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FEATURES Meets EIA RS-485 Standard 30 Mb/s Data Rate Single +5 V Supply -7 V to +12 V Bus Common-Mode Range High Speed, Low Power BiCMOS Thermal Shutdown Protection Short Circuit Protection Zero Skew Driver Driver Propagation Delay: 10 ns Receiver Propagation Delay: 25 ns High Z Outputs with Power Off Superior Upgrade for LTC1485 APPLICATIONS Low Power RS-485 Systems DTE-DCE Interface Packet Switching Local Area Networks Data Concentration Data Multiplexers Integrated Services Digital Network (ISDN)
+5 V Low Power EIA RS-485 Transceiver ADM1485
FUNCTIONAL BLOCK DIAGRAM 8-Lead
ADM1485
RO R VCC
RE
B
DE
A
DI
D
GND
GENERAL DESCRIPTION
The ADM1485 is a differential line transceiver suitable for high speed bidirectional data communication on multipoint bus transmission lines. It is designed for balanced data transmission and complies with both EIA Standards RS-485 and RS-422. The part contains a differential line driver and a differential line receiver. Both the driver and the receiver may be enabled independently. When disabled, the outputs are tristated. The ADM1485 operates from a single +5 V power supply. Excessive power dissipation caused by bus contention or by output shorting is prevented by a thermal shutdown circuit. This feature forces the driver output into a high impedance state if during fault conditions a significant temperature increase is detected in the internal driver circuitry. Up to 32 transceivers may be connected simultaneously on a bus, but only one driver should be enabled at any time. It is important therefore that the remaining disabled drivers do not load the bus. To ensure this, the ADM1485 driver features high output impedance when disabled and also when powered down.
This minimizes the loading effect when the transceiver is not being utilized. The high impedance driver output is maintained over the entire common-mode voltage range from -7 V to +12 V. The receiver contains a fail safe feature which results in a logic high output state if the inputs are unconnected (floating). The ADM1485 is fabricated on BiCMOS, an advanced mixed technology process combining low power CMOS with fast switching bipolar technology. All inputs and outputs contain protection against ESD; all driver outputs feature high source and sink current capability. An epitaxial layer is used to guard against latch-up. The ADM1485 features extremely fast switching speeds. Minimal driver propagation delays permit transmission at data rates up to 30 Mbits/s while low skew minimizes EMI interference. The part is fully specified over the commercial and industrial temperature range and is available in an 8-lead DIL/SOIC package.
REV. A
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: 781/329-4700 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 (c) Analog Devices, Inc., 2000
ADM1485-SPECIFICATIONS (V
Parameter DRIVER Differential Output Voltage, VOD VOD3 |VOD| for Complementary Output States Common-Mode Output Voltage VOC |VOD| for Complementary Output States Output Short Circuit Current (VOUT = High) Output Short Circuit Current (VOUT = Low) CMOS Input Logic Threshold Low, VINL CMOS Input Logic Threshold High, VINH Logic Input Current (DE, DI) RECEIVER Differential Input Threshold Voltage, VTH Input Voltage Hysteresis, VTH Input Resistance Input Current (A, B) Logic Enable Input Current (RE) CMOS Output Voltage Low, VOL CMOS Output Voltage High, VOH Short Circuit Output Current Tristate Output Leakage Current POWER SUPPLY CURRENT ICC (Outputs Enabled) ICC (Outputs Disabled)
Specifications subject to change without notice.
CC
= +5 V
Max 5.0 5.0 5.0 5.0 0.2 3 0.2 250 250 0.8 1.0
5%. All specifications TMIN to TMAX unless otherwise noted.)
Unit V V V V V V V mA mA V V A V mV k mA mA A V V mA A mA mA Test Conditions/Comments R = , Figure 1 VCC = 5 V, R = 50 (RS-422), Figure 1 R = 27 (RS-485), Figure 1 VTST = -7 V to +12 V, Figure 2 R = 27 or 50 , Figure 1 R = 27 or 50 , Figure 1 R = 27 or 50 -7 V VO +12 V -7 V VO +12 V
Min
Typ
2.0 1.5 1.5
35 35 2.0
-0.2 70 12
+0.2
+1 -0.8 1 0.4 4.0 7 85 1.0 1.35 0.7 2.2 1
-7 V VCM +12 V VCM = 0 V -7 V VCM +12 V VIN = 12 V VIN = -7 V IOUT = +4.0 mA IOUT = -4.0 mA VOUT = GND or VCC 0.4 V VOUT +2.4 V Outputs Unloaded, Digital Inputs = GND or VCC Outputs Unloaded, Digital Inputs = GND or VCC
TIMING SPECIFICATIONS (V
Parameter
CC
= +5 V
5%. All specifications TMIN to TMAX unless otherwise noted.)
