LMS485ECNA

LMS485E Low Power RS-485 / RS-422 Differential Bus Transceiver November 2003 LMS485E Low Power RS-485 / RS-422 Differential Bus Transceiver General Description The LMS485E is a low power differential bus/line transceiver designed for high speed bidirectional data communication on multipoint bus transmission lines. It is designed for balanced transmission lines. It meets ANSI Standards TIA/EIA RS422-B, TIA/EIA RS485-A and ITU recommendation and V.11 and X.27. The driver outputs and receiver inputs have ± 15kV ESD protection. The LMS485E combines a TRISTATE™ differential line driver and differential input receiver, both of which operate from a single 5.0V power supply. The driver and receiver have an active high and active low, respectively, that can be externally connected to function as a direction control. The driver outputs and receiver inputs are internally connected to form a differential input/output (I/O) bus port that is designed to offer minimum loading to bus whenever the driver is disabled or when VCC = 0V. These ports feature wide positive and negative common mode voltage ranges, making the device suitable for multipoint applications in noisy environments. The LMS485E is available in 8-Pin SOIC and 8-pin DIP packages. It is a drop-in replacement to Maxim’s MAX485E. Features n n n n n n n n n n n n Meet ANSI standard RS-485 and RS-422 Data rate 2.5 Mbps Single supply voltage operation, 5V Wide input and output voltage range Thermal shutdown protection Short circuit protection Low quiescent current 800µA (max) Allows up to 32 transceivers on the bus Open circuit fail-safe for receiver Extended operating temperature range −40˚C to 85˚C Drop-in replacement to MAX485E Available in 8-pin SOIC and 8-pin DIP packages Applications n n n n n n n n Low power RS-485 systems Network hubs, bridges, and routers Point of sales equipment (ATM, barcode scanners,…) Local area networks (LAN) Integrated service digital network (ISDN) Industrial programmable logic controllers High speed parallel and serial applications Multipoint applications with noisy environment Typical Application 20086601 A typical multipoint application is shown in the above figure. Terminating resistor, RT are typically required but only located at the two ends of the cable. Pull-up and pull-down resistors maybe required at the end of the bus to provide fail-safe biasing. The biasing resistors provide a bias to the cable when all drivers are in TRI-STATE, See National Application Note, AN-847 for further information. © 2003 National Semiconductor Corporation DS200866 www.national.com LMS485E Connection Diagram 8-Pin SOIC / DIP 20086602 Top View Truth Table DRIVER SECTION RE* X X X RECEIVER SECTION RE* L L H L Note: * = Non Terminated, Open Input only X = Irrelevant Z = TRI-STATE H = High level L = Low level DE H H L DE L L X L DI H L X A-B ≥ +0.2V ≤ −0.2V X OPEN * A H L Z B L H Z RO H L Z H www.national.com 2 LMS485E Pin Descriptions Pin # I/O 1 2 3 O I I Name RO RE* DE 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 be high also if the inputs (A and B) are open (non-terminated). Receiver Output Enable: RO is enabled when RE* is low; RO is in TRI-STATEwhen RE* is high Driver Output Enable: The driver outputs (A and B) are enabled when DE is high; they are in TRI-STATETRI-STATE ® when DE is low. Pins A and B also function as the receiver input pins (see below) 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 Ground Non-inverting Driver Output and Receiver Input pin. Driver output levels conform to RS-485 signaling levels Inverting Driver Output and Receiver Input pin. Driver Output levels conform to RS-485 signaling levels Power Supply: 4.75V ≤ VCC ≤ 5.25V 4 5 6 7 8 I NA I/O I/O NA DI GND A B VCC Ordering Information Package Part Number LMS485ECM 8-Pin SOIC LMS485ECMX LMS485EIM LMS485EIMX 8-Pin