19-0453; Rev 0; 1/96 Complete, Isolated, 3.3V RS-485/RS-422 Data Interface The MAX3480A/MAX3480B are electrically isolated RS-485/RS-422 data-communications interfaces. Transceivers, optocouplers, and a transformer are all included in one low-cost, 28-pin DIP package. A single +3.3V supply on the logic side powers both sides of the interface. The MAX3480B features reduced-slew-rate drivers that minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free data transmission at data rates up to 250kbps. The MAX3480A's driver slew rate is not limited, allowing transmission rates up to 2.5Mbps. These devices typically draw 180mA of quiescent supply current. The MAX3480B provides a low-power shutdown mode in which it consumes only 0.2A. Drivers are short-circuit current limited and are protected against excessive power dissipation by thermal shutdown circuitry that places the driver outputs into a high-impedance state. The receiver input has a fail-safe feature that guarantees a logic-high output if the input is open circuit. The MAX3480A/MAX3480B typically withstand 1600VRMS (1 minute) or 2000VRMS (1 second). Their isolated inputs and outputs meet RS-485/RS-422 specifications. ____________________________Features Isolated Data Interface to 1600VRMS (1 minute) Slew-Rate-Limited Data Transmission (MAX3480B) High-Speed, Isolated, 2.5Mbps RS-485 Interface (MAX3480A) -7V to +12V Common-Mode Input Voltage Range with Respect to Isolated Ground Single +3.3V Supply Current Limiting and Thermal Shutdown for Driver Overload Protection Standard 28-Pin DIP Package __________________Pin Configuration TOP VIEW MAX3480A/B ________________________Applications Isolated RS-485/RS-422 Data Interface Transceivers for EMI-Sensitive Applications Industrial-Control Local Area Networks Automatic Test Equipment HVAC/Building Control Networks ______________Ordering Information PART MAX3480ACPI MAX3480AEPI MAX3480BCPI MAX3480BEPI TEMP. RANGE PIN-PACKAGE 0C to +70C -40C to +85C 0C to +70C -40C to +85C 28 Plastic DIP 28 Plastic DIP 28 Plastic DIP 28 Plastic DIP DATA RATE (kbps) 2500 2500 250 250 VCC1 1 28 AC1 VCC2 2 27 AC2 D1 3 26 ISO VCC1 D2 4 25 B GND1 5 24 ISO RO DRV MAX845 MAX485 MAX487 23 A FS 6 SD 7 22 ISO DI IN VCC3 8 21 ISO DE IN DI 9 20 ISO COM1 VCC4 10 19 ISO DI DRV 18 ISO VCC2 DE 11 17 ISO DE DRV GND2 12 16 ISO COM2 RO 13 VCC5 14 15 ISO RO LED ISOLATION BARRIER DIP ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800 MAX3480A/MAX3480B _______________General Description MAX3480A/MAX3480B Complete, Isolated, 3.3V RS-485/RS-422 Data Interface ABSOLUTE MAXIMUM RATINGS LED Forward Current (DI, DE, ISO RO LED) ......................50mA Continuous Power Dissipation (TA = +70C) Plastic DIP (derate 9.09mW/C above +70C) ...............727mW Operating Temperature Ranges MAX3480_CPI ......................................................0C to +70C MAX3480_EPI ...................................................-40C to +85C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10sec) .............................+300C With Respect to GND: Supply Voltage (VCC1, VCC2, VCC4, VCC5) .........-0.3V to +3.8V Supply Voltage (VCC3) ..........................................-0.3V to +7V Control Input Voltage (SD, FS) ................-0.3V to (VCC + 0.3V) Receiver Output Voltage (RO).................-0.3V to (VCC + 0.3V) With Respect to ISO COM: Control Input Voltage (ISO DE _) .........