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| 19-1941; Rev 0; 4/01 15kV ESD-Protected, Isolated, 3.3V RS-485/RS-422 Data Interfaces General Description The MAX3480EA/MAX3480EB are electrically isolated RS-485/RS-422 data-communications interfaces. The RS-485/RS-422 I/O pins are protected against 15kV electrostatic discharge (ESD) shocks, without latchup. 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 MAX3480EB 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 160kbps. The MAX3480EA's driver slew rate is not limited, allowing transmission rates up to 2.5Mbps. 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 MAX3480EA/MAX3480EB are guaranteed to withstand 1260VRMS (1min) or 1520VRMS (1s). Their isolated inputs and outputs meet RS-485/RS-422 specifications. ____________________________Features o Isolated Data Interface Guaranteed to 1260VRMS (1min) o 15kV ESD Protection for I/O Pins o Slew-Rate-Limited Data Transmission (160kbps for MAX3480EB) o High-Speed, Isolated, 2.5Mbps RS-485 Interface (MAX3480EA) o Single +3.3V Supply o Current Limiting and Thermal Shutdown for Driver Overload Protection o Standard 28-Pin DIP Package o Allows Up to 128 Transceivers on the Bus MAX3480EA/MAX3480EB Pin Configuration TOP VIEW MAX3480EA MAX3480EB VCC1 1 VCC2 D1 D2 GND1 FS SD VCC3 DI 2 3 4 5 6 7 8 9 MAX845 MAX485E MAX487E 28 AC1 27 AC2 26 ISO VCC1 25 B 24 ISO RO DRV 23 A 22 ISO DI IN 21 ISO DE IN 20 ISO COM1 19 ISO DI DRV 18 ISO VCC2 17 ISO DE DRV 16 ISO COM2 15 ISO RO LED ________________________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 Telecom Ordering Information PART MAX3480EACPI MAX3480EAEPI MAX3480EBCPI MAX3480EBEPI TEMP. RANGE PINPACKAGE* DATA RATE (kbps) 2500 2500 250 250 0C to +70C 28 Plastic DIP -40C to +85C 28 Plastic DIP 0C to +70C 28 Plastic DIP -40C to +85C 28 Plastic DIP VCC4 10 DE 11 GND2 12 RO 13 VCC5 14 *See Reliability section at end of data sheet. ISOLATION BARRIER DIP ________________________________________________________________ Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com. 15kV ESD-Protected, Isolated, 3.3V RS-485/RS-422 Data Interfaces MAX3480EA/MAX3480EB ABSOLUTE MAXIMUM RATINGS 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 (VCC3 + 0.3V) Receiver Output Voltage (RO).............-0.3V to (VCC5 + 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 LED Forward Current (DI, DE, ISO RO LED) ......................50mA Continuous Power Dissipation (TA = +70C) 28-Pin Plastic DIP (derate 9.09mW/C above +70C) ..727mW Operating Temperature Ranges MAX3480E_CPI..................................................0C to +70C MAX3480E_EPI ...............................................-40C to +85C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C 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 = 0, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25C.) (Notes 1, 2) PARAMETER Switch Frequency SYMBOL fSWL fSWH FS = 0 FS = VCC or open MAX3480EA, DE = VCC or open MAX3480EB, DE = VCC or open SD = VCC3 High Low FS low FS high DE, DI, Figure 1 DE, DI, Figure 1 TA = +25C, 1min (Note 4) High Low TA = +25C, VISO = 50VDC = 1MHz A, B, Y, and Z pins, tested