PRELIMINARY TECHNICAL DATA Ultra-Low Power RS-485/RS-422 Transceiver with Low EMI and +/-10kV ESD Protection a ADM1487 Preliminary Technical Data FEATURES Low Power - 120µA Max ICC with Driver Disabled GENERAL DESCRIPTION The ADM1487 is an ultra-low power RS-485/RS-422 transceiver consisting of one driver and one receiver per package. Quiescent operating current is typically 80µA and 1µA in shutdown mode. The driver and receiver both have three-state outputs. This allows multiple drivers to be connected to an RS-485/RS-422 bus, or several receiver outputs to be connected to a serial data bus. The driver will maintain a high-impedance output state even with power off, while the receiver features fail-safe operation that guarantees a logic high output if the inputs are left open-circuit. High Input Impedance — Up to 256 Transceivers on Bus Low-Current (1µA) Shutdown Mode Slew Rate Control for Error-Free Data Transmission and Low EMI ±10kV ESD Protection (Human Body Model) on RS-485 I/O pins Thermal Protection of Driver Glitch-Free Driver Power-Up Allows Hot Connection Driver Maintains High Output Impedance with Power Off The device has slew-rate limited drivers to minimize electromagnetic interference (EMI) and reduce reflections caused by incorrectly terminated cables. Wide Common-Mode Range Allows ±7V Ground Differences Between Devices Pin-Compatible with Industry Standard 75176 APPLICATIONS Battery-Powered RS-485/RS-422 Systems Level Translation FUNCTIONAL BLOCK DIAGRAM RO 1 8 VCC R RE 2 7 B DE 3 6 A DI 4 5 GND D ADM1487 REV. PrC 08/02 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 www.analog.com Fax: 781/326-8703 Analog Devices, Inc., 2002 –1– PRELIMINARY TECHNICAL DATA ADM1487 ADM1487 SPECIFICATIONS DC ELECTRICAL CHARACTERISTICS (VCC = +5V ±5%, TA = 0°C TO +70°C, UNLESS OTHERWISE NOTED) Parameter Min Typ Differential Driver Output Voltage,VOD1 Differential Driver Output Voltage, VOD2 2.0 1.5 Change in Magnitude of Driver Differential Output Voltage for Complementary Output States, VOD Driver Common-Mode Output Voltage, VOC Change in Magnitude of Driver Common-Mode Output Voltage for Complementary Output States, |VOC| Input High Voltage (DE, DI, RE), VIH Max Units 5 V Unloaded, IO = 0 5 V V Figure 1, R = 50 (RS-422) Figure 1, R = 27 (RS-485) 0.2 V Figure 1, R = 27 or R = 50 3 V Figure 1, R = 27 or R = 50 0.2 V R = 27 or R = 50 2 V Input Low Voltage (DE, DI, RE), VIL 0.8 V Input Current (DE, DI, RE), IIN1 ±2 µA 0.30 -0.15 mA mA 0.2 V Input Current (A, B), IIN2 Differential Input Threshold Voltage for Receiver, VTH -0.2 Receiver Input Hysteresis, VTH Receiver Output High Voltage, VOH Test Conditions/Comments 45 mV 3.5 DE = 0, VCC= 0V or 5.25V, VIN = 12V DE = 0, VCC = 0V or 5.25V, VIN = –7V –7V VCM 12V VCM = 0V V IO =-4mA, VID = 200mV Receiver Output Low Voltage, VOL 0.4 V IO = 4mA, VID = –200mV Three-State (High Impedance) Output Current at Receive, IOZR ±1 µA VCC = Max, 0.4V Vo 2.4V k –7V VCM 12V Receiver Input Resistance, RIN 70 Supply Current, ICC Supply Current in Shutdown Mode, ISHDN Driver Short-Circuit Ourrent, IOSD1 35 Driver Short-Circuit Ourrent, IOSD2 35 Receiver Short-Circuit Current, IOSR 7 96 120 80 200 120 µA µA No Load, Output Enabled No Load, Output