MAXIM MAX3480BEPI

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