+5 V Low Power EIA RS-485 Transceiver ADM1485

Transcription

1 a FETUES Meets EI S-8 Standard 3 Mb/s Data ate Single + V Supply 7 V to +12 V us Common-Mode ange High Speed, Low Power icmos Thermal Shutdown Protection Short Circuit Protection Zero Skew Driver Driver Propagation Delay: 1 ns eceiver Propagation Delay: 2 ns High Z Outputs with Power Off Superior Upgrade for LTC18 PPLICTIONS Low Power S-8 Systems DTE-DCE Interface Packet Switching Local rea Networks Data Concentration Data Multiplexers Integrated Services Digital Network (ISDN) + V Low Power EI S-8 Transceiver DM18 FUNCTIONL LOCK DIGM O 1 8 V CC E DE 2 3 DM18 DI D GND 7 6 GENEL DESCIPTION The DM18 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 EI Standards S-8 and S-22. The part contains a differential line driver and a differential line receiver. oth the driver and the receiver may be enabled independently. When disabled, the outputs are tristated. The DM18 operates from a single + 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 DM18 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 DM18 is fabricated on icmos, an advanced mixed technology process combining low power CMOS with fast switching bipolar technology. ll inputs and outputs contain protection against ESD; all driver outputs feature high source and sink current capability. n epitaxial layer is used to guard against latch-up. The DM18 features extremely fast switching speeds. Minimal driver propagation delays permit transmission at data rates up to 3 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. EV. Information furnished by nalog Devices is believed to be accurate and reliable. However, no responsibility is assumed by nalog 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 nalog Devices. One Technology Way, P.O. ox 916, Norwood, M , U.S.. Tel: 617/329-7 Fax: 617/

2 DM18 SPECIFICTIONS (V CC = + V %. ll specifications T MIN to T MX unless otherwise noted.) Parameter Min Typ Max Units Test Conditions/Comments DIVE Differential Output Voltage, V OD. V =, Figure V V CC = V, = Ω (S-22), Figure V = 27 Ω (S-8), Figure 1 V OD3 1.. V V TST = 7 V to +12 V, Figure 2 V OD for Complementary Output States.2 V = 27 Ω or Ω, Figure 1 Common-Mode Output Voltage V OC 3 V = 27 Ω or Ω, Figure 1 V OD for Complementary Output States.2 V = 27 Ω or Ω Output Short Circuit Current (V OUT = High) 3 2 m 7 V V O +12 V Output Short Circuit Current (V OUT = Low) 3 2 m 7 V V O +12 V CMOS Input Logic Threshold Low, V INL.8 V CMOS Input Logic Threshold High, V INH 2. V Logic Input Current (DE, DI) ±1. µ ECEIVE Differential Input Threshold Voltage, V TH V 7 V V CM +12 V Input Voltage Hysteresis, V TH 7 mv V CM = V Input esistance 12 kω 7 V V CM +12 V Input Current (, ) + 1 m V IN = 12 V.8 m V IN = 7 V Logic Enable Input Current (E) ±1 µ CMOS Output Voltage Low,. V I OUT = +. m CMOS Output Voltage High, V OH. V I OUT =. m Short Circuit Output Current 7 8 m V OUT = GND or V CC Tristate Output Leakage Current ±1. µ. V V OUT +2. V POWE SUPPLY CUENT I CC (Outputs Enabled) m Outputs Unloaded, Digital Inputs = GND or V CC I CC (Outputs Disabled).7 1 m Outputs Unloaded, Digital Inputs = GND or V CC Specifications subject to change without notice. TIMING SPECIFICTIONS Parameter Min Typ Max Units Test Conditions/Comments DIVE Propagation Delay Input to Output T PLH, T PHL ns L Diff = Ω C L1 = C L2 = 1 pf, Figure 3 Driver O/P to O/P T SKEW ns L Diff = Ω C L1 = C L2 = 1 pf, Figure 3 Driver ise/fall Time T, T F 2 1 ns L Diff = Ω C L1 = C L2 = 1 pf, Figure 3 Driver Enable to Output Valid 1 2 ns Driver Disable Timing 1 2 ns ECEIVE Propagation Delay Input to Output T PLH, T PHL 18 2 ns C L = 1 pf, Figure Skew T PLH T PHL ns eceiver Enable T EN1 1 2 ns Figure 6 eceiver Disable T EN2 1 2 ns Figure 6 Specifications subject to change without notice. (V CC = + V %. ll specifications T MIN to T MX unless otherwise noted.) 2 EV.