-0.3V to (ISO VCC + 0.3V) Driver Input Voltage (ISO DI _).........-0.3V to (ISO VCC + 0.3V) Receiver Output Voltage (ISO RO _) ......-0.3V to (ISO VCC + 0.3V) Driver Output Voltage (A, B)................................-8V to +12.5V Receiver Input Voltage (A, B)..............................-8V to +12.5V 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 absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VCC = VCC1 = VCC2 = VCC4 = VCC5 = 3.0V to 3.6V, FS = 0V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = VCC1 = VCC2 = VCC4 = VCC5 = 3.3V and TA = +25C.) (Notes 1, 2, 3) PARAMETER Supply Voltage Switch Frequency Operating Supply Current Shutdown Supply Current (Note 3) SYMBOL CONDITIONS VS 3.0 3.3 3.6 V fSWH FS = VCC or open 900 ICC MAX3480A, RL = 180 DE = VCC or open RL = 54 280 MAX3480B, RL = 120 DE = VCC or open RL = 54 240 High VFSL Low FS Input Pull-Up Current IFSL FS low FS Input Leakage Current IFSM FS high Input High Voltage VIH DE, DI (Figure 1) Input Low Voltage VIL RISO DE, DI (Figure 1) TA = +25C, VISO = 50VDC Isolation Capacitance CISO TA = +25C, VISO = 50VDC Differential Driver Output (no load) VOD1 Differential Driver Output (with load) VOD2 Change in Magnitude of Driver Output Voltage for Complementary Output States VOD VOC kHz 260 200 0.2 0.8 50 10 A V 0.4 10,000 V M 10 pF 8 V 2 R = 27 (RS-485), Figure 3 R = 27 or 50, Figure 3 V pA VCC - 0.4 100 mA A 2.4 R = 50 (RS-422) 2 UNITS 600 VFSH Driver Common-Mode Output MAX FS = 0V SD = VCC3 Isolation Resistance TYP fSWL ISHDN FS Input Threshold MIN 1.5 5 Differential 0.3 Common Mode 0.3 V V R = 27 or 50, Figure 4 _______________________________________________________________________________________ 4 V Complete, Isolated, 3.3V RS-485/RS-422 Data Interface (VCC = VCC1 = VCC2 = VCC4 = VCC5 = 3.0V to 3.6V, FS = 0V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = VCC1 = VCC2 = VCC4 = VCC5 = 3.3V and TA = +25C.) (Notes 1, 2, 3) PARAMETER Input Current (A, B) SYMBOL ISO IIN Receiver Input Resistance Receiver Differential Threshold CONDITIONS DE = 0V, VCC = 0V or 3.6V RIN -7V VCM 12V VTH -7V VCM 12V MIN TYP MAX VIN = 12V VIN = 12V MAX3480A VIN = -7V 0.8 -0.8 VIN = 12V 0.25 MAX3480B UNITS 1.0 VIN = -7V mA -0.2 MAX3480A 12 MAX3480B k 48 -0.2 0.2 V Receiver Input Hysteresis VTH VCM = 0V Receiver Output/Receiver Output Low Voltage VOL DI = VCC 0.4 V Receiver Output/Receiver Output High Current IOH VOUT = 3.6V, DI = 0V 250 A ISO IOSD -7V VO 12V (Note 4) Driver Short-Circuit Current 70 mV 100 mA SWITCHING CHARACTERISTICS--MAX3480A (VCC = VCC1 = VCC2 = VCC4 = VCC5 = 3.0V to 3.6V, FS = 0V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = VCC1 = VCC2 = VCC4 = VCC5 = 3.3V and TA = +25C.) PARAMETER Driver Input to Output Propagation Delay SYMBOL tPLH tPHL CONDITIONS MIN Figures 4, 6; RDIFF = 54, CL1 = CL2 = 100pF TYP MAX 100 275 100 275 UNITS ns Driver Output Skew (Note 5) tSKEW Figures 4, 6; RDIFF = 54, CL1 = CL2 = 100pF 25 90 ns Driver Rise or Fall Time tR, tF Figures 4, 6; RDIFF = 54, CL1 = CL2 = 100pF 15 40 ns Driver Enable to Output High tZH Figures 5, 7; CL = 100pF, S2 closed 0.2 1.5 s Driver Enable to Output Low tZL Figures 5, 7; CL = 100pF, S1 closed 0.2 1.5 s Driver Disable Time from High tHZ Figures 5, 7; CL = 15pF, S2 closed 0.3 1.5 s Driver Disable Time from Low tLZ Figures 5, 7; CL = 15pF, S1 closed 0.3 1.5 s Figures 4, 8; RDIFF = 54, CL1 = CL2 = 100pF 100 225 100 225 Receiver Input