2.5 kV Isolated RS-485 Transceivers with Integrated Transformer Driver ADM2482E/ADM2487E FEATURES FUNCTIONAL BLOCK DIAGRAM VDD1 VDD2 D1 D2 OSC DE GALVANIC ISOLATION TxD RxD Y Z A B RE GND1 GND2 07379-001 Isolated RS-485/RS-422 transceivers, configurable as half duplex or full duplex Integrated oscillator driver for external transformer ±15 kV ESD protection on RS-485 input/output pins Complies with TIA/EIA-485-A-98 and ISO 8482:1987(E) Data rate: 500 kbps/16 Mbps 5 V or 3.3 V operation (VDD1) 256 nodes on bus True fail-safe receiver inputs 2500 V rms isolation for 1 minute Reinforced insulation 560 V peak High common-mode transient immunity: >25 kV/μs Thermal shutdown protection Operating temperature range: −40°C to +85°C Wide-body, 16-lead SOIC package Figure 1. APPLICATIONS Isolated RS-485/RS-422 interfaces Industrial field networks Multipoint data transmission systems GENERAL DESCRIPTION The ADM2482E/ADM2487E are isolated data transceivers with ±15 kV ESD protection and are suitable for high speed, halfduplex or full-duplex communication on multipoint transmission lines. For half-duplex operation, the transmitter outputs and receiver inputs share the same transmission line. Transmitter Output Pin Y is linked externally to Receiver Input Pin A, and Transmitter Output Pin Z to Receiver Input Pin B. The parts are designed for balanced transmission lines and comply with TIA/EIA- 485-A-98 and ISO 8482:1987(E). The devices employ the Analog Devices, Inc., iCoupler® technology to combine a 3-channel isolator, a three-state differential line driver, and a differential input receiver into a single package. An on-chip oscillator outputs a pair of square waveforms that drive an external transformer to provide isolated power. The logic side of the device can be powered with either a 5 V or a 3.3 V supply, and the bus side is powered with an isolated 3.3 V supply. The ADM2482E/ADM2487E driver has an active high enable, and the receiver has an active low enable. The driver output enters a high impedance state when the driver enable signal is low. The receiver output enters a high impedance state when the receiver enable signal is high. The device has current-limiting and thermal shutdown features to protect against output short circuits and situations where bus contention might cause excessive power dissipation. The part is fully specified over the industrial temperature range of −40°C to +85°C and is available in a 16-lead, wide-body SOIC package. Rev. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.461.3113 ©2008 Analog Devices, Inc. All rights reserved. ADM2482E/ADM2487E TABLE OF CONTENTS Features .............................................................................................. 1 Typical Performance Characteristics ........................................... 10 Applications ....................................................................................... 1 Circuit Description......................................................................... 13 Functional Block Diagram .............................................................. 1 Electrical Isolation...................................................................... 13 General Description ......................................................................... 1 Truth Tables................................................................................. 13 Revision History ............................................................................... 2 Thermal Shutdown .................................................................... 14 Specifications..................................................................................... 3 True Fail-Safe Receiver Inputs .................................................. 