at Human Body Model 100 1260 2.4 1 1 10,000 10 15 8 R = 50 (RS-422) R = 27 (RS-485), Figure 3 R = 27 or 50, Figure 3 Differential Common mode 2 1.5 5 0.3 V 0.3 0.8 VCC - 0.4 0.4 10 2.4 0.8 50 RL = RL = 54 RL = RL = 54 CONDITIONS MIN TYP 60 900 130 220 80 180 0.2 A V A pA V V VRMS V M pF kV V V 200 250 mA MAX UNITS kHz Operating Supply Current ICC Shutdown Supply Current (Note 3) FS Input Threshold FS Input Pullup Current FS Input Leakage Current Input High Voltage Input Low Voltage Isolation Voltage Shutdown Input Threshold Isolation Resistance Isolation Capacitance ESD Protection Differential Driver Output (No Load) Differential Driver Output Change in Magnitude of Driver Output Voltage for Complementary Output States ISHDN VFSH VFSL IFSL IFSM VIH VIL VISO VSDH VSDL RISO CISO ESD VOD1 VOD2 VOD 2 _______________________________________________________________________________________ 15kV ESD-Protected, Isolated, 3.3V RS-485/RS-422 Data Interfaces ELECTRICAL CHARACTERISTICS (continued) (VCC = VCC1 = VCC2 = VCC4 = VCC5 = +3.0V to +3.6V, FS = 0, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25C.) (Notes 1, 2) PARAMETER Driver Common-Mode Output SYMBOL VOC CONDITIONS R = 27 or 50, Figure 4 DE = 0, VCC = 0 or +3.6V -7V VCM 12V VCM = 0 DI = VCC VOUT = +3.6V, DI = 0 -7V VO 12V (Note 5) 100 MAX3480EA MAX3480EB MAX3480EA MAX3480EB VIN = +12V VIN = -7V VIN = +12V VIN = -7V 48 48 -0.2 70 0.4 250 0.2 MIN TYP MAX 4 0.25 -0.2 0.25 -0.2 k V mV V A mA mA UNITS V MAX3480EA/MAX3480EB Input Current (A, B) ISO IIN Receiver Input Resistance Receiver Differential Threshold Receiver Input Hysteresis Receiver Output Low Voltage Receiver Output High Current Driver Short-Circuit Current RIN VTH VTH VOL IOH ISO IOSD -7V VCM 12V SWITCHING CHARACTERISTICS--MAX3480EA (VCC = VCC1 = VCC2 = VCC4 = VCC5 = +3.0V to +3.6V, FS = 0, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25C.) PARAMETER Driver Input to Output Propagation Delay Driver Output Skew Driver Rise or Fall Time Driver Enable to Output High Driver Enable to Output Low Driver Disable Time from High Driver Disable Time from Low Receiver Input to Output Propagation Delay SYMBOL tPLH tPHL tSKEW tR, tF tZH tZL tHZ tLZ tPLH tPHL tSKD fMAX CONDITIONS Figures 4, 6; RDIFF = 54, CL1 = CL2 = 100pF Figures 4, 6; RDIFF = 54, CL1 = CL2 = 100pF (Note 5) Figures 4, 6; RDIFF = 54, CL1 = CL2 = 100pF Figures 5, 7; CL = 100pF, S2 closed Figures 5, 7; CL = 100pF, S1 closed Figures 5, 7; CL = 15pF, S2 closed Figures 5, 7; CL = 15pF, S1 closed Figures 4, 8; RDIFF = 54, CL1 = CL2 = 100pF Figures 4, 8; RDIFF = 54, CL1 = CL2 = 100pF tSKEW, tSKD 25% of data period 2.5 MIN TYP 100 100 25 15 0.5 0.5 0.6 0.6 100 120 20 MAX 275 275 100 50 1.8 1.8 1.8 1.8 225 225 100 UNITS ns ns ns s s s s ns ns Mbps tPLH - tPHL Differential Receiver Skew Maximum Data Rate _______________________________________________________________________________________ 3 15kV ESD-Protected, Isolated, 3.3V RS-485/RS-422 Data Interfaces MAX3480EA/MAX3480EB SWITCHING CHARACTERISTICS--MAX3480EB (VCC = VCC1 = VCC2 = VCC4 = VCC5 = +3.0V to +3.6V, FS = 0, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC = +3.3V and TA = +25C.) PARAMETER Driver Input to Output Propagation Delay Driver Output Skew Driver Rise or Fall Time Driver Enable to Output High Driver Enable to Output Low Driver Disable Time from Low Driver Disable Time from High Receiver Input to Output Propagation Delay SYMBOL tPLH tPHL tSKEW tR, tF tZH tZL tLZ tHZ tPLH tPHL tSKD fMAX CONDITIONS Figures 4, 6; RDIFF = 54, CL1 = CL2 = 100pF Figures 4, 6; RDIFF = 54, CL1 = CL2 = 100pF Figures 4, 6; RDIFF = 54, CL1 = CL2 = 100pF Figures 5, 7; CL = 100pF, S2 closed Figures 5, 7; CL = 100pF, S1 closed Figures 5, 7; CL = 15pF, S1 closed Figures 5, 7; CL = 15pF, S2 closed Figures 4, 8; RDIFF = 54, CL1 = CL2 = 100pF Figures 4, 8; RDIFF = 54, CL1 = CL2 = 100pF tSKEW, tSKD 25% of data period 160 MIN TYP 1.5 1.2 300 1.0 1.2 1.0 1.5 2.0 0.6 1.4 750 MAX 3.0 3.0 1200 2.0 4.5 4.5 4.5 4.5 3.0 3.0 1500 UNITS s ns s s s s s s ns kbps tPLH - tPHL Differential Receiver Skew Maximum Data Rate 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 MAX3480EA/MAX3480EB). Note 3: Shutdown supply current is the current at VCC1 when shutdown is enabled. Note 4: Limit guaranteed by applying 1520VRMS for 1s. Test voltage is applied between all pins on one side of the package to all pins on the other side of the package. For example, between pins 1 and 14, and 15 and 28. Note 5: Applies to peak current. See Typical Operating Characteristics and Applications Information. 4 _______________________________________________________________________________________ 15kV ESD-Protected, Isolated, 3.3V RS-485/RS-422 Data Interfaces __________________________________________Typical Operating Characteristics (VCC_ = +3.3V, TA = +25C, Figure 1, unless otherwise noted.) MAX3480EA/MAX3480EB DRIVER DIFFERENTIAL OUTPUT VOLTAGE vs. TEMPERATURE MAX3480EA/EB toc01 OUTPUT CURRENT vs. DRIVER OUTPUT HIGH VOLTAGE MAX3480EA/EB toc02 OUTPUT CURRENT vs. DRIVER OUTPUT LOW VOLTAGE 160 OUTPUT CURRENT (mA) 140 120 100 80 60 40 20 0 MAX3480EA/EB toc03 3.0 DIFFERENTIAL OUTPUT VOLTAGE (V) 2.9 2.8 2.7 2.6 2.5 2.4 2.3 2.2 2.1 2.0 -40 -20 0 20 40 60 80 TEMPERATURE (C) DI = HIGH OR OPEN RL = 54 -100 -90 -80 OUTPUT CURRENT (mA) -70 -60 -50 -40 -30 -20 -10 0 -6 -4 -2 0 2 4 6 OUTPUT HIGH VOLTAGE (V) 180 0 2 4 6 8 10 12 OUTPUT LOW VOLTAGE (V) RECEIVER OUTPUT LOW VOLTAGE vs. TEMPERATURE MAX3480EA/EB toc04 RECEIVER OUTPUT HIGH VOLTAGE vs. TEMPERATURE 4.75 OUTPUT HIGH VOLTAGE (V) 4.50 4.25 4.00 3.75 3.50 3.25 3.00 MEASURED AT ISO RO DRV IRO = 8mA MAX3480EA/EB toc05 0.8 0.7 OUTPUT LOW VOLTAGE (V) 0.6 0.5 0.4 0.3 0.2 0.1 0 -40 MEASURED AT ISO RO DRV IRO = 8mA 5.00 -20 0 20 40 60 80 -40 -20 0 20 40 60 80 TEMPERATURE (C) TEMPERATURE (C) OUTPUT CURRENT vs. RECEIVER OUTPUT LOW VOLTAGE MAX3480EA/EB toc06 OUTPUT CURRENT vs. RECEIVER OUTPUT HIGH VOLTAGE MEASURED AT ISO RO DRV 70 OUTPUT CURRENT (mA) 60 50 40 30 20 10 0 MAX3480EA/EB toc07 80 70 OUTPUT CURRENT (mA) 60 50 40 30 20 10 0 0 MEASURED AT ISO RO DRV 80 1.0 2.0 3.0 4.0 5.0 0 1.0 2.0 3.0 4.0 5.0 OUTPUT LOW VOLTAGE (V) DIFFERENTIAL OUTPUT VOLTAGE (V) _______________________________________________________________________________________ 5 15kV ESD-Protected, Isolated, 3.3V RS-485/RS-422 Data Interfaces