DS1487 DS1487 Low Power RS-485 ¼ Unit Load Multipoint Transceiver Literature Number: SNLS132
DS1487 Low Power RS-485 1⁄4 Unit Load Multipoint Transceiver General Description Features 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 transceiver presents 1⁄4 unit loading to the RS-485 bus allowing up to 128 nodes to be connected together without the use of repeaters.
DS1487 Absolute Maximum Ratings (Note 2) M Package N Package Storage Temperature Range Lead Temperature Range (Soldering, 4 sec.) ESD (HBM) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage (VCC) +12V Enable Input Voltage (RE (Note 1), DE) −0.5V to (VCC + 0.5V) Driver Input Voltage (DI) −0.5V to (VCC + 0.
DS1487 Switching Characteristics Over Supply Voltage and Operating Temperature Ranges, unless otherwise specified (Notes 4, 8, 9) Symbol Parameter Conditions Min Typ Max Units RL = 54Ω, CL = 100 pF 10 40 80 ns 10 39 80 ns tPLHD Driver Differential Propagation Delay — Low to High tPHLD Driver Differential Propagation Delay — High to Low tSKEW Differential Skew |tPHLD − tPLHD| 0 1 10 ns tr Driver Rise Time 3 25 50 ns tf Driver Fall Time 3 25 50 ns tZH Driver Enable to O
DS1487 Parameter Measurement Information (Continued) DS012920-8 FIGURE 7. DS012920-5 DS012920-9 FIGURE 4. FIGURE 8. DS012920-10 *Note: Non Terminated, Open Input only FIGURE 9. DS012920-6 FIGURE 5. DS012920-7 DS012920-11 FIGURE 6. FIGURE 10. DS012920-12 *Note: Non Terminated, Open Input only FIGURE 11. www.national.
DS1487 Parameter Measurement Information (Continued) DS012920-13 *Note: Non Terminated, Open Input only FIGURE 12. DS012920-14 *Note: Non Terminated, Open Input only FIGURE 13. Pin Descriptions Pin # I/O Name Function 1 O RO 2 I RE (Note 1) 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).
DS1487 Applications Information A typical multipoint application is shown in the following figure. Note that termination is typically required but is only located at the two ends of the cable (not on every node). Commonly pull up and pull down resistors may be required at one end of the bus to provide a failsafe bias. These resistors provide 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.
DS1487 Physical Dimensions inches (millimeters) unless otherwise noted Order Number DS1487N NS Package Number N08E 7 www.national.
DS1487 Low Power RS-485 1⁄4 Unit Load Multipoint Transceiver Notes LIFE SUPPORT POLICY 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.
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