19-0259; Rev 5; 5/05 Complete, Isolated RS-485/RS-422 Data Interface _________________General Description Next-Generation Device Features M The MAX1480A/MAX1480B/MAX1480C/MAX1490A/ ♦♦ For Integrated ESD Protection A MAX1490B are complete, electrically isolated, RS-485/ MAX1480E/MAX1490E: ±15kV ESD-Protected, X RS-422 data-communications interface solutions in a Isolated RS-485/RS-422 Data Interfaces hybrid microcircuit. Transceivers, optocouplers, and a ♦♦ For Space-Constrained Applications 1 transformer provide a complete interface in a standard MAX3157: High CMRR, RS-485 Transceiver with 4 DIP package. A single +5V supply on the logic side pow- ±50V Isolation 8 ers both sides of the interface. _______________Ordering Information 0 The MAX1480B/MAX1480C/MAX1490B feature reduced- A slew-rate drivers that minimize EMI and reduce reflec- PART† TEMP RANGE PIN-PACKAGE tions caused by improperly terminated cables, allowing / MAX1480ACPI 0°C to +70°C 28 Wide Plastic DIP B error-free data transmission at data rates up to 250kbps. MAX1480AEPI -40°C to +85°C 28 Wide Plastic DIP / The MAX1480A/MAX1490A driver slew rate is not limited, C allowing transmission rates up to 2.5Mbps. The Ordering Information continued at end of data sheet. MAX1480A/B/C are designed for half-duplex communi- †Data rate for “A” parts is up to 2.5Mbps. Data rate for “B” and /M “C” parts is up to 250kbps. cation, while the MAX1490A/B feature full-duplex com- munication. A _____________________Selection Table Drivers are short-circuit current limited and protected X against excessive power dissipation by thermal shut- DRIVER 1 HALF/ DATA SLEW- down circuitry that places the driver outputs into a high- ENABLE PART FULL RATE RATE 4 impedance state. The receiver input has a fail-safe TIME DUPLEX (MBPS) LIMITED 9 feature that guarantees a known output (RO low for the (µs) MAX1480A/B/C, RO high for the MAX1490A/B) if the 0 MAX1480A Half 2.5 No 0.2 input is open circuit. A MAX1480B Half 0.25 Yes 35 The MAX1480A/MAX1480B/MAX1480C/MAX1490A/ / MAX1480C Half 0.25 Yes 0.5 B MAX1490B typically withstand 1600VRMS (1 minute) or 2000VRMS (1 second). Their isolated outputs meet all MAX1490A Full 2.5 No — RS-485/RS-422 specifications. The MAX1480A/B/C are MAX1490B Full 0.25 Yes — available in a 28-pin DIP package, and the MAX1490A/B are available in a 24-pin DIP package. Pin Configurations ________________________Applications TOP VIEW Isolated RS-485/RS-422 Data Interface VCC1 1 24 AC1 MAX1490A/B Transceivers for EMI-Sensitive Applications VCC2 2 23 AC2 Industrial-Control Local Area Networks D1 3 22 ISO VCC1 Automatic Test Equipment D2 4 21 ISO RO DRV HVAC/Building Control Networks GND1 5 20 A FS 6 MAX845 MAX488MAX490 19 B SD 7 18 Z VCC3 8 17 Y DI 9 16 ISO COM1 VCC4 10 15 ISO DI DRV RO 11 14 ISO VCC2 GND2 12 13 ISO RO LED ISOLATION BARRIER DIP Pin Configurations continued at end of data sheet. ________________________________________________________________Maxim Integrated Products 1 For pricing, delivery, and ordering information,please contact Maxim Directat 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

Complete, Isolated RS-485/RS-422 Data Interface B ABSOLUTE MAXIMUM RATINGS / With Respect to GND_ LED Forward Current (DI, DE, ISO RO LED)......................50mA A Supply Voltage (VCC_)...........................................-0.3V to +6V Continuous Power Dissipation (TA= +70°C) 0 Control Input Voltage (SD, FS)...............-0.3V to (VCC_+ 0.3V) 24-Pin Plastic DIP (derate 8.7mW°C above +70°C).....696mW 9 Receiver Output Voltage (RO, RO)........-0.3V to (VCC_+ 0.3V) 28-Pin Plastic DIP (derate 9.09mW/°C above +70°C)..727mW Output Switch Voltage (D1, D2)........................................+12V Operating Temperature Ranges 4 With Respect to ISO COM_ MAX1480_CPI/MAX1490_CPG............................0°C to +70°C 1 Control Input Voltage (ISO DE_ )....-0.3V to (ISO VCC_+ 0.3V) MAX1480_EPI/MAX1490_EPG.........................-40°C to +85°C X Driver Input Voltage (ISO DI_ ).......-0.3V to (ISO VCC_+ 0.3V) Storage Temperature Range.............................-65°C to +160°C Receiver Output Voltage (ISO RO_)...-0.3V to (ISO VCC_+ 0.3V) Lead Temperature (soldering, 10s).................................+300°C A Driver Output Voltage (A, B, Y, Z )......................-8V to +12.5V Receiver Input Voltage (A, B)..............................-8V to +12.5V M Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional / operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to C absolute maximum rating conditions for extended periods may affect device reliability. / B ELECTRICAL CHARACTERISTICS A/ (VCC_= 5V ±10%, VFS= VCC_, TA= TMINto TMAX, unless otherwise noted. Typical values are at VCC_= 5V and TA= +25°C.) (Notes 1, 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 0 8 fSWL VFS = 0V 535 Switch Frequency kHz 4 fSWH FS = VCC_ or open 725 1 MAX1480A, RL = ∞, +25°C only 60 90 X DE´ = VCC_ or open RL = 54Ω 120 A MAX1480B, RL = ∞, +25°C only 35 45 M DE´ = VCC_ or open RL = 54Ω 95 MAX1480C, RL = ∞, +25°C only 35 75 Operating Supply Current ICC DE´ = VCC_ or open RL = 54Ω 95 mA RL = ∞, +25°C only 100 150 MAX1490A RL = 54Ω 170 RL = ∞, +25°C only 65 125 MAX1490B RL = 54Ω 130 Shutdown Supply Current ISHDN SD = VCC_ 0.2 µA (Note 3) VSDH High 2.4 Shutdown Input Threshold V VSDL Low 0.8 Shutdown Input Leakage Current 10 pA VFSH High 2.4 FS Input Threshold V VFSL Low 0.8 FS Input Pullup Current FS low 50 µA FS Input Leakage Current FS high 10 pA Input High Voltage VIH DE´, DI´ VCC_ - 0.4 V Input Low Voltage VIL DE´, DI´ 0.4 V Isolation Resistance RISO TA = +25°C, VISO = 50VDC 100 10,000 MΩ Isolation Capacitance CISO TA = +25°C, VISO = 50VDC 10 pF Differential Driver Output VOD1 8 V (No Load) 2 _______________________________________________________________________________________

