a ESD Protected, EMC Compliant, 3.3 V, 20 Mbps, EIA RS-485 Transceiver ADM3485E FEATURES Operates with +3.3 V Supply ESD Protection: 8 kV Meets IEC1000-4-2 EFT Protection: 2 kV Meets IEC1000-4-4 EIA RS-422 and RS-485 Compliant Over Full CM Range 19 k Input Impedance Up to 50 Transceivers on Bus 20 Mbps Data Rate Short Circuit Protection Specified Over Full Temperature Range Thermal Shutdown Interoperable with 5 V Logic 1 mA Supply Current 2 nA Shutdown Current 8 ns Skew FUNCTIONAL BLOCK DIAGRAM ADM3485E RO R RE B A DE DI D APPLICATIONS Telecommunications DTE-DCE Interface Packet Switching Local Area Networks Data Concentration Data Multiplexers Integrated Services Digital Network (ISDN) AppleTalk Industrial Controls GENERAL DESCRIPTION The ADM3485E is a low power differential line transceiver designed to operate using a single +3.3 V power supply. Low power consumption makes it ideal for power sensitive applications. It is suitable for communication on multipoint bus transmission lines. Internal protection against electrostatic discharge (ESD) and electrical fast transient (EFT) allows operation in electrically harsh environments. It is intended for balanced data transmission and complies with both EIA Standards RS-485 and RS-422. It contains a differential line driver and a differential line receiver, and is suitable for half duplex data transfer. The input impedance is 19 kΩ allowing up to 50 transceivers to be connected on the bus. 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. The receiver contains a fail-safe feature that results in a logic high output state if the inputs are unconnected (floating). The ADM3485E is fabricated on BiCMOS, an advanced mixed technology process combining low power CMOS with fast switching bipolar technology. The ADM3485E is fully specified over the industrial temperature range and is available in 8-lead DIP and SOIC packages. 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 © Analog Devices, Inc., 2000 ADM3485E–SPECIFICATIONS (V Parameter DRIVER Differential Output Voltage, VOD Min CC = +3.3 V 0.3 V. All specifications TMIN to TMAX unless otherwise noted.) Typ Logic Enable Input Current (RE) Output Voltage Low, VOL Output Voltage High, VOH Short Circuit Output Current Three-State Output Leakage Current Units Test Conditions/Comments 0.2 3 0.2 0.8 V V V V V V V V µA mA RL = 100 Ω, Figure 1, VCC > 3.1 V RL = 54 Ω, Figure 1 RL = 60 Ω, Figure 2, –7 V < VTST < +12 V R = 54 Ω or 100 Ω, Figure 1 R = 54 Ω or 100 Ω, Figure 1 R = 54 Ω or 100 Ω, Figure 1 V mV kΩ mA mA µA V V mA µA –7 V < VCM < +12 V VCM = 0 V –7 V < VCM < +12 V VIN = +12 V VIN = –7 V 2.0 1.5 1.5 ∆|VOD| for Complementary Output States Common-Mode Output Voltage VOC ∆|VOC| for Complementary Output States CMOS Input Logic Threshold Low, VINL CMOS Input Logic Threshold High, VINH 2.0 Logic Input Current (DE, DI, RE) Output Short Circuit Current RECEIVER Differential Input Threshold Voltage, VTH Input Voltage Hysteresis, ∆VTH Input Resistance Input Current (A, B) Max ± 1.0 ± 250 –0.2 12 +0.2 50 19 +1 –0.8 ±1 0.4 VCC – 0.4 V ± 60 ± 1.0 POWER SUPPLY CURRENT ICC Supply Current in Shutdown ESD/EFT IMMUNITY ESD Protection EFT Protection VO = –7 V or +12 V IOUT = +2.5 mA IOUT = –1.5 mA VOUT = GND or VCC VCC = 3.6 V, 0 V < VOUT < VCC 1 1.2 1 1.2 0.002 1 mA mA µA Outputs Unloaded, DE = VCC, RE = 0 V DE = 0 V, RE = 0 V DE = 0 V, RE = VCC ±8 ±2 kV kV IEC1000-4-2 A, B Pins Contact Discharge IEC1000-4-4, A, B Pins Specifications subject to change without notice. –2– REV. A ADM3485E TIMING SPECIFICATIONS (V CC = +3.3 V, TA = +25C) Parameter Min Typ Max Units Test Conditions/ Comments DRIVER