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. n n n n n n n The transceiver draws 200 µA of supply current when unloaded 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 (VOD3). 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 packages. Connection and Logic Diagram n n n n Meets TIA/EIA RS-485 multipoint standard Allows up to 128 transceivers on the bus (1⁄4 U.L.) Guaranteed full load output voltage (VOD3) Low quiescent current: 200 µA typ −7V to +12V common-mode input voltage range TRI-STATE outputs on driver and receiver 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 Half-duplex flow through pinout Operates from a single 5V supply Current-limiting and thermal shutdown for driver overload protection Pin and functional compatible with MAX1487 Truth Table DRIVER SECTION DIP and SOIC RE (Note 1) DE DI A B X H H H L X H L L H X L X Z Z RECEIVER SECTION DS012920-1 *Note: Non Terminated, Open Input only Order Number Temp. Range Package/### DS1487N 0˚C to +70˚C DIP/N08E DS1487M 0˚C to +70˚C SOP/M08A RE (Note 1) DE A-B RO L L ≥+0.2V H L L ≤−0.2V L H X 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. © 1999 National Semiconductor Corporation DS012920 www.national.com DS1487 Low Power RS-485 1⁄4 Unit Load Multipoint Transceiver July 1998 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 + 0.5V) Driver Output Voltage (A, B) −14V to +14V Receiver Input Voltage (A, B) −14V to +14V Receiver Output Voltage (RO) −0.5V to (VCC + 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 0.76W 0.47W −65˚C to +150˚C +260˚C ≥2 kV Recommended Operating Conditions Supply Voltage (VCC) Operating Free Air Temperature (TA) DS1487 Bus Common Mode Voltage Min +4.75 Typ +5.0 0 −7 +25 Max Units +5.25 V +70 +12 ˚C V Electrical Characteristics Over Supply Voltage and Operating Temperature Ranges, unless otherwise specified (Notes 3, 4) Symbol Parameter VOD1 Differential Driver Output Voltage VOD2 Differential Driver Output Voltage with Load ∆VOD Change in Magnitude of Output Conditions (No Load) RL = 50Ω, (RS422), Figure 1 RL = 27Ω, (RS485), Figure 1 RL = 27Ω or 50Ω (Note 5) Pin Min A, B 1.5 Typ Max Units 5 2 2.8 1.5 2.3 V V 5 V 0.2 |V| 5 V 3 V 0.2 |V| Differential Voltage VOD3 Differential Driver Output Voltage — Full Load with Max VCM R1 = 54Ω, R2 = 375Ω VTEST = −7V to +12V, Figure 2 RL = 27Ω or 50Ω, Figure 1 1.5 VOC Driver Common-Mode Output Voltage ∆VOC Change in Magnitude of Common-Mode Output Voltage VIH Input High Voltage DI, DE, VIL Input Low Voltage RE (Note 1) IIN1 Input Current IIN2 Input Current (Note 6) DE = 0V, VCC = 0V or 5.25V 0 RL = 27Ω or 50Ω, Figure 1 (Note 5) VIN = 0V or VCC VIN = +12V VIN = −7V A, B VTH Receiver Differential Threshold Voltage −7V ≤ VCM ≤ +12V ∆VTH Receiver Input Hysteresis VOH Receiver Output High Voltage VOL Receiver Output Low Voltage VCM = 0V IO = −4 mA, VID = 0.2V IO = 4 mA, VID = −0.2V IOZR TRI-STATE Output Current at Receiver 0.4V ≤ VO ≤ 2.4V RIN Receiver Input Resistance No-Load Supply Current (Note 7) −7V ≤ VIN ≤ +12V DE = VCC, RE (Note 1) = 0V or VCC DE = 0V, RE (Note 1) = 0V or VCC A, B ICC Driver Short Circuit Current, VO = HIGH Driver Short Circuit Current, VO = LOW −7V ≤ VO ≤ +12V A, B Receiver Short Circuit Current VO = GND IOSD1 IOSD2 IOSR www.national.com 2.0 2.0 V ±2 µA 250 µA 0 −100 −200 µA 0 190 −0.2 0.2 70 RO 48 VCC RO 7 V mV 3.5 −7V ≤ VO ≤ +12V 2 V 0.8 V 0.5 V ±1 µA 68 kΩ 200 500 200 500 µA µA 250 mA −250 mA 85 mA Switching Characteristics Over Supply Voltage and Operating Temperature Ranges, unless otherwise specified (Notes 4, 8, 9) Symbol Parameter Min Typ Max Units 10 40 80 ns Driver Differential Propagation Delay — High to Low 10 39 80 ns 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 Output High 50 200 ns tZL Driver Enable to Output