Complete, Isolated RS-485/RS-422 Data Interface ELECTRICAL CHARACTERISTICS (continued) M (VCC_= 5V ±10%, VFS= VCC_, TA= TMINto TMAX, unless otherwise noted. Typical values are at VCC_= 5V and TA= +25°C.) (Notes 1, 2) A PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS X Differential Driver Output R = 50Ω (RS-422) 2 VOD2 V 1 (With Load) R = 27Ω (RS-485), Figure 4 1.5 5.0 4 Change in Magnitude of R = 27Ω or 50Ω, Differential 0.3 8 Differential Output Voltage for ΔVOD V Complementary Output States Figure 4 Common mode 0.3 0 A Driver Common-Mode Output Voltage VOC R = 27Ω or 50Ω, Figure 4 4 V / B MAX1480A/B/C 1 DE´ = 0V, VIN = 12V MAX1490A/B 0.25 /C Input Current (A, B) ISO IIN VCC_ = 0V mA MAX1480A/B/C 0.8 / or 5.5V VIN = -7V M MAX1490A/B 0.2 A MAX1480A/B/C 48 Receiver Input Resistance RIN -7V ≤ VCM ≤ 12V MAX1490A/B 12 kΩ X Receiver Differential Threshold 1 VTH -7V ≤ VCM ≤ 12V -0.2 +0.2 V Voltage 4 Receiver Input Hysteresis ΔVTH VCM = 0V 70 mV 9 Receiver Output/Receiver Output Using resistor values listed in 0 VOL 0.4 V Low Voltage Tables 1 and 2 A Receiver Output/Receiver Output / IOH VOUT = 5.5V 250 µA B High Current Driver Short-Circuit Current ISO IOSD -7V ≤ VO ≤ 12V (Note 4) 100 mA SWITCHING CHARACTERISTICS—MAX1480A/MAX1490A (VCC_= 5V ±10%, FS = VCC_, TA= TMINto TMAX, unless otherwise noted. Typical values are at VCC_= 5V and TA= +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Driver Input to Output tPLH Figures 5 and 7, RDIFF = 54Ω, CL1 = CL2 100 275 ns Propagation Delay tPHL = 100pF 100 275 Figures 5 and 7, RDIFF = 54Ω, CL1 = CL2 Driver Output Skew tSKEW 25 90 ns = 100pF Figures 5 and 7, RDIFF = 54Ω, CL1 = CL2 Driver Rise or Fall Time tR, tF 15 40 ns = 100pF Driver Enable to Output High tZH Figures 6 and 8, CL = 100pF, S2 closed 0.2 1.5 µs (MAX1480A Only) Driver Enable to Output Low tZL Figures 6 and 8, CL = 100pF, S1 closed 0.2 1.5 µs (MAX1480A Only) Driver Disable Time from Low tLZ Figures 6 and 8, CL = 15pF, S1 closed 0.2 1.5 µs (MAX1480A Only) Driver Disable Time from High tHZ Figures 6 and 8, CL = 15pF, S2 closed 0.2 1.5 µs (MAX1480A Only) Receiver Input to Output tPLH Figures 5 and 10, RDIFF = 54Ω, CL1 = CL2 100 225 ns Propagation Delay tPHL = 100pF 100 225 _______________________________________________________________________________________ 3

Complete, Isolated RS-485/RS-422 Data Interface B SWITCHING CHARACTERISTICS—MAX1480A/MAX1490A (continued) A/ (VCC_= 5V ±10%, FS = VCC_, TA= TMINto TMAX, unless otherwise noted. Typical values are at VCC_= 5V and TA= +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 0 9 |tPLH - tPHL| Differential Receiver Figures 5 and 10, RDIFF = 54Ω, CL1 = CL2 tSKD 20 ns Skew = 100pF 4 1 Maximum Data Rate fMAX tPLH, tPHL < 50% of data period 2.5 Mbps X Time to Shutdown tSHDN 100 µs A Shutdown to Driver Output High tZH(SHDN) Figures 6 and 9, CL = 100pF, S2 closed 3 10 µs M Shutdown to Driver Output Low tZL(SHDN) Figures 6 and 9, CL = 100pF, S1 closed 3 10 µs / C / B / SWITCHING CHARACTERISTICS—MAX1480B/MAX1480C/MAX1490B A 0 (VCC_= 5V ±10%, FS = VCC_, TA= TMINto TMAX, unless otherwise noted. Typical values are at VCC_= 5V and TA= +25°C.) 8 PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 4 Driver Input to Output tPLH Figures 5 and 7, RDIFF = 54Ω, 2 3.0 µs 1 Propagation Delay tPHL CL1 = CL2 = 100pF 2 3.0 X Figures 5 and 7, RDIFF = 54Ω, Driver Output Skew tSKEW 900 1600 ns A CL1 = CL2 = 100pF M Figures 5 and 7, RDIFF = 54Ω, Driver Rise or Fall Time tR, tF 1.0 2.0 µs CL1 = CL2 = 100pF Driver Enable to Output High tZH Figures 6 and 8, CL = 100pF, S2 closed 35 100 µs (MAX1480B Only) Driver Enable to Output Low tZL Figures 6 and 8, CL = 100pF, S1 closed 35 100 µs (MAX1480B Only) Driver Disable Time from Low tLZ Figures 6 and 8, CL = 15pF, S1 closed 13 50 µs (MAX1480B Only) Driver Disable Time from High tHZ Figures 6 and 8, CL = 15pF, S2 closed 13 50 µs (MAX1480B Only) Driver Enable to Output High tZH Figures 6 and 8, CL = 100pF, S2 closed 0.5 4.5 µs (MAX1480C Only) Driver Enable to Output Low tZL Figures 6 and 8, CL = 100pF, S1 closed 0.5 4.5 µs (MAX1480C Only) 4 _______________________________________________________________________________________

Complete, Isolated RS-485/RS-422 Data Interface SWITCHING CHARACTERISTICS—MAX1480B/MAX1480C/MAX1490B (continued) M (VCC_= 5V ±10%, FS = VCC_, TA= TMINto TMAX, unless otherwise noted. Typical values are at VCC_= 5V and TA= +25°C.) A PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS X Driver Disable Time from Low tLZ Figures 6 and 8, CL = 15pF, S1 closed 2.0 4.5 µs 1 (MAX1480C Only) 4 Driver Disable Time from High tHZ Figures 6 and 8, CL = 15pF, S2 closed 2.0 4.5 µs 8 (MAX1480C Only) 0 Receiver Input to Output tPLH Figures 5 and 10, RDIFF = 54Ω, 2 3.0 A µs Propagation Delay tPHL CL1 = CL2 = 100pF 2 3.0 / B |tPLH - tPHL| Differential Receiver Figures 5 and 10, RDIFF = 54Ω, Skew tSKD CL1 = CL2 = 100pF 1200 ns /C Maximum Data Rate fMAX tPLH, tPHL < 50% of data period 0.25 Mbps , Time to Shutdown tSHDN 100 µs M Shutdown to Driver Output High tZH(SHDN) Figures 6 and 9, CL = 100pF, S2 closed 35 100 µs A Shutdown to Driver Output Low tZL(SHDN) Figures 6 and 9, CL = 100pF, S1 closed 35 100 µs X Note 1: All currents into device pins are positive; all currents out of device pins are negative. All voltages are referenced to logic- side ground (GND_), unless otherwise specified. 1 Note 2: For DE´ and DI´pin descriptions, see Detailed Block Diagram and Typical Application Circuit (Figure 1 for MAX1480A/ 4 MAX1480B/MAX1480C, Figure 2 for MAX1490A/MAX1490B). 9 Note 3: Shutdown supply current is the current at VCC1and VCC2when shutdown is enabled. 0 Note 4: Applies to peak current (see Typical Operating Characteristics). Although the MAX1480A/B/C and MAX1490A/B provide electrical isolation between logic ground and signal paths, they do not provide isolation between external shields and the A signal paths (see Isolated Common Connectionsection). / B _______________________________________________________________________________________ 5

