LTC1535CSW

LTC1535 Isolated RS485 Transceiver FEATURES s s s s s s DESCRIPTIO ® s s s s s s 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 68kΩ Input Impedance Allows Up to 128 Nodes Thermal Shutdown 8kV ESD Protection On Driver Outputs and Receiver Inputs Available in 28-Lead SW Package The LTC®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 68kΩ 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. , LTC and LT are registered trademarks of Linear Technology Corporation. APPLICATIO S s s s s Isolated RS485 Receiver/Driver RS485 with Large Common Mode Voltage Breaking RS485 Ground Loops Multiple Unterminated Line Taps TYPICAL APPLICATIO ** CTX02-14659 1/2 BAT54C + 2 10µF 1/2 BAT54C 2 VCC 10µF 3 ST2 420kHz 1 VCC ST1 2 11 GND2 14 VCC2 + 1 LOGIC COMMON 1 FLOATING RS485 COMMON 2 ** TRANSFORMER COOPER (561) 241-7876 RO 28 RO R RE DE DI 27 26 25 4 1 RE DE DI GND D Y Z SLO U A B RO2 16 15 17 TWISTED-PAIR CABLE 13 12 18 1535 TA01 U U 1535fa 1 LTC1535 ABSOLUTE (Note 1) AXI U RATI GS PACKAGE/ORDER I FOR ATIO TOP VIEW VCC 1 ST1 2 ST2 3 GND 4 28 RO 27 RE 26 DE 25 DI 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 ........................................ 0°C ≤ TA ≤ 70°C LTC1535I ..................................... – 40°C ≤ TA ≤ 85°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C ORDER PART NUMBER LTC1535CSW LTC1535ISW GND2 11 Z 12 Y 13 VCC2 14 SW PACKAGE 28-LEAD PLASTIC SO 18 SLO 17 RO2 16 A 15 B TJMAX = 125°C, θJA = 125°C/W Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS SYMBOL VCC VCC2 ICC ICC2 VOD1 VOD2 VOC IOSD1 PARAMETER VCC Supply Range VCC2 Supply Range VCC Supply Current VCC2 Supply Current Differential Driver Output Differential Driver Output Driver Output Common Mode Voltage Driver Short-Circuit Current VOUT = HIGH VOUT = LOW Logic Input High Voltage Logic Input Low Voltage Input Current (A, B) Receiver Input Threshold Receiver Input Hysteresis Receiver Input Impedance The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, VCC2 = 5V unless otherwise noted. CONDITIONS q q MIN 4.5 4.5 TYP MAX 5.5 7.5 UNITS V V mA mA mA V V V Transformer Not Driven (Note 10) R = 27Ω, Figure 2 No Load No Load R = 50Ω (RS422) (Note 2), VCC2 = 4.5V R = 27Ω(RS485), Figure 2, VCC2 = 4.5V DC Level, R = 50Ω, Figure 2 Driver Enabled (DE = 1) –7V ≤ VCM ≤ 10V –7V ≤ VCM ≤ 10V DE, DI, RE SLO DE, DI, RE SLO (Note 3) –7V ≤ VCM ≤ 12V, (Note 4) –7V ≤ VCM ≤ 12V 0°C ≤ TA ≤ 0°C – 40°C ≤ TA ≤ 85°C VIN = 12V VIN = – 7V q q q q q q q q q q q q q q q q q q q 13 63 7 2 1.5 2.0 60 60 2 4 28 73 12 5 2 2.5 100 100 1.7 2.2 1.7 1.8 0.8 1 0.25 –0.20 3.0 150 150 VIH VIL IIN VTH ∆VTH RIN –200 10 5 50 –90 30 30 68 –10 70 70 100 1535fa 2 U V mA mA V V V V mA mA mV mV mV kΩ W U U WW W LTC1535 The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, VCC2 = 5V unless otherwise noted. SYMBOL VIOC VOH VOL IOZ VOH2 VOL2 fSW RSWH RSWL IREL IREH VUVL VUVH VISO PARAMETER Receiver Input Open Circuit Voltage RO