Maxim MAX3480EBEPI -15kv esd-protected, isolated, 3.3v rs-485/rs-422 data interface Datasheet

19-1941; Rev 0; 4/01
±15kV ESD-Protected, Isolated, 3.3V
RS-485/RS-422 Data Interfaces
____________________________Features
♦ Isolated Data Interface Guaranteed to 1260VRMS
(1min)
Drivers are short-circuit current limited and are protected against excessive power dissipation by thermal
shutdown circuitry that places the driver outputs into a
high-impedance state. The receiver input has a fail-safe
feature that guarantees a logic-high output if the input
is open circuit.
The MAX3480EA/MAX3480EB are guaranteed to withstand 1260VRMS (1min) or 1520VRMS (1s). Their isolated
inputs and outputs meet RS-485/RS-422 specifications.
♦ Allows Up to 128 Transceivers on the Bus
________________________Applications
Isolated RS-485/RS-422 Data Interface
Transceivers for EMI-Sensitive Applications
Industrial-Control Local Area Networks
Automatic Test Equipment
HVAC/Building Control Networks
Telecom
Ordering Information
PART
MAX3480EACPI
MAX3480EAEPI
MAX3480EBCPI
MAX3480EBEPI
TEMP.
RANGE
PINPACKAGE*
0°C to +70°C 28 Plastic DIP
DATA
RATE
(kbps)
2500
♦ ±15kV ESD Protection for I/O Pins
♦ Slew-Rate-Limited Data Transmission (160kbps for
MAX3480EB)
♦ High-Speed, Isolated, 2.5Mbps RS-485 Interface
(MAX3480EA)
♦ Single +3.3V Supply
♦ Current Limiting and Thermal Shutdown for
Driver Overload Protection
♦ Standard 28-Pin DIP Package
Pin Configuration
TOP VIEW
MAX3480EA
MAX3480EB
VCC1 1
28 AC1
VCC2
2
27 AC2
D1
3
26 ISO VCC1
D2
4
25 B
GND1
5
MAX485E
MAX487E
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
-40°C to +85°C 28 Plastic DIP
2500
0°C to +70°C 28 Plastic DIP
250
GND2 12
-40°C to +85°C 28 Plastic DIP
250
RO 13
*See Reliability section at end of data sheet.
24 ISO RO DRV
MAX845
17 ISO DE DRV
16 ISO COM2
VCC5 14
15 ISO RO LED
ISOLATION BARRIER
DIP
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1
MAX3480EA/MAX3480EB
General Description
The MAX3480EA/MAX3480EB are electrically isolated
RS-485/RS-422 data-communications interfaces. The
RS-485/RS-422 I/O pins are protected against ±15kV
electrostatic discharge (ESD) shocks, without latchup.
Transceivers, optocouplers, and a transformer are all
included in one low-cost, 28-pin DIP package. A single
+3.3V supply on the logic side powers both sides of the
interface.
The MAX3480EB features reduced-slew-rate drivers
that minimize EMI and reduce reflections caused by
improperly terminated cables, allowing error-free data
transmission at data rates up to 160kbps. The
MAX3480EA’s driver slew rate is not limited, allowing
transmission rates up to 2.5Mbps.
