DS485 DS485 Low Power RS-485/RS-422 Multipoint Transceiver Literature Number: SNLS122B DS485 Low Power RS-485/RS-422 Multipoint Transceiver General Description Features The DS485 is a low-power transceiver for RS-485 and RS422 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 A 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 (R) (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 logichigh output if the input is open circuit. n n n n n n n n n n Meets TIA/EIA RS-485 multipoint standard Guaranteed full load output voltage (V OD3) Low quiescent current: 200 A 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 The DS485 is available in surface mount and DIP packages and is characterized for Industrial and Commercial temperature range operation. n n Connection and Logic Diagram Truth Table DIP and SOIC DRIVER SECTION RE* DE DI A B X H H H L X H L L H X L X Z Z RECEIVER SECTION 01288001 Order Number Temp. Range Package/### DS485N 0C to +70C DIP/N08E DS485M 0C to +70C SOP/M08A DS485TN -40C to +85C DIP/N08E DS485TM -40C to +85C 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 (R) is a registered trademark of National Semiconductor Corporation. (c) 2004 National Semiconductor Corporation DS012880 www.national.com DS485 Low Power RS-485/RS-422 Multipoint Transceiver July 1998 DS485 Absolute Maximum Ratings (Note 1) N Package Storage Temperature Range If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage (VCC) -0.5V to (VCC + 0.5V) Driver Input Voltage (DI) -0.5V to (VCC + 0.5V) Driver Output Voltage (A, B) (Soldering, 4 sec.) Receiver Output Voltage (RO) +260C 2 kV ESD (HBM) Recommended Operating Conditions -14V to +14V Receiver Input Voltage (A, B) -65C to +150C Lead Temperature Range +12V Enable Input Voltage (RE*, DE) 0.47W -14V to +14V Min -0.5V to (VCC + 0.5V) Supply Voltage (VCC) Maximum Package Power Dissipation @ +25C M Package 1.19W Operating Free Air N Package 0.74W Temperature (TA) Derate M Package 9.5 mW/C above +25C DS485 Derate N Package 6.0 mW/C above +25C DS485T M Package Max Units V 0 +25 +70 C -40 +25 +85 C +12 V Bus Common Mode Voltage Maximum Package Power Dissipation @ +70C Typ +4.75 +5.0 +5.25 -7 0.76W Electrical Characteristics Over Supply Voltage and Operating Temperature Ranges, unless otherwise specified (Notes 2, 3) Symbol Parameter Conditions Pin Min Typ VOD1 Differential Driver Output Voltage (No Load) VOD2 Differential Driver Output Voltage RL = 50, (RS422), Figure 1 2 2.8 with Load RL = 27, (RS485), Figure 1 1.5 2.3 VOD Change in Magnitude of Output RL = 27 or 50 (Note 4) A, B Max Units 5 V V 5 V 0.2 |V| 5 V Differential Voltage VOD3 Differential Driver Output Voltage -- R1 = 54, R2 = 375 Full Load with Max VCM VTEST = -7V to +12V, Figure 5 VOC Driver Common-Mode Output Voltage RL = 27 or 50, Figure 1 VOC Change in Magnitude of Common-Mode RL = 27 or 50, Figure 1 (Note 4) 1.5 2.0 3 V 0.2 |V| 0.8 V Output Voltage VIH Input High Voltage VIL Input Low Voltage IIN1 Input Current VIN = 0V or VCC DI, DE, RE* IIN2 Input Current (Note 5) VIN = +12V A, B DE = 0V, VCC = 0V or 5.25V VIN = -7V VTH Receiver Differential Threshold Voltage -7V VCM +12V 2.0 V -0.2 2 A 1.0 mA -0.8 mA 0.2 V VTH Receiver Input Hysteresis VCM = 0V VOH Receiver Output High Voltage IO = -4 mA, VID = 0.2V VOL Receiver Output Low Voltage IO = 4 mA, VID = -0.2V 0.4 IOZR TRI-STATE Output Current at Receiver 0.4V VO 2.4V 1 RIN Receiver Input Resistance -7V VIN +12V A, B ICC No-Load Supply Current (Note 6) DE = VCC, RE* = 0V or VCC VCC 70 RO Driver Short Circuit Current, VO = HIGH -7V VO +12V IOSD2 Driver Short Circuit Current, VO = LOW -7V VO +12V IOSR Receiver Short Circuit Current 0V VO VCC www.national.com 2 A, B RO V 12 DE = 0V, RE* = 0V or VCC IOSD1 mV 3.5 V A k 200 900 A 200 500 A 35 250 mA 35 250 mA 7 85 mA DS485 Switching Characteristics Over Supply Voltage and Operating Temperature Ranges, unless otherwise specified (Notes 3, 7, 8) Symbol Parameter 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 Conditions Min Typ Max Units 10 40 65 ns 10 39 65 ns 1 10 ns 3 25 40 ns 3 25 40 ns RL = 54, CL = 100 pF tZH Driver Enable to Output High CL = 100 pF 170 ns tZL Driver Enable to Output Low CL = 100 pF 170 ns tLZ Driver Disable from Output Low CL = 15 pF 170 ns tHZ Driver Disable from Output High CL = 15 pF tPLHD Receiver Differential Propagation Delay -- Low to High CL = 15 pF (RO) tPHLD Receiver Differential Propagation Delay -- High to Low tSKEW Differential Skew |tPHLD - tPLHD| 170 ns 70 190 320 ns 70 210 320 ns 20 50 ns 110 ns 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 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 = +25C. 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 = 50. 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 DS485 Parameter Measurement Information 01288003 01288002 FIGURE 5. VOD3 FIGURE 1. VOD 01288004 FIGURE 2. 01288005 FIGURE 6. 01288006 FIGURE 3. 01288007 FIGURE 7. 01288009 FIGURE 8. 01288008 FIGURE 4. www.national.com 4 DS485 Parameter Measurement Information (Continued) 01288010 FIGURE 9. 01288011 FIGURE 10. 01288012 FIGURE 11. 01288013 FIGURE 12. 5 www.national.com DS485 Parameter Measurement Information (Continued) 01288014 FIGURE 13. Pin Descriptions Pin # I/O Name Function Receiver Output: If A > B by 200 mV, RO will be high; If A < B by 200 mV, RO will be low. RO will 1 O RO 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 be high also if the inputs (A and B) are open (non-terminated). 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 0C to +70C 128 -40C to +85C 64 Ultra Low Power Transceiver Ultra Low Power Transceiver 0C to +70C 128 Auto-Sleep Mode -40C to +85C 64 Auto-Sleep Mode 0C to +70C 128 Adjustable Slew Rate Control -40C to +85C 64 Adjustable Slew Rate Control 6 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 01288016 7 www.national.com DS485 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 +150C. 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. Applications Information DS485 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 www.national.com 8 DS485 Low Power RS-485/RS-422 Multipoint Transceiver Notes 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. For the most current product information visit us at www.national.com. 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