* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download MAX1490AEPG WORD
Wien bridge oscillator wikipedia , lookup
Power MOSFET wikipedia , lookup
UniPro protocol stack wikipedia , lookup
Phase-locked loop wikipedia , lookup
Loudspeaker wikipedia , lookup
Regenerative circuit wikipedia , lookup
Flip-flop (electronics) wikipedia , lookup
Integrating ADC wikipedia , lookup
Radio transmitter design wikipedia , lookup
Voltage regulator wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Immunity-aware programming wikipedia , lookup
Two-port network wikipedia , lookup
Power electronics wikipedia , lookup
Wilson current mirror wikipedia , lookup
Schmitt trigger wikipedia , lookup
Operational amplifier wikipedia , lookup
Valve audio amplifier technical specification wikipedia , lookup
Valve RF amplifier wikipedia , lookup
Transistor–transistor logic wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Current mirror wikipedia , lookup
19-0259; Rev 5; 5/05 Complete, Isolated RS-485/RS-422 Data Interface The MAX1480A/MAX1480B/MAX1480C/MAX1490A/ MAX1490B are complete, electrically isolated, RS-485/ RS-422 data-communications interface solutions in a hybrid microcircuit. Transceivers, optocouplers, and a transformer provide a complete interface in a standard DIP package. A single +5V supply on the logic side powers both sides of the interface. The MAX1480B/MAX1480C/MAX1490B feature reducedslew-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 MAX1480A/MAX1490A driver slew rate is not limited, allowing transmission rates up to 2.5Mbps. The MAX1480A/B/C are designed for half-duplex communication, while the MAX1490A/B feature full-duplex communication. Drivers are short-circuit current limited and protected against excessive power dissipation by thermal shutdown circuitry that places the driver outputs into a highimpedance state. The receiver input h as a fail-safe feature that guarantees a known output (RO low for the MAX1480A/B/C, RO high for the MAX1490A/B/C) if the input is open circuit. The MAX1480A/MAX1480B/MAX1480C/MAX1490A/ MAX1490B typically withstand 1600VRMS (1 minute) or 2000VRMS (1 second). Their isolated outputs meet all RS-485/RS-422 specifications. The MAX1480A/B/C are available in a 28-pin DIP package, and the MAX1490A/B are available in a 24-pin DIP package. Applications Next-Generation Device Features ♦ For Integrated ESD Protection MAX1480E/MAX1490E: ±15kV ESD-Protected, Isolated RS-485/RS-422 Data Interfaces ♦ For Space-Constrained Applications MAX3157: High CMRR, RS-485 Transceiver with ±50V Isolation Ordering Information PART† TEMP RANGE PIN-PACKAGE MAX1480ACPI 0°C to +70°C 28 Wide Plastic DIP MAX1480AEPI -40°C to +85°C 28 Wide Plastic DIP Ordering Information continued at end of data sheet. †Data rate for “A” parts is up to 2.5Mbps. Data rate for “B” and “C” parts is up to 250kbps. Selection Table PART HALF/ FULL DUPLEX DATA RATE (MBPS) SLEWRATE LIMITED DRIVER ENABLE TIME (µS) MAX1480A Half 2.5 No 0.2 MAX1480B Half 0.25 Yes 35 MAX1480C Half 0.25 Yes 0.5 MAX1490A Full 2.5 No — MAX1490B Full 0.25 Yes — Pin Configurations TOP VIEW 1 24 AC1 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 GND1 5 20 A HVAC/Building Control Networks FS 6 MAX488 MAX490 VCC1 MAX845 Isolated RS-485/RS-422 Data Interface 19 B 7 18 Z VCC3 8 17 Y SD DI 9 MAX1490A/B 16 ISO COM1 15 ISO DI DRV VCC4 10 RO 11 14 ISO VCC2 13 ISO RO LED GND2 12 ISOLATION BARRIER DIP Pin Configurations continued at end of data sheet. Maxim Integrated Products 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. 1 MAX1480A/B/C/MAX1490A/B General Description MAX1480A/B/C/MAX1490A/B Complete, Isolated RS-485/RS-422 Data Interface ABSOLUTE MAXIMUM RATINGS With Respect to GND_ Supply Voltage (VCC_)...........................................-0.3V to +6V Control Input Voltage (SD, FS)...............-0.3V to (VCC_ + 0.3V) Receiver Output Voltage (RO, RO) ........-0.3V to (VCC_ + 0.3V) Output Switch Voltage (D1, D2)........................................+12V 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, Y, Z ) ......................-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 = +70°C) 24-Pin Plastic DIP (derate 8.7mW°C above +70°C) .....696mW 28-Pin Plastic DIP (derate 9.09mW/°C above +70°C) ..727mW Operating Temperature Ranges MAX1480_CPI/MAX1490_CPG ............................0°C to +70°C MAX1480_EPI/MAX1490_EPG .........................-40°C to +85°C Storage Temperature Range .............................-65°C to +160°C Lead Temperature (soldering, 10s) .................................