DS1487_11 TI1 | Alldatasheet
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DS1487 Low Power RS-485 ¼ Unit Load Multipoint Transceiver Literature Number: SNLS132
Low Power RS-485 1⁄4 Unit Load Multipoint Transceiver General Description The DS1487 is a low-power transceiver for RS-485 and RS-422 communication. The device contains one driver and one receiver. The drivers slew rate allows for operation up to 2.0 Mbps (see Applications Information section). The trans- ceiver presents 1⁄4 unit loading to the RS-485 bus allowing up to 128 nodes to be connected together without the use of re- peaters. The transceiver draws 200 µA of supply current when un- loaded or fully loaded with the driver disabled and operates from a single +5V supply. The driver is short-circuit current limited and is protected against excessive power dissipation by thermal shutdown circuitry that places the driver outputs into TRI-STATE (High Impedance state) under fault conditions. The driver guarantees a minimum of 1.5V differential output voltage with maximum loading across the common mode range OD3 ). The receiver has a failsafe feature that guarantees a logic-high output if the input is open circuit. The DS1487 is available in surface mount and DIP pack- ages.
Features
n Meets TIA/EIA RS-485 multipoint standard n Allows up to 128 transceivers on the bus (1⁄4 U.L.) n Guaranteed full load output voltage (VOD3 ) n Low quiescent current: 200 µA typ n −7V to +12V common-mode input voltage range n TRI-STATE outputs on driver and receiver n AC performance: — Driver transition time: 25 ns typ — Driver propagation delay: 40 ns typ — Driver skew: 1 ns typ — Receiver propagation delay: 200 ns typ — Receiver skew: 20 ns typ n Half-duplex flow through pinout n Operates from a single 5V supply n Current-limiting and thermal shutdown for driver overload protection n Pin and functional compatible with MAX1487 Connection and Logic Diagram Order Number Temp. Range Package/ ### DS1487N 0˚C to +70˚C DIP/N08E DS1487M 0˚C to +70˚C SOP/M08A Truth Table DRIVER SECTION RE (Note 1) DE DI A B XHHHL XHL LH XLXZZ RECEIVER SECTION RE (Note 1) DE A-B RO LL ≥+0.2V H LL ≤−0.2V L HX X Z L L OPEN (Note 1) H X = indeterminate Z = TRI-STATE Note 1:Non Terminated, Open Input only TRI-STATE® is a registered trademark of National Semiconductor Corporation. DIP and SOIC DS012920-1 *Note: Non Terminated, Open Input only July 1998 DS1487 Low Power RS-4851⁄4Unit Load Multipoint Transceiver © 2000 National Semiconductor Corporation DS012920 www.national.com
Absolute Maximum Ratings(Note 2) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage (V CC ) +12V Enable Input Voltage (RE (Note 1), DE) −0.5V to (V CC + 0.5V) Driver Input Voltage (DI) −0.5V to (V CC + 0.5V) Driver Output Voltage (A, B) −14V to +14V Receiver Input Voltage (A, B) −14V to +14V Receiver Output Voltage (RO) −0.5V to (V CC + 0.5V) Maximum Package Power Dissipation@ +25˚C M Package 1.19W N Package 0.74W Derate M Package 9.5 mW/˚C above +25˚C Derate N Package 6.0 mW/˚C above +25˚C Maximum Package Power Dissipation @ +70˚C M Package 0.76W N Package 0.47W Storage Temperature Range −65˚C to +150˚C Lead Temperature Range (Soldering, 4 sec.) +260˚C ESD (HBM) ≥2k V Recommended Operating Conditions Min Typ Max Units Supply Voltage (VCC ) +4.75 +5.0 +5.25 V Operating Free Air Temperature (T DS1487 0 +25 +70 ˚C Bus Common Mode Voltage −7 +12 V
Electrical Characteristics
Over Supply Voltage and Operating Temperature Ranges, unless otherwise specified (Notes 3, 4) Symbol Parameter Conditions Pin Min Typ Max Units VOD1 Differential Driver Output Voltage (No Load) A, B 1.5 5 V VOD2 Differential Driver Output Voltage RL =5 0Ω , (RS422),Figure 1 2 2.8 V with Load R L =2 7Ω , (RS485),Figure 1 1.5 2.3 5 V ΔVOD Change in Magnitude of Output R L =2 7Ω or 50Ω (Note 5) 0.2 |V| Differential Voltage VOD3 Differential Driver Output Voltage — R1 = 54Ω , R2 = 375Ω 1.5 2.0 5 V Full Load with Max VCM VTEST = −7V to +12V,Figure 2 VOC Driver Common-Mode Output Voltage RL =2 7Ω or 50Ω ,Figure 1 03 V ΔVOC Change in Magnitude of Common-Mode Output Voltage R L =2 7Ω or 50Ω ,Figure 1(Note 5) 0.2 |V| VIH Input High Voltage DI, DE, 2.0 V VIL Input Low Voltage RE (Note 1) 0.8 V IIN1 Input Current V IN =0 Vo rVCC ±2µ A IIN2 Input Current (Note 6) V IN = +12V A, B 0 190 250 µA DE = 0V, VCC = 0V or 5.25V V IN = −7V 0 −100 −200 µA VTH Receiver Differential Threshold Voltage ΔVTH Receiver Input Hysteresis V CM =0 V 7 0 m V VOH Receiver Output High Voltage I O = −4 mA, VID = 0.2V RO 3.5 V VOL Receiver Output Low Voltage I O = 4 mA, VID = −0.2V 0.5 V IOZR TRI-STATE Output Current at Receiver 0.4V ≤ VO ≤ 2.4V ±1µ A R IN Receiver Input Resistance −7V ≤ VIN ≤ +12V A, B 48 68 k Ω ICC No-Load Supply Current (Note 7) DE = V CC , RE (Note 1) = 0V or VCC VCC 200 500 µA DE = 0V, RE (Note 1) = 0V or VCC 200 500 µA IOSD1 Driver Short Circuit Current, VO = HIGH −7V ≤ VO ≤ +12V A, B 250 mA IOSD2 Driver Short Circuit Current, VO = LOW −7V ≤ VO ≤ +12V −250 mA IOSR Receiver Short Circuit Current V O = GND RO 7 85 mA DS1487 www.national.com 2
