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19-1940; Rev 0; 4/01
15kV ESD-Protected, Isolated RS-485/RS-422 Data Interfaces
_________________General Description
The MAX1480EA/MAX1480EC/MAX1490EA/MAX1490EB are complete, electrically isolated, RS-485/RS-422 data communications interface solutions in a hybrid microcircuit. The RS-485/RS-422 I/O pins are protected against 15kV electrostatic discharge (ESD) shocks, without latchup. 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 MAX1480EC/MAX1490EB feature 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 MAX1480EA/MAX1490EA driver slew rate is not limited, allowing transmission rates up to 2.5Mbps. The MAX1480EA/MAX1480EC are designed for half-duplex communication, while the MAX1490EA/MAX1490EB 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 MAX1480EA/MAX1480EC, RO high for the MAX1490EA/ MAX1490EB) if the input is open circuit. The MAX1480EA/MAX1480EC/MAX1490EA/MAX1490EB withstand 1260VRMS (1min) or 1520VRMS (1s). Their isolated outputs meet all RS-485/RS-422 specifications. The MAX1480EA/MAX1480EC are available in a 28-pin DIP package, and the MAX1490EA/MAX1490EB are available in a 24-pin DIP package. .
____________________________Features
o Isolated Data Interface, Guaranteed to 1260VRMS (1min) o 15kV ESD Protection on I/O Pins o Slew-Rate Limited for Errorless Data Transmission (MAX1480EC/MAX1490EB) o High-Speed, Isolated, 2.5Mbps RS-485/RS-422 Interface (MAX1480EA/MAX1490EA) o Full-Duplex Data Communication (MAX1490EA/MAX1490EB) o Single +5V Supply o Current Limiting and Thermal Shutdown for Driver Overload Protection o Standard 0.6in DIP Packages 28-Pin DIP (MAX1480EA/MAX1480EC) 24-Pin DIP (MAX1490EA/MAX1490EB)
MAX1480E/MAX1490E
_______________Ordering Information
PART MAX1480EACPI MAX1480EAEPI 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 C parts is up to 250kbps. *See Reliability section at end of data sheet.
Pin Configurations
TOP VIEW
VCC1 VCC2 D1 D2 GND1 1 2 3 4 5
MAX845E MAX488E MAX490E
24 AC1 23 AC2
________________________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
MAX1490EA/ MAX1490EB
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
FS 6 SD 7
VCC3 8 DI 9
VCC4 10 RO 11 GND2 12
DIP Selector Guide appears at end of data sheet. Pin Configurations continued at end of data sheet. 1
________________________________________________________________ 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.
15kV ESD-Protected, Isolated RS-485/RS-422 Data Interfaces MAX1480E/MAX1490E
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 MAX1480E_CPI/MAX1490E_CPI ........................0C to +70C MAX1480E_EPI/MAX1490E_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_ = +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 = 0 FS = VCC_ or open MAX1480EA, DE = VCC_ or open MAX1480EC, DE = VCC_ or open MAX1490EA MAX1490EB Shutdown Supply Current (Note 3) Shutdown Input Threshold Shutdown Input Leakage Current FS Input Threshold FS Input Pullup Current FS Input Leakage Current Input High Voltage Input Low Voltage Isolation Voltage Isolation Resistance Isolation Capacitance Differential Driver Output (No Load) Differential Driver Output (with Load) VIH VIL VISO RISO CISO VOD1 VOD2 R = 50 (RS-422) R = 27 (RS-485), Figure 4 2 1.5 VFSH VFSL High Low FS low FS high DE, DI, Figures 1 and 2 DE, DI, Figures 1 and 2 TA = +25C, 1min (Note 4) TA = +25C, VISO = 50VDC TA = +25C, f = 1MHz 1260 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 CONDITIONS MIN TYP 535 725 85 145 55 120 130 180 65 130 0.2 120 120 180 125 mA MAX UNITS kHz mA
Operating Supply Current
ICC