to Output Propagation Delay tPLH - tPHL Differential Receiver Skew Maximum Data Rate tPLH tPHL tSKD Figures 4, 8; RDIFF = 54, CL1 = CL2 = 100pF fMAX tPLH, tPHL < 50% of data period 20 2.5 ns ns Mbps _______________________________________________________________________________________ 3 MAX3480A/MAX3480B ELECTRICAL CHARACTERISTICS (continued) MAX3480A/MAX3480B Complete, Isolated, 3.3V RS-485/RS-422 Data Interface SWITCHING CHARACTERISTICS--MAX3480B (VCC = VCC1 = VCC2 = VCC4 = VCC5 = 3.0V to 3.6V, FS = 0V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = VCC1 = VCC2 = VCC4 = VCC5 = 3.3V and TA = +25C.) PARAMETER Driver Input to Output Propagation Delay SYMBOL tPLH tPHL CONDITIONS MIN Figures 4, 6; RDIFF = 54, CL1 = CL2 = 100pF TYP MAX 1.0 2.0 1.0 2.0 UNITS s Driver Output Skew tSKEW Figures 4, 6; RDIFF = 54, CL1 = CL2 = 100pF 100 800 ns Driver Rise or Fall Time tR, tF Figures 4, 6; RDIFF = 54, CL1 = CL2 = 100pF 1.0 2.0 s Driver Enable to Output High tZH Figures 5, 7; CL = 100pF, S2 closed 50 100 s Driver Enable to Output Low tZL Figures 5, 7; CL = 100pF, S1 closed 50 100 s Driver Disable Time from Low tLZ Figures 5, 7; CL = 15pF, S1 closed 13 50 s Driver Disable Time from High tHZ Figures 5, 7; CL = 15pF, S2 closed 13 50 s Receiver Input to Output Propagation Delay tPLH Figures 4, 8; RDIFF = 54, CL1 = CL2 = 100pF 0.8 2.0 0.8 2.0 tPLH - tPHL Differential Receiver Skew Maximum Data Rate tPHL tSKD Figures 4, 8; RDIFF = 54, CL1 = CL2 = 100pF fMAX tPLH, tPHL < 50% of data period 50 0.25 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 (GND1, GND2), unless otherwise specified. Note 2: For DE and DI pin descriptions, see Detailed Block Diagram and Typical Application Circuit (Figure 1 for MAX3480A/MAX3480B). Note 3: Shutdown supply current is the current at VCC1 when shutdown is enabled. Note 4: Applies to peak current. See Typical Operating Characteristics and Applications Information. 4 _______________________________________________________________________________________ s ns Mbps Complete, Isolated, 3.3V RS-485/RS-422 Data Interface 2.7 2.6 2.5 2.4 2.3 160 OUTPUT CURRENT (mA) -80 -70 -60 -50 -40 -30 140 120 100 80 60 2.2 -20 40 2.1 -10 20 2.0 0 20 40 60 0 -6 80 -4 TEMPERATURE (C) -2 0 2 4 4 6 8 10 12 RECEIVER OUTPUT HIGH VOLTAGE vs. TEMPERATURE 0.6 0.5 0.4 0.3 0.2 5.00 MEASURED AT ISO RO DRV IRO = 8mA 4.75 OUTPUT HIGH VOLTAGE (V) MAX3480 A/B-04 MEASURED AT ISO RO DRV IRO = 8mA 0.7 2 OUTPUT LOW VOLTAGE (V) OUTPUT HIGH VOLTAGE (V) RECEIVER OUTPUT LOW VOLTAGE vs. TEMPERATURE 0.8 0 6 4.50 4.25 4.00 3.75 3.50 3.25 0.1 3.00 0 -40 80 -20 20 0 40 60 -40 80 -20 0 20 40 60 80 TEMPERATURE (C) TEMPERATURE (C) OUTPUT CURRENT vs. RECEIVER OUTPUT LOW VOLTAGE OUTPUT CURRENT vs. RECEIVER OUTPUT HIGH VOLTAGE MEASURED AT ISO RO DRV -30 60 50 40 30 20 MEASURED AT ISO RO DRV -25 OUTPUT CURRENT (mA) 70 MAX3480 A/B-02 0 MAX3480 A/B-01 -20 OUTPUT LOW VOLTAGE (V) -40 MAX3480 A/B-05 -90 OUTPUT CURRENT (mA) 2.8 180 MAX3480 A/B-06 -100 MAX3480A/B-08 DI = HIGH OR OPEN RL = 54 2.9 OUTPUT CURRENT (mA) DIFFERENTIAL OUTPUT VOLTAGE (V) 3.0 OUTPUT CURRENT vs. DRIVER OUTPUT LOW VOLTAGE OUTPUT CURRENT vs. DRIVER OUTPUT HIGH VOLTAGE MAX3480 A/B-03 DRIVER DIFFERENTIAL OUTPUT VOLTAGE vs. TEMPERATURE -20 -15 -10 -5 10 0 0 0 1.0 2.0 3.0 4.0 OUTPUT LOW VOLTAGE (V) 5.0 0 1.0 2.0 3.0 4.0 5.0 OUTPUT HIGH VOLTAGE (V) _______________________________________________________________________________________ 