SW Package (R) n n n n n n n n n n n Applications n n n n Isolated RS485 Receiver/Driver RS485 with Large Common Mode Voltage Breaking RS485 Ground Loops Multiple Unterminated Line Taps The LTC(R)1535 is an isolated RS485 full-duplex differential line transceiver. Isolated RS485 is ideal for systems where the ground loop is broken to allow for much larger common mode voltage ranges. An internal capacitive isolation barrier provides 2500VRMS of isolation between the line transceiver and the logic level interface. The powered side contains a 420kHz push-pull converter to power the isolated RS485 transceiver. Internal full-duplex communication occurs through the capacitive isolation barrier. The transceiver meets RS485 and RS422 requirements. The driver and receiver feature three-state outputs, with the driver maintaining high impedance over the entire common mode range. The drivers have short-circuit current limits in both directions and a slow slew rate select to minimize EMI or reflections. The 68k receiver input allows up to 128 node connections. A fail-safe feature defaults to a high output state when the receiver inputs are open or shorted. L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Analog Devices, Inc. All other trademarks are the property of their respective owners. Typical Application ** CTX02-14659 1/2 BAT54C + 10F 2 2 VCC 10F 1 + VCC ST1 1/2 BAT54C 3 ST2 2 11 14 GND2 VCC2 420kHz A 1 LOGIC COMMON 28 RO RO R B 1 FLOATING RS485 COMMON 2 RE 27 DE 26 DI 25 ** EATON (888) 414-2645 4 RO2 RE Y DE D DI Z SLO GND 1 16 15 TWISTED-PAIR CABLE 17 13 12 18 1535 TA01 1535fc For more information www.linear.com/LTC1535 1 LTC1535 Absolute Maximum Ratings Pin Configuration (Note 1) VCC to GND..................................................................6V VCC2 to GND2...............................................................8V Control 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 13V Driver Output Voltage (Driver Enabled) to GND2................. (VCC2 - 13V) to 10V Receiver Input Voltage to GND2............................... 14V Receiver Output Voltage................-0.3V to (VCC + 0.3V) Operating Temperature Range LTC1535C...........................................0C TA 70C LTC1535I....................................... -40C TA 85C Storage Temperature Range...................- 65C to 150C Lead Temperature (Soldering, 10 sec).................... 300C Order Information TOP VIEW VCC 1 28 RO ST1 2 27 RE ST2 3 26 DE GND 4 25 DI GND2 11 18 SLO Z 12 17 RO2 Y 13 16 A VCC2 14 15 B SW PACKAGE 28-LEAD PLASTIC SO TJMAX = 125C, JA = 125C/W http://www.linear.com/product/LTC1535#orderinfo LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC1535CSW#PBF LTC1535CSW#TRPBF 1535 28-Lead Plastic SO 0C to 70C LTC1535ISW#PBF LTC1535ISW#TRPBF 1535 28-Lead Plastic SO -40C to 85C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix. 2 1535fc For more information www.linear.com/LTC1535 LTC1535 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 5V, VCC2 = 5V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS VCC VCC Supply Range l VCC2 VCC2 Supply Range l 4.5 5.5 V 4.5 7.5 V ICC VCC Supply Current Transformer Not Driven (Note 10) l 13 28 mA ICC2 VCC2 Supply Current R = 27, Figure 2 No Load l l 63 7 73 12 mA mA VOD1 Differential Driver Output No Load l 5 V VOD2 Differential Driver Output R = 50 (RS422) (Note 2), VCC2 = 4.5V R = 27(RS485), Figure 2, VCC2 = 4.5V l