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LTC1535 Isolated RS485 Transceiver
FEATURES
s s s s s s
DESCRIPTIO
(R)
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 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
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.
, 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
+
10F 2
1/2 BAT54C 2 VCC 10F 1 LOGIC COMMON 1 FLOATING RS485 COMMON 2 ** TRANSFORMER COOPER (561) 241-7876 RE DE DI 27 26 25 4 1 RE DE DI GND RO 28 RO 3 ST2 420kHz 1 VCC ST1
2 11 GND2 14 VCC2
+
R
D
U
A B RO2 16 15 17 TWISTED-PAIR CABLE Y Z SLO 13 12 18
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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 ........................................ 0C TA 70C LTC1535I ..................................... - 40C TA 85C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
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 = 125C, JA = 125C/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 = 25C. 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 = 27, Figure 2 No Load No Load R = 50 (RS422) (Note 2), VCC2 = 4.5V R = 27(RS485), Figure 2, VCC2 = 4.5V DC Level, R = 50, 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 0C TA 0C - 40C TA 85C 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
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V mA mA V V V V mA mA mV mV mV k
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LTC1535
The q 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 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 A 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 A A 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 = 25C. VCC = 5V, VCC2 = 5V, R = 27 (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) 0C TA 70C - 40C TA 85C
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
% %
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LTC1535
ELECTRICAL CHARACTERISTICS
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 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 = 54 100 90 80 70 60 50 -50 -25 RL = OPEN RL = 120 90 80 VCC2 = 6V 6.0 VCC2 = 5V
VCC2 CURRENT (mA)
VCC CURRENT (mA)
60 50 40 30 20 fDI = fMAX SLO = 0V RL = 54 0
VCC2 VOLTAGE (V)
0
25 50 75 100 125 150 TEMPERATURE (C)
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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 = 54 0 25 50 75 100 125 150 TEMPERATURE (C)
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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
70
RL = 54, VCC = 5V 5.5 RL = 54, VCC = 4.5V 5.0 COOPER CTX02-14659 TRANSFORMER
VCC2 = 4.5V
10 -50 -25
25 50 75 100 125 150 TEMPERATURE (C)
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4.5 -50 -25
0
25 50 75 100 125 150 TEMPERATURE (C)
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Driver Differential Output Rise/ Fall Time vs Temperature
800 VCC2 = 5V, 4.5V SLO = VCC2 RL = 54 700 600 500 400 300
Driver Differential Output Rise/ Fall Time vs Temperature
SLO = 0V RL = 54 VCC2 = 5V
VCC2 = 4.5V
35 30 25 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (C)
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200 -50 -25
0
25 50 75 100 125 150 TEMPERATURE (C)
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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)
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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)
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Driver Output Low Voltage vs Output Current
5 TA = 25C 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)
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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 = 54 0 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (C)
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0 -50 -25
0
25 50 75 100 125 150 TEMPERATURE (C)
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Driver Differential Output Voltage vs Output Current
5 VCC = 5.5V VCC = 5V TA = 25C 4
Driver Output High Voltage vs Output Current
TA = 25C
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)
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Driver Differential Output Voltage vs VCC2 Supply Voltage
5.0 TA = 25C RL = 60
Receiver Output Voltage vs Load Current
TA = 25C 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
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0
0
1
2
3 4 5 6 7 LOAD CURRENT (mA)
8
9
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LTC1535
PI FU CTIO S
POWER SIDE VCC (Pin 1): 5V Supply. Bypass to GND with 10F 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 10F 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
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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
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EN FAULT
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LTC1535
TEST CIRCUITS
ILOAD ** CTX02-14659 1/2 BAT54C IEXT VCC2
+
10F 2
IVCC2
1/2 BAT54C 2 VCC 10F 1 RO fRO = MAX BAUD RATE 27 26 25 4 1 LOGIC COMMON 1 FLOATING RS485 COMMON 2 RE DE DI GND 28 RO 3 ST2 420kHz
2 11 GND2 14 VCC2
+
1
VCC
ST1
A R B RO2
16 15 17 Y Z C1 50pF 18 2 SLOW SLEW RATE JUMPER 2 2 RL C2 50pF
Y D Z SLO
13 12
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** TRANSFORMER COOPER (561) 241-7876
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
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Z
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Figure 2. Driver DC Test Load
Figure 3. Receiver Timing Test Load
3V DE Y DI Z R
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R
CL1
S1 OUTPUT UNDER TEST 500 S2 CL
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VCC
CL2
Figure 4. Driver Timing Test Circuit
Figure 5. Driver Timing Test Load
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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
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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
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Figure 8. Receiver Propagation Delays
3V RE 0V 5V RO 1.5V t SJ RO 0V tZH t SJ t HZ t SJ
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1.5V
1.5V
Figure 9. Receiver Enable and Disable Times
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t SJ
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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
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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 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 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 10F 1 4 1 LOGIC COMMON 1 FLOATING RS485 COMMON 2 GND 3 ST2 420kHz
+
1
VCC
ST1
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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
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VCC2 vs ILOAD
+
10F
IVCC2
8
VCC = 5.5V 4 VCC = 5V VCC = 4.5V 2
2 11 GND2 14 VCC2
0 0
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50 100 TOTAL LOAD CURRENT, ILOAD (mA)
150
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** TRANSFORMER COOPER (561) 241-7876
Figure 10
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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
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Figure 11. Detecting Fault Conditions
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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 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 VCC RO RE LTC1535 DI FAULT GND
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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
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PART NUMBER CTX02-14659 CTX02-14608
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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
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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
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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
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APPLICATIO S I FOR ATIO
DI
Y-Z
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Figure 13. Driver Propagation Delay with Sample Jitter. SLO = VCC2
Z
Y
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Figure 15. Driver Output. R = 27, VCC2 = 5V, SLO = VCC2
Y-Z
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Figure 17. Driver Differential Output. R = 27, VCC2 = 5V, SLO = VCC2
U
DI Y-Z
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Figure 14. Driver Propagation Delay with Sample Jitter. SLO = 0V
Z
Y
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Figure 16. Driver Output. R = 27, VCC2 = 5V, SLO = 0V
Y-Z
1535 F18.tif
Figure 18. Driver Differential Output. R = 27, 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 10F 1 RO 28 RO
+
1
VCC
ST1
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
+
10F 2
1/2 BAT54C 3 ST2 420kHz
2 11 GND2 14 VCC2
A R B RO2
16 120 15 17
13 120 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 x 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 10F 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
10F 16V TANT 1F
IN SHDN
OUT 10F BYP
+
GND
10F 10V TANT
2
1/2 BAT54C ST2 LTC1535 G1 G2 VCC2 A B Y Z
+
2
10F 10V TANT LTC2402 FO SCK SDO CS GND VCC FSSET CH1 CH0 ZSSET
10F 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
(c) LINEAR TECHNOLOGY CORPORATION 1999

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