a FEATURES Meets EIA RS-485 Standard 5 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 LTC485 APPLICATIONS Low Power RS-485 Systems DTE-DCE Interface Packet Switching Local Area Networks Data Concentration Data Multiplexers Integrated Services Digital Network (ISDN) PRODUCT DESCRIPTION The ADM485 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 ADM485 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 ADM485 driver features high output impedance when disabled and also when powered down. +5 V Low Power EIA RS-485 Transceiver ADM485 FUNCTIONAL BLOCK DIAGRAM ADM485 RO 1 R 8 VCC RE 2 7 B DE 3 6 A DI 4 D 5 GND 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 ADM485 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 ADM485 features extremely fast switching speeds. Minimal driver propagation delays permit transmission at data rates up to 5 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-pin DIL/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 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 Fax: 617/326-8703 ADM485-SPECIFICATIONS (V Parameter Min CC = +5 V 6 5%. All specifications TMIN to TMAX unless otherwise noted) Typ DRIVER Differential Output Voltage, VOD 2.0 1.5 1.5 VOD3 |VOD| for Complementary Output States Common-Mode Output Voltage VOC |VOC| for Complementary Output States Output Short Circuit Current (VOUT = High) 35 Output Short Circuit Current (VOUT = Low) 35 CMOS Input Logic Threshold Low, VINL CMOS Input Logic Threshold High, VINH 2.0 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 Max Units Test Conditions/Comments 5.0 5.0 5.0 5.0 0.2 3 0.2 250 250 0.8 V V V V V V V mA mA V V A 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 -7 V VCM +12 V VCM = 0 V -7 V VCM +12 V VIN = 12 V VIN = -7 V 85 1.0 V mV k mA mA A V V mA A 2.2 1 mA mA Outputs Unloaded, Digital Inputs = GND or VCC Outputs Unloaded, Digital Inputs = GND or VCC 1.0 -0.2 +0.2 70 12 +1 -0.8 1 0.4 4.0 7 POWER SUPPLY CURRENT ICC (Outputs Enabled) ICC (Outputs Disabled) 1.35 0.7 IOUT = +4.0 mA IOUT = -4.0 mA VOUT = GND or VCC 0.4 V VOUT +2.4 V Specifications subject to change without notice. Timing Specifications (V CC = +5 V 6 5%. All specifications TMIN to TMAX unless otherwise noted.) Parameter 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 Min Typ Max Units Test Conditions/Comments 2 10 0 2 10 10 15 5 10 25 25 ns ns ns ns ns 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 18 25 0 15 15 40 5 25 25 ns ns ns ns CL = 15 pF, Figure 5 Figure 6 Figure 6 Specifications subject to change without notice. -2- REV. 0 ADM485 ABSOLUTE MAXIMUM RATINGS* PIN FUNCTION DESCRIPTION (TA = +25C unless otherwise noted) 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-Pin DIP . . . . . . . . . . . . . . . . . . . . 500 mW JA, Thermal Impedance . . . . . . . . . . . . . . . . . . . . +130C/W Power Dissipation 8-Pin SOIC . . . . . . . . . . . . . . . . . . 450 mW JA, Thermal Impedance . . . . . . . . . . . . . . . . . . . . +170C/W Power Dissipation 8-Pin 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 Vapour 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 and functional operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum ratings for extended periods 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. 