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PRELIMINARY TECHNICAL DATA
a
Low-Current (1nA) Shutdown Mode
High-Speed (10Mbps), Fail-Safe, RS-485/RS-422 Transceivers with Slew-Rate-Limiting and 15kV ESD Protection ADM3082/ADM3085/ADM3088
GENERAL DESCRIPTION
FEATURES Enhanced Slew Rate Limiting for Error-Free Data Transmission Fail-Safe Receiver Operation while Maintaining EIA/TIA-485 compatibility High Input Impedance -- Up to 256 Transceivers on Bus 15kV ESD Protection (Human Body Model) on RS-485 I/O pins Pin-Compatible with Industry Standard 75176 APPLICATIONS Enhanced Replacement for Industry-Standard Parts EMI-Sensitive Systems Level Translation LANs for Industrial Control Applications
The ADM3082/ADM3085/ADM3088 are high-speed RS-485/RS-422 transceivers consisting of one driver and one receiver per package. The devices feature fail-safe operation, ensuring a logic-high receiver output when the receiver inputs are open-circuit or short-circuit. This guarantees that the receiver output will be high if all the transmitters on a terminated bus are disabled (high-impedance). The ADM3082 has a slew-rate limited driver to minimize electromagnetic interference (EMI) and reduce reflections caused by incorrectly terminated cables. This allows errorfree transmission at data rates up to 115kbps. The ADM3085 offers a higher slew rate allowing data rates up to 500kbps, while the ADM3088 has a driver whose slew rate is not limited, allowing data rates up to 10Mbps. All devices in the family feature 15kV electrostatic discharge (ESD) protection and high receiver input impedance (1/8 unit load), allowing up to 256 transceivers on the bus. The devices have low current drain of 375A unloaded, or fully loaded with the drivers disabled, and feature an ultra-low power (1nA) shutdown mode.
FUNCTIONAL BLOCK DIAGRAM
RO RE DE DI
1 R 2 3 4 D
8 7 6 5
VCC B A G ND
AD M 30 82/A D M 308 5/AD M 3088
REV. PrA 02/02
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 which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 World Wide Web Site: http://www.analog.com Fax: 617/326-8703 (c) Analog Devices, Inc., 2002
PRELIMINARY TECHNICAL DATA ADM3082/ADM3085/ADM3088
ADM3082/ADM3085/ADM3088 SPECIFICATIONS
DC ELECTRICAL CHARACTERISTICS (VCC = +5V 5%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25C.) (Note 1)
DRIVER Parameter Differential Driver Output, V OD1 Differential Driver Output,VOD2 Change-in-Magnitude of Differential Common-Mode Output Voltage, V OD Driver Common-Mode Output Voltage, VOC Change-in-Magnitude of Common-Mode Voltage, Input High Voltage,VIH1 (DE, DI, RE) Input Low Voltage, VlL1 (DE, DI, RE) DI Input Hysteresis, VHYS Input Current, IIN1 (DE, DI, RE) Input Current (A and B), IIN4 100 2 125 -75 Output Leakage (Y and Z), Full Duplex, IO -100 Driver Short-Circuit,V OD1 Output Current 25 -250 250 125 VOC 2.0 0.8 V V mV A A A A A mA mA mA DE VIN DE VIN DE VIN DE VIN -7V 0V 0V = = = = = = = = GND, VCC = GND or 5.25V, 12V GND, VCC = GND or 5.25V, -7V GND, VCC = GND or 5.25V, 12V GND, VCC = GND or 5.25V, -7V VOUT VOUT VOUT VCC (Note 3) 12V (Note 3) VCC (Note 3) 2.0 1.5 0.2 3 0.2 Min Typ Max 5 Units Test Conditions/Comments V V V V V V Figure 1 (No Load) Figure 1, R = 50 Figure 1, R = 27 Figure 1, R = 50 (Note 2) Figure 1, R = 50 Figure 1, R = 50 (Note 2) (RS-422) (RS-485) or R = 27 or R = 27 or R = 27
