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19-0259; Rev 2a; 2/98
Complete, Isolated RS-485/RS-422 Data Interface
_________________General Description
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 has 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.
____________________________Features
o Isolated Data Interface, Typically to 1600VRMS (1 minute) o Slew-Rate Limited for Errorless Data Transmission (MAX1480B/MAX1480C/MAX1490B) o High-Speed, Isolated, 2.5Mbps RS-485/RS-422 Interface (MAX1480A/MAX1490A) o Full-Duplex Data Communication (MAX1490A/B) o -7V to +12V Common-Mode Input Voltage Range with Respect to Isolated Ground o Single +5V Supply o Current Limiting and Thermal Shutdown for Driver Overload Protection o Standard 0.6" DIP Package: 28-Pin DIP (MAX1480A/B/C) 24-Pin DIP (MAX1490A/B)
MAX1480A/B/C, MAX1490A/B
_______________Ordering Information
PART MAX1480ACPI MAX1480AEPI TEMP. RANGE 0C to +70C -40C to +85C PIN-PACKAGE 28 Wide Plastic DIP 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.
__________________Pin Configurations
TOP VIEW
_____________________Selection Table
PART HALF/ FULL DUPLEX Half Half Half Full Full DATA RATE (Mbps) 2.5 0.25 0.25 2.5 0.25 SLEWRATE LIMITED No Yes Yes No Yes DRIVER ENABLE TIME (s) 0.2 35 0.5 -- --
VCC1 VCC2 D1 D2 GND1
1 2 3 4 5
MAX845 MAX488 MAX490
24 AC1 23 AC2
MAX1490A/B
22 ISO VCC1 21 ISO RO DRV 20 A 19 B 18 Z 17 Y 16 ISO COM1 15 ISO DI DRV 14 ISO VCC2 13 ISO RO LED ISOLATION BARRIER
MAX1480A MAX1480B MAX1480C MAX1490A MAX1490B
FS 6 SD 7
VCC3 8 DI 9
VCC4 10
________________________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
RO 11 GND2 12
DIP Pin Configurations continued at end of data sheet.
________________________________________________________________ Maxim Integrated Products
1
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Complete, Isolated RS-485/RS-422 Data Interface MAX1480A/B/C, MAX1490A/B
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 = +70C) 24-Pin Plastic DIP (derate 8.7mWC above +70C) .....696mW 28-Pin Plastic DIP (derate 9.09mW/C above +70C) ..727mW Operating Temperature Ranges MAX1480_CPI/MAX1490_CPI..............................0C to +70C MAX1480_EPI/MAX1490_EPI ...........................-40C to +85C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10sec) .............................+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_ = 5V 10%, VFS = VCC_, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC_ = 5V and TA = +25C.) (Notes 1, 2) PARAMETER Switch Frequency SYMBOL fSWL fSWH VFS = 0V FS = VCC_ or open MAX1480A, DE = VCC_ or open MAX1480B, DE = VCC_ or open Operating Supply Current ICC MAX1480C, DE = VCC_ or open MAX1490A MAX1490B Shutdown Supply Current (Note 3) Shutdown Input Threshold Shutdown Input Leakage Current FS Input Threshold FS Input Pull-Up Current FS Input Leakage Current Input High Voltage Input Low Voltage Isolation Resistance Isolation Capacitance Differential Driver Output (no load) VIH VIL RISO CISO VOD1 VFSH VFSL High Low FS low FS high DE, DI DE, DI TA = +25C, VISO = 50VDC TA = +25C, VISO = 50VDC 100 10,000 10 8 VCC_ - 0.4 0.4 2.4 0.8 50 10 ISHDN VSDH VSDL SD = VCC_ High Low 2.4 0.8 10 RL = RL = 54 RL = RL = 54 RL = RL = 54 RL = RL = 54 RL = RL = 54 CONDITIONS MIN TYP 535 725 60 120 35 95 35 95 100 170 65 130 0.2 90 45 75 150 125 MAX UNITS kHz
mA
A V pA V A pA V V M pF V
2
_______________________________________________________________________________________
Complete, Isolated RS-485/RS-422 Data Interface
ELECTRICAL CHARACTERISTICS (continued)
(VCC_ = 5V 10%, VFS = VCC_, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC_ = 5V and TA = +25C.) (Notes 1, 2) PARAMETER Differential Driver Output (with load) Change in Magnitude of Driver Output Voltage for Complementary Output States Driver Common-Mode Output SYMBOL VOD2 CONDITIONS R = 50 (RS-422) R = 27 (RS-485), Figure 4 Differential R = 27 or 50, Figure 4 Common Mode VOC R = 27 or 50, Figure 4 DE = 0V, VCC_ = 0V or 5.5V -7V VCM 12V -7V VCM 12V VCM = 0V Using resistor values listed in Tables 1 and 2 VOUT = 5.5V -7V VO 12V (Note 4) 100 VIN = 12V VIN = -7V MAX1490A/B MAX1480A/B/C MAX1490A/B MAX1480A/B/C 12 -0.2 70 0.4 250 0.2 0.3 4 0.25 1 0.2 0.8 k V mV V A mA mA V MIN 2 1.5 5 0.3 V TYP MAX UNITS V