5 MAX3480A/MAX3480B __________________________________________Typical Operating Characteristics (VCC_ = 3.3V, TA = +25C, unless otherwise noted.) ____________________________Typical Operating Characteristics (continued) (VCC_ = 3.3V, TA = +25C, unless otherwise noted.) MAX3480A DRIVER ENABLE (AB) AND RECEIVER OUTPUT (RO) MAX3480A DRIVER INPUT (AB) AND RECEIVER OUTPUT (RO) MAX3480A SUPPLY CURRENT vs. SUPPLY VOLTAGE DE HIGH, 50 LOAD 300 SUPPLY CURRENT (mA) A A, 1V/div 2V/div B RO, 74HC240, DI, 2V/div MAX3480A-11 350 DE INPUT, 1V/div DE INPUT, 2V/div B, 2V/div 250 200 DE HIGH, 100 LOAD DE LOW, DI LOW 150 DE LOW, DI HIGH 100 50 0 3.0 100ns/div CIRCUIT OF FIGURE 2, TERMINATION: 100 MAX3480B DRIVER INPUT (AB) AND RECEIVER OUTPUT (RO) MAX3480B DRIVER ENABLE (AB) AND RECEIVER OUTPUT (RO) 3.4 3.6 3.8 MAX3480B SUPPLY CURRENT vs. SUPPLY VOLTAGE 300 DE INPUT, 1V/div A, 1V/div 2V/div B RO, 74HC240, DI, 2V/div DE HIGH, 50 LOAD 250 SUPPLY CURRENT (mA) DE INPUT, 2V/div A 3.2 SUPPLY VOLTAGE (V) B, 2V/div MAX3480B-12 100ns/div CIRCUIT OF FIGURE 2, TERMINATION: 100 DE HIGH, 100 LOAD 200 150 DE LOW, DI LOW 100 DE LOW, DI HIGH 50 0 25s/div 1s/div CIRCUIT OF FIGURE 2, TERMINATION: 100 3.0 CIRCUIT OF FIGURE 2, TERMINATION: 100 3.2 3.4 SUPPLY VOLTAGE (V) DRIVER ENABLE TIME vs. TEMPERATURE DRIVER DISABLE TIME vs. TEMPERATURE MAX3480B 10 RL = 54, DI = 0V MEASURED FROM DE TO VALID OUTPUT 1 MAX3480A/B-9 100 DRIVER DISABLE TIME (s) MAX3480A/B-10 100 DRIVER ENABLE TIME (s) MAX3480A/MAX3480B Complete, Isolated, 3.3V RS-485/RS-422 Data Interface MAX3480B 10 RL = 54, DI = 0V MEASURED FROM DE TO VALID OUTPUT 1 MAX3480A MAX3480A 0.1 0.1 -40 -20 0 20 40 TEMPERATURE (C) 6 60 80 -40 -20 0 20 40 60 TEMPERATURE (C) _______________________________________________________________________________________ 80 3.6 3.8 Complete, Isolated, 3.3V RS-485/RS-422 Data Interface PIN NAME FUNCTION PINS ON THE NON-ISOLATED SIDE 1 VCC1 Logic-Side (non-isolated side) +3.3V Supply Voltage Input. Connect to pins 2, 10, and 14. 2 VCC2 Logic-Side (non-isolated side) +3.3V Supply Voltage Input. Connect to pins 1, 10, and 14. 3, 4 D1, D2 Boost-Voltage Generator Outputs. See Figures 1 and 2. 5, 12 GND1, GND2 Logic-Side Ground Inputs. Must be connected; not internally connected. 6 FS Frequency Switch Input. If FS = VCC, switch frequency is high; if FS = 0V, switch frequency is low (normal connection). 7 SD Power-Supply Shutdown Input. Must be connected to logic ground. 8 VCC3 9 DI 10 VCC4 11 DE Driver-Enable Input. The driver outputs, A and B, are enabled by bringing DE high. The driver outputs are high impedance when DE is low. If the driver outputs 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 LED cathode through R2 (Table 1 of Figure 2). 13 RO Receiver Output. If A > B by 200mV, RO will be low; if A < B by 200mV, RO will be high. Open collector; must have pull-up (R3) to VCC (Table 1 of Figure 2). 