MAX3480EA/MAX3480EB
±15kV ESD-Protected, Isolated, 3.3V
RS-485/RS-422 Data Interfaces
ABSOLUTE MAXIMUM RATINGS
With Respect to GND
Supply Voltage (VCC1, VCC2, VCC4, VCC5) .......-0.3V to +3.8V
Supply Voltage (VCC3) ........................................-0.3V to +7V
Control Input Voltage (SD, FS) ............-0.3V to (VCC3 + 0.3V)
Receiver Output Voltage (RO).............-0.3V to (VCC5 + 0.3V)
With Respect to ISO COM
Control Input Voltage (ISO DE _)......-0.3V to (ISO VCC_ + 0.3V)
Driver Input Voltage (ISO DI _) .....-0.3V to (ISO VCC_ + 0.3V)
Receiver Output Voltage (ISO RO _) ..-0.3V to (ISO VCC_ + 0.3V)
Driver Output Voltage (A, B)..............................-8V to +12.5V
Receiver Input Voltage (A, B)............................-8V to +12.5V
LED Forward Current (DI, DE, ISO RO LED) ......................50mA
Continuous Power Dissipation (TA = +70°C)
28-Pin Plastic DIP (derate 9.09mW/°C above +70°C) ..727mW
Operating Temperature Ranges
MAX3480E_CPI..................................................0°C to +70°C
MAX3480E_EPI ...............................................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VCC = VCC1 = VCC2 = VCC4 = VCC5 = +3.0V to +3.6V, FS = 0, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC =
+3.3V and TA = +25°C.) (Notes 1, 2)
PARAMETER
Switch Frequency
Operating Supply Current
Shutdown Supply Current (Note 3)
SYMBOL
CONDITIONS
MIN
TYP
fSWL
FS = 0
60
fSWH
FS = VCC or open
900
ICC
MAX3480EA,
DE´ = VCC or open
RL = ∞
130
RL = 54Ω
220
MAX3480EB,
DE´ = VCC or open
RL = ∞
80
RL = 54Ω
180
MAX
kHz
250
200
ISHDN
SD = VCC3
VFSH
High
VFSL
Low
0.8
FS Input Pullup Current
IFSL
FS low
50
FS Input Leakage Current
IFSM
FS high
Input High Voltage
VIH
DE´, DI´, Figure 1
Input Low Voltage
VIL
DE´, DI´, Figure 1
FS Input Threshold
Isolation Voltage
0.2
10
High
VSDL
Low
Isolation Resistance
RISO
TA = +25°C, VISO = ±50VDC
Isolation Capacitance
CISO
ƒ = 1MHz
ESD Protection
ESD
A, B, Y, and Z pins, tested at Human Body
Model
Differential Driver Output
(No Load)
VOD1
Differential Driver Output
VOD2
Change in Magnitude of Driver
Output Voltage for
Complementary Output States
∆VOD
Shutdown Input Threshold
2
1260
2.4
0.8
MΩ
10
pF
±15
kV
2
R = 27Ω (RS-485), Figure 3
R = 27Ω or 50Ω,
Figure 3
V
10,000
8
R = 50Ω (RS-422)
V
VRMS
1
1
100
µA
V
0.4
TA = +25°C, 1min (Note 4)
V
pA
VCC - 0.4
VISO
mA
µA
2.4
VSDH
UNITS
1.5
5
Differential
0.3
Common mode
0.3
V
V
V
_______________________________________________________________________________________
±15kV ESD-Protected, Isolated, 3.3V
RS-485/RS-422 Data Interfaces
(VCC = VCC1 = VCC2 = VCC4 = VCC5 = +3.0V to +3.6V, FS = 0, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VCC =
+3.3V and TA = +25°C.) (Notes 1, 2)
PARAMETER
Driver Common-Mode Output
Input Current (A, B)
SYMBOL
VOC
ISO IIN
CONDITIONS
DE´ = 0,
VCC = 0 or
+3.6V
MAX3480EA
MAX3480EB
RIN
Receiver Differential Threshold
VTH
-7V ≤ VCM ≤ 12V
Receiver Input Hysteresis
∆VTH
VCM = 0
Receiver Output Low Voltage
VOL
DI´ = VCC
IOH
VOUT = +3.6V, DI´ = 0
Receiver Output High Current
Driver Short-Circuit Current
ISO IOSD
TYP
R = 27Ω or 50Ω, Figure 4
-7V ≤ VCM ≤
12V
Receiver Input Resistance
MIN
VIN = +12V
MAX
UNITS
4
V
0.25
VIN = -7V
-0.2
VIN = +12V
0.25
VIN = -7V
mA
-0.2
MAX3480EA
48
MAX3480EB
48
kΩ
-0.2
0.2
70
0.4
250
-7V ≤ VO ≤ 12V (Note 5)
V
mV
100
V
µA
mA
SWITCHING CHARACTERISTICS—MAX3480EA
(VCC = VCC1 = VCC2 = VCC4 = VCC5 = +3.0V to +3.6V, FS = 0, TA = TMIN to TMAX, unless otherwise noted. Typical values are at
VCC = +3.3V and TA = +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
tSKEW
Figures 4, 6; RDIFF = 54Ω,
CL1 = CL2 = 100pF (Note 5)
25
100
ns
Driver Rise or Fall Time
tR, tF
Figures 4, 6; RDIFF = 54Ω,
CL1 = CL2 = 100pF
15
50
ns
Driver Enable to Output High
tZH
Figures 5, 7; CL = 100pF, S2 closed
0.5
1.8
µs
Driver Enable to Output Low
tZL
Figures 5, 7; CL = 100pF, S1 closed
0.5
1.8
µs
Driver Disable Time from High
tHZ
Figures 5, 7; CL = 15pF, S2 closed
0.6
1.8
µs
Driver Disable Time from Low
tLZ
Figures 5, 7; CL = 15pF, S1 closed
0.6
1.8
µs
Figures 4, 8; RDIFF = 54Ω,
CL1 = CL2 = 100pF
100
225
120
225
20
100
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
tSKEW, tSKD ≤ 25% of data period
2.5
ns
ns
Mbps
_______________________________________________________________________________________
3
MAX3480EA/MAX3480EB
ELECTRICAL CHARACTERISTICS (continued)
MAX3480EA/MAX3480EB
±15kV ESD-Protected, Isolated, 3.3V
RS-485/RS-422 Data Interfaces
SWITCHING CHARACTERISTICS—MAX3480EB
(VCC = VCC1 = VCC2 = VCC4 = VCC5 = +3.0V to +3.6V, FS = 0, TA = TMIN to TMAX, unless otherwise noted. Typical values are at
VCC = +3.3V and TA = +25°C.)