MAX3480EA/MAX3480EB Typical Operating Characteristics (continued) (VCC_ = +3.3V, TA = +25C, Figure 1, unless otherwise noted.) MAX3480EA DRIVER INPUT (AB) AND RECEIVER OUTPUT (RO) MAX3480EA/EB toc08 MAX3480EA DRIVER ENABLE (AB) AND RECEIVER OUTPUT (RO) MAX3480EA/EB toc09 MAX3480EA SUPPLY CURRENT vs. SUPPLY VOLTAGE DE INPUT, 1V/div SUPPLY CURRENT (mA) DI INPUT, 2V/div DE HIGH, 50 LOAD 300 250 200 150 100 50 0 DE LOW, DI HIGH, RL = A 2V/div B RO, 74HC240, 2V/div DE HIGH, 100 LOAD DE LOW, DI LOW, RL = A, 1V/div B, 2V/div 100ns/div CIRCUIT OF FIGURE 2, TERMINATION: 100 100ns/div CIRCUIT OF FIGURE 2, TERMINATION: 100 3.0 3.2 3.4 3.6 3.8 SUPPLY VOLTAGE (V) MAX3480EB DRIVER INPUT (AB) AND RECEIVER OUTPUT (RO) MAX3480EA/EB toc11 MAX3480EB DRIVER ENABLE (DE) AND DRIVER OUTPUT (AB) MAX3480EA/EB toc12 MAX3480EB SUPPLY CURRENT vs. SUPPLY VOLTAGE DE 1V/div SUPPLY CURRENT (mA) DE HIGH, 50 LOAD 250 200 150 DE LOW, DI LOW, RL = 100 DE LOW, DI HIGH, RL = 50 0 DE HIGH, 100 LOAD MAX3480EA/EB toc13 300 DI INPUT, 2V/div A 2V/div B A 2V/div B 2V/div RO, 74HC240, 2V/div 1s/div 20s/div 3.0 3.2 3.4 3.6 3.8 SUPPLY VOLTAGE (V) DRIVER ENABLE TIME vs. TEMPERATURE MAX3480EA/EB toc14 DRIVER ENABLE TIME vs. TEMPERATURE MAX3480EA/EB TOC15 2.5 2.0 DRIVER ENABLE TIME (s) MAX3480EB 1.5 RL = 54, DI = 0 MEASURED FROM DE TO VALID OUTPUT MAX3480EA DRIVER ENABLE TIME (s) 2.0 MAX3480EB 1.5 RL = 54, DI = 0V MEASURED FROM DE TO VALID OUTPUT 1.0 MAX3480EA 1.0 0.5 0 -40 -20 0 20 40 60 80 TEMPERATURE (C) 0.5 -40 -20 0 20 40 60 80 TEMPERATURE (C) 6 _______________________________________________________________________________________ MAX3480EA/EB toc10 350 15kV ESD-Protected, Isolated, 3.3V RS-485/RS-422 Data Interfaces ______________________________________________________________Pin Description PIN 1 2 3, 4 5, 12 6 7 8 9 10 NAME VCC1 VCC2 D1, D2 GND1, GND2 FS SD VCC3 DI VCC4 FUNCTION Logic-Side (Nonisolated Side) +3.3V Supply Voltage Input. Connect to pins 2, 10, and 14. Logic-Side (Nonisolated Side) +3.3V Supply Voltage Input. Connect to pins 1, 10, and 14. Boost-Voltage Generator Outputs. See Figures 1 and 2. Logic-Side Ground Inputs. Must be connected; not internally connected. Frequency Switch Input. If VFS = VCC, switch frequency is high; if FS = 0, switch frequency is low (normal connection). Power-Supply Shutdown Input. Must be connected to logic ground. 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). Logic-Side (Nonisolated Side) +3.3V Supply Voltage Input. Connect to pins 1, 2, and 14. 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). Receiver Output. If A > B by 200mV, RO is low; if A < B by 200mV, RO is high. Open collector; must have pullup (R3) to VCC (Table 1). Logic-Side (Nonisolated Side) +3.3V Supply Voltage Input. Connect to pins 1, 2, and 10. PINS ON THE NONISOLATED SIDE MAX3480EA/MAX3480EB 11 DE 13 14 RO VCC5 _______________________________________________________________________________________ 7 15kV ESD-Protected, Isolated, 3.3V RS-485/RS-422 Data Interfaces MAX3480EA/MAX3480EB _________________________________________________Pin Description (continued) PIN NAME FUNCTION PINS ON THE ISOLATED RS-485/RS-422 SIDE 15 16 ISO RO LED ISO COM2 Isolated Receiver-Output LED Anode (Input). If A > B by 200mV, ISO RO LED is high; if A < B by 200mV, ISO RO LED is low. 