+300°C 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_ = 5V ±10%, VFS = VCC_, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC_ = 5V and TA = +25°C.) (Notes 1, 2) PARAMETER Switch Frequency Operating Supply Current SYMBOL CONDITIONS 535 fSWH FS = VCC_ or open 725 ICC MAX1480A, DE´ = VCC_ or open RL = ∞, +25°C only 60 RL = 54Ω 120 MAX1480B, DE´ = VCC_ or open RL = ∞, +25°C only 35 RL = 54Ω 95 MAX1480C, DE´ = VCC_ or open RL = ∞, +25°C only 35 RL = 54Ω 95 RL = ∞, +25°C only 100 RL = 54Ω 170 MAX1490B Shutdown Input Threshold ISHDN SD = VCC_ VSDH High VSDL Low VFSH High VFSL Low RL = ∞, +25°C only 65 RL = 54Ω 130 FS low FS Input Leakage Current FS high Input Low Voltage VIH DE´, DI´ VIL DE´, DI´ Isolation Resistance RISO TA = +25°C, VISO = 50VDC Isolation Capacitance CISO TA = +25°C, VISO = 50VDC Differential Driver Output (No Load) VOD1 2 90 45 75 mA 150 125 µA 2.4 0.8 V pA 2.4 0.8 50 10 V µA pA V VCC_ - 0.4 0.4 100 UNITS kHz 10 FS Input Pullup Current Input High Voltage MAX 0.2 Shutdown Input Leakage Current FS Input Threshold TYP VFS = 0V MAX1490A Shutdown Supply Current (Note 3) MIN fSWL V 10,000 MΩ 10 pF 8 V Complete, Isolated RS-485/RS-422 Data Interface (VCC_ = 5V ±10%, VFS = VCC_, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC_ = 5V and TA = +25°C.) (Notes 1, 2) PARAMETER SYMBOL Differential Driver Output (With Load) VOD2 Change in Magnitude of Differential Output Voltage for Complementary Output States ∆VOD Driver Common-Mode Output Voltage VOC Input Current (A, B) ISO IIN CONDITIONS R = 50Ω (RS-422) DE´ = 0V, VCC_ = 0V or 5.5V VIN = 12V VIN = -7V RIN -7V ≤ VCM ≤ 12V Receiver Differential Threshold Voltage VTH -7V ≤ VCM ≤ 12V ∆VTH 1.5 MAX 5.0 Differential 0.3 Common mode 0.3 UNITS V V R = 27Ω or 50Ω, Figure 4 Receiver Input Resistance Receiver Input Hysteresis TYP 2 R = 27Ω (RS-485), Figure 4 R = 27Ω or 50Ω, Figure 4 MIN 4 MAX1480A/B/C V 1 MAX1490A/B 0.25 MAX1480A/B/C 0.8 MAX1490A/B 0.2 MAX1480A/B/C 48 MAX1490A/B 12 kΩ -0.2 +0.2 70 VCM = 0V mA V mV Receiver Output/Receiver Output Low Voltage VOL Using resistor values listed in Tables 1 and 2 0.4 V Receiver Output/Receiver Output High Current IOH VOUT = 5.5V 250 µA Driver Short-Circuit Current ISO IOSD -7V ≤ VO ≤ 12V (Note 4) 100 mA SWITCHING CHARACTERISTICS—MAX1480A/MAX1490A (VCC_ = 5V ±10%, FS = VCC_, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC_ = 5V and TA = +25°C.) PARAMETER Driver Input to Output Propagation Delay SYMBOL tPLH tPHL CONDITIONS Figures 5 and 7, RDIFF = 54Ω, CL1 = CL2 = 100pF MIN TYP MAX 100 275 100 275 UNITS ns tSKEW Figures 5 and 7, RDIFF = 54Ω, CL1 = CL2 = 100pF 25 90 ns tR, tF Figures 5 and 7, RDIFF = 54Ω, CL1 = CL2 = 100pF 15 40 ns Driver Enable to Output High (MAX1480A Only) tZH Figures 6 and 8, CL = 100pF, S2 closed 0.2 1.5 µs Driver Enable to Output Low (MAX1480A Only) tZL Figures 6 and 8, CL = 100pF, S1 closed 0.2 1.5 µs Driver Disable Time from Low (MAX1480A Only) tLZ Figures 6 and 8, CL = 15pF, S1 closed 0.2 1.5 µs Driver Disable Time from High (MAX1480A Only) tHZ Figures 6 and 8, CL = 15pF, S2 closed 0.2 1.5 µs tPLH Figures 5 and 10, RDIFF = 54Ω, CL1 = CL2 = 100pF 100 225 100 225 Driver Output Skew Driver Rise or Fall Time Receiver Input to Output Propagation Delay tPHL ns 3 MAX1480A/B/C/MAX1490A/B ELECTRICAL CHARACTERISTICS (continued) MAX1480A/B/C/MAX1490A/B Complete, Isolated RS-485/RS-422 Data Interface SWITCHING CHARACTERISTICS—MAX1480A/MAX1490A (continued) (VCC_ = 5V ±10%, FS = VCC_, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC_ = 5V and TA = +25°C.) PARAMETER |tPLH - tPHL| Differential Receiver Skew Maximum Data Rate Time to Shutdown SYMBOL CONDITIONS tSKD Figures 5 and 10, RDIFF = 54Ω, CL1 = CL2 = 100pF fMAX tPLH, tPHL < 50% of data period MIN TYP MAX 20 ns 2.5 Mbps 100 tSHDN UNITS µs Shutdown to Driver Output High tZH(SHDN) Figures 6 and 9, CL = 100pF, S2 closed 3 10 µs Shutdown to Driver Output Low tZL(SHDN) Figures 6 and 9, CL = 100pF, S1 closed 3 10 µs SWITCHING CHARACTERISTICS—MAX1480B/MAX1480C/MAX1490B (VCC_ = 5V ±10%, FS = VCC_, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC_ = 5V and TA = +25°C.) PARAMETER Driver Input to Output Propagation Delay Driver Output Skew Driver Rise or Fall Time SYMBOL tPLH tPHL CONDITIONS Figures 5 and 7, RDIFF = 54Ω, CL1 = CL2 = 100pF MIN TYP MAX 2 3.0 2 3.0 UNITS µs tSKEW Figures 5 and 7, RDIFF = 54Ω, CL1 = CL2 = 100pF 900 1600 ns tR, tF Figures 5 and 7, RDIFF = 54Ω, CL1 = CL2 = 100pF 1.0 2.0 µs Driver Enable to Output High (MAX1480B Only) tZH Figures 6 and 8, CL = 100pF, S2 closed 35 100 µs Driver Enable to Output Low (MAX1480B Only) tZL Figures 6 and 8, CL = 100pF, S1 closed 35 100 µs Driver Disable Time from Low (MAX1480B Only) tLZ Figures 6 and 8, CL = 15pF, S1 closed 13 50 µs Driver Disable