MAX3480BEPI [MAXIM]
Complete, Isolated, 3.3V RS-485/RS-422 Data Interface; 完整的，孤立的， 3.3V的RS - 485 / RS - 422数据接口
| 型号： | MAX3480BEPI |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Complete, Isolated, 3.3V RS-485/RS-422 Data Interface |
| 文件： | 总16页 (文件大小：159K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-0453; Rev 0; 1/96
Co m p le t e , Is o la t e d , 3 .3 V
RS -4 8 5 /RS -4 2 2 Da t a In t e rfa c e
/MAX3480B
_______________Ge n e ra l De s c rip t io n
____________________________Fe a t u re s
The MAX3480A/MAX3480B a re e le c tric a lly isola te d
RS-485/RS-422 d a ta -c ommunic a tions inte rfa c e s .
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.
♦ Isolated Data Interface to 1600V
(1 minute)
RMS
♦ Slew-Rate-Limited Data Transmission (MAX3480B)
♦ High-Speed, Isolated, 2.5Mbps RS-485 Interface
(MAX3480A)
♦ -7V to +12V Common-Mode Input Voltage Range
The MAX3480B features reduced-slew-rate drivers that
minimize EMI a nd re d uc e re fle c tions c a us e d b y
improperly terminated cables, allowing error-free data
tra ns mis s ion a t d a ta ra te s up to 250kb p s . The
MAX3480A’s driver slew rate is not limited, allowing
transmission rates up to 2.5Mbps.
with Respect to Isolated Ground
♦ Single +3.3V Supply
♦ Current Limiting and Thermal Shutdown for
Driver Overload Protection
♦ Standard 28-Pin DIP Package
These devices typically draw 180mA of quiescent sup-
ply current. The MAX3480B provides a low-power shut-
down mode in which it consumes only 0.2µA.
Drivers are short-circuit current limited and are protect-
ed 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.
__________________P in Co n fig u ra t io n
The MAX3480A/MAX3480B typically withstand 1600V
RMS
(1 minute) or 2000V
(1 second). Their isolated inputs
RMS
and outputs meet RS-485/RS-422 specifications.
TOP VIEW
MAX3480A/B
________________________Ap p lic a t io n s
Isolated RS-485/RS-422 Data Interface
Transceivers for EMI-Sensitive Applications
Industrial-Control Local Area Networks
Automatic Test Equipment
V
AC1
CC1
1
2
28
27
26
25
24
23
22
21
V
CC2
AC2
D1
D2
ISO V
3
CC1
B
4
HVAC/Building Control Networks
ISO RO DRV
GND1
5
MAX845
MAX485
MAX487
6
FS
A
______________Ord e rin g In fo rm a t io n
SD
ISO DI IN
7
V
CC3
8
ISO DE IN
ISO COM1
DATA
DI
PART
TEMP. RANGE PIN-PACKAGE RATE
(kbps)
9
20
19
18
17
V
CC4
10
ISO DI DRV
MAX3480ACPI
MAX3480AEPI
MAX3480BCPI
MAX3480BEPI
0°C to +70°C 28 Plastic DIP
-40°C to +85°C 28 Plastic DIP
0°C to +70°C 28 Plastic DIP
-40°C to +85°C 28 Plastic DIP
2500
2500
250
ISO V
CC2
DE 11
ISO DE DRV
GND2
12
13
14
250
RO
16 ISO COM2
ISO RO LED
V
CC5
15
ISOLATION BARRIER
DIP
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
Co m p le t e , Is o la t e d , 3 .3 V
RS -4 8 5 /RS -4 2 2 Da t a In t e rfa c e
ABSOLUTE MAXIMUM RATINGS
With Respect to GND:
LED Forward Current (DI, DE, ISO RO LED) ......................50mA
Supply Voltage (V
V
CC
V
CC
V ) .........-0.3V to +3.8V
CC
5
Continuous Power Dissipation (T = +70°C)
CC
A
1,
2,
4,
Supply Voltage (V
Control Input Voltage (SD, FS) ................-0.3V to (V + 0.3V)
) ..........................................-0.3V to +7V