A V pA V A pA V V VRMS M pF V V
5
2
_______________________________________________________________________________________
15kV ESD-Protected, Isolated RS-485/RS-422 Data Interfaces MAX1480E/MAX1490E
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 Change in Magnitude of Driver Output Voltage for Complementary Output States Driver Common-Mode Output SYMBOL VOD VOC CONDITIONS Differential R = 27 or 50, Figure 4 Common mode R = 27 or 50, Figure 4 MAX1490EA/ MAX1490EB MAX1480EA/ MAX1480EC MAX1490EA/ MAX1490EB MAX1480EA/ MAX1480EC (MAX1480E_) (MAX1490E_) 48 12 -0.2 70 0.4 250 100 15 0.2 0.3 4 1.0 0.25 mA 0.8 0.2 k V mV V A mA kV V MIN TYP MAX 0.3 V UNITS
VIN = +12V Input Current (A, B) ISO IIN DE = 0, VCC_ = 0 or +5.5V VIN = -7V
Receiver Input Resistance Receiver Differential Threshold Receiver Input Hysteresis Receiver Output Low Voltage Receiver Output High Current Driver Short-Circuit Current ESD Protection
RIN VTH VTH VOL IOH ISO IOSD ISO IOSD
-7V VCM +12V -7V VCM +12V VCM = 0
Using resistor values listed in Tables 1 and 2 VOUT = 5.5V -7V VO 12V (Note 5) A, B, Y, and Z pins, tested using Human Body Model, Figures 1 and 2
SWITCHING CHARACTERISTICS--MAX1480EA/MAX1490EA
(VCC_ = +5V 10%, VFS = 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 (MAX1480EA Only) Driver Enable to Output Low (MAX1480EA Only) Driver Disable Time from Low (MAX1480EA Only) Driver Disable Time from High (MAX1480EA Only) Receiver Input to Output Propagation Delay SYMBOL tPLH tPHL tSKEW tR, tF tZH tZL tLZ tHZ tPLH tPHL 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 MIN TYP 90 60 30 15 1.0 1.0 0.5 0.5 120 90 MAX 275 275 100 50 1.8 1.8 1.8 1.8 225 225 UNITS ns ns ns s s s s ns
_______________________________________________________________________________________
3
15kV ESD-Protected, Isolated RS-485/RS-422 Data Interfaces MAX1480E/MAX1490E
SWITCHING CHARACTERISTICS--MAX1480EA/MAX1490EA (continued)
(VCC_ = +5V 10%, VFS = VCC_, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC_ = +5V and TA = +25C.) PARAMETER |tPLH - tPHL| Differential Receiver Skew Maximum Data Rate Time to Shutdown Shutdown to Driver Output High Shutdown to Driver Output Low SYMBOL tSKD fMAX tSHDN tZH(SHDN) tZH(SHDN) CONDITIONS Figures 5 and 10, RDIFF = 54, CL1 = CL2 = 100pF tSKEW, tSKD, tPHL 25% of data period Figures 6 and 9, CL = 100pF, S2 closed Figures 6 and 9, CL = 100pF, S1 closed 2.5 100 3 3 15 15 MIN TYP 30 MAX 150 UNITS ns Mbps s s s
SWITCHING CHARACTERISTICS--MAX1480EC/MAX1490EB
(VCC_ = +5V 10%, VFS = 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 (MAX1480EC Only) Driver Enable to Output Low (MAX1480EC Only) Driver Disable Time from Low (MAX1480EC Only) Driver Disable Time from High (MAX1480EC 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 SYMBOL tPLH tPHL tSKEW tR, tF 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 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 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 tSKEW, tSKD 25% of data period 160 100 3 3 15 15 MIN TYP 1.4 1.1 300 1.0 1.4 1.4 2.0 1.7 0.9 1.1 200 MAX 3.0 3.0 1200 2.0 4.5 4.5 4.5 4.5 3.0 3.0 UNITS s ns s s s s s s ns kbps s s s
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 MAX1480EA/ MAX1480EC, Figure 2 for MAX1490EA/MAX1490EB). Note 3: Shutdown supply current is the current at VCC1 and VCC2 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, e.g., between pins 1-14 and pins 15-28 on the 28-pin package. Note 5: Applies to peak current (see Typical Operating Characteristics). Although the MAX1480EA/MAX1480EC and MAX1490EA/MAX1490EB 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).