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PRELIMINARY TECHNICAL DATA ADM3082/ADM3085/ADM3088
ADM3082/ADM3085/ADM3088 SPECIFICATIONS (continued)
DC ELECTRICAL CHARACTERISTICS (VCC = +5V 5%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25C.) (Note 1)
RECEIVER Parameter Receiver Differential Threshold Voltage, VTH Receiver Input Hysteresis, VTH VCC -1 .5 0.4 1 96 7 95 Min -200 Typ -125 25 Max -50 Units Test Conditions/Comments mV mV V V A k mA IO = -4mA, VID = -50mV IO = 4mA, VID = -200mV 0.4V -7V 0V VO VCM VRO 2.4V 12V VCC -7V VCM 12V
Receiver Output High Voltage, VOH Receiver Output Low Voltage, VOL Three-State Output Current at Receiver, IOZR Receiver Input Resistance, RIN Receiver Output Short-Circuit Current, IOSR
SUPPLY CURRENT Parameter Supply Current, ICC Min Typ 430 375 Supply Current in Shutdown Mode, ISHDN ESD Protection for Y, Z, A, B
NOTES
1 2
Max 900 600 10
Units Test Conditions/Comments A A A kV No DE No DE load, RE = DI = GND or VCC, = VCC load, RE = DI = GND or VCC, = GND
0.001 15
DE = GND, VRE = VCC Human Body Model
All currents into the device are positive; all currents out of the device are negative. All voltages are referred to device ground unless otherwise noted. DO and VCC are the changes in VOD and VOC, respectively, when the DI input changes state. 3 Maximum current level applies to peak current just prior to foldback-current limiting; minimum current level applies during current limiting.
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PRELIMINARY TECHNICAL DATA ADM3082/ADM3085/ADM3088
ADM3082/ADM3085/ADM3088 SPECIFICATIONS (continued)
SWITCHING CHARACTERISTICS--ADM3082 (VCC = +5V 5%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25C.) (Note 1)
Parameter Driver Input-to-Output, tDPLH Driver Input-to-Output, tDPHL Driver Output Skew,|tDPLH-tDPHL|, tDSKEW Driver Rise or Fall Time, tDR, tDF Maximum Data Rate, fMAX Driver Enable to Output High, tDZH Driver Enable to Output Low, tDZL Driver Disable Time from Low, tDLZ Driver Disable Time from High, tDHZ Receiver Input to Output, tRPLH, tRPHL Differential Receiver Skew, tRSKD |tRPLH - tRPHL| Receiver Enable to Output Low, tRZL Receiver Enable to Output High, tRZH Receiver Disable Time from Low, tRLZ Receiver Disable Time from High, tRHZ Time to Shutdown, tSHDN Driver Enable from Shutdown to Output High, tDZH(SHDN) Driver Enable from Shutdown to Output Low, tDZL(SHDN) Receiver Enable from Shutdown to Output High, tRZH(SHDN) Receiver Enable from Shutdown to Output Low, tRZL(SHDN) 50 127 3 20 20 20 20 200 667 115 3500 3500 100 100 200 30 50 50 50 50 600 6000 6000 3500 3500 Min 500 500 Typ 2030 2030 -3 1320 Max 2600 2600 200 2500 Units Test Conditions/Comments ns ns ns ns kbps ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns Figures 5 and 6, CL = 100pF, S2 closed Figures 5 and 6, CL = 100pF, S1 closed Figures 5 and 6, CL = l5pF, S1 closed Figures 4 and 5, CL = l5pF, S2 closed Figure 7; |VID| 2.0V; rise and fall time of VID Figure 7; |VID| 2.0V; rise and fall time of VID l5ns l5ns Figures 2 and 3, RDIFF = 54 , CL1 = CL2 = 100pF Figures 2 and 3, RDIFF = 54 , CL1 = CL2 = 100pF Figures 2 and 3, RDIFF = 54 , CL1 = CL2 = 100pF