Plastic DIP (derate 9.09mW/°C above +70°C) ...............727mW
Operating Temperature Ranges
CC3
CC
Receiver Output Voltage (RO).................-0.3V to (V + 0.3V)
With Respect to ISO COM:
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
CC
Control Input Voltage (ISO DE _) .........-0.3V to (ISO V + 0.3V)
CC
Driver Input Voltage (ISO DI _).........-0.3V to (ISO V + 0.3V)
CC
Receiver Output Voltage (ISO RO _)......-0.3V to (ISO V + 0.3V)
CC
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
(V = V
= V
= V
= V
= 3.0V to 3.6V, FS = 0V, T = T
to T , unless otherwise noted. Typical values are at
MAX
CC
CC1
CC2
CC4
CC5
A
MIN
V
CC
= V
= V
= V
= V
= 3.3V and T = +25°C.) (Notes 1, 2, 3)
A
CC5
CC1
CC2
CC4
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
3.3
MAX
UNITS
Supply Voltage
V
S
3.0
3.6
V
/MAX3480B
f
FS = 0V
600
900
180
280
120
240
0.2
SWL
Switch Frequency
kHz
mA
f
FS = V or open
CC
SWH
MAX3480A,
R
R
= ∞
260
200
L
L
DE = V or open
= 54Ω
´
CC
Operating Supply Current
I
CC
MAX3480B,
R = ∞
L
DE = V or open
R = 54Ω
L
´
CC
Shutdown Supply Current (Note 3)
FS Input Threshold
I
SD = V
µA
V
SHDN
CC3
V
High
2.4
FSH
V
Low
0.8
50
FSL
FS Input Pull-Up Current
FS Input Leakage Current
Input High Voltage
I
FS low
µA
pA
V
FSL
I
FS high
10
FSM
V
V
- 0.4
DE , DI (Figure 1)
IH
CC
´
´
Input Low Voltage
V
IL
0.4
8
V
DE , DI (Figure 1)
´
´
Isolation Resistance
R
T
A
= +25°C, V
= 50V
DC
100
10,000
10
MΩ
pF
V
ISO
ISO
ISO
Isolation Capacitance
Differential Driver Output (no load)
C
T
A
= +25°C, V
= 50V
ISO DC
V
OD1
R = 50Ω (RS-422)
R = 27Ω (RS-485), Figure 3
2
Differential Driver Output (with load)
V
OD2
V
1.5
5
Change in Magnitude of Driver
Output Voltage for Complementary
Output States
Differential
Common Mode
0.3
R = 27Ω or 50Ω,
Figure 3
∆V
V
V
OD
0.3
4
Driver Common-Mode Output
V
OC
R = 27Ω or 50Ω, Figure 4
2
_______________________________________________________________________________________
Co m p le t e , Is o la t e d , 3 .3 V
RS -4 8 5 /RS -4 2 2 Da t a In t e rfa c e
/MAX3480B
ELECTRICAL CHARACTERISTICS (continued)
(V = V
= V
= V
= V
= 3.0V to 3.6V, FS = 0V, T = T
to T , unless otherwise noted. Typical values are at
MAX
CC
CC1
CC2
CC4
CC5
A
MIN
V
CC
= V
= V
= V
= V
= 3.3V and T = +25°C.) (Notes 1, 2, 3)
A
CC5
CC1
CC2
CC4
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
1.0
UNITS
V = 12V
IN
MAX3480A
V
= -7V
= 12V
= -7V
-0.8
0.25
-0.2
IN
DE = 0V,
´
Input Current (A, B)
ISO I
mA
IN
V
IN
V
CC
= 0V or 3.6V
MAX3480B
V
IN
MAX3480A
MAX3480B
12
Receiver Input Resistance
R
-7V ≤ V ≤ 12V
kΩ
IN
CM
48
70
Receiver Differential Threshold
Receiver Input Hysteresis
V
TH
-7V ≤ V ≤ 12V
-0.2
0.2
V
CM
∆V
V
CM
= 0V
mV
TH
Receiver Output/Receiver Output
Low Voltage
V
OL
0.4
V
DI = V
´ CC
Receiver Output/Receiver Output
High Current
I
OH
250
µA
V
OUT
= 3.6V, DI = 0V
´
Driver Short-Circuit Current
ISO I
-7V ≤ V ≤ 12V (Note 4)
100
mA
OSD
O
SWITCHING CHARACTERISTICS—MAX3480A
(V
= V
= V
= V
= V
= 3.0V to 3.6V, FS = 0V, T = T
to T , unless otherwise noted. Typical values are at
MAX
CC
CC1
CC2
CC4
CC5
A
MIN
V
CC
= V
= V
= V
= V = 3.3V and T = +25°C.)
