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High Speed, ESD-Protected, Half-/Full-Duplex, iCoupler Isolated RS-485 Transceiver
ADM2491E
FEATURES
Isolated, RS-485/RS-422 transceiver, configurable as half- or full-duplex 8 kV ESD protection on RS-485 input/output pins 16 Mbps data rate Complies with ANSI TIA/EIA RS-485-A-1998 and ISO 8482: 1987(E) Suitable for 5 V or 3.3 V operation (VDD1) High common-mode transient immunity: >25 kV/s Receiver has open-circuit, fail-safe design 32 nodes on the bus Thermal shutdown protection Safety and regulatory approvals pending UL recognition: 5000 V rms isolation voltage for 1 minute, per UL 1577 VDE certificate of conformity DIN V VDE V 0884-10 (VDE V 0884-10): 2006-12 Reinforced insulation, VIORM = 848 V peak Operating temperature range: -40C to +85C Wide body, 16-lead SOIC package
FUNCTIONAL BLOCK DIAGRAM
VDD1 VDD2
ADM2491E
DE GALVANIC ISOLATION
Y Z
TxD
A B
06985-001
RxD RE GND1 GND2
Figure 1.
APPLICATIONS
Isolated RS-485/RS-422 interfaces Industrial field networks INTERBUS Multipoint data transmission systems
GENERAL DESCRIPTION
The ADM2491E is an isolated data transceiver with 8 kV ESD protection and is suitable for high speed, half- or full-duplex communication on multipoint transmission lines. For halfduplex operation, the transmitter outputs and the 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 ADM2491E is designed for balanced transmission lines and complies with ANSI TIA/EIA RS-485-A-1998 and ISO 8482: 1987(E). The device employs Analog Devices, Inc., iCoupler(R) technology to combine a 3-channel isolator, a threestate differential line driver, and a differential input receiver into a single package. The differential transmitter outputs and receiver inputs feature electrostatic discharge circuitry that provides protection to 8 kV using the human body model (HBM). The logic side of the device can be powered with either a 5 V or a 3.3 V supply, whereas the bus side requires an isolated 5 V supply. The device has current-limiting and thermal shutdown features to protect against output short circuits and situations where bus contention could cause excessive power dissipation. The ADM2491E is available in a wide body, 16-lead SOIC package and operates over the -40C to +85C temperature range.
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)2007 Analog Devices, Inc. All rights reserved.
ADM2491E TABLE OF CONTENTS
Features .............................................................................................. 1 Applications....................................................................................... 1 Functional Block Diagram .............................................................. 1 General Description ......................................................................... 1 Revision History ............................................................................... 2 Specifications..................................................................................... 3 Timing Specifications .................................................................. 4 Package Characteristics ............................................................... 4 Regulatory Information (Pending) ............................................ 4 Insulation and Safety-Related Specifications............................ 5 VDE 0884 Insulation Characteristics (Pending)...................... 5 Absolute Maximum Ratings............................................................ 6 ESD Caution.................................................................................. 6 Pin Configuration and Functional Descriptions.......................... 7 Test Circuits....................................................................................... 8 Switching Characteristics .................................................................9 Typical Performance Characteristics ........................................... 10 Circuit Description......................................................................... 12 Electrical Isolation...................................................................... 12 Truth Tables................................................................................. 12 Thermal Shutdown .................................................................... 13 Fail-Safe Receiver Inputs ........................................................... 13 Magnetic Field Immunity.......................................................... 13 Applications Information .............................................................. 14 Isolated Power Supply Circuit .................................................. 14 PCB Layout ................................................................................. 14 Typical Applications................................................................... 15 Outline Dimensions ....................................................................... 16 Ordering Guide .......................................................................... 16
REVISION HISTORY
10/07--Revision 0: Initial Version
Rev. 0 | Page 2 of 16
ADM2491E SPECIFICATIONS
All voltages are relative to their respective ground; 3.0 V VDD1 5.5 V, 4.5 V VDD2 5.5 V. All minimum/maximum specifications apply over the entire recommended operation range, unless otherwise noted. All typical specifications are at TA = 25C, VDD1 = VDD2 = 5.0 V, unless otherwise noted. Table 1.