Complete, Isolated RS-485/RS-422 Data Interface B __________________________________________Typical Operating Characteristics A/ (VCC_= 5V, FS = VCC_, TA = +25°C, unless otherwise noted.) 0 9 OUTPUT CURRENT vs. OUTPUT CURRENT vs. RECEIVER OUTPUT HIGH VOLTAGE 4 RECEIVER OUTPUT LOW VOLTAGE RECEIVER OUTPUT HIGH VOLTAGE vs. TEMPERATURE MAX1 CURRENT (mA) 4567800000 MEASURED AT ISO RO DRV MAX1480/90A/B-01 CURRENT (mA) ----12235050 MEASURED AT ISO RO DRV MAX1480/90A/B-02 GH VOLTAGE (V) 44445.....0257005050 MIROE A=S 8UmRAED AT ISO RO DRV MAX1480/90A/B-03 , T T HI /C OUTPU 2300 OUTPU -10 OUTPUT 33..5705 B -5 10 3.25 / A 0 0 3.00 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 -40 -20 0 20 40 60 80 OUTPUT LOW VOLTAGE (V) OUTPUT HIGH VOLTAGE (V) TEMPERATURE (°C) 8 4 RECEIVER OUTPUT LOW VOLTAGE OUTPUT CURRENT vs. OUTPUT CURRENT vs. 1 vs. TEMPERATURE DRIVER OUTPUT LOW VOLTAGE DRIVER OUTPUT HIGH VOLTAGE MAX LTAGE (V) 0000....5678 MIROE A=S 8UmRAED AT ISO RO DRV MAX1480/90A/B-04 NT (mA) 111168420000 MAX1480/90A/B-05 NT (mA) -1----6789000000 MAX1480/90A/B-06 W VO 0.4 URRE 100 URRE -50 OUTPUT LO 00..23 OUTPUT C 8600 OUTPUT C --3400 40 -20 0.1 20 -10 0 0 0 -40 -20 0 20 40 60 80 0 1 2 3 4 5 6 7 8 9 10 11 12 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 TEMPERATURE (°C) OUTPUT LOW VOLTAGE (V) OUTPUT HIGH VOLTAGE (V) DRIVER OUTPUT CURRENT DRIVER DIFFERENTIAL OUTPUT VOLTAGE MAX1480B/MAX1480C/MAX1490B vs. DIFFERENTIAL OUTPUT VOLTAGE vs. TEMPERATURE SHUTDOWN CURRENT vs. TEMPERATURE OUTPUT CURRENT (mA) 23456780000000 DI´ = HIGH OR OPEN MAX1480/90A/B-07 ERENTIAL OUTPUT VOLTAGE (V) 22222223........34567890 RDLI´ = = 5 H4ΩIGH OR OPEN MAX1480/90A/B-08 μSHUTDOWN CURRENT (A) 0000000.......11223340505050 SDMDEE´ A= (S MVUCARCXE_1D, 4 DA8I0T´B V=/ CCVC CO1C NA_LN YD) V=C VCC2C_ MAX1480/90A/B-09 FF 2.2 10 DI 2.1 0.05 0 2.0 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 -40 -20 0 20 40 60 80 -40 -20 0 20 40 60 80 DIFFERENTIAL OUTPUT VOLTAGE (V) TEMPERATURE (°C) TEMPERATURE (°C) 6 _______________________________________________________________________________________

Complete, Isolated RS-485/RS-422 Data Interface _____________________________Typical Operating Characteristics (continued) M (VCC_= 5V, FS = VCC_, TA = +25°C, unless otherwise noted.) A X MAX1480A MAX1480B MAX1480C SUPPLY CURRENT vs. TEMPERATURE SUPPLY CURRENT vs. TEMPERATURE SUPPLY CURRENT vs. TEMPERATURE 1 URRENT (mA) 11118024600000 DE´ = VCC VVVCCCCCC === 554...505VVV RRLL = = 5 ∞4Ω MAX1480/90A/B-10 URRENT (mA) 11180240000 VVVCCCCCC === 554...055VVV RL = 54Ω MAX1480/90A/B-11 URRENT (mA) 111789120000000 DE´ = VCC VVVCCCCCC === 554...505VVV RL = 54Ω MAX1480/90A/B-12 480A/B SUPPLY C 6400 VCC = 5.5V VCC = 4.5V VCC = 5.0V SUPPLY C 6400 DE´ =V CVCC C= 5.5V VCC = 5.0V RL = ∞ SUPPLY C 654000 VCC = 5.0V VCC = 5.5V RL = ∞ /C, 20 30 M 0 20 VCC = 4.5V 20 VCC = 4.5V -40 -20 0 20 40 60 80 -40 -20 0 20 40 60 80 -40 -20 0 20 40 60 80 A TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C) X MAX1490A MAX1490B 1 SUPPLY CURRENT vs. TEMPERATURE SUPPLY CURRENT vs. TEMPERATURE 4 URRENT (mA) 121140680000 VVVCCCCCC === 554...505VVV RL = 54Ω MAX1480/90A/B-13 URRENT (mA) 111111012453000000 VVVCCCCCC === 455...505VVV RL = 54Ω MAX1480/90A/B-14 90A/B C C SUPPLY 120 VCC = 5.0V VCC = 5.5V RL = ∞ SUPPLY 9800 VCC = 5.0V VCC = 5.5V RL = ∞ 70 100 60 80 VCC = 4.5V 50 VCC = 4.5V -40 -20 0 20 40 60 80 -40 -20 0 20 40 60 80 TEMPERATURE (°C) TEMPERATURE (°C) DRIVER DISABLE TIME DRIVER ENABLE TIME vs. TEMPERATURE vs. TEMPERATURE 100 100 μs) MAX1480B MAX1480/90A/B-15a μs) MAX1480B MAX1480/90A/B-15b ME ( 10 ME ( 10 DRIVER DISABLE TI 1 RVLD I´= =5 40ΩV M EASURMEADX F1R4O8M0C DRIVER ENABLE TI 1 RVDLDE I´´= T =5O 40 ΩVV AMLEIDA MSOUUARTXEP1DU4 8TF0RCOM DE´ TO VALID OUTPUT MAX1480A MAX1480A 0.1 0.1 -40 -20 0 20 40 60 80 -40 -20 0 20 40 60 80 TEMPERATURE (°C) TEMPERATURE (°C) _______________________________________________________________________________________ 7