MAX1480A/B/C, MAX1490A/B
VOD
Input Current (A, B)
ISO IIN
Receiver Input Resistance Receiver Differential Threshold Receiver Input Hysteresis Receiver Output/Receiver Output Low Voltage Receiver Output/Receiver Output High Current Driver Short-Circuit Current
RIN VTH VTH VOL IOH ISO IOSD
SWITCHING CHARACTERISTICS--MAX1480A/MAX1490A
(VCC_ = 5V 10%, FS = VCC_, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC_ = 5V and TA = +25C.) PARAMETER Driver Input to Output Propagation Delay Driver Output Skew Driver Rise or Fall Time Driver Enable to Output High (MAX1480A only) Driver Enable to Output Low (MAX1480A only) Driver Disable Time from Low (MAX1480A only) Driver Disable Time from High (MAX1480A only) Receiver Input to Output Propagation Delay SYMBOL tPLH tPHL tSKEW tR, tF tZH tZL tLZ tHZ tPLH tPHL tSKD CONDITIONS Figures 5 and 7, RDIFF = 54, CL1 = CL2 = 100pF Figures 5 and 7, RDIFF = 54, CL1 = CL2 = 100pF Figures 5 and 7, RDIFF = 54, CL1 = CL2 = 100pF Figures 6 and 8, CL = 100pF, S2 closed Figures 6 and 8, CL = 100pF, S1 closed Figures 6 and 8, CL = 15pF, S1 closed Figures 6 and 8, CL = 15pF, S2 closed Figures 5 and 10, RDIFF = 54, CL1 = CL2 = 100pF Figures 5 and 10, RDIFF = 54, CL1 = CL2 = 100pF MIN TYP 100 100 25 15 0.2 0.2 0.2 0.2 100 100 20 MAX 275 275 90 40 1.5 1.5 1.5 1.5 225 225 UNITS ns ns ns s s s s ns ns
ItPLH - tPHLI Differential Receiver Skew
_______________________________________________________________________________________
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Complete, Isolated RS-485/RS-422 Data Interface MAX1480A/B/C, MAX1490A/B
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 = +25C.) PARAMETER Maximum Data Rate Time to Shutdown Shutdown to Driver Output High Shutdown to Driver Output Low Driver Input to Output Propagation Delay Driver Output Skew Driver Rise or Fall Time Driver Enable to Output High (MAX1480B only) Driver Enable to Output Low (MAX1480B only) Driver Disable Time from Low (MAX1480B only) Driver Disable Time from High (MAX1480B only) Driver Enable to Output High (MAX1480C only) Driver Enable to Output Low (MAX1480C only) Driver Disable Time from Low (MAX1480C only) Driver Disable Time from High (MAX1480C only) Receiver Input to Output Propagation Delay SYMBOL fMAX tSHDN tZH(SHDN) tZL(SHDN) tPLH tPHL tSKEW tR, tF tZH tZL tLZ tHZ tZH tZL tLZ tHZ tPLH tPHL tSKD fMAX tSHDN tZH(SHDN) tZL(SHDN) Figures 6 and 9, CL = 100pF, S2 closed Figures 6 and 9, CL = 100pF, S1 closed Figures 6 and 9, CL = 100pF, S2 closed Figures 6 and 9, CL = 100pF, S1 closed Figures 5 and 7, RDIFF = 54, CL1 = CL2 = 100pF Figures 5 and 7, RDIFF = 54, CL1 = CL2 = 100pF Figures 5 and 7, RDIFF = 54, CL1 = CL2 = 100pF Figures 5 and 7, RDIFF = 54, CL1 = CL2 = 100pF Figures 6 and 8, CL = 100pF, S2 closed Figures 6 and 8, CL = 100pF, S1 closed Figures 6 and 8, CL = 15pF, S1 closed Figures 6 and 8, CL = 15pF, S2 closed Figures 6 and 8, CL = 100pF, S2 closed Figures 6 and 8, CL = 100pF, S1 closed Figures 6 and 8, CL = 15pF, S1 closed Figures 6 and 8, CL = 15pF, S2 closed Figures 5 and 10, RDIFF = 54, CL1 = CL2 = 100pF Figures 5 and 10, RDIFF = 54, CL1 = CL2 = 100pF tPLH, tPHL < 50% of data period 0.25 100 35 35 100 100 CONDITIONS tPLH, tPHL < 50% of data period MIN 2.5 100 3 3 1.0 1.0 100 1.0 35 35 13 13 0.5 0.5 2.0 2.0 0.8 0.8 200 10 10 2.0 2.0 800 2.0 100 100 50 50 4.5 4.5 4.5 4.5 2.0 2.0 TYP MAX UNITS Mbps s s s s ns s s s s s s s s s s ns Mbps s s s
ItPLH - tPHLI Differential Receiver Skew Maximum Data Rate
Time to Shutdown Shutdown to Driver Output High Shutdown to Driver Output Low
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).