Parameter SUPPLY CURRENT Power Supply Current, Logic Side TxD/RxD Data Rate = 2 Mbps TxD/RxD Data Rate = 16 Mbps Power Supply Current, Bus Side TxD/RxD Data Rate = 2 Mbps TxD/RxD Data Rate = 16 Mbps DRIVER Differential Outputs Differential Output Voltage, Loaded Symbol Min Typ Max Unit Test Conditions
IDD1 IDD1
3.0 6
mA mA
Unloaded output Half-duplex configuration, RTERMINATION = 120 , see Figure 5 Unloaded output VDD2 = 5.5 V, half-duplex configuration, RTERMINATION = 120 , see Figure 5
IDD2 IDD2
4.0 50
mA mA
|VOD|
2.0 1.5 1.5
5.0 5.0 5.0 0.2 3.0 0.2 100
V V V V V V A A mA V V A
RL = 100 (RS-422), see Figure 3 RL = 54 (RS-485), see Figure 3 -7 V VTEST1 12 V, see Figure 4 RL = 54 or 100 , see Figure 3 RL = 54 or 100 , see Figure 3 RL = 54 or 100 , see Figure 3 DE = 0 V, VDD2 = 0 V or 5 V, VIN = 12 V DE = 0 V, VDD2 = 0 V or 5 V, VIN = -7 V
|VOD| for Complementary Output States Common-Mode Output Voltage |VOC| for Complementary Output States Output Leakage Current (Y, Z) Short-Circuit Output Current Logic Inputs DE, RE, TxD Input Threshold Low Input Threshold High Input Current RECEIVER Differential Inputs Differential Input Threshold Input Voltage Hysteresis Input Current (A, B) Line Input Resistance Logic Outputs Output Voltage Low Output Voltage High Short-Circuit Current Three-State Output Leakage COMMON-MODE TRANSIENT IMMUNITY 1
1
|VOD| VOC |VOC| IO IO IOS VILTxD VIHTRxD ITxD
-100 250 0.25 x VDD1 -10 +0.01 0.7 x VDD1 +10
VTH VHYS II RIN VOLRxD VOHRxD IOZR
-0.2 30
+0.2 +1.0
-0.8 12 0.2 VDD1 - 0.2 0.4 100 1 25
V mV mA mA k V V mA A kV/s
VOC = 0 V VOC = 12 V VOC = -7 V
VDD1 - 0.3
IORxD = 1.5 mA, VA - VB = -0.2 V IORxD = -1.5 mA, VA - VB = 0.2 V VDD1 = 5.5 V, 0 V < VOUT < VDD1 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.
Rev. 0 | Page 3 of 16
ADM2491E
TIMING SPECIFICATIONS
TA = -40C to +85C Table 2.
Parameter DRIVER Maximum Data Rate Propagation Delay Pulse Width Distortion, PWD = |tPYLH - tPYHL|, PWD = |tPZLH - tPZHL| Single-Ended Output Rise/Fall Times Enable Time Disable Time RECEIVER Propagation Delay Pulse Width Distortion, PWD = |tPLH - tPHL| Enable Time Disable Time Symbol Min 16 tPLH, tPHL tPWD, tPWD tR, tF 45 60 7 20 55 55 Typ Max Unit Mbps ns ns ns ns ns Test Conditions
RL = 54 , CL1 = C L2 = 100 pF, see Figure 6 and Figure 10 RL = 54 , CL1 = CL2 = 100 pF, see Figure 6 and Figure 10 RL = 54 , CL1 = CL2 = 100 pF, see Figure 6 and Figure 10 RL = 110 , CL = 50 pF, see Figure 8 and Figure 11 RL = 110 , CL = 50 pF, see Figure 8 and Figure 11 CL = 15 pF, see Figure 7 and Figure 12 CL = 15 pF, see Figure 7 and Figure 12 RL = 1 k, CL = 15 pF, see Figure 9 and Figure 13 RL = 1 k, CL = 15 pF, see Figure 9 and Figure 13
tPLH, tPHL tPWD
60 10 13 13
ns ns ns ns
PACKAGE CHARACTERISTICS
Table 3.