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 pullup (R4 in Figure 1) to ISO VCC and be connected to ISO DE IN for normal operation (Table 1). Isolated-Supply Positive Input Voltage. Connect to ISO VCC1. 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 pullup (R5 in Figure 1) to ISO VCC and be connected to ISO DI IN for normal operation (Table 1). Isolated-Supply Common Output. Connect to ISO COM2. If RS-485 wires have a shield, connect ISO COM1 to shield through 100 resistor. Isolated Driver-Enable Input. Connect to ISO DE DRV for normal operation. Isolated Driver Input. Connect to ISO DI DRV for normal operation. Noninverting Driver Output and Noninverting Receiver Input Isolated Receiver-Output Drive. Connect to ISO RO LED through R6 (Table 1 and Figure 1). Inverting Driver Output and Inverting Receiver Input Isolated Supply Positive Output Voltage. Connect to ISO VCC2. Internal Connections. Leave these pins unconnected. 17 ISO DE DRV 18 19 ISO VCC2 ISO DI DRV 20 21 22 23 24 25 26 27, 28 ISO COM1 ISO DE IN ISO DI IN A ISO RO DRV B ISO VCC1 AC2, AC1 Note: For DE and DI pin descriptions, see Detailed Block Diagram. 8 _______________________________________________________________________________________ 15kV ESD-Protected, Isolated, 3.3V RS-485/RS-422 Data Interfaces _______________Detailed Description The MAX3480EA/MAX3480EB 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 VCC3 isolation barrier (Figure 1). Power is transferred from the logic side (nonisolated 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. ISO VCC1 MAX3480EA/MAX3480EB MAX845 Q FS OSC 1.1MHz/ 1.6MHz T F/F N D1 ISO DI IN D D2 ISO DE IN ISO RO DRV RE R MAX3480EA: MAX485E MAX3480EB: MAX487E B A Q N SD GND1 ISO COM1 EXTERNAL RS-485/RS-422 WIRING TERMINATING RESISTOR (ONE RESISTOR ON EACH END) 28 AC1 (MAKE NO CONNECTION) 27 AC2 (MAKE NO CONNECTION) 26 ISO VCC1 B 25 ISO RO DRV 24 MAX845 MAX485E MAX487E 23 A ISO DI IN 22 21 ISO DE IN R4* R5* NOTE: RESISTOR R8 PROTECTS THE MAX3480E FROM TRANSIENT CURRENTS BETWEEN SHIELD AND A AND B. SHIELD (OPTIONAL) R6* B R7* A SH SHIELD (OPTIONAL) TWISTED PAIR TO OTHER TRANSCEIVERS RL TWISTED PAIR TO OTHER TRANSCEIVERS RL VIN +3.0V TO +3.6V C1 22F C2 0.1F D1, D2 1N914 VCC1 VCC2 MAX3480EA/EB 1 2 D1 3 D2 4 5 BOOSTED V+ C3 0.01F GND1 FS 6 SD VCC3 7 8 9 10 11 12 13 14 R1* DI LOGIC I/O R2* DE DI VCC4 DE GND2 20 ISO COM1 19 ISO DI DRV 18 ISO VCC2 17 ISO DE DRV 16 15 ISOLATION BARRIER ISO COM2 ISO RO LED R8 100 RO RO R3* VCC5 ISOLATION COMMON *SEE TABLE 1. LOGIC GROUND C4 270pF 4kV Figure 1. Detailed Block Diagram Table 1. Pullup and LED Drive Resistors PART MAX3480EA MAX3480EB R1 () 100 100 R2 () 100 100 R3 () 680 2000 R4 () 3600 3600 R5 () 1000 3600 R6 () 200 200 R7 () Open 430 _______________________________________________________________________________________ 9 15kV ESD-Protected, Isolated, 3.3V RS-485/RS-422 Data Interfaces MAX3480EA/MAX3480EB The MAX3480EB 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 160kbps. The MAX3480EA's driver slew rates are not limited, allowing transmission rates up to 2.5Mbps. 