Min 2 Typ 10 0 2 10 10 25 0 15 15 Max 15 5 10 25 25 40 5 25 25 Unit ns ns ns ns ns ns ns ns ns Test Conditions/Comments RL Diff = 54 CL1 = CL2 = 100 pF, Figure 3 RL Diff = 54 CL1 = CL2 = 100 pF, Figure 3 RL Diff = 54 CL1 = CL2 = 100 pF, Figure 3
DRIVER Propagation Delay Input to Output TPLH, TPHL Driver O/P to O/P TSKEW Driver Rise/Fall Time TR, TF Driver Enable to Output Valid Driver Disable Timing RECEIVER Propagation Delay Input to Output TPLH, TPHL Skew |TPLH-TPHL| Receiver Enable TEN1 Receiver Disable TEN2
Specifications subject to change without notice.
18
CL = 15 pF, Figure 5 Figure 6 Figure 6
-2-
REV. A
ADM1485
ABSOLUTE MAXIMUM RATINGS*
(TA = +25C unless otherwise noted)
PIN FUNCTION DESCRIPTION
VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +7 V Inputs Driver Input (DI) . . . . . . . . . . . . . . . .-0.3 V to VCC + 0.3 V Control Inputs (DE, RE) . . . . . . . . . . -0.3 V to VCC + 0.3 V Receiver Inputs (A, B) . . . . . . . . . . . . . . . . . -14 V to +14 V Outputs Driver Outputs . . . . . . . . . . . . . . . . . . . . . . . -14 V to +14 V Receiver Output . . . . . . . . . . . . . . . . .-0.5 V to VCC + 0.5 V Power Dissipation 8-Lead DIP . . . . . . . . . . . . . . . . . 500 mW JA, Thermal Impedance . . . . . . . . . . . . . . . . . . +130C/W Power Dissipation 8-Lead SOIC . . . . . . . . . . . . . . . . 450 mW JA, Thermal Impedance . . . . . . . . . . . . . . . . . . +170C/W Power Dissipation 8-Lead Cerdip . . . . . . . . . . . . . . . 500 mW JA, Thermal Impedance . . . . . . . . . . . . . . . . . . +125C/W Operating Temperature Range Commercial (J Version) . . . . . . . . . . . . . . . . . 0C to +70C Industrial (A Version) . . . . . . . . . . . . . . . . -40C to +85C Storage Temperature Range . . . . . . . . . . . -65C to +150C Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . +300C Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . . +215C Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . . +220C
*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 listed in the operational sections of this specification is not implied. Exposure to absolute maximum ratings for extended periods of time may affect device reliability.
Pin Mnemonic Function 1 RO Receiver Output. When enabled if A > B by 200 mV, then RO = High. If A < B by 200 mV, then RO = Low. Receiver Output Enable. A low level enables the receiver output, RO. A high level places it in a high impedance state. Driver Output Enable. A high level enables the driver differential outputs, A and B. A low level places it in a high impedance state. Driver Input. When the driver is enabled a logic Low on DI forces A low and B high while a logic High on DI forces A high and B low. Ground Connection, 0 V. Noninverting Receiver Input A/Driver Output A. Inverting Receiver Input B/Driver Output B. Power Supply, 5 V 5%.
PIN CONFIGURATION
2
RE
3
DE
4
DI
5 6 7 8
GND A B VCC
RO 1 RE 2
8
VCC
Table I. Transmitting
B TOP VIEW DE 3 (Not to Scale) 6 A
7
ADM1485
RE X X X
INPUTS DE 1 1 0
DI 1 0 X
OUTPUTS B A 0 1 Z 1 0 Z Model ADM1485JN ADM1485JR ADM1485AN ADM1485AR ADM1485AQ
DI 4
5
GND
ORDERING GUIDE
Temperature Range 0C to +70C 0C to +70C -40C to +85C -40C to +85C -40C to +85C
Package Option N-8 SO-8 N-8 SO-8 Q-8
Table II. Receiving
INPUTS RE 0 0 0 1 DE 0 0 0 0 A-B +0.2 V -0.2 V Inputs Open X
OUTPUT RO 1 0 1 Z
CAUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the ADM1485 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high-energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
WARNING!