Time from High (MAX1480B Only) tHZ Figures 6 and 8, CL = 15pF, S2 closed 13 50 µs Driver Enable to Output High (MAX1480C Only) tZH Figures 6 and 8, CL = 100pF, S2 closed 0.5 4.5 µs Driver Enable to Output Low (MAX1480C Only) tZL Figures 6 and 8, CL = 100pF, S1 closed 0.5 4.5 µs 4 Complete, Isolated RS-485/RS-422 Data Interface (VCC_ = 5V ±10%, FS = VCC_, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC_ = 5V and TA = +25°C.) PARAMETER SYMBOL TYP MAX UNITS Figures 6 and 8, CL = 15pF, S1 closed 2.0 4.5 µs tHZ Figures 6 and 8, CL = 15pF, S2 closed 2.0 4.5 µs tPLH Figures 5 and 10, RDIFF = 54Ω, CL1 = CL2 = 100pF 2 3.0 2 3.0 Driver Disable Time from Low (MAX1480C Only) tLZ Driver Disable Time from High (MAX1480C Only) Receiver Input to Output Propagation Delay |tPLH - tPHL| Differential Receiver Skew Maximum Data Rate Time to Shutdown Shutdown to Driver Output High Shutdown to Driver Output Low tPHL CONDITIONS tSKD Figures 5 and 10, RDIFF = 54Ω, CL1 = CL2 = 100pF fMAX tPLH, tPHL < 50% of data period MIN 1200 ns 0.25 Mbps 100 tSHDN µs µs tZH(SHDN) Figures 6 and 9, CL = 100pF, S2 closed 35 100 µs tZL(SHDN) Figures 6 and 9, CL = 100pF, S1 closed 35 100 µs Note 1: All currents into device pins are positive; all currents out of device pins are negative. All voltages are referenced to logicside ground (GND_), unless otherwise specified. Note 2: For DE´ and DI´ pin descriptions, see Detailed Block Diagram and Typical Application Circuit (Figure 1 for MAX1480A/ MAX1480B/MAX1480C, Figure 2 for MAX1490A/MAX1490B). Note 3: Shutdown supply current is the current at VCC1 and VCC2 when shutdown is enabled. 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 signal paths (see Isolated Common Connection section). 5 MAX1480A/B/C, MAX1490A/B SWITCHING CHARACTERISTICS—MAX1480B/MAX1480C/MAX1490B (continued) Typical Operating Characteristics (VA =_ +=25 5V °C , ,Fu Sn=leV ssCC o_th, eTrAw= ise+2n5o°te Cd,.u)nless otherwise noted.) CC 30 -15 -10 20 -5 10 0 OUTPUT CURRENT vs. DRIVER OUTPUT LOW VOLTAGE 0.3 MAX1480/90A/B-05 160 0.2 3.75 3.50 140 120 100 80 60 -50 -40 -30 -10 0 80 0 0 1 2 3 4 5 6 7 8 DRIVER DIFFERENTIAL OUTPUT VOLTAGE vs. TEMPERATURE 50 40 30 20 10 OUTPUT HIGH VOLTAGE (V) MAX1480/90A/B-08 DIFFERENTIAL OUTPUT VOLTAGE (V) DRIVER OUTPUT CURRENT vs. DIFFERENTIAL OUTPUT VOLTAGE MAX1480/90A/B-07 OUTPUT LOW VOLTAGE (V) DI´ = HIGH OR OPEN DI´ = HIG H OR OPEN RL = 54Ω 2.9 2.8 2.7 2.6 2.5 2.4 2.3 2.2 2.0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 DIFFERENTIAL OUTPUT VOLTAGE (V) MAX1480B/MAX1480C/MAX1490B SHUTDOWN CURRENT vs. TEMPERATURE SD = VCC_, DI´ = VCC_ 0.35 DE´ (MAX1480B/C ONLY) = VCC_ MEASURED AT VCC1 AND VCC2 0.25 0.20 0.15 0.10 0.05 2.1 0 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 9 10 11 12 TEMPERATURE (°C) 70 80 -60 0 60 60 -70 -20 40 40 -80 20 20 20 -90 0.1 0 0 -100 40 -20 -20 OUTPUT CURRENT vs. DRIVER OUTPUT HIGH VOLTAGE 180 OUTPUT CURRENT (mA) 0.4 4.00 TEMPERATURE (°C) OUTPUT CURRENT (mA) RECEIVER OUTPUT LOW VOLTAGE vs. TEMPERATURE 0.5 4.25 3.00 -40 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 OUTPUT HIGH VOLTAGE (V) 0.6 -40 6 0 OUTPUT LOW VOLTAGE (V) MEASURED AT ISO RO DRV IRO = 8mA 0.7 OUTPUT LOW VOLTAGE (V) 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 MAX1480/90A/B-04 0.8 4.50 3.25 0 0 MEASURED AT ISO RO DRV IRO = 8mA MAX1480/90A/B-06 40 -20 4.75 MAX1480/90A/B-09 50 -25 5.00 OUTPUT HIGH VOLTAGE (V) 60 MEASURED AT ISO RO DRV SHUTDOWN CURRENT (A) OUTPUT CURRENT (mA) 70 -30 RECEIVER OUTPUT HIGH VOLTAGE vs. TEMPERATURE MAX1480/90A/B-02 MEASURED AT ISO RO DRV OUTPUT CURRENT (mA) MAX1480/90A/B-01 80 OUTPUT CURRENT vs. RECEIVER OUTPUT HIGH VOLTAGE MAX1480/90A/B-03 OUTPUT CURRENT vs. RECEIVER OUTPUT LOW VOLTAGE OUTPUT CURRENT (mA) MAX1480A/B/C, MAX1490A/B Complete, Isolated RS-485/RS-422 Data Interface 0 -40 -20 0 20 40 TEMPERATURE (°C) 60 80 -40 -20 0 20 40 TEMPERATURE (°C) 60 80 Complete, Isolated RS-485/RS-422 Data Interface 80 RL = 60 40 VCC = 5.5V VCC = 4.5V VCC = 5.0V 100 VCC = 4.5V 80 60 VCC = 5.0V VCC = 5.0V RL = ∞ 110 100 V = 4.5V DE´ = VCC 70 VCC = 5.5V 30 20 20 0 0 20 40 60 -40 80 -20 0 20 40 60 -40 80 VCC = 5.0V VCC = 4.5V 140 RL = VCC = 5.0V 150 VCC = 4.5V 80 VCC = 5.0V 80 RL = 54 110 100 80 VCC = 5.0V VCC = 5.5V RL = -20 0 20 40 60 0 20 40 60 DRIVER DISABLE TIME vs. TEMPERATURE DRIVER ENABLE TIME vs. TEMPERATURE MAX1480/90A/B-15a 10 MAX1480C RL = 54 VDI´ = 0V MEASURED FROM DE´ TO VALID OUTPUT 0 20 40 TEMPERATURE (°C) 80 100 MAX1480B 10 RL = 54 VDI´ = 0V MEASURED FROM DE´ TO VALID OUTPUT 1 MAX1480C MAX1480A MAX1480A 0.1 -20 -20 TEMPERATURE (°C) MAX1480B -40 -40 80 TEMPERATURE (°C) 100 1 VCC = 4.5V 50 DRIVER ENABLE TIME (s) -40 