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2.5 kV Isolated RS-485 Transceivers with Integrated Transformer Driver ADM2482E/ADM2487E
FEATURES
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/s Thermal shutdown protection Operating temperature range: -40C to +85C Wide-body, 16-lead SOIC package
FUNCTIONAL BLOCK DIAGRAM
VDD1 D1 D2 OSC DE GALVANIC ISOLATION VDD2
Y Z
TxD
A B
07379-001
RxD RE
GND1
GND2
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(R) 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 -40C to +85C 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 (c)2008 Analog Devices, Inc. All rights reserved.
ADM2482E/ADM2487E TABLE OF CONTENTS
Features .............................................................................................. 1 Applications ....................................................................................... 1 Functional Block Diagram .............................................................. 1 General Description ......................................................................... 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Timing Specifications .................................................................. 4 Package Characteristics ............................................................... 5 Insulation and Safety-Related Specifications ............................ 5 Test Circuits ................................................................................... 6 Switching Characteristics ............................................................ 7 Absolute Maximum Ratings............................................................ 8 ESD Caution .................................................................................. 8 Pin Configuration and Function Descriptions ............................. 9 Typical Performance Characteristics ........................................... 10 Circuit Description......................................................................... 13 Electrical Isolation...................................................................... 13 Truth Tables................................................................................. 13 Thermal Shutdown .................................................................... 14 True Fail-Safe Receiver Inputs .................................................. 14 Magnetic Field Immunity.......................................................... 14 Applications Information .............................................................. 15 Printed Circuit Board Layout ................................................... 15 Isolated Power Supply Circuit .................................................. 15 Typical Applications ................................................................... 16 Outline Dimensions ....................................................................... 17 Ordering Guide .......................................................................... 17
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 = 25C, 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 ADM2482E TxD/RxD Data Rate = 16 Mbps Power-Supply Current, Bus Side TxD/RxD Data Rate < 500 kbps ADM2487E TxD/RxD Data Rate = 500 kbps Symbol Min Typ Max Unit Test Conditions
IDD1 IDD1 IDD1
3.5 4 6.0
mA mA mA