ESD SENSITIVE DEVICE
REV. A
-3-
ADM1485 Test Circuits
VCC R VOD R VOC DE IN 0V OR 3V DE B A RL S1 CL VOUT S2
Figure 1. Driver Voltage Measurement Test Circuit
Figure 4. Driver Enable/Disable Test Circuit
375
A
VOD3
60 375
VTST
B
RE CL
VOUT
Figure 2. Driver Voltage Measurement Test Circuit 2
Figure 5. Receiver Propagation Delay Test Circuit
+1.5V VCC S1 -1.5V RE CL RE IN VOUT RL S2
A RLDIFF B
CL1
CL2
Figure 3. Driver Propagation Delay Test Circuit
Figure 6. Receiver Enable/Disable Test Circuit
Switching Characteristics
3V 1.5V 0V B 1/2VO VO A TSKEW VO 0V -VO 10% POINT TR TF 10% POINT 90% POINT TSKEW 90% POINT TPLH 1.5V
A, B
TPHL
0V
0V
TPLH
TPHL VOH
RO
1.5V
1.5V VOL
Figure 9. Receiver Propagation Delay
3V
Figure 7. Driver Propagation Delay, Rise/Fall Timing
3V DE 1.5V 1.5V 0V TZL TLZ
TZL TLZ RE 1.5V 1.5V 0V
A, B
2.3V VOL +0.5V VOL TZH THZ VOH VOH -0.5V 2.3V 0V
R
1.5V O/P LOW TZH O/P HIGH THZ VOH VOH -0.5V VOL +0.5V VOL
A, B
R 0V
1.5V
Figure 8. Driver Enable/Disable Timing
Figure 10. Receiver Enable/Disable Timing
-4-
REV. A
Typical Performance Characteristics-ADM1485
40 36
OUTPUT CURRENT - mA
0 -2
5.0 I = 8mA
28 24 20 16 12 8 4 0 0 0.5 1.0 1.5 OUTPUT VOLTAGE - Volts 2.0
-6 -8 -10 -12 -14 -16 -18 -20 3.5 4.0 4.5 OUTPUT VOLTAGE - Volts 5.0
OUTPUT VOLTAGE - Volts
OUTPUT CURRENT - mA
32
-4
4.9
4.8
4.7
4.6
4.5 -50
-25
0 25 50 75 TEMPERATURE - C
100
125
Figure 11. Receiver Output Low Voltage vs. Output Current
Figure 12. Receiver Output High Voltage vs. Output Current
Figure 13. Receiver Output High Voltage vs. Temperature
0.4 I = 8mA
96
2.4
DIFFERENTIAL VOLTAGE - Volts
0
84
OUTPUT VOLTAGE - Volts
OUTPUT CURRENT - mA
72 60 48 36 24 12
2.3
0.3
2.2
0.2
2.1
0.1 -50
-25
0 25 50 75 TEMPERATURE - C
100
125
0
1 2 3 OUTPUT VOLTAGE - Volts
4
2.0 -50
-25
0 25 50 75 TEMPERATURE - C
100
125
Figure 14. Receiver Output Low Voltage vs. Temperature
Figure 15. Driver Differential Output Voltage vs. Output Current
Figure 16. Driver Differential Output Voltage vs. Temperature, RL = 54
100 90
0 -10
1.00 0.95
OUTPUT CURRENT - mA
OUTPUT CURRENT - mA
SUPPLY CURRENT - mA
80 70 60 50 40 30 20 10 0 0 1 2 3 OUTPUT VOLTAGE - Volts 4
-20 -30 -40 -50 -60 -70 -80 -90 -100 0 1 2 3 4 OUTPUT VOLTAGE - Volts 5
0.90 0.85 0.80 0.75
DRIVER ENABLED
DRIVER DISABLED 0.70 0.65 0.60 -50
-25
0 25 50 75 TEMPERATURE - C
100
125
Figure 17. Driver Output Low Voltage vs. Output Current
Figure 18. Driver Output High Voltage vs. Output Current
Figure 19. Supply Current vs. Temperature
REV. A
-5-
ADM1485-Typical Performance Characteristics
5 1.0 0.9
100 90
4
0.8
TIME - ns
3
TIME - ns
0.7
2
0.6
10
1
0%
0.5
1V
0 -50 -25 0 25 50 75 TEMPERATURE - C 100 125 0.4 -50 -25 0 25 50 75 TEMPERATURE - C 100 125
1V
5ns
Figure 20. Receiver tPLH-tPHL vs. Temperature
Figure 21. Driver Skew vs. Temperature
Figure 22. Unloaded Driver Differential Outputs
100 90
100 90
100 90
10
0%
10 0%
10
0%
500mV
500mV
5ns
1V
1V
5
5 10ns
HO
1V
1V
5
5 10ns
HO
Figure 23. Loaded Driver Differential Outputs
Figure 24. Driver/Receiver Propagation Delays Low to High
Figure 25. Driver/Receiver Propagation Delays High to Low
RT
RT
D
D
R
R
R D D
R
Figure 26. Typical RS-485 Network
-6-
REV. A
ADM1485
APPLICATIONS INFORMATION
Differential Data Transmission
Differential data transmission is used to reliably transmit data at high rates over long distances and through noisy environments. Differential transmission nullifies the effects of ground shifts and noise signals which appear as common-mode voltages on the line. There are two main standards approved by the Electronics Industries Association (EIA) which specify the electrical characteristics of transceivers used in differential data transmission. The RS-422 standard specifies data rates up to 10 MBaud and line lengths up to 4000 ft. A single driver can drive a transmission line with up to 10 receivers. In order to cater for true multipoint communications, the RS-485 standard was defined. This standard meets or exceeds all the requirements of RS-422 but also allows for up to 32 drivers and 32 receivers to be connected to a single bus. An extended common-mode range of -7 V to +12 V is defined. The most significant difference between RS-422 and RS-485 is the fact that the drivers may be disabled thereby allowing more than one (32 in fact) to be connected to a single line. Only one driver should be enabled at time, but the RS-485 standard contains additional specifications to guarantee device safety in the event of line contention.