DRIVER DISABLE TIME (s) 60 70 100 40 VCC = 5.5V 130 SUPPLY CURRENT (mA) SUPPLY CURRENT (mA) 180 20 MAX1490B SUPPLY CURRENT vs. TEMPERATURE MAX1480/90A/B-13 200 120 0 TEMPERATURE (°C) MAX1490A SUPPLY CURRENT vs. TEMPERATURE 160 -20 TEMPERATURE (°C) TEMPERATURE (°C) MAX1480/90A/B-14 -20 MAX1480/90A/B-15b -40 VCC = 5.0V 90 40 40 20 MAX1480/90A/B-12 120 120 SUPPLY CURRENT (mA) VCC = 4.5V DE´ = VCC MAX1480/90A/B-11 VCC = 5.0V 140 SUPPLY CURRENT (mA) VCC = 5.5V 140 SUPPLY CURRENT (mA) RL = 54 MAX1480/90A/B-10 160 MAX1480C SUPPLY CURRENT vs. TEMPERATURE MAX1480B SUPPLY CURRENT vs. TEMPERATURE MAX1480A SUPPLY CURRENT vs. TEMPERATURE 0.1 60 80 -40 -20 0 20 40 60 80 TEMPERATURE (°C) 7 MAX1480A/B/C, MAX1490A/B Typical Operating Characteristics (continued) (VCC_ = 5V, FS = VCC_, TA = +25°C, unless otherwise noted.) Typical Operating Characteristics (continued) (VCC_ = 5V, FS = VCC_, VDI´ = 0V, DE´ toggled 0V to 5V at 5kHz, TA = +25°C, unless otherwise noted.) MAX1480/90-19 MAX1480/90-20 MAX1480A DRIVER DISABLE TIME MAX1480A DRIVER ENABLE TIME DRIVER OUTPUT B 2V/div DRIVER OUTPUT B 2V/div DE´ 2V/div DE´ 2V/div 200ns/div 200ns/div MAX1480B DRIVER ENABLE TIME MAX1480/90-18 MAX1480/90-17 MAX1480B DRIVER DISABLE TIME DRIVER OUTPUT B 2V/div DRIVER OUTPUT B 2V/div DE´ 2V/div DE´ 2V/div 5s/div MAX1480C DRIVER ENABLE TIME MAX1480C DRIVER DISABLE TIME MAX1480/90-26 10s/div MAX1480/90-25 MAX1480A/B/C, MAX1490A/B Complete, Isolated RS-485/RS-422 Data Interface 500ns/div 8 DRIVER OUTPUT B 2V/div DRIVER OUTPUT B 2V/div DE´ 2V/div DE´ 2V/div 500ns/div Complete, Isolated RS-485/RS-422 Data Interface (VCC_ = 5V, FS = VCC_, DE´ = VCC_, VDI´ = 0V to 5V at 1.25MHz, TA = +25°C, unless otherwise noted.) MAX1480A/MAX1490A RECEIVER tPHL MAX1480A/MAX1490A RECEIVER tPLH MAX1480/90-21 MAX1480/90-22 RECEIVER INPUT A 1V/div RECEIVER INPUT B 1V/div RECEIVER INPUT B 1V/div RECEIVER INPUT A 1V/div RO 2V/div RO 2V/div 20ns/div 20ns/div MAX1480B/MAX1480C/MAX1490B RECEIVER tPHL MAX1480B/MAX1480C/MAX1490B RECEIVER tPLH MAX1480/90-23 MAX1480/90-24 RECEIVER INPUT A 1V/div RECEIVER INPUT A 1V/div RECEIVER INPUT B 1V/div RECEIVER INPUT B 1V/div RO 2V/div RO 2V/div 200ns/div 500ns/div MAX1480/90-16 POWER-UP DELAY TO DRIVER OUTPUTS VALID DRIVER OUTPUT B (Z FOR MAX1490) 2V/div SD 2V/div 1s/div VDI´ = 0V VSD = 5V TO 0V AT 1kHz 9 MAX1480A/B/C, MAX1490A/B Typical Operating Characteristics (continued) MAX1480A/B/C, MAX1490A/B Complete, Isolated RS-485/RS-422 Data Interface Pin Description PIN MAX1480A/B/C MAX1490A/B NAME FUNCTION PINSON ONTHE THENON-ISOLATED NON-ISOLATEDSIDE SIDE PINS 1, 2, 8, 10 3, 4 1, 2, 8, 10 3, 4 VCC1–VCC4 D1, D2 5 5 GND1 6 6 FS Frequency Select Input. If FS = VCC_ or is open, switch frequency is high; if FS = GND, switch frequency is low. For optimal performance and minimal supply current, connect FS to VCC_ or leave unconnected. 7 7 SD Shutdown Input. Ground for normal operation. When high, the power oscillator is disabled. DI Driver Input. 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 high and output B low. Drives internal LED cathode through a resistor (Table 1 of Figure 1 for MAX1480A/B/C, Table 2 of Figure 2 for MAX1490A/B). 9 9 Logic-Side Ground. Connect to GND2 (pin 12). 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 a resistor (Table 1 of Figure 1). — 11 RO Receiver Output. If A > B by 200mV, RO will be high; if A < B by 200mV, RO will be low. Open collector; must have pullup to VCC (Table 2 of Figure 2). 12 12 GND2 13 — RO 14 THE ISOLATED — RS-485/RS-422 VCC5SIDE PINS ON PINS ON THE ISOLATED RS-485/RS-422 SIDE 10 Logic-Side (nonisolated side) +5V Supply Voltages Internal Connections. Leave these pins unconnected. 15 13 ISO RO LED 16 — ISO COM2 17 — ISO DE DRV 18 14 ISO VCC2 Logic-Side Ground. Connect to GND1 (pin 5). Receiver Output. If A > B by 200mV, RO will be low; if A < B by 200mV, RO will be high. Open collector; must have pullup to VCC_ (Table 1 of Figure 1). Logic-Side (non-isolated side) +5V Supply Voltage Isolated Receiver Output LED. Internal LED anode in MAX1480A/B/C and 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). Isolated Common. Connect to ISO COM1 (pin 20). Isolated Driver-Enable Drive. 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. Opencollector 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 pin 22 for MAX1490A/B). 19 15 ISO DI DRV 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 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). 