Output High Voltage RO Output Low Voltage Driver Output Leakage RO2 Output High Voltage RO2 Output Low Voltage DC Converter Frequency DC Converter Impedance High DC Converter Impedance Low RE Output Low Current RE Output High Current Undervoltage Low Threshold Undervoltage High Threshold Isolation Voltage RE Sink Current, Fault = 0 RE Source Current, Fault = 1 RE Fault = 1, (Note 5) RE Fault = 0, (Note 5) 1 Minute, (Note 6) 1 Second IRO = – 4mA, VCC = 4.5V IRO = 4mA, VCC = 4.5V Driver Disabled (DE = 0) IRO2 = – 4mA, VCC = 4.5V IRO2 = 4mA, VCC = 4.5V q q q q q q q q q q q ELECTRICAL CHARACTERISTICS CONDITIONS MIN 3.7 TYP 3.4 4.0 0.4 1 MAX UNITS V V 0.8 V µA V 3.7 290 3.9 0.4 420 4 2.5 0.8 590 6 5 – 80 130 4.25 4.40 V kHz Ω Ω µA µA V V VRMS VRMS – 40 80 3.70 4.05 2500 3000 – 50 100 4.00 4.20 The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, VCC2 = 5V, R = 27Ω (RS485) unless otherwise noted. SYMBOL tSJ fMAX tPLH tPHL tr, tf tZH tZL tLZ tHZ tPLH tPHL tPLH tPHL tr, tf tLZ tHZ tSTART tTOF PARAMETER Data Sample Jitter Max Baud Rate Driver Input to Output Driver Input to Output Driver Rise or Fall Time Driver Enable to Output Driver Enable to Output Driver Disable to Output Driver Disable to Output Receiver Input to RO Receiver Input to RO Receiver Input to RO2 Receiver Input to RO2 Receiver Rise or Fall Time Receiver Disable to Output Receiver Disable to Output Initial Start-Up Time Data Time-Out Fault ST1, ST2 Duty Cycle CONDITIONS Figure 8, (Note 7) Jitter = 10% Max, SLO = 1, (Note 8) DE = 1, SLO = 1, Figure 4, Figure 6 DE = 1, SLO = 0, Figure 4, Figure 6 DE = 1, SLO = 1, Figure 4, Figure 6 DE = 1, SLO = 0, Figure 4, Figure 6 DE = 1, SLO = 1, Figure 4, Figure 6 DE = 1, SLO = 0, VCC = VCC2 = 4.5V DI = 1, SLO = 1, Figure 5, Figure 7 DI = 0, SLO = 1, Figure 5, Figure 7 DI = 0, SLO = 1, Figure 5, Figure 7 DI = 1, SLO = 1, Figure 5, Figure 7 RE = 0, Figure 3, Figure 8 RE = 0, Figure 3, Figure 8 RE = 0, Figure 3, Figure 8 RE = 0, Figure 3, Figure 8 RE = 0, Figure 3, Figure 8 Figure 3, Figure 9 Figure 3, Figure 9 (Note 9) (Note 9) 0°C ≤ TA ≤ 70°C – 40°C ≤ TA ≤ 85°C q q q q q q q q q q q q q q q q SWITCHI G CHARACTERISTICS U MIN 250 TYP 250 410 600 1300 600 1300 MAX 285 855 1560 855 1560 100 1000 1400 1400 1300 1300 855 855 UNITS ns kBd ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns 150 20 500 1000 1000 700 700 600 600 30 30 20 30 30 1200 1200 56 57 % % 1535fa 3 LTC1535 ELECTRICAL CHARACTERISTICS Note 1: Absolute Maximum Ratings are those values beyond which the life 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 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 reenables when greater than VUVH. The fault can be monitored through 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 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. TYPICAL PERFOR A CE CHARACTERISTICS VCC Supply Current vs Temperature 130 VCC = 5V 120 110 COOPER CTX02-14659 TRANSFORMER RL = 54Ω 