Figures 7 and 8; CL = 100pF, S1 closed Figures 7 and 8, CL = 100pF, S2 closed Figures 7 and 8, CL = 100pF, S1 closed Figures 7 and 8 CL = 100pF, S2 closed (Note 5) Figures 5 and 6, CL = l5pF, S2 closed Figures 5 and 6, CL = l5pF, S1 closed Figures 7 and 8, CL = 100pF, S2 closed Figures 7 and 8, CL = 100pF, S1 closed
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PRELIMINARY TECHNICAL DATA ADM3082/ADM3085/ADM3088
ADM3082/ADM3085/ADM3088 SPECIFICATIONS (continued)
SWITCHING CHARACTERISTICS--ADM3085 (VCC = +5V 5%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25C.) (Note 1)
Parameter Driver Input-to-Output, tDPLH Driver Input-to-Output, tDPHL Driver Output Skew,|tDPLH - tDPHL|, tDSKEW Driver Rise or Fall Time, tDR, tDF Maximum Data Rate, fMAX Driver Enable to Output High, tDZH Driver Enable to Output Low, tDZL Driver Disable Time from Low, tDLZ Driver Disable Time from High, tDHZ Receiver Input to Output, tRPLH, tRPHL Differential Receiver Skew, tRSKD |tRPLH - tRPHL| Receiver Enable to Output Low, tRZL Receiver Enable to Output High, tRZH Receiver Disable Time from Low, tRLZ Receiver Disable Time from High, tRHZ Time to Shutdown, tSHDN Driver Enable from Shutdown to Output High, tDZH(SHDN) Driver Enable from Shutdown to Output Low, tOZL(SHDN) Receiver Enable from Shutdown to Output High, tRZH(SHDN) Receiver Enable from Shutdown to Output Low, tRZL(SHDN) 50 127 3 20 20 20 20 200 200 500 2500 2500 100 100 200 30 50 50 50 50 600 4500 4500 3500 3500 Min 250 250 Typ 720 720 -3 530 Max 1000 1000 100 750 Units Test Conditions/Comments ns ns ns ns kbps ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns Figures 5 and 6, CL = 100pF, S2 closed Figures 5 and 6, CL = 100pF, S1 closed Figures 5 and 6, CL = l5pF, S1 closed Figures 5 and 6, CL = l5pF, S2 closed Figure 7; |VID| 2.0V; rise and fall time of VID Figure 7; |VID| 2.0V; rise and fall time of VID l5ns l5ns Figures 2 and 3 RDIFF = 54 , CL1 = CL2 = 100pF Figures 2 and 3, RDIFF = 54 , CL1 = CL2 = 100pF Figures 2 and 3, RDIFF = 54 , CL1 = CL2 = 100pF
Figures 7 and 8 CL = 100pF, S1 closed Figures 7 and 8, CL = 100pF, S2 closed Figures 7 and 8, CL = 100pF, S1 closed Figures 7 and 8, CL = 100pF, S2 closed (Note 5) Figures 5 and 6, CL = l5pF, S2 closed Figures 5 and 6, CL = l5pF, S1 closed Figures 7 and 8, CL = 100pF, S2 closed Figures 7 and 8, CL = 100pF, S1 closed
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PRELIMINARY TECHNICAL DATA ADM3082/ADM3085/ADM3088
ADM3082/ADM3085/ADM3088 SPECIFICATIONS (continued)
SWITCHING CHARACTERISTICS--ADM3088 (VCC = +5V 5%, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +5V and TA = +25C.) (Note 1)
Parameter Driver Input-to-Output, tDPLH Driver Input-to-Output, tDPHL Driver Output Skew,|tDPLH -tDPHL|, tDSKEW Driver Rise or Fall Time, tDR, tDF Maximum Data Rate, fMAX Driver Enable to Output High, tDZH Driver Enable to Output Low, tDZL Driver Disable Time from Low, tDLZ Driver Disable Time from High, tDHZ Receiver Input-to-Output, tRPLH, tRPHL DifferentialReceiver Skew, tRSKD |tRPLH - tRPHL| Receiver Enable to Output Low, tRZL Receiver Enable to Output High, tRZH Receiver Disable Time from Low, tRLZ Receiver Disable Time from High, tRHZ Time to Shutdown, tSHDN Driver Enable from Shutdown toOutput High, tDZH(SHDN) Driver Enable from Shutdown to Output Low, tDZL(SHDN) Receiver Enable from Shutdown to Output High, tRZH(SHDN) Receiver Enable from Shutdown to Output Low, tRZL(SHDN)