Disabled 1 10 µA DE = 0V, RE = VCC 250 mA VOUT = HIGH, –7V VO 12V mA VOUT = LOW, –7V Vo 12V mA 0V VO VOC 250 85 –2– Rev. PrC PRELIMINARY TECHNICAL DATA ADM1487 ADM1487 SPECIFICATIONS (continued) ELECTRICAL CHARACTERISTICS (VCC = +5V ±5%, TA = -40°C TO +85°C, UNLESS OTHERWISE NOTED) Parameter Min Typ Differential Driver Output Voltage, VOD1 Differential Driver Output Voltage, VOD2 2.0 1.5 Driver Common-Mode Output Voltage, VOC Differential Input Threshold Voltage for Receiver, VTH –0.2 Receiver Input Hysteresis, VTH 45 Supply Current, ICC 120 80 1 Supply Current in Shutdown Mode, ISHDN Max Units Test Conditions/Comments 5 V Unloaded, IO = 0 5 V V Figure 1, R = 50 (RS-422) Figure 1, R = 27 (RS-485) 3 V Figure 1, R = 27 or R = 50 0.2 V –7V VCM 12V mV VCM = 0V 200 120 µA µA No Load, Output Enabled No Load, Output Disabled 10 µA DE = 0V, RE = VCC Driver Input to Output High, tDPLH 150 1200 ns Figures 2, 3, RDIFF= 54, CL1 = CL2 = 100pF Driver Input to Output Low, tDPHL 150 1200 ns Figures 2, 3, RDIFF= 54, CL1 = CL2 = 100pF 600 ns Figures 2, 3, RDIFF= 54, CL1 = CL2 = 100pF 2000 ns Figures 2, 3, RDIFF= 54, CL1 = CL2 = 100pF 100 Driver Output to Output, tSKEW Driver Rise or Fall Time, tDR, tDF 150 Receiver Input to Output High, tRPLH 30 140 250 ns Figures 2, 4, RDIFF= 54, CL1 = CL2 = 100pF Receiver Input to Output Low, tRHL 30 140 250 ns Figures 2, 4, RDIFF= 54, CL1 = CL2 = 100pF ns Figures 2, 4, RDIFF= 54, CL1 = CL2 = 100pF Differential Receiver Skew, tSKD |tRPLH-tRPHL| Maximum Data Rate, fMAX 13 250 kbps SWITCHING CHARACTERISTICS (VCC = +5V ±5%, TA = -40°C TO +85°C, UNLESS OTHERWISE NOTED) Parameter Min Typ Driver Input to Output High, tDPLH 150 1200 ns Figures 2, 3, RDIFF= 54, CL1 = CL2 = 100pF Driver Input to Output, tDPHL 150 1200 ns Figures 2, 3, RDIFF= 54, CL1 = CL2 = 100pF 600 ns Figures 2, 3, RDIFF= 54, CL1 = CL2 = 100pF 250 Driver Output to Output, tSKEW Max Units Test Conditions/Comments Driver Rise or Fall Time, tDR, tDF 150 1200 ns Figures 2, 3, RDIFF= 54, CL1 = CL2 = 100pF Driver Enable to Output High, tDZH 100 1500 ns Figures 5, 6, CL = 100pF, S2 Closed Driver Enable to Output Low, tDZL 100 1500 ns Figures 5, 6, CL = 100pF, S1 Closed Driver Disable Time from Low, tDLZ 150 1500 ns Figures 5, 6, CL = l5pF, S1 Closed Rev. PrC –3– PRELIMINARY TECHNICAL DATA ADM1487 ADM1487 SPECIFICATIONS (continued) SWITCHING CHARACTERISTICS (VCC = +5V ±5%, TA = -40°C TO +85°C, UNLESS OTHERWISE NOTED) Parameter Min Driver Disable Time from High, tDHZ 150 Receiver Input to Output, tRPLH 30 Receiver Input to Output Low, tRPHL 30 Typ Max Units Test Conditions/Comments 1500 ns Figures 5, 6, CL= l5pF, S2 Closed 140 250 ns Figures.2, 4, RDIFF= 54, CL1 = CL2 = 100pF 140 250 ns Figures.2, 4, RDIFF= 54, CL1 = CL2 = 100pF ns Figures.2, 4, RDIFF= 54, CL1 = CL2 = 100pF DifferentialReceiverSkew, tSKD |tPLH-tPHL| 13 Receiver Enable to Output Low, tRZL 20 50 ns Figures 7, 8, CRL = l5pF, S1 Closed Receiver Enable to Output High, tRZH 20 50 ns Figures 7, 8, CRL = l5pF, S2 Closed Receiver Disable from Low, tRLZ 20 50 ns Figures 7, 8, CRL = l5pF, S1 Closed Receiver Disable from High, tRHZ 20 50 ns Figures 7, 8, CRL = l5pF, S2 Closed Maximum Data Rate, fMAX 250 Time to Shutdown, tSHDN 50 kbps 600 ns DE = 0, RE = low