90 80 VCC2 = 6V 6.0 VCC2 = 5V VCC2 CURRENT (mA) VCC CURRENT (mA) 100 90 80 70 60 50 –50 –25 RL = OPEN RL = 120Ω 60 50 40 30 20 fDI = fMAX SLO = 0V RL = 54Ω 0 VCC2 VOLTAGE (V) 0 25 50 75 100 125 150 TEMPERATURE (°C) 1535 G01 Maximum Baud Rate vs Temperature 500 65 60 400 fMAX (kHz) TIME (ns) 55 50 45 40 200 VCC = VCC2 = 4.5V SLO = VCC2 RL = 54Ω 0 25 50 75 100 125 150 TEMPERATURE (°C) 1535 G04 300 TIME (ns) 100 –50 –25 4 UW VCC2 Supply Current vs Temperature 6.5 VCC2 Supply Voltage vs Temperature fDI = 250kHz SLO = 0V RL = OPEN, VCC = 5V RL = 54Ω, VCC = 5V 5.5 RL = 54Ω, VCC = 4.5V 5.0 COOPER CTX02-14659 TRANSFORMER 70 VCC2 = 4.5V 10 –50 –25 25 50 75 100 125 150 TEMPERATURE (°C) 1535 G02 4.5 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 1535 G03 Driver Differential Output Rise/ Fall Time vs Temperature 800 VCC2 = 5V, 4.5V SLO = VCC2 RL = 54Ω 700 600 500 400 300 Driver Differential Output Rise/ Fall Time vs Temperature SLO = 0V RL = 54Ω VCC2 = 5V VCC2 = 4.5V 35 30 25 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 1535 G05 200 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 1535 G06 1535fa LTC1535 TYPICAL PERFOR A CE CHARACTERISTICS Switcher Frequency vs Temperature 600 VCC = 5V VCC2 = 6V OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) 500 FREQUENCY (kHz) 3 VCC2 = 5V 2 VCC2 = 4.5V 4 400 300 200 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 1535 G07 Receiver Output High Voltage vs Temperature 4.5 VCC = 5V OUTPUT VOLTAGE (V) I = 8mA 4 OUTPUT VOLTAGE (V) 4.0 VCC = 4.5V 3.5 5 3 OUTPUT VOLTAGE (V) 3.0 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 1535 G10 Driver Output Low Voltage vs Output Current 5 TA = 25°C 4 OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) 4 VCC = 6V 3 VCC = 5V VCC = 4.5V 5 OUTPUT VOLTAGE (V) 2 1 0 0 10 20 30 40 50 60 70 80 90 100 110 OUTPUT CURRENT (mA) 1535 G13 UW Driver Differential Output Voltage vs Temperature 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 Receiver Output Low Voltage vs Temperature I = 8mA VCC = 4.5V VCC = 5V 1 SLO = VCC2 RL = 54Ω 0 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 1535 G08 0 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) 1535 G09 Driver Differential Output Voltage vs Output Current 5 VCC = 5.5V VCC = 5V TA = 25°C 4 Driver Output High Voltage vs Output Current TA = 25°C 3 VCC = 4.5V 2 VCC = 5V VCC = 5.5V 2 VCC = 4.5V 1 1 0 0 10 20 30 40 50 60 70 OUTPUT CURRENT (mA) 80 90 0 0 10 20 30 40 50 60 70 80 90 100 110 OUTPUT CURRENT (mA) 1535 G12 1535 G11 Driver Differential Output Voltage vs VCC2 Supply Voltage 5.0 TA = 25°C RL = 60Ω Receiver Output Voltage vs Load Current TA = 25°C VCC = 5V OUTPUT HIGH, SOURCING 4.0 4.5 3 1.0 OUTPUT LOW, SINKING 0.5 2 1 4.5 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 1535fa 5 LTC1535 PI FU CTIO S POWER SIDE VCC (Pin 1): 5V Supply. Bypass to GND with 10µF capacitor. 