CC1
CC2
CC4
CC5 A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
t
t
PLH
PHL
100
100
275
275
Driver Input to Output
Propagation Delay
Figures 4, 6; R
= 54Ω,
= 54Ω,
= 54Ω,
DIFF
ns
C
= C = 100pF
L2
L1
Figures 4, 6; R
DIFF
t
Driver Output Skew (Note 5)
Driver Rise or Fall Time
SKEW
25
15
90
40
ns
ns
C
= C = 100pF
L2
L1
Figures 4, 6; R
DIFF
t , t
R
F
C
= C = 100pF
L2
L1
t
t
Driver Enable to Output High
Driver Enable to Output Low
Driver Disable Time from High
Driver Disable Time from Low
ZH
Figures 5, 7; C = 100pF, S2 closed
0.2
0.2
0.3
0.3
100
100
1.5
1.5
1.5
1.5
225
225
µs
µs
µs
µs
L
t
ZL
Figures 5, 7; C = 100pF, S1 closed
L
HZ
Figures 5, 7; C = 15pF, S2 closed
L
t
LZ
Figures 5, 7; C = 15pF, S1 closed
L
t
PLH
PHL
Receiver Input to Output
Propagation Delay
Figures 4, 8; R
= 54Ω,
DIFF
ns
C
= C = 100pF
L2
t
L1
t
t
PLH - PHL Differential
Figures 4, 8; R
= 54Ω,
DIFF
t
SKD
20
ns
C
= C = 100pF
L2
Receiver Skew
L1
f
t
t
Maximum Data Rate
MAX
PLH, PHL < 50% of data period
2.5
Mbps
_______________________________________________________________________________________
3
Co m p le t e , Is o la t e d , 3 .3 V
RS -4 8 5 /RS -4 2 2 Da t a In t e rfa c e
SWITCHING CHARACTERISTICS—MAX3480B
(V
= V
= V
= V
= V
= 3.0V to 3.6V, FS = 0V, T = T
to T , unless otherwise noted. Typical values are at
MAX
CC
CC1
CC2
CC4
CC5
A
MIN
V
CC
= V
= V
= V
= V = 3.3V and T = +25°C.)
CC1
CC2
CC4
CC5 A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
t
t
1.0
1.0
2.0
2.0
PLH
Driver Input to Output
Propagation Delay
Figures 4, 6; R
= 54Ω,
= 54Ω,
= 54Ω,
DIFF
µs
C
= C = 100pF
L2
L1
PHL
Figures 4, 6; R
DIFF
Driver Output Skew
t
100
1.0
800
2.0
ns
µs
SKEW
C
= C = 100pF
L2
L1
Figures 4, 6; R
DIFF
Driver Rise or Fall Time
t , t
R
F
C
= C = 100pF
L2
L1
Driver Enable to Output High
Driver Enable to Output Low
Driver Disable Time from Low
Driver Disable Time from High
t
Figures 5, 7; C = 100pF, S2 closed
50
50
100
100
50
µs
µs
µs
µs
L
ZH
t
Figures 5, 7; C = 100pF, S1 closed
L
ZL
LZ
t
Figures 5, 7; C = 15pF, S1 closed
13
L
t
Figures 5, 7; C = 15pF, S2 closed
13
50
L
HZ
t
0.8
0.8
2.0
2.0
PLH
PHL
Receiver Input to Output
Propagation Delay
Figures 4, 8; R
= 54Ω,
DIFF
µs
C
= C = 100pF
L2
L1
t
t
- t
Differential
Figures 4, 8; R
= 54Ω,
PLH PHL
DIFF
t
50
ns
SKD
8
C
= C = 100pF
L1 L2
Receiver Skew
Maximum Data Rate
f
t
, t
< 50% of data period
0.25
Mbps
PLH PHL
MAX
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 V
when shutdown is enabled.
CC1
Note 4: Applies to peak current. See Typical Operating Characteristics and Applications Information.
4
_______________________________________________________________________________________
Co m p le t e , Is o la t e d , 3 .3 V
RS -4 8 5 /RS -4 2 2 Da t a In t e rfa c e
/MAX3480B
__________________________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s
(V
CC_
= 3.3V, T = +25°C, unless otherwise noted.)