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 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 500ns for the MAX3480EA and 1s for the MAX3480EB. 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. EXTERNAL RS-485/RS-422 WIRING TERMINATING RESISTOR (ONE RESISTOR ON EACH END) 28 AC1 (MAKE NO CONNECTION) 27 AC2 (MAKE NO CONNECTION) 26 ISO VCC1 B 25 24 MAX845 MAX485E MAX487E ISO RO DRV B R7* A ISO DI IN ISO DE IN R4* R5* NOTE: RESISTOR R8 PROTECTS THE MAX3480E FROM TRANSIENT CURRENTS BETWEEN SHIELD AND A AND B. SHIELD (OPTIONAL) SH SHIELD (OPTIONAL) TWISTED PAIR TO OTHER TRANSCEIVERS RL TWISTED PAIR TO OTHER TRANSCEIVERS RL VIN +3.0V TO +3.6V C1 22F 6V C2 0.1F D1, D2 1N914 VCC1 VCC2 MAX3480EA/EB 1 2 D1 3 D2 4 GND1 5 FS 6 SD VCC3 7 8 9 10 11 12 13 14 ISOLATION BARRIER BOOSTED V+ C3 0.01F 74HC240 4 6 DI DE 2 17 18 3 8 15 13 20 RO 9 11 10 *SEE TABLE 1. LOGIC GROUND RECEIVER OUTPUT R3* 16 14 12 5 DRIVER ENABLE 7 R2* DRIVER INPUT R1* 23 A 22 21 R6* DI VCC4 DE GND2 RO VCC5 20 ISO COM1 19 ISO DI DRV 18 ISO VCC2 17 ISO DE DRV 16 15 ISO COM2 ISO RO LED R8 100 ISOLATION COMMON C4 270pF 4kV Figure 2. Typical Application Circuit 10 ______________________________________________________________________________________ 15kV ESD-Protected, Isolated, 3.3V RS-485/RS-422 Data Interfaces _________________________________________________________________Test Circuits ISOLATION BARRIER A R VOD R B VOC +3.3V DE ISOLATION BARRIER +3.3V CL1 A DI RDIFF VID B CL2 B MAX3480EA/MAX3480EB D A R R3 RO Figure 3. Driver DC Test Load Figure 4. Driver/Receiver Timing Test Circuit 500 OUTPUT UNDER TEST CL S1 ISO VCC1, ISO VCC2 S2 Figure 5. Driver Timing Test Load _______________________________________________________Switching Waveforms VCC_ - 0.4V VCC_ - 0.4V 2 tPLH tPHL VCC_ - 0.4V 2 1/2 VO A, B VO A 1/2 VO VDIFF VO 0 -VO 10% tR 90% VDIFF = VA - VB 90% tF tSKEW = | tPLH - tPHL | 10% VOL A, B 2.3V 0 tZH tHZ 2.3V OUTPUT NORMALLY LOW OUTPUT NORMALLY HIGH VOH - 0.5V VOL + 0.5V DE VCC_ - 0.4V DI VCC_ - 0.4V 2 VCC_ - 0.4V 2 0 0 tZL tLZ B Figure 6. Driver Propagation Delays and Transition Times Figure 7. Driver Enable and Disable Times ______________________________________________________________________________________ 11 15kV ESD-Protected, Isolated, 3.3V RS-485/RS-422 Data Interfaces MAX3480EA/MAX3480EB __Switching Waveforms (continued) The MAX3480EA/MAX3480EB withstand 1260V RMS (1 min) or 1560VRMS (1s). The isolated outputs of these devices meet all RS-485/RS-422 specifications. Boost Voltage VOH VOL VID -VID 0 1.5V tPHL INPUT tSKD = |tPLH - tPHL| OUTPUT tPLH 0 1.5V RO V B - VA The MAX3480EA/MAX3480EB require 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 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. Figure 8. Receiver Propagation Delays Driver Output Protection 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. Resistor R8 (Figures 1 and 2) 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 MAX3480EA/MAX3480EB can be damaged. Although unlikely, this condition can occur during installation. The MAX3480EA/MAX3480EB provide