Parameter Resistance (Input to Output) 1 Capacitance (Input to Output)1 Input Capacitance 2 Input IC Junction-to-Case Thermal Resistance Output IC Junction-to-Case Thermal Resistance
1
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
2
Device considered a 2-terminal device: Pin 1, Pin 2, Pin 3, Pin 4, Pin 5, Pin 6, Pin 7, and Pin 8 are shorted together and Pin 9, Pin 10, Pin 11, Pin 12, Pin 13, Pin 14, Pin 15, and Pin 16 are shorted together. Input capacitance is from any input data pin to ground.
REGULATORY INFORMATION (PENDING)
Table 4.
UL 1 To be recognized under 1577 component recognition program1 5000 V rms isolation voltage
1 2
VDE 2 To be certified according to DIN V VDE V 0884-10 (VDE V 0884-10): 2006-122 Reinforced insulation, 846 V peak
In accordance with UL 1577, each ADM2491E is proof tested by applying an insulation test voltage 6000 V rms for 1 second (current leakage detection limit = 10 A). In accordance with DIN V VDE V 0884-10, each ADM2491E is proof tested by applying an insulation test voltage 1590 V peak for 1 second (partial discharge detection limit = 5 pC).
Rev. 0 | Page 4 of 16
ADM2491E
INSULATION AND SAFETY-RELATED SPECIFICATIONS
Table 5.
Parameter Rated Dielectric Insulation Voltage Minimum External Air Gap (Clearance) Minimum External Tracking (Creepage) Minimum Internal Gap (Internal Clearance) Tracking Resistance (Comparative Tracking Index) Isolation Group Symbol L(I01) L(I02) Value 5000 7.7 8.1 0.017 >175 IIIa Unit V rms mm min mm min mm min 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 Insulation distance through insulation DIN IEC 112/VDE 0303 Part 1 Material Group (DIN VDE 0110, 1/89)
CTI
VDE 0884 INSULATION CHARACTERISTICS (PENDING)
This isolator is suitable for basic electrical isolation only within the safety limit data. Maintenance of the safety data must be ensured by means of protective circuits. An asterisk (*) on a package denotes VDE 0884 approval for 848 V peak working voltage. Table 6.
Description Installation Classification per DIN VDE 0110 for Rated Mains Voltage 300 V rms 450 V rms 600 V rms Climatic Classification Pollution Degree (DIN VDE 0110, see Table 1) Maximum Working Insulation Voltage Input-to-Output Test Voltage, Method b1 VIORM x 1.875 = VPR, 100% Production Tested, tm = 1 sec, Partial Discharge < 5 pC Input-to-Output Test Voltage, Method a After Environmental Tests, Subgroup 1 VIORM x 1.6 = VPR, tm = 60 sec, Partial Discharge < 5 pC After Input and/or Safety Test, Subgroup 2/Subgroup 3 VIORM x 1.2 = VPR, tm = 60 sec, Partial Discharge < 5 pC Highest Allowable Overvoltage (Transient Overvoltage, tTR = 10 sec) Safety-Limiting Values (Maximum Value Allowed in the Event of a Failure; see Figure 20) Case Temperature Input Current Output Current Insulation Resistance at TS, VIO = 500 V Symbol Characteristic I to IV I to II I to II 40/105/21 2 846 1590 Unit
VIORM VPR VPR
V peak V peak
1357 1018 VTR TS IS, INPUT IS, OUTPUT RS 6000 150 265 335 >109
V peak V peak V peak C mA mA
Rev. 0 | Page 5 of 16
ADM2491E ABSOLUTE MAXIMUM RATINGS
TA = 25 C, unless otherwise noted. Each voltage is relative to its respective ground. Table 7.