20 16 ISO COM1 Isolated Common. For MAX1480A/B/C, connect to ISO COM2 (pin 16) (Figures 1 and 2). Complete, Isolated RS-485/RS-422 Data Interface PIN MAX1480A/B/C MAX1490A/B NAME FUNCTION PINS ON THE ISOLATED RS-485/RS-422 SIDE (continued) — 17 Y Noninverting Driver Output — 18 Z Inverting Driver Output — — 19 20 B A Inverting Receiver Input Noninverting Receiver Input 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 21 ISO RO DRV 25 — B 26 27, 28 22 23, 24 ISO VCC1 AC2, AC1 Noninverting Driver Output and Noninverting Receiver Input Isolated Receiver-Output Drive. Connect to ISO RO LED through a resistor (Table 1 of Figure 1 for MAX1480A/B/C, Table 2 of Figure 2 for MAX1490A/B). Inverting Driver Output and Inverting Receiver Input Isolated Supply Voltage Source Internal Connections. Leave these pins unconnected. Note: 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). Detailed Description The MAX1480A/MAX1480B/MAX1480C/MAX1490A/ MAX1490B are complete, electrically isolated, RS-485/ RS-422 data-communications interface solutions. Transceivers, optocouplers, a power driver, and a transformer in one standard 28-pin DIP package (24pin for the MAX1490A/B) provide a complete interface. Signals and power are internally transported across the isolation barrier (Figures 1, 2). 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 +5V supply on the logic side powers both sides of the interface. The MAX1480A/B/C offer half-duplex communications while the MAX1490A/B feature full-duplex communication. The functional input/output relationships are shown in Tables 3–6. The MAX1480B/MAX1480C/MAX1490B feature reducedslew-rate drivers that minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free transmission at data rates up to 250kbps. The MAX1480A/MAX1490A driver slew rate is not limited, allowing transmission rates up to 2.5Mbps. The MAX1480B/MAX1480C/MAX1490B shutdown feature reduces supply current to as low as 0.2µA by using the SD pin (see Low-Power Shutdown Mode section). Use the FS pin to select between high and low switching frequencies for the isolated power driver. The driver switches at the lower frequency 535kHz when FS is low, and at the higher frequency 725kHz when FS is high. The FS pin has a weak internal pull-up that switches the device to the high-frequency mode when FS is left unconnected. With FS high or open, no-load supply current is reduced by approximately 4mA, and by up to 8mA when fully loaded. For optimal performance and minimal supply current, connect FS to VCC_ or leave unconnected. 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 RO (logic-low RO) output if the input is open circuit. On the MAX1480A/B/C, the driver outputs are enabled by bringing DE´ high. Driver-enable times are typically 0.2µs for the MAX1480A, 35µs for the MAX1480B, and 0.5µs for the MAX1480C. Allow time for the devices to be enabled before sending data (see the Driver Enable Time vs. Temperature graph in the Typical Operating Characteristics). 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. 11 MAX1480A/B/C, MAX1490A/B Pin Description (continued) MAX1480A/B/C, MAX1490A/B Complete, Isolated RS-485/RS-422 Data Interface VCC3 ISO VCC1 D1 MAX845 Q FS OSC 1.07MHz/ 1.45MHz MAX1480A: MAX1487 MAX1480B: MAX487 MAX1480C: MAX487 N T F/F B ISO DI IN D D2 Q N ISO DE IN A ISO RO DRV R GND1 SD RE ISO COM1 EXTERNAL RS-485/RS-422 WIRING VIN 5V C1 C2 22F 0.1F TERMINATING RESISTOR (ONE RESISTOR ON EACH END) MAX1480A/B/C VCC1 1 28 AC1 (MAKE NO CONNECTION) VCC2 2 27 AC2 (MAKE NO CONNECTION) 26 ISO VCC1 B 25 D1 3 D2 4 GND1 5 FS 6 SD 74HC86 OR EQUIVALENT DI VCC3 R1 DRIVER INPUT DI´ DE DI VCC4 R2 DRIVER ENABLE DE DE´ R3 RECEIVER OUTPUT 24 MAX845 MAX1487 MAX487 A 7 8 21 ISO DE IN 9 20 10 19 ISO DI DRV 11 18 ISO VCC2 TWISTED PAIR TO OTHER TRANSCEIVERS SH R6 RL R4 ISO COM1 SHIELD (OPTIONAL) R5 NOTE: RESISTOR R7 PROTECTS THE MAX1480A/B/C FROM TRANSIENT CURRENTS BETWEEN SHIELD AND TRANSMISSION LINES. R7 100 17 ISO DE DRV 16 ISO COM2 15 ISO RO LED 14 LOGIC GROUND SHIELD (OPTIONAL) ISO RO DRV 22 ISO DI IN GND2 12 VCC5 RL B 23 A RO 13 RO TWISTED PAIR TO OTHER TRANSCEIVERS 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/ MAX1490B typically withstand 1600VRMS (1 minute) or 2000VRMS (1 second). The logic inputs can be driven from TTL/CMOS-logic with a series resistor, and the received data output can directly drive TTL or CMOSlogic families with only resistive pullup. 