Differential Output Delay TDD Differential Output Transition Time Propagation Delay Input to Output TPLH, TPHL Driver O/P to O/P TSKEW 1 1 7 8 22 35 15 35 8 ns ns ns ns RL = 60 Ω, CL1 = CL2 = 15 pF, Figure 3 RL = 60 Ω, CL1 = CL2 = 15 pF, Figure 3 RL = 27 Ω, CL1 = CL2 = 15 pF, Figure 7 RL = 54 Ω, CL1 = CL2 = 15 pF, Figure 3 45 40 650 90 80 110 ns ns ns RL = 110 Ω, CL = 50 pF, Figure 2 RL = 110 Ω, CL = 50 pF, Figure 2 RL = 110 Ω, CL = 15 pF, Figure 2 190 65 300 90 10 50 45 500 ns ns ns ns ns ns CL = 15 pF, Figure 8 CL = 15 pF, Figure 8 CL = 15 pF, Figure 6 CL = 15 pF, Figure 6 CL = 15 pF, Figure 6 ENABLE/DISABLE Driver Enable to Output Valid Driver Disable Timing Driver Enable from Shutdown RECEIVER Time to Shutdown Propagation Delay Input to Output TPLH, TPHL Skew TPLH–TPHL Receiver Enable TEN Receiver Disable TDEN Receiver Enable from Shutdown 80 25 25 25 Specifications subject to change without notice. TIMING SPECIFICATIONS (V CC = +3.3 V 0.3 V, TA = TMIN to TMAX) Parameter Min Typ Max Units Test Conditions/ Comments DRIVER Differential Output Delay TDD Differential Output Transition Time Propagation Delay Input to Output TPLH, TPHL Driver O/P to O/P TSKEW 1 2 7 8 22 70 15 70 10 ns ns ns ns RL = 60 Ω, CL1 = CL2 = 15 pF, Figure 3 RL = 60 Ω, CL1 = CL2 = 15 pF, Figure 3 RL = 27 Ω, CL1 = CL2 = 15 pF, Figure 7 RL = 54 Ω, CL1 = CL2 = 15 pF, Figure 3 45 40 650 110 110 110 ns ns ns RL = 110 Ω, CL = 50 pF, Figure 2 RL = 110 Ω, CL = 50 pF, Figure 2 RL = 110 Ω, CL = 15 pF, Figure 2 190 65 500 115 20 50 50 600 ns ns ns ns ns ns CL = 15 pF, Figure 8 CL = 15 pF, Figure 8 CL = 15 pF, Figure 6 CL = 15 pF, Figure 6 CL = 15 pF, Figure 6 ENABLE/DISABLE Driver Enable to Output Valid Driver Disable Timing Driver Enable from Shutdown RECEIVER Time to Shutdown Propagation Delay Input to Output TPLH, TPHL Skew TPLH–TPHL Receiver Enable TEN Receiver Disable TDEN Receiver Enable from Shutdown 50 25 25 25 Specifications subject to change without notice. REV. A –3– ADM3485E Operating Temperature Range Industrial (A Version) . . . . . . . . . . . . . . . . –40°C to +85°C Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . +300°C Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . . +215°C Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . +220°C ESD Rating: Air (Human Body Model, All Pins) . . . . . >4 kV ESD Rating: IEC1000-4-2 Contact (A, B Pins) . . . . . . >8 kV EFT Rating: IEC1000-4-4 (A, B Pins) . . . . . . . . . . . . . >2 kV ABSOLUTE MAXIMUM RATINGS* (TA = +25°C 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) . . . . . . . . . . . . . . . –7.5 V to +12.5 V Outputs Driver Outputs . . . . . . . . . . . . . . . . . . . . . –7.5 V to +12.5 V Receiver Output . . . . . . . . . . . . . . . . . –0.5 V to VCC + 0.5 V Power Dissipation 8-Lead DIP . . . . . . . . . . . . . . . . . 800 mW θJA, Thermal Impedance . . . . . . . . . . . . . . . . . . . . 140°C/W Power Dissipation 8-Lead SOIC . . . . . . . . . . . . . . . . 650 mW θJA, Thermal Impedance . . . . . . . . . . . . . . . . . . . . 115°C/W *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. ORDERING GUIDE Model Temperature Range Package Description Package Options ADM3485EAN ADM3485EAR –40°C to +85°C –40°C to +85°C Plastic DIP Small Outline (SOIC) N-8 SO-8 PIN CONFIGURATION DIP/SOIC RO 1 8 VCC RE 2 ADM3485E 7 B DE 3 DI 4 TOP VIEW 6 A (Not to Scale) 5 GND PIN FUNCTION DESCRIPTIONS Mnemonic Pin DIP/ SOIC RO RE 1 2 DE 3 DI 4 GND A B VCC 5 6 7 8 Function Receiver Output. High when A > B by 200 mV or low when A < B by 200 mV. Receiver Output Enable. With RE low, the receiver output RO is enabled. With RE high, the output goes high