PARAMETER
Driver Input to Output
Propagation Delay
SYMBOL
tPLH
tPHL
CONDITIONS
MIN
Figures 4, 6; RDIFF = 54Ω,
CL1 = CL2 = 100pF
TYP
MAX
1.5
3.0
1.2
3.0
UNITS
µs
Driver Output Skew
tSKEW
Figures 4, 6; RDIFF = 54Ω,
CL1 = CL2 = 100pF
300
1200
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
1.2
4.5
µs
Driver Enable to Output Low
tZL
Figures 5, 7; CL = 100pF, S1 closed
1.0
4.5
µs
Driver Disable Time from Low
tLZ
Figures 5, 7; CL = 15pF, S1 closed
1.5
4.5
µs
Driver Disable Time from High
tHZ
Figures 5, 7; CL = 15pF, S2 closed
2.0
4.5
µs
Receiver Input to Output
Propagation Delay
tPLH
Figures 4, 8; RDIFF = 54Ω,
CL1 = CL2 = 100pF
0.6
3.0
1.4
3.0
750
1500
tPLH - tPHL Differential
Receiver Skew
Maximum Data Rate
tPHL
tSKD
Figures 4, 8; RDIFF = 54Ω,
CL1 = CL2 = 100pF
fMAX
tSKEW, tSKD ≤ 25% of data period
160
µs
ns
kbps
Note 1: All currents into device pins are positive; all currents out of device pins are negative. All voltages are referenced to
logic-side ground (GND1, GND2), unless otherwise specified.
Note 2: For DE´ and DI´ pin descriptions, see Detailed Block Diagram and Typical Application Circuit (Figure 1 for
MAX3480EA/MAX3480EB).
Note 3: Shutdown supply current is the current at VCC1 when shutdown is enabled.
Note 4: Limit guaranteed by applying 1520VRMS for 1s. Test voltage is applied between all pins on one side of the package to all
pins on the other side of the package. For example, between pins 1 and 14, and 15 and 28.
Note 5: Applies to peak current. See Typical Operating Characteristics and Applications Information.
4
_______________________________________________________________________________________
±15kV ESD-Protected, Isolated, 3.3V
RS-485/RS-422 Data Interfaces
DRIVER DIFFERENTIAL OUTPUT VOLTAGE
vs. TEMPERATURE
2.5
2.4
2.3
-70
-60
-50
-40
-30
120
100
80
60
2.2
-20
40
2.1
-10
20
2.0
0
0
20
40
60
0
80
-6
-4
TEMPERATURE (°C)
-2
0
2
4
6
0.5
0.4
0.3
0.2
5.00
3.75
3.50
3.25
40
60
80
-40
-20
0
TEMPERATURE (°C)
20
40
60
80
TEMPERATURE (°C)
OUTPUT CURRENT
vs. RECEIVER OUTPUT LOW VOLTAGE
OUTPUT CURRENT
vs. RECEIVER OUTPUT HIGH VOLTAGE
80
MAX3480EA/EB toc06
80
12
4.00
3.00
20
10
4.25
0
0
8
4.50
0.1
-20
6
MEASURED AT ISO RO DRV
IRO = 8mA
4.75
OUTPUT HIGH VOLTAGE (V)
MAX3480EA/EB toc04
0.6
-40
4
RECEIVER OUTPUT HIGH VOLTAGE
vs. TEMPERATURE
MEASURED AT ISO RO DRV
IRO = 8mA
0.7
2
OUTPUT LOW VOLTAGE (V)
RECEIVER OUTPUT LOW VOLTAGE
vs. TEMPERATURE
0.8
0
OUTPUT HIGH VOLTAGE (V)
MAX3480EA/EB toc05
-20
OUTPUT LOW VOLTAGE (V)
MEASURED AT ISO RO DRV
70
60
50
40
30
60
50
40
30
20
20
10
10
0
MEASURED AT ISO RO DRV
70
OUTPUT CURRENT (mA)
-40
MAX3480EA/EB toc03
140
MAX3480EA/EB toc07
2.6
160
OUTPUT CURRENT (mA)
-80
2.7
180
MAX3480EA/EB toc02
-90
OUTPUT CURRENT (mA)
2.8
OUTPUT CURRENT
vs. DRIVER OUTPUT LOW VOLTAGE
-100
MAX3480EA/EB toc01
DI´ = HIGH OR OPEN
RL = 54Ω
2.9
OUTPUT CURRENT (mA)
DIFFERENTIAL OUTPUT VOLTAGE (V)
3.0
OUTPUT CURRENT
vs. DRIVER OUTPUT HIGH VOLTAGE
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
DIFFERENTIAL OUTPUT VOLTAGE (V)
_______________________________________________________________________________________
5
MAX3480EA/MAX3480EB
__________________________________________Typical Operating Characteristics
(VCC_ = +3.3V, TA = +25°C, Figure 1, unless otherwise noted.)
