DS485 Low Power RS-485/RS-422 Multipoint Transceiver General Description Features The DS485 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 2.5 Mbps (see Applications Information section). The transceiver draws 200 µA of supply current when unloaded or fully loaded with the driver disabled and operates from a single +5V supply. n n n n n n 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 DS485 is available in surface mount and DIP packages and is characterized for Industrial and Commercial temperature range operation. n n n n Connection and Logic Diagram Truth Table n n Meets TIA/EIA RS-485 multipoint standard Guaranteed full load output voltage (V OD3) 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 Allows up to 32 transceivers on the bus Current-limiting and thermal shutdown for driver overload protection Industrial temperature range operation Pin and functional compatible with MAX485 and LTC485 DRIVER SECTION DIP and SOIC RE* DE DI A X H H H L X H L L H X L X Z Z B RECEIVER SECTION DS012880-1 Order Number DS485N Temp. Range 0˚C to +70˚C Package/### DIP/N08E DS485M 0˚C to +70˚C SOP/M08A DS485TN −40˚C to +85˚C DIP/N08E DS485TM −40˚C to +85˚C SOP/M08A RE* DE A-B RO L L ≥+0.2V H L L ≤−0.2V L H X X Z L L OPEN* H *Note: Non Terminated, Open Input only X = indeterminate Z = TRI-STATE TRI-STATE ® is a registered trademark of National Semiconductor Corporation. © 1999 National Semiconductor Corporation DS012880 www.national.com DS485 Low Power RS-485/RS-422 Multipoint Transceiver July 1998 Absolute Maximum Ratings (Note 1) 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 −0.5V to (VCC + 0.5V) Enable Input Voltage (RE*, DE) 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 M Package 0.76W 0.47W −65˚C to +150˚C +260˚C ≥2 kV Recommended Operating Conditions Supply Voltage (VCC) Operating Free Air Temperature (TA) DS485 DS485T Bus Common Mode Voltage Min +4.75 Typ +5.0 Max +5.25 Units V 0 −40 −7 +25 +25 +70 +85 +12 ˚C ˚C V Max Units Electrical Characteristics Over Supply Voltage and Operating Temperature Ranges, unless otherwise specified (Notes 2, 3) 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 4) Pin Min Typ A, B 5 2 2.8 1.5 2.3 V V 5 V 0.2 |V| 5 V Differential Voltage VOD3 Differential Driver Output Voltage — Full Load with Max VCM VOC Driver Common-Mode Output Voltage ∆VOC Change in Magnitude of Common-Mode R1 = 54Ω, R2 = 375Ω VTEST = −7V to +12V, Figure 5 RL = 27Ω or 50Ω, Figure 1 RL = 27Ω or 50Ω, Figure 1 (Note 4) 1.5 2.0 3 V 0.2 |V| Output Voltage VIH Input High Voltage VIL Input Low Voltage IIN1 Input Current IIN2 Input Current (Note 5) DE = 0V, VCC = 0V or 5.25V VIN = 0V or VCC VIN = +12V VIN = −7V DI, DE, RE* −7V ≤ VCM ≤ +12V VCM = 0V Receiver Differential Threshold Voltage ∆VTH Receiver Input Hysteresis VOH Receiver Output High Voltage VOL Receiver Output Low Voltage 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 6) −7V ≤ VIN ≤ +12V DE = VCC, RE* = 0V or VCC DE = 0V, RE* = 0V or VCC A, B ICC −7V ≤ VO ≤ +12V A, B IOSD2 Driver Short Circuit Current, VO = HIGH Driver Short Circuit Current, VO = LOW IOSR Receiver Short Circuit Current 0V ≤ VO ≤ VCC www.national.com −0.2 0.8 V ±2 µA 1.0 mA −0.8 mA 0.2 70 RO RO V mV 3.5 V 0.4 V ±1 µA 12 VCC −7V ≤ VO ≤ +12V 2 V A, B VTH IOSD1 2.0 kΩ 200 900 200 500 µA µA 35 250 mA 35 250 mA 7 85 mA Switching Characteristics Over Supply Voltage and Operating Temperature Ranges, unless otherwise specified (Notes 3, 7, 8) Symbol Parameter Conditions RL = 54Ω, CL = 100 pF Min Typ Max Units 10 40 65 ns 10 39 65 ns 1 10 ns 3 25 40 ns 3 25 40 ns CL = 100 pF CL = 100 pF CL = 15 pF 170 ns 170 ns 170 ns CL = 15 pF CL = 15 pF (RO) 170 ns tPLHD Driver Differential Propagation Delay — Low to High tPHLD Driver Differential Propagation Delay — High to Low tSKEW Differential Skew |tPHLD − tPLHD| tr Driver Rise Time