Unloaded output Half-duplex configuration, RTERMINATION = 120 , see Figure 8 Half-duplex configuration, RTERMINATION = 120 , see Figure 8 Unloaded output VDD2 = 3.6 V, half-duplex configuration, RTERMINATION = 120 , see Figure 8 VDD2 = 3.6 V, half-duplex configuration, RTERMINATION = 120 , see Figure 8
IDD2 IDD2
17 40
mA mA
ADM2482E TxD/RxD Data Rate = 16 Mbps
IDD2
50
mA
DRIVER Differential Outputs Differential Output Voltage, Loaded
|VOD2| |VOD3| |VOD| VOC |VOC| IOS IO
2.0 1.5 1.5
|VOD| for Complementary Output States Common-Mode Output Voltage |VOC| for Complementary Output States Short-Circuit Output Current Output Leakage Current (Y, Z)
5.0 5.0 5.0 0.2 3.0 0.2 250 125
V V V V V V mA A A
RL = 100 (RS-422), see Figure 2 RL = 54 (RS-485), see Figure 2 -7 V VTEST +12 V, see Figure 3 RL = 54 or 100 , see Figure 2 RL = 54 or 100 , see Figure 2 RL = 54 or 100 , see Figure 2 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
-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)
VIL VIH II
0.25 x VDD1 -10 +0.01 0.7 x VDD1 +10
V V A
VTH VHYS II
-200
-125 15
-30 125
mV mV A A k
-125 Line Input Resistance Logic Outputs Output Voltage Low Output Voltage High Short Circuit Current Tristate Output Leakage Current RIN VOLRxD VOHRxD IOS IOZR 96 0.2 VDD1 - 0.2 0.4 100 1
-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 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
VDD1 - 0.3
V V mA A
Rev. 0 | Page 3 of 20
ADM2482E/ADM2487E
Parameter TRANSFORMER DRIVER Oscillator Frequency Switch-On Resistance Start-Up Voltage COMMON-MODE TRANSIENT IMMUNITY 1
1
Symbol fOSC RON VSTART
Min 400 230
Typ 500 330 0.5 2.2
Max 600 430 1.5 2.5
Unit kHz kHz V kV/s
Test Conditions VDD1 = 5.0 V VDD1 = 3.3 V
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 = -40C to +85C 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 tDPLH, tDPHL tDSKEW tDR, tDF tZL, tZH tLZ, tHZ tPLH, tPHL tSKEW tZL, tZH tLZ, tHZ Min Typ Max 100 8 15 120 150 110 8 13 13 Unit ns ns ns ns ns ns ns ns ns Test Conditions RDIFF = 54 , CL = 100 pF, see Figure 4 and Figure 9 RDIFF = 54 , CL = 100 pF, see Figure 4 and Figure 9 RDIFF = 54 , CL = 100 pF, see Figure 4 and Figure 9 RL = 110 , CL = 50 pF, see Figure 5 and Figure 11 RL = 110 , CL = 50 pF, see Figure 5 and Figure 11 CL = 15 pF, see Figure 6 and Figure 10 CL = 15 pF, see Figure 6 and Figure 10 RL = 1 k, CL = 15 pF, see Figure 7 and Figure 12 RL = 1 k, 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 tDPLH, tDPHL tDSKEW tDR, tDF tZL, tZH tLZ, tHZ tPLH, tPHL tSKEW tZL, tZH tLZ, tHZ Min 250 200 Typ Max 700 100 1100 2.5 200 200 30 13 13 Unit ns ns ns s ns ns ns ns ns Test Conditions RDIFF = 54 , CL = 100 pF, see Figure 4 and Figure 9 RDIFF = 54 , CL = 100 pF, see Figure 4 and Figure 9 RDIFF = 54 , CL = 100 pF, see Figure 4 and Figure 9 RL = 110 , CL = 50 pF, see Figure 5 and Figure 11 RL = 110 , CL = 50 pF, see Figure 5 and Figure 11 CL = 15 pF, see Figure 6 and Figure 10 CL = 15 pF, see Figure 6 and Figure 10 RL = 1 k, CL = 15 pF, see Figure 7 and Figure 12 RL = 1 k, CL = 15 pF, see Figure 7 and Figure 12
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 Output IC Junction-to-Case Thermal Resistance
1 2
Symbol RI-O CI-O CI JCI JCO
Min
Typ 1012 3 4 33 28
Max
Unit 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) Minimum External Tracking (Creepage) Minimum Internal Gap (Internal Clearance) Tracking Resistance (Comparative Tracking Index) Symbol Value 2500 560 5.7 min 6.1 min 0.017 min >175 Unit V rms V peak mm mm mm V 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