Parameter Storage Temperature Ambient Operating Temperature VDD1 VDD2 Logic Input Voltages Bus Terminal Voltages Logic Output Voltages Average Output Current, per Pin ESD (Human Body Model) on A, B, Y, and Z pins Rating -55C to +150C -40C to +85C -0.5 V to +7 V -0.5 V to +6 V -0.5 V to VDD1 + 0.5 V -9 V to +14 V -0.5 V to VDD1 + 0.5 V 35 mA 8 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. Absolute maximum ratings apply individually only, not in combination.
ESD CAUTION
Rev. 0 | Page 6 of 16
ADM2491E PIN CONFIGURATION AND FUNCTIONAL DESCRIPTIONS
VDD1 1 GND1 2 RxD 3 RE 4 TxD 6 NC 7 GND1 8
16 15
VDD2 GND2 A
TOP VIEW 13 B DE 5 (Not to Scale) 12 Z
11 10 9
ADM2491E
14
Y NC
06985-002
GND2
NC = NO CONNECT
Figure 2. ADM2491E Pin Configuration
Table 8. Pin Function Descriptions
Pin No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Mnemonic VDD1 GND1 RxD RE DE TxD NC GND1 GND2 NC Y Z B A GND2 VDD2 Description Power Supply (Logic Side). Decoupling capacitor to GND1 required; capacitor value should be between 0.01 F and 0.1 F. Ground (Logic Side). Receiver Output. Receiver Enable Input. Active low logic input. When this pin is low, the receiver is enabled; when high, the receiver is disabled. Driver Enable Input. Active high logic input. When this pin is high, the driver (transmitter) is enabled; when low, the driver is disabled. Transmit Data. No Connect. This pin must be left floating. Ground (Logic Side). 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). Decoupling capacitor to GND2 required; capacitor value should be between 0.01 F and 0.1 F.
Rev. 0 | Page 7 of 16
ADM2491E TEST CIRCUITS
VOD RL 2 RL 2 VOC
Y RLDIFF
06985-003
CL1 CL2
06985-006
Z
Figure 3. Driver Voltage Measurement
Figure 6. Driver Propagation Delay
375
A
VOD 60 VTEST
B
375
06985-004
CL
Figure 4. Driver Voltage Measurement
Figure 7. Receiver Propagation Delay
VDD1
VDD2
Y
VOUT S1 CL RL
VCC
ADM2491E
DE
06985-007
VOUT
0V OR 3V DE
Y Z RTERMINATION
S2
06985-008
GALVANIC ISOLATION
Z
TxD
Figure 8. Driver Enable/Disable
A B
RxD RE
+1.5V -1.5V
06985-005
S1 A B RE
VOUT RL CL
VCC
S2
06985-009
GND1
GND2
RE IN
Figure 5. Supply Current Measurement Test Circuit
Figure 9. Receiver Enable/Disable
Rev. 0 | Page 8 of 16
ADM2491E SWITCHING CHARACTERISTICS
VDD1 TxD 0V Z 1/2VOUT VOUT Y 1.5V 1.5V
tPLH
tPHL
A, B
0V
0V
tPLH
tPWD = |tPLH - tPHL|
tPHL VOH
Y, Z VOL
06985-010
10% POINT
10% POINT
VOL
tR
tF
Figure 10. Driver Propagation Delay, Rise/Fall Timing
Figure 12. Receiver Propagation Delay
VDD1 DE 0.5VDD1 0.5VDD1 0V
RE 0.5VDD1 0.5VDD1
VDD1
tZL
2.3V
tLZ
tZL
1.5V OUTPUT LOW
tLZ
0V
Y, Z
VOL + 0.5V VOL
RxD
VOL + 0.5V VOL
tZH
Y, Z 2.3V
tHZ
VOH
06985-011
tZH
VOH - 0.5V 0V
RxD 0V 1.5V
OUTPUT HIGH
tHZ
VOH
06985-013
VOH - 0.5V 0V
Figure 11. Driver Enable/Disable Delay
Figure 13. Receiver Enable/Disable Delay
Rev. 0 | Page 9 of 16