Cable and Data Rate
showing a multipoint transmission network is illustrated in Figure 26. An RS-485 transmission line can have as many as 32 transceivers on the bus. Only one driver can transmit at a particular time but multiple receivers may be enabled simultaneously. As with any transmission line, it is important that reflections are minimized. This may be achieved by terminating the extreme ends of the line using resistors equal to the characteristic impedance of the line. Stub lengths of the main line should also be kept as short as possible. A properly terminated transmission line appears purely resistive to the driver.
Thermal Shutdown
The ADM1485 contains thermal shutdown circuitry which 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 and disables the driver outputs. The thermal sensing 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 140C.
Propagation Delay
The ADM1485 features very low propagation delay ensuring maximum baud rate operation. The driver is well balanced ensuring distortion free transmission. Another important specification is a measure of the skew between the complementary outputs. Excessive skew impairs the noise immunity of the system and increases the amount of electromagnetic interference (EMI).
Receiver Open-Circuit Fail Safe
The transmission line of choice for RS-485 communications is a twisted pair. Twisted pair cable tends to cancel common-mode noise and also causes cancellation of the magnetic fields generated by the current flowing through each wire, thereby, reducing the effective inductance of the pair. The ADM1485 is designed for bidirectional data communications on multipoint transmission lines. A typical application
The receiver input includes a fail-safe feature which guarantees a logic high on the receiver when the inputs are open circuit or floating.
Table III. Comparison of RS-422 and RS-485 Interface Standards
Specification Transmission Type Maximum Cable Length Minimum Driver Output Voltage Driver Load Impedance Receiver Input Resistance Receiver Input Sensitivity Receiver Input Voltage Range No of Drivers/Receivers Per Line
RS-422 Differential 4000 ft. 2 V 100 4 k min 200 mV -7 V to +7 V 1/10
RS-485 Differential 4000 ft. 1.5 V 54 12 k min 200 mV -7 V to +12 V 32/32
REV. A
-7-
ADM1485
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Lead SOIC (SO-8)
0.1968 (5.00) 0.1890 (4.80)
8 5 4
0.1574 (4.00) 0.1497 (3.80) PIN 1
1
0.2440 (6.20) 0.2284 (5.80)
0.0500 (1.27) BSC 0.0098 (0.25) 0.0040 (0.10) SEATING PLANE 0.0688 (1.75) 0.0532 (1.35) 0.0192 (0.49) 0.0138 (0.35) 8 0.0098 (0.25) 0 0.0075 (0.19)
0.0196 (0.50) 0.0099 (0.25)
45
0.0500 (1.27) 0.0160 (0.41)
8-Lead Plastic DIP (N-8)
0.430 (10.92) 0.348 (8.84)
8 5
0.280 (7.11) 0.240 (6.10) 0.325 (8.25) 0.300 (7.62) 0.060 (1.52) 0.015 (0.38) 0.130 (3.30) MIN 0.015 (0.381) 0.008 (0.204) 0.195 (4.95) 0.115 (2.93)
1
4
PIN 1 0.100 (2.54) BSC 0.210 (5.33) MAX 0.160 (4.06) 0.115 (2.93)
0.022 (0.558) 0.070 (1.77) SEATING 0.014 (0.356) 0.045 (1.15) PLANE
8-Lead Cerdip (Q-8)
0.005 (0.13) MIN
8
0.055 (1.4) MAX
5
0.310 (7.87) 0.220 (5.59)
1 4
PIN 1 0.405 (10.29) MAX 0.200 (5.08) MAX 0.060 (1.52) 0.015 (0.38) 0.150 (3.81) MIN SEATING PLANE 15 0
0.320 (8.13) 0.290 (7.37)
0.200 (5.08) 0.125 (3.18) 0.023 (0.58) 0.100 0.070 (1.78) 0.014 (0.36) (2.54) 0.030 (0.76) BSC
0.015 (0.38) 0.008 (0.20)
-8-
REV. A
PRINTED IN U.S.A.
C1818-0-6/00 (rev. A) 00063

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