14 Timing Specifications .................................................................. 4 Magnetic Field Immunity.......................................................... 14 Package Characteristics ............................................................... 5 Applications Information .............................................................. 15 Insulation and Safety-Related Specifications ............................ 5 Printed Circuit Board Layout ................................................... 15 Test Circuits ................................................................................... 6 Isolated Power Supply Circuit .................................................. 15 Switching Characteristics ............................................................ 7 Typical Applications ................................................................... 16 Absolute Maximum Ratings............................................................ 8 Outline Dimensions ....................................................................... 17 ESD Caution .................................................................................. 8 Ordering Guide .......................................................................... 17 Pin Configuration and Function Descriptions ............................. 9 REVISION HISTORY 5/08—Revision 0: Initial Version Rev. 0 | Page 2 of 20 ADM2482E/ADM2487E SPECIFICATIONS All voltages are relative to their respective ground; 3.0 V ≤ VDD1 ≤ 5.5 V, 3.0 V ≤ VDD2 ≤ 3.6 V. All minimum/maximum specifications apply over the entire recommended operation range, unless otherwise noted. All typical specifications are at TA = 25°C, VDD1 = 5 V, VDD2 = 3.3 V, unless otherwise noted. Table 1. Parameter SUPPLY CURRENT Power-Supply Current, Logic Side TxD/RxD Data Rate < 500 kbps ADM2487E TxD/RxD Data Rate = 500 kbps Max Unit Test Conditions IDD1 IDD1 3.5 4 mA mA ADM2482E TxD/RxD Data Rate = 16 Mbps IDD1 6.0 mA Unloaded output Half-duplex configuration, RTERMINATION = 120 Ω, see Figure 8 Half-duplex configuration, RTERMINATION = 120 Ω, see Figure 8 Power-Supply Current, Bus Side TxD/RxD Data Rate < 500 kbps ADM2487E TxD/RxD Data Rate = 500 kbps IDD2 IDD2 17 40 mA mA ADM2482E TxD/RxD Data Rate = 16 Mbps IDD2 50 mA 5.0 5.0 5.0 0.2 3.0 0.2 250 125 V V V V V V mA μA DRIVER Differential Outputs Differential Output Voltage, Loaded ∆|VOD| for Complementary Output States Common-Mode Output Voltage ∆|VOC| for Complementary Output States Short-Circuit Output Current Output Leakage Current (Y, Z) Symbol |VOD2| |VOD3| ∆|VOD| VOC ∆|VOC| IOS IO Min Typ 2.0 1.5 1.5 −100 Logic Inputs Input Threshold Low Input Threshold High Input Current RECEIVER Differential Inputs Differential Input Threshold Voltage Input Voltage Hysteresis Input Current (A, B) Line Input Resistance Logic Outputs Output Voltage Low Output Voltage High Short Circuit Current Tristate Output Leakage Current μA VIL VIH II 0.25 × VDD1 −10 +0.01 VTH VHYS II −200 −125 15 RIN VOLRxD VOHRxD IOS IOZR 0.7 × VDD1 +10 −30 125 mV mV μA −7 V < VCM < +12 V VOC = 0 V DE = 0 V, VDD = 0 V or 3.6 V, VIN = 12 V DE = 0 V, VDD = 0 V or 3.6 V, VIN = −7 V −7 V < VCM < +12 V 96 kΩ 0.4 100 ±1 Rev. 0 | Page 3 of 20 DE = 0 V, RE = 0 V, VCC = 0 V or 3.6 V, VIN = 12 V DE = 0 V, RE = 0 V, VCC = 0 V or 3.6 V, VIN = −7 V DE, RE, TxD DE, RE, TxD DE, RE, TxD μA 0.2 VDD1 − 0.2 RL = 100 Ω (RS-422), see Figure 2 RL = 54 Ω (RS-485), see Figure 2 −7 V ≤ VTEST ≤ +12 V, see Figure 3 RL = 54 Ω or 100 Ω, see Figure 2 RL = 54 Ω or 100 Ω, see Figure 2 RL = 54 Ω or 100 Ω, see Figure 2 V V μA −125 VDD1 − 0.3 Unloaded output VDD2 = 3.6 V, half-duplex configuration, RTERMINATION = 120 Ω, see Figure 8 VDD2 = 3.6 V, half-duplex configuration, RTERMINATION = 120 Ω, see Figure 8 V V mA μA IORxD = 1.5 mA, VA − VB = −0.2 V IORxD = −1.5 mA, VA − VB = 0.2 V VDD1 = 5.0 V, 0 V < VO < VDD1 ADM2482E/ADM2487E Parameter TRANSFORMER DRIVER Oscillator Frequency Symbol Min Typ Max Unit Test Conditions fOSC 400 230 RON VSTART 600 430 1.5 2.5 kHz kHz Ω V kV/μs VDD1 = 5.0 V VDD1 = 3.3 V Switch-On Resistance Start-Up Voltage COMMON-MODE TRANSIENT IMMUNITY 1 500 330 0.5 2.2 1 25 VCM = 1 kV, transient magnitude = 800 V CM is the maximum common-mode voltage slew rate that can be sustained while maintaining specification-compliant operation. VCM is the common-mode potential difference between the logic and bus sides. The transient magnitude is the range over which the common-mode is slewed. The common-mode voltage slew rates apply to both rising and falling common-mode voltage edges. TIMING SPECIFICATIONS TA = −40°C to +85°C Table 2. ADM2482E Parameter DRIVER Propagation Delay Output Skew Rise Time/Fall Time Enable Time Disable Time RECEIVER Propagation Delay Output Skew Enable Time Disable Time Symbol Min Typ Max Unit Test Conditions tDPLH, tDPHL tDSKEW tDR, tDF tZL, tZH tLZ, tHZ 100 8 15 120 150 ns ns ns ns ns RDIFF = 54 Ω, CL = 100 pF, see Figure 4 and Figure 9 RDIFF = 54 Ω, CL = 100 pF, see Figure 4 and Figure 9 RDIFF = 54 Ω, CL = 100 pF, see Figure 4 and Figure 9 RL = 110 Ω, CL = 50 pF, see Figure 5 and Figure 11 RL = 110 Ω, CL = 50 pF, see Figure 5 and Figure 11 tPLH, tPHL tSKEW tZL, tZH tLZ, tHZ 110 8 13 13 ns ns ns ns CL = 15 pF, see Figure 6 and Figure 10 CL = 15 pF, see Figure 6 and Figure 10 RL = 1 kΩ, CL = 15 pF, see Figure 7 and Figure 12 RL = 1 kΩ, CL = 15 pF, see Figure 7 and Figure 12 Max Unit Test Conditions 700 100 1100 2.5 200 ns ns ns μs ns RDIFF = 54 Ω, CL = 100 pF, see Figure 4 and Figure 9 RDIFF = 54 Ω, CL = 100 pF, see Figure 4 and Figure 9 RDIFF = 54 Ω, CL = 100 pF, see Figure 4 and Figure 9 RL = 110 Ω, CL = 50 pF, see Figure 5 and Figure 11 RL = 110 Ω, CL = 50 pF, see Figure 5 and Figure 11 200 30 13 13 ns ns ns ns CL = 15 pF, see Figure 6 and Figure 10 CL = 15 pF, see Figure 6 and Figure 10 RL = 1 kΩ, CL = 15 pF, see Figure 7 and Figure 12 RL = 1 kΩ, CL = 15 pF, see Figure 7 and Figure 12 Table 3. ADM2487E Parameter DRIVER Propagation Delay Output Skew Rise Time/Fall Time Enable Time Disable Time RECEIVER Propagation Delay Output Skew Enable Time Disable Time Symbol Min tDPLH, tDPHL tDSKEW tDR, tDF tZL, tZH tLZ, tHZ 250 tPLH, tPHL tSKEW tZL, tZH tLZ, tHZ 200 Typ Rev. 0 | Page 4 of 20 ADM2482E/ADM2487E PACKAGE CHARACTERISTICS Table 4. Parameter Resistance (Input-Output) 1 Capacitance (Input-Output)1 Input Capacitance 2 Input IC Junction-to-Case Thermal Resistance Symbol RI-O CI-O CI θJCI Output IC Junction-to-Case Thermal Resistance θJCO 1 2 Min Typ 1012 3 4 33 Max 28 Unit Ω pF pF °C/W °C/W Test Conditions f = 1 MHz Thermocouple located at center of package underside Thermocouple located at center of package underside This device is considered a 2-terminal device: Pin 1 to Pin 8 are shorted together and Pin 9 to Pin 16 are shorted together. Input capacitance is from any input data pin to ground. INSULATION AND SAFETY-RELATED SPECIFICATIONS Table 5. Parameter Rated Dielectric Insulation Voltage Maximum Working Insulation Voltage Minimum External Air Gap (Clearance) Symbol L(I01) Value 2500 560 5.7 min Unit V rms V peak mm Minimum External Tracking (Creepage) L(I02) 6.1 min mm Minimum Internal Gap (Internal Clearance) Tracking Resistance (Comparative Tracking Index) CTI 0.017 min >175 mm V Rev. 0 | Page 5 of 20 Conditions 1-minute duration Measured from input terminals to output terminals, shortest distance through air Measured from input terminals to output terminals, shortest distance along body Distance through insulation DIN IEC 