impedance. If RE is high and DE low, the ADM3485E enters a shutdown 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, 3.3 V ± 0.3 V. –4– REV. A ADM3485E Test Circuits 375 R/2 VOD R/2 VOD3 VOC RL VTST VCC 375 Figure 1. Driver Voltage Measurement Test Circuit Figure 5. Driver Voltage Measurement Test Circuit 2 VCC VCC +1.5V 0V OR 3V DE RL S1 S1 S2 RL –1.5V CL VOUT RE DE IN S2 CL VOUT RE IN Figure 2. Driver Enable/Disable Test Circuit Figure 6. Receiver Enable/Disable Test Circuit VOM RL DI CL1 D DE IN RLDIFF CL VOUT CL2 VOUT S1 VCC Figure 3. Driver Differential Output Delay Test Circuit DI CL1 D RLDIFF 0V A B CL2 Figure 7. Driver Propagation Delay Test Circuit R VID RE +1.5V Figure 4. Driver/Receiver Propagation Delay Test Circuit REV. A 3V RO VOUT RE CL Figure 8. Receiver Propagation Delay Test Circuit –5– ADM3485E Switching Characteristics 3V 1.5V 0V 1.5V 3V tPLH DE 1.5V 1.5V tPLH B 0V tZL 1/2 VO tLZ VO A tSKEW VO 90% POINT 1.5V D tSKEW 90% POINT O/P LOW tZH VOL + 0.25V VOL tHZ 0V –VO 10% POINT D 10% POINT tR 1.5V tF VOH O/P HIGH VOH – 0.25V 0V Figure 9. Driver Propagation Delay, Rise/Fall Timing Figure 11. Driver Enable/Disable Timing 3V RE 1.5V 1.5V 0V A–B 0V 0V tPLH tZL tPLH RO 1.5V R O/P LOW tZH VOH 1.5V tLZ VOL tHZ R 1.5V VOL + 0.25V 1.5V O/P HIGH VOH VOH – 0.25V VOL 0V Figure 10. Receiver Propagation Delay Figure 12. Receiver Enable/Disable Timing –6– REV. A 14 12 12 10 OUTPUT CURRENT – mA OUTPUT CURRENT – mA Typical Performance Characteristics–ADM3485E 10 8 6 4 6 4 2 2 0 0 0 0.5 1.5 2.5 1.0 2.0 OUTPUT LOW VOLTAGE – V 0 3.5 3.0 Figure 13. Output Current vs. Receiver Output Low Voltage 0.8 3.30 0.7 3.25 0.6 0.5 0.4 0.3 0.2 0.1 –50 0.5 1.5 2.5 1.0 2.0 OUTPUT HIGH VOLTAGE – V 3.5 3.0 Figure 16. Output Current vs. Receiver Output High Voltage RECEIVER O/P HIGH VOLTAGE – V RECEIVER OUTPUT LOW VOLTAGE – V 8 3.20 3.15 3.10 3.05 3.00 2.95 –30 –10 10 30 50 70 90 2.90 –50 110 –30 –10 TEMPERATURE – C Figure 14. Receiver Output Low Voltage vs. Temperature 10 30 50 70 TEMPERATURE – C 90 110 Figure 17. Receiver Output High Voltage vs. Temperature 120 2.6 2.4 2.3 80 VOD – V DRIVER OUTPUT CURRENT – mA 2.5 100 60 2.2 2.1 2.0 40 1.9 1.8 20 1.7 0 0 0.5 1.5 2.5 1.0 2.0 DIFFERENTIAL OUTPUT VOLTAGE – V 1.6 –50 3.0 Figure 15. Driver Output Current vs. Differential Output Voltage REV. A –30 –10 10 30 50 70 TEMPERATURE – C 90 110 Figure 18. Driver Differential Output Voltage vs. Temperature –7– ADM3485E 1.20 100 1.15 90 1.10 80 70 ICC (mA) DE = VCC, RE = X 1.00 ICC – nA ICC – mA 1.05 0.95 0.90 ICC (mA) RE = LO, DE = LO 0.85 60 50 40 30 0.80 20 0.75 10 0.70 –50 –30 –10 90 10 30 50 70 TEMPERATURE – C 0 –40 110 Figure 19. Supply Current vs. Temperature Specification RS-422 RS-485 Transmission Type Maximum Data Rate 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 10 MB/s 4000 ft. ±2 V 100 Ω 4 kΩ min ± 200 mV –7 V to +7 V 1/10 Differential 10 MB/s 4000 ft. ± 1.5 V 54 Ω 12 kΩ min ± 200 mV –7 V to +12 V 32/32 RE DE DI B A X X 0 1 1 1 0 0 1 0 X X 0 1 Hi-Z Hi-Z 1 0 Hi-Z Hi-Z Two coupling methods are used for ESD testing, contact discharge and air-gap discharge. Contact discharge calls for a direct connection to the unit being tested. Air-gap discharge uses a higher test voltage but does not make direct contact with the unit under test. With air discharge, the discharge gun is moved toward the unit under test, developing an arc across the air gap, hence the term air-discharge. This method is influenced by humidity, temperature, barometric pressure, distance and rate of closure of the discharge gun. The contact-discharge method, while less realistic, is more repeatable and is gaining acceptance and