12 Low-Power Shutdown Mode The SD pin shuts down the oscillator on the internal power driver. With the primary side in shutdown, no power is transferred across the isolation barrier. The DI and DE optocouplers, however, still consume current if the drive signals on the nonisolated side are low. Therefore, leave DI´ and DE´ high or floating when in shutdown mode. Complete, Isolated RS-485/RS-422 Data Interface MAX1480A/B/C, MAX1490A/B VCC3 D1 MAX845 Q OSC 1.07MHz/ 1.45MHz FS N A R T F/F ISO RO DRV D2 Q B ISO DI DRV N MAX1490A: MAX490 MAX1490B: MAX488 Z D SD Y GND1 MAX1490A/B VIN 5V C1 VCC1 C2 VCC2 22F 0.1F D1 EXTERNAL RS-485/RS-422 WIRING 1 24 AC1 (MAKE NO CONNECTION) 2 23 AC2 (MAKE NO CONNECTION) 3 22 ISO VCC1 B SD 7 18 Z Z VCC3 8 17 Y R2 VCC4 10 R4 15 ISO DI DRV 14 ISO VCC2 R0 11 13 ISO RO LED GND2 12 ISOLATION BARRIER RL SHIELD (OPTIONAL) RL TWISTED PAIR TO OTHER TRANSCEIVERS Y R5, 100 16 ISO COM1 DI 9 DI´ RO MAX488 MAX490 19 B MAX845 A R1 DRIVER INPUT RECEIVER OUTPUT RL 20 A FS 6 DI TWISTED PAIR TO OTHER TRANSCEIVERS 21 ISO RO DRV D2 4 GND1 5 74HC86 OR EQUIVALENT TERMINATING RESISTOR (ONE RESISTOR ON EACH END) RL SH1 SH2 SHIELD (OPTIONAL) R6, 100 R3 NOTE: RESISTORS R5 AND R6 PROTECT THE MAX1490A/B FROM TRANSIENT CURRENTS BETWEEN SHIELD AND TRANSMISSION LINES. ISOLATED COMMON 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/ MAX1490B supply current is reduced to as low as 0.2µA. The high-speed optocouplers on the MAX1480A/ MAX1480C/MAX1490A consume an additional 10mA through VCC5 (VCC4 for the MAX1490A). Therefore, to completely shut down these devices, use an external Pchannel MOSFET as shown in Figure 3. In normal opera- tion, SD is low, turning the MOSFET on and thereby providing power to all the VCC_ pins. When SD is pulled high, the power oscillator is disabled and the switch is turned off, disconnecting power from the DI and DE optocouplers. In normal operating mode, the switch carries only the optocoupler currents, so an on-resistance of several ohms will not significantly degrade efficiency. 13 MAX1480A/B/C, MAX1490A/B Complete, Isolated RS-485/RS-422 Data Interface VIN 5V Si943304 VCC1 1 28 AC1 VCC2 2 27 AC2 D1 3 26 ISO VCC1 D2 4 25 B GND1 5 P FS 6 SHUTDOWN R1 DI 24 ISO RO DRV MAX845 MAX1487 22 ISO DI IN VCC3 8 21 ISO DE IN DI 20 ISO COM1 9 19 ISO DI DRV DE 11 R3 18 ISO VCC2 GND2 12 17 ISO DE DRV RO 13 RO 23 A SD 7 VCC4 10 DE MAX1480A VCC5 16 ISO COM2 15 ISO RO LED 14 ISOLATION BARRIER GND Figure 3. MAX1480A Low-Power Shutdown Mode Test Circuits ISOLATION BARRIER ISOLATION BARRIER (DE´) R D R VOC DI´ D RDIFF VID CL2 Figure 4. Driver DC Test Load 14 ( ) ARE FOR THE MAX1480A/B/C CL1 VOD R RO (RO)* * OPTOCOUPLER OUTPUTS. SEE FIGURES 1 AND 2 FOR DETAILED BLOCK DIAGRAM AND TYPICAL APPLICATION CIRCUIT. Figure 5. Driver/Receiver Timing Test Circuit Complete, Isolated RS-485/RS-422 Data Interface ISO VCC_ S1 500 OUTPUT UNDER TEST CL S2 Figure 6. Driver Timing Test Load Switching Waveforms VCC_ - 0.4V DI´ VCC_ - 0.4V 2 VCC_ - 0.4V 2 0V tPLH VCC_ -0.4V DE´ tPHL VCC_ - 0.4V VCC_ - 0.4V 2 2 0V 1/2 VO VO A 2.3V OUTPUT NORMALLY LOW VOL 1/2 VO VO VDIFF 0V -VO VDIFF = V (A) - V (B) 90% 10% 90% tR tLZ tZL A, B B OUTPUT NORMALLY HIGH A, B VOH - 0.5V 2.3V 10% 0V tF tZH tSKEW = tPLH - tPHL Figure 7. Driver Propagation Delays and Transition Times tHZ Figure 8. Driver Enable and Disable Times INPUT VID 2.4V SD 0.8V 1.6V tZL(SHDN) -VID V A - VB MAX1490A/B OUTPUT tSHDN A, B VOL 0V 0V 1.6V 2.3V OUTPUT NORMALLY LOW VOL + 0.5V VOL + 0.5V RO VOH VOL 1.5V tPLH 1.5V tPHL OUTPUT NORMALLY HIGH A, B VOH - 0.5V 2.3V 0V tZH(SHDN) Figure 9. Times to/from Shutdown tSHDN RO VOH VOL 1.5V tPHL MAX1480A/B/C OUTPUT 1.5V tSKEW = tPLH - tPHL tPLH Figure 10. Receiver Propagation Delays 15 MAX1480A/B/C, MAX1490A/B Test Circuits (continued) MAX1480A/B/C, MAX1490A/B Complete, Isolated RS-485/RS-422 Data Interface MAX1480B/MAX1480C/MAX1490B: Reduced EMI and Reflections The MAX1480B/MAX1480C/MAX1490B are slew-ratelimited, minimizing EMI and reducing reflections caused by improperly terminated cables. Figure 11 shows both the driver output waveform of a MAX1480A/MAX1490A transmitting a 150kHz signal and the Fourier analysis of that waveform. High-frequency harmonics with large amplitudes are evident. Figure 12 shows the same information for the slew-ratelimited MAX1480B/MAX1480C/MAX1490B transmitting the same signal. The high-frequency harmonics have much lower amplitudes, and therefore the potential for EMI is significantly reduced. Function Tables Half-Duplex Devices (MAX1480A/MAX1480B/MAX1480C) Table 3. Transmitting INPUTS* 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 Table 4. Receiving INPUTS* DE´ 10dB/div 0Hz OUTPUT (RO) 0 VA - V B ≥ +0.2V 0 ≤ -0.2V 1 0 Open 0 0 5MHz Full-Duplex Devices (MAX1490A/MAX1490B) 500kHz/div 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 0Hz 5MHz 500kHz/div Figure 12. Driver Output Waveform and FFT Plot of MAX1480B/MAX1480C/MAX1490B Transmitting a 150kHz Signal 16 INPUT (VA - VB) OUTPUT (RO) ≥ +0.2V 1 ≤ -0.2V 0 Open 1 Complete, Isolated RS-485/RS-422 Data Interface MAX1480A/B/C, MAX1490A/B