Complete, Isolated RS-485/RS-422 Data Interface B _____________________________Typical Operating Characteristics (continued) A/ (VCC_= 5V, FS = VCC_, VDI´= 0V, DE´toggled 0V to 5V at 5kHz, TA = +25°C, unless otherwise noted.) 0 MAX1480A MAX1480A DRIVER ENABLE TIME DRIVER DISABLE TIME 9 14 MAX1480/90-19 MAX1480/90-20 X DRIVER DRIVER OUTPUT B OUTPUT B A 2V/div 2V/div M , DE´ DE´ C 2V/div 2V/div / B / 200ns/div 200ns/div A VCC_ = 5.0V, DI´= 0V VCC_ = 5.0V, DI´ = 0V 0 DE´ TOGGLED 0V TO 5V AT 5kHz DE´ TOGGLED 0V TO 5V AT 5kHz 8 MAX1480B MAX1480B 4 DRIVER ENABLE TIME DRIVER DISABLE TIME 1 AX MAX1480/90-17DRIVER MAX1480/90-18 OUTPUT B DRIVER M 2V/div OUTPUT B 2V/div DE´ DE´ 2V/div 2V/div 10μs/div 5μs/div VCC_ = 5.0V, DI´= 0V VCC_ = 5.0V, DI´= 0V DE´ TOGGLED 0V TO 5V AT 5kHz DE´ TOGGLED 0V TO 5V AT 5kHz MAX1480C MAX1480C DRIVER ENABLE TIME DRIVER DISABLE TIME MAX1480/90-25 MAX1480/90-26 DRIVER DRIVER OUTPUT B OUTPUT B 2V/div 2V/div DE´ DE´ 2V/div 2V/div 500ns/div 500ns/div VCC_ = 5.0V, DI´= 0V VCC_ = 5.0V, DI´ = 0V DE´TOGGLED0VTO5VAT5kH DE´ TOGGLED 0V TO 5V AT 5kHz 8 _______________________________________________________________________________________

Complete, Isolated RS-485/RS-422 Data Interface _____________________________Typical Operating Characteristics (continued) M (VCC_= 5V, FS = VCC_, DE´= VCC_, VDI´ = 0V to 5V at 1.25MHz, TA = +25°C, unless otherwise noted.) A MAX1480A/MAX1490A MAX1480A/MAX1490A X RECEIVER tPHL RECEIVER tPLH 1 MAX1480/90-21 MAX1480/90-22 4 RECEIVER RECEIVER INPUT A INPUT B 8 1V/div 1V/div 0 A RECEIVER RECEIVER / INPUT B INPUT A B 1V/div 1V/div / C RO/RO RO/RO , 2V/div 2V/div M 20ns/div 20ns/div A VCC_ = 5.0V, DE´= VCC_ VCC_ = 5.0V, DE´= VCC_ X DI´ = 0V TO 5V AT 1.25MHz DI´ = 0V TO 5V AT 1.25MHz 1 MAX1480B/MAX1480C/MAX1490B MAX1480B/MAX1480C/MAX1490B 4 RECEIVER tPHL RECEIVER tPLH MAX1480/90-23 MAX1480/90-24 9 RECEIVER RECEIVER 0 INPUT A INPUT A A 1V/div 1V/div / B RECEIVER RECEIVER INPUT B INPUT B 1V/div 1V/div RO/RO RO/RO 2V/div 2V/div 200ns/div 500ns/div VCC_ = 5.0V, DE´= VCC_ VCC_ = 5.0V, DE´= VCC_ DI´= 0V TO 5V AT 125kHz DI´= 0V TO 5V AT 125kHz POWER-UP DELAY TO DRIVER OUTPUTS VALID MAX1480/90-16 DRIVER OUTPUT B (Z FOR MAX1490) 2V/div SD 2V/div 1μs/div VDI´ = 0V VSD = 5V TO 0V AT 1kHz _______________________________________________________________________________________ 9

Complete, Isolated RS-485/RS-422 Data Interface B ________________________________________________________________Pin Description / A PIN 0 NAME FUNCTION MAX1480A/B/C MAX1490A/B 9 4 PPININSS O ONN T THHEE N NOONN-I-SISOOLLAATTEEDD S SIDIDEE 1 1, 2, 8, 10 1, 2, 8, 10 VCC1–VCC4 Logic-Side (nonisolated side) +5V Supply Voltages X 3, 4 3, 4 D1, D2 Internal Connections. Leave these pins unconnected. 5 5 GND1 Logic-Side Ground. Connect to GND2 (pin 12). A Frequency Select Input. If FS = VCC_or is open, switch frequency is high; if FS M 6 6 FS = GND, switch frequency is low. For optimal performance and minimal supply current, connect FS to VCC_or leave unconnected. , Shutdown Input. Ground for normal operation. When high, the power oscillator is C 7 7 SD disabled. / B Driver Input. With DE´high (MAX1480A/B/C only), a low on DI´forces output A A/ 9 9 DI lBo wlo wan. dD roivuetpsu int tBe rhniaglh L. ESDim cilaatrhlyo, dae h tihgrho uognh D aI´ refosricsetosr o(Tuatpbulet A1 hoifg Fhig aunrde o1u ftoprut 0 MAX1480A/B/C, Table 2 of Figure 2 for MAX1490A/B). 8 Driver-Enable Input. The driver outputs, A and B, are enabled by bringing DE´ 4 high. The driver outputs are high impedance when DE´is low. If the driver out- 1 11 — DE puts are enabled, the device functions as a line driver. While the driver outputs are high impedance, the device functions as a line receiver. Drives internal X LED cathode through a resistor (Table 1 of Figure 1). A Receiver Output. If A > B by 200mV, RO will be high; if A < B by 200mV, RO M — 11 RO will be low. Open collector; must have pullup to VCC(Table 2 of Figure 2). 12 12 GND2 Logic-Side Ground. Connect to GND1 (pin 5). Receiver Output. If A > B by 200mV, ROwill be low; if A < B by 200mV, ROwill 13 — RO be high. Open collector; must have pullup to VCC_(Table 1 of Figure 1). 14 — VCC5 Logic-Side (non-isolated side) +5V Supply Voltage PPININSS O ONN T THHEE I SISOOLLAATTEEDD R RSS-4-48855/R/RSS-4-42222 S SIDIDEE Isolated Receiver Output LED. Internal LED anode in MAX1480A/B/C and LED 15 13 ISO RO LED cathode in MAX1490A/B. Connect to ISO RO DRV through a resistor (Table 1 of Figure 1 for MAX1480A/B/C; Table 2 of Figure 2 for MAX1490A/B). 16 — ISO COM2 Isolated Common. Connect to ISO COM1 (pin 20). Isolated Driver-Enable Drive. The driver outputs, A and B, are enabled by bring- ing DE´high. The driver outputs are high impedance when DE´ is low. If the driv- er outputs are enabled, the device functions as a line driver. While the driver 17 — ISO DE DRV outputs are high impedance, the device functions as a line receiver. Open- collector output; must have pullup to ISO VCC_and be connected to ISO DE IN for normal operation (Table 1 of Figure 1). Isolated Supply Voltage. Connect to ISO VCC1(pin 26 for MAX1480A/B/C, or 18 14 ISO VCC2 pin 22 for MAX1490A/B). Isolated Driver-Input Drive. With DE´high (MAX1480A/B/C only), a low on DI´ forces output A low and output B high. Similarly, a high on DI´forces output A 19 15 ISO DI DRV high and output B low. Connect to ISO DI IN (on the MAX1480A/B/C only) for normal operation. Open-collector output; connect a pullup resistor to ISO VCC_ (Table 1 of Figure 1 for MAX1480A/B/C; Table 2 of Figure 2 for MAX1490A/B). Isolated Common. For MAX1480A/B/C, connect to ISO COM2 (pin 16) 20 16 ISO COM1 (Figures 1 and 2). 10 ______________________________________________________________________________________