NOTES
5
Min
Typ 34 34 -2.5 14
Max 60 60 10 25
Units Test Conditions/Comments ns ns ns ns Mbps Figures 2 and 5, RDIFF = 54 , CL1 = CL2 = 100pF Figures 2 and 5, RDIFF = 54 , CL1 = CL2 = 100pF Figures 7 and 9, RDIFF = 54 , CL1 = CL2 = 100pF
10 150 150 100 100 106 0 20 20 20 20 50 200 150 10 50 50 50 50 600 250 250 3500 3500
ns ns ns ns ns ns ns ns ns ns ns ns ns ns ns
Figures 5 and 6, CL = 100pF, S2 closed Figures 5 and 6, CL = 100pF, S1 closed Figures 5 and 6, CL = l5pF, S1 closed Figures 5 and 6, CL = l5pF, S2 closed Figure 7; |VID| 2.0V; rise and fall time of VID l5ns
Figures 7; |VID| 2.0V; rise and fall time of VID l5ns Figures 7 and 8, CL = 100pF, S1 closed Figures 7 and 8, CL = 100pF, S2 closed Figures 7 and 8, CL = 100pF, S1 closed Figures 7 and 8, CL = 100pF, S2 closed (Note 5) Figures 5 and 6, CL = l5pF, S2 closed Figures 5 and 6, CL = l5pF, S1 closed Figures 7 and 8, CL = 100pF, S2 closed Figures 7 and 8, CL = 100pF, S1 closed
The device is put into shutdown by bringing RE high and DE low. If the enable inputs are in this state for less than 50ns, the device is guaranteed not to enter shutdown. If the enable inputs are in this state for at least 600ns, the device is guaranteed to have entered shutdown.
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PRELIMINARY TECHNICAL DATA ADM3082/ADM3085/ADM3088
ADM3082/ADM3085/ADM3088 TEST CIRCUITS AND TIMING
Y R VOD R S1 Z VOC O UT P UT UN D E R TEST CR L 15p F 500 TEST P O INT VCC
S2
Figure 1. Driver DC Load Test Circuit
3V
Figure 5. Test Load for Driver Enable/Disable Time Test
DE CL 1 DI VOD2 R D IFF CL2 Y, Z V OL 5V DE 0V tDZL(S HD N) , t DZL 2.3V O U T PU T N O R M A LL Y L O W tDL Z V O L+0.5V 1.5V
Y, Z
O U T PU T N O R M A LL Y HIG H 2.3V t DZH (SH DN ) t DZH t DH Z
Figure 2. Test Load for Driver Timing Tests
V OL
V O H -0.5V
Figure 6. Driver Enable and Disable Times
5V DI 0V tDP LH t DP H L VCC Z V0 Y V 0 /2 V DIFF = V Y - V Z V DIFF V0 0 -V 0 t DR t S KE W = |t DP LH -tDP H L | t DF RO CRL 15p F 90% 10% 90% 10% S1 TEST P O INT 1k 1.5V
Figure 3. Driver Propagation Delays
S2
A 1V B -1 V t RP HL VOH RO VOL tRP LH 1 .5 V
1k
Figure 7. Test Load for Receiver Enable/Disable Time Test
Figure 4. Receiver Propagation Delays
RE
5V 0V V CC RO t RZ L (S HDN ) , t RZ L 1.5V O UT PU T NO R M A LL Y L O W t RL Z V O L +0.5V 1.5V
RO 0V
1.5V
O UT PU T NO R M A LL Y HIG H t R HZ
V O H -0.5V
t R ZH(S HD N) , t R ZH
Figure 8. Receiver Enable and Disable Delay Times
REV. PrA 02/02
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PRELIMINARY TECHNICAL DATA ADM3082/ADM3085/ADM3088
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
RO RE DE DI 1 2 3 4 8 7 6 5 VCC B A G ND
Supply Voltage (VCC) . . . . . . . . . . . . . . . . . . . . . . . . . . +7V Logic Input Voltage . . . . . . . . . . . . -0.3V to (V CC+0.3V) Driver Output Voltage (A, B) . . . . . . . . . . . . . . . . . . 13V Receiver Input Voltage (A, B) . . . . . . . . . . . . . . . . . . 13V Receiver Input Voltage, Full Duplex (A, B) . . . . . . 13V Receiver Output Voltage (RO) . . . -0.3V to (V CC+0.3V) Continuous Power Dissipation 8-Pin Plastic DIP (derate 9.09mW/oC above +70oC) . . . . . . . . . . . 727mW 8-Pin Plastic SO (derate 5.88mW/oC above +70oC) . . . . . . . . . . . 471mW Maximum Junction Temperature (T J max) . . . . . . . 150 C Storage Temperature Range . . . . . . . . . -65C to +150C Lead Temperature, Soldering Vapor Phase 60 sec . . . . . . . . . . . . . . . . . . . . . . . . . +215C Infra-Red 15 sec . . . . . . . . . . . . . . . . . . . . . . . . . . . +200C