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_______________________________________________________________________________________
Complete, Isolated RS-485/RS-422 Data Interface
__________________________________________Typical Operating Characteristics
(VCC_ = 5V, FS = VCC_, TA = +25C, unless otherwise noted.)
MAX1480A/B/C, MAX1490A/B
OUTPUT CURRENT vs. RECEIVER OUTPUT LOW VOLTAGE
MAX1480/90A/B-01
OUTPUT CURRENT vs. RECEIVER OUTPUT HIGH VOLTAGE
MAX1480/90A/B-02
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
MAX1480/90A/B-03
80 70 OUTPUT CURRENT (mA) 60 50 40 30 20 10 0 0
MEASURED AT ISO RO DRV
-30 -25 OUTPUT CURRENT (mA) -20 -15 -10 -5 0
MEASURED AT ISO RO DRV
5.00
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 OUTPUT LOW VOLTAGE (V)
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 OUTPUT HIGH VOLTAGE (V)
-40
-20
0
20
40
60
80
TEMPERATURE (C)
RECEIVER OUTPUT LOW VOLTAGE vs. TEMPERATURE
MAX1480/90A/B-04
OUTPUT CURRENT vs. DRIVER OUTPUT LOW VOLTAGE
MAX1480/90A/B-05
OUTPUT CURRENT vs. DRIVER OUTPUT HIGH VOLTAGE
-90 -80 OUTPUT CURRENT (mA) -70 -60 -50 -40 -30 -20 -10 0
MAX1480/90A/B-06
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
180 160 OUTPUT CURRENT (mA) 140 120 100 80 60 40 20 0
-100
-20
0
20
40
60
80
0
1
2
34
5
6
78
9 10 11 12
-7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 OUTPUT HIGH VOLTAGE (V)
TEMPERATURE (C)
OUTPUT LOW VOLTAGE (V)
DRIVER OUTPUT CURRENT vs. DIFFERENTIAL OUTPUT VOLTAGE
MAX1480/90A/B-07
DRIVER DIFFERENTIAL OUTPUT VOLTAGE vs. TEMPERATURE
MAX1480/90A/B-08
MAX1480B/MAX1480C/MAX1490B SHUTDOWN CURRENT vs. TEMPERATURE
0.35 SHUTDOWN CURRENT (A) 0.30 0.25 0.20 0.15 0.10 0.05 0 SD = VCC_, DI = VCC_ DE (MAX1480B/C ONLY) = VCC_ MEASURED AT VCC1 AND VCC2
MAX1480/90A/B-09
80 DI = HIGH OR OPEN 70 OUTPUT CURRENT (mA) 60 50 40 30 20 10 0 0
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 DI = HIGH OR OPEN RL = 54
0.40
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 DIFFERENTIAL OUTPUT VOLTAGE (V)
-40
-20
0
20
40
60
80
-40
-20
0
20
40
60
80
TEMPERATURE (C)
TEMPERATURE (C)
_______________________________________________________________________________________
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Complete, Isolated RS-485/RS-422 Data Interface MAX1480A/B/C, MAX1490A/B
_____________________________Typical Operating Characteristics (continued)
(VCC_ = 5V, FS = VCC_, TA = +25C, unless otherwise noted.)