Complete, Isolated RS-485/RS-422 Data Interface ___________________________________________________Pin Description (continued) M A PIN NAME FUNCTION X MAX1480A/B/C MAX1490A/B 1 PINS ON THE ISOLATED RS-485/RS-422 SIDE (continued) 4 — 17 Y Noninverting Driver Output 8 — 18 Z Inverting Driver Output 0 — 19 B Inverting Receiver Input A — 20 A Noninverting Receiver Input / 21 — ISO DE IN Isolated Driver-Enable Input. Connect to ISO DE DRV for normal operation. B 22 — ISO DI IN Isolated Driver Input. Connect to ISO DI DRV for normal operation. / C 23 — A Noninverting Driver Output and Noninverting Receiver Input Isolated Receiver-Output Drive. Connect to ISO RO LED through a resistor , 24 21 ISO RO DRV (Table 1 of Figure 1 for MAX1480A/B/C, Table 2 of Figure 2 for MAX1490A/B). M 25 — B Inverting Driver Output and Inverting Receiver Input A 26 22 ISO VCC1 Isolated Supply Voltage Source X 27, 28 23, 24 AC2, AC1 Internal Connections. Leave these pins unconnected. 1 Note: For DE´and DI´pin descriptions, see Detailed Block Diagram and Typical Application Circuit(Figure 1 for MAX1480A/B/C, 4 Figure 2 for MAX1490A/B). 9 0 Detailed Description Use the FS pin to select between high and low switching A frequencies for the isolated power driver. The driver The MAX1480A/MAX1480B/MAX1480C/MAX1490A/ switches at the lower frequency 535kHz when FS is low, / MAX1490B are complete, electrically isolated, RS-485/ B and at the higher frequency 725kHz when FS is high. The RS-422 data-communications interface solutions. FS pin has a weak internal pull-up that switches the Transceivers, optocouplers, a power driver, and a device to the high-frequency mode when FS is left transformer in one standard 28-pin DIP package (24- unconnected. With FS high or open, no-load supply pin for the MAX1490A/B) provide a complete interface. current is reduced by approximately 4mA, and by up to Signals and power are internally transported across the 8mA when fully loaded. For optimal performance and isolation barrier (Figures 1, 2). Power is transferred from minimal supply current, connect FS to VCC_ or leave the logic side (nonisolated side) to the isolated side of unconnected. the barrier through a center-tapped transformer. Signals cross the barrier through high-speed optocou- Drivers are short-circuit current limited and are protect- plers. A single +5V supply on the logic side powers ed against excessive power dissipation by thermal both sides of the interface. The MAX1480A/B/C offer shutdown circuitry that puts the driver outputs into a half-duplex communications while the MAX1490A/B high-impedance state. The receiver input has a fail-safe feature full-duplex communication. The functional feature that guarantees a logic-high RO (logic-low RO) input/output relationships are shown in Tables 3–6. output if the input is open circuit. The MAX1480B/MAX1480C/MAX1490B feature reduced- On the MAX1480A/B/C, the driver outputs are enabled slew-rate drivers that minimize EMI and reduce reflec- by bringing DE´ high. Driver-enable times are typically tions caused by improperly terminated cables, allowing 0.2µs for the MAX1480A, 35µs for the MAX1480B, and error-free transmission at data rates up to 250kbps. The 0.5µs for the MAX1480C. Allow time for the devices to be MAX1480A/MAX1490A driver slew rate is not limited, enabled before sending data (see the Driver Enable allowing transmission rates up to 2.5Mbps. Time vs. Temperature graph in the Typical Operating Characteristics). When enabled, driver outputs function The MAX1480B/MAX1480C/MAX1490B shutdown feature as line drivers. Driver outputs are high impedance when reduces supply current to as low as 0.2µA by using the DE´is low. While outputs are high impedance, they func- SD pin (see the Low-Power Shutdown Mode section). tion as line receivers. ______________________________________________________________________________________ 11

Complete, Isolated RS-485/RS-422 Data Interface B / A VCC3 ISO VCC1 0 MAX845 D1 9 Q MAX1480A: MAX1487 N MAX1480B: MAX487 4 FS 1.0O7SMCHz/ T F/F ISO DI IN MAX1480C: MAX487 B 1 1.45MHz D2 D X Q N ISO DE IN A A ISO RO DRV R M SD GND1 RE , C ISO COM1 / EXTERNAL RS-485/RS-422 WIRING B TERMINATING RESISTOR / MAX1480A/B/C (ONE RESISTOR ON EACH END) A VIN VCC1 1 28 AC1 (MAKE NO CONNECTION) 5V TWISTED PAIR 0 C1 C2 VCC2 2 27 AC2 (MAKE NO CONNECTION) TO OTHER TRANSCEIVERS 8 22μF 0.1μF D1 3 26 ISO VCC1 B RL B 4 D2 4 25 SHIELD (OPTIONAL) GND1 ISO RO DRV 1 5 24 X FS 6 MAX845 MMAAXX1448877 23 A A TO OTTHWERIS TTREADN PSACIREIVERS A 74HC86 SD 7 22 ISO DI IN R6 SH RL OR EQUIVALENT VCC3 8 21 ISO DE IN M DI DRIVER INPUT R1 DI 9 20 ISO COM1 R4 SHIELD (OPTIONAL) DI´ VCC4 10 19 ISO DI DRV R2 DE DRIVER ENABLE DE´ DE 11 18 ISO VCC2 R5 R7 N O T E : TRHESE IMSTAOXR1 4R870 PAR/BO/TCE FCRTOSM TRANSIENT R3 GND2 12 17 ISO DE DRV 100Ω CURRENTS BETWEEN SHIELD AND RECEIVER OUTPUT TRANSMISSION LINES. RO 13 16 ISO COM2 RO VCC5 ISO RO LED 14 15 LOGIC GROUND ISOLATION BARRIER ISOLATED COMMON Table 1. Pull-Up and LED Drive Resistors PART R1 (Ω) R2 (Ω) R3 (Ω) R4 (Ω) R5 (Ω) R6 (Ω) MAX1480A 200 200 1000 4300 1000 200 MAX1480B 200 510 3000 2200 3000 200 MAX1480C 200 200 3000 3000 3000 200 Figure 1. MAX1480A/MAX1480B/MAX1480C Detailed Block Diagram and Typical Application Circuit The MAX1480A/MAX1480B/MAX1480C/MAX1490A/ Low-Power Shutdown Mode MAX1490B typically withstand 1600VRMS (1 minute) or The SD pin shuts down the oscillator on the internal power 2000VRMS (1 second). The logic inputs can be driven driver. With the primary side in shutdown, no power is from TTL/CMOS-logic with a series resistor, and the transferred across the isolation barrier. The DI and DE received data output can directly drive TTL or CMOS- optocouplers, however, still consume current if the drive logic families with only resistive pullup. signals on the nonisolated side are low. Therefore, leave DI´ and DE´ high or floating when in shutdown mode. 12 ______________________________________________________________________________________