Typical Operating Characteristics (continued)
(VCC_ = +3.3V, TA = +25°C, Figure 1, unless otherwise noted.)
MAX3480EA DRIVER ENABLE (AB)
AND RECEIVER OUTPUT (RO)
MAX3480EA/EB toc08
MAX3480EA
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX3480EA/EB toc09
DI´ INPUT,
2V/div
350
DE´ INPUT,
1V/div
A, 1V/div
2V/div
B
RO,
74HC240,
2V/div
B, 2V/div
DE´ HIGH, 50Ω LOAD
300
SUPPLY CURRENT (mA)
A
MAX3480EA/EB toc10
MAX3480EA DRIVER INPUT (AB)
AND RECEIVER OUTPUT (RO)
250
200
DE´ HIGH, 100Ω LOAD
DE´ LOW, DI´ LOW, RL = ∞
150
DE´ LOW, DI´ HIGH, RL = ∞
100
50
0
100ns/div
CIRCUIT OF FIGURE 2, TERMINATION: 100Ω
MAX3480EB DRIVER INPUT (AB)
AND RECEIVER OUTPUT (RO)
MAX3480EB DRIVER ENABLE (DE´)
AND DRIVER OUTPUT (AB)
3.0
3.4
3.6
3.8
MAX3480EB
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX3480EA/EB toc12
MAX3480EA/EB toc11
3.2
SUPPLY VOLTAGE (V)
DI´ INPUT,
2V/div
300
DE´
1V/div
SUPPLY CURRENT (mA)
250
A
2V/div
B
A
2V/div
B
2V/div
MAX3480EA/EB toc13
100ns/div
CIRCUIT OF FIGURE 2, TERMINATION: 100Ω
DE´ HIGH, 50Ω LOAD
DE´ HIGH,
100Ω LOAD
200
150
DE´ LOW, DI´ LOW, RL = ∞
100
DE´ LOW, DI´ HIGH, RL = ∞
RO,
74HC240,
2V/div
50
0
20µs/div
1µs/div
3.0
3.2
3.4
3.6
SUPPLY VOLTAGE (V)
DRIVER ENABLE TIME
vs. TEMPERATURE
DRIVER ENABLE TIME
vs. TEMPERATURE
DRIVER ENABLE TIME (µs)
2.0
MAX3480EB
1.5
RL = 54Ω, DI´ = 0
MEASURED FROM DE´
TO VALID OUTPUT
1.0
0.5
MAX3480EA/EB TOC15
2.0
MAX3480EA/EB toc14
2.5
DRIVER ENABLE TIME (µs)
MAX3480EA/MAX3480EB
±15kV ESD-Protected, Isolated, 3.3V
RS-485/RS-422 Data Interfaces
MAX3480EB
1.5
RL = 54Ω, DI´ = 0V MEASURED FROM
DE´ TO VALID OUTPUT
1.0
MAX3480EA
MAX3480EA
0
0.5
-40
-20
0
20
40
TEMPERATURE (°C)
6
60
80
-40
-20
0
20
40
60
TEMPERATURE (°C)
_______________________________________________________________________________________
80
3.8
±15kV ESD-Protected, Isolated, 3.3V
RS-485/RS-422 Data Interfaces
PIN
NAME
FUNCTION
PINS ON THE NONISOLATED SIDE
1
VCC1
Logic-Side (Nonisolated Side) +3.3V Supply Voltage Input. Connect to pins 2, 10, and 14.