MAX1480A SUPPLY CURRENT vs. TEMPERATURE
MAX1480/90A/B-10
MAX1480B SUPPLY CURRENT vs. TEMPERATURE
MAX1480/90A/B-11
MAX1480C SUPPLY CURRENT vs. TEMPERATURE
110 100 SUPPLY CURRENT (mA) 90 80 70 60 50 40 30 20 VCC = 4.5V -40 -20 0 20 40 60 80 VCC = 5.5V VCC = 5.0V RL = DE = VCC VCC = 5.5V VCC = 5.0V VCC = 4.5V RL = 54
MAX1480/90A/B-12
160 140 SUPPLY CURRENT (mA) 120 100 80 60 40 20 0 -40 -20 0 20 40 60 80 TEMPERATURE (C) VCC = 5.5V VCC = 5.0V DE = VCC VCC = 5.5V VCC = 5.0V VCC = 4.5V RL = RL = 54
140 120 SUPPLY CURRENT (mA) 100 80 DE = VCC 60 VCC = 5.5V 40 20 -40 -20 0 20 VCC = 4.5V 40 60 80 TEMPERATURE (C) VCC = 5.0V RL = VCC = 5.5V VCC = 5.0V VCC = 4.5V RL = 54
120
VCC = 4.5V
TEMPERATURE (C)
MAX1490A SUPPLY CURRENT vs. TEMPERATURE
MAX1480/90A/B-13
MAX1490B SUPPLY CURRENT vs. TEMPERATURE
VCC = 5.5V VCC = 5.0V VCC = 4.5V RL = 54 140 130 SUPPLY CURRENT (mA) 120 110 100 90 80 70 VCC = 5.0V VCC = 5.5V RL =
MAX1480/90A/B-14
200 VCC = 5.5V 180 SUPPLY CURRENT (mA) VCC = 5.0V 160 140 VCC = 5.5V 120 100 80 -40 -20 0 20 VCC = 4.5V 40 60 80 VCC = 5.0V RL = VCC = 4.5V RL = 54
150
60 50 -40 -20 0 20 40
VCC = 4.5V 60 80
TEMPERATURE (C)
TEMPERATURE (C)
DRIVER DISABLE TIME vs. TEMPERATURE
MAX1480/90A/B-15a
DRIVER ENABLE TIME vs. TEMPERATURE
MAX1480/90A/B-15b
100
100
DRIVER DISABLE TIME (s)
DRIVER ENABLE TIME (s)
MAX1480B 10
MAX1480B 10 RL = 54 VDI = 0V MEASURED FROM DE TO VALID OUTPUT 1 MAX1480C
1
MAX1480C RL = 54 VDI = 0V MEASURED FROM DE TO VALID OUTPUT MAX1480A -40 -20 0 20 40 60 80
MAX1480A 0.1 -40 -20 0 20 40 60 80 TEMPERATURE (C)
0.1
TEMPERATURE (C)
6
_______________________________________________________________________________________
Complete, Isolated RS-485/RS-422 Data Interface
_____________________________Typical Operating Characteristics (continued)
(VCC_ = 5V, FS = VCC_, VDI = 0V, DE toggled 0V to 5V at 5kHz, TA = +25C, unless otherwise noted.)
MAX1480A DRIVER ENABLE TIME
MAX1480/90-19
MAX1480A/B/C, MAX1490A/B
MAX1480A DRIVER DISABLE TIME
MAX1480/90-20
DRIVER OUTPUT B 2V/div
DRIVER OUTPUT B 2V/div
DE 2V/div
DE 2V/div
200ns/div VCC_ = 5.0V, DI= 0V DE TOGGLED 0V TO 5V AT 5kHz
200ns/div VCC_ = 5.0V, DI = 0V DE TOGGLED 0V TO 5V AT 5kHz
MAX1480B DRIVER ENABLE TIME
MAX1480/90-17
MAX1480B DRIVER DISABLE TIME
MAX1480/90-18
DRIVER OUTPUT B 2V/div
DRIVER OUTPUT B 2V/div
DE 2V/div
DE 2V/div
10s/div VCC_ = 5.0V, DI= 0V DE TOGGLED 0V TO 5V AT 5kHz
5s/div VCC_ = 5.0V, DI= 0V DE TOGGLED 0V TO 5V AT 5kHz
MAX1480C DRIVER ENABLE TIME
MAX1480/90-25
MAX1480C DRIVER DISABLE TIME
MAX1480/90-26
DRIVER OUTPUT B 2V/div
DRIVER OUTPUT B 2V/div
DE 2V/div
DE 2V/div
500ns/div VCC_ = 5.0V, DI= 0V DE TOGGLED 0V TO 5V AT 5kHz
500ns/div VCC_ = 5.0V, DI = 0V DE TOGGLED 0V TO 5V AT 5kHz
_______________________________________________________________________________________
7
Complete, Isolated RS-485/RS-422 Data Interface MAX1480A/B/C, MAX1490A/B
_____________________________Typical Operating Characteristics (continued)
(VCC_ = 5V, FS = VCC_, DE = VCC_, VDI = 0V to 5V at 1.25MHz, TA = +25C, unless otherwise noted.)