3 DM18 SOLUTE MXIMUM TINGS* (T = +2 C unless otherwise noted) V CC V Inputs Driver Input (DI) V to V CC +.3 V Control Inputs (DE, E) V to V CC +.3 V eceiver Inputs (, ) V to +1 V Outputs Driver Outputs V to +1 V eceiver Output V to V CC +. V Power Dissipation 8-Pin DIP mw θ J, Thermal Impedance C/W Power Dissipation 8-Pin SOIC mw θ J, Thermal Impedance C/W Power Dissipation 8-Pin Cerdip mw θ J, Thermal Impedance C/W Operating Temperature ange Commercial (J Version) C to +7 C Industrial ( Version) C to +8 C Storage Temperature ange C to +1 C Lead Temperature (Soldering, 1 sec) C Vapour Phase (6 sec) C Infrared (1 sec) C *Stresses above those listed under bsolute Maximum atings 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 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 FUNCTION DESCIPTION Pin Mnemonic Function 1 O eceiver Output. When enabled if > by 2 mv, then O = High. If < by 2 mv, then O = Low. 2 E eceiver Output Enable. low level enables the receiver output, O. high level places it in a high impedance state. 3 DE Driver Output Enable. high level enables the driver differential outputs, and. low level places it in a high impedance state. DI Driver Input. When the driver is enabled a logic Low on DI forces low and high while a logic High on DI forces high and low. GND Ground Connection, V. 6 Noninverting eceiver Input /Driver Output. 7 Inverting eceiver Input /Driver Output. 8 V CC Power Supply, V ± %. PIN CONFIGUTION Table I. Transmitting INPUTS OUTPUTS E DE DI X X 1 1 X X Z Z Table II. eceiving INPUTS OUTPUT E DE - O +.2 V 1.2 V Inputs Open 1 1 X Z ODEING GUIDE Temperature Package Model ange Option DM18JN C to +7 C N-8 DM18J C to +7 C -8 DM18N C to +8 C N-8 DM18 C to +8 C -8 DM18Q C to +8 C Q-8 CUTION ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as V readily accumulate on the human body and test equipment and can discharge without detection. lthough the DM18 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. WNING! ESD SENSITIVE DEVICE EV. 3

4 DM18 Test Circuits V CC V OD V OC V O 3V DE S1 C L L V OUT S2 DE IN Figure 1. Driver Voltage Measurement Test Circuit Figure. Driver Enable/Disable Test Circuit 37Ω V OD3 6Ω V TST E V OUT C L 37Ω Figure 2. Driver Voltage Measurement Test Circuit 2 Figure. eceiver Propagation Delay Test Circuit LDIFF C L1 C L2 +1.V 1.V S1 E C L L V OUT V CC S2 Figure 3. Driver Propagation Delay Test Circuit E IN Figure 6. eceiver Enable/Disable Test Circuit Switching Characteristics 3V V 1.V 1.V T PLH V V T PHL VO 1/2VO T PLH T PHL V OH VO 9% POINT T SKEW T SKEW 9% POINT O 1.V 1.V V VO 1% POINT T T F 1% POINT Figure 9. eceiver Propagation Delay Figure 7. Driver Propagation Delay, ise/fall Timing 3V 3V E 1.V 1.V DE 1.V 1.V V V T ZL T LZ T ZL T LZ, 2.3V +.V 1.V O/P LOW +.V, T ZH 2.3V T HZ V OH.V V OH T ZH 1.V O/P HIGH T HZ V OH.V V OH V V Figure 8. Driver Enable/Disable Timing Figure 1. eceiver Enable/Disable Timing EV.