2
VCC2
Logic-Side (Nonisolated 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 VFS = VCC, switch frequency is high; if FS = 0, switch frequency is low
(normal connection).
7
SD
Power-Supply Shutdown Input. Must be connected to logic ground.
8
VCC3
9
DI
10
VCC4
Boosted V+ Voltage Input. Must be connected as shown in Figures 1 and 2.
Driver Input. With DE´ high, a low on DI´ forces output A low and output B high. Similarly, a high on
DI´ forces output A high and output B low. Drives internal LED cathode through R1 (Table 1).
Logic-Side (Nonisolated Side) +3.3V Supply Voltage Input. Connect to pins 1, 2, and 14.
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).
13
RO
Receiver Output. If A > B by 200mV, RO is low; if A < B by 200mV, RO is high. Open collector; must
have pullup (R3) to VCC (Table 1).
14
VCC5
Logic-Side (Nonisolated Side) +3.3V Supply Voltage Input. Connect to pins 1, 2, and 10.
_______________________________________________________________________________________
7
MAX3480EA/MAX3480EB
______________________________________________________________Pin Description
MAX3480EA/MAX3480EB
±15kV ESD-Protected, Isolated, 3.3V
RS-485/RS-422 Data Interfaces
_________________________________________________Pin Description (continued)
PIN
NAME
FUNCTION
PINS ON THE ISOLATED RS-485/RS-422 SIDE
15
ISO RO
LED
16
ISO COM2
Isolated Receiver-Output LED Anode (Input). If A > B by 200mV, ISO RO LED is high; if A < B by
200mV, ISO RO LED is low.
Isolated-Supply Common Input. Connect to ISO COM1.
Isolated Driver-Enable Drive Input. The driver outputs, A and B, are enabled by bringing DE´ high.
The driver outputs are high impedance when DE´ is low. If the driver outputs are enabled, the
device functions as a line driver. While the driver outputs are high impedance, the device functions
as a line receiver. Open collector output; must have pullup (R4 in Figure 1) to ISO VCC and be
connected to ISO DE IN for normal operation (Table 1).
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
pullup (R5 in Figure 1) to ISO VCC and be connected to ISO DI IN for normal operation (Table 1).
20
ISO COM1
Isolated-Supply Common Output. Connect to ISO COM2. If RS-485 wires have a shield, connect
ISO COM1 to shield through 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
25
B
26
ISO VCC1
Isolated Supply Positive Output Voltage. Connect to ISO VCC2.
27, 28
AC2, AC1
Internal Connections. Leave these pins unconnected.
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 and Figure 1).
Inverting Driver Output and Inverting Receiver Input
Note: For DE´ and DI´ pin descriptions, see Detailed Block Diagram.
8
_______________________________________________________________________________________
±15kV ESD-Protected, Isolated, 3.3V
RS-485/RS-422 Data Interfaces
The MAX3480EA/MAX3480EB are electrically isolated,
RS-485/RS-422 data-communications interface solutions. Transceivers, optocouplers, a power driver, and a
transformer are in one standard 28-pin DIP package.
Signals and power are internally transported across the
ISO VCC1
VCC3
OSC
1.1MHz/
1.6MHz
FS
MAX3480EA: MAX485E
MAX3480EB: MAX487E
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
22µF
D1, D2
1N914
C2
0.1µF
VCC1
1
28 AC1 (MAKE NO CONNECTION)
VCC2
2
27 AC2 (MAKE NO CONNECTION)
D1 3
D2
BOOSTED V+
C3
0.01µF
GND1
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)
MAX3480EA/EB
MAX845
MAX485E
MAX487E
7
23 A
ISO DI IN
22
8
21
9
20 ISO COM1
10
19 ISO DI DRV
11
18 ISO VCC2
12
17 ISO DE DRV
13
16
15
14
LOGIC GROUND
RL
B
R7*
SHIELD (OPTIONAL)
A
R6*
TWISTED PAIR
TO OTHER TRANSCEIVERS
SH
RL
ISO DE IN
SHIELD (OPTIONAL)
R4*
R5*
R8
100Ω
ISO COM2
NOTE: RESISTOR R8 PROTECTS THE
MAX3480E FROM TRANSIENT
CURRENTS BETWEEN SHIELD AND
A AND B.
ISO RO LED
ISOLATION BARRIER
*SEE TABLE 1.
