General Description
The MAX3157 is a high CMRR RS-485/RS-422 data-com-
munications interface providing 50V isolation in a
hybrid microcircuit. A single +5V supply on the logic side
powers both sides of the interface, with external 50V
capacitors transferring power from the logic side to the
isolated side. Each MAX3157 contains one transmitter
and one receiver and is guaranteed to operate at data
rates up to 250kbps. Drivers are short-circuit current lim-
ited and protected against excessive power dissipation
by thermal shutdown circuitry that places the driver out-
puts into a high-impedance state. The receiver input has
a fail-safe feature that guarantees a logic high receiver
output if the inputs are open, shorted, or connected to a
terminated transmission line with all drivers disabled.
The MAX3157 typically draws 25mA of supply current
when unloaded or when fully loaded with the driver dis-
abled. Supply current drops to 25A when the device is
placed in shutdown mode. The device is pin selectable
between half- and full-duplex mode and also features
independently programmable receiver and transmitter
output phase through separate pins. The MAX3157 is a
low-cost replacement for opto-isolated transceivers. For
fully isolated RS-485/RS-422 transceivers, refer to the
MAX1480 family data sheet.
________________________Applications
Industrial Controls
Level Translators
Telecommunications
Local Area Networks
Features
o 50V Isolated Data Interface
o +5V Single Supply
o Low-Cost Replacement for Opto-Isolated
Transceivers
o True Fail-Safe Receiver While Maintaining
EIA/TIA-485 Compliance
o Pin-Selectable Full/Half-Duplex Operation
o Phase Controls to Correct for Twisted-Pair
Reversal
o 25A Low-Power Shutdown Mode
o Thermal Shutdown for Driver Overload Protection
o 28-Pin SSOP Package
o Slew Rate Limited Reduced EMI
MAX3157
High CMRR RS-485 Transceiver
with 50V Isolation
________________________________________________________________ Maxim Integrated Products
1
MAX3157
C1HI C2LO C2HI
C1LO
TXP
RXP
DE
DI
RE
RO
GND
A
B
Y
Z
YR
ZR
AR
BR
MICRO
RT = 100
V
CC
0.1
F
C3
1
F
C4
10nF
C1
0.047
F
C2
0.047
F
50V
GND OFFSET
ISOCOM
RG
REMOTE GND
REMOTE MICRO
RS-485
NODE
V
CC
H/F
ISOV
CC
Typical Operating Circuit
19-1778; Rev 3; 11/01
Ordering Information
Pin Configurations appear at end of data sheet.
PART
TEMP. RANGE
PIN-PACKAGE
MAX3157CAI
0
C to +70C
28 SSOP
MAX3157EAI
-40
C to +85C
28 SSOP
MAX3157CPI
0
C to +70C
28 PDIP
MAX3157EPI
-40
C to +85C
28 PDIP
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.
MAX3157
High CMRR RS-485 Transceiver
with 50V Isolation
2
_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
All voltages referenced to GND unless otherwise noted.
ELECTRICAL CHARACTERISTICS
(V
CC
= +5V 5%, YR = ZR = AR = BR = ISOCOM, C1 = C2 = 0.047F, C3 = C4 = 1F, T
A
= T
MIN
to T
MAX
, unless otherwise noted.
Typical values are at V
CC
= +5V and T
A
= +25C.) (Note 1)
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.
Supply Voltage (V
CC
).............................................................+7V
Cable Ground (ISOCOM) ....................................................75V
Isolated Supply ISOVCC Relative to Cable Ground
(ISOCOM) ............................................................................+7V
Digital Input, Output Voltage
(DI, DE, RE, TXP, RXP, RO)......................-0.3V to (V
CC
+ 0.3V)
Digital Inputs (H/F) Relative to Cable Ground
(ISOCOM) ..........................................-0.3V to (ISOVCC + 0.3V)
Driver Output Voltage (Y, Z), Relative to Cable Ground
(ISOCOM).............................................................-8V to +12.5V
Receiver Input Voltage (A, B), Relative to Cable Ground
(ISOCOM).............................................................-8V to +12.5V
Termination Connections (YR, ZR, AR, BR) Relative to Cable