112/VDE 0303-1 ADM2482E/ADM2487E TEST CIRCUITS VOD2 RL 2 RL 2 VOC Y S1 S2 CL 50pF Z DE Figure 5. Driver Enable/Disable 375Ω A 375Ω V TEST Z Figure 3. Driver Voltage Measurement VOUT RE B CL Figure 6. Receiver Propagation Delay +1.5V VCC S1 Y TxD CL RL –1.5V RE CL RE IN Figure 4. Driver Propagation Delay Figure 7. Receiver Enable/Disable VDD2 VDD1 VDD2 GALVANIC ISOLATION DE TxD Y Z 120Ω A RxD B GND2 Figure 8. Supply-Current Measurement Test Circuit Rev. 0 | Page 6 of 20 07379-005 RE GND1 S2 VOUT 07379-009 CL 07379-006 RDIFF Z 07379-008 60Ω 07379-004 VOD3 RL 110Ω TxD Figure 2. Driver Voltage Measurement TxD VCC VOUT Y 07379-003 Z 07379-007 Y TxD ADM2482E/ADM2487E SWITCHING CHARACTERISTICS VDD1 VDD1 /2 VDD1 /2 VDD1 0V tDPLH tDPHL DE Z 0.5VDD1 0.5VDD1 0V 1/2VO tZL VO tLZ 2.3V Y Y, Z VDIFF –VO VDIFF = V(Y) – V(Z) VOL tZH 90% POINT tHZ 2.3V VOH 10% POINT 10% POINT tDR tDF VOH – 0.5V Y, Z 0V Figure 9. Driver Propagation Delay, Rise/Fall Timing 07379-012 90% POINT 07379-010 +VO VOL + 0.5V Figure 11. Driver Enable/Disable Timing 0.7VDD1 RE 0.5VDD1 0.5VDD1 0.3VDD1 0V 0V tPLH tPHL tZL tLZ 1.5V RxD tZH VOH VOL + 0.5V OUTPUT LOW VOL tHZ OUTPUT HIGH 1.5V tSKEW = |tPLH – tPHL| 1.5V VOL 07379-011 RxD Figure 10. Receiver Propagation Delay RxD 1.5V VOH VOH – 0.5V 0V Figure 12. Receiver Enable/Disable Timing Rev. 0 | Page 7 of 20 07379-013 A–B ADM2482E/ADM2487E ABSOLUTE MAXIMUM RATINGS All voltages are relative to their respective ground; TA = 25°C, unless otherwise noted. Table 6. Parameter VDD1 VDD2 Digital Input Voltages (DE, RE, TxD) Digital Output Voltages RxD D1, D2 Driver Output/Receiver Input Voltage Operating Temperature Range Storage Temperature Range Average Output Current per Pin ESD (Human Body Model) on A, B, Y and Z pins Lead Temperature Soldering (10 sec) Vapor Phase (60 sec) Infrared (15 sec) Rating −0.5 V to +6 V −0.5 V to +6 V −0.5 V to VDD1 + 0.5 V −0.5 V to VDD1 + 0.5 V 13 V −9 V to +14 V −40°C to +85°C −55°C to +150°C −35 mA to +35 mA ±15 kV Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ESD CAUTION 300°C 215°C 220°C Rev. 0 | Page 8 of 20 ADM2482E/ADM2487E D1 1 16 VDD2 D2 2 15 GND2 14 A 13 B 12 Z RE 6 11 Y DE 7 10 NC TxD 8 9 GND2 GND1 3 VDD1 4 RxD 5 ADM2482E/ ADM2487E TOP VIEW (Not to Scale) NC = NO CONNECT 07379-002 PIN CONFIGURATION AND FUNCTION DESCRIPTIONS Figure 13. Pin Configuration Table 7. Pin Function Descriptions Pin No. 1 2 3 4 Mnemonic D1 D2 GND1 VDD1 5 RxD 6 RE 7 8 9 10 11 12 13 14 15 16 DE TxD GND2 NC Y Z B A GND2 VDD2 Description Transformer Driver Terminal 1. Transformer Driver Terminal 2. Ground, Logic Side. Power Supply, Logic Side (3.3 V or 5 V). Decoupling capacitor to GND1 required; capacitor value should be between 0.01 μF and 0.1 μF. Receiver Output Data. This output is high when (A – B) > +200 mV and low when (A – B) < –200 mV. The output is tristated when the receiver is disabled, that is, when RE is driven high. Receiver Enable Input. This is an active-low input. Driving this input low enables the receiver; driving it high disables the receiver. Driver Enable Input. Driving this input high enables the driver; driving it low disables the driver. Transmit Data. Ground, Bus Side. No Connect. This pin must be left floating. Driver Noninverting Output. Driver Inverting Output. Receiver Inverting Input. Receiver Noninverting Input. Ground, Bus Side. Power Supply, Bus Side (Isolated 3.3 V Supply). Decoupling capacitor to GND2 required; capacitor value should be between 0.01 μF and 0.1 μF. Rev. 0 | Page 9 of 20 ADM2482E/ADM2487E TYPICAL PERFORMANCE CHARACTERISTICS 2.30 60 NO LOAD 54Ω LOAD 120Ω LOAD 50 SUPPLY CURRENT IDD1 (mA) 2.20 2.15 2.10 2.05 60 85 0 –40 60 85 NO LOAD 54Ω LOAD 120Ω LOAD 30 25 20 15 10 5 10 35 TEMPERATURE (°C) 60 85 tDPHL 400 300 200 100 0 –40 07379-030 –15 tDPLH 500 –20 0 20 40 60 07379-033 DRIVER PROPAGATION DELAY (ns) SUPPLY CURRENT IDD2 (mA) 10 35 TEMPERATURE (°C) 600 35 80 TEMPERATURE (°C) Figure 15. ADM2487E IDD2 Supply Current vs. Temperature (See Figure 8) (Data Rate = 500 kbps, VDD1 = 5 V, VDD2 = 3.3 V, DE = 1 V, RE = 0 V) Figure 18. ADM2487E Driver Propagation Delay vs. Temperature 4.0 70 NO LOAD 54Ω LOAD 120Ω LOAD 65 DRIVER PROPAGATION DELAY (ns) 3.9 SUPPLY CURRENT IDD1 (mA) –15 Figure 17. ADM2482E Supply Current vs. Temperature (See Figure 8) (Data Rate = 16 Mbps, VDD1 = 5 V, VDD2 = 3.3 V, DE = 1, RE =0 V) 40 3.8 3.7 3.6 3.5 3.4 3.3 3.2 60 tDPLH 55 tDPHL 50 45 40 35 30 25 –15 10 35 TEMPERATURE (°C) 60 85 20 –40 07379-031 3.1 –40 20 07379-032 10 35 TEMPERATURE (°C) 07379-029 –15 Figure 14. ADM2487E IDD1 Supply Current vs. Temperature (Data Rate = 500 kbps, VDD1 = 5 V, VDD2 = 3.3 V, DE = 1 V, RE = 0 V) 0 –40 30 10 2.00 1.95 –40 40 Figure 16. ADM2482E IDD1 Supply Current vs. Temperature (Data Rate = 16 Mbps, VDD1 = 5 V, VDD2 = 3.3 V, DE = 1 V, RE = 0 V) Rev. 0 | Page 10 of 20 –15 10 35 TEMPERATURE (°C) 60 85 07379-034 SUPPLY CURRENT IDD1 (mA) 2.25 NO LOAD 54Ω LOAD 120Ω LOAD Figure 19. ADM2482E Driver Propagation Delay vs. Temperature ADM2482E/ADM2487E 0.32 0 0.30 –20 OUTPUT VOLTAGE (V) –30 –40 –50 0.28 0.26 0.24 0.22 –60 0 1 2 3 4 0.20 –40 07379-016 –70 5 OUTPUT VOLTAGE (V) –20 0 20 40 60 07379-019 OUTPUT CURRENT (mA) –10 80 TEMPERATURE (°C) Figure 23. Receiver Output Low Voltage vs. Temperature (IDD2 = 4 mA) Figure 20. Output Current vs. Receiver Output High Voltage 60 D1 40 1 30 20 D2 10 0 1 2 3 4 07379-017 0 5 OUTPUT VOLTAGE (V) CH1 2.0V Ω CH2 2.0V Ω M400ns 125MS/s 8.0ns/pt Figure 21. Output Current vs. Receiver Output Low Voltage A CH2 1.52V 07379-020 2 1.52V 07379-021 OUTPUT CURRENT (mA) 50 Figure 24. Switching Waveforms (50 Ω Pull-Up to VDD1 on D1 and D2) 4.75 D1 4.73 4.72 1 4.71 D2 4.70 4.69 4.68 4.67 –40 –20 0 20 40 60 80 TEMPERATURE (°C) 07379-018 OUTPUT VOLTAGE (V) 4.74 Figure 22. Receiver Output High Voltage vs. Temperature (IDD2 = –4 mA) CH1 2.0V Ω CH2 2.0V Ω M80ns 625MS/s 1.6ns/pt A CH2 Figure 25. Switching Waveforms (Break-Before-Make, 50 Ω Pull-Up to VDD1 on D1 and D2) Rev. 0 | Page 11 of 20 ADM2482E/ADM2487E T TxD 1 TxD Z, B 1 2 Z, B 2 Y, A Y, A RxD 4 RxD CH2 2.00V CH4 2.00V M 200ns T 47.80% A CH2 1.72V CH1 2.0V Ω CH2 2.0V Ω CH3 2.0V Ω CH4 2.0V Ω Figure 26. ADM2487E Driver/Receiver Propagation Delay, Low to High (RDIFF = 54 Ω, CL1 = CL2 = 100 pF) M 40.0ns 1.25GS/s IT 16.0ps/pt A CH2 1.68V 07379-037 CH1 2.00V CH3 2.00V 07379-035 4 Figure 28. ADM2482E Driver/Receiver Propagation Delay, High to Low (RDIFF = 54 Ω, CL1 = CL2 = 100 pF) T 1 TxD TxD Z, B 1 2 Z, B Y, A Y, A 2 RxD 4 RxD CH2 2.00V CH4 2.00V M 200ns T 48.60% A CH2 1.72V CH1 2.0V Ω CH2 2.0V Ω CH3 2.0V Ω CH4 2.0V Ω Figure 27. ADM2487E Driver/Receiver Propagation Delay, High to Low (RDIFF = 54 Ω, CL1 = CL2 = 100 pF) M 40.0ns 1.25GS/s IT 16.0ps/pt A CH2 1.68V 07379-038 CH1 2.00V CH3 2.00V 07379-036 4 Figure 29. ADM2482E Driver/Receiver Propagation Delay, Low to High (RDIFF = 54 Ω, CL1 = CL2 = 100 pF) Rev. 0 | Page 12 of 20 ADM2482E/ADM2487E CIRCUIT DESCRIPTION ELECTRICAL ISOLATION TRUTH TABLES In the ADM2482E/ADM2487E, electrical isolation is implemented on the logic side of the interface. Therefore, the part has two main sections: a digital isolation section and a transceiver section (see Figure 30). Driver input and data enable applied to the TxD and DE pins, respectively, and referenced to logic ground (GND1) are coupled across an isolation barrier to appear at the transceiver section referenced to isolated ground (GND2). Similarly, the receiver output, referenced to isolated ground in the transceiver section, is coupled across the isolation barrier to