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 Side RS485 Driver. Do not float. DE (Pin 26): Transmit Enable TTL Input to the Isolated Side RS485 Driver. A high level enables the driver. Do not float. 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.) RO (Pin 28): Receive Data TTL Output. ISOLATED SIDE GND2 (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. This output is always enabled and is unaffected by RE. SLO (Pin 18): Slow Slew Rate Control of RS485 Driver. A low level forces the driver outputs into slow slew rate mode. BLOCK DIAGRA 1 28 VCC RO 27 RE 26 25 DE DI 4 GND 6 W U U U POWER SIDE 1 ISOLATED SIDE 1.3 + 2 ST1 3 ST2 420kHz 11 GND2 14 VCC2 12.75k 63.5k A 27.25k 16 DECODE ENCODE R 12.75k B 27.25k 63.5k RO2 Y 17 13 12 18 15 FAULT ENCODE EN DECODE D Z SLO 100k VCC2 1535 BD EN FAULT 1535fa LTC1535 TEST CIRCUITS ILOAD ** CTX02-14659 1/2 BAT54C IEXT VCC2 + 2 10µF IVCC2 1/2 BAT54C 2 VCC 10µF 3 ST2 420kHz 2 11 GND2 14 VCC2 + 1 1 VCC ST1 A 28 RO R B RO2 27 26 25 4 1 LOGIC COMMON 1 FLOATING RS485 COMMON 2 ** TRANSFORMER COOPER (561) 241-7876 RE DE DI GND D Y Z SLO 16 15 17 Y Z C1 50pF 18 2 SLOW SLEW RATE JUMPER 2 2 RL C2 50pF RO fRO = MAX BAUD RATE 13 12 1535 F01 Figure 1. Self-Oscillation at Maximum Data Rate (Test Configuration for the First Six Typical Performance Characteristics Curves) Y R VOD R VOC RECEIVER OUTPUT TEST POINT S1 1k VCC CRL 1k S2 1535 F03 Z 1535 F02 Figure 2. Driver DC Test Load Figure 3. Receiver Timing Test Load 3V DE Y DI Z R 1535 F04 R CL1 S1 OUTPUT UNDER TEST 500Ω S2 CL 1535 F05 VCC CL2 Figure 4. Driver Timing Test Circuit Figure 5. Driver Timing Test Load 1535fa 7 LTC1535 SWITCHI G TI E WAVEFOR S 3V DI 0V t PLH Z VO Y VO 0V –VO 80% 20% tr t SJ 80% 20% t SJ tf 1535 F06 1.5V Figure 6. Driver Propagation Delays 3V DE 0V 5V Y, Z VOL VOH Y, Z 0V t ZH 2.3V 2.3V t ZL 1.5V Figure 7. Driver Enable and Disable Times VOH RO VOL t PHL VOD2 A–B –VOD2 0V 1.5V OUTPUT tr ≤ 10ns, tf ≤ 10ns INPUT t PLH 0V 1535 F08 Figure 8. Receiver Propagation Delays 3V RE 0V 5V RO 1.5V t SJ RO 0V tZH t SJ t HZ t SJ 1535 F09 1.5V 1.5V Figure 9. Receiver Enable and Disable Times 1535fa 8 W t SJ W U tr ≤ 10ns, tf ≤ 10ns t PHL 1.5V VDIFF = V(Y) – V(Z) tr ≤ 10ns, tf ≤ 10ns t LZ OUTPUT NORMALLY LOW 1.5V 0.5V OUTPUT NORMALLY HIGH t HZ t SJ t SJ 0.5V 1535 F07 t SJ 1.5V tr ≤ 10ns, tf ≤ 10ns tZL t LZ OUTPUT NORMALLY LOW 1.5V 0.5V t SJ OUTPUT NORMALLY HIGH 0.5V LTC1535 APPLICATIO S I FOR ATIO Isolation Barrier and Sampled Communication 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 1µs to 2µs. A time-out fault will occur if communication from the isolated side fails. Faults can be monitored on the RE pin. 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. ** CTX02-14659 1/2 BAT54C 2 6 VCC2 (V) 1/2 BAT54C 2 VCC 10µF 3 ST2 420kHz + 1 1 VCC ST1 4 1 GND 1535 F10 LOGIC COMMON 1 FLOATING RS485 COMMON 2 U Push-Pull DC/DC Converter 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 Cooper CTX02-14659 transformer. 