to high transition Driver Enable from Shutdown to Output High, tDZH(SHDN) 2000 ns Figures 5, 6, CL = 100pF, S2 Closed Driver Enable from Shutdown to Output Low, tDZL(SHDN) 2000 ns Figures 5, 6, CL = 100pF, S1 Closed Receiver Enable from Shutdown to Output High, tRZH(SHDN) 2000 ns Figures 7, 8, CL = l5pF, S2 Closed Receiver Enable from Shutdown to Output Low, tRZL(SHDN) 2000 ns Figures 7, 8, CL = l5pF, S1 Closed 200 NOTES 1 Absolute maximum ratings are those beyond which the safety of the device cannot be guaranfeed. All currents into device pins are positive; all currents out ot device pins are negative. All voltages are referenced to device ground unless otherwise specified. 3 All typicals are given for Vcc = 5V and Tp = 25°C. 4 The ADM1487 is not tested and is not quality-assurance sampled at -40°C and at 85°C. These specifications are guaranteed by design, correlation, andlor inference from 0°C, 25°C and/or 70°C tests. 2 PIN CONFIGURATION ABSOLUTE MAXIMUM RATINGS Supply Voltage (Vcc) . . . . . . . . . . . . . . . . . . . . . . . . . . 12V Control Input Voltage . . . . . . . . . . . –0.5V to Vcc + 0.5V Driver Input Voltage . . . . . . . . . . . –0.5V to Vcc + 0.5V Driver Output Voltage . . . . . . . . . . . . . . . . . . . . . . . . ±14V Receiver InputVoltage . . . . . . . . . . . . . . . . . . . . . . . . ±14V Receiver Output Voltage . . . . . . . . . –0.5V to Vcc + 0.5V Operating Temperature Range . . . . . . 0°C TA 70°C Lead Temperature (Soldering, 10 sec) . . . . . . . . . 300°C *Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. THERMAL CHARACTERISTICS 8-Pin Plastic DIP Package θJA = tbd K/Watt, θJC = tbd K/Watt 8-Pin Plastic SO Package θJA = tbd K/Watt, θJC = tbd K/Watt –4– RO 1 RE 2 ADM1487 7 B DE 3 TOP VIEW (Not to Scale) 6 A DI 4 8 VCC 5 GND ORDERING INFORMATION Model Temperature Range Package Option ADM1487JN 0°C to +70°C 8 Pin Plastic DIP ADM1487JR 0°C to +70°C 8 Pin SO ADM1487AN –40°C to +85°C 8 Pin Plastic DIP ADM1487AR 8 Pin SO –40°C to +85°C Rev. PrC PRELIMINARY TECHNICAL DATA ADM1487 ADM1487 TEST CIRCUITS AND TIMING A VCC R VOD TEST POINT R S1 A VOC 500V OUTPUT UNDER TEST CRL 15pF S2 Figure 1. Driver DC Load Test Circuit 3V Figure 5. Test Load for Driver Enable/Disable Time Test DE A VOD2 D f = 1MHz, tr # 10ns, tf # 10ns CL1 A DI R RDIFF B 3V CL2 DE RO 5V 15pF A, B VOL VOH A, B VOL Figure 2. Driver/Receiver Timing Test Circuit tDLZ tDZL(SHDN), tDZL 2.3V 2.3 Vt VOL+ 0.5V OUTPUT NORMALLY LOW OUTPUT NORMALLY HIGH VOH- 0.5V tDHZ DZH(SHDN), tDZH f = 1MHz, tr # 10ns, tf # 10ns 3V DI 1.5V 0V B Figure 6. Driver Enable and Disable Times 1.5V 0V tDPLH tDPHL VCC B V0 A V0/2 VDIFF V0 0V -V0 TEST POINT VDIFF = VA - VB 10% 90% 90% tDR 10% S1 tDF RO tSKEW = |tDPLH-tDPHL| CRL 15pF Figure 3. Driver Propagation Delays f = 1MHz, tr # 10ns, tf # 10ns A VOD2 1kV S2 1kV B -VOD2 VOH tRPHL tRPLH Figure 7. Test Load for Receiver Enable/Disable Time Test 1.5V RO VOL f = 1MHz, tr # 10ns, tf # 10ns 3V RE Figure 4. Receiver Propagation Delays 1.5 V 0V tRZL(SHDN), tRZL 5V RO 1.5 V 5V RO 0V tRLZ OUTPUT NORMALLY LOW 0.5V OUTPUT NORMALLY HIGH 1.5 V tRZH(SHDN), tRZH 0.5V tRHZ Figure 8. Receiver Enable and Disable Delay Times Rev. PrC –5– PRELIMINARY TECHNICAL DATA ADM1487 ADM1487 TYPICAL