A
OUTPUT CURRENT
DRIVER DIFFERENTIAL OUTPUT VOLTAGE
OUTPUT CURRENT
vs. DRIVER OUTPUT LOW VOLTAGE
vs. TEMPERATURE
vs. DRIVER OUTPUT HIGH VOLTAGE
180
160
140
120
100
80
3.0
2.9
-100
DI´ = HIGH OR OPEN
L
-90
R = 54Ω
2.8
2.7
2.6
-80
-70
-60
2.5
2.4
2.3
2.2
-50
-40
-30
-20
60
40
20
0
2.1
2.0
-10
0
0
2
4
6
8
10
12
-40
-20
0
20 40
60 80
-6
-4
-2
0
2
4
6
OUTPUT LOW VOLTAGE (V)
TEMPERATURE (°C)
OUTPUT HIGH VOLTAGE (V)
RECEIVER OUTPUT HIGH VOLTAGE
vs. TEMPERATURE
RECEIVER OUTPUT LOW VOLTAGE
vs. TEMPERATURE
5.00
4.75
4.50
4.25
4.00
3.75
3.50
0.8
0.7
0.6
0.5
0.4
0.3
0.2
MEASURED AT ISO RO DRV
RO
MEASURED AT ISO RO DRV
RO
I
= 8mA
I
= 8mA
3.25
3.00
0.1
0
-40
-20
0
20 40
60 80
-40
-20
0
20 40
60 80
TEMPERATURE (°C)
TEMPERATURE (°C)
OUTPUT CURRENT
OUTPUT CURRENT
vs. RECEIVER OUTPUT HIGH VOLTAGE
vs. RECEIVER OUTPUT LOW VOLTAGE
-30
-25
80
70
60
50
40
30
20
MEASURED AT ISO RO DRV
MEASURED AT ISO RO DRV
-20
-15
-10
-5
0
10
0
0
1.0
2.0
3.0
4.0
5.0
0
1.0
2.0
3.0
4.0
5.0
OUTPUT HIGH VOLTAGE (V)
OUTPUT LOW VOLTAGE (V)
_______________________________________________________________________________________
5
Co m p le t e , Is o la t e d , 3 .3 V
RS -4 8 5 /RS -4 2 2 Da t a In t e rfa c e
____________________________Typ ic a l Op e ra t in g Ch a ra c t e ris t ic s (c o n t in u e d )
(V
CC_
= 3.3V, T = +25°C, unless otherwise noted.)
A
MAX3480A DRIVER ENABLE (AB)
AND RECEIVER OUTPUT (RO)
MAX3480A DRIVER INPUT (AB)
AND RECEIVER OUTPUT (RO)
MAX3480A
SUPPLY CURRENT vs. SUPPLY VOLTAGE
350
300
250
200
150
100
DE´ INPUT,
DE´ HIGH, 50Ω LOAD
DE´ INPUT,
1V/div
2V/div
DE´ HIGH, 100Ω LOAD
DE´ LOW, DI´ LOW
A
A, 1V/div
B, 2V/div
2V/div
B
RO,
74HC240,
DI,
DE´ LOW, DI´ HIGH
2V/div
50
0
3.0
3.2
3.4
3.6
3.8
100ns/div
100ns/div
CIRCUIT OF FIGURE 2, TERMINATION: 100Ω
SUPPLY VOLTAGE (V)
CIRCUIT OF FIGURE 2, TERMINATION: 100Ω
MAX3480B DRIVER INPUT (AB)
AND RECEIVER OUTPUT (RO)
MAX3480B DRIVER ENABLE (AB)
AND RECEIVER OUTPUT (RO)
8
MAX3480B
SUPPLY CURRENT vs. SUPPLY VOLTAGE
300
250
DE´ INPUT,
1V/div
DE´ INPUT,
2V/div
DE´ HIGH, 50Ω LOAD
DE´ HIGH,
200
150
100
50
A, 1V/div
B, 2V/div
100Ω LOAD
A
2V/div
B
DE´ LOW, DI´ LOW
DE´ LOW, DI´ HIGH
RO,
74HC240,
DI,
2V/div
0
25µs/div
3.0
3.2
3.4
3.6
3.8
1µs/div
CIRCUIT OF FIGURE 2, TERMINATION: 100Ω
CIRCUIT OF FIGURE 2, TERMINATION: 100Ω
SUPPLY VOLTAGE (V)
DRIVER ENABLE TIME
vs. TEMPERATURE
DRIVER DISABLE TIME
vs. TEMPERATURE
100
100
10
MAX3480B
MAX3480B
10
1
R = 54Ω, DI´ = 0V MEASURED FROM
L
R = 54Ω, DI´ = 0V MEASURED FROM
DE´ TO VALID OUTPUT
L
DE´ TO VALID OUTPUT
1
MAX3480A
MAX3480A
0.1
0.1
-40 -20
0
20
40
60
80
-40 -20
0
20
40
60
80
TEMPERATURE (°C)
TEMPERATURE (°C)
6
_______________________________________________________________________________________
Co m p le t e , Is o la t e d , 3 .3 V
RS -4 8 5 /RS -4 2 2 Da t a In t e rfa c e
/MAX3480B
______________________________________________________________P in De s c rip t io n
PIN
NAME
FUNCTION
PINS ON THE NON-ISOLATED SIDE
1
2
V
Logic-Side (non-isolated side) +3.3V Supply Voltage Input. Connect to pins 2, 10, and 14.