electrical isolation between logic ground and signal paths; they do not provide isolation from external shields and the signal paths. When in doubt, do not connect the shield. The MAX3480EA/MAX3480EB can be damaged if resistor R8 is shorted out. Function Tables Table 2. Transmitting INPUTS DE 1 1 0 DI 1 0 X B 0 1 High-Z OUTPUTS A 1 0 High-Z X = Don't care High-Z = High impedance Table 3. Receiving INPUTS DE 0 0 0 A-B +0.2V -0.2V Inputs open OUTPUT -- -- RO 0 1 0 Applications Information The MAX3480EA/MAX3480EB provide extra protection against ESD. The MAX3480EA/MAX3480EB are intended for harsh environments where high-speed communication is important. These devices eliminate the need for transient suppressor diodes or the use of discrete protection components. The standard (non-E) MAX3480A/MAX3480B are recommended for applications where cost is critical. 12 ______________________________________________________________________________________ 15kV ESD-Protected, Isolated, 3.3V RS-485/RS-422 Data Interfaces MAX3480EA/MAX3480EB RC 1M CHARGE-CURRENT LIMIT RESISTOR HIGHVOLTAGE DC SOURCE RD 1500 DISCHARGE RESISTANCE DEVICE UNDER TEST IP 100% 90% AMPERES Ir PEAK-TO-PEAK RINGING (NOT DRAWN TO SCALE) Cs 100pF STORAGE CAPACITOR 36.8% 10% 0 0 tRL TIME tDL CURRENT WAVEFORM Figure 9. Human Body ESD Test Model Figure 10. Human Body Model Current Waveform 15kV ESD Protection As with all Maxim devices, ESD-protection structures are incorporated on all pins to protect against electrostatic discharges encountered during handling and assembly. The driver outputs and receiver inputs have extra protection against static electricity. Maxim's engineers developed state-of-the-art structures to protect these pins against ESD of 15kV without damage. The ESD structures withstand high ESD in all states: normal operation, shutdown, and power-down. After an ESD event, Maxim's MAX3480EA/MAX3480EB keep working without latchup. An isolation capacitor of 270pF 4kV should be placed between ISO COM and logic ground for optimal performance against an ESD pulse with respect to logic ground. ESD protection can be tested in various ways; the transmitter outputs and receiver inputs of this product family are characterized for protection to 15kV using the Human Body Model. 100pF capacitor charged to the ESD voltage of interest, which is then discharged into the test device through a 1.5k resistor. Machine Model The Machine Model for ESD tests all pins using a 200pF storage capacitor and zero discharge resistance. Its objective is to simulate the stress caused by contact that occurs with handling and assembly during manufacturing. Of course, all pins require this protection during manufacturing--not just inputs and outputs. Therefore, after PC board assembly, the Machine Model is less relevant to l/O ports. The MAX3480EA/MAX3480EB are designed for bidirectional data communications on multipoint bus-transmission lines. Figure 11 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 MAX3480EB is more tolerant of imperfect termination and stubs off the main line. The MAX3480EA/MAX3480EB are specified and characterized using the resistor values shown in Table 1. 