l 2 1.5 2 VOC Driver Output Common Mode Voltage DC Level, R = 50, Figure 2 l 2.0 2.5 3.0 V IOSD1 Driver Short-Circuit Current VOUT = HIGH VOUT = LOW Driver Enabled (DE = 1) -7V VCM 10V -7V VCM 10V l l 60 60 100 100 150 150 mA mA VIH Logic Input High Voltage DE, DI, RE SLO l l 2 4 1.7 2.2 VIL Logic Input Low Voltage DE, DI, RE SLO l l IIN Input Current (A, B) (Note 3) 1.7 1.8 V V V V 0.8 1 V V VIN = 12V l 0.25 mA VIN = -7V l -0.20 mA VTH Receiver Input Threshold -7V VCM 12V, (Note 4) l -200 -90 -10 mV VTH Receiver Input Hysteresis -7V VCM 12V 0C TA 70C l 10 30 70 mV - 40C TA 85C l 5 30 70 mV l 50 68 100 k RIN Receiver Input Impedance VIOC Receiver Input Open Circuit Voltage VOH RO Output High Voltage IRO = - 4mA, VCC = 4.5V l VOL RO Output Low Voltage IRO = 4mA, VCC = 4.5V l IOZ Driver Output Leakage Driver Disabled (DE = 0) VOH2 RO2 Output High Voltage IRO2 = - 4mA, VCC = 4.5V l VOL2 RO2 Output Low Voltage IRO2 = 4mA, VCC = 4.5V l fSW DC Converter Frequency l RSWH DC Converter Impedance High RSWL DC Converter Impedance Low IREL RE Output Low Current IREH RE Output High Current VUVL 3.7 3.4 V 4.0 V 0.4 0.8 1 3.7 V A 3.9 V 0.4 0.8 V 420 590 kHz l 4 6 l 2.5 5 290 RE Sink Current, Fault = 0 l -40 -50 -80 A RE Source Current, Fault = 1 l 80 100 130 A Undervoltage Low Threshold RE Fault = 1, (Note 5) l 3.70 4.00 4.25 V VUVH Undervoltage High Threshold RE Fault = 0, (Note 5) l 4.05 4.20 4.40 V VISO Isolation Voltage 1 Minute, (Note 6) 1 Second 2500 3000 VRMS VRMS 1535fc For more information www.linear.com/LTC1535 3 LTC1535 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 5V, VCC2 = 5V, R = 27 (RS485) unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX 250 285 UNITS tSJ Data Sample Jitter Figure 8, (Note 7) l fMAX Max Baud Rate Jitter = 10% Max, SLO = 1, (Note 8) l tPLH Driver Input to Output DE = 1, SLO = 1, Figure 4, Figure 6 DE = 1, SLO = 0, Figure 4, Figure 6 l l 600 1300 855 1560 ns ns tPHL Driver Input to Output DE = 1, SLO = 1, Figure 4, Figure 6 DE = 1, SLO = 1, Figure 4, Figure 6 l l 600 1300 855 1560 ns ns tr, tf Driver Rise or Fall Time DE = 1, SLO = 1, Figure 4, Figure 6 DE = 1, SLO = 0, VCC = VCC2 = 4.5V l l 20 500 100 1000 ns ns tZH Driver Enable to Output DI = 1, SLO = 1, Figure 5, Figure 7 l 1000 1400 ns tZL Driver Enable to Output DI = 0, SLO = 1, Figure 5, Figure 7 l 1000 1400 ns tLZ Driver Disable to Output DI = 0, SLO = 1, Figure 5, Figure 7 l 700 1300 ns tHZ Driver Disable to Output DI = 1, SLO = 1, Figure 5, Figure 7 l 700 1300 ns tPLH Receiver Input to RO RE = 0, Figure 3, Figure 8 l 600 855 ns tPHL Receiver Input to RO RE = 0, Figure 3, Figure 8 l 600 855 ns tPLH Receiver Input to RO2 RE = 0, Figure 3, Figure 8 30 ns tPHL Receiver Input to RO2 RE = 0, Figure 3, Figure 8 30 ns tr, tf Receiver Rise or Fall Time RE = 0, Figure 3, Figure 8 20 ns tLZ Receiver Disable to Output Figure 3, Figure 9 30 ns tHZ Receiver Disable to Output Figure 3, Figure 9 30 ns tSTART Initial Start-Up Time (Note 9) 1200 ns tTOF Data Time-Out Fault (Note 9) 1200 ns ST1, ST2 Duty Cycle 0C TA 70C -40C TA 85C Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: RS422 50 specification based on RS485 27 test. Note 3: IIN is tested at VCC2 = 5V, guaranteed by design from GND2 VCC2 5.25V. Note 4: Input fault conditions on the RS485 receiver are detected with a fixed receiver offset. The offset is such that an input short or open will result in a high data output. Note 5: The low voltage detect faults when VCC2 or VCC drops below VUVL and re-enables when greater than VUVH . The fault can be monitored through the weak driver output on RE. 4 l l 250 150 410 ns kBd 56 57 % % Note 6: Value derived from 1 second test. Note 7: The input signals are internally sampled and encoded. The internal sample rate determines the data output jitter since the internal sampling is asynchronous with respect to the external data. Nominally, a 4MHz internal sample rate gives 250ns of sampling uncertainty in the input signals. 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 fault condition. Data time-out is the time a fault is indicated on RE after data communication has stopped. Note 10: ICC measured with no load, ST1 and ST2 floating. 1535fc For more information www.linear.com/LTC1535 LTC1535 Typical Performance Characteristics VCC Supply Current vs Temperature VCC CURRENT (mA) 90 EATON CTX02-14659 TRANSFORMER 110 90 RL = 120 80 70 RL = OPEN 60 50 -50 -25 0 6.5 VCC2 = 6V 80 RL = 54 100 70 6.0 VCC2 = 5V 60 50 VCC2 = 4.5V 40 30 20 10 -50 -25 25 50 75 100 125 150 TEMPERATURE (C) 0 60 55 Driver Differential Output Rise/Fall Time vs Temperature 800 VCC2 = 5V, 4.5V SLO = VCC2 RL = 54 700 SLO = 0V RL = 54 VCC2 = 5V 600 50 45 40 500 VCC2 = 4.5V 400 300 30 25 -50 -25 25 50 75 100 125 150 TEMPERATURE (C) 0 200 -50 -25 25 50 75 100 125 150 TEMPERATURE (C) 1535 G04 600 Receiver Output Low Voltage vs Temperature 4 1.0 VCC = 5V 0.9 VCC2 = 6V 300 VCC2 = 5V 2 VCC2 = 4.5V 1 1535 G07 0 -50 -25 0 VCC = 4.5V 0.7 VCC = 5V 0.6 0.5 0.4 0.3 0.2 SLO = VCC2 RL = 54 25 50 75 100 125 150 TEMPERATURE (C) I = 8mA 0.8 3 OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) 400 25 50 75 100 125 150 TEMPERATURE (C) 1535 G06 Driver Differential Output Voltage vs Temperature 500 0 1535 G05 Switcher Frequency vs Temperature FREQUENCY (kHz) 25 50 75 100 125 150 TEMPERATURE (C) 35 VCC = VCC2 = 4.5V SLO = VCC2 RL = 54 0 0 1535 G03 TIME (ns) TIME (ns) fMAX (kHz) 400 200 -50 -25 EATON CTX02-14659 TRANSFORMER 4.5 -50 -25 25 50 75 100 125 150 TEMPERATURE (C) 65 0 RL = 54, VCC = 4.5V Driver Differential Output Rise/Fall Time vs Temperature 500 100 -50 -25 5.5 1535 G02 Maximum Baud Rate vs Temperature 300 fDI = 250kHz SLO = 0V RL = OPEN, VCC = 5V RL = 54, VCC = 5V 5.0 fDI = fMAX SLO = 0V RL = 54 1535 G01 200 VCC2 Supply Voltage vs Temperature VCC2 VOLTAGE (V) 120 VCC = 5V VCC2 CURRENT (mA) 130 VCC2 Supply Current vs Temperature 0.1 25 50 75 100 125 150 TEMPERATURE (C) 1535 G08 0 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (C) 1535 G09 1535fc For more information www.linear.com/LTC1535 5 LTC1535 Typical Performance Characteristics Receiver Output High Voltage vs Temperature Driver Differential Output Voltage vs Output Current 5 VCC = 5V 4.0 VCC = 4.5V 3.5 0 4 3 2 0 25 50 75 100 125 150 TEMPERATURE (C) VCC = 4.5V 0 10 20 30 40 50 60 70 OUTPUT CURRENT (mA) 1535 G10 5 5 VCC = 5V 1 0 0 10 20 30 40 50 60 70 80 90 100 110 OUTPUT CURRENT (mA) 1535 G13 6 VCC = 5V 2 0 90 VCC = 5.5V 0 10 20 30 40 50 60 70 80 90 100 110 OUTPUT CURRENT (mA) 1535 G12 Receiver Output Voltage vs Load Current 5.0 3 2 1 4.5 TA = 25C VCC = 5V 4.5 4 OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) 4 2 80 TA = 25C RL = 60 VCC = 4.5V VCC = 4.5V 1 Driver Differential Output Voltage vs VCC2 Supply Voltage TA = 25C VCC = 6V 3 1535 G11 Driver Output Low Voltage vs Output Current 3 TA = 25C VCC = 5V 1 3.0 -50 -25 