DIP LMS485ECNA LMS485EINA Package Marking LMS485ECM LMS485EIM LMS485ECNA LMS485EINA Transport Media 95 Units/Rail 2.5k Units Tape and Reel 95 Units/Rail 2.5k Units Tape and Reel 40 Units/Rail 40 Units/Rail N08E M08A NSC Drawing 3 www.national.com LMS485E Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage, VCC (Note 2) Input Voltage, VIN (DI, DE, or RE) Voltage Range at Bus Terminals (AB) Receiver Output Package Thermal Impedance, θJA SOIC DIP Junction Temperature (Note 3) Operating Free-Air Temperature Range, TA Commercial Industrial Storage Temperature Range Soldering Information Infrared or Convection (20 sec.) Lead Temperature Range 235˚C +260˚C 0˚C to 70˚C −40˚C to 85˚C −65˚C to 150˚C 125˚ C/W 92˚ C/W 150˚C Supply Voltage, VCC Voltage at any Bus Terminal (Separately or Common Mode) High-Level Input Voltage, VIH (Note 5) Low-Level Input Voltage, VIL (Note 5) Differential Input Voltage, VID (Note 6) 6V −0.3V to VCC + 0.3V −7V to 12V −0.3V to VCC + 0.3V ESD Rating (Human Body Model)(Note 4) Bus Pins Other Pins ESD Rating (Machine Model) All Pins 200V 15kV 2kV Operating Ratings Min Nom Max 4.75 −7 2 0.8 5.0 5.25 12 V V V V V ± 12 Electrical Characteristics Over recommended ranges of supply voltage and operating free-air temperature (unless otherwise noted) Symbol Driver Section |VOD1| |VOD2| ∆VOD Differential Output Voltage Differential Output Voltage Change in Magnitude of Driver Differential Output Voltage for Complementary Output States Common Mode Output Voltage R = ∞ (Figure 1) R = 50Ω (Figure 1) , RS-422 R = 27Ω (Figure 1) , RS-485 R = 27Ω or 50Ω (Figure 1) , (Note 7) 2.0 1.5 5.0 0.2 V 5.25 V V Parameter Conditions Min Typ Max Units VOC ∆VOC R = 27Ω or 50Ω (Figure 1) 3.0 0.2 V V Change in Magnitude of R = 27Ω or 50Ω (Figure 1), (Note 7) Driver Common-Mode Output Voltage for Complementary Output States CMOS Input Logic Threshold High CMOS Input Logic Threshold Low Logic Input Current Input Current (A, B) DE, DI, RE DE, DI, RE DE, DI, RE DE = 0V, VCC = 0V or 5.25V VIN = 12V VIN = − 7V −7V ≤ VCM ≤ + 12V VCM = 0 IOH = 4 mA, VID = −200 mV 3.5 −0.2 95 2.0 VIH VIL IIN1 IIN2 V 0.8 V µA mA ±2 0.25 −0.2 +0.2 Receiver Section VTH ∆VTH VOH Differential Input Threshold Voltage Input Hysteresis (VTH+− VTH−) CMOS High-level Output Voltage V mV V www.national.com 4 LMS485E Electrical Characteristics Symbol VOL IOZR RIN ICC IOSD1 IOSD2 IOSR Parameter CMOS Low-level Output Voltage Tristate Output Leakage Current Input Resistance Supply Current Driver Short-circuit Output Current Driver Short-circuit Output Current Receiver Short-circuit Output Current (Continued) Over recommended ranges of supply voltage and operating free-air temperature (unless otherwise noted) Conditions IOL = −4 mA, VID = 200 mV 0.4V ≤ VO ≤ + 2.4V − 7V ≤VCM ≤ +12V DE = VCC, RE = GND or VCC DE = 0V, RE = GND or VCC VO = high, −7V ≤ VCM ≤ +12V VO = low, − 7V ≤VCM ≤ +12V 0 V ≤ VO ≤ VCC 12 400 360 800 560 250 250 95 mA mA mA Min Typ Max 0.4 Units V µA kΩ µA ±1 Power Supply Current Switching Characteristics Driver TPLH, TPHL TSKEW TR, TF TZH, TZL THZ, TLZ Receiver TPLH, TPHL TSKEW TZH, TZL THZ, TLZ FMAX Propagation Delay Input to Output Receiver Output Skew Receiver Enable Time Receiver Disable Time Maximum Data Rate RL = 54Ω, CL = 100 pF RL = 54Ω, CL = 100 pF CL = 15 pF CL = 15 pF 2.5 20 90 5 20 20 50 50 200 ns ns ns ns Mbps Propagation Delay Input to Output Driver Output Skew Driver Rise and Fall Time Driver Enable to Ouput Valid Time Driver Output Disable Time RL = 54Ω, CL = 100 pF RL = 54Ω, CL = 100 pF RL = 54Ω, CL = 100 pF CL = 100 pF CL = 15 pF 3 10 40 5 10 25 35 80 10 40 70 70 ns ns ns ns ns Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but specific performance is not guaranteed. For guaranteed specifications and the test conditions, see the Electrical Characteristics. Note 2: All voltage values, except