preference over the air-gap method. Although very little energy is contained within an ESD pulse, the extremely fast rise time, coupled with high voltages, can cause failures in unprotected semiconductors. Catastrophic destruction can occur immediately as a result of arcing or heating. Even if catastrophic failure does not occur immediately, the device may suffer from parametric degradation, which may result in degraded performance. The cumulative effects of continuous exposure can eventually lead to complete failure. Receiving Outputs RO 0 0 0 1 X X X X > +0.2 V < –0.2 V Inputs O/C X 1 0 1 Hi-Z 80 ESD TESTING Table III. Receiving Truth Table A–B 60 The protection structure achieves ESD protection up to ± 8 kV according to IEC1000-4-2, and EFT protection up to ± 2 kV on all I-O lines. Outputs DE 20 40 TEMPERATURE – C The ADM3485E uses protective clamping structures on its inputs and outputs that clamp the voltage to a safe level and dissipate the energy present in ESD (Electrostatic) and EFT (Electrical Fast Transients) discharges. Transmitting RE 0 ESD/EFT TRANSIENT PROTECTION SCHEME Table II. Transmitting Truth Table Inputs –20 Figure 20. Shutdown Current vs. Temperature Table I. Comparison of RS-422 and RS-485 Interface Standards Inputs ICC (mA) I-O lines are particularly vulnerable to ESD damage. Simply touching or plugging in an I-O cable can result in a static discharge that can damage or completely destroy the interface product connected to the I-O port. It is extremely important, therefore, to have high levels of ESD protection on the I-O lines. It is possible that the ESD discharge could induce latchup in the device under test, so it is important that ESD testing on the I-O pins be carried out while device power is applied. This type of testing is more representative of a real-world I-O discharge where the equipment is operating normally when the discharge occurs. –8– REV. A ADM3485E Four severity levels are defined in terms of an open-circuit voltage as a function of installation environment. The installation environments are defined as 100% 90% IPEAK 1. 2. 3. 4. Well-Protected Protected Typical Industrial Severe Industrial 36.8% V 10% t TIME t tDL tRL 300ms Figure 21. Human Body Model Current Waveform 16ms V 5ns Table IV. ESD Test Results ESD Test Method I-O Pins IEC1000-4-2: Contact ± 8 kV 50ns t 0.2/0.4ms 100% Figure 23. IEC1000-4-4 Fast Transient Waveform 90% Table V shows the peak voltages for each of the environments. IPEAK Table V. Peak Voltages 10% 0.1 TO 1ns TIME t Level V PEAK (kV) PSU VPEAK (kV) I-O 1 2 3 4 0.5 1 2 4 0.25 0.5 1 2 30ns 60ns A simplified circuit diagram of the actual EFT generator is illustrated in Figure 24. Figure 22. IEC1000-4-2 ESD Current Waveform FAST TRANSIENT BURST IMMUNITY (IEC1000-4-4) IEC1000-4-4 (previously 801-4) covers electrical fast-transient/ burst (EFT) immunity. Electrical fast transients occur as a result of arcing contacts in switches and relays. The tests simulate the interference generated when, for example, a power relay disconnects an inductive load. A spark is generated due to the well known back EMF effect. In fact, the spark consists of a burst of sparks as the relay contacts separate. The voltage appearing on the line, therefore, consists of a burst of extremely fast transient impulses. A similar effect occurs when switching on fluorescent lights. HIGH VOLTAGE SOURCE CC L RM CD 50 OUTPUT ZS Figure 24. EFT Generator These transients are coupled onto the signal lines using an EFT coupling clamp. The clamp is 1 m long and completely surrounds the cable, providing maximum coupling capacitance (50 pF to 200 pF