TA = 25C VCC = 5.5V 4 OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) 5 I = 8mA OUTPUT VOLTAGE (V) 4.5 Driver Output High Voltage vs Output Current OUTPUT HIGH, SOURCING 4.0 1.0 OUTPUT LOW, SINKING 0.5 5 5.5 6 6.5 7 VCC2 SUPPLY VOLTAGE (V) 7.5 1535 G14 0 0 1 2 3 4 5 6 7 LOAD CURRENT (mA) 8 9 1535 G15 1535fc For more information www.linear.com/LTC1535 LTC1535 Pin Functions Power Side Isolated Side VCC (Pin 1): 5V Supply. Bypass to GND with 10F capacitor. GND2 (Pin 11): Isolated Side Power Ground. ST1 (Pin 2): DC Converter Output 1 to DC Transformer. ST2 (Pin 3): DC Converter Output 2 to DC Transformer. GND (Pin 4): 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 10F capacitor. DI (Pin 25): Transmit Data TTL Input to the Isolated Side RS485 Driver. Do not float. B (Pin 15): Differential Receiver Inverting Input. DE (Pin 26): Transmit Enable TTL Input to the Isolated Side RS485 Driver. A high level enables the driver. Do not float. RO2 (Pin 17): Isolated Side Receiver TTL Output. This output is always enabled and is unaffected by RE. RE (Pin 27): Receive Data Output Enable TTL Input. A low level enables the receiver. This pin also provides a fault output signal. (See Figure 11.) A (Pin 16): Differential Receiver Noninverting Input. SLO (Pin 18): Slow Slew Rate Control of RS485 Driver. A low level forces the driver outputs into slow slew rate mode. RO (Pin 28): Receive Data TTL Output. Block Diagram POWER SIDE 1 ISOLATED SIDE 1.3 + 1.3 2 3 ST1 ST2 11 14 GND2 VCC2 12.75k 63.5k A 420kHz 1 28 VCC DECODE 27.25k ENCODE R RO 12.75k 27.25k 27 RE 25 4 DE RO2 Y DECODE D Z EN DI SLO EN GND B 63.5k FAULT ENCODE 26 16 FAULT 15 17 13 12 18 100k VCC2 1535 BD 1535fc For more information www.linear.com/LTC1535 7 LTC1535 Test Circuit ILOAD IEXT ** CTX02-14659 VCC2 1/2 BAT54C + IVCC2 10F 2 1/2 BAT54C 2 VCC 10F 1 + ST1 VCC 2 3 ST2 11 14 GND2 VCC2 420kHz A 1 28 RO RO R B fRO = MAX BAUD RATE 27 26 25 RO2 RE Y DE D DI Z SLO GND 4 1 16 15 17 FLOATING RS485 COMMON 1 2 RL Z 12 C1 50pF 18 1535 F01 LOGIC COMMON Y 13 C2 50pF 2 2 SLOW SLEW RATE JUMPER ** EATON (888) 414-2645 2 Figure 1. Self-Oscillation at Maximum Data Rate (Test Configuration for the First Six Typical Performance Characteristics Curves) Y VOD VOC CRL R Z S1 TEST POINT RECEIVER OUTPUT R 1k VCC S2 1535 F03 1535 F02 Figure 2. Driver DC Test Load Figure 3. Receiver Timing Test Load 3V S1 DE DI 1k Y R Z R CL1 VCC 500 OUTPUT UNDER TEST CL CL2 S2 1535 F05 1535 F04 Figure 4. Driver Timing Test Circuit 8 Figure 5. Driver Timing Test Load 1535fc For more information www.linear.com/LTC1535 LTC1535 switching time waveforms 3V tr 10ns, tf 10ns 1.5V DI 1.5V 0V tPLH Z Y tPHL VO VO 0V -VO 80% 20% tr 80% 20% VDIFF = V(Y) - V(Z) tSJ tf tSJ 1535 F06 Figure 6. Driver Propagation Delays 3V tr 10ns, tf 10ns 1.5V DE 1.5V 0V Y, Z tLZ tZL 5V 2.3V OUTPUT NORMALLY LOW 0.5V 2.3V OUTPUT NORMALLY HIGH 0.5V VOL Y, Z VOH 0V tHZ tZH 1535 F07 tSJ tSJ Figure 7. Driver Enable and Disable Times RO tSJ VOH tSJ 1.5V VOL tPHL VOD2 A-B -VOD2 1.5V OUTPUT tPLH tr 10ns, tf 10ns 0V 0V INPUT 1535 F08 Figure 8. Receiver Propagation Delays 3V RE 1.5V RO 1.5V tr 10ns, tf 10ns 0V tZL 5V 1.5V tLZ OUTPUT NORMALLY LOW tSJ RO 1.5V 0V tZH 0.5V tSJ OUTPUT NORMALLY HIGH 0.5V tHZ tSJ 1535 F09 tSJ Figure 9. Receiver Enable and Disable Times 1535fc For more information www.linear.com/LTC1535 9 LTC1535 Applications Information Isolation Barrier and Sampled Communication Push-Pull