2 RE Receiver Output Enable. A low level enables the receiver output, RO. A high level places it in a high impedance state. 3 DE Driver Output Enable. A high level enables the driver differential outputs, A and B. A low level places it in a high impedance state. 4 DI 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. 5 GND Ground Connection, 0 V. 6 A Noninverting Receiver Input A/Driver Output A. 7 B Inverting Receiver Input B/Driver Output B. 8 VCC Power Supply, 5 V 5%. PIN CONFIGURATION Table I. Transmitting INPUTS DE RE X X X 1 1 0 DI 1 0 X B OUTPUT A 0 1 Z RE DE A-B 0 0 0 1 0 0 0 0 +0.2 V -0.2 V Inputs Open X 1 0 1 Z 2 DI 1 0 Z OUTPUT RO 1 RE DE 3 V 7 B TOP VIEW (Not to Scale) 6 A 5 GND 4 CC Model Temperature Range Package Option ADM485JN ADM485JR ADM485AN ADM485AR ADM485AQ 0C to +70C 0C to +70C -40C to +85C -40C to +85C -40C to +85C N-8 R-8 N-8 R-8 Q-8 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 ADM485 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. REV. 0 8 ADM485 ORDERING GUIDE Table II. Receiving INPUTS RO -3- WARNING! ESD SENSITIVE DEVICE ADM485 Test Circuits VCC RL A R DE R S2 S1 0V OR 3V VOD B V CL VOC OUT DE IN Figure 1. Driver Voltage Measurement Test Circuit Figure 4. Driver Enable/Disable Test Circuit A 375 V OD3 V 60 V B TST OUT RE C L 375 Figure 2. Driver Voltage Measurement Test Circuit 2 Figure 5. Receiver Propagation Delay Test Circuit V +1.5V A RL RLDIFF S2 -1.5V RE C CL L2 B CC S1 CL1 VOUT RE IN Figure 3. Driver Propagation Delay Test Circuit Figure 6. Receiver Enable/Disable Test Circuit Switching Characteristics 3V 1.5V 1.5V TPLH 0V B 0V 0V PLH TPHL A-B T PHL 1/2VO T VO V OH A T TSKEW VO RO SKEW 90% POINT 1.5V 1.5V 90% POINT V 0V -VO 10% POINT OL 10% POINT TF TR Figure 9. Receiver Propagation Delay Figure 7. Driver Propagation Delay, Rise/Fall Timing 3V 3V RE DE 1.5V 1.5V 1.5V 1.5V 0V 0V TZL TLZ LZ 1.5V R 2.3V A, B T TZL VOL THZ TZH A, B 2.3V VOL+ 0.5V O/P LOW VOL+ 0.5V VOL T TZH HZ V VOH OH O/P HIGH VOH - 0.5V R 1.5V V OH - 0.5V 0V 0V Figure 8. Driver Enable/Disable Timing Figure 10. Receiver Enable/Disable Timing -4- REV. 0 0 36 -2 32 -4 28 24 20 16 12 8 5.0 I = 8mA OUTPUT VOLTAGE - Volts 40 OUTPUT CURRENT - mA OUTPUT CURRENT - mA Typical Performance Characteristics-ADM485 -6 -8 -10 -12 -14 -16 4 0.5 1.0 1.5 OUTPUT VOLTAGE - Volts -20 3.5 2.0 Figure 11. Receiver Output Low Voltage vs. Output Current 4.0 4.5 OUTPUT VOLTAGE - Volts 4.6 DIFFERENTIAL VOLTAGE - Volts OUTPUT CURRENT - mA 0.2 72 60 48 36 24 12 0 25 50 75 TEMPERATURE - C 100 0 125 1 2 3 OUTPUT VOLTAGE - Volts 4 0 90 -10 80 -20 OUTPUT CURRENT - mA 100 70 60 50 40 30 20 0 1 2 3 OUTPUT VOLTAGE - Volts Figure 17. Driver Output Low Voltage vs. Output Current 4 2.1 -25 0 25 50 75 100 125 Figure 16. Driver Differential Output Voltage vs. Temperature, RL = 54 0.95 -30 -40 -50 -60 -70 -80 0.90 DRIVER ENABLED 0.85 0.80 0.75 DRIVER DISABLED 0.70 0.65 -100 0 2.2 1.00 -90 10 125 TEMPERATURE - C Figure 15. Driver Differential Output Voltage vs. Output Current Figure 14. Receiver Output Low Voltage vs. Temperature 100 2.3 2.0 -50 0 -25 SUPPLY CURRENT - mA 0.1 -50 0 25 50 75 TEMPERATURE - C 2.4 84 0.3 -25 Figure 13. Receiver Output High Voltage vs. Temperature 96 I = 8mA OUTPUT VOLTAGE - Volts 4.7 4.5 -50 5.0 Figure 12. Receiver Output