Ground (ISOCOM)................................................-8V to +12.5V
Charge-Pump Capacitance Low
(C1LO, C2LO) .......................................-0.3V to (V
CC
+ 0.3V)
Charge-Pump Capacitance High (C1HI, C2HI) Relative
to Cable Ground (ISOCOM) ...........-0.3V to (ISOVCC + 0.3V)
Continuous Power Dissipation
28-Pin SSOP (derate 10.8mW/C above +70C) ........860mW
28-Pin PDIP (derate 14.3mW/C above +70C)........1143mW
Operating Temperature Ranges
MAX3157C_I .....................................................0C to +70C
MAX3157E_I ..................................................-40C to +85C
Junction Temperature ......................................................+150C
Storage Temperature Range ............................-65C to +160C
Lead Temperature (soldering, 10s) ................................+300C
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DRIVER
Differential Driver Output,
No Load
V
OD1
Figure 1, R = 10M
6
V
Figure 1, R = 50
(RS-422)
2.0
Differential Driver Output,
Loaded
V
OD2
Figure 1, R = 27
(RS-485)
1.5
V
Change in Magnitude of
Differential Output Voltage
(Note 2)
V
OD
Figure 1, R = 50
or R = 27
0.2
V
Driver Common-Mode Voltage
V
OC
Figure 1, R = 50
or R = 27,
V
OC
relative to ISOCOM
3.5
V
Change in Magnitude of
Common-Mode Voltage
(Note 2)
V
OC
Figure 1, R = 50
or R = 27
0.2
V
Input High Voltage
V
IH
DE, DI, RE, TXP, RXP, relative to GND,
H/F relative to ISOCOM
2.0
V
Input Low Voltage
V
IL
DE, DI, RE, TXP, RXP, relative to GND,
H/F relative to ISOCOM
0.8
V
DI Input Hysteresis
V
HYS
100
mV
I
IN1
DE, DI, RE
2
Input Current
I
IN2
H/F, TXP, RXP internal pulldown
10
40
A
DE = GND, V
CC
= GND or 5.25V, -7V
(V
IN
-
V
ISOCOM
)
12V, AR = BR = ISOCOM
-5.0
8.0
Input Current (A and B)
I
IN3
DE = GND, V
CC
= GND or 5.25V, -7V
(V
IN
-
V
ISOCOM
)
12V, AR open, BR open
-0.58
1.0
mA
MAX3157
High CMRR RS-485 Transceiver
with 50V Isolation
_______________________________________________________________________________________
3
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +5V 5%, YR = ZR = AR = BR = ISOCOM, C1 = C2 = 0.047F, C3 = C4 = 1F, T
A
= T
MIN
to T
MAX
, unless otherwise noted.
Typical values are at V
CC
= +5V and T
A
= +25C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DE = GND, V
CC
= GND or 5.25V, -7V
(V
IN
-
V
ISOCOM
)
12V, YR = ZR = ISOCOM
-5.0
8.0
Output Leakage (Y and Z)
Full Duplex
I
O
DE = GND, V
CC
= GND or 5.25V, -7V
(V
IN
-
V
ISOCOM
)
12V, YR open, ZR open
-0.58
1.0
mA
I
OSD1
V
ISOCOM
- 7V
V
OUT
V
ISOVCC
-250
Driver Short-Circuit Output
Current (Note 3)
I
OSD2
V
ISOCOM
- 7V
V
OUT
V
ISOCOM
+12V
250
mA
RECEIVER
Receiver Differential Threshold
Voltage
V
TH
-7V
V
CM
- V
ISOCOM
12V
-200
-125
-50
m V
Receiver Input Hysteresis
V
TH
25
mV
Receiver Output High Voltage
V
OH
I
O
= -4mA, V
ID
= -50mV
V
CC
- 1.5
V
Receiver Output Low Voltage
V
OL
I
O
= 4mA, V
ID
= -200mV
0.4
V
Three-State Output Current at
Receiver
I
OZR
0.4V
V
O
2.4V
1
A
-7V
V
CM
- V
ISOCOM
12V, AR = BR =
ISOCOM
1.5
Receiver Input Resistance
R
IN
-7V
V
CM
- V
ISOCOM
12V, AR open,
BR open
12
k
Receiver Output Short-Circuit
Current
I
OSR
0V
V
RO
V
CC
7
100
mA
SUPPLY CURRENT
Supply Current
I
CC
No load, RE = DE = DI = GND or V
CC
25
85
mA
DE = GND, RE = V
CC
, V
ISOCOM
= GND
25
60
Supply Current in Shutdown
Mode
I
SHDN
DE = GND, RE = V
CC
, V
ISOCOM
=
50V
600
A
Maximum Ground Differential
V
GND
DE = GND, RE = V
CC
,
| ISOCOM leakage |
600A
50
V
SWITCHING CHARACTERISTICS
(V
CC
= +5V 5%, YR = ZR = AR = BR = ISOCOM, C1 = C2 = 0.047F, C3 = C4 = 1F. Typical values are at V
CC
= +5V and T
A
= +25C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
t
DPLH
Figures 3 and 5, R
DIFF
= 54
,
C
L1
= C
L2
= 100pF
400
1400
2000
Driver Input to Output
t
DPHL
Figures 3 and 5, R
DIFF
= 54
,
C
L1
= C
L2
= 100pF
400
1400
2000
ns
Driver Output Skew
| t
DPLH