4
_______________________________________________________________________________________
15kV ESD-Protected, Isolated RS-485/RS-422 Data Interfaces
__________________________________________Typical Operating Characteristics
(VCC_ = +5V, VFS = VCC_, Figures 1 and 2, TA = +25C, unless otherwise noted.)
MAX1480E/MAX1490E
OUTPUT CURRENT vs. RECEIVER OUTPUT LOW VOLTAGE
MAX1480E/90E TOC01
OUTPUT CURRENT vs. RECEIVER OUTPUT HIGH VOLTAGE
MAX1480E/90E TOC02
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
MAX1480E/90E TOC03
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
MAX1480E/90E TOC04
OUTPUT CURRENT vs. DRIVER OUTPUT LOW VOLTAGE
MAX1480E/90E TOC05
OUTPUT CURRENT vs. DRIVER OUTPUT HIGH VOLTAGE
-90 -80 OUTPUT CURRENT (mA) -70 -60 -50 -40 -30 -20 -10 0
MAX1480E/90E TOC06
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
MAX1480E/90E TOC07
DRIVER DIFFERENTIAL OUTPUT VOLTAGE vs. TEMPERATURE
MAX1480E/90E TOC08
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= VCC_(MAX1480EC ONLY) MEASURED AT VCC1 AND VCC2
MAX1480E/90E TOC09
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)
_______________________________________________________________________________________
5
15kV ESD-Protected, Isolated RS-485/RS-422 Data Interfaces MAX1480E/MAX1490E
____________________________Typical Operating Characteristics (continued)
(VCC_ = +5V, VFS = VCC_, Figures 1 and 2, TA = +25C, unless otherwise noted.)
MAX1480EA SUPPLY CURRENT vs. TEMPERATURE
MAX1480E/90E TOC10
MAX1480EC 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 = +5V RL = DE = VCC VCC = +5.5V VCC = +5V VCC = +4.5V RL = 54
MAX1480E/90E T0C11
MAX1490EA SUPPLY CURRENT vs. TEMPERATURE
VCC = +5.5V 180 SUPPLY CURRENT (mA) VCC = +5V 160 140 VCC = +5.5V 120 100 80 -40 -20 0 20 VCC = +4.5V 40 60 80 VCC = +5V RL = VCC = +4.5V RL = 54
MAX1480E/90E TOC12
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 = +5V DE = VCC VCC = +5.5V VCC = +5V VCC = +4.5V RL = RL = 54
120
200
VCC = +4.5V
TEMPERATURE (C)
TEMPERATURE (C)
MAX1490EB SUPPLY CURRENT vs. TEMPERATURE
VCC = +5.5V VCC = +5V VCC = +4.5V RL = 54 140 130 SUPPLY CURRENT (mA) 120 110 100 90 80 70 60 50 -40 -20 0 20 40 VCC = +4.5V 60 80 VCC = +5V VCC = +5.5V RL =
MAX1480E/90E TOC13
150
TEMPERATURE (C)
MAX1480EA/MAX1490EA RECEIVER tPHL
MAX1480E/90E toc14
MAX1480EA/MAX1490EA RECEIVER tPLH
MAX1480E/90E toc15
RECEIVER INPUT A 1V/div
RECEIVER INPUT B 1V/div
RECEIVER INPUT B 1V/div RO 2V/div 20ns/div VCC_ = 5.0V, DE= VCC_
RECEIVER INPUT A 1V/div RO 2V/div
20ns/div VCC_ = 5.0V, DE= VCC_ DI = 0V TO 5V AT 1 25MHz
6
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15kV ESD-Protected, Isolated RS-485/RS-422 Data Interfaces
_____________________________Typical Operating Characteristics (continued)
(VCC_ = +5V, VFS = VCC_, VDI = 0, DE toggled 0 to 5V at 5kHz, Figures 1 and 2, TA = +25C, unless otherwise noted.)