appear at the RxD pin referenced to logic ground. The truth tables in this section use the abbreviations found in Table 8. iCoupler Technology The digital signals transmit across the isolation barrier using iCoupler technology. This technique uses chip scale transformer windings to couple the digital signals magnetically from one side of the barrier to the other. Digital inputs are encoded into waveforms that are capable of exciting the primary transformer winding. At the secondary winding, the induced waveforms are decoded into the binary value that was originally transmitted. Positive and negative logic transitions at the input cause narrow pulses (~1 ns) to be sent to the decoder, via the transformer. The decoder is bistable and is, therefore, either set or reset by the pulses, indicating input logic transitions. In the absence of logic transitions at the input for more than ~1 μs, a periodic set of refresh pulses indicative of the correct input state are sent to ensure dc correctness at the output. If the decoder receives no internal pulses for more than about 5 μs, then the input side is assumed to be unpowered or nonfunctional, in which case the output is forced to a default state (see Table 8). VDD1 VDD2 D1 D2 OSC ISOLATION BARRIER DE ENCODE DECODE TxD ENCODE DECODE Table 8. Truth Table Abbreviations Letter H I L X Z NC Table 9. Transmitting Supply Status VDD1 VDD2 On On On On On On On Off Off On Off Off DECODE RE DIGITAL ISOLATION GND1 Outputs RxD On On On On On On Off >−0.03 V <−0.2 V −0.2 V < A − B < −0.03 V Inputs open X X X L or NC L or NC L or NC L or NC H L or NC L or NC H L I H Z H L B TRANSCEIVER GND2 Outputs Z L H Z Z Z Z RE Z R Y H L Z Z Z Z A−B 07379-022 ENCODE Inputs TxD H L X X X X Supply Status VDD1 VDD2 A RxD DE H H L X L X Table 10. Receiving Y D Description High level Indeterminate Low level Irrelevant High impedance (off ) Disconnected Figure 30. ADM2482E/ADM2487E Digital Isolation and Transceiver Sections Rev. 0 | Page 13 of 20 On On On On On Off Off Inputs ADM2482E/ADM2487E MAGNETIC FIELD IMMUNITY The limitation on the magnetic field immunity of the iCoupler is set by the condition in which an induced voltage in the receiving coil of the transformer is large enough to either falsely set or reset the decoder. The following analysis defines the conditions under which this may occur. The 3 V operating condition of the ADM2482E/ADM2487E is examined because it represents the most susceptible mode of operation. The pulses at the transformer output have an amplitude greater than 1 V. The decoder has a sensing threshold of about 0.5 V, thus establishing a 0.5 V margin in which induced voltages can be tolerated. The voltage induced across the receiving coil is given by ⎛ −dβ ⎞ 2 V =⎜ ⎟∑ πrn ; n = 1, 2, K , N ⎝ dt ⎠ where: β is the magnetic flux density (gauss). N is the number of turns in the receiving coil. rn is the radius of the nth turn in the receiving coil (cm). 1 0.1 0.01 0.001 1k 10k 100k 1M 10M MAGNETIC FIELD FREQUENCY (Hz) 100M 07379-023 The receiver inputs have a true fail-safe feature that ensures that the receiver output is high when the inputs are open or shorted. During line-idle conditions, when no driver on the bus is enabled, the voltage across a terminating resistance at the receiver input decays to 0 V. With traditional transceivers, receiver input thresholds specified between −200 mV and +200 mV mean that external bias resistors are required on the A and B pins to ensure that the receiver outputs are in a known state. The true fail-safe receiver input feature eliminates the need for bias resistors by specifying the receiver input threshold between −30 mV and −200 mV. The guaranteed negative threshold means that when the voltage between A and B decays to 