*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.
AD M 30 88/ AD M 30 85/ AD M 30 88
T O P V IE W (No t to S cale)
ORDERING
INFORMATION
Model ADM3082JN ADM3082JR
Temperature Range 0C to +70C 0C to +70C
Package Option 8 Pin Plastic DIP 8 Pin SO 8 Pin Plastic DIP 8 Pin SO 8 Pin Plastic DIP 8 Pin SO 8 Pin Plastic DIP 8 Pin SO 8 Pin Plastic DIP 8 Pin SO 8 Pin Plastic DIP 8 Pin SO
ADM3082AN -40C to +85C ADM3082AR ADM3085JN ADM3085JR -40C to +85C 0C to +70C 0C to +70C
THERMAL CHARACTERISTICS
8-Pin Plastic DIP Package JA = tbd K/Watt, JC = tbd K/Watt 8-Pin Plastic SO Package JA = tbd K/Watt, JC = tbd K/Watt
ADM3085AN -40C to +85C ADM3085AR ADM3088JN ADM3088JR -40C to +85C 0C to +70C 0C to +70C
ADM3088AN -40C to +85C ADM3088AR -40C to +85C
ADM3082/ADM3085/ADM3088TYPICALPERFORMANCECHARACTERISTICS
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TPC1. No-load Supply Current vs. Temperature
TPC2. Output Current vs. Receiver Output High Voltage
TPC3. Output Current vs. Receiver Output Low Voltage
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PRELIMINARY TECHNICAL DATA ADM3082/ADM3085/ADM3088 ADM3082/ADM3085/ADM3088 TYPICAL PERFORMANCE CHARACTERISTICS (continued)
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TPC4. Receiver Output High Voltage vs. Temperature
TPC5. Receiver Output Low Voltage vs. Temperature
TPC6. Shutdown Current vs. Temperature
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TPC7. ADM3082 Driver Propagation Delay vs. Temperature
TPC8. ADM3085 Driver Propagation Delay vs. Temperature
TPC9. ADM3088 Driver Propagation Delay vs. Temperature
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TPC10. ADM3082/5 ReceIver Propagation Delay vs. Temperature
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TPC11. ADM3088 Receiver Propagation Delay vs. Temperature
TPC12. Driver Differential Output Voltage vs. Temperature
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PRELIMINARY TECHNICAL DATA ADM3082/ADM3085/ADM3088 ADM3082/ADM3085/ADM3088 TYPICAL PERFORMANCE CHARACTERISTICS (continued)
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TPC13. Driver Output Current vs. Differential Output Voltage
TPC14. Output Current vs. Driver Output High Voltage
TPC15. Output Current vs. Driver Output Low Voltage
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TPC16. ADM3082 Driver Propagation Delay
TPC17. ADM3085 Driver Propagation Delay
TPC18. ADM3088 Driver Propagation Delay
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TPC19. ADM3082/5 Receiver Propagation Delay
TPC20. ADM3088 Receiver Propagation Delay
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PRELIMINARY TECHNICAL DATA ADM3082/ADM3085/ADM3088
PIN FUNCTION DESCRIPTION
Pin Mnemonic 1 2 3 4 5 6 7 8 RO RE DE DI GND A B VCC