tf Driver Fall Time tZH Driver Enable to Output High tZL Driver Enable to Output Low tLZ Driver Disable from Output Low tHZ Driver Disable from Output High tPLHD Receiver Differential Propagation Delay — Low to High tPHLD Receiver Differential Propagation Delay — High to Low tSKEW Differential Skew |tPHLD − tPLHD| tZH Receiver Enable to Output High tZL Receiver Enable to Output Low 110 ns tLZ Receiver Disable from Output Low 110 ns tHZ Receiver Disable from Output High fmax Maximum Data Rate 70 190 320 ns 70 210 320 ns 20 50 ns 110 ns CL = 15 pF 110 (Note 9) 2.5 ns Mbps Note 1: “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 2: Current into device pins is defined as positive. Current out of device pins is defined as negative. All voltages are referenced to ground except VOD1/2/3 and VID. Note 3: All typicals are given for: VCC = +5.0V, TA = +25˚C. Note 4: ∆|VOD| and ∆|VOC| are changes in magnitude of V OD and VOCrespectively, that occur when the input changes state. Note 5: IIN2 includes the receiver input current and driver TRI-STATE leakage current. Note 6: Supply current specification is valid for loaded transmitters when DE = 0V or enabled (DE = H) with no load. Note 7: f = 1 MHz, tr and tf ≤ 6 ns, ZO = 50Ω. Note 8: CL includes jig and probe capacitance. Note 9: fmax is the guaranteed data rate for 50 ft of twisted pair cable. f max 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)/40 ns = 2.5 Mb/s. Higher data rates may be supported by allowing larger ratios. 3 www.national.com Parameter Measurement Information DS012880-3 DS012880-2 FIGURE 5. VOD3 FIGURE 1. VOD DS012880-4 FIGURE 2. DS012880-5 FIGURE 6. DS012880-6 FIGURE 3. DS012880-7 FIGURE 7. DS012880-9 FIGURE 8. DS012880-8 FIGURE 4. www.national.com 4 Parameter Measurement Information (Continued) DS012880-10 FIGURE 9. DS012880-11 FIGURE 10. DS012880-12 FIGURE 11. DS012880-13 FIGURE 12. DS012880-14 FIGURE 13. 5 www.national.com 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* Receiver Output Enable: RO is enabled when RE* is low; RO is in TRI-STATE when RE* 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 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 Ground Power Supply: 4.75V ≤ VCC ≤ 5.25V Related National Low Power RS-485 Transceivers Part Number DS36C278 DS36C278T DS36C279 DS36C279T DS36C280 DS36C280T www.national.com Temperature Number of Range XCVRs on Bus Comments 0˚C to +70˚C 128 Ultra Low Power Transceiver −40˚C to +85˚C 64 Ultra Low Power Transceiver 0˚C to +70˚C 128 Auto-Sleep Mode −40˚C to +85˚C 64 Auto-Sleep Mode 0˚C to +70˚C 128 Adjustable Slew Rate Control −40˚C to +85˚C 64 Adjustable Slew Rate Control 6 Applications Information 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. 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. The DS485 is a low power transceiver designed for use in RS-485 multipoint applications. The DS485 can transmit data up to 2.5 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 DS485 provides a standard unit load to the RS-485 bus across the common mode range of −7V to +12V. This allows up to 32 transceivers (standard unit load) to be connected to the bus. More transceivers may be connected to the bus if they support a reduced unit load (see DS36C278). The DS485 also guarantees the driver’s output differential voltage into a worst case load that models standard termination loads and 32 unit loads 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. Multipoint RS-485 Application DS012880-16 7 www.national.com 8 Physical Dimensions inches (millimeters) unless otherwise noted Order Number DS485M or DS485TM NS Package Number M08A Order Number DS485N or DS485TN NS Package Number N08E 9 www.national.com DS485 Low Power RS-485/RS-422 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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