06985-012
VOH
RxD
90% POINT 90% POINT
1.5V
1.5V
ADM2491E TYPICAL PERFORMANCE CHARACTERISTICS
2.58 NO LOAD 2.56
IDD1 SUPPLY CURRENT (mA)
60
50
2.54 2.52 2.50 2.48 2.46 2.44 2.42 -40
10 40
100 LOAD
DELAY (ns)
tPLH tPHL
30
54 LOAD
20
-20
0
20
40
60
80
06985-014
-20
0
20
40
60
80
TEMPERATURE (C)
TEMPERATURE (C)
Figure 14. IDD1 Supply Current vs. Temperature
Figure 17. Receiver Propagation Delay vs. Temperature
60
: 2.12V @: 7.72V
54 LOAD
TxD
50
IDD2 SUPPLY CURRENT (mA)
40
100 LOAD
1
Z Y
30
20
3
RxD
10
NO LOAD
4
06985-032
-20
0
20
40
60
80
TEMPERATURE (C)
06985-015
0 -40
CH1 2V CH3 2V
CH2 2V CH4 2V
M20ns T 48ns
A CH1
2.32V
Figure 15. IDD2 Supply Current vs. Temperature
Figure 18. Driver/Receiver Propagation Delay, Low to High (RLDIFF = 54 , CL1 = CL2 = 100 pF)
60
50
tPZHL tPYLH tPZLH
TxD
1
: 2.12V @: 7.72V
40
DELAY (ns)
tPYHL
30
Z Y
20
3
10
RxD
4
-20
0
20
40
60
80
TEMPERATURE (C)
06985-034
0 -40
CH1 2V CH3 2V
CH2 2V CH4 2V
M20ns T 48ns
A CH1
3.24V
Figure 16. Driver Propagation Delay vs. Temperature
Figure 19. Driver/Receiver Propagation Delay, High to Low (RLDIFF = 54 , CL1 = CL2 = 100 pF)
Rev. 0 | Page 10 of 16
06985-033
06985-035
0 -40
ADM2491E
350 300 250
4.76 4.75
SAFETY-LIMITING CURRENT (mA)
4.74 4.73
SIDE 2
200 150
VOLTAGE (V)
200
06985-020
4.72 4.71 4.70 4.69 4.68 4.67 4.66
SIDE 1
100 50 0
-20
0
20
40
60
80
TEMPERATURE (C)
Figure 20. Thermal Derating Curve, Dependence of Safety-Limiting Values with Case Temperature per VDE 0884
Figure 23. Receiver Output High Voltage vs. Temperature, IRxD = -4 mA
0 -2
0.35 0.30 0.25
VOLTAGE (V)
OUTPUT CURRENT (mA)
-4 -6 -8 -10 -12 -14 4.0
0.20 0.15 0.10 0.05
RECEIVER OUTPUT VOLTAGE (V)
-20
0
20
40
60
80
TEMPERATURE (C)
Figure 21. Output Current vs. Receiver Output High Voltage
Figure 24. Receiver Output Low Voltage vs. Temperature, IRxD = -4 mA
16 14
OUTPUT CURRENT (mA)
12 10 8 6 4 2 0
0
0.2
0.4
0.6
0.8
1.0
1.2
RECEIVER OUTPUT VOLTAGE (V)
Figure 22. Output Current vs. Receiver Output Low Voltage
06985-022
Rev. 0 | Page 11 of 16
06985-037
4.2
4.4
4.6
4.8
5.0
06985-021
0 -40
06985-036
0
50
100 150 CASE TEMPERATURE (C)
4.65 -40
ADM2491E CIRCUIT DESCRIPTION
ELECTRICAL ISOLATION
In the ADM2491E, 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 25). The driver input signal, which is applied to the TxD pin and referenced to logic ground (GND1), is coupled across an isolation barrier to appear at the transceiver section referenced to isolated ground (GND2). Similarly, the receiver input, which is 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 shown in Table 9. Table 9. Truth Table Abbreviations
Letter H L I X Z NC Description High level Low level Indeterminate Irrelevant High impedance (off ) Disconnected
iCoupler Technology
The digital signals are transmitted 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.