Logic-Side (non-isolated side) +3.3V Supply Voltage Input. Connect to pins 1, 10, and 14.
Boost-Voltage Generator Outputs. See Figures 1 and 2.
CC
1
2
V
CC
3, 4
D1, D2
GND1,
GND2
5, 12
6
Logic-Side Ground Inputs. Must be connected; not internally connected.
Frequency Switch Input. If FS = V , switch frequency is high; if FS = 0V, switch frequency is low
CC
(normal connection).
FS
7
8
SD
Power-Supply Shutdown Input. Must be connected to logic ground.
V
CC
Boosted V+ Voltage Input. Must be connected as shown in Figures 1 and 2.
3
4
Driver Input. With DE high, a low on DI forces output A low and output B high. Similarly, a high on DI
´
´
´
9
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.
10
V
CC
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
´
11
DE
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).
Receiver Output. If A > B by 200mV, RO will be low; if A < B by 200mV, RO will be high. Open collector;
13
14
RO
must have pull-up (R3) to V (Table 1 of Figure 2).
CC
V
CC5
Logic-Side (non-isolated side) +3.3V Supply Voltage Input. Connect to pins 1, 2, and 10.
_______________________________________________________________________________________
7
Co m p le t e , Is o la t e d , 3 .3 V
RS -4 8 5 /RS -4 2 2 Da t a In t e rfa c e
_________________________________________________P in De s c rip t io n (c o n t in u e d )
PIN
NAME
FUNCTION
PINS ON THE ISOLATED RS-485/RS-422 SIDE
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.
15
16
ISO COM2
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
´
ISO DE
DRV
17
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 V and be connected to ISO DE IN for
CC
normal operation (Table 1 of Figure 2).
18
19
ISO V
Isolated-Supply Positive Input Voltage. Connect to ISO V
.
CC2
CC1
Isolated Driver-Input Drive. With DE high, a low on DI forces output A low and output B high. Similarly,
´
´
ISO DI DRV
a high on DI forces output A high and output B low. Open-collector output; must have pull-up (R5) to
´
ISO V and be connected to ISO DI IN for normal operation (Table 1 of Figure 2).
CC
Isolated-Supply Common Output. Connect to ISO COM2. If RS-485 wires have a shield, connect ISO
COM1 to shield via 100Ω resistor.
20
ISO COM1
21
22
23
ISO DE IN
ISO DI IN
A
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.
/MAX3480B
ISO RO
DRV
24
Isolated Receiver-Output Drive. Connect to ISO RO LED through R6 (Table 1 of Figure 2).
Inverting Driver Output and Inverting Receiver Input
25
26
B
ISO V
Isolated Supply Positive Output Voltage. Connect to ISO V
CC2.
CC1
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
_______________________________________________________________________________________
Co m p le t e , Is o la t e d , 3 .3 V
RS -4 8 5 /RS -4 2 2 Da t a In t e rfa c e
/MAX3480B
The MAX3480B features reduced-slew-rate drivers that
_______________De t a ile d De s c rip t io n
minimize EMI a nd re d uc e re fle c tions c a us e d b y
improperly terminated cables, allowing error-free trans-
mission 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 solu-
tions. 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
op e ra tion, whic h s e le c ts a s witc hing fre q ue nc y of
approximately 600kHz. Connect to high for a higher
900kHz switching frequency.