differential I/O bus voltage, are with respect to the network ground terminal. Note 3: The maximum power dissipation is a function of TJ(MAX), θJA, and TA. The maximum allowable power dissipation at any ambient temperature, TA, is PD = (TJ(MAX) - TA)/θJA. All numbers apply for packages soldered directly into a PC board. Note 4: ESD rating based upon human body model, 100 pF discharged through 1.5 kΩ. Note 5: Voltage limits apply to DI, DE, RE pins. Note 6: Differential input/output bus voltage is measured at the non-inverting terminal A with respect to the inverting terminal B. Note 7: |∆VOD| and |∆VOC| are changes in magnitude of VOD and VOC, respectively when the input changes from high to low levels. Note 8: Peak current 5 www.national.com LMS485E Typical Performance Characteristics Output Current vs. Receiver Output Low Voltage Output Current vs. Receiver Output High Voltage 20086613 20086614 Receiver Output High Voltage vs. Temperature Receiver Output Low-Voltage vs. Temperature 20086615 20086616 Driver Output Current vs. Differential Output Voltage Driver Differential Output Voltage vs. Temperature 20086617 20086618 www.national.com 6 LMS485E Typical Performance Characteristics Output Current vs. Driver Output Low Voltage (Continued) Output Current vs. Driver Output High Voltage 20086619 20086620 Supply Current vs. Temperature 20086621 7 www.national.com LMS485E Parameter Measuring Information 20086603 FIGURE 1. Test Circuit for VOD and VOC 20086604 FIGURE 2. Test Circuit for VOD3 20086605 FIGURE 3. Test Circuit for Driver Propagation Delay 20086606 FIGURE 4. Test Circuit for Driver Enable / Disable www.national.com 8 LMS485E Parameter Measuring Information (Continued) 20086607 FIGURE 5. Test Circuit for Receiver Propagation Delay 20086608 FIGURE 6. Test Circuit for Receiver Enable / Disable 9 www.national.com LMS485E Switching Characteristics 20086611 20086609 FIGURE 9. Receiver Propagation Delay FIGURE 7. Driver Propagation Delay, Rise / Fall Time 20086612 20086610 FIGURE 10. Receiver Enable / Disable Time FIGURE 8. Driver Enable / Disable Time www.national.com 10 LMS485E Application Information POWER LINE NOISE FILTERING A factor to consider in designing power and ground is noise filtering. A noise filtering circuit is designed to prevent noise generated by the integrated circuit (IC) as well as noise entering the IC from other devices. A common filtering method is to place by-pass capacitors (Cbp) between the power and ground lines. Placing a by-pass capacitor (Cbp) with the correct value at the proper location solves many power supply noise problems. Choosing the correct capacitor value is based upon the desired noise filtering range. Since capacitors are not ideal, they may act more like inductors or resistors over a specific frequency range. Thus, many times two by-pass capacitors may be used to filter a wider bandwidth of noise. It is highly recommended to place a larger capacitor, such as 10µF, between the power supply pin and ground to filter out low frequencies and a 0.1µF to filter out high frequencies. By-pass capacitors must be mounted as close as possible to the IC to be effective. Longs leads produce higher impedance at higher frequencies due to stray inductance. Thus, this will reduce the by-pass capacitor’s effectiveness. Surface mounted chip capacitors are the best solution because they have lower inductance. 20086622 FIGURE 11. Placement of by-pass Capacitors, Cbp 11 www.national.com LMS485E Physical Dimensions inches (millimeters) unless otherwise noted 8-Pin SOIC NS Package Number M08A 8-Pin DIP NS Package Number N08E www.national.com 12 LMS485E Low Power RS-485 / RS-422 Differential Bus 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. 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. 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