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 Cooper CTX02-14608 transformer may be used. ILOAD IEXT W U U VCC2 vs ILOAD + IVCC2 10µF 8 VCC = 5.5V 4 VCC = 5V VCC = 4.5V 2 2 11 GND2 14 VCC2 0 0 50 100 TOTAL LOAD CURRENT, ILOAD (mA) 150 1535 F10a ** TRANSFORMER COOPER (561) 241-7876 Figure 10 1535fa 9 LTC1535 APPLICATIO S I FOR ATIO 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. RE POLL DE FAULT BUFFER POLL FAULT FAULT INDICATED WHEN RE IS THREE-STATED 1535 F11 Figure 11. Detecting Fault Conditions 10 U 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 shortcircuited. 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 100µA pull-up current to indicate a fault and 50µA 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 VCC RO RE LTC1535 DI FAULT GND 1535fa W U U LTC1535 APPLICATIO S I FOR ATIO Table 1. List of Transformers Designed for LTC1535 DC ISOLATION VOLTAGE PHONE (1 Second) NUMBER 500V 500V 1.25kV 500V 100V 500V (561) 241-7876 (0 89) 636-2 80 00 (800) 888-7724 (605) 886-4385 (33) 3 84 35 04 04 03-3667-3320 (775) 852-0140 3.75kVAC (561) 241-7876 MANUFACTURER Cooper Cooper Epcos AG (Germany) B78304-A1477-A3 (USA) Midcom Pulse FEE (France) Sumida (Japan) Transpower 31160R P1597 S-167-5779 TTI7780-SM Table 2. Fault Mode Behavior FUNCTION (PINS) DC/DC Converter (2, 3) RO (28) RE = 0V RE = VCC RE = Floating RO2 (17) Driver Outputs Y and Z (13,12) Communication Across Isolation Barrier Fault Indicator on RE (27) VCC > VUVH VCC2 > VUVH On Active Hi-Z Active Active Active Active Low VCC < VUVL VCC2 > VUVH On Forced High Hi-Z Hi-Z Active Hi-Z Disabled High VCC > VUVH VCC2 < VUVL On Forced High Hi-Z Hi-Z Active Hi-Z Disabled High VCC < VUVL VCC2 > VUVL On Forced High Hi-Z Hi-Z Active Hi-Z Disabled High THERMAL SHUTDOWN Off Forced High Hi-Z Hi-Z Active Hi-Z Disabled High Table 3. Driver Function Table INPUTS RE X X X DE 1 1 0 DI 1 0 X A 1 0 Z OUTPUTS B 0 1 Z Note: Z = high impedance, X = don’t care U PART NUMBER CTX02-14659 CTX02-14608 W U U Table 4. Receiver Function Table INPUTS RE 0 0 0 0 1 1 1 1 DE X X X X X X X X A–B ≥ VTH(MAX) ≤ VTH(MIN) Inputs Open Inputs Shorted ≥ VTH(MAX) ≤ VTH(MIN) Inputs Open Inputs Shorted RO 1 0 1 1 Z Z Z Z OUTPUTS RO2 1 0 1 1 1 0 1 1 Note: Z = high impedance, X = don’t care 1535fa 11 LTC1535 APPLICATIO S I FOR ATIO High Voltage Considerations The LTC1535 eliminates ground loops on data communication 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∅ 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 LTC1535 B GND2 2 Z 2 EQUIPMENT SAFETY GROUND EARTH GROUND FLOATING RS485 COMMON 2 Figure 12. Detecting Wiring Faults 1535fa 12 U provide a path to shunt static charge safely to ground. Again, two resisitors 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 hyteresis is included to minimize the effects of noise on the line signals. If the receiver inputs are floating or shorted, a designed-in 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 2 R1* 