Drivers are short-circuit current limited and are protect-
ed against excessive power dissipation by thermal
ISO V
CC1
V
CC3
D1
MAX3480A: MAX485
MAX3480B: MAX487
MAX845
Q
F/F
B
N
ISO DI IN
D
OSC
1.1MHz/
1.6MHz
T
FS
A
ISO DE IN
D2
Q
N
ISO RO DRV
R
RE
GND1
SD
ISO COM1
EXTERNAL RS-485/RS-422 WIRING
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
MAX3480A/B
V
IN
V
CC1
AC1 (MAKE NO CONNECTION)
AC2 (MAKE NO CONNECTION)
1
2
28
27
26
25
24
23
22
21
20
19
18
17
16
15
TWISTED PAIR
TO OTHER TRANSCEIVERS
3.0V TO 3.6V
C1
22µF
C2
0.1µF
V
CC2
D1, D2
1N914
D1
D2
ISO V
CC1
R
L
3
B
B
4
BOOSTED V+
R7
SHIELD (OPTIONAL)
ISO RO DRV
GND1
FS
5
A
C3
0.01uF
TWISTED PAIR
TO OTHER TRANSCEIVERS
MAX485
MAX487
MAX845
A
6
R6
SD
ISO DI IN
SH
7
R
L
200Ω
V
CC3
ISO DE IN
8
R1
R2
R4
SHIELD (OPTIONAL)
DI
ISO COM1
9
DI´
R5
V
CC4
ISO DI DRV
10
11
12
13
14
NOTE: RESISTOR R8 PROTECTS THE
MAX3480 FROM TRANSIENT
CURRENTS BETWEEN SHIELD AND
“A” & “B”.
LOGIC
DE´
DE
ISO V
CC2
I/O
R8
100Ω
GND2
RO
ISO DE DRV
ISO COM2
RO
R3
V
CC5
ISO RO LED
ISOLATION BARRIER
ISOLATION COMMON
LOGIC GROUND
Figure 1. Detailed Block Diagram
_______________________________________________________________________________________
9
Co m p le t e , Is o la t e d , 3 .3 V
RS -4 8 5 /RS -4 2 2 Da t a In t e rfa c e
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 MAX3480A/MAX3480B typ ic a lly withs ta nd
1600V (1 minute) or 2000V (1 second). The iso-
RMS
RMS
lated 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
re c e ive d d a ta outp ut c a n d ire c tly d rive a ny of the
TTL/CMOS-logic families with only a resistive pull-up.
The driver outputs are enabled by bringing DE´ high.
Drive r-e na b le time s a re typ ic a lly 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
outp uts a re hig h imp e d a nc e , the y func tion a s line
receivers.
Bo o s t Vo lt a g e
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
/MAX3480B
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
MAX3480A/B
V
IN
V
CC1
AC1 (MAKE NO CONNECTION)
AC2 (MAKE NO CONNECTION)
1
2
28
27
26
25
24
23
22
21
20
19
18
17
16
15
TWISTED PAIR
TO OTHER TRANSCEIVERS
3.0V TO 3.6V
C1
22µF
C2
V
CC2
D1, D2
1N914
D1
D2
ISO V
CC1
R
L
0.1µF
3
B
6V
B
4
BOOSTED V+
C3
SHIELD (OPTIONAL)
R7
GND1
ISO RO DRV
5
A
0.01µF
TWISTED PAIR
TO OTHER TRANSCEIVERS
MAX485
MAX487
MAX845
FS
A
6
74HC240
16
14
4
6
R6
200Ω
SD
ISO DI IN
SH
7
R
L
V
CC3
ISO DE IN
8
R1
18
2
R4
SHIELD (OPTIONAL)
8
DRIVER INPUT
12
5
DI
ISO COM1
DI
9
R5
3
V
CC4
ISO DI DRV
17
15
10
11
12
13
14
DE
DRIVER ENABLE
NOTE: RESISTOR R8 PROTECTS
THE MAX3480 FROM TRANSIENT
CURRENTS BETWEEN SHIELD AND
“A” & “B”.