Parameter Measurement Information(Continued) Pin Descriptions Pin I/O Name Function 1 O RO Receiver Output: If A > B by 200 mV, RO will be high; If A< B by 200 mV, RO will be low. RO will be high also if the inputs (A and B) are open (non-terminated). 2 I RE (Note 1) Receiver Output Enable: RO is enabled when RE (Note 1) is low; RO is in TRI-STATE when RE (Note 1) is high.
3 I DE Driver Output Enable: The driver outputs (A and B) are enabled when DE is high; they are in
TRI-STATE when DE is low. Pins A and B also function as the receiver input pins (see below). 4 I DI Driver Input: A low on DI forces A low and B high while a high on DI forces A high and B low when the driver is enabled.
5 NA GND Ground
6 I/O A Non-inverting Driver Output and Receiver Input pin. Driver output levels conform to RS-485 signaling levels. 7 I/O B Inverting Driver Output and Receiver Input pin. Driver output levels conform to RS-485 signaling levels. 8N A V CC Power Supply: 4.75V≤ VCC ≤ 5.25V Applications Information The DS1487 is a low power transceiver designed for use in RS-485 multipoint applications. The DS1487 can transmit data up to 2.0 Mbps based on a ratio of driver transition time to the unit interval (bit time) of 10%. This maximum data rate may be further limited by the interconnecting media. The DS1487 provides a 1⁄4 unit load to the RS-485 bus across the common mode range of −7V to +12V. This allows up to 128 transceivers ( 1⁄4 unit load) to be connected to the bus. The DS1487 also guarantees the driver’s output differential volt- age into a worst case load that models standard termination loads and 32 unit loads (=128 DS1487’s) referenced to the maximum common mode voltage extremes. With a minimum of 1.5V swing into this load, a 1.3V differential noise margin is supported along with the standard common mode rejec- tion range of the receivers. DS012920-13 *Note: Non Terminated, Open Input only FIGURE 12. DS012920-14 *Note: Non Terminated, Open Input only FIGURE 13. DS1487 www.national.com5
Applications Information(Continued) Due to the multipoint nature of the bus, contention between drivers may occur. This will not cause damage to the drivers since they feature short-circuit protection and also thermal shutdown protection. Thermal shutdown senses die tem- perature and puts the driver outputs into TRI-STATE if a fault condition occurs that causes excessive power dissipation which can elevate the junction temperature to +150˚C. A typical multipoint application is shown in the following fig- ure. Note that termination is typically required but is only lo- cated at the two ends of the cable (not on every node). Com- monly pull up and pull down resistors may be required at one end of the bus to provide a failsafe bias. These resistors pro- vide a bias to the line when all drivers are in TRI-STATE. See National Application Note 847 for a complete discussion of failsafe biasing of differention buses. DS012920-16 DS1487 www.national.com 6
Physical Dimensionsinches (millimeters) unless otherwise noted Order Number DS1487N DS1487 www.national.com7
NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. National Semiconductor Corporation Americas Tel: 1-800-272-9959 Fax: 1-800-737-7018 Email: support@nsc.com National Semiconductor Europe Fax: +49 (0) 180-530 85 86 Email: europe.support@nsc.com Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Français Tel: +33 (0) 1 41 91 87 90 National Semiconductor Asia Pacific Customer Response Group Tel: 65-2544466 Fax: 65-2504466 Email: ap.support@nsc.com National Semiconductor Japan Ltd. Tel: 81-3-5639-7560 Email: nsj.crc@jksmtp.nsc.com Fax: 81-3-5639-7507 www.national.com DS1487 Low Power RS-485 1⁄4 Unit Load Multipoint Transceiver National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
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