TERMINATING RESISTOR (ONE RESISTOR ON EACH END) B DI D 120 DE A A B A B 100 RE R RE R RE D RO DE D DI RO DE VIN 5V C1 C2 22F 0.1F DI VCC1 1 28 AC1 (MAKE NO CONNECTION) VCC2 2 27 AC2 (MAKE NO CONNECTION) 26 ISO VCC1 D1 3 FS 6 SD 74HC86 OR EQUIVALENT DI VCC3 DRIVER INPUT R1 DI VCC4 DE DRIVER ENABLE R2 R3 RECEIVER OUTPUT RO TERMINATING RESISTOR (ONE RESISTOR ON EACH END) MAX1480A/B/C DE GND2 24 ISO RO DRV MAX845 MAX487 MAX1487 ISO DI IN 22 8 21 ISO DE IN 9 20 ISO COM1 10 19 ISO DI DRV 11 18 ISO VCC2 12 17 ISO DE DRV RO 13 VCC5 14 A 23 A 7 LOGIC GROUND B 25 B D2 4 GND1 5 RO R 16 R6 120 SH R4 R5 SHIELD (OPTIONAL) NOTE: RESISTOR R7 PROTECTS THE MAX1480A/B/C FROM TRANSIENT CURRENTS BETWEEN SHIELD AND TRANSMISSION LINES. R7 100 ISO COM2 15 ISO RO LED ISOLATION BARRIER ISOLATED COMMON Figure 13. Typical Half-Duplex RS-485/RS-422 Network 17 Applications Information 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 entire common-mode range (see the Typical Operating Characteristics). In addition, a thermal shutdown circuit forces the driver outputs into a high-impedance state if the die temperature rises excessively. Propagation Delay Skew Typical propagation delays are shown in the Typical Operating Characteristics using the test circuit of Figure 5. Propagation delay skew is simply the difference between the low-to-high and high-to-low propagation delay. Small driver/receiver skew times help reduce EMI and reflections by maintaining balanced differential signals. The receiver skew time, I tPLH - tPHL I, is typically under 100ns for the MAX1480A/MAX1490A and under 1µs for the MAX1480B/MAX1480C/MAX1490B. The driver skew time is typicall y 25ns f or the MAX1480A/MAX1490A and 100ns for the MAX1480B/ MAX1480C/MAX1490B. C1 C2 22F 0.1F VCC1 1 VCC2 2 Layout Considerations The MAX1480A/MAX1480B/MAX1480C/MAX1490A/ MAX1490B pinouts enable optimal PC board layout by minimizing interconnect lengths and crossovers. For maximum isolation, the “isolation barrier” should not be breached except by the MAX1480A/ MAX1480B/MAX1480C/MAX1490A/MAX1490B . 23 AC2 (MAKE NO CONNECTION) D1 3 22 ISO VCC1 D2 4 21 ISO RO DRV 74HC86 OR EQUIVALENT R1 DI DRIVER INPUT DI´ R2 MAX488 MAX490 FS 6 RECEIVER OUTPUT 20 A A 19 B B SD 7 18 Z Z 17 Y Y DI 9 16 ISO COM1 VCC4 10 15 ISO DI DRV 13 ISO RO LED ISOLATION BARRIER LOGIC GROUND Figure 14. Typical Full-Duplex RS-485/RS-422 Network R4 SH2 120 SHIELD (OPTIONAL) ISOLATED COMMON NOTE: RESISTORS R5 AND R6 PROTECT THE MAX1490A/B FROM TRANSIENT CURRENTS BETWEEN SHIELD AND TRANSMISSION LINES. D B 120 R A R6, 100 R3 120 Z SHIELD (OPTIONAL) R5, 100 SH1 14 ISO VCC2 GND2 12 Y 120 VCC3 8 RO 11 18 The MAX1480A/MAX1480B/MAX1480C are designed for bidirectional data communications on multipoint bus-transmission lines. The MAX1490A/MAX1490B are designed for full-duplex bidirectional communications that are primarily point-to-point. Figures 13 and 14 show half-duplex and full-duplex typical network application circuits, respectively. 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 slew-rate-limited MAX1480B/ MAX1480C/MAX1490B are more tolerant of imperfect termination and stubs off the main line. 24 AC1 (MAKE NO CONNECTION) GND1 5 RO DI and DE are intended to be driven through a series current-limiting resistor. Directly grounding these pins destroys the device. MAX1490A/B VIN 5V MAX845 MAX1480A/B/C, MAX1490A/B Complete, Isolated RS-485/RS-422 Data Interface DI RO Complete, Isolated RS-485/RS-422 Data Interface The DI and DE (MAX1480A/B/C only) inputs are the cathodes of LEDs whose anodes are connected to the supply. These points are best driven by a CMOS-logic gate with a series resistor to limit the current. The resistor values shown in Tables 1 and 2 are recommended when the 74HC86 gate or equivalent is used. These values may need to be adjusted if a driving gate with dissimilar series resistance is used. A shield trace connected to the ground on each side of the barrier can help intercept capacitive currents that might otherwise couple into the signal path. In a double-sided or multilayer board, these shield traces should be present on all conductor layers. Try to maximize the width of the isolation barrier wherever possible; a clear space of at least 0.25 inches between ground and isolated common is suggested. All pull-up resistors are based on optocoupler specifications in order to optimize the devices’ data-transfer rates. Isolated Common Connection The isolated common may be completely floating with respect to the logic ground and the effective network ground. The receiver input resistors will cause the isolated common voltage to go to the mean voltage of the receiver