DC/DC Converter The LTC1535 uses the SW-28 isolated lead frame package to provide capacitive isolation barrier between the logic interface and the RS485 driver/receiver pair. The barrier provides 2500VRMS of isolation. Communication between the two sides uses the isolation capacitors in a multiplexed way to communicate full-duplex data across this barrier (see Figure 20 and Block Diagram). The data is sampled and encoded before transmitting across the isolation barrier, which will add sampling jitter and delay to the signals (see Figures 13 and 14). The sampling jitter is approximately 250ns with a nominal delay of 600ns. At 250kBd rate, this represents 6.2% total jitter. The nominal DE signal to the driver output delay is 875ns 125ns, which is longer due to the encoding. Communication start-up time is approximately 1s to 2s. A time-out fault will occur if communication from the isolated side fails. Faults can be monitored on the RE pin. The powered side contains a full-bridge open-loop driver, optimized for use with a single primary and center-tapped secondary transformer. Figure 10 shows the DC/DC converter in a configuration that can deliver up to 100mA of current to the isolated side using a Eaton CTX02-14659 transformer. The maximum baud rate can be determined by connecting in self-oscillation mode as shown in Figure 1. In this configuration, with SLO = VCC2 , the oscillation frequency is set by the internal sample rate. With SLO = 0V, the frequency is reduced by the slower output rise and fall times. Table 1 lists examples of transformers which are suitable for use in the LTC1535's DC/DC converter using the circuit topology shown in Figure 10. While this secondary circuit topology is recommended, other secondary circuit topologies are possible which allows for different Because the DC/DC converter is open-loop, care in choosing low impedance parts is important for good regulation. Care must also be taken to not exceed the VCC2 recommended maximum voltage of 7.5V when there is very light loading. The isolated side contains a low voltage detect circuit to ensure that communication across the barrier will only occur when there is sufficient isolated supply voltage. If the output of the DC/DC converter is overloaded, the supply voltage will trip the low voltage detection at 4.2V. For higher voltage stand-off, the Eaton CTX02-14608 transformer may be used. ILOAD VCC2 vs ILOAD IEXT ** CTX02-14659 8 1/2 BAT54C + IVCC2 10F 6 1/2 BAT54C 2 VCC 10F + 1 VCC 4 GND 3 ST1 ST2 420kHz VCC2 (V) 2 2 11 14 GND2 VCC2 VCC = 5.5V VCC = 4.5V 2 0 1 1 1535 F10 LOGIC COMMON FLOATING RS485 COMMON 1 2 VCC = 5V 4 0 50 100 TOTAL LOAD CURRENT, ILOAD (mA) 150 1535 F10a ** EATON (888) 414-2645 Figure 10 10 1535fc For more information www.linear.com/LTC1535 LTC1535 Applications Information transformer configurations. The DC/DC converter driver's Thevenin equivalent resistance is approximately 4 and the transformer's volt-second rating should be greater than 7Vs. Driver Output and Slow Slew Rate Control The LTC1535 uses a proprietary driver output stage that allows a common mode voltage range that extends beyond the power supplies. Thus, the high impedance state is maintained over the full RS485 common mode range. The output stage provides 100mA of short-circuit current limiting in both the positive and negative directions. Thus, even under short-circuit conditions, the supply voltage from