Complete, Isolated RS-485/RS-422 Data Interface M A VCC3 X MAX845 D1 1 Q N 4 FS 1.0O7MSCHz/ T F/F R A 8 1.45MHz D2 ISO RO DRV B 0 Q N ISO DI DRV MAX1490A: MAX490 MAX1490B: MAX488 Z A D / B SD GND1 Y / C , MAX1490A/B M VIN EXTERNAL RS-485/RS-422 WIRING 5V C1 C2 VCC1 1 24 AC1 (MAKE NO CONNECTION) TERMINATING RESISTOR A (ONE RESISTOR ON EACH END) 22μF 0.1μF VCC2 2 23 AC2 (MAKE NO CONNECTION) X TWISTED PAIR D1 3 22 ISO VCC1 TO OTHER TRANSCEIVERS 1 D2 4 21 ISO RO DRV RL RL 4 GND1 5 20 A A 9 74HC86 SFDS 67 MAX845 MAX488MAX490 1189 BZ BZ RL TO OSTHTHIWEELRIDS TT (REOADPN TPSIAOCINREAIVLE)RS 0A OR EQUIVALENT VCC3 8 17 Y Y R1 R5, 100Ω RL / DI DRIVER INPUT DI 9 16 ISO COM1 SH1 B DI´ VCC4 10 15 ISO DI DRV R4 SH2 SHIELD (OPTIONAL) RECEIVER OUTPUT R2 R0 11 14 ISO VCC2 R6, 100Ω RO GND2 12 13 ISO RO LED R3 NOTE: RESISTORS R5 AND R6 PROTECT THE MAX1490A/B FROM TRANSIENT ISOLATION BARRIER ISOLATED COMMON CURRENTS BETWEEN SHIELD AND TRANSMISSION LINES. LOGIC GROUND Table 2. Pull-Up and LED Drive Resistors PART R1 (Ω) R2 (Ω) R3 (Ω) R4 (Ω) MAX1490A 200 1000 330 1000 MAX1490B 200 3000 330 3000 Figure 2. MAX1490A/MAX1490B Detailed Block Diagram and Typical Application Circuit Under these conditions, the MAX1480B/MAX1480C/ tion, SD is low, turning the MOSFET on and thereby pro- MAX1490B supply current is reduced to as low as 0.2µA. viding power to all the VCC_pins. When SD is pulled high, the power oscillator is disabled and the switch is turned The high-speed optocouplers on the MAX1480A/ off, disconnecting power from the DI and DE optocou- MAX1480C/MAX1490A consume an additional 10mA plers. In normal operating mode, the switch carries only through VCC5 (VCC4 for the MAX1490A). Therefore, to the optocoupler currents, so an on-resistance of several completely shut down these devices, use an external P- ohms will not significantly degrade efficiency. channel MOSFET as shown in Figure 3. In normal opera- ______________________________________________________________________________________ 13

Complete, Isolated RS-485/RS-422 Data Interface B / A 0 9 4 1 MAX1480A X VIN VCC1 1 28 AC1 5V VCC2 2 27 AC2 A M D1 3 26 ISO VCC1 D2 4 25 B , Si943304 GND1 5 24 ISO RO DRV C P FS 6 MAX845 MAX1487 23 A / B SD 7 22 ISO DI IN SHUTDOWN A/ VCC3 8 21 ISO DE IN R1 0 DI DI 9 20 ISO COM1 8 VCC4 10 19 ISO DI DRV R2 4 DE DE 11 18 ISO VCC2 1 R3 GND2 12 17 ISO DE DRV X RO 13 16 ISO COM2 RO A VCC5 14 15 ISO RO LED M ISOLATION BARRIER GND Figure 3. MAX1480A Low-Power Shutdown Mode Test Circuits ISOLATION BARRIER ISOLATION BARRIER R (DE´) CL1 ( ) ARE FOR D VOD THE MAX1480A/B/C RDIFF R VOC DI´ D VID R RO (RO)* * OPTOCOUPLER CL2 OUTPUTS. SEE FIGURES 1 AND 2 FOR DETAILED BLOCK DIAGRAM AND TYPICAL APPLICATION CIRCUIT. Figure 4. Driver DC Test Load Figure 5. Driver/Receiver Timing Test Circuit 14 ______________________________________________________________________________________

Complete, Isolated RS-485/RS-422 Data Interface ____________________________________________________Test Circuits (continued) M A X 1 4 ISO VCC_ 500Ω S1 8 OUTPUT 0 UNDER TEST CL A S2 / B / C , Figure 6. Driver Timing Test Load M Switching Waveforms A X 1 VCC_ - 0.4V VCC_ - 0.4V VCC_ - 0.4V 2 2 VCC_ -0.4V 4 VCC_ - 0.4V VCC_ - 0.4V 9 DI´ 0V DE´ 2 2 tPLH tPHL 1/2 VO 0V 0 A B tZL tLZ A, B / A VO VOL 2.3V OUTPUT NORMALLY LOW VOL + 0.5V B 1/2 VO VDIFF = V (A) - V (B) OUTPUT NORMALLY HIGH VO A, B VDIFF 0V 10% 90% 90% 10% 2.3V VOH - 0.5V -VO 0V tR tF tZH tHZ tSKEW = ⎢tPLH - tPHL ⎢ Figure 7. Driver Propagation Delays and Transition Times Figure 8. Driver Enable and Disable Times VID INPUT 2.4V 0V 0V SD 1.6V 1.6V -VID 0.8V VA - VB tZL(SHDN) tSHDN MAX1490A/B A, B OUTPUT VOL 2.3V OUTPUT NORMALLY LOW VOL + 0.5V RO VVOOHL 1.5VtPLH 1.5V tPHL OUTPUT NORMALLY HIGH A, B 2.3V VOH - 0.5V RO VOH MAX1480A/B/C 0V VOL 1.5V OUTPUT 1.5V tZH(SHDN) tSHDN tPHL tPLH tSKEW = ⏐tPLH - tPHL⏐ Figure 9. Times to/from Shutdown Figure 10. Receiver Propagation Delays ______________________________________________________________________________________ 15