L(I01) L(I02)
CTI
Rev. 0 | Page 5 of 20
ADM2482E/ADM2487E
TEST CIRCUITS
Y
TxD VOD2 RL 2 RL 2
VOUT
VOC
07379-003
VCC
Z
Y TxD DE Z S1
RL 110
07379-007
CL 50pF
S2
Figure 2. Driver Voltage Measurement
Figure 5. Driver Enable/Disable
Y
TxD VOD3 60
375
A VOUT CL
Figure 3. Driver Voltage Measurement
07379-004
B
Figure 6. Receiver Propagation Delay
+1.5V
Y
TxD RDIFF
S1
CL
-1.5V
07379-006
RL RE CL VOUT
07379-008
Z
375 V TEST
RE
VCC
S2
07379-009
Z
CL
RE IN
Figure 4. Driver Propagation Delay
Figure 7. Receiver Enable/Disable
VDD2 VDD1 VDD2 DE
GALVANIC ISOLATION
Y Z 120
TxD
A B
RxD RE GND1 GND2
Figure 8. Supply-Current Measurement Test Circuit
Rev. 0 | Page 6 of 20
07379-005
ADM2482E/ADM2487E
SWITCHING CHARACTERISTICS
VDD1 VDD1 /2 0V VDD1 /2
VDD1
tDPLH
Z 1/2VO VO Y
tDPHL
DE
0.5VDD1
0.5VDD1 0V
tZL
2.3V
tLZ
Y, Z
+VO VDIFF -VO 10% POINT 90% POINT 90% POINT
VOL + 0.5V
VDIFF = V(Y) - V(Z)
tZH
Y, Z
07379-010
VOL 2.3V
tHZ
VOH
07379-012
10% POINT
VOH - 0.5V 0V
tDR
tDF
Figure 9. Driver Propagation Delay, Rise/Fall Timing
Figure 11. Driver Enable/Disable Timing
0.7VDD1
RE
0.5VDD1
0.5VDD1 0.3VDD1
A-B
0V
0V
tZL
1.5V OUTPUT LOW
tLZ
tPLH
tPHL
VOH
RxD
VOL + 0.5V VOL
tZH
OUTPUT HIGH RxD 0V
tHZ
VOH
07379-013
RxD
1.5V
07379-011
tSKEW = |tPLH - tPHL|
1.5V
1.5V
VOH - 0.5V
VOL
Figure 10. Receiver Propagation Delay
Figure 12. Receiver Enable/Disable Timing
Rev. 0 | Page 7 of 20
ADM2482E/ADM2487E ABSOLUTE MAXIMUM RATINGS
All voltages are relative to their respective ground; TA = 25C, 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 -40C to +85C -55C to +150C -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
300C 215C 220C
Rev. 0 | Page 8 of 20
ADM2482E/ADM2487E PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
D1 1 D2 2 GND1 3 VDD1 4 RxD 5 RE 6 DE 7 TxD 8 NC = NO CONNECT
16 15
VDD2 GND2 A B Z Y NC
07379-002
ADM2482E/ ADM2487E
TOP VIEW (Not to Scale)
14 13 12 11 10 9
GND2
Figure 13. Pin Configuration
Table 7. Pin Function Descriptions
Pin No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Mnemonic D1 D2 GND1 VDD1 RxD RE 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 F and 0.1 F. 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 F and 0.1 F.
Rev. 0 | Page 9 of 20
ADM2482E/ADM2487E TYPICAL PERFORMANCE CHARACTERISTICS
2.30 2.25
SUPPLY CURRENT IDD1 (mA)
60 NO LOAD 54 LOAD 120 LOAD NO LOAD 54 LOAD 120 LOAD
50
2.20 2.15 2.10 2.05 2.00 1.95 -40
SUPPLY CURRENT IDD1 (mA)
07379-029
40
30
20
10
-15
10 35 TEMPERATURE (C)
60
85
-15
10 35 TEMPERATURE (C)
60
85
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)
40 35
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)
600
DRIVER PROPAGATION DELAY (ns)
tDPLH
500
SUPPLY CURRENT IDD2 (mA)
30 25 20 15 10 5
NO LOAD 54 LOAD 120 LOAD
tDPHL
400
300
200
100
07379-030
-15
10 35 TEMPERATURE (C)
60
85
-20
0
20
40
60
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)
4.0 3.9 NO LOAD 54 LOAD 120 LOAD
Figure 18. ADM2487E Driver Propagation Delay vs. Temperature
70 65
DRIVER PROPAGATION DELAY (ns)
SUPPLY CURRENT IDD1 (mA)
3.8 3.7 3.6 3.5 3.4 3.3 3.2
07379-031
60 55 50 45 40 35 30 25
tDPLH tDPHL
-15
10 35 TEMPERATURE (C)
60
85
-15
10 35 TEMPERATURE (C)
60
85
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)
Figure 19. ADM2482E Driver Propagation Delay vs. Temperature