MAX1480A/MAX1490A RECEIVER tPHL
MAX1480/90-21
MAX1480A/MAX1490A RECEIVER tPLH
MAX1480/90-22
RECEIVER INPUT A 1V/div
RECEIVER INPUT B 1V/div
RECEIVER INPUT B 1V/div RO 2V/div
RECEIVER INPUT A 1V/div RO 2V/div
20ns/div VCC_ = 5.0V, DE= VCC_ DI = 0V TO 5V AT 1.25MHz
20ns/div VCC_ = 5.0V, DE= VCC_ DI = 0V TO 5V AT 1.25MHz
MAX1480B/MAX1480C/MAX1490B RECEIVER tPHL
MAX1480/90-23
MAX1480B/MAX1480C/MAX1490B RECEIVER tPLH
MAX1480/90-24
RECEIVER INPUT A 1V/div RECEIVER INPUT B 1V/div
RECEIVER INPUT A 1V/div RECEIVER INPUT B 1V/div
RO 2V/div 200ns/div VCC_ = 5.0V, DE= VCC_ DI= 0V TO 5V AT 125kHz VCC_ = 5.0V, DE= VCC_ DI= 0V TO 5V AT 125kHz
RO 2V/div
500ns/div
POWER-UP DELAY TO DRIVER OUTPUTS VALID
MAX1480/90-16
DRIVER OUTPUT B (Z FOR MAX1490) 2V/div
SD 2V/div
1s/div VDI = 0V VSD = 5V TO 0V AT 1kHz
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_______________________________________________________________________________________
Complete, Isolated RS-485/RS-422 Data Interface
________________________________________________________________Pin Description
PIN MAX1480A/B/C MAX1490A/B NAME FUNCTION
MAX1480A/B/C, MAX1490A/B
PINS ON THE NON-ISOLATED SIDE PINS ON THE NON-ISOLATED SIDE 1, 2, 8, 10 1, 2, 8, 10 VCC1-VCC4 3, 4 3, 4 D1, D2 5 5 GND1 6 6 FS
Logic-Side (non-isolated side) +5V Supply Voltages Internal Connections. Leave these pins unconnected. Logic-Side Ground. Connect to GND2 (pin 12). 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. Shutdown Input. Ground for normal operation. When high, the power oscillator is disabled. 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). 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). Receiver Output. If A > B by 200mV, RO will be high; if A < B by 200mV, RO will be low. Open collector; must have pull-up to VCC (Table 2 of Figure 2). 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 pull-up 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 pull-up to ISO VCC_ and be tied 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). 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 pull-up resistor to ISO VCC_ (Table 1 of Figure 1 for MAX1480A/B/C; Table 2 of Figure 2 for MAX1490A/B). Isolated Common. For MAX1480A/B/C, connect to ISO COM2 (pin 16) (Figures 1 and 2). 9
7
7
SD
9
9
DI
11
--
DE
-- 12 13 14
11 12 -- --
RO GND2 RO VCC5
PINS ON THE ISOLATED RS-485/RS-422 SIDE PINS ON THE ISOLATED RS-485/RS-422 SIDE 15 16 13 -- ISO RO LED ISO COM2
17
--
ISO DE DRV
18
14
ISO VCC2
19
15
ISO DI DRV
20
16
ISO COM1
_______________________________________________________________________________________
Complete, Isolated RS-485/RS-422 Data Interface MAX1480A/B/C, MAX1490A/B
___________________________________________________Pin Description (continued)
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 B Inverting Receiver Input -- 20 A 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 Noninverting Driver Output and Noninverting Receiver Input 24 25 26 27, 28 21 -- 22 23, 24 ISO RO DRV B ISO VCC1 AC2, AC1 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 (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 +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 0.2A 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 0.2s for the MAX1480A, 35s for the MAX1480B, and 0.5s 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.