- t
DPHL
|
t
DSKEW
Figures 3 and 5, R
DIFF
= 54
,
C
L1
= C
L2
= 100pF
250
ns
Driver Rise or Fall Time
t
DR
, t
DF
Figures 3 and 5, R
DIFF
= 54
,
C
L1
= C
L2
=100pF
200
1200
2200
ns
Maximum Data Rate
f
MAX
250
kbps
MAX3157
High CMRR RS-485 Transceiver
with 50V Isolation
4
_______________________________________________________________________________________
SWITCHING CHARACTERISTICS (continued)
(V
CC
= +5V 5%, YR = ZR = AR = BR = ISOCOM, C1 = C2 = 0.047F, C3 = C4 = 1F. Typical values are at V
CC
= +5V and T
A
= +25C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Driver Enable to Output High
t
DZH
Figures 4 and 6, C
L
= 100pF, S2 closed
3500
ns
Driver Enable to Output Low
t
DZL
Figures 4 and 6, C
L
= 100pF, S1 closed
3500
ns
Driver Disable Time from Low
t
DLZ
Figures 4 and 6, C
L
= 15pF, S1 closed
300
ns
Driver Disable Time from High
t
DHZ
Figures 4 and 6, C
L
= 15pF, S2 closed
300
ns
Receiver Input to Output
t
RPLH
,
t
RPHL
Figures 7 and 9;
| V
ID
| 2.0V
440
600
ns
Differential Receiver Skew
|t
RPLH
- t
RPHL
|
t
RSKEW
Figures 7 and 9;
| V
ID
| 2.0V
20
ns
Receiver Enable to Output Low
t
RZL
Figures 2 and 8, C
L
= 100pF, S1 closed
20
50
ns
Receiver Enable to Output High
t
RZH
Figures 2 and 8, C
L
= 100pF, S2 closed
20
50
ns
Receiver Disable Time from Low
t
RLZ
Figures 2 and 8, C
L
= 100pF, S1 closed
200
500
ns
Receiver Disable Time from High
t
RHZ
Figures 2 and 8, C
L
= 100pF, S2 closed
200
500
ns
Time to Shutdown
t
SHDN
(Note 4)
50
200
700
ns
Driver Enable from Shutdown to
Output High
t
DZH
(SHDN)
Figures 4 and 6, C
L
= 15pF, S2
closed
0.2
1
ms
Driver Enable from Shutdown to
Output Low
t
DZL
(SHDN)
Figures 4 and 6, C
L
= 15pF, S1 closed
0.2
1
ms
Receiver Enable from Shutdown
to Output High
t
RZH
(SHDN)
Figures 2 and 8, C
L
= 100pF, S2 closed
0.2
1
m s
Receiver Enable from Shutdown
to Output Low
t
RZL
(SHDN)
Figures 2 and 8, C
L
= 100pF, S1 closed
0.2
1
ms
Charge-Pump Oscillating
Frequency
f
OSC
1.3
MHz
Note 1: All currents into the device are positive; all currents out of the device are negative. All voltages are referred to device
ground unless otherwise noted.
Note 2:
V
OD
and
V
OC
are the changes in V
OD
and V
OC
, respectively, when the DI input changes state.
Note 3: Current level applies to peak current just prior to foldback-current limiting.
Note 4: The device is put into shutdown by bringing RE high and DE low. If the enable inputs are in this state for less than 50ns,
the device is guaranteed not to enter shutdown. If the enable inputs are in this state for at least 700ns, the device is guaran-
teed to have entered shutdown.
MAX3157
High CMRR RS-485 Transceiver
with 50V Isolation
_______________________________________________________________________________________
5
0
40
20
60
120
140
100
80
160
-40
-20 -10 0 10 20 30
-30
40 50 60 70 80 90
SUPPLY CURRENT vs. TEMPERATURE
MAX1357toc01
TEMPERATURE (
C)
SUPPY CURRENT (mA)
R
L
= 54
NO LOAD
-300
-100
-200
200
100
0
300
-40
-20 -10 0 10 20 30
-30
40 50 60 70 80 90
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
MAX1357toc02
TEMPERATURE (
C)
SUPPY CURRENT (
A)
V
ISOCOM
= -50V
V
ISOCOM
= 0
V
ISOCOM
= +50V
0
10
5
25
20
15
40
35
30
45
0
2
1
3
4
5
6
RECEIVER OUTPUT CURRENT
vs. RECEIVER OUTPUT LOW VOLTAGE
MAX3157toc03
OUTPUT LOW VOLTAGE (V)
OUTPUT CURRENT (mA)
0
6
2
4
12
10
8
18
16
14
20
0
2.0 2.5
1.5
1.0
0.5
3.0 3.5 4.0 4.5 5.0 5.5
RECEIVER OUTPUT CURRENT
vs. RECEIVER OUTPUT HIGH VOLTAGE
MAX3157toc04
OUTPUT HIGH VOLTAGE (V)
OUTPUT CURRENT (mA)
0
0.15
0.10
0.05
0.25
0.20
0.45
0.40
0.35
0.30
0.50
-40
-20
0
20
40
60
80
100
RECEIVER OUTPUT LOW VOLTAGE
vs. TEMPERATURE
MAX3157toc05
TEMPERATURE (
C)
OUTPUT LOW VOLTAGE (V)
I
RO
= 8mA
3.95
4.05
4.00
4.15
4.10
4.35
4.30
4.25
4.20
4.40
-40
-20
0
20
40
60
80
100
RECEIVER OUTPUT HIGH VOLTAGE
vs. TEMPERATURE
MAX3157toc06
TEMPERATURE (
C)
OUTPUT VOLTAGE