Rev. 0 | Page 10 of 20
07379-034
3.1 -40
20 -40
07379-033
0 -40
0 -40
07379-032
0 -40
ADM2482E/ADM2487E
0 -10
0.32
0.30
OUTPUT VOLTAGE (V)
OUTPUT CURRENT (mA)
-20 -30 -40 -50 -60 -70 0 1 2 3 4 5 OUTPUT VOLTAGE (V)
0.28
0.26
0.24
0.22
07379-016
-20
0
20
40
60
80
TEMPERATURE (C)
Figure 20. Output Current vs. Receiver Output High Voltage
Figure 23. Receiver Output Low Voltage vs. Temperature (IDD2 = 4 mA)
60
D1
50
OUTPUT CURRENT (mA)
40
30
1
20
D2
2
10
07379-017
0
1
2
3
4
5
OUTPUT VOLTAGE (V)
CH1 2.0V CH2 2.0V M400ns 125MS/s 8.0ns/pt
A CH2
1.52V
Figure 21. Output Current vs. Receiver Output Low Voltage
Figure 24. Switching Waveforms (50 Pull-Up to VDD1 on D1 and D2)
4.75 4.74 4.73 4.72 4.71 4.70 4.69 4.68 4.67 -40
1
D1
OUTPUT VOLTAGE (V)
D2
07379-018
-20
0
20
40
60
80
TEMPERATURE (C)
CH1 2.0V CH2 2.0V M80ns 625MS/s 1.6ns/pt
A CH2
1.52V
Figure 22. Receiver Output High Voltage vs. Temperature (IDD2 = -4 mA)
Figure 25. Switching Waveforms (Break-Before-Make, 50 Pull-Up to VDD1 on D1 and D2)
Rev. 0 | Page 11 of 20
07379-021
07379-020
0
07379-019
0.20 -40
ADM2482E/ADM2487E
T
TxD
1
TxD
1
2
Z, B
Z, B
2
Y, A
Y, A
RxD
4
07379-035
4
RxD
CH1 2.00V CH3 2.00V
CH2 2.00V CH4 2.00V
M 200ns T 47.80%
A CH2
1.72V
CH1 2.0V CH2 2.0V CH3 2.0V CH4 2.0V
M 40.0ns 1.25GS/s IT 16.0ps/pt A CH2 1.68V
Figure 26. ADM2487E Driver/Receiver Propagation Delay, Low to High (RDIFF = 54 , CL1 = CL2 = 100 pF)
Figure 28. ADM2482E Driver/Receiver Propagation Delay, High to Low (RDIFF = 54 , CL1 = CL2 = 100 pF)
T
1
TxD Z, B
TxD
1
Z, B
2
2
Y, A
Y, A
RxD
RxD
4
07379-036
4
CH1 2.00V CH3 2.00V
CH2 2.00V CH4 2.00V
M 200ns T 48.60%
A CH2
1.72V
CH1 2.0V CH2 2.0V CH3 2.0V CH4 2.0V
M 40.0ns 1.25GS/s IT 16.0ps/pt A CH2 1.68V
Figure 27. ADM2487E Driver/Receiver Propagation Delay, High to Low (RDIFF = 54 , CL1 = CL2 = 100 pF)
Figure 29. ADM2482E Driver/Receiver Propagation Delay, Low to High (RDIFF = 54 , CL1 = CL2 = 100 pF)
Rev. 0 | Page 12 of 20
07379-038
07379-037
ADM2482E/ADM2487E CIRCUIT DESCRIPTION
ELECTRICAL ISOLATION
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.
TRUTH TABLES
The truth tables in this section use the abbreviations found in Table 8. Table 8. Truth Table Abbreviations
Letter H I L X Z NC Description High level Indeterminate Low level Irrelevant High impedance (off ) Disconnected
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 s, 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 s, 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 D1 D2 OSC VDD2
Table 9. Transmitting
Supply Status VDD1 VDD2 On On On On On On On Off Off On Off Off DE H H L X L X Inputs TxD H L X X X X Y H L Z Z Z Z Outputs Z L H Z Z Z Z
Table 10. Receiving
Supply Status VDD1 VDD2 On On On On On On Off On On On On On Off Off Inputs A-B >-0.03 V <-0.2 V -0.2 V < A - B < -0.03 V Inputs open X X X RE L or NC L or NC L or NC L or NC H L or NC L or NC Outputs RxD H L I H Z H L
ISOLATION BARRIER ENCODE DECODE
DE
Y TxD ENCODE DECODE D Z
A RxD RE DIGITAL ISOLATION TRANSCEIVER
07379-022
ENCODE
DECODE
R
B
GND1
GND2
Figure 30. ADM2482E/ADM2487E Digital Isolation and Transceiver Sections
Rev. 0 | Page 13 of 20
ADM2482E/ADM2487E
THERMAL SHUTDOWN
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 150C is reached. As the device cools, the drivers are re-enabled at a temperature of 140C. 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.