Complete, Isolated RS-485/RS-422 Data Interface B MAX1480B/MAX1480C/MAX1490B: _____________________Function Tables / Reduced EMI and Reflections A The MAX1480B/MAX1480C/MAX1490B are slew-rate- Half-Duplex Devices 0 limited, minimizing EMI and reducing reflections (MAX1480A/MAX1480B/MAX1480C) 9 caused by improperly terminated cables. Figure 11 shows both the driver output waveform of a 4 MAX1480A/MAX1490A transmitting a 150kHz signal Table 3. Transmitting 1 and the Fourier analysis of that waveform. High-fre- INPUTS* OUTPUTS X quency harmonics with large amplitudes are evident. A Figure 12 shows the same information for the slew-rate- DE´ DI´ B A limited MAX1480B/MAX1480C/MAX1490B transmitting 1 1 0 1 M the same signal. The high-frequency harmonics have 1 0 1 0 much lower amplitudes, and therefore the potential for 0 X High-Z High-Z , EMI is significantly reduced. C X = Don’t care / High-Z = High impedance B / A Table 4. Receiving 0 8 INPUTS* OUTPUT 4 DE´ VA- VB (RO) 1 10dB/div 0 ≥+0.2V 0 X 0 ≤-0.2V 1 A 0 Open 0 M 0Hz 5MHz 500kHz/div Full-Duplex Devices (MAX1490A/MAX1490B) Figure 11. Driver Output Waveform and FFT Plot of MAX1480A/MAX1490A Transmitting a 150kHz Signal Table 5. Transmitting INPUT* OUTPUTS (DI´) Z Y 1 0 1 0 1 0 *For DE´ and DI´ pin descriptions, see Detailed Block Diagram and Typical Application Circuit (Figure 1 for MAX1480A/B/C, Figure 2 for MAX1490A/B). 10dB/div Table 6. Receiving INPUT OUTPUT (VA- VB) (RO) 0Hz 5MHz ≥+0.2V 1 500kHz/div ≤-0.2V 0 Figure 12. Driver Output Waveform and FFT Plot of Open 1 MAX1480B/MAX1480C/MAX1490B Transmitting a 150kHz Signal 16 ______________________________________________________________________________________

Complete, Isolated RS-485/RS-422 Data Interface M TERMINATING RESISTOR A (ONE RESISTOR ON EACH END) X 1 B 4 DI D 120Ω 8 DE 0 A A A B A B R RO / 100Ω B / RE C RE R RE R , M D D A RO DE DI RO DE DI X 1 4 9 0 A / B TERMINATING RESISTOR VIN MAX1480A/B/C (ONE RESISTOR ON EACH END) 5V VCC1 1 28 AC1 (MAKE NO CONNECTION) C1 C2 VCC2 2 27 AC2 (MAKE NO CONNECTION) 22μF 0.1μF D1 3 26 ISO VCC1 B B D2 4 25 GND1 5 24 ISO RO DRV 120Ω A FS 6 MAX845 MAX487 23 A MAX1487 R6 74HC86 SD 7 22 ISO DI IN R4 SH SHIELD OR EQUIVALENT VCC3 8 21 ISO DE IN (OPTIONAL) R1 DI DRIVER INPUT DI ISO COM1 NOTE: RESISTOR R7 PROTECTS 9 20 R5 THE MAX1480A/B/C FROM VCC4 10 19 ISO DI DRV TRANSIENT CURRENTS R2 DE DRIVER ENABLE DE 11 18 ISO VCC2 BTRETAWNSEMENIS SSHIOIENL DLI NANESD. R7 R3 GND2 12 17 ISO DE DRV 100Ω RECEIVER OUTPUT RO 13 16 ISO COM2 RO VCC5 ISO RO LED 14 15 LOGIC GROUND ISOLATION BARRIER ISOLATED COMMON Figure 13. Typical Half-Duplex RS-485/RS-422 Network ______________________________________________________________________________________ 17

Complete, Isolated RS-485/RS-422 Data Interface B Driver Output Protection ___________Applications Information A/ Tchuerrreen at raen tdw op omweecrh adnisissmipsa ttioo np rceavuesnet de xbcye sfasuivlets oourt pbuyt DI and DE are intended to be driven through a series current-limiting resistor. Directly grounding 0 bus contention. A foldback current limit on the output these pins destroys the device. stage provides immediate protection against short cir- 9 cuits over the entire common-mode range (see the The MAX1480A/MAX1480B/MAX1480C are designed 4 Typical Operating Characteristics). In addition, a ther- for bidirectional data communications on multipoint 1 mal shutdown circuit forces the driver outputs into a bus-transmission lines. The MAX1490A/MAX1490B are X high-impedance state if the die temperature rises designed for full-duplex bidirectional communications A excessively. that are primarily point-to-point. Figures 13 and 14 show half-duplex and full-duplex typical network appli- M Propagation Delay Skew cation circuits, respectively. To minimize reflections, Typical propagation delays are shown in the Typical terminate the line at both ends with its characteristic , Operating Characteristicsusing the test circuit of impedance, and keep stub lengths off the main line as C Figure 5. Propagation delay skew is simply the differ- short as possible. The slew-rate-limited MAX1480B/ / ence between the low-to-high and high-to-low propaga- MAX1480C/MAX1490B are more tolerant of imperfect B tion delay. Small driver/receiver skew times help termination and stubs off the main line. / reduce EMI and reflections by maintaining balanced A differential signals. Layout Considerations 0 The MAX1480A/MAX1480B/MAX1480C/MAX1490A/ The receiver skew time, I tPLH - tPHLI, is typically under MAX1490B pinouts enable optimal PC board layout by 8 100ns for the MAX1480A/MAX1490A and under 1µs for minimizing interconnect lengths and crossovers. 4 the MAX1480B/MAX1480C/MAX1490B. • For maximum isolation, the “isolation barrier” should 1 The driver skew time is typically 25ns for the not be breached except by the MAX1480A/ X MAX1480A/MAX1490A and 100ns for the MAX1480B/ MAX1480B/MAX1480C/MAX1490A/MAX1490B. MAX1480C/MAX1490B. A M MAX1490A/B VIN 5V C1 C2 VCC1 1 24 AC1 (MAKE NO CONNECTION) 22μF 0.1μF VCC2 2 23 AC2 (MAKE NO CONNECTION) D1 3 22 ISO VCC1 120Ω Y D2 4 21 ISO RO DRV 120Ω D DI GND1 5 20 A A Z FS 6 MAX845 MAX488MAX490 19 B B SHIELD (OPTIONAL) SD 7 18 Z Z 120Ω 74HC86 B OR EQUIVALENT R1 VCC3 8 17 Y R5, 100ΩY 120Ω R RO DI DI 9 16 ISO COM1 SH1 A DRIVER INPUT DI´ R2 VCC4 10 15 ISO DI DRV R4 SH2 SHIELD (OPTIONAL) RO 11 14 ISO VCC2 R6, 100Ω RO RECEIVER OUTPUT R3 NOTE: RESISTORS R5 AND R6 PROTECT GND2 12 13 ISO RO LED THE MAX1490A/B FROM TRANSIENT CURRENTS BETWEEN SHIELD AND ISOLATION BARRIER ISOLATED COMMON TRANSMISSION LINES. LOGIC GROUND Figure 14. Typical Full-Duplex RS-485/RS-422 Network 18 ______________________________________________________________________________________