TWISTED PAIR
TO OTHER TRANSCEIVERS
ISOLATION COMMON
C4
270pF
4kV
Figure 1. Detailed Block Diagram
Table 1. Pullup and LED Drive Resistors
PART
R1 (Ω)
R2 (Ω)
R3 (Ω)
R4 (Ω)
R5 (Ω)
R6 (Ω)
R7 (Ω)
MAX3480EA
100
100
680
3600
1000
200
Open
MAX3480EB
100
100
2000
3600
3600
200
430
_______________________________________________________________________________________
9
MAX3480EA/MAX3480EB
isolation barrier (Figure 1). Power is transferred from the
logic side (nonisolated side) to the isolated side of the
barrier through a center-tapped transformer. Signals
cross the barrier through high-speed optocouplers. A
single +3.3V supply on the logic side powers both
sides of the interface.
_______________Detailed Description
MAX3480EA/MAX3480EB
±15kV ESD-Protected, Isolated, 3.3V
RS-485/RS-422 Data Interfaces
The MAX3480EB features reduced-slew-rate drivers
that minimize EMI and reduce reflections caused by
improperly terminated cables, allowing error-free transmission at data rates up to 160kbps. The MAX3480EA’s
driver slew rates are not limited, allowing transmission
rates up to 2.5Mbps.
shutdown circuitry that puts the driver outputs into a
high-impedance state. The receiver input has a fail-safe
feature that guarantees a logic-high output if the input
is open circuit.
The driver outputs are enabled by bringing DE´ high.
Driver-enable times are typically 500ns for the
MAX3480EA and 1µs for the MAX3480EB. Allow time
for the devices to be enabled before sending data.
When enabled, driver outputs function as line drivers.
Driver outputs are high impedance when DE´ is low.
While outputs are high impedance, they function as line
receivers.
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
EXTERNAL RS-485/RS-422 WIRING
VIN
+3.0V TO +3.6V
C1
22µF
6V
C2
0.1µF
D1, D2
1N914
74HC240
DI
DE
18
2
17
4
16
6
14
8
3
12
15
5
13
7
1
28 AC1 (MAKE NO CONNECTION)
VCC2
2
27 AC2 (MAKE NO CONNECTION)
FS 6
VCC3
DRIVER INPUT
R1*
DI
VCC4
DRIVER ENABLE
DE
GND2
20
RO
11
9
RECEIVER OUTPUT
26 ISO VCC1
B
25
D1 3
SD
R2*
RO
VCC1
D2 4
GND1
5
BOOSTED V+
C3
0.01µF
R3*
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
MAX3480EA/EB
VCC5
24
MAX845
MAX485E
MAX487E
SHIELD (OPTIONAL)
R7*
A
TWISTED PAIR
TO OTHER TRANSCEIVERS
23 A
ISO DI IN
22
8
21
9
20 ISO COM1
10
19 ISO DI DRV
11
18
12
17 ISO DE DRV
13
16
14
15
ISOLATION BARRIER
RL
B
ISO RO DRV
7
10
TWISTED PAIR
TO OTHER TRANSCEIVERS
SH
R6*
RL
ISO DE IN
R4*
SHIELD (OPTIONAL)
R5*
ISO VCC2
R8
100Ω
ISO COM2
NOTE: RESISTOR R8 PROTECTS
THE MAX3480E FROM TRANSIENT
CURRENTS BETWEEN SHIELD AND
A AND B.
ISO RO LED
ISOLATION COMMON
*SEE TABLE 1.
LOGIC GROUND
C4
270pF
4kV
Figure 2. Typical Application Circuit
10
______________________________________________________________________________________
±15kV ESD-Protected, Isolated, 3.3V
RS-485/RS-422 Data Interfaces
ISOLATION BARRIER
A
ISOLATION BARRIER
+3.3V
+3.3V
DE
R
´
CL1
A
VOD
DI
R
D
´
RDIFF
VID
R
RO
B
B
VOC
R3
A
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
´
0
VCC_ - 0.4V
VCC_ - 0.4V
2
VCC_ - 0.4V
2
tPHL
tPLH
VCC_ - 0.4V
2
VCC_ - 0.4V
2
0
tZL
tLZ
A, B
VO
VOL
A
1/2 VO
VO
0
-VO
´
1/2 VO
B
VDIFF
DE
10%
tR
2.3V OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
A, B
VDIFF = VA - VB
VOH - 0.5V
2.3V
90%
90%
10%
tF
VOL + 0.5V
0
tZH
tHZ
tSKEW = | tPLH - tPHL |
Figure 6. Driver Propagation Delays and Transition Times
Figure 7. Driver Enable and Disable Times
______________________________________________________________________________________
11
MAX3480EA/MAX3480EB
_________________________________________________________________Test Circuits
MAX3480EA/MAX3480EB
±15kV ESD-Protected, Isolated, 3.3V
RS-485/RS-422 Data Interfaces
__Switching Waveforms (continued)
The MAX3480EA/MAX3480EB withstand 1260V RMS
(1 min) or 1560VRMS (1s). The isolated outputs of these
devices meet all RS-485/RS-422 specifications.