inputs. If using shielded cable, connect the isolated common to the shield through a 100 resistor. In the case of the MAX1490, each shield should have its own 100 resistor (Figures 1, 2, 13, and 14). Pullup and LED Drive Resistors The MAX1480A/MAX1480B/MAX1480C/MAX1490A/ MAX1490B are specified and characterized using the resistor values shown in Table 1 of Figure 1 and Table 2 of Figure 2. Altering the recommended values can degrade performance. +5V +5V ETWORK SEGMENT A 2 8 10 14 A B 26 3k 13 24 1 2 9 3k MAX1480C 200 4 9 11 3 13 DRIVER ENABLE B>A 200 23 A 25 B 74HC04 MAX1480C 19 22 17 21 3k 2 8 10 14 200 23 25 NETWORK SEGMENT B 3k DRIVER ENABLE 200 A>B 26 3k 19 22 17 21 11 3k 24 200 200 15 15 5 7 12 5 7 12 +5V 51k 1000pF 16 15 2 B +5V 7 14 Q 13 10 B Q 4 9 A 74HC123 1 A 51k 1000pF 6 Q 5 74HC123 Q 12 CLR CLR 3 11 Figure 15. Doubly Isolated RS-485 Repeater 19 MAX1480A/B/C, MAX1490A/B Connections and components from one side should not be located near those of the other side. MAX1480A/B/C, MAX1490A/B Complete, Isolated RS-485/RS-422 Data Interface Doubly Isolated RS-485 Repeater The RS-422/RS-485 standard is specified for cable lengths up to 4000 feet. When approaching or exceeding the specified maximum cable length, a groundpotential difference of several tens of volts can easily develop. This difference can be either DC, AC, at power-line frequency, or any imaginable noise or impulse waveform. It is typically very low impedance so that if a connection between the two grounds is attempted, very large currents may flow. These currents are by their nature unstable and unpredictable. In addition, they may cause noise to be injected into sensitive instrumentation and, in severe cases, might actually cause physical damage to such equipment. Figure 15 shows a half-duplex (two-wire), bidirectional, party-line repeater system that prevents interference and/or damage from ground-potential differences. Two MAX1480A/MAX1480B/MAX1480C isolated RS-485 transceivers are used to isolate each of the network segments from the electrical environment of the repeater. The MAX1480A/MAX1480B/MAX1480C also regenerate bus signals that may have been degraded by line attenuation or dispersion. 20 In the idle state, both transmitters are disabled, while all receivers in the system are enabled. If any device on the system has information for any other device, it starts sending its data onto the bus. Each data transmission on the bus retriggers the one-shot, keeping the sending transmitter enabled until there are no more transmissions. All receivers receive all data; if this is undesirable, the protocol must allow for an address field so receivers can ignore data not directed to them. Each node must refrain from transmitting when data already exists on the bus, and must resend data that is corrupted by the collisions that inevitably occur with a party-line system. With the repeater of Figure 15, there might be transmitters up to 8000 feet apart. That represents more than 8µs (assuming 1ns/foot of delay) in which two nodes could be transmitting simultaneously. The circuit in Figure 15 can be used either directly as shown, with the slew-rate-limited MAX1480B/ MAX1480C, for data transfer rates up to 250kbps, or with the MAX1480A for data rates up to 2.5Mbps (see Table 1 for pullup and LED resistor values when using the MAX1480A or MAX1480B). If dual-port isolation is not needed, one of the MAX1480C devices can be replaced by a MAX487 for 250kbps applications. Complete, Isolated RS-485/RS-422 Data Interface PART† TEMP RANGE Pin Configurations (continued) PIN-PACKAGE MAX1480BCPI 0°C to +70°C 28 Wide Plastic DIP MAX1480BEPI -40°C to +85°C 28 Wide Plastic DIP MAX1480CCPI 0°C to +70°C 28 Wide Plastic DIP MAX1480CEPI -40°C to +85°C 28 Wide Plastic DIP TOP VIEW MAX1480A/B/C VCC1 1 28 AC1 24 Wide Plastic DIP VCC2 2 27 AC2 -40°C to +85°C 24 Wide Plastic DIP D1 3 26 ISO VCC1 MAX1490BCPG 0°C to +70°C 24 Wide Plastic DIP D2 4 25 B MAX1490BEPG -40°C to +85°C 24 Wide Plastic DIP GND1 5 MAX1490ACPG MAX1490AEPG 0°C to +70°C †Data rate for “A” parts is up to 2500kbps. Data rate for “B” and 24 ISO RO DRV MAX845 MAX487 MAX1487 FS 6 23 A SD 7 22 ISO DI IN VCC3 8 21 ISO DE IN DI 9 20 ISO COM1 19 ISO DI DRV VCC4 10 DE 11 18 ISO VCC2 17 ISO DE DRV GND2 12 16 ISO COM2 RO 13 VCC5 14 15 ISO RO LED ISOLATION BARRIER DIP Package Information For the latest package outline information, go to www.maxim-ic.com/packages. 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 © 2005 Maxim Integrated Products Printed USA 21 is a registered trademark of Maxim Integrated Products, Inc. MAX1480A/B/C, MAX1490A/B Ordering Information (continued)