Complete, Isolated RS-485/RS-422 Data Interface Connections and components from one side should The DI and DE (MAX1480A/B/C only) inputs are the M not be located near those of the other side. cathodes of LEDs whose anodes are connected to the • A shield trace connected to the ground on each side supply. These points are best driven by a CMOS-logic A of the barrier can help intercept capacitive currents gate with a series resistor to limit the current. The resis- X tor values shown in Tables 1 and 2 are recommended that might otherwise couple into the signal path. In a 1 when the 74HC86 gate or equivalent is used. These double-sided or multilayer board, these shield traces values may need to be adjusted if a driving gate with 4 should be present on all conductor layers. dissimilar series resistance is used. 8 • Try to maximize the width of the isolation barrier All pull-up resistors are based on optocoupler specifica- 0 wherever possible; a clear space of at least 0.25 tions in order to optimize the devices’ data-transfer rates. A inches between ground and isolated common is suggested. / Isolated Common Connection B Pullup and LED Drive Resistors The isolated common may be completely floating with / respect to the logic ground and the effective network C The MAX1480A/MAX1480B/MAX1480C/MAX1490A/ ground. The receiver input resistors will cause the iso- MAX1490B are specified and characterized using the , lated common voltage to go to the mean voltage of the resistor values shown in Table 1 of Figure 1 and Table M receiver inputs. If using shielded cable, connect the 2 of Figure 2. Altering the recommended values can degrade performance. isolated common to the shield through a 100Ω resistor. A In the case of the MAX1490, each shield should have its own 100Ωresistor (Figures 1, 2, 13, and 14). X 1 4 9 +5V +5V 0 A NETWORK SEGMENT A NETWORK SEGMENT B 2 8 1014 3kΩ 2 81014 / A 23 200Ω 23 A B 13 1 2 9 B 25 25 B 26 74HC04 3kΩ 26 3kΩ MAX1480C 200Ω MAX1480C 3kΩ 9 4 3 13 3kΩ 19 19 3kΩ 22 DRIVER DRIVER 22 17 17 ENABLE ENABLE 21 200Ω B > A A > B 200Ω 21 24 11 11 24 200Ω 200Ω 15 15 5 712 5 712 +5V51kΩ 1000pF +5V 51kΩ 1000pF 16 15 14 7 6 2 B Q 13 10 B Q 5 74HC123 74HC123 1 A Q 4 9 A Q 12 CLR CLR 3 11 Figure 15. Doubly Isolated RS-485 Repeater ______________________________________________________________________________________ 19

Complete, Isolated RS-485/RS-422 Data Interface B Doubly Isolated RS-485 Repeater In the idle state, both transmitters are disabled, while all / The RS-422/RS-485 standard is specified for cable receivers in the system are enabled. If any device on A lengths up to 4000 feet. When approaching or exceed- the system has information for any other device, it starts 0 ing the specified maximum cable length, a ground- sending its data onto the bus. Each data transmission potential difference of several tens of volts can easily on the bus retriggers the one-shot, keeping the sending 9 develop. This difference can be either DC, AC, at transmitter enabled until there are no more transmis- 4 power-line frequency, or any imaginable noise or sions. All receivers receive all data; if this is undesir- 1 impulse waveform. It is typically very low impedance so able, the protocol must allow for an address field so X that if a connection between the two grounds is receivers can ignore data not directed to them. A attempted, very large currents may flow. These cur- Each node must refrain from transmitting when data rents are by their nature unstable and unpredictable. In already exists on the bus, and must resend data that is M addition, they may cause noise to be injected into sen- corrupted by the collisions that inevitably occur with a sitive instrumentation and, in severe cases, might actu- party-line system. With the repeater of Figure 15, there , ally cause physical damage to such equipment. C might be transmitters up to 8000 feet apart. That repre- Figure 15 shows a half-duplex (two-wire), bidirectional, sents more than 8µs (assuming 1ns/foot of delay) in / B party-line repeater system that prevents interference which two nodes could be transmitting simultaneously. and/or damage from ground-potential differences. Two / The circuit in Figure 15 can be used either directly as A MAX1480A/MAX1480B/MAX1480C isolated RS-485 shown, with the slew-rate-limited MAX1480B/MAX1480C, transceivers are used to isolate each of the network 0 for data transfer rates up to 250kbps, or with the segments from the electrical environment of the 8 MAX1480A for data rates up to 2.5Mbps (see Table 1 repeater. The MAX1480A/MAX1480B/MAX1480C also for pullup and LED resistor values when using the 4 regenerate bus signals that may have been degraded MAX1480A, MAX1480B, or MAX1480C). If dual-port iso- 1 by line attenuation or dispersion. lation is not needed, one of the MAX1480C devices can X be replaced by a MAX487 for 250kbps applications. A M 20 ______________________________________________________________________________________

Complete, Isolated RS-485/RS-422 Data Interface Pin Configurations (continued) Ordering Information (continued) M PART† TEMP RANGE PIN-PACKAGE A TOP VIEW MAX1480BCPI 0°C to +70°C 28 Wide Plastic DIP X MAX1480A/B/C MAX1480BEPI -40°C to +85°C 28 Wide Plastic DIP 1 MAX1480CCPI 0°C to +70°C 28 Wide Plastic DIP 4 VCC1 1 28 AC1 MAX1480CEPI -40°C to +85°C 28 Wide Plastic DIP 8 VCC2 2 27 AC2 MAX1490ACPG 0°C to +70°C 24 Wide Plastic DIP 0 D1 3 26 ISO VCC1 MAX1490AEPG -40°C to +85°C 24 Wide Plastic DIP A D2 4 25 B MAX1490BCPG 0°C to +70°C 24 Wide Plastic DIP / B GND1 5 24 ISO RO DRV MAX1490BEPG -40°C to +85°C 24 Wide Plastic DIP / MAX845 MAX487 C FS 6 MAX1487 23 A †Data rate for “A” parts is up to 2.5Mbps. Data rate for “B” and “C” parts is up to 250kbps. , SD 7 22 ISO DI IN M VCC3 8 21 ISO DE IN Package Information DI 9 20 ISO COM1 A For the latest package outline information and land patterns, VCC4 10 19 ISO DI DRV go to www.maxim-ic.com/packages. Note that a “+”, “#”, or X DE 11 18 ISO VCC2 “-” in the package code indicates RoHS status only. Package 1 drawings may show a different suffix character, but the drawing 4 GND2 12 17 ISO DE DRV pertains to the package regardless of RoHS status. 9 RO 13 16 ISO COM2 PACKAGE TYPE PACKAGE CODE DOCUMENT NO. 0 VCC5 14 15 ISO RO LED 28 PDIP P28M-1 21-0044 A / B ISOLATION BARRIER DIP Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________21 © 2005 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.

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