0 V, the receiver output is guaranteed to be high. 10 Figure 31. Maximum Allowable External Magnetic Flux Density For example, at a magnetic field frequency of 1 MHz, the maximum allowable magnetic field of 0.2 kgauss induces a voltage of 0.25 V at the receiving coil. This is about 50% of the sensing threshold and does not cause a faulty output transition. Similarly, if such an event occurs during a transmitted pulse and is the worst-case polarity, it reduces the received pulse from >1.0 V to 0.75 V, still well above the 0.5 V sensing threshold of the decoder. Figure 32 shows the magnetic flux density values in terms of more familiar quantities, such as maximum allowable current flow at given distances away from the ADM2482E/ADM2487E transformers. 1000 DISTANCE = 1m 100 DISTANCE = 5mm 10 DISTANCE = 100mm 1 0.1 0.01 1k 10k 100k 1M 10M MAGNETIC FIELD FREQUENCY (Hz) 100M 07379-024 TRUE FAIL-SAFE RECEIVER INPUTS 100 MAXIMUM ALLOWABLE MAGNETIC FLUX DENSITY (kGAUSS) The ADM2482E/ADM2487E contain thermal shutdown circuitry that protects the part from excessive power dissipation during fault conditions. Shorting the driver outputs to a low impedance source can result in high driver currents. The thermal sensing circuitry detects the increase in die temperature under this condition and disables the driver outputs. This circuitry is designed to disable the driver outputs when a die temperature of 150°C is reached. As the device cools, the drivers are re-enabled at a temperature of 140°C. Given the geometry of the receiving coil and an imposed requirement that the induced voltage is, at most, 50% of the 0.5 V margin at the decoder, a maximum allowable magnetic field can be determined using Figure 31. MAXIMUM ALLOWABLE CURRENT (kA) THERMAL SHUTDOWN Figure 32. Maximum Allowable Current for Various Current-to-ADM2482E/ADM2487E Spacings With combinations of strong magnetic field and high frequency, any loops formed by PCB traces could induce error voltages large enough to trigger the thresholds of succeeding circuitry. Care should be taken in the layout of such traces to avoid this possibility. Rev. 0 | Page 14 of 20 ADM2482E/ADM2487E APPLICATIONS INFORMATION PRINTED CIRCUIT BOARD LAYOUT The isolated RS-485 transceiver of the ADM2482E/ADM2487E requires no external interface circuitry for the logic interfaces. Power supply bypassing is required at the input and output supply pins (see Figure 33). Bypass capacitors are most conveniently connected between Pin 3 and Pin 4 for VDD1 and between Pin 15 and Pin 16 for VDD2. The capacitor value must be between 0.01 μF and 0.1 μF. The total lead length between both ends of the capacitor and the input power supply pin must not exceed 20 mm. Bypassing Pin 9 and Pin 16 is also recommended unless the ground pair on each package side is connected close to the package. VDD1 RxD RE DE If the ADM2482E/ADM2487E are powered by 5 V on the logic side, then a step-down transformer should be used. For optimum efficiency, the transformer turns ratio should be chosen to ensure just enough headroom for the ADP1710 LDO to output a regulated 3.3 V output under all operating conditions. VDD2 ADM2482E OR ADM2487E TOP VIEW (Not to Scale) TxD GND2 A B Z Y NC GND2 NC = NO CONNECT 07379-025 D2 GND1 When the ADM2482E/ADM2487E are powered by 3.3 V on the logic side, a step-up transformer is required to compensate for the forward voltage drop of the Schottky diodes and the voltage drop across the regulator. The transformer turns ratio should be chosen to ensure just enough headroom for the ADP1710 LDO to output a regulated 3.3 V output under all operating conditions. ISOLATION BARRIER LDO 1N5817 Figure 33. Recommended Printed Circuit Board Layout VCC In applications involving high common-mode transients, care must be taken to ensure that board coupling across the isolation barrier is minimized. Furthermore, the board layout must be designed such that any coupling that does occur equally affects all pins on a given component side. 10µF MLC T1 VCC 100nF Failure to ensure this can cause voltage differentials between pins exceeding the absolute maximum ratings of the device, thereby leading to latch-up or permanent damage. 