VDD1 ISOLATION BARRIER VDD2
Table 10. 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 L X Y H L Z Z Z Z Outputs Z L H Z Z Z Z
DE
ENCODE
DECODE
Table 11. Receiving
Supply Status Inputs A - B (V) >0.2 <-0.2 -0.2 < A - B < +0.2 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
Y Z
TxD
ENCODE
DECODE
D
RxD RE
DECODE
ENCODE
R
A B
DIGITAL ISOLATION GND1
TRANSCEIVER GND2
06985-025
VDD1 On On On On On On Off
VDD2 On On On On On Off Off
Output RxD H L I H Z H L
Figure 25. ADM2491E Digital Isolation and Transceiver Sections
Rev. 0 | Page 12 of 16
ADM2491E
THERMAL SHUTDOWN
MAXIMUM ALLOWABLE MAGNETIC FLUX DENSITY (kGAUSS)
100
The ADM2491E contains 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.
10
1
0.1
0.01
FAIL-SAFE RECEIVER INPUTS
The receiver inputs include a fail-safe feature that guarantees a logic high on the RxD pin when the A and B inputs are floating or open circuited.
10k 100k 1M 10M MAGNETIC FIELD FREQUENCY (Hz)
100M
Figure 26. Maximum Allowable External Magnetic Flux Density
MAGNETIC FIELD IMMUNITY
Because iCoupler devices use a coreless technology, no magnetic components are present and the problem of magnetic saturation of the core material does not exist. Therefore, iCoupler devices have essentially infinite dc field immunity. The following analysis defines the conditions under which this may occur. The 3 V operating condition of the ADM2491E is examined because it represents the most susceptible mode of operation. The limitation on the ac magnetic field immunity of the iCoupler is set by the condition that induced an error voltage in the receiving coil (the bottom coil in this case) that was large to either falsely set or reset the decoder. The voltage induced across the bottom coil is given by
-d V = - rn 2 ; n = 1, 2, . . . , N dt
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 27 shows the magnetic flux density values in terms of more familiar quantities, such as maximum allowable current flow, at given distances away from the ADM2491E transformers.
1000 DISTANCE = 1m 100 DISTANCE = 5mm 10 DISTANCE = 100mm 1
where (if the pulses at the transformer output are greater than 1.0 V in amplitude): is the magnetic flux density (gauss). N is the number of turns in receiving coil. rn is the radius of nth turn in receiving coil (cm). The decoder has a sensing threshold of about 0.5 V; therefore, there is a 0.5 V margin in which induced voltages can be tolerated. 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 is calculated, as shown in Figure 26.
MAXIMUM ALLOWABLE CURRENT (kA)
0.1
10k 100k 1M 10M MAGNETIC FIELD FREQUENCY (Hz)
100M
Figure 27. Maximum Allowable Current for Various Current-to-ADM2491E Spacings
With combinations of strong magnetic field and high frequency, any loops formed by printed circuit board 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 13 of 16
06985-027
0.01 1k
06985-026
0.001 1k
ADM2491E APPLICATIONS INFORMATION
ISOLATED POWER SUPPLY CIRCUIT
The ADM2491E requires isolated power capable of 5 V at up to approximately 75 mA (this current is dependant on the data rate and termination resistors used) to be supplied between the VDD2 and the GND2 pins. A transformer driver circuit with a center-tapped transformer and LDO can be used to generate the isolated 5 V supply, as shown in Figure 28. The center-tapped transformer provides electrical isolation of the 5 V power supply. The primary winding of the transformer is excited with a pair of square waveforms that are 180 out of phase with each other. A pair of Schottky diodes and a smoothing capacitor are used to create a rectified signal from the secondary winding. The ADP3330 linear voltage regulator provides a regulated power supply to the bus-side circuitry (VDD2) of the ADM2491E.