14 VCC5 Boosted V+ Voltage Input. Must be connected as shown in Figures 1 and 2. Driver Input. With DE high, a low on DI forces output A low and output B high. Similarly, a high on DI forces output A high and output B low. Drives internal LED cathode through R1 (Table 1 of Figure 2). Logic-Side (non-isolated side) +3.3V Supply Voltage Input. Connect to pins 1, 2, and 14. Logic-Side (non-isolated side) +3.3V Supply Voltage Input. Connect to pins 1, 2, and 10. _______________________________________________________________________________________ 7 MAX3480A/MAX3480B ______________________________________________________________Pin Description MAX3480A/MAX3480B Complete, Isolated, 3.3V RS-485/RS-422 Data Interface _________________________________________________Pin Description (continued) PIN NAME FUNCTION PINS ON THE ISOLATED RS-485/RS-422 SIDE 15 ISO RO LED Isolated Receiver-Output LED Anode (input). If A > B by 200mV, ISO RO LED will be high; if A < B by 200mV, ISO RO LED will be low. 16 ISO COM2 17 ISO DE DRV 18 ISO VCC2 19 ISO DI DRV Isolated Driver-Input Drive. With DE high, a low on DI forces output A low and output B high. Similarly, a high on DI forces output A high and output B low. Open-collector output; must have pull-up (R5) to ISO VCC and be connected to ISO DI IN for normal operation (Table 1 of Figure 2). 20 ISO COM1 Isolated-Supply Common Output. Connect to ISO COM2. If RS-485 wires have a shield, connect ISO COM1 to shield via 100 resistor. 21 ISO DE IN Isolated Driver-Enable Input. Connect to ISO DE DRV for normal operation. 22 ISO DI IN Isolated Driver Input. Connect to ISO DI DRV for normal operation. 23 A 24 ISO RO DRV Isolated-Supply Common Input. Connect to ISO COM1. Isolated Driver-Enable Drive Input. The driver outputs, A and B, are enabled by bringing DE high. The driver outputs are high impedance when DE is low. If the driver outputs are enabled, the device functions as a line driver. While the driver outputs are high impedance, the device functions as a line receiver. Open collector output; must have pull-up (R4) to ISO VCC and be connected to ISO DE IN for normal operation (Table 1 of Figure 2). Isolated-Supply Positive Input Voltage. Connect to ISO VCC1. Noninverting Driver Output and Noninverting Receiver Input. Isolated Receiver-Output Drive. Connect to ISO RO LED through R6 (Table 1 of Figure 2). 25 B 26 ISO VCC1 Inverting Driver Output and Inverting Receiver Input Isolated Supply Positive Output Voltage. Connect to ISO VCC2. 27, 28 AC2, AC1 Internal Connections. Leave these pins unconnected. Note: For DE and DI pin descriptions, see Detailed Block Diagram and Typical Application Circuit. 8 _______________________________________________________________________________________ Complete, Isolated, 3.3V RS-485/RS-422 Data Interface The MAX3480B features reduced-slew-rate drivers that minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free transmission at data rates up to 250kbps. The MAX3480A's driver slew rates are not limited, allowing transmission rates up to 2.5Mbps. The MAX3480A/MAX3480B are electrically isolated, RS-485/RS-422 data-communications interface solutions. Transceivers, optocouplers, a power driver, and a transformer are in one standard 28-pin DIP package. Signals and power are internally transported across the isolation barrier (Figure 1). Power is transferred from the logic side (non-isolated side) to the isolated side of the barrier through a center-tapped transformer. Signals cross the barrier through high-speed optocouplers. A single +3.3V supply on the logic side powers both sides of the interface. The frequency-select FS is connected to GND_ in normal operation, which selects a switching frequency of approximately 600kHz. Connect to high for a higher 900kHz switching frequency. Drivers are short-circuit current limited and are protected against excessive power dissipation by thermal ISO