MAX1480EC/MAX1490EB RECEIVER tPHL
MAX1480E/90E toc16
MAX1480E/MAX1490E
MAX1480EC/MAX1490EB RECEIVER tPLH
MAX1480E/90E toc17
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 VCC = 5 0V DE= VCC
RO 2V/div
500ns/div
MAX1480EC DRIVER ENABLE TIME
MAX1480E/90E TOC18
MAX1480EC DRIVER DISABLE TIME
MAX1480E/90E TOC19
DRIVER OUTPUT B 2V/div
DRIVER OUTPUT B 2V/div
DE 2V/div
DE 2V/div
500ns/div VCC = 5.0V, DI= 0V VCC = 5.0V, DI = 0V
500ns/div
MAX1480EA/MAX1490EA POWER-UP DELAY TO DRIVER OUTPUTS VALID
MAX1480E/90E TOC20
DRIVER OUTPUT B (Z FOR MAX1490) 2V/div
SD 2V/div
1s/div VDI = 0 VSD = 5V TO 0 AT 1kHz
_______________________________________________________________________________________
7
15kV ESD-Protected, Isolated RS-485/RS-422 Data Interfaces MAX1480E/MAX1490E
________________________________________________________________Pin Description
PIN MAX1480EA/ MAX1480EC 1, 2, 8, 10 3, 4 5 6 MAX1490EA/ MAX1490EB 1, 2, 8, 10 3, 4 5 6 NAME FUNCTION
VCC1-VCC4 D1, D2 GND1 FS
Logic-Side (Nonisolated 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 (MAX1480EA/MAX1480EC 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 (see Table 1 for MAX1480EA/MAX1480EC, Table 2 for MAX1490EA/MAX1490EB). 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). Receiver Output. If A > B by 200mV, RO is high; if A < B by 200mV, RO is low. Open collector; must have pullup to VCC (Table 2). Logic-Side Ground. Connect to GND1 (pin 5). Receiver Output. If A > B by 200mV, RO is low; if A < B by 200mV, RO is high. Open collector; must have pullup to VCC (Table 1). Logic-Side (Nonisolated Side) +5V Supply Voltage Isolated Receiver Output LED. Internal LED anode in MAX1480EA/MAX1480EC and LED cathode in MAX1490EA/MAX1490EB. Connect to ISO RO DRV through a resistor (Table 1 for MAX1480EA/MAX1480EC; Table 2 for MAX1490EA/MAX1490EB). 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. Open-collector output; must have pullup to ISO VCC_ and be connected to ISO DE IN for normal operation (Table 1). Isolated Supply Voltage. Connect to ISO VCC1 (pin 26 for MAX1480EA/ MAX1480EC, or pin 22 for MAX1490EA/MAX1490EB). Isolated Driver-Input Drive. With DE high (MAX1480EA/MAX1480EC 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 MAX1480EA/MAX1480EC only) for normal operation. Open-collector output; connect a pullup resistor to ISO VCC_ (Table 1 for MAX1480EA/MAX1480EC, Table 2 for MAX1490EA/MAX1490EB). Isolated Common. For MAX1480EA/MAX1480EC, connect to ISO COM2 (pin 16) (Figures 1 and 2).
7
7
SD
9
9
DI
11
--
DE
-- 12 13 14
11 12 -- --
RO GND2 RO VCC5
15 16
13 --
ISO RO LED ISO COM2
17
--
ISO DE DRV
18
14
ISO VCC2
19
15
ISO DI DRV
20 8
16
ISO COM1
_______________________________________________________________________________________
15kV ESD-Protected, Isolated RS-485/RS-422 Data Interfaces
___________________________________________________Pin Description (continued)
PIN MAX1480EA/ MAX1480EC -- -- -- -- 21 22 23 24 25 26 27, 28 MAX1490EA/ MAX1490EB 17 18 19 20 -- -- -- 21 -- 22 23, 24 NAME Y Z B A ISO DE IN ISO DI IN A ISO RO DRV B ISO VCC1 AC2, AC1 FUNCTION Noninverting Driver Output Inverting Driver Output Inverting Receiver Input Noninverting Receiver Input 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 a resistor (see Table 1 for MAX1480EA/MAX1480EC, Table 2 for MAX1490EA/MAX1490EB). Inverting Driver Output and Inverting Receiver Input Isolated Supply Voltage Source Internal Connections. Leave these pins unconnected.
MAX1480E/MAX1490E
Note: For DE and DI pin descriptions, see Detailed Block Diagram and Typical Application Circuit (Figure 1 for MAX1480EA/ MAX1480EC, Figure 2 for MAX1490EA/MAX1490EB).