the open-loop DC converter will remain high enough for proper communication across the isolation barrier. The driver output will be disabled in the event of a thermal shutdown and a fault condition will be indicated through the RE weak output. The CMOS level SLO pin selects slow or fast slew rates on the RS485 driver output (see Figures 15, 16, 17, 18 for typical waveforms). The SLO input has an internal 100k pull-up resistor. When SLO is low, the driver outputs are slew rate limited to reduce high frequency edges. Left open or tied high, SLO defaults to fast edges. The part draws more current during slow slew rate edges. Monitoring Faults on RE The RE pin can be used to monitor the following fault conditions: low supply voltages, thermal shutdown or a time-out fault when there is no data communication across the barrier. During a fault, the receiver output, RO, defaults to a high state (see Table 2). Open circuit or short-circuit conditions on the twisted pair do not cause a fault indication. However, the RS485 receiver defaults to a high output state when the receiver input is open or short-circuited. The RE pin has a weak current drive output mode for indicating fault conditions. This fault state can be polled using a bidirectional microcontroller I/O line or by using the circuit in Figure 11, where the control to RE is threestated and the fault condition read back from the RE pin. The weak drive has 100A pull-up current to indicate a fault and 50A pull-down current for no fault. This allows the RE pin to be polled without disabling RE on nonfault conditions. Both sides contain a low voltage detect circuit. A voltage less than 4.2V on the isolated side disables communication. VCC RO RE VCC RE LTC1535 DI POLL FAULT DE FAULT GND BUFFER POLL FAULT FAULT INDICATED WHEN RE IS THREE-STATED 1535 F11 Figure 11. Detecting Fault Conditions 1535fc For more information www.linear.com/LTC1535 11 LTC1535 Applications Information Table 1. Examples of Transformers Compatible with the LTC1535 MANUFACTURER WE-Midcom PART NUMBER 750311542 750031160 31160R Eaton Murata Power Solutions DC ISOLATION VOLTAGE (1 SECOND) PHONE NUMBER/WEBSITE 1.25kV (800) 643-2661 http://www.we-online.com 1.25kV 760390014 3.125kVAC 750313638 6.25kVAC CTX02-14659 CTX02-14659-R CTX02-14608 500V 3.75kVAC 78253/55JC 1.5kV 78253/55JVC 4kV Minntronix 4810796R 3kVAC Pulse Electronics P1597NL 500V PH9085.034NL 2.5kV S-167-5779 100V Sumida (Japan) (888) 414-2645 http://www.murata-ps.com (605) 884-0195 http://minntronix.com/ http://www.pulseelectronics.com/ 03-3667-3320 http://www.sumida.com/ Table 2. Fault Mode Behavior VCC > VUVH VCC2 > VUVH On VCC < VUVL VCC2 > VUVH On VCC > VUVH VCC2 < VUVL On VCC < VUVL VCC2 > VUVL On THERMAL SHUTDOWN Off RE = 0V Active Forced-High Forced-High Forced High Forced-High RE = VCC Hi-Z Hi-Z Hi-Z Hi-Z Hi-Z Active Hi-Z Hi-Z Hi-Z Hi-Z FUNCTION (PINS) DC/DC Converter (2, 3) RO (28) RE = Floating RO2 (17) Active Active Active Active Active Driver Outputs Y and Z (13, 12) Active Hi-Z Hi-Z Hi-Z Hi-Z Communications Across Isolation Barrier Active Disabled Disabled Disabled Disabled Low High High High High Fault Indicator on RE (27) Table 3. Driver Function Table Table 4. Receiver Function Table INPUTS OUTPUTS INPUTS OUTPUTS RE DE DI Y Z RE DE A-B X 1 1 1 0 0 X VTH(MAX X 1 0 0 1 0 X X 0 X Z 2 0 X 0 1 Note: Z = high impedance, X = don't care RO R02 1 1 VTH(MIN) 0 0 Inputs Open 1 1 X Inputs