Description Receiver Output. When RE is low and A - B (more positive than) -50mV, RO will be high. When RE is low and A - B (more negative than) -200mV, RO will be low. Receiver Output Enable. Take RE low to enable RO; RO is high impedance when RE is high. Take RE high and DE low to enter low-power shutdown mode. Driver Output Enable. Take DE high to enable driver outputs. These outputs are high impedance when DE is low. Take RE high and DE low to enter low-power shutdown mode. Driver Input. With DE high, a low on DI forces non-inverting output low and inverting output high. Similarly, a high on DI forces non-inverting output high and inverting output low. Ground Non-Inverting Receiver Input and Non-Inverting Driver Output Inverting Receiver Input and Inverting Driver Output Positive Supply 4.75V =V CC =5.25V
DEVICE TRUTH TABLES TRANSMITTING RECEIVING
INPUTS RE X X 0 1 DE 1 1 0 0 DI 1 0 X X
OUTPUTS B/Z 0 1 High-Z A/Y 1 0 High-Z RE 0 0 0 1 1 X = Don't care
INPUTS DE X X X 1 0 A-B -0.05V -0.2V Open/shorted X X
OUTPUT RO 1 0 1 High-Z Shutdown
Shutdown
Shutdown mode, driver and receiver outputs high impedance
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PRELIMINARY TECHNICAL DATA ADM3082/ADM3085/ADM3088
DETAILED DESCRIPTION HIGH INPUT IMPEDANCE
The ADM3082, ADM3085 and ADM3088 are highspeed RS-485/RS-422 transceivers offering enhanced performance over industry-standard devices All devices in the family contain one driver and one receiver, but there is a choice of performance options. The devices feature failsafe operation, which means that a logic-high receiver output is guaranteed when the receiver inputs are open-circuit or short-circuit, or when they are connected to a terminated transmission line with all drivers disabled (see the section on Fail-Safe Operation).
SLEW RATE CONTROL
The input impedance of the devices is 96k , which is 8 times higher than the standard RS-485 load of 12k . A standard driver can driver 32 standard loads, so up to 256 ADM308X receivers, or a combination of ADM308X and other devices up to 32 unit loads, may be connected to an RS-422/RS485 bus driven by a single driver.
SHUTDOWN MODE
All the devices have a low power shutdown mode that is enabled by taking RE high and DE low. If shutdown mode is not used, the fact that DE is activehigh and RE is active-low offers a convenient way of switching the device between transmit and receive, by tying DE and RE together. This is useful, for example, in applications using half duplex operation and where several receiver outputs are connected to a serial bus. The device is guaranteed not to enter shutdown mode if DE and RE are driven in this way. If DE is low and RE is high for less than 50ns the device will not enter shutdown. If DE is low and RE is high for greater than 600ns, the device is guaranteed to enter shutdown.
FAIL-SAFE OPERATION
The ADM3082 features a controlled slew-rate driver that minimize electromagnetic interference (EMI) and reduce reflections caused by incorrectly terminated cables, allowing error-free data transmission rates up to 115kbps (see the section on Reduced EMI and Reflections). The ADM3085 offers a higher limit on driver output slew-rate, allowing data transmission rates up to 500kbps. The driver slew rate of the ADM3088 is not limited, offering data transmission rates up to 10Mbps.