PERFORMANCE CHARACTERISTICS AW A I IT NG T DA A AW TPC1. No-load Supply Current vs. Temperature AW AI N TI G T DA A I IT NG A AW TPC2. Output Current vs. Receiver Output High Voltage A AW TPC4. Receiver Output High Voltage vs. Temperature T A D AI N TI G T DA AI N TI G A TPC3. Output Current vs. Receiver Output Low Voltage A AW TPC5. Receiver Output Low Voltage vs. Temperature T DA AI N TI G T DA A TPC6. Shutdown Current vs. Temperature PIN FUNCTION DESCRIPTION Pin Mnemonic Description 1 RO Receiver Output. When RE is low and A - B (more positive than) 200mV, RO will be high. When RE is low and A - B (more negative than) –200mV, RO will be low. 2 RE Receiver Output Enable. Take RE low to enable RO; RO is high impedance when RE is high. Take RE high and DE low to enter low-power shutdown mode. 3 DE Driver Output Enable. Take DE high to enable driver outputs. These outputs are high impedance when DE is low. Take RE high and DE low to enter low-power shutdown mode. 4 DI Driver Input. With DE high, a low on DI forces non-inverting output low and inverting output high. Similarly, a high on DI forces non-inverting output high and inverting output low. 5 GND Ground 6 A Non-Inverting Receiver Input and Non-Inverting Driver Output 7 B Inverting Receiver Input and Inverting Driver Output 8 VCC Positive Supply 4.75V =VCC =5.25V –6– Rev. PrC PRELIMINARY TECHNICAL DATA ADM1487 DEVICE TRUTH TABLES TRANSMITTING RECEIVING INPUTS OUTPUTS INPUTS OUTPUT RE DE DI Z Y RE DE A-B RO X 1 1 0 1 0 X 0.2V 1 X 1 0 1 0 0 X -0.2V 0 0 0 X High-Z High-Z 0 X Open/shorted 1 0 X 1 0 X Shutdown* 1 Shutdown* X = Don’t care *In shutdown mode, driver and receiver outputs high impedance CIRCUIT DESCRIPTION SHUTDOWN MODE The ADM1487 is a differential input, differential output transceiver designed RS-485/RS-422 serial data communications over twisted-pair cables. It is a half-duplex device intended for alternate transmission and reception of data over a single twisted-pair cable, and the driver outputs and receiver inputs are internally linked and brought out to a single pair of pins. Its principal features include ultra-low power operation, a controlled slew-rate driver that minimizes electromagnetic interference (EMI) and signals reflections due to incorrectly terminated lines, and high input impedance that allows up to 256 receivers to be connected to a bus. THREE-STATE BUS CONNECTION The ADM1487 has a Driver Enable pin (DE) that enables the driver outputs when taken high or puts the driver outputs into a high-impedance state when taken low. This allows several driver outputs to be connected to an RS-422/ RS-485 bus. Similarly, the device has a (active-low) Receiver Enable pin (RE). Taking this low enables the receiver, while taking it high puts the receiver outputs into a high-impedance state. This allows several receiver outputs to be connected to a serial data bus. The input impedance of the device is 96k, which is 8 times higher than the standard RS-485 load of 12k. A standard driver can driver 32 standard loads, so up to 256 ADM1487 receivers, or a combination of ADM1487 and other devices up to 32 unit loads, may be connected to an RS-422/RS485 bus driven by a single driver. LOW POWER OPERATION The ADM1487 