Shorted 1 1 X VTH(MAX) Z 1 1 X VTH(MIN) Z 0 1 X Inputs Open Z 1 1 X Inputs Shorted Z 1 Note: Z = high impedance, X = don't care 12 1535fc For more information www.linear.com/LTC1535 LTC1535 Applications Information High Voltage Considerations The LTC1535 eliminates ground loops on data commun ication lines. However, such isolation can bring potentially dangerous voltages onto the circuit board. An example would be accidental faulting to 117V AC at some point on the cable which is then conducted to the PC board. Figure 12 shows how to detect and warn the user or installer that a voltage fault condition exists on the twisted pair or its shield. A small (3.2mm) glow lamp is connected between GND2 (the isolated ground) and the equipment's safety "earth" ground. If a potential of more than 75V AC is present on the twisted pair or shield, B1 will light, indicating a wiring fault. Resistors R3 and R4 are used to ballast the current in B1. Two resistors are necessary because they can only stand off 200V each, as well as for power dissipation. As shown, the circuit can withstand a direct fault to a 440V 3-phase system. Other problems introduced by floating the twisted pair include the collection of static charge on the twisted pair, its shield and the attached circuitry. Resistors R1 and R2 provide a path to shunt static charge safely to ground. Again, two resistors are necessary to withstand high voltage faults. Electrostatic spikes, electromagnetically induced transients and radio frequency pickup are shunted by addition capacitor C1. Receiver Inputs Fail-Safe The LTC1535 features an input common mode range covering the entire RS485 specified range of -7V to 12V. Differential signals of greater than 200mV within the specified input common mode range will be converted to TTL compatible signals at the receiver outputs, RO and RO2. A small amount of input hysteresis is included to minimize the effects of noise on the line signals. If the receiver inputs are floating or shorted, a designedin receiver offset guarantees a fail-safe logic high at the receiver outputs. If a fail-safe logic low is desired, connect as shown in Figure 19. A Y TWISTED-PAIR NETWORK LTC1535 B GND2 Z 2 2 2 R1* 470k R2* 470k C1*** 10nF R3** 100k R4** 100k B1 CN2R (JKL) EQUIPMENT SAFETY GROUND EARTH GROUND * IRC WCR1206 ** IRC WCR1210 *** PANASONIC ECQ-U2A103MV FLOATING RS485 COMMON 2 1535 F12 Figure 12. Detecting Fault Conditions For more information www.linear.com/LTC1535 1535fc 13 LTC1535 Applications Information DI DI Y-Z Y-Z 1535 F14 1535 F13 Figure 13. Driver Propagation Delay with Sample Jitter. SLO = VCC2 Figure 14. Driver Propagation Delay with Sample Jitter. SLO = 0V Z Z Y Y 1535 F15 1535 F16 Figure 16. Driver Output. R = 27, VCC2 = 5V, SLO = 0V Figure 15. Driver Output. R = 27, VCC2 = 5V, SLO = VCC2 Y-Z Y-Z 1535 F17 Figure 17. Driver Differential Output. R = 27, VCC2 = 5V, SLO = VCC2 14 1535 F18 Figure 18. Driver Differential Output. R = 27, VCC2 = 5V, SLO = 0V 1535fc For more information www.linear.com/LTC1535 LTC1535 Typical Application 3V DE DI Y R Z R CL1 CL2 1535 TA02 Figure 19. Fail-Safe Logic "0" RO RE DE DI A B Y Z LTC1535 TTL INPUT RO RE DE DI 30k LTC1535 A B Y Z TTL INPUT 30k 1535 TA02b (20a) Noninverting (20b) Inverting Figure 20. Configuring Receiver for TTL Level Input. Y and Z Outputs Are TTL Compatible with No Modification Full-Duplex Connection ** CTX02-14659 1/2 BAT54C + 10F 