VCC ISOLATION BARRIER SD103C + TRANSFORMER DRIVER VCC IN 22F SD ERR NR 78253 SD103C GND OUT 5V + 10F
PCB LAYOUT
The ADM2491E isolated RS-485 transceiver requires no external interface circuitry for the logic interfaces. Power supply bypassing is required at the input and output supply pins (see Figure 29). Bypass capacitors are conveniently connected between Pin 1 and Pin 2 for VDD1 and between Pin 15 and Pin 16 for VDD2. The capacitor value should 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 should not exceed 20 mm. Bypassing between Pin 1 and Pin 8 and between Pin 9 and Pin 16 should also be considered unless the ground pair on each package side is connected close to the package.
VDD1 GND1 RxD RE DE TxD NC GND1 VDD2 GND2 A B Z Y NC GND2
ADM2491E
NC = NO CONNECT
ADP3330
Figure 29. Recommended Printed Circuit Board Layout
VCC
VDD1
VDD2
ADM2491E
06985-028
In applications involving high common-mode transients, care should be taken to ensure that board coupling across the isolation barrier is minimized. Furthermore, the board layout should be designed such that any coupling that does occur equally affects all pins on a given component side. Failure to ensure this could cause voltage differentials between pins exceeding the absolute maximum ratings of the device, thereby leading to latch-up or permanent damage.
GND1
GND2
Figure 28. Isolated Power Supply Circuit
Rev. 0 | Page 14 of 16
06985-029
ADM2491E
TYPICAL APPLICATIONS
Figure 30 and Figure 31 show typical applications of the ADM2491E in half-duplex and full-duplex RS-485 network configurations. Up to 32 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,
ADM2491E
A RxD RE DE TxD D Z Y R2 A B Z Y A B Z Y R B RT RT Z Y D VCC R1
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 = 32 A B
ADM2491E
R RxD RE DE TxD
R
D
R
D
ADM2491E
RxD RE DE TxD
ADM2491E
RxD RE DE TxD
06985-030
NOTES 1. RT IS EQUAL TO THE CHARACTERISTIC IMPEDANCE OF THE CABLE. 2. ISOLATION NOT SHOWN.
Figure 30. ADM2491E Typical Half-Duplex RS-485 Network
MASTER A RxD RE DE TxD D Z Y R B
VDD R1 RT
MAXIMUM NUMBER OF NODES = 32 SLAVE Y D Z VDD R1 RT R2 TxD DE RE R RxD
R2
B A
ADM2491E
A SLAVE B Z Y A B Z Y SLAVE
ADM2491E
R
ADM2491E
RxD RE
D
R
D
ADM2491E
DE TxD
RxD RE
DE TxD
06985-031
NOTES 1. RT IS EQUAL TO THE CHARACTERISTIC IMPEDANCE OF THE CABLE.
Figure 31. ADM2491E Typical Full -Duplex RS-485 Network
Rev. 0 | Page 15 of 16
ADM2491E 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)
8 0 0.33 (0.0130) 0.20 (0.0079)
45
SEATING PLANE
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.
Figure 32. 16-Lead Standard Small Outline Package [SOIC_W] Wide Body (RW-16) Dimensions shown in millimeters and (inches)
ORDERING GUIDE
Model ADM2491EBRWZ 1 ADM2491EBRWZ-REEL71
1
Temperature Range -40C to +85C -40C to +85C
Package Description 16-Lead Standard Small Outline Package, Wide Body [SOIC_W] 16-Lead Standard Small Outline Package, Wide Body [SOIC_W]
032707-B
Package Option RW-16 RW-16
Z = RoHS Compliant Part.
(c)2007 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. D06985-0-10/07(0)
Rev. 0 | Page 16 of 16

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