Low 65 200 ns tLZ Driver Disable from Output Low CL = 100 pF CL = 100 pF CL = 15 pF 80 200 ns tHZ Driver Disable from Output High 80 200 ns tPLHD Receiver Differential Propagation Delay — Low to High CL = 15 pF CL = 15 pF (RO) 30 190 400 ns tPHLD Receiver Differential Propagation Delay — High to Low 30 210 400 ns tSKEW Differential Skew |tPHLD − tPLHD| 0 20 50 ns tZH Receiver Enable to Output High 45 150 ns tZL Receiver Enable to Output Low 40 150 ns tLZ Receiver Disable from Output Low 50 150 ns tHZ Receiver Disable from Output High 55 150 ns fmax Maximum Data Rate tPLHD Driver Differential Propagation Delay — Low to High tPHLD Conditions RL = 54Ω, CL = 100 pF CL = 15 pF (Note 10) 2.0 Mbps Note 2: “Absolute Maximum Ratings” are those values beyond which the safety of the device cannot be guaranteed. They are not meant to imply that the devices should be operated at these limits. The table of “Electrical Characteristics” specifies conditions of device operation. Note 3: Current into device pins is defined as positive. Current out of device pins is defined as negative. All voltages are referenced to ground except VOD1/2/3and VID. Note 4: All typicals are given for: VCC = +5.0V, TA = +25˚C. Note 5: ∆|VOD| and ∆|VOC| are changes in magnitude of VOD and VOC respectively, that occur when the input changes state. Note 6: IIN2 includes the receiver input current and driver TRI-STATE leakage current. Note 7: Supply current specification is valid for loaded transmitters when DE = 0V or enabled (DE = H) with no load. Note 8: f = 1 MHz, tr and tf ≤ 6 ns, ZO = 50Ω. Note 9: CL includes jig and probe capacitance. Note 10: fmax is the guaranteed data rate for 50 ft of twisted pair cable. fmax may be conservatively determined from the ratio of driver transition time (tr) to the data rate unit interval (1/fmax). Using a 10% ratio yields fmax = (0.1)/50 ns = 2.0 Mb/s. Higher data rates may be supported by allowing larger ratios. Parameter Measurement Information DS012920-2 FIGURE 1. VOD DS012920-4 FIGURE 3. DS012920-3 FIGURE 2. VOD3 3 www.national.com 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.com 4 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). 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 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. 8 NA VCC 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). Receiver Output Enable: RO is enabled when RE (Note 1) is low; RO is in TRI-STATE when RE (Note 1) is high. Ground Power Supply: 4.75V ≤ VCC ≤ 5.25V Applications Information DS1487 also guarantees the driver’s output differential voltage 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 rejection range of the receivers. 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 5 www.national.com 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. (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 temperature 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. DS012920-16 www.national.com 6 Physical Dimensions inches (millimeters) unless otherwise noted Order Number DS1487N NS Package Number N08E 7 www.national.com DS1487 Low Power RS-485 1⁄4 Unit Load Multipoint Transceiver 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 OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 2. A critical component is any component of a life support 1. Life support devices or systems are devices or sysdevice or system whose failure to perform can be reatems which, (a) are intended for surgical implant into sonably expected to cause the failure of the life support the body, or (b) support or sustain life, and whose faildevice or system, or to affect its safety or effectiveness. ure 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. 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