Detailed Description
The MAX1480EA/MAX1480EC/MAX1490EA/MAX1490EB are complete, electrically isolated, RS-485/RS-422 datacommunications interface solutions. Transceivers, optocouplers, a power driver, and a transformer in one standard 28-pin DIP package (24-pin package for the MAX1490EA/MAX1490EB) 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 highspeed optocouplers. A single +5V supply on the logic side powers both sides of the interface. The MAX1480EA/MAX1480EC offer half-duplex communications while the MAX1490EA/MAX1490EB feature fullduplex communication. The functional input/output relationships are shown in Tables 3 through 6. The MAX1480EC/MAX1490EB feature 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 MAX1480EA/MAX1490EA driver slew rate is not limited, allowing transmission rates up to 2.5Mbps. The MAX1480EC/MAX1490EB shutdown feature reduces supply current to as low as 0.2A by using the SD pin (see Low-Power Shutdown Mode section).
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 MAX1480EA/MAX1480EC, the driver outputs are enabled by bringing DE high. Driver-enable time is typically 1.0s. Allow time for the devices to be enabled before sending data (see Typical Operating Characteristics). When enabled, driver outputs function as line drivers. Driver outputs are high impedance when DE is low. When outputs are high impedance, they function as line receivers. The MAX1480EA/MAX1480EC/MAX1490EA/MAX1490EB withstand 1260VRMS (1min) or 1520VRMS (1s). The logic inputs can be driven from TTL/CMOS logic with a series resistor, and the received data output can directly drive TTL or CMOS-logic families with only a resistive pullup.
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 nonsolated side are low. Therefore, leave DI and DE high or floating when in shutdown mode. Under these conditions, the MAX1480EC/MAX1490EB supply current is reduced to as low as 0.2A.
9
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15kV ESD-Protected, Isolated RS-485/RS-422 Data Interfaces MAX1480E/MAX1490E
VCC3 ISO VCC1 MAX845E Q FS OSC 1.07MHz/ 1.45MHz T F/F D2 Q N ISO DE IN ISO RO DRV SD GND1 RE R N ISO DI IN D A D1 MAX1480EA: MAX1487E MAX1480EC: MAX487E B
ISO COM1 EXTERNAL RS-485/RS-422 WIRING MAX1480EA MAX1480EC 1 2 28 AC1 (MAKE NO CONNECTION) 27 AC2 (MAKE NO CONNECTION) 26 ISO VCC1 B 25 24 MAX845E MAX1487E MAX487E ISO RO DRV A R6* R4* SH B SHIELD (OPTIONAL) TWISTED PAIR TO OTHER TRANSCEIVERS RL SHIELD (OPTIONAL) TERMINATING RESISTOR (ONE RESISTOR ON EACH END) TWISTED PAIR TO OTHER TRANSCEIVERS RL
VIN +5V C1 22F C2 0.1F
VCC1 VCC2
D1 3 D2 4 GND1 5 FS 6 SD
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 17 ISO DE DRV 16 15 ISOLATION BARRIER ISO COM2 ISO RO LED
R5* R7 100
NOTE: RESISTOR R7 PROTECTS THE MAX1480EA FROM TRANSIENT CURRENTS BETWEEN SHIELD AND TRANSMISSION LINES.
RO 13 VCC5 14
*SEE TABLE 1.
LOGIC GROUND
ISOLATED COMMON
270pF 4kV
Figure 1. MAX1480EA/MAX1480EC Detailed Block Diagram and Application Circuit
Table 1. Pullup and LED Drive Resistors for Figure 1
PART MAX1480EA MAX1480EC R1 () 200 200 R2 () 200 200 R3 () 1000 3000 R4 () 4300 3000 R5 () 1000 3000 R6 () 200 200
The high-speed optocouplers on the MAX1480EA/ MAX1480EC/MAX1490EA consume an additional 10mA through VCC5 (VCC4 for the MAX1490EA). Therefore, to completely shut down these devices, use an external Pchannel MOSFET as shown in Figure 3. In normal operation, 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 opto10
couplers. In normal operating mode, the switch carries only the optocoupler currents, so an on-resistance of several ohms does not significantly degrade efficiency.