5 Typical Performance Characteristics DM18. OUTPUT CUENT m OUTPUT CUENT m I = 8m TEMPETUE C 1 12 Figure 11. eceiver Output Low Figure 12. eceiver Output High Figure 13. eceiver Output High Voltage vs. Temperature I = 8m OUTPUT CUENT m DIFFEENTIL VOLTGE Volts TEMPETUE C TEMPETUE C Figure 1. eceiver Output Low Voltage vs. Temperature Figure 1. Driver Differential Output Figure 16. Driver Differential Output Voltage vs. Temperature, L = Ω 1 1. OUTPUT CUENT m OUTPUT CUENT m SUPPLY CUENT m DIVE ENLED DIVE DISLED TEMPETUE C 1 12 Figure 17. Driver Output Low Figure 18. Driver Output High Figure 19. Supply Current vs. Temperature EV.

6 DM18 Typical Performance Characteristics TIME ns 3 2 TIME ns % 1 V 1 V ns TEMPETUE C TEMPETUE C 12 Figure 2. eceiver t PLH t PHL vs. Temperature Figure 21. Driver Skew vs. Temperature Figure 22. Unloaded Driver Differential Outputs % 1 % 1 % mv mv ns 1 V 1 V 1ns H O 1 V 1 V 1ns H O Figure 23. Loaded Driver Differential Outputs Figure 2. Driver/eceiver Propagation Delays Low to High Figure 2. Driver/eceiver Propagation Delays High to Low T T D D D D Figure 26. Typical S-8 Network 6 EV.

7 DM18 PPLICTIONS INFOMTION 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 ssociation (EI) which specify the electrical characteristics of transceivers used in differential data transmission. The S-22 standard specifies data rates up to 1 Maud and line lengths up to ft. single driver can drive a transmission line with up to 1 receivers. In order to cater for true multipoint communications, the S-8 standard was defined. This standard meets or exceeds all the requirements of S-22 but also allows for up to 32 drivers and 32 receivers to be connected to a single bus. n extended common-mode range of 7 V to +12 V is defined. The most significant difference between S-22 and S-8 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 S-8 standard contains additional specifications to guarantee device safety in the event of line contention. Cable and Data ate The transmission line of choice for S-8 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 DM18 is designed for bidirectional data communications on multipoint transmission lines. typical application showing a multipoint transmission network is illustrated in Figure 26. n S-8 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. s 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. properly terminated transmission line appears purely resistive to the driver. Thermal Shutdown The DM18 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 1 C is reached. s the device cools, the drivers are re-enabled at 1 C. Propagation Delay The DM18 features very low propagation delay ensuring maximum baud rate operation. The driver is well balanced ensuring distortion free transmission. nother 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). eceiver 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. Table III. Comparison of S-22 and S-8 Interface Standards Specification S-22 S-8 Transmission Type Differential Differential Maximum Cable Length ft. ft. Minimum Driver Output Voltage ±2 V ±1. V Driver Load Impedance 1 Ω Ω eceiver Input esistance kω min 12 kω min eceiver Input Sensitivity ±2 mv ±2 mv eceiver Input Voltage ange 7 V to +7 V 7 V to +12 V No of Drivers/eceivers Per Line 1/1 32/32 EV. 7

8 DM18 OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 8-Lead SOIC (-8) PIN (.).197 (3.8).2 (6.2).228 (.8) C /93.98 (.2). (.1).1968 (.).189 (.8). (1.27) SC.192 (.9).138 (.3).12 (2.9).9 (2.39).98 (.2).7 (.19) (.) x.99 (.2). (1.27).16 (.1) 8-Pin Plastic DIP (N-8) 8 PIN 1.28 (7.11).2 (6.1) 1.3 (1.92).38 (8.8).32 (8.2).3 (7.62).21 (.33) MX.6 (1.2).1 (.38).19 (.9).11 (2.93).16 (.6).11 (2.93).13 (3.3) MIN.1 (.381).8 (.2).22 (.8).1 (.36).1 (2.) SC.7 (1.77). (1.1) SETING PLNE 8-Pin Cerdip (Q-8). (.13) MIN. (1.) MX 8 PIN 1.2 (.8) MX.2 (.8).12 (3.18) 1.23 (.8).1 (.36). (1.29) MX.1 (2.) SC.7 (1.78).3 (.76).31 (7.87).22 (.9).6 (1.2).1 (.38).1 (3.81) MIN SETING PLNE.32 (8.13).29 (7.37).1 (.38).8 (.2) 1 PINTED IN U.S.. 8 EV.