RECEIVER INPUT FILTERING
The receivers of all devices incorporate input hysteresis. In addition, when operating in 115kbps or 500kbps mode, the receivers of the ADM3082 and ADM3085 incorporate input filtering. This enhances noise immunity with differential signals that have very slow rise and fall times, but it does increase propagation delay by 20%.
HALF-/FULL-DUPLEX OPERATION
The ADM3082, ADM3085, and ADM3088 are dedicated half-duplex devices (driver outputs internally linked to receiver inputs). Figure 29 shows a typical half-duplex connection between two devices.
THREE-STATE BUS CONNECTION
The ADM3082/ADM3085/ADM3088 offer true fail-safe operation while remaining fully compliant with the 200mV EIA/TIA-485 standard. A logic-high receiver output is guaranteed when the receiver inputs are shorted together or open-circuit, or when they are connected to a terminated transmission line with all drivers disabled. This is done by setting the receiver threshold between -50mV and -200mV. If the differential receiver input voltage (A-B) is greater than or equal to -50mV, RO is logic high. If A-B is less than or equal to -200mV, RO is logic low. In the case of a terminated bus with all transmitters disabled, the receiver's differential input voltage is pulled to 0V by ADM308X family, which results in a logic high with a 50mV minimum noise margin.
ENHANCED ESD PROTECTION
All the devices have a Driver Enable pin (DE) that enables the driver outputs when taken high or puts the driver outputs into a high-impedance state when taken low. This allows several driver outputs to be connected to an RS-422/RS-485 bus. Similarly, all the devices have a (active-low) Receiver Enable pin (RE). Taking this low enables the receiver, while taking it high puts the receiver outputs into a high-impedance state. This allows several receiver outputs to be connected to a serial data bus.
All Analog Devices parts incorporate protection against electrostatic discharge (ESD) to protect the devices during handling, assembly and normal operation. In addition, the ADM308X family has enhanced ESD protection up to 15kV on the receiver inputs and driver outputs (A, B) to protect against severe operational conditions such as line transients, connection and disconnection.
RE C E IV E R O UT P UT (RO ) RE C E IV E R E NA BL E (R E ) DR IV E R E NA BL E (DE ) DA T A IN (D I)
100n 1 R 2 3 4 D 7 RT 6 5 +5V (V C C ) 8
+5V (V C C ) 5 6 RT 7 R 8 100n AD M 308 2/5/8 1 2 D 4 3 DA T A IN (D I) DR IV E R E NA BL E (DE ) RE C E IV E R E NA BL E (R E ) RE C E IV E R O UT P UT (RO )
AD M 308 2/5/8
Figure 29. Half-Duplex Configuration for ADM3082, ADM3085 or ADM3088
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PRELIMINARY TECHNICAL DATA ADM3082/ADM3085/ADM3088
CURRENT LIMIT AND THERMAL SHUTDOWN
The ADM3082/ADM3085/ADM3088 incorporate two protection mechanisms to guard the drivers against shortcircuits, bus contention or other fault conditions. The first is a foldback current-limited output stage that protects the driver against short-circuits over the entire common-mode voltage range. The second is a thermal shutdown circuit that puts the driver outputs into a high-impedance state if the die temperature exceeds a safe limit.
REDUCED EMI AND REFLECTIONS
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The ADM3082 and ADM3085 incorporate slew-rating limiting in the drivers. This reduces reflections due to incorrect cable termination and minimizes electromagnetic interference (EMI). Figures 9 to 11 show driver output waveforms and Fourier analyses of 20kHz signals for the three different slew-rate settings. It can be seen that the harmonic content is greatly reduced for the ADM3085 and still further for the ADM3082 (Figures 10 and 9 respectively).
Figure 11. ADM3088 Driver Output Waveform and FFT Plot
The length of an unterminated stub that can be driven with only minor reflections depends on the rise time of the transmitter. A conservative estimate for this is given by the following equation: L (metres) = tR / 49.2 where tR is the transmitter's rise time in ns (multiply result by 3.28 for answer in feet).