DE
ISO V
CC2
13
7
R8
100
R2
GND2
RO
ISO DE DRV
ISO COM2
20
9
R3
V
CC5
11
RECEIVER OUTPUT
ISO RO LED
RO
10
ISOLATION COMMON
ISOLATION BARRIER
LOGIC GROUND
Table 1. Pull-Up and LED Drive Resistors
PART
R1 (Ω)
R2 (Ω)
R3 (Ω)
R4 (Ω)
3000
R5 (Ω)
1000
R6 (Ω)
200
R7 (Ω)
Open
470
MAX3480A
MAX3480B
150
130
680
130
330
2000
2200
3000
200
Figure 2. Typical Application Circuit
10 ______________________________________________________________________________________
Co m p le t e , Is o la t e d , 3 .3 V
RS -4 8 5 /RS -4 2 2 Da t a In t e rfa c e
/MAX3480B
_________________________________________________________________Te s t Circ u it s
ISOLATION BARRIER
ISOLATION BARRIER
3.3V
A
3.3V
DE
C
´
R
R
L1
R3
A
A
R
DIFF
V
OD
D
R
B
RO
V
ID
DI
´
B
V
OC
C
L2
B
Figure 3. Driver DC Test Load
Figure 4. Driver/Receiver Timing Test Circuit
ISO V
CC1,
ISO V
CC2
S1
S2
500Ω
OUTPUT
UNDER TEST
C
L
Figure 5. Driver Timing Test Load
_______________________________________________________S w it c h in g Wa ve fo rm s
V
_ - 0.4V
V
CC
_ - 0.4V
CC
V
CC
_ - 0.4V
2
V _ - 0.4V
CC
V
CC
_ - 0.4V
2
V
CC
_ - 0.4V
2
DE
DI
´
2
´
0V
0V
t
t
PHL
PLH
1/2 V
O
t
t
LZ
ZL
B
A
A, B
V
2.3V
V
+ 0.5V
- 0.5V
O
OUTPUT NORMALLY LOW
OUTPUT NORMALLY HIGH
OL
V
OL
1/2 V
O
V
DIFF
= V - V
A B
A, B
0V
V
O
V
OH
2.3V
V
DIFF
90%
90%
0V
-V
10%
10%
O
t
t
HZ
ZH
t
R
t
F
t
t
- t
SKEW = | PLH PHL |
Figure 6. Driver Propagation Delays and Transition Times
Figure 7. Driver Enable and Disable Times
______________________________________________________________________________________ 11
Co m p le t e , Is o la t e d , 3 .3 V
RS -4 8 5 /RS -4 2 2 Da t a In t e rfa c e
g oe s to a p p roxima te ly d oub le the s up p ly volta g e .
__Sw itc hing Wa ve form s (c ontinue d)
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-switch-
ing, small-signal diodes, such as the 1N914, 1N4148,
or CMPD2838. The nominal value of the primary filter
capacitor C3 is 0.01µF.
V
OH
RO
1.5V
1.5V
0V
V
OL
OUTPUT
Drive r Ou t p u t P ro t e c t io n
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 cir-
cuits over the whole common-mode voltage range (see
Typical Operating Characteristics). In addition, a ther-
mal shutdown circuit forces the driver outputs into a
hig h-imp e d a nc e s ta te if the d ie te mp e ra ture ris e s
excessively.
t
t
PLH
PHL
V
ID
V - V
B
A
0V
-V
INPUT
ID
Figure 8. Receiver Propagation Delays
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.
____________________Func tion Ta ble s
/MAX3480B
Table 2. Transmitting
INPUTS
OUTPUTS
B
0
A
DE´
DI´
1
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.
1
1
0
1
0
0
1
X
High-Z
High-Z
X = Don't care
High-Z = High impedance
Table 3. Receiving
INPUTS
OUTPUT
–—–
RO
A-B
DE´
0
≥ +0.2V
≤ -0.2V
0
1
0
0
0
Inputs open
12 ______________________________________________________________________________________
Co m p le t e , Is o la t e d , 3 .3 V
RS -4 8 5 /RS -4 2 2 Da t a In t e rfa c e
/MAX3480B
__________Ap p lic a t io n s In fo rm a t io n
The MAX3480A/MAX3480B are designed for bidirection-
al data communications on multipoint bus-transmission
lines. Figure 9 shows a typical network application cir-
cuit. 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 MAX3480B is more tolerant of imperfect ter-
mination and stubs off the main line.
The MAX3480A/MAX3480B are specified and charac-
terized using the resistor values shown in Table 1 of
Fig ure 2. Alte ring the re c omme nd e d va lue s c a n
degrade performance.
The DI and DE inputs are the cathodes of LEDs whose
anodes are connected to V . These points are best
CC
driven by a 3.3V CMOS-logic gate with a series resis-
tor to limit the current. The resistor values shown in
Table 1 are recommended when the 74HC240 gate or
e q uiva le nt is us e d . The s e va lue s ma y ne e d to b e
adjusted if a driving gate with dissimilar series resis-
tance is used. DI and DE are intended to be driven
throug h a s e rie s c urre nt-limiting re s is tor. Dire c tly
grounding these pins destroys the device.