2 1/2 BAT54C 2 VCC 1 + 10F VCC 3 ST1 ST2 2 11 14 GND2 VCC2 420kHz A 1 28 RO 27 RE VCC 1 26 25 DI RO R RO2 RE Y DE D DI Z SLO GND 4 B 1 16 120 15 17 13 120 12 18 1535 TA02c LOGIC COMMON FLOATING RS485 COMMON 1 2 ** EATON (888) 414-2645 1535fc For more information www.linear.com/LTC1535 15 .420 MIN 16 For more information www.linear.com/LTC1535 2 3 .030 .005 TYP .050 BSC 0 - 8 TYP N/2 .325 .005 .045 .005 1 .050 (1.270) BSC .093 - .104 (2.362 - 2.642) NOTE 3 N 28 2 27 3 26 4 25 INCHES (MILLIMETERS) 2. DRAWING NOT TO SCALE 3. 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 4. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm) NOTE: 1. DIMENSIONS IN .016 - .050 (0.406 - 1.270) NOTE 3 .291 - .299 (7.391 - 7.595) NOTE 4 .010 - .029 x 45 (0.254 - 0.737) RECOMMENDED SOLDER PAD LAYOUT .009 - .013 (0.229 - 0.330) .005 (0.127) RAD MIN 1 N (Reference LTC DWG # 05-08-1690 Rev A) .014 - .019 (0.356 - 0.482) TYP .697 - .712 (17.70 - 18.08) NOTE 4 SW Package Variation: SW28(16) 28-Lead Plastic Small Outline (Wide .300 Inch) 11 18 12 17 13 16 .037 - .045 (0.940 - 1.143) .394 - .419 (10.007 - 10.643) S28 (WIDE) REV A 0915 .004 - .012 (0.102 - 0.305) 14 N/2 15 LTC1535 Package Description Please refer to http://www.linear.com/product/LTC1535#packaging for the most recent package drawings. 1535fc LTC1535 Revision History (Revision history begins at Rev B) REV DATE DESCRIPTION PAGE NUMBER B 12/09 Update Manufacturer's Information on Typical Application and Figure 10 Revise Receiver Input Hysteresis Conditions 3 Revise Block Diagram 7 Revise Figure 1. 8 Update Tables 1 and 3 C 8/17 1, 10 Updated External Transformer Recommendations 12 1, 5, 8, 10, 12, 15 1535fc Information 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 representation that the interconnection of its information circuits as described herein will not infringe on existing patent rights. For more www.linear.com/LTC1535 17 LTC1535 Typical Application Complete, Isolated 24-Bit Data Acquisition System 1/2 BAT54C LT1761-5 + T1 10F 16V TANT IN OUT SHDN BYP 10F 1F GND + 10F 10V TANT 2 + 1/2 BAT54C RO ST1 RE DE DI VCC1 "SDO" "SCK" LOGIC 5V 1 10F 10V TANT + ST2 LTC1535 G1 1 1 VCC2 G2 2 ISOLATION BARRIER 1 2 A B Y Z = LOGIC COMMON 2 10F CERAMIC 10F 10V TANT LTC2402 FO SCK SDO CS GND 1k 2 2 VCC FSSET CH1 CH0 ZSSET 1535 TA05 = FLOATING COMMON 2 T1 = EATON CTX02-14659 (888) 414-2645 Related Parts PART NUMBER DESCRIPTION COMMENTS LTM2881 Isolated RS485/RS422 Module Transceiver + Power 20Mbps 2500VRMS Isolation with Power in LGA/BGA Package LTM2885 6500VRMS Isolated RS485/RS422 Module Transceiver + Power 20Mbps 6500VRMS Isolation with Power in LGA/BGA Package LTC2862A 60V Fault Protected 3V to 5.5V RS485/RS422 Transceiver 60V Tolerant, 40kV HBM ESD, IEC Level 4 ESD and EFT, 25V Common Mode Range, 20Mbps or 250kbps LTC2861 20Mbps RS485 Transceivers with Integrated Switchable Termination Full Duplex 15kV ESD LTC2856/LTC2857/ 20Mbps and Slew Rate Limited 15kV RS485/RS422 Transceivers LTC2858 Low EMI 250kbps, Micropower Shutdown LT1785/LT1791 60V Fault Protected RS485 Transceiver, Half/Full-Duplex 15kV ESD Protection, Industry Standard Pinout LTC2870/LTC2871 RS232/RS485 Multiprotocol Transceivers with Integrated Termination 20Mbps RS485 and 500kbps RS232, 26kV ESD, 3V to 5.5V Operation 18 1535fc LT 0817 REV C * PRINTED IN USA For more information www.linear.com/LTC1535 www.linear.com/LTC1553 LINEAR TECHNOLOGY CORPORATION 2009