10
______________________________________________________________________________________
Complete, Isolated RS-485/RS-422 Data Interface MAX1480A/B/C, MAX1490A/B
VCC3 ISO VCC1
MAX845
Q FS OSC 1.07MHz/ 1.45MHz T F/F N
D1
MAX1480A: MAX1487 MAX1480B: MAX487 MAX1480C: MAX487
ISO DI IN D2 D ISO DE IN ISO RO DRV R RE
B
Q
N
A
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 24 ISO RO DRV A R6 R4 SH B SHIELD (OPTIONAL) TWISTED PAIR TO OTHER TRANSCEIVERS RL SHIELD (OPTIONAL) TWISTED PAIR TO OTHER TRANSCEIVERS RL
VIN 5V C1 22F C2 0.1F
VCC1 VCC2
MAX1480A/B/C
1 2
D1 3 D2 4 GND1 5 FS 6 SD
MAX845
MAX1487 MAX487
23 A 22 ISO DI IN 21 ISO DE IN
74HC86 OR EQUIVALENT DI DRIVER INPUT DI DE DRIVER ENABLE DE RECEIVER OUTPUT RO R2 R3 R1
7 8 9 10 11 12
VCC3 DI VCC4 DE GND2
20 ISO COM1 19 ISO DI DRV 18 ISO VCC2
R5 R7 100
17 ISO DE DRV 16 15 ISOLATION BARRIER ISO COM2 ISO RO LED
NOTE: RESISTOR R7 PROTECTS THE MAX1480A/B/C FROM TRANSIENT CURRENTS BETWEEN SHIELD AND TRANSMISSION LINES.
RO 13 VCC5 14
LOGIC GROUND
ISOLATED COMMON
Table 1. Pull-Up and LED Drive Resistors
PART MAX1480A MAX1480B MAX1480C R1 () 200 200 200 R2 () 200 510 200 R3 () 1000 3000 3000 R4 () 4300 2200 3000 R5 () 1000 3000 3000 R6 () 200 200 200
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 pull-up.
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 non-isolated side are low. Therefore, leave DI and DE high or floating when in shutdown mode.
11
______________________________________________________________________________________
Complete, Isolated RS-485/RS-422 Data Interface MAX1480A/B/C, MAX1490A/B
VCC3 D1 N R D2 Q N ISO RO DRV ISO DI DRV A B
MAX845
Q FS OSC 1.07MHz/ 1.45MHz T F/F
MAX1490A: MAX490 MAX1490B: MAX488
D
Z
SD
GND1
Y
MAX1490A/B
VIN 5V C1 22F C2 0.1F D1 VCC1 VCC2 1 2 3 24 AC1 (MAKE NO CONNECTION) 23 AC2 (MAKE NO CONNECTION) 22 ISO VCC1 21 ISO RO DRV 20 A
MAX845 MAX488 MAX490
EXTERNAL RS-485/RS-422 WIRING TERMINATING RESISTOR (ONE RESISTOR ON EACH END) TWISTED PAIR TO OTHER TRANSCEIVERS RL A B Z Y R5, 100 R4 R6, 100 R3 NOTE: RESISTORS R5 AND R6 PROTECT THE MAX1490A/B FROM TRANSIENT CURRENTS BETWEEN SHIELD AND TRANSMISSION LINES. SH1 SH2 SHIELD (OPTIONAL) RL SHIELD (OPTIONAL) TWISTED PAIR TO OTHER TRANSCEIVERS RL RL
D2 4 GND1 5
FS 6 SD 7 74HC86 OR EQUIVALENT DI DRIVER INPUT DI RECEIVER OUTPUT RO R2 R1 VCC3 8 DI 9 VCC4 10 R0 11 GND2 12
19 B 18 Z 17 Y 16 ISO COM1 15 ISO DI DRV 14 ISO VCC2 13 ISO RO LED
ISOLATION BARRIER LOGIC GROUND
ISOLATED COMMON
Table 2. Pull-Up and LED Drive Resistors
PART MAX1490A MAX1490B R1 () 200 200 R2 () 1000 3000 R3 () 330 330 R4 () 1000 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 0.2A. 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 opera12
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.