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. DI and DE are intended to be ESD Test Conditions The +15kV ESD test specifications apply only to the A, B, Y, and Z I/O pins. The test surge may be referenced to either the ISO COM or to the nonisolated GND (this presupposes that a bypass capacitor is installed between VCC2 and the nonisolated GND). Human Body Model Figure 9 shows the Human Body Model, and Figure 10 shows the current waveform it generates when discharged into a low impedance. This model consists of a ______________________________________________________________________________________ 13 15kV ESD-Protected, Isolated, 3.3V RS-485/RS-422 Data Interfaces MAX3480EA/MAX3480EB driven through a series current-limiting resistor. Directly grounding these pins destroys the device. Reliability These products contain transformers, optocouplers, and capacitors, in addition to several monolithic ICs and diodes. As such, the reliability expectations more closely represent those of discrete optocouplers, rather than the more robust characteristics of monolithic silicon ICs. The reliability testing programs for these multicomponent devices may be viewed on the Maxim website (www.maxim-ic.com) under Technical Support, Technical Reference, Multichip Products. Table 4. Maxim's 15kV ESD-Protected Isolated RS-485 Product Family PART MAX1480EA MAX1480EC MAX1490EA MAX1490EB MAX3480EA MAX3480EB NO. OF Tx/Rx 1/1 1/1 1/1 1/1 1/1 1/1 GUARANTEED DATA RATE (Mbps) 2.50 0.25 2.50 0.25 2.50 0.25 FULL/HALF DUPLEX Half Half Full Full Half Half SLEW-RATE LIMITED No Yes No Yes No Yes NO. OF Tx/Rx ON BUS 32 32 32 32 32 128 SUPPLY VOLTAGE (V) 5.0 5.0 5.0 5.0 3.3 3.3 14 ______________________________________________________________________________________ 15kV ESD-Protected, Isolated, 3.3V RS-485/RS-422 Data Interfaces MAX3480EA/MAX3480EB TERMINATING RESISTOR (ONE RESISTOR ON EACH END) B 120 A A B A B R D DI DE RO RE RE R D RE R D RO DE DI RO DE DI VIN +3.0V TO +3.6V C1 22F 6V C2 0.1F D1, D2 1N914 VCC1 VCC2 D1 D2 BOOSTED V+ C3 0.01F MAX3480EA/EB 1 2 3 4 MAX845 MAX485E MAX487E TERMINATING RESISTOR (ONE RESISTOR ON EACH END) 28 AC1 (MAKE NO CONNECTION) 27 AC2 (MAKE NO CONNECTION) 26 ISO VCC1 25 B 24 ISO RO DRV R7* A R6* R4* SH SHIELD (OPTIONAL) 120 B GND1 5 FS 6 SD 7 VCC3 23 A 22 ISO DI IN 21 ISO DE IN 74HC240 4 6 16 14 12 5 DRIVER ENABLE R2* 7 DRIVER INPUT R1* DI DE 2 17 18 3 8 9 10 11 12 13 14 ISOLATION BARRIER 8 15 13 20 DI VCC4 DE GND2 RO 20 ISO COM1 19 ISO DI DRV 18 ISO VCC2 17 ISO DE DRV 16 15 ISO COM2 ISO RO LED ISOLATION COMMON NOTE: RESISTOR R8 PROTECTS THE MAX3480E FROM TRANSIENT CURRENTS BETWEEN SHIELD AND A AND B. R8 100 R5* RO 9 10 11 RECEIVER OUTPUT R3* VCC5 *SEE TABLE 1. LOGIC GROUND C4 270pF 4kV Figure 11. Typical RS-485/RS-422 Network ______________________________________________________________________________________ 15 15kV ESD-Protected, Isolated, 3.3V RS-485/RS-422 Data Interfaces MAX3480EA/MAX3480EB Package Information PDIPW.EPS 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) 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. |
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