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For example, the rise time of the ADM3082 is typically 1320ns, which results in acceptable waveforms with stub lengths up to 27 metres. This is not the ultimate limit on unterminated stub length, as a system can still work if the waveformis allowed to settle before sampling the data. The RS-485/RS-422 standard covers line lengths up to 4000 feet (1219 metres). Driver output and receiver output waveforms for the three slew rate settings, driving a 4000 foot cable, are shown in figures 12 to 14.
Figure 9 ADM3082 Driver Output Waveform and FFT Plot
AW
AI
N TI
G
DA
TA
AW
A
I IT
NG
T DA
A
Figure 12. Driver Input, Driver Output and Receiver Output Waveforms of ADM3082, Driving 4000ft (1219m) of Cable at 50kHz
Figure 10. ADM3085 Driver Output Waveform and FFT Plot
REV. PrA 02/02
-13-
PRELIMINARY TECHNICAL DATA ADM3082/ADM3085/ADM3088
APPLICATIONS
AW
T AI
I
NG
AT D
A
Figures 15 shows a typical application of the device on a half--duplex network. The line should be terminated at both ends to minimize reflections and any stubs off the main line should be kept as short as possible.
120
RO RE DE DI
R
B A
D
Figure 13. Driver Input, Driver Output and Receiver Output Waveforms of ADM3085, Driving 4000ft (1219m) of Cable at 50kHz
RO RE DE DI
R
B A
D
AW
AI
TI
NG
D
A AT
RO RE DE DI
R
B A
D
RO RE DE DI
R
B A
D
Figure 14. Driver Input, Driver Output and Receiver Output Waveforms of ADM3088, Driving 4000ft (1219m) of Cable at 200kHz
120 AD M 3082, ADM 3084, AD M 308 5 O R AD M 3089 W IT H H /F = V C C
For line lengths in excess of 1220 metres the line should be split into smaller sections with intermediate repeaters.
OUTLINE 8-Pin Plastic Dual-In-Line Package (N-8)
0.43 0 (10 .92 ) 0.34 8 (8.84 )
8 5
Figure 15. Typical Half-Duplex Network Application
DIMENSIONS 8-Pin SO Package (R-8)
0.19 6 8 (5 . 00) 0.18 9 0 (4 . 80)
Dimensions shown in inches and (mm).
0. 280 (7.11 ) 0. 240 (6.10 )
14
85
0. 244 0 (6. 20 ) 0. 325 (8.25 ) 0. 228 4 (5. 80 ) 0. 300 (7.62 ) 0.19 5 (4. 95) 0.11 5 (2. 93) P IN 1
1 4
0.15 7 4 (4 .00 ) 0.14 9 7 (3 .80 )
P IN 1 0.21 0 (5.33 ) MAX 0.16 0 (4.06 ) 0.11 5 (2.93 )
0. 060 (1.52 ) 0. 015 (0.38 ) 0.1 3 0 (3 .30 ) M IN S E A T IN G PLANE
0. 102 (2.59) 0. 094 (2.39)
0.01 9 6 (0 . 50) 0.00 9 9 (0 . 25)
x 45
0. 015 (0.3 81 ) 0. 008 (0.2 04 )
0.02 2 (0.5 58 ) 0.1 0 0 0.07 0 (1.77 ) 0.01 4 (0.3 56 ) (2 .54 ) 0.04 5 (1.15 ) BSC
0.009 8 (0. 25 ) 0.004 0 (0. 10 ) SE A TIN G PLANE 0.0 5 00 (1 .27 ) BS C 0.01 9 2 (0 . 49) 0.01 3 8 (0 . 35) 0.00 9 8 (0 . 25) 0.00 7 5 (0 . 19) 8 0
0.05 0 0 (1 .27 ) 0.01 6 0 (0 .41 )
-14-
REV. PrA 02/02

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