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15kV ESD-Protected, Isolated RS-485/RS-422 Data Interfaces MAX1480E/MAX1490E
VCC3 D1 N R D2 Q N ISO RO DRV ISO DI DRV MAX1490EA: MAX490E MAX1490EB: MAX488E D SD GND1 Y A B Z
MAX845 Q FS OSC 1.07MHz/ 1.45MHz T F/F
VIN +5V VCC1 C1 22F C2 0.1F VCC2 D1 1 2 3
MAX1490EA/ MAX1490EB
24 AC1 (MAKE NO CONNECTION) 23 AC2 (MAKE NO CONNECTION) 22 ISO VCC1 21 ISO RO DRV 20 A
MAX488E MAX490E MAX845
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 MAX1490EA/MAX1490EB 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 *SEE TABLE 2. LOGIC GROUND 270 pF 4kV
ISOLATED COMMON
Figure 2. MAX1490EA/MAX1490EB Detailed Block Diagram and Typical Application Circuit
Table 2. Pullup and LED Drive Resistors for Figure 2
PART MAX1490EA MAX1490EB R1 () 200 200 R2 () 1000 3000 R3 () 330 330 R4 () 1000 3000
MAX1480EC/MAX1490EB: Reduced EMI and Reflections
The MAX1480EC/MAX1490EB are slew-rate-limited, minimizing EMI and reducing reflections caused by improperly terminated cables. Figure 11 shows both the driver output waveform of a MAX1480EA/ MAX1490EA 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-rate-limited
MAX1480EC/MAX1490EB transmitting the same signal. The high-frequency harmonics have much lower amplitudes, and therefore the potential for EMI is significantly reduced.
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 cir11
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15kV ESD-Protected, Isolated RS-485/RS-422 Data Interfaces MAX1480E/MAX1490E
MAX1480EA
VIN +5V VCC1 1 VCC2 2 D1 3 D2 4 Si9433DY P GND1 5 FS 6 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 MAX845 MAX1487E 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
GND
Figure 3. MAX1480EA Low-Power Shutdown Mode
Test Circuits
ISOLATION BARRIER ISOLATION BARRIER (DE) R D VOD R VOC DI D VID CL2 CL1 RDIFF ( ) ARE FOR THE MAX1480EA/MAX1480EC. R RO (RO)* * OPTOCOUPLER OUTPUTS. SEE FIGURES 1 AND 2 FOR DETAILED BLOCK DIAGRAM AND TYPICAL APPLICATION CIRCUIT. ISOLATION BARRIER
Figure 4. Driver DC Test Load 12
Figure 5. Driver/Receiver Timing Test Circuit
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15kV ESD-Protected, Isolated RS-485/RS-422 Data Interfaces
____________________________________________________Test Circuits (continued)
MAX1480E/MAX1490E
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 DE 1/2 VO 0 VCC_ - 0.4V 2 tZL VO A 1/2 VO VO VDIFF 0 -VO 10% tR tSKEW = tPLH - tPHL VDIFF = V (A) - V (B) 90% 90% tF 10% A, B VOL A, B 2.3V 0 tZH tHZ 2.3V OUTPUT NORMALLY LOW OUTPUT NORMALLY HIGH VOH - 0.5V VOL + 0.5V tLZ VCC_ - 0.4V 2
VCC_ - 0.4V DI 0
B
Figure 7. Driver Propagation Delays and Transition Times
Figure 8. Driver Enable and Disable Times
VID INPUT 0 0
2.4V SD 0.8V 1.6V 1.6V -VID VA - V B
tZL(SHDN) A, B VOL A, B 2.3V 0 tZH(SHDN)
tSHDN VOL + 0.5V RO VOH VOL
MAX1490EA/MAX1490EB OUTPUT 1.5V tPLH 1.5V
2.3V OUTPUT NORMALLY LOW OUTPUT NORMALLY HIGH
tPHL
VOH - 0.5V tSHDN
RO
VOH VOL 1.5V
MAX1480EA/MAX1480EC 1.5V OUTPUT tSKEW = tPLH - tPHL tPLH
tPHL
Figure 9. Times to/from Shutdown
Figure 10. Receiver Propagation Delays 13
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15kV ESD-Protected, Isolated RS-485/RS-422 Data Interfaces MAX1480E/MAX1490E
cuits over the entire common-mode range (see Typical Operating Characteristics). In addition, a thermal shutdown circuit forces the driver outputs into a high-im pedance state if the die temperature rises excessively.