Boost Voltage
The MAX3480EA/MAX3480EB require external diodes
on the primary of the transformer to develop the boost
voltage for the power oscillator. In normal operation,
whenever one of the oscillator outputs (D1 and D2)
goes low, the other goes to approximately double the
supply voltage. Since the circuit is symmetrical, the two
outputs can be combined with diodes, filtered, and
used to power the oscillator itself.
The diodes on the primary side may be any fast-switching, small-signal diodes, such as the 1N914, 1N4148,
or CMPD2838. The nominal value of the primary filter
capacitor C3 is 0.01µF.
VOH
RO
1.5V
VOL
V B - VA
tPHL
VID
-VID
OUTPUT
0
1.5V
tPLH
0
INPUT
tSKD = |tPLH - tPHL|
Figure 8. Receiver Propagation Delays
Driver Output Protection
Function Tables
Table 2. Transmitting
INPUTS
OUTPUTS
DE´
DI´
B
A
1
1
0
1
1
0
1
0
0
X
High-Z
High-Z
X = Don't care
High-Z = High impedance
Table 3. Receiving
INPUTS
12
There are two mechanisms to prevent excessive output
current and power dissipation caused by faults or by
bus contention. A foldback current limit on the output
stage provides immediate protection against short circuits over the whole common-mode voltage range (see
Typical Operating Characteristics). In addition, a thermal shutdown circuit forces the driver outputs into a
high-impedance state if the die temperature rises
excessively.
Resistor R8 (Figures 1 and 2) provides additional protection by current limiting between the shield and the
two signal wires. In the event that shielded cable is
used and an external voltage or transient is inadvertently applied between the shield and the signal wires,
the MAX3480EA/MAX3480EB can be damaged.
Although unlikely, this condition can occur during
installation.
The MAX3480EA/MAX3480EB provide electrical isolation between logic ground and signal paths; they
do not provide isolation from external shields and
the signal paths. When in doubt, do not connect the
shield. The MAX3480EA/MAX3480EB can be damaged if resistor R8 is shorted out.
DE´
A-B
OUTPUT
–—–
RO
0
≥ +0.2V
0
0
≤ -0.2V
1
Applications Information
0
Inputs open
0
The MAX3480EA/MAX3480EB provide extra protection
against ESD. The MAX3480EA/MAX3480EB are intended for harsh environments where high-speed communication is important. These devices eliminate the
need for transient suppressor diodes or the use of
discrete protection components. The standard (non-E)
MAX3480A/MAX3480B are recommended for applications where cost is critical.
______________________________________________________________________________________
±15kV ESD-Protected, Isolated, 3.3V
RS-485/RS-422 Data Interfaces
RD
1500Ω
CHARGE-CURRENT
LIMIT RESISTOR
IP 100%
90%
DISCHARGE
RESISTANCE
Ir
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
AMPERES
HIGHVOLTAGE
DC
SOURCE
Cs
100pF
STORAGE
CAPACITOR
DEVICE
UNDER
TEST
36.8%
10%
0
0
Figure 9. Human Body ESD Test Model
±15kV ESD Protection
As with all Maxim devices, ESD-protection structures
are incorporated on all pins to protect against electrostatic discharges encountered during handling and
assembly. The driver outputs and receiver inputs have
extra protection against static electricity. Maxim’s engineers developed state-of-the-art structures to protect
these pins against ESD of ±15kV without damage. The
ESD structures withstand high ESD in all states: normal
operation, shutdown, and power-down. After an ESD
event, Maxim’s MAX3480EA/MAX3480EB keep working
without latchup. An isolation capacitor of 270pF 4kV
should be placed between ISO COM and logic ground
for optimal performance against an ESD pulse with
respect to logic ground.
ESD protection can be tested in various ways; the
transmitter outputs and receiver inputs of this product
family are characterized for protection to ±15kV using
the Human Body Model.