______________________________________________________________________________________
Complete, Isolated RS-485/RS-422 Data Interface MAX1480A/B/C, MAX1490A/B
VIN 5V
VCC1 1 VCC2 2 D1 3 D2 4 Si943304 P GND1 5 FS 6
28 AC1 27 AC2
MAX1480A
26 ISO VCC1 25 B 24 ISO RO DRV
MAX845
MAX1487
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
SHUTDOWN R1 DI R2 DE R3 RO
SD 7 VCC3 8 DI 9 VCC4 10 DE 11 GND2 12 RO 13 VCC5 14 ISOLATION BARRIER
GND
Figure 3. MAX1480A Low-Power Shutdown Mode
_________________________________________________________________Test Circuits
ISOLATION BARRIER ISOLATION BARRIER (DE) R D VOD R VOC D VID CL2 CL1 RDIFF ( ) ARE FOR THE MAX1480A/B/C R RO (RO)* * OPTOCOUPLER OUTPUTS. SEE FIGURES 1 AND 2 FOR DETAILED BLOCK DIAGRAM AND TYPICAL APPLICATION CIRCUIT. ISOLATION BARRIER
DI
Figure 4. Driver DC Test Load
Figure 5. Driver/Receiver Timing Test Circuit
13
______________________________________________________________________________________
Complete, Isolated RS-485/RS-422 Data Interface MAX1480A/B/C, MAX1490A/B
____________________________________________________Test Circuits (continued)
500 OUTPUT UNDER TEST CL
S1
ISO VCC_
S2
Figure 6. Driver Timing Test Load
_______________________________________________________Switching Waveforms
VCC_ - 0.4V 2 tPLH tPHL VCC_ - 0.4V 2
VCC_ - 0.4V DI 0V
VCC_ -0.4V DE 0V VCC_ - 0.4V 2 tZL tLZ VOL + 0.5V VCC_ - 0.4V 2
1/2 VO
B VO A 1/2 VO VO VDIFF 0V -VO 10% tR tSKEW = tPLH - tPHL VDIFF = V (A) - V (B) 90% 90% tF 10%
A, B VOL A, B 2.3V 0V tZH tHZ 2.3V OUTPUT NORMALLY LOW OUTPUT NORMALLY HIGH VOH - 0.5V
Figure 7. Driver Propagation Delays and Transition Times
Figure 8. Driver Enable and Disable Times
VID INPUT 0V 0V
2.4V SD 0.8V 1.6V 1.6V -VID VA - VB
tZL(SHDN) A, B VOL A, B 2.3V 0V tZH(SHDN)
tSHDN VOL + 0.5V RO VOH VOL 1.5V tPLH
MAX1490A/B OUTPUT 1.5V
2.3V OUTPUT NORMALLY LOW OUTPUT NORMALLY HIGH
tPHL
VOH - 0.5V tSHDN
RO
VOH VOL 1.5V tPHL
MAX1480A/B/C OUTPUT
1.5V tPLH
tSKEW = tPLH - tPHL
Figure 9. Times to/from Shutdown
14
Figure 10. Receiver Propagation Delays
______________________________________________________________________________________
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)
MAX1480A/B/C, MAX1490A/B
Table 3. 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 4. Receiving
INPUTS* DE
10dB/div
VA - VB +0.2V -0.2V Open
OUTPUT (RO) 0 1 0
0 0 0
0Hz 500kHz/div
5MHz
Full-Duplex Devices (MAX1490A/MAX1490B)
Figure 11. Driver Output Waveform and FFT Plot of MAX1480A/MAX1490A Transmitting a 150kHz Signal
Table 5. Transmitting
INPUT* (DI) 1 0 Z 0 1 OUTPUTS Y 1 0
10dB/div
* 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).
Table 6. Receiving
0Hz 500kHz/div 5MHz
INPUT (VA - VB) +0.2V -0.2V Open
OUTPUT (RO) 1 0 1 15
Figure 12. Driver Output Waveform and FFT Plot of MAX1480B/MAX1480C/MAX1490B Transmitting a 150kHz Signal
______________________________________________________________________________________
Complete, Isolated RS-485/RS-422 Data Interface MAX1480A/B/C, MAX1490A/B
TERMINATING RESISTOR (ONE RESISTOR ON EACH END)
B 120 A A B A B 100 RE RE R D RE R D R D
DI DE RO
RO DE
DI
RO DE
DI
VIN 5V C1 22F C2 0.1F
VCC1 VCC2
MAX1480A/B/C
1 2
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 A R6 R4 SH SHIELD (OPTIONAL) NOTE: RESISTOR R7 PROTECTS THE MAX1480A/B/C FROM TRANSIENT CURRENTS BETWEEN SHIELD AND TRANSMISSION LINES. R7 100 120 B
D1 3 D2 4 GND1 5 FS 6 SD 7 VCC3 R1 8 9 10 11 12
MAX845
MAX487 MAX1487
23 A 22 ISO DI IN 21 ISO DE IN
74HC86 OR EQUIVALENT DI DRIVER INPUT
DI VCC4 DE GND2
20 ISO COM1 19 ISO DI DRV 18 ISO VCC2
R5
DE
DRIVER ENABLE
R2 R3
17 ISO DE DRV 16 15 ISOLATION BARRIER ISO COM2 ISO RO LED
RECEIVER OUTPUT RO
RO 13 VCC5 14 LOGIC GROUND
ISOLATED COMMON
Figure 13. Typical Half-Duplex RS-485/RS-422 Network
16 ______________________________________________________________________________________
Complete, Isolated RS-485/RS-422 Data Interface
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 Typical Operating Characteristics). In addition, a thermal shutdown circuit forces the driver outputs into a highimpedance state if the die temperature rises excessively.