High Voltage vs. Output Current 0.4 OUTPUT CURRENT - mA 4.8 -18 0 0.0 REV. 0 4.9 0 1 2 3 4 OUTPUT VOLTAGE - Volts Figure 18. Driver Output High Voltage vs. Output Current -5- 5 0.60 -50 -25 0 25 50 75 TEMPERATURE - C 100 Figure 19. Supply Current vs. Temperature 125 ADM485-Typical Performance Characteristics 5 1.0 0.9 4 100 90 0.8 TIME - ns TIME - ns 3 2 0.7 0.6 10 1 0 -50 0% 0.5 -25 0 25 50 75 TEMPERATURE - C 100 1 V 0.4 -50 125 Figure 20. Receiver tPLH-tPHL, vs. Temperature -25 0 25 50 75 TEMPERATURE - C 100 Figure 22. Unloaded Driver Differential Outputs Figure 21. Driver Skew vs. Temperature 100 100 90 90 90 10 10 10 0% 0% 0% 500m V 1 V 5n s Figure 23. Loaded Driver Differential Outputs 1 V 5 5 5n s 125 100 500m V 1 V 1 V 10ns HO Figure 24. Driver/Receiver Propagation Delays Low to High RT 1 V 5 5 10ns HO Figure 25. Driver/Receiver Propagation Delays High to Low RT D D R R R R D D Figure 26. Typical RS-485 Network -6- REV. 0 ADM485 APPLICATIONS INFORMATION 32 transceivers on the bus. Only one driver can transmit at a particular time but multiple receivers may be enabled simultaneously. 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. 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 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. The ADM485 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 reenabled at 140C. 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. Propagation Delay The ADM485 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). Cable and Data Rate 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. Receiver Open-Circuit Fail Safe The receiver input includes a fail-safe feature which guarantees a logic high on the receiver when the inputs are open circuit or floating. The ADM485 is designed for bidirectional data communications on multipoint transmission lines. A typical application showing a multipoint transmission network is illustrated in Figure 26. An RS-485 transmission line can have as many as Table III. Comparison of RS-422 and RS-485 Interface Standards REV. 0 Specification RS-422 RS-485 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 Differential 4000 ft. 2 V 100 4 k min 200 mV -7 V to +7 V 1/10 Differential 4000 ft. 1.5 V 54 12 k min 200 mV -7 V to +12 V 32/32 -7- ADM485 OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 8 5 1 4 C1817-18-7/93 8-Lead SOIC (R-8) 0.1574 (4.00) 0.1497 (3.80) PIN 1 0.2440 (6.20) 0.2284 (5.80) 0.1968 (5.00) 0.1890 (4.80) 0.0196 (0.50) x 45 0.0099 (0.25) 0.102 (2.59) 0.094 (2.39) 0.0098 (0.25) 0.0040 (0.10) 0.0500 (1.27) BSC 0.0192 (0.49) 0.0138 (0.35) 0.0098 (0.25) 0.0075 (0.19) 8 0 0.0500 (1.27) 0.0160 (0.41) 8-Pin Plastic DIP (N-8) 8 5 0.280 (7.11) 0.240 (6.10) PIN 1 1 4 0.325 (8.25) 0.300 (7.62) 0.430 (10.92) 0.348 (8.84) 0.060 (1.52) 0.015 (0.38) 0.210 (5.33) MAX 0.130 (3.30) MIN 0.160 (4.06) 0.115 (2.93) 0.100 (2.54) BSC 0.022 (0.558) 0.014 (0.356) 0.070 (1.77) 0.045 (1.15) 0.195 (4.95) 0.115 (2.93) 0.015 (0.381) 0.008 (0.204) SEATING PLANE 8-Pin Cerdip (Q-8) 0.005 (0.13) MIN 8 0.055 (1.4) MAX 5 0.310 (7.87) 0.220 (5.59) PIN 1 4 0.320 (8.13) 0.290 (7.37) 0.405 (10.29) MAX 0.200 (5.08) MAX PRINTED IN U.S.A. 1 0.060 (1.52) 0.015 (0.38) 0.150 (3.81) MIN 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) 15 0 SEATING PLANE -8- REV. 0