______________________________________________________________________________________ 13
Co m p le t e , Is o la t e d , 3 .3 V
RS -4 8 5 /RS -4 2 2 Da t a In t e rfa c e
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
B
A
DI
D
120Ω
DE
RO
A
B
A
B
R
RE
R
R
RE
RE
D
D
RO DE
DI
RO DE
DI
/MAX3480B
TERMINATING RESISTOR
(ONE RESISTOR ON EACH END)
MAX3480A/B
V
IN
V
CC1
AC1 (MAKE NO CONNECTION)
AC2 (MAKE NO CONNECTION)
1
2
3
4
5
6
7
8
9
28
27
26
25
24
23
22
21
20
19
18
17
16
15
3.0V to 3.6V
C2
0.1µF
C1
22µF
6V
V
CC2
D1
D2
D1, D2
1N914
ISO V
CC1
B
B
BOOSTED V+
R7
ISO RO DRV
A
GND1
FS
C3
0.01µF
120Ω
A
MAX485
MAX487
MAX845
74HC240
16
14
4
6
8
R6, 200Ω
ISO DI IN
ISO DE IN
ISO COM1
ISO DI DRV
SD
SH
SHIELD
(OPTIONAL)
R4
V
CC3
R1
130Ω
18
2
DRIVER INPUT
12
5
DI
DI
R5
3
V
CC4
17
15
13
10
11
12
13
14
DE
R2
DRIVER ENABLE
DE
ISO V
CC2
7
R8
100Ω
GND2
RO
ISO DE DRV
ISO COM2
20
R3
V
CC5
RECEIVER OUTPUT
9
11
ISO RO LED
RO
NOTE: RESISTOR R8
PROTECTS THE MAX3480
FROM TRANSIENT
CURRENTS BETWEEN
SHIELD AND “A” & “B”.
10
ISOLATION BARRIER
ISOLATED COMMON
LOGIC GROUND
Figure 9. Typical RS-485/RS-422 Network
14 ______________________________________________________________________________________
Co m p le t e , Is o la t e d , 3 .3 V
RS -4 8 5 /RS -4 2 2 Da t a In t e rfa c e
/MAX3480B
Table 4. Maxim’s Isolated RS-485 Product Family
GUARANTEED
DATA RATE
(Mbps)
SUPPLY
VOLTAGE
(V)
No. OF
Tx/Rx
FULL/HALF
DUPLEX
SLEW-RATE
LIMITED
No. OF Tx/Rx
ON BUS
PART
MAX1480A
MAX1480B
MAX1490A
MAX1490B
MAX3480A
MAX3480B
1/1
1/1
1/1
1/1
1/1
1/1
2.50
0.25
2.50
0.25
2.50
0.25
Half
Half
Full
Full
Half
Half
No
Yes
No
32
32
5.0
5.0
5.0
5.0
3.3
3.3
32
Yes
No
32
32
Yes
128
________________________________________________________P a c k a g e In fo rm a t io n
INCHES
MILLIMETERS
DIM
MIN
MAX
0.200
–
MIN
–
MAX
5.08
–
E
A
–
A2
A3
E1
A1 0.015
A2 0.125
A3 0.055
0.38
3.18
1.40
0.41
1.14
0.20
1.27
15.24
13.34
2.54
15.24
–
D
A
0.175
0.080
0.020
0.065
0.012
0.090
0.625
0.575
–
4.45
2.03
0.51
1.65
0.30
2.29
15.88
14.61
–
B
0.016
B1 0.045
0.008
D1 0.050
0.600
E1 0.525
0.100
eA 0.600
0°-15°
C
A1
e
C
L
E
eA
eB
B1
B
e
–
–
D1
eB
L
–
0.700
0.150
17.78
3.81
0.120
3.05
Plastic DIP
PLASTIC
INCHES
MILLIMETERS
PKG. DIM PINS
MIN
MAX MIN MAX
DUAL-IN-LINE
PACKAGE
(0.600 in.)
P
P
P
D
D
D
24
28
40
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
Co m p le t e , Is o la t e d , 3 .3 V
RS -4 8 5 /RS -4 2 2 Da t a In t e rfa c e
/MAX3480B
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 __________________Ma x im In t e g ra t e d P ro d u c t s , 1 2 0 S a n Ga b rie l Drive , S u n n yva le , CA 9 4 0 8 6 (4 0 8 ) 7 3 7 -7 6 0 0
© 1996 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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