ESD Test Conditions
The +15kV ESD test specifications apply only to the A, B,
Y, and Z I/O pins. The test surge may be referenced to
either the ISO COM or to the nonisolated GND (this presupposes that a bypass capacitor is installed between
VCC2 and the nonisolated GND).
Human Body Model
Figure 9 shows the Human Body Model, and Figure 10
shows the current waveform it generates when discharged into a low impedance. This model consists of a
tRL
TIME
tDL
CURRENT WAVEFORM
Figure 10. Human Body Model Current Waveform
100pF capacitor charged to the ESD voltage of interest,
which is then discharged into the test device through a
1.5kΩ resistor.
Machine Model
The Machine Model for ESD tests all pins using a 200pF
storage capacitor and zero discharge resistance. Its
objective is to simulate the stress caused by contact that
occurs with handling and assembly during manufacturing. Of course, all pins require this protection during
manufacturing—not just inputs and outputs. Therefore,
after PC board assembly, the Machine Model is less relevant to l/O ports.
The MAX3480EA/MAX3480EB are designed for bidirectional data communications on multipoint bus-transmission lines. Figure 11 shows a typical network application
circuit. To minimize reflections, terminate the line at both
ends with its characteristic impedance, and keep stub
lengths off the main line as short as possible. The slewrate-limited MAX3480EB is more tolerant of imperfect termination and stubs off the main line.
The MAX3480EA/MAX3480EB are specified and characterized using the resistor values shown in Table 1.
Altering the recommended values can degrade performance.
The DI and DE inputs are the cathodes of LEDs whose
anodes are connected to VCC. These points are best
driven by a +3.3V CMOS-logic gate with a series
resistor to limit the current. The resistor values shown
in Table 1 are recommended when the 74HC240 gate
or equivalent is used. DI and DE are intended to be
______________________________________________________________________________________
13
MAX3480EA/MAX3480EB
RC
1MΩ
MAX3480EA/MAX3480EB
±15kV ESD-Protected, Isolated, 3.3V
RS-485/RS-422 Data Interfaces
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.
driven through a series current-limiting resistor.
Directly grounding these pins destroys the device.
Reliability
These products contain transformers, optocouplers,
and capacitors, in addition to several monolithic ICs
and diodes. As such, the reliability expectations more
Table 4. Maxim’s ±15kV ESD-Protected Isolated RS-485 Product Family
PART
NO. OF
Tx/Rx
GUARANTEED
DATA RATE
(Mbps)
FULL/HALF
DUPLEX
SLEW-RATE
LIMITED
NO. OF Tx/Rx
ON BUS
SUPPLY
VOLTAGE
(V)
MAX1480EA
1/1
2.50
Half
No
32
5.0
MAX1480EC
1/1
0.25
Half
Yes
32
5.0
MAX1490EA
1/1
2.50
Full
No
32
5.0
MAX1490EB
1/1
0.25
Full
Yes
32
5.0
MAX3480EA
1/1
2.50
Half
No
32
3.3
MAX3480EB
1/1
0.25
Half
Yes
128
3.3
14
______________________________________________________________________________________
±15kV ESD-Protected, Isolated, 3.3V
RS-485/RS-422 Data Interfaces
MAX3480EA/MAX3480EB
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
B
D
120Ω
DE
A
A
B
A
B
DI
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
4
16
6
14
8
3
12
15
DRIVER INPUT
R1*
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
MAX485E
MAX487E
MAX845
RECEIVER OUTPUT
R3*
VCC5
10
LOGIC GROUND
ISO DE IN
21
9
20 ISO COM1
10
19 ISO DI DRV
11
18 ISO VCC2
12
17 ISO DE DRV
13
16
14
B
R7*
A
23 A
8
15
ISOLATION BARRIER
*SEE TABLE 1.
ISO RO DRV
22 ISO DI IN
SD 7
VCC3
DRIVER ENABLE
13
1
GND1 5
FS
6
C3
0.01µF
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
MAX3480EA/EB
R6*
120Ω
SH
SHIELD
(OPTIONAL)
R4*
R5*
R8
100Ω
ISO COM2
ISO RO LED
ISOLATION
COMMON
NOTE: RESISTOR R8
PROTECTS THE MAX3480E
FROM TRANSIENT
CURRENTS BETWEEN
SHIELD AND A AND B.
C4
270pF
4kV
Figure 11. Typical RS-485/RS-422 Network
______________________________________________________________________________________
15
MAX3480EA/MAX3480EB
±15kV ESD-Protected, Isolated, 3.3V
RS-485/RS-422 Data Interfaces
PDIPW.EPS
Package Information
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
© 2001 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.