draws very little supply current (typically 80µA) when the driver outputs are disabled or unloaded. This will increase by up to 72µA if the driver outputs are enabled (but unloaded) and applying the maximum output swing of 5V across the receiver input resistors. However, in practical applications with the device driving and RS-485/RS422 cable or bus, the current drain is dominated by the current sourced into the line termination resistors and any other devices on the bus. With a half-termination (120 load) between the driver outputs, the load current can be in excess of 13mA as the drivers force a minimum of 1.5V across the line, and can be greater than 25mA with a fully terminated 60 line attached. Rev. PrC If RE is taken high while DE is taken low, the device will enter a low-power shutdown mode, in which the supply current is typically 1µA. If the driver outputs are active immediately before shutdown (DE high), the supply current will not drop to 1µ until the driver outputs have settled to their three-state mode, which can take up to 2.6µs worst-case. If DE is already low and shutdown is entered by taking RE high, the supply current will drop to 1µA very quickly. When RE is taken low and/or DE is takem high, the device will wake up within 3.5µs. If shutdown mode is not used, the fact that DE is activehigh and RE is active-low offers a convenient way of switching the device between transmit and receive, by tying DE and RE together. This is useful, for example, in applications using half duplex operation and where several receiver outputs are connected to a serial bus. The device is guaranteed not to enter shutdown mode if DE and RE are driven in this way. If DE is low and RE is high for less than 50ns the device will not enter shutdown. If DE is low and RE is high for greater than 600ns, the device is guaranteed to enter shutdown. RECEIVER INPUTS The ADM1487 receiver has an input common-mode range covering the entire RS-485 range of –7V to 12V. Internal 96k input resistors from each line terminal to ground provide a 1/8 unit load to the RS485 bus. Differential signals greater than ±200mV within the specified input common-mode range are converted to a TTLcompatible logic signal at the receiver output. A small amount of input hysteresis is included to minimize the effects of noise on the line signals. If the line is terminated or the receiver inputs are shorted together, the receiver output will retain the last valid line signal due to the 45mV of hysteresis incorporated in the receiver circuit. If the receiver inputs are left floating (unterminated), an internal pull-up of 10µA at the A input will force the receiver output to a guranteed high output state. DRIVER OUTPUT STAGE The RS-485 specification requires that a transceiver withstand common-mode voltages of up to 12V above or –7V below system ground at the RS-485 line connections. In addition, the transceiver must be protected against both ESD and latch-up. This precludes the use of conventional –7– PRELIMINARY TECHNICAL DATA ADM1487 CMOS outout stages, which include parasitic diodes from their driver outputs to each supply rail and can latch up when these diodes conduct. VCC CURRENT LIMIT AND THERMAL SHUTDOWN The ADM1487 