470k R2* 470k C1*** 10nF R3** 100k R4** 100k B1 CN2R (JKL) * IRC WCR1206 ** IRC WCR1210 *** PANASONIC ECQ-U2A103MV 1535 F12 W U U LTC1535 APPLICATIO S I FOR ATIO DI Y–Z 1535 F13.tif Figure 13. Driver Propagation Delay with Sample Jitter. SLO = VCC2 Z Y 1535 F15.tif Figure 15. Driver Output. R = 27Ω, VCC2 = 5V, SLO = VCC2 Y–Z 1535 F17.tif Figure 17. Driver Differential Output. R = 27Ω, VCC2 = 5V, SLO = VCC2 U DI Y–Z 1535 F14.tif W U U Figure 14. Driver Propagation Delay with Sample Jitter. SLO = 0V Z Y 1535 F16.tif Figure 16. Driver Output. R = 27Ω, VCC2 = 5V, SLO = 0V Y–Z 1535 F18.tif Figure 18. Driver Differential Output. R = 27Ω, VCC2 = 5V, SLO = 0V 1535fa 13 LTC1535 TYPICAL APPLICATIO S 3V DE Y DI Z R 1535 F04 RO RE DE DI (20a) Noninverting Figure 20. Configuring Receiver for TTL Level Input. Y and Z Outputs Are TTL Compatible with No Modification 2 VCC 10µF + 1 1 VCC ST1 RO 28 RO RE 1 VCC DI 27 26 25 4 1 RE DE DI GND D Y Z SLO LOGIC COMMON 1 14 U R CL1 CL2 Figure 19. Fail-Safe Logic “0” LTC1535 A B Y Z TTL INPUT 30k RO RE DE DI LTC1535 A B Y Z TTL INPUT 30k 1535 TA05 (20b) Inverting Full-Duplex Connection ** CTX02-14659 1/2 BAT54C + 2 10µF 1/2 BAT54C 3 ST2 420kHz 2 11 GND2 14 VCC2 A R B RO2 16 120Ω 15 17 13 120Ω 12 18 1535 TA02 FLOATING RS485 COMMON 2 ** TRANSFORMER COOPER (561) 241-7876 1535fa LTC1535 PACKAGE DESCRIPTIO SW Package 28-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) INCHES (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 SIDE NOTE: 1. DIMENSIONS IN 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 circuits as described herein will not infringe on existing patent rights. U .697 – .712* (17.70 – 18.08) 28 27 26 25 18 17 16 15 NOTE 1 .394 – .419 (10.007 – 10.643) 1 2 3 4 11 12 13 14 .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) 0502 1535fa 15 LTC1535 TYPICAL APPLICATIO “SDO” “SCK” LOGIC 5V RO ST1 RE DE DI VCC1 10µF 10V TANT + 1 1 RELATED PARTS PART NUMBER LT1424-5 LTC1485 LTC1531 LT1785/LT1791 LTC1690 DESCRIPTION Isolated Flyback Switching Regulator High Speed RS485 Transceiver Self-Powered Isolated Comparator ± 60V Fault Protected RS485 Transceiver, Half/Full-Duplex Full-Duplex RS485 Transceiver COMMENTS ± 5% Accurate with No Optoisolator Required 10Mbps, Pin Compatible with LTC485 2.5V Isolated Reference, 3000VRMS Isolation ±15kV ESD Protection, Industry Standard Pinout ±15kV ESD Protection, Fail-Safe Receiver 16 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 q FAX: (408) 434-0507 q www.linear.com U Complete, Isolated 24-Bit Data Acquisition System 1/2 BAT54C LT1761-5 + T1 10µF 16V TANT 1µF IN SHDN OUT 10µF BYP GND + 10µF 10V TANT 2 1/2 BAT54C ST2 LTC1535 G1 G2 VCC2 A B Y Z + 2 10µF 10V TANT LTC2402 FO SCK SDO CS GND VCC FSSET CH1 CH0 ZSSET 10µF CERAMIC 2 1k 1 2 1 2 = LOGIC COMMON = FLOATING COMMON 2 2 ISOLATION BARRIER 1535 TA03 T1 = COOPER CTX02-14659 1535fa LT/TP 1103 1K REV A • PRINTED IN USA © LINEAR TECHNOLOGY CORPORATION 1999