___________Applications Information
DI and DE are intended to be driven through a series current-limiting resistor. Directly grounding these pins destroys the device. 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.
MAX1480A/B/C, MAX1490A/B
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 1s for the MAX1480B/MAX1480C/MAX1490B. The driver skew time is typically 25ns for the MAX1480A/MAX1490A and 100ns for the MAX1480B/ MAX1480C/MAX1490B.
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.
VIN 5V C1 22F C2 0.1F VCC1 VCC2 1 2
MAX1490A/B
24 AC1 (MAKE NO CONNECTION) 23 AC2 (MAKE NO CONNECTION) 22 ISO VCC1 21 ISO RO DRV 20 A
MAX845 MAX488 MAX490
D1 3 D2 4 GND1 5 FS 6 SD 7 74HC86 OR EQUIVALENT DI DRIVER INPUT RO DI VCC3 R1 8
120 A B Z Y R5, 100 SH1 R4 SH2 R6, 100 R3 NOTE: RESISTORS R5 AND R6 PROTECT THE MAX1490A/B FROM TRANSIENT CURRENTS BETWEEN SHIELD AND TRANSMISSION LINES. SHIELD (OPTIONAL) 120 SHIELD (OPTIONAL)
Y 120 Z D DI
19 B 18 Z 17 Y 16 ISO COM1 15 ISO DI DRV 14 ISO VCC2 13 ISO RO LED
B 120 A R RO
DI 9 R2 VCC4 10 RO 11 RECEIVER OUTPUT GND2 12 ISOLATION BARRIER LOGIC GROUND
ISOLATED COMMON
Figure 14. Typical Full-Duplex RS-485/RS-422 Network
______________________________________________________________________________________ 17
Complete, Isolated RS-485/RS-422 Data Interface MAX1480A/B/C, MAX1490A/B
Connections and components from one side should not be located near those of the other side. * 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. 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. 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, tie 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).
Pull-Up 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 NETWORK SEGMENT A 2 8 10 14 A B 23 25 26 3k 19 22 17 21 24 200 15 5 7 12 +5V +5V 74HC04 9 200 DRIVER ENABLE B>A 4 3 DRIVER ENABLE 200 A>B 3k 13 3k 1 2 200 9
+5V NETWORK SEGMENT B 2 8 10 14 23 25 26 A B
MAX1480C
MAX1480C
13
3k 19 22 17 21 24 200 15 3k
3k
11
200
11
5 7 12
51k 1000pF 15 14 Q 13 74HC123
51k 1000pF 7 6 Q5 74HC123
16 2B
10 B
1A CLR 3
Q4
9A CLR 11
Q 12
Figure 15. Doubly Isolated RS-485 Repeater
18 ______________________________________________________________________________________
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. 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 8s (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 pull-up 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.
MAX1480A/B/C, MAX1490A/B
______________________________________________________________________________________
19
Complete, Isolated RS-485/RS-422 Data Interface MAX1480A/B/C, MAX1490A/B
_Ordering Information (continued)
PART MAX1480BCPI MAX1480BEPI MAX1480CCPI MAX1480CEPI MAX1490ACPG MAX1490AEPG MAX1490BCPG MAX1490BEPG TEMP. RANGE 0C to +70C -40C to +85C 0C to +70C -40C to +85C 0C to +70C -40C to +85C 0C to +70C -40C to +85C PIN-PACKAGE 28 Wide Plastic DIP 28 Wide Plastic DIP 28 Wide Plastic DIP 28 Wide Plastic DIP 24 Wide Plastic DIP 24 Wide Plastic DIP 24 Wide Plastic DIP 24 Wide Plastic DIP
VCC1 1 VCC2 2 D1 3 D2 4 GND1 5 FS 6 SD 7 VCC3 8 DI 9 VCC4 10 DE 11 GND2 12 RO 13 VCC5 14
____Pin Configurations (continued)
TOP VIEW
MAX1480A/B/C
28 AC1 27 AC2 26 ISO VCC1 25 B 24 ISO RO DRV
Data rate for "A" parts is up to 2500kbps. Data rate for "B" and
MAX845
"C" parts is up to 250kbps.
MAX487 MAX1487
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
ISOLATION BARRIER
DIP
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
20 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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