_____________________Function Tables
Half-Duplex Devices (MAX1480EA/MAX1480EC)
Propagation Delay Skew
Propagation delay skew is 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.
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
0 500kHz/div
5MHz
Full-Duplex Devices (MAX1490EA/MAX1490EB)
Figure 11. Driver Output Waveform and FFT Plot of MAX1480EA/MAX1490EA 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 MAX1480EA/ MAX1480EC, Figure 2 for MAX1490EA/MAX1490EB).
Table 6. Receiving
0 500kHz/div 5MHz
INPUT (VA - VB) +0.2V -0.2V Open
OUTPUT (RO) 1 0 1
Figure 12. Driver Output Waveform and FFT Plot of MAX1480EC/ MAX1490EB Transmitting a 150kHz Signal
14
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15kV ESD-Protected, Isolated RS-485/RS-422 Data Interfaces
___________Applications Information
These E versions of the MAX1480EA/MAX1480EC/ 1490EA/MAX1490EB provide extra protection against ESD. The rugged MAX1480EA/MAX1480EC/MAX1490EA/ MAX1490EB 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) MAX1480A/MAX1480C/MAX1490A/MAX1490B are recommended for applications where cost is critical.
Human Body Model
Figure 13 shows the Human Body Model, and Figure 14 shows the current waveform it generates when discharged into low impedance. This model consists of a 100pF capacitor charged to the ESD voltage of interest, which is then discharged into the test device through a 1.5k resistor.
MAX1480E/MAX1490E
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. All pins require this protection during manufacturing--not just inputs and outputs. Therefore, after PC board assembly, the Machine Model is less relevant to I/O ports. The MAX1480EA/MAX1480EC are designed for bidirectional data communications on multipoint bus-transmission lines. The MAX1490EA/MAX1490EB are designed for full-duplex bidirectional communications that are primarily point-to-point. Figures 15 and 16 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 MAX1480EC/MAX1490EB are more tolerant of imperfect termination and stubs off the main line.
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 powered down. After an ESD event, Maxim's MAX1480EA/MAX1480EC/MAX1490EA/ MAX1490EB keep working without latchup. An isolation capacitor of 270pF 4kV should be placed between ISO COM and logic ground for optional 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.
Layout Considerations
The MAX1480EA/MAX1480EC/MAX1490EA/MAX1490EB 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 MAX1480EA/
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 (Figures 1 and 2).
R C 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 13. Human Body ESD Test Model
Figure 14. Human Body Current Waveform 15
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15kV ESD-Protected, Isolated RS-485/RS-422 Data Interfaces MAX1480E/MAX1490E
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
MAX1480EA/ MAX1480EC
VCC1 VCC2 C1 22F C2 0.1F 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 MAX1480EA/MAX1480EC FROM TRANSIENT CURRENTS BETWEEN SHIELD AND TRANSMISSION LINES. 120 B
D1 3 D2 4 GND1 5 FS 6 SD 7 VCC3 R1 8 9 10 11 12 MAX845E MAX487E MAX1487E
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 17 ISO DE DRV 16 15 ISOLATION BARRIER 270pF 4kV ISO COM2 ISO RO LED
R5
DE
DRIVER ENABLE
R2 R3
RECEIVER OUTPUT RO
R7 100
RO 13 VCC5 14 LOGIC GROUND
ISOLATED COMMON
Figure 15. Typical Half-Duplex RS-485/RS-422 Network 16 ______________________________________________________________________________________
15kV ESD-Protected, Isolated RS-485/RS-422 Data Interfaces MAX1480E/MAX1490E
VIN +5V C1 22F VCC1 C2 0.1F VCC2 1 2
MAX1490EA/ MAX1490EB
24 AC1 (MAKE NO CONNECTION) 23 AC2 (MAKE NO CONNECTION) 22 ISO VCC1 21 ISO RO DRV 20 A
MAX845E MAX488E MAX490E
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 MAX1490EA/MAX1490EB 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 270pF 4kV
Figure 16. Typical Full-Duplex RS-485/RS-422 Network
MAX1480EC/MAX1490EA/MAX1490EB. 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.
