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LTC1535

1535fb

TYPICAL APPLICATION

FEATURES DESCRIPTION

Isolated RS485 Transceiver

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 2500V

RMS

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 reﬂ ections. 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.

APPLICATIONS

UL Rated Isolated RS485: 2500V

RMS

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

Isolated RS485 Receiver/Driver

RS485 with Large Common Mode Voltage

Breaking RS485 Ground Loops

Multiple Unterminated Line Taps

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

SLO

RO2

1535 TA01

GND

LOGIC COMMON

FLOATING RS485 COMMON

** COOPER (888) 414-2645

420kHz

1411

GND2

1/2 BAT54C

CC2

ST1 ST2

10μF

CTX02-14659

TWISTED-PAIR

CABLE

Summary of content (18 pages)

PAGE 1
LTC1535 Isolated RS485 Transceiver FEATURES DESCRIPTION n 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.
PAGE 2
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................
PAGE 3
LTC1535 ELECTRICAL CHARACTERISTICS The l 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.
PAGE 4
LTC1535 ELECTRICAL CHARACTERISTICS The l 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.
PAGE 5
LTC1535 TYPICAL PERFORMANCE CHARACTERISTICS VCC Supply Current vs Temperature VCC2 Supply Current vs Temperature 90 VCC = 5V COOPER CTX02-14659 TRANSFORMER 120 80 VCC2 CURRENT (mA) VCC CURRENT (mA) 110 RL = 54Ω 100 90 RL = 120Ω 80 70 RL = OPEN 60 50 –50 –25 0 6.5 VCC2 = 6V 70 6.0 VCC2 = 5V 60 50 VCC2 = 4.5V 40 30 20 0 60 55 800 VCC2 = 5V, 4.5V SLO = VCC2 RL = 54Ω 700 VCC2 = 5V 600 50 45 500 VCC2 = 4.
PAGE 6
LTC1535 TYPICAL PERFORMANCE CHARACTERISTICS Receiver Output High Voltage vs Temperature Driver Differential Output Voltage vs Output Current 4.5 Driver Output High Voltage vs Output Current 5 5 I = 8mA VCC = 5V TA = 25°C VCC = 5.5V TA = 25°C 4.0 VCC = 4.5V 3.5 4 VCC = 5V OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) 4 3 2 VCC = 4.5V 1 3.0 –50 –25 0 0 25 50 75 100 125 150 TEMPERATURE (°C) 0 10 20 30 40 50 60 70 OUTPUT CURRENT (mA) 5 5.
PAGE 7
LTC1535 PIN FUNCTIONS POWER SIDE ISOLATED SIDE VCC (Pin 1): 5V Supply. Bypass to GND with 10μF 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 10μF capacitor.
PAGE 8
LTC1535 TEST CIRCUIT ILOAD IEXT ** CTX02-14659 VCC2 1/2 BAT54C + IVCC2 10μF 2 1/2 BAT54C 2 VCC 1 + ST1 VCC 2 3 ST2 11 14 GND2 VCC2 420kHz 10μF 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 Y 13 C1 50pF 18 FLOATING RS485 COMMON 1 2 C2 50pF 2 1535 F01 LOGIC COMMON RL Z 12 2 SLOW SLEW RATE JUMPER ** COOPER (888) 414-2645 2 Figure 1.
PAGE 9
LTC1535 SWITCHING TIME WAVEFORMS 3V tr ≤ 10ns, tf ≤ 10ns 1.5V DI 1.5V 0V tPLH tPHL Z VO Y VO 0V –VO 80% tr 80% 20% VDIFF = V(Y) – V(Z) 20% tSJ 1535 F06 tf tSJ Figure 6. Driver Propagation Delays 3V tr ≤ 10ns, tf ≤ 10ns 1.5V DE 1.5V 0V tLZ tZL 5V Y, Z 2.3V OUTPUT NORMALLY LOW 0.5V 2.3V OUTPUT NORMALLY HIGH 0.5V VOL VOH Y, Z 0V tHZ tZH 1535 F07 tSJ tSJ Figure 7. Driver Enable and Disable Times tSJ tSJ VOH 1.5V RO tPHL VOD2 A–B –VOD2 1.
PAGE 10
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).
PAGE 11
LTC1535 APPLICATIONS INFORMATION Driver Output and Slow Slew Rate Control Monitoring Faults on RE 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.
PAGE 12
LTC1535 APPLICATIONS INFORMATION Table 1. List of Transformers Designed for LTC1535 PART NUMBER DC ISOLATION VOLTAGE (1 SECOND) PHONE NUMBER Cooper CTX02-14659 500V (888) 414-2645 Cooper CTX02-14608 3.75kVAC (888) 414-2645 B78304-A1477-A3 500V 31160R 1.
PAGE 13
LTC1535 APPLICATIONS INFORMATION 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.
PAGE 14
LTC1535 APPLICATIONS INFORMATION DI DI Y-Z Y-Z 1535 F13 Figure 13. Driver Propagation Delay with Sample Jitter. SLO = VCC2 1535 F14 Figure 14. Driver Propagation Delay with Sample Jitter. SLO = 0V Z Z Y Y 1535 F15 1535 F16 Figure 16. Driver Output. R = 27Ω, VCC2 = 5V, SLO = 0V Figure 15. Driver Output. R = 27Ω, VCC2 = 5V, SLO = VCC2 Y-Z Y-Z 1535 F17 Figure 17. Driver Differential Output. R = 27Ω, VCC2 = 5V, SLO = VCC2 1535 F18 Figure 18. Driver Differential Output.
PAGE 15
LTC1535 TYPICAL APPLICATION 3V DE Y R Z R CL1 DI 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.
PAGE 16
LTC1535 PACKAGE DESCRIPTION SW Package 28-Lead Plastic Small Outline Isolation Barrier (Wide .300 Inch) (Reference LTC DWG # 05-08-1690) .697 – .712* (17.70 – 18.08) 28 27 26 25 18 17 16 15 .394 – .419 (10.007 – 10.643) NOTE 2 1 2 3 11 4 12 13 14 .291 – .299** (7.391 – 7.595) .093 – .104 (2.362 – 2.642) .010 – .029 s 45° (0.254 – 0.737) 0° – 8° TYP .009 – .013 (0.229 – 0.330) NOTE 2 .016 – .050 (0.406 – 1.270) NOTE: 1. DIMENSIONS IN .050 (1.270) BSC .014 – .019 (0.356 – 0.
PAGE 17
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 1, 10 Revise Receiver Input Hysteresis Conditions 3 Revise Block Diagram 7 Revise Figure 1. 8 Update Tables 1 and 3 12 1535fb Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use.
PAGE 18
LTC1535 TYPICAL APPLICATION Complete, Isolated 24-Bit Data Acquisition System 1/2 BAT54C LT1761-5 + T1 10μF 16V TANT IN OUT SHDN BYP 10μF + GND 1μF 10μF 10V TANT 2 + 1/2 BAT54C RO ST1 RE DE DI VCC1 “SDO” “SCK” LOGIC 5V 1 10μF 10V TANT + VCC2 ST2 LTC1535 G1 G2 1 1 2 ISOLATION BARRIER 1 A B Y Z = LOGIC COMMON 2 10μF CERAMIC 10μF 10V TANT LTC2402 FO SCK SDO CS GND 1k 2 VCC FSSET CH1 CH0 ZSSET 1535 TA05 = FLOATING COMMON 2 2 2 T1 = COOPER CTX02-14659 (888) 414-2645 RELAT