VCC1 VCC3 OSC 1.1MHz/ 1.6MHz FS MAX3480A: MAX485 MAX3480B: MAX487 D1 MAX845 Q N ISO DI IN B D T F/F A ISO DE IN D2 Q N ISO RO DRV R RE GND1 SD ISO COM1 EXTERNAL RS-485/RS-422 WIRING VIN 3.0V TO 3.6V C1 C2 22F 0.1F D1, D2 1N914 VCC1 1 28 AC1 (MAKE NO CONNECTION) VCC2 2 27 AC2 (MAKE NO CONNECTION) D1 3 D2 BOOSTED V+ GND1 C3 0.01uF VCC3 R1 DI VCC4 LOGIC I/O DE R2 DE GND2 RO RO R3 VCC5 26 ISO VCC1 B 25 ISO RO DRV 24 4 5 FS 6 SD DI TERMINATING RESISTOR (ONE RESISTOR ON EACH END) MAX3480A/B MAX845 MAX485 MAX487 7 23 A ISO DI IN 22 8 21 9 20 ISO COM1 19 ISO DI DRV 11 18 ISO VCC2 12 17 ISO DE DRV 13 16 15 ISOLATION BARRIER RL B R7 SHIELD (OPTIONAL) A R6 200 TWISTED PAIR TO OTHER TRANSCEIVERS SH RL ISO DE IN 10 14 TWISTED PAIR TO OTHER TRANSCEIVERS R4 SHIELD (OPTIONAL) R5 R8 100 ISO COM2 NOTE: RESISTOR R8 PROTECTS THE MAX3480 FROM TRANSIENT CURRENTS BETWEEN SHIELD AND "A" & "B". ISO RO LED ISOLATION COMMON LOGIC GROUND Figure 1. Detailed Block Diagram _______________________________________________________________________________________ 9 MAX3480A/MAX3480B _______________Detailed Description MAX3480A/MAX3480B Complete, Isolated, 3.3V RS-485/RS-422 Data Interface shutdown circuitry that puts the driver outputs into a high-impedance state. The receiver input has a fail-safe feature that guarantees a logic-high output if the input is open circuit. The driver outputs are enabled by bringing DE high. Driver-enable times are typically 200ns for the MAX3480A and 50s for the MAX3480B. Allow time for the devices to be enabled before sending data. When enabled, driver outputs function as line drivers. Driver outputs are high impedance when DE is low. While outputs are high impedance, they function as line receivers. The MAX3480A/MAX3480B typically withstand 1600VRMS (1 minute) or 2000VRMS (1 second). The isolated outputs of these devices meet all RS-485/RS-422 specifications. The logic inputs can be driven from any TTL/CMOS-logic family with a series resistor, and the received data output can directly drive any of the TTL/CMOS-logic families with only a resistive pull-up. Boost Voltage The MAX3480 requires external diodes on the primary of the transformer to develop the boost voltage for the power oscillator. In normal operation, whenever one of the oscillator outputs (D1 and D2) goes low, the other EXTERNAL RS-485/RS-422 WIRING VIN 3.0V TO 3.6V C1 C2 22F 6V D1, D2 1N914 0.1F 74HC240 DI DE 18 2 17 4 16 6 14 8 3 12 15 5 13 7 27 AC2 (MAKE NO CONNECTION) VCC3 DRIVER INPUT R1 DI VCC4 DRIVER ENABLE DE GND2 RO 11 RECEIVER OUTPUT 26 ISO VCC1 B 25 D1 3 FS 6 20 9 28 AC1 (MAKE NO CONNECTION) 2 SD R2 RO 1 VCC2 D2 4 GND1 5 BOOSTED V+ C3 0.01F R3 TERMINATING RESISTOR (ONE RESISTOR ON EACH END) MAX3480A/B VCC1 VCC5 24 MAX845 MAX485 MAX487 ISO RO DRV RL B SHIELD (OPTIONAL) R7 A TWISTED PAIR TO OTHER TRANSCEIVERS 23 A ISO DI IN 7 22 8 21 9 20 ISO COM1 10 19 ISO DI DRV 11 18 12 17 13 16 14 15 R6 200 SH RL ISO DE IN R4 SHIELD (OPTIONAL) R5 ISO VCC2 R8 100 ISO DE DRV ISO COM2 NOTE: RESISTOR R8 PROTECTS THE MAX3480 FROM TRANSIENT CURRENTS BETWEEN SHIELD AND "A" & "B". ISO RO LED 10 LOGIC GROUND TWISTED PAIR TO OTHER TRANSCEIVERS ISOLATION COMMON ISOLATION BARRIER Table 1. Pull-Up and LED Drive Resistors PART R1 () R2 () R3 () R4 () R5 () R6 () R7 () MAX3480A 150 130 680 3000 1000 200 Open MAX3480B 130 330 2000 2200 3000 200 470 Figure 2. Typical Application Circuit 10 ______________________________________________________________________________________ Complete, Isolated, 3.3V RS-485/RS-422 Data Interface ISOLATION BARRIER A ISOLATION BARRIER 3.3V 3.3V DE R CL1 A VOD D DI R VID R RO B B VOC R3 A RDIFF CL2 B Figure 3. Driver DC Test Load Figure 4. Driver/Receiver Timing Test Circuit S1 500 ISO VCC1, ISO VCC2 OUTPUT UNDER TEST CL S2 Figure 5. Driver Timing Test Load _______________________________________________________Switching Waveforms VCC_ - 0.4V DI 0V VCC_ - 0.4V VCC_ - 0.4V 2 VCC_ - 0.4V 2 tPHL tPLH VCC_ - 0.4V 2 VCC_ - 0.4V 2 0V 1/2 VO tZL B tLZ A, B VO VOL A 1/2 VO VO VDIFF 0V -VO DE 10% tR VDIFF = VA - VB 2.3V OUTPUT NORMALLY LOW OUTPUT NORMALLY HIGH A, B 90% 90% VOH - 0.5V 2.3V 10% tF VOL + 0.5V 0V tZH tHZ tSKEW = | tPLH - tPHL | Figure 6. Driver Propagation Delays and Transition Times Figure 7. Driver Enable and Disable Times ______________________________________________________________________________________ 11 MAX3480A/MAX3480B _________________________________________________________________Test Circuits MAX3480A/MAX3480B Complete, Isolated, 3.3V RS-485/RS-422 Data Interface __Switching Waveforms (continued) VOH RO 1.5V VOL tPHL VID VB - VA -VID OUTPUT 0V 1.5V Driver Output Protection tPLH There are two mechanisms to prevent excessive output current and power dissipation caused by faults or by bus contention. A foldback current limit on the output stage provides immediate protection against short circuits over the whole common-mode voltage range (see Typical Operating Characteristics). In addition, a thermal shutdown circuit forces the driver outputs into a high-impedance state if the die temperature rises excessively. 0V INPUT Figure 8. Receiver Propagation Delays ____________________Function Tables Table 2. Transmitting INPUTS goes to approximately double the supply voltage. Since the circuit is symmetrical, the two outputs can be combined with diodes, filtered, and used to power the oscillator itself. The diodes on the primary side may be any fast-switching, small-signal diodes, such as the 1N914, 1N4148, or CMPD2838. The nominal value of the primary filter capacitor C3 is 0.01F. OUTPUTS DE DI B A 1 1 0 1 1 0 1 0 0 X High-Z High-Z X = Don't care High-Z = High impedance Resistor R8 provides additional protection by current limiting between the shield and the two signal wires. In the event that shielded cable is used and an external voltage or transient is inadvertently applied between the shield and the signal wires, the MAX3480 can be damaged. Although unlikely, this condition can occur during installation. The MAX3480 provides electrical isolation between logic ground and signal paths; it does not provide isolation from external shields and the signal paths. When in doubt, do not connect the shield. The MAX3480 can be damaged if resistor R8 is shorted out. Table 3. Receiving INPUTS 12 DE A-B OUTPUT ---- RO 0 +0.2V 0 0 -0.2V 1 0 Inputs open 0 ______________________________________________________________________________________ Complete, Isolated, 3.3V RS-485/RS-422 Data Interface MAX3480A/MAX3480B __________Applications Information The MAX3480A/MAX3480B are designed for bidirectional data communications on multipoint bus-transmission lines. Figure 9 shows a typical network application circuit. To minimize reflections, terminate the line at both ends with its characteristic impedance, and keep stub lengths off the