22µF VDD1 D1 D2 ADP1710 Rev. 0 | Page 15 of 20 3.3V 10µF EN GND VDD2 ISOLATED 3.3V 100nF GND2 ISOLATED POWER SUPPLY CIRCUIT The ADM2482E/ADM2487E integrate a transformer driver that, when used with an external transformer and linear voltage regulator (LDO), generates an isolated 3.3 V power supply to be supplied between VDD2 and GND2, as shown in Figure 34. OUT 1N5817 ADM2482E/ ADM2487E GND1 IN Figure 34. Applications Diagram 07379-026 D1 Pin D1 and Pin D2 of the ADM2482E/ADM2487E drive a center-tapped Transformer T1. A pair of Schottky diodes and a smoothing capacitor are used to create a rectified signal from the secondary winding. The ADP1710 LDO provides a regulated 3.3 V power supply to the ADM2482E/ ADM2487E bus-side circuitry (VDD2). ADM2482E/ADM2487E line must be terminated at the receiving end in its characteristic impedance, and stub lengths off the main line must be kept as short as possible. For half-duplex operation, this means that both ends of the line must be terminated, because either end can be the receiving end. TYPICAL APPLICATIONS Figure 35 and Figure 36 show typical applications of the ADM2482E/ADM2487E in half-duplex and full-duplex RS-485 network configurations. Up to 256 transceivers can be connected to the RS-485 bus. To minimize reflections, the MAXIMUM NUMBER OF TRANSCEIVERS ON BUS = 256 ADM2482E/ ADM2487E RxD R A A B B RE TxD Z D RxD R RE RT RT DE ADM2482E/ ADM2487E DE Z Y D Y A B ADM2482E/ ADM2487E R Z Y A D RxD RE B ADM2482E/ ADM2487E DE TxD Z R TxD Y D RxD RE DE TxD 07379-027 NOTES 1. RT IS EQUAL TO THE CHARACTERISTIC IMPEDANCE OF THE CABLE. 2. ISOLATION NOT SHOWN. Figure 35. ADM2482E/ADM2487E Typical Half-Duplex RS-485 Network MAXIMUM NUMBER OF NODES = 256 MASTER SLAVE A R RxD B Y D RT RE DE Z D B RT Y A ADM2482E/ ADM2487E RE R RxD ADM2482E/ ADM2487E A B Z Y A B Z Y SLAVE SLAVE R ADM2482E/ ADM2487E RxD RE R D DE TxD RxD RE D ADM2482E/ ADM2487E DE TxD NOTES 1. RT IS EQUAL TO THE CHARACTERISTIC IMPEDANCE OF THE CABLE. Figure 36. ADM2482E/ADM2487E Typical Full-Duplex RS-485 Network Rev. 0 | Page 16 of 20 07379-028 DE TxD TxD Z ADM2482E/ADM2487E OUTLINE DIMENSIONS 10.50 (0.4134) 10.10 (0.3976) 9 16 7.60 (0.2992) 7.40 (0.2913) 8 1.27 (0.0500) BSC 0.30 (0.0118) 0.10 (0.0039) COPLANARITY 0.10 0.51 (0.0201) 0.31 (0.0122) 10.65 (0.4193) 10.00 (0.3937) 0.75 (0.0295) 0.25 (0.0098) 2.65 (0.1043) 2.35 (0.0925) SEATING PLANE 45° 8° 0° 0.33 (0.0130) 0.20 (0.0079) 1.27 (0.0500) 0.40 (0.0157) COMPLIANT TO JEDEC STANDARDS MS-013- AA CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS (IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN. 032707-B 1 Figure 37. 16-Lead Standard Small Outline Package [SOIC_W] Wide Body (RW-16) Dimensions shown in millimeters and (inches) ORDERING GUIDE Model ADM2482EBRWZ 1 ADM2482EBRWZ-REEL71 ADM2487EBRWZ1 ADM2487EBRWZ-REEL71 1 Data Rate (Mbps) 16 16 0.5 0.5 Temperature Range −40°C to +85°C −40°C to +85°C −40°C to +85°C −40°C to +85°C Z = RoHS Compliant Part. Rev. 0 | Page 17 of 20 Package Description 16-Lead SOIC_W 16-Lead SOIC_W 16-Lead SOIC_W 16-Lead SOIC_W Package Option RW-16 RW-16 RW-16 RW-16 ADM2482E/ADM2487E NOTES Rev. 0 | Page 18 of 20 ADM2482E/ADM2487E NOTES Rev. 0 | Page 19 of 20 ADM2482E/ADM2487E NOTES ©2008 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D07379-0-5/08(0) Rev. 0 | Page 20 of 20