incorporates two protection mechanisms to guard the drivers against short-circuits, bus contention or other fault conditions. The first is a current-limited output stage that protects the driver against short-circuits over the entire common-mode voltage range by limiting the output current to about 70mA. Under extreme fault condtions where the current limit is not effective, a thermal shutdown circuit puts the driver outputs into a high-impedance state if the die temperature exceeds 150°C, and does not turn them back on until the temperature has fallen to 130°C. S CH O T T KY RE V E RS E -BIA S E D W H E N O UT P UT > V CC +V D P A RA S ITIC DIO DE D P S C HO TT K Y R E V ER S E -B IAS E D W HE N O U TP U T < GND - VD P A RA S IT IC D IO D E D P ENHANCED ESD PROTECTION All Analog Devices parts incorporate protection against electrostatic discharge (ESD) to protect the devices during handling, assembly and normal operation. In addition, the ADM1487 has enhanced ESD protection up to ±10kV on the A and B I/O pins to protect against severe operational conditions such as line transients, connection and disconnection. Figure 9. ADM1487 Driver Output Stage The ADM1487 output includes Schottky diodes in series with the positive supply to the drain of the P-channel output device and in series with the drain of the N-channel output device. These diodes prevent the P-channel's parasitic diode from conducting when the output voltage exceeds VCC and prevent the N-channel's parasitic diode from conducting when the output voltage falls below ground. APPLICATION INFORMATION Figure 10 shows a typical application of the ADM1487. This is a half-duplex RS-485/RS-422 network. Up to 254 additional ADM1487s can be connected along the cable (termination resistors are only required at each end). SLEW RATE CONTROL The driver output stage of the ADM1487 has a controlled slew rate to minmize signal reflections on incorrectly terminated lines and to reduce electromagnetic interference (EMI). RECEIVER OUTPUT (RO) RECEIVER ENABLE (RE) DRIVER ENABLE (DE) DATA +5V (VCC ) CABLE TERMINATED AT ENDS 100n 1 8 R 2 7 B 5 6 RT 3 6 4 5 D RT A +5V (VCC) B A B A IN (DI) 7 4 DI 3 DE 2 RE 1 RO R 8 100n ADDITIONAL ADM1487s ADM1487 D ADM1487 Figure 10. Typical Half-Duplex RS-485/RS-422 Network OUTLINE DIMENSIONS Dimensions shown in inches and (mm). 8-Pin Plastic Dual-In-Line Package (N-8) 8-Pin SO Package (R-8) 0. 43 0 (10 . 92 ) 0. 19 6 8 (5 . 00 ) 0. 34 8 (8.84 ) 8 0. 18 9 0 (4 . 80 ) 5 0. 28 0 (7.11 ) 85 0. 24 0 (6.10 ) 14 P IN 1 0. 06 0 (1. 52 ) 0. 01 5 (0. 38 ) 0.21 0 (5. 33 ) MAX 0. 16 0 (4.06 ) 0. 11 5 (2.93 ) 0. 02 2 (0.5 58 ) 0.1 0 0 0.07 0 (1. 77 ) 0. 01 4 (0.3 56 ) (2 .54 ) 0.04 5 (1. 15 ) BS C 0.1 3 0 (3 .30 ) M IN S E A TI N G PLANE 0. 15 7 4 (4 . 00 ) 0. 24 4 0 (6 . 20 ) 0. 32 5 (8. 25 ) 0. 22 8 4 (5 . 80 ) 0. 30 0 (7. 62 ) 1 4 0. 14 9 7 (3 . 80 ) 0. 19 5 (4. 95 ) 0. 11 5 (2. 93 ) PIN 1 0. 01 5 (0. 3 81 ) 0. 10 2 (2.59 ) 0. 01 9 6 (0 .50 ) 0. 09 4 (2.39 ) 0. 00 9 9 (0 .25 ) x 45 0. 00 9 8 (0 .25 ) 0. 00 8 (0. 2 04 ) 0. 00 4 0 (0 .10 ) S E A TI N G PL A N E –8– 0. 0 5 00 (1 . 27 ) BSC 0. 01 9 2 (0 . 49 ) 0. 01 3 8 (0 . 35 ) 0. 00 9 8 (0 .25 ) 0. 00 7 5 (0 .19 ) 8 0 0. 05 0 0 (1 .27 ) 0. 01 6 0 (0 .41 ) Rev. PrC