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 pullup 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 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 MAX1490EA/MAX1490EB, each shield should have its own 100 resistor (Figures 1, 2, 15, and 16).
Pullup and LED Drive Resistors
The MAX1480EA/MAX1480EC/MAX1490EA/MAX1490EB are specified and characterized using the resistor values shown in Tables 1 and 2. Altering the recommended values can degrade performance. DI and DE are intended to be driven through a series current-limiting resistor. Directly grounding these pins destroys the device. The DI and DE (MAX1480EA/MAX1480EC only) inputs are the cathodes of LEDs whose anodes are connected to the supply. These points are best driven by a CMOSlogic gate with a series resistor to limit the current. The
Double-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 ground-potential 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 cur17
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15kV ESD-Protected, Isolated RS-485/RS-422 Data Interfaces MAX1480E/MAX1490E
rents 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 17 shows a half-duplex (2-wire), bidirectional, party-line repeater system that prevents interference and/or damage from ground-potential differences. Two MAX1480EA/MAX1480EC isolated RS-485 transceivers are used to isolate each of the network segments from the electrical environment of the repeater. The MAX1480EA/MAX1480EC 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
+5V NETWORK SEGMENT A 2 8 10 14 A B 23 25 26 3k 3k 19 22 17 21 24 200 15 5 7 12 +5V +5V 5 7 12 15 74HC04 9 200 DRIVER ENABLE B>A 4 3 DRIVER ENABLE 200 A>B 3k 13 3k 1 2 200 9 2 8 10 14 23 25 26 A B
corrupted by the collisions that inevitably occur with a party-line system. With the repeater of Figure 17, 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 17 can be used either directly as shown, with the slew-rate-limited MAX1480EC, for data transfer rates up to 160kbps, or with the MAX1480EA for data rates up to 2.5Mbps (see Table 1 for pullup and LED resistor values when using the MAX1480EA). If dualport isolation is not needed, one of the MAX1480EC devices can be replaced by a MAX487E for 250kbps applications.
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.
+5V NETWORK SEGMENT B
MAX1480EC
MAX1480EC
13
3k 19 22 17 21 24 200 3k
11
200
11
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 17. Double-Isolated RS-485 Repeater 18 ______________________________________________________________________________________
15kV ESD-Protected, Isolated RS-485/RS-422 Data Interfaces
Ordering Information (continued)
PART MAX1480ECCPI MAX1480ECEPI MAX1490EACPG MAX1490EAEPG MAX1490EBCPG MAX1490EBEPG up to 250kbps. TEMP. RANGE 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 24 Wide Plastic DIP 24 Wide Plastic DIP 24 Wide Plastic DIP 24 Wide Plastic DIP TOP VIEW
VCC1 1 VCC2 2 D1 3 D2 4 GND1 5 FS 6 SD 7 MAX845 MAX487E MAX1487E 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 ISOLATION BARRIER
Pin Configurations (continued)
MAX1480E/MAX1490E
MAX1480EA/ MAX1480EC
Data rate for A parts is up to 2500kbps. Data rate for C parts is
Selector Guide
PART HALF/ FULL DUPLEX Half Half Full Full DATA RATE (Mbps) 2.5 0.25 2.5 0.25 SLEWRATE LIMITED No Yes No Yes
VCC3 8 DI 9 VCC4 10 DE 11 GND2 12 RO 13 VCC5 14
MAX1480EA MAX1480EC MAX1490EA MAX1490EB
This device is constructed using a unique set of packaging techniques that impose a limit on the thermal profile the device can be exposed to during board-level solder attach and rework. Maxim recommends the use of the solder profiles recommended in the industry-standard specification, JEDEC 020A, paragraph 7.6, Table 3 for IR/VPR and Convection Reflow processes. Preheating, per this standard, is required. Hand or wave soldering is not recommended.
DIP
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600___________________ 19 (c) 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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