100
MAXIMUM ALLOWABLE MAGNETIC FLUX DENSITY (kGAUSS)
10
1
TRUE FAIL-SAFE RECEIVER INPUTS
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.
0.1
0.01
10k 100k 1M 10M MAGNETIC FIELD FREQUENCY (Hz)
100M
Figure 31. Maximum Allowable External Magnetic Flux Density
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
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
MAXIMUM ALLOWABLE CURRENT (kA)
DISTANCE = 1m 100 DISTANCE = 5mm 10 DISTANCE = 100mm 1
-d 2 V = rn ; n = 1, 2, K , N dt
where: 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).
0.1
10k 100k 1M 10M MAGNETIC FIELD FREQUENCY (Hz)
100M
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
07379-024
0.01 1k
07379-023
0.001 1k
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 F and 0.1 F. 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.
D1 D2 GND1 VDD1 RxD RE DE TxD NC = NO CONNECT VDD2
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). 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. 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.
ISOLATION BARRIER 1N5817 VCC 10F MLC VCC 22F
ADM2482E OR ADM2487E
TOP VIEW (Not to Scale)
GND2 A B Z Y GND2
07379-025
NC
Figure 33. Recommended Printed Circuit Board Layout
LDO IN OUT
3.3V
10F
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. 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.
100nF
ADP1710
EN GND
T1
1N5817
VDD1
D1
D2
VDD2
ISOLATED 3.3V 100nF
ADM2482E/ ADM2487E
GND1 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.
Figure 34. Applications Diagram
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07379-026
ADM2482E/ADM2487E
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 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.
MAXIMUM NUMBER OF TRANSCEIVERS ON BUS = 256
ADM2482E/ ADM2487E
RxD RE DE TxD
A B RT Z RT
A B
ADM2482E/ ADM2487E
R
RxD RE
R
Z Y A B Z Y A B Z Y D
DE TxD
D
Y
ADM2482E/ ADM2487E
R
D
ADM2482E/ ADM2487E
R
D
RxD RE
DE TxD
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
MASTER
MAXIMUM NUMBER OF NODES = 256
A Y
SLAVE
RxD RE DE TxD
R B Z D Y
RT
D Z
TxD DE
B
RE
RT
A
R
RxD
ADM2482E/ ADM2487E
A
SLAVE
ADM2482E/ ADM2487E
B Z Y A B Z Y
SLAVE
R
ADM2482E/ ADM2487E
RxD RE
D
R
D
ADM2482E/ ADM2487E
07379-028
DE TxD
RxD RE
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
ADM2482E/ADM2487E OUTLINE DIMENSIONS
10.50 (0.4134) 10.10 (0.3976)
16 9
7.60 (0.2992) 7.40 (0.2913)
1 8
10.65 (0.4193) 10.00 (0.3937)
1.27 (0.0500) BSC 0.30 (0.0118) 0.10 (0.0039) COPLANARITY 0.10 0.51 (0.0201) 0.31 (0.0122)
2.65 (0.1043) 2.35 (0.0925)
0.75 (0.0295) 0.25 (0.0098)
45
8 0 0.33 (0.0130) 0.20 (0.0079) 1.27 (0.0500) 0.40 (0.0157)
SEATING PLANE
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.
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 -40C to +85C -40C to +85C -40C to +85C -40C to +85C
Package Description 16-Lead SOIC_W 16-Lead SOIC_W 16-Lead SOIC_W 16-Lead SOIC_W
032707-B
Package Option RW-16 RW-16 RW-16 RW-16
Z = RoHS Compliant Part.
Rev. 0 | Page 17 of 20
ADM2482E/ADM2487E NOTES
Rev. 0 | Page 18 of 20
ADM2482E/ADM2487E NOTES
Rev. 0 | Page 19 of 20
ADM2482E/ADM2487E NOTES
(c)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

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