main line as short as possible. The slewrate-limited MAX3480B is more tolerant of imperfect termination and stubs off the main line. The MAX3480A/MAX3480B are specified and characterized using the resistor values shown in Table 1 of Figure 2. Altering the recommended values can degrade performance. The DI and DE inputs are the cathodes of LEDs whose anodes are connected to VCC. These points are best driven by a 3.3V CMOS-logic gate with a series resistor to limit the current. The resistor values shown in Table 1 are recommended when the 74HC240 gate or equivalent is used. These values may need to be adjusted if a driving gate with dissimilar series resistance is used. DI and DE are intended to be driven through a series current-limiting resistor. Directly grounding these pins destroys the device. ______________________________________________________________________________________ 13 MAX3480A/MAX3480B Complete, Isolated, 3.3V RS-485/RS-422 Data Interface TERMINATING RESISTOR (ONE RESISTOR ON EACH END) B DI D 120 DE A A B A B RO R RE R RE RE R D RO DE D DI RO DE VIN DI VCC1 3.0V to 3.6V C1 22F 6V C2 0.1F D1, D2 1N914 VCC2 D1 D2 BOOSTED V+ 74HC240 DI DE 2 17 18 3 16 4 6 14 8 12 15 DRIVER INPUT VCC3 R1 130 DI VCC4 5 R2 DE 7 GND2 20 RO RO 9 11 28 AC1 (MAKE NO CONNECTION) 2 27 AC2 (MAKE NO CONNECTION) 3 26 ISO VCC1 4 25 B 24 MAX845 MAX485 MAX487 RECEIVER OUTPUT R3 VCC5 ISO RO DRV B R7 A 23 A 22 ISO DI IN SD 7 DRIVER ENABLE 13 1 GND1 5 FS 6 C3 0.01F TERMINATING RESISTOR (ONE RESISTOR ON EACH END) MAX3480A/B ISO DE IN 8 21 9 20 ISO COM1 10 19 ISO DI DRV 11 18 ISO VCC2 12 17 ISO DE DRV 13 16 14 15 R6, 200 SH ISOLATION BARRIER R5 R8 100 ISO COM2 ISO RO LED ISOLATED COMMON Figure 9. Typical RS-485/RS-422 Network 14 SHIELD (OPTIONAL) R4 10 LOGIC GROUND 120 ______________________________________________________________________________________ NOTE: RESISTOR R8 PROTECTS THE MAX3480 FROM TRANSIENT CURRENTS BETWEEN SHIELD AND "A" & "B". Complete, Isolated, 3.3V RS-485/RS-422 Data Interface MAX3480A/MAX3480B Table 4. Maxim's Isolated RS-485 Product Family PART No. OF Tx/Rx GUARANTEED DATA RATE (Mbps) FULL/HALF DUPLEX MAX1480A 1/1 2.50 MAX1480B 1/1 0.25 MAX1490A 1/1 2.50 MAX1490B 1/1 0.25 MAX3480A 1/1 2.50 Half MAX3480B 1/1 0.25 Half SUPPLY VOLTAGE (V) SLEW-RATE LIMITED No. OF Tx/Rx ON BUS Half No 32 5.0 Half Yes 32 5.0 Full No 32 5.0 Full Yes 32 5.0 No 32 3.3 Yes 128 3.3 ________________________________________________________Package Information DIM E A2 A3 D A E1 0-15 A1 C e L B1 B eA eB D1 Plastic DIP PLASTIC DUAL-IN-LINE PACKAGE (0.600 in.) A A1 A2 A3 B B1 C D1 E E1 e eA eB L INCHES MAX MIN 0.200 - - 0.015 0.175 0.125 0.080 0.055 0.020 0.016 0.065 0.045 0.012 0.008 0.090 0.050 0.625 0.600 0.575 0.525 - 0.100 - 0.600 0.700 - 0.150 0.120 PKG. DIM PINS P P P D D D 24 28 40 MILLIMETERS MIN MAX - 5.08 0.38 - 3.18 4.45 1.40 2.03 0.41 0.51 1.14 1.65 0.20 0.30 1.27 2.29 15.24 15.88 13.34 14.61 2.54 - 15.24 - - 17.78 3.05 3.81 INCHES MILLIMETERS MIN MAX MIN MAX 1.230 1.270 31.24 32.26 1.430 1.470 36.32 37.34 2.025 2.075 51.44 52.71 21-0044A ______________________________________________________________________________________ 15 MAX3480A/MAX3480B Complete, Isolated, 3.3V RS-485/RS-422 Data Interface 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. 16 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 (c) 1996 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.