typ) between the clamp and the cable. High energy transients are capacitively coupled onto the signal lines. Fast rise times (5 ns) as specified by the standard result in very effective coupling. This test is very severe since high voltages are coupled onto the signal lines. The repetitive transients can often cause problems, where single pulses do not. Destructive latchup may be induced due to the high energy content of the transients. Note that this stress is applied while the interface products are powered up and are transmitting data. The EFT test applies hundreds of pulses with higher energy than ESD. Worst case transient current on an I-O line can be as high as 40 A. The fast transient burst test, defined in IEC1000-4-4, simulates this arcing and its waveform is illustrated in Figure 23. It consists of a burst of 2.5 kHz to 5 kHz transients repeating at 300 ms intervals. It is specified for both power and data lines. REV. A RC –9– ADM3485E Test results are classified according to the following Cable and Data Rate 1. Normal performance within specification limits. 2. Temporary degradation or loss of performance that is selfrecoverable. 3. Temporary degradation or loss of function or performance that requires operator intervention or system reset. 4. Degradation or loss of function that is not recoverable due to damage. 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. 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 that appear as common-mode voltages on the line. Two main standards are 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. 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. Receiver Open-Circuit Fail-Safe The receiver input includes a fail-safe feature that guarantees a logic high on the receiver when the inputs are open circuit or floating. The RS-485 standard was defined to cater to true multipoint communications. This standard meets or exceeds all the requirements of RS-422, but also allows multiple drivers and receivers to be connected to a single bus. An extended commonmode 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 to be connected to a single line. Only one driver should be enabled at a time, but the RS-485 standard contains additional specifications to guarantee device safety in the event of line contention. The ADM3485E is designed for bidirectional data communications on multipoint transmission lines. A typical application showing a multipoint transmission network is illustrated in Figure 23. Only one driver can transmit at a particular time, but multiple receivers may be enabled simultaneously. Table VI. Comparison of RS-422 and RS-485 Interface Standards 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 Differential 4000 ft. ±2 V 100 Ω 4 kΩ min ± 200 mV –7 V to +7 V Differential 4000 ft. ± 1.5 V 54 Ω 12 kΩ min ± 200 mV –7 V to +12 V –10– REV. A ADM3485E OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 0.430 (10.92) 0.348 (8.84) 8 5 0.280 (7.11) 0.240 (6.10) 1 4 0.325 (8.25) 0.300 (7.62) 0.060 (1.52) 0.015 (0.38) PIN 1 0.210 (5.33) MAX 0.130 (3.30) MIN 0.160 (4.06) 0.115 (2.93) 0.022 (0.558) 0.100 0.070 (1.77) 0.014 (0.356) (2.54) 0.045 (1.15) BSC SEATING PLANE 0.195 (4.95) 0.115 (2.93) 0.015 (0.381) 0.008 (0.204) C3338–0–5/00 (rev. A) 00075 8-Lead Plastic DIP (N-8) 8-Lead SOIC (SO-8) 0.1968 (5.00) 0.1890 (4.80) 0.1574 (4.00) 0.1497 (3.80) 8 5 1 4 0.2440 (6.20) 0.2284 (5.80) PIN 1 0.0196 (0.50) 45 0.0099 (0.25) 0.0500 (1.27) BSC 0.0098 (0.25) 0.0040 (0.10) 0.0192 (0.49) 0.0138 (0.35) 8 0.0500 (1.27) 0.0098 (0.25) 0 0.0160 (0.41) 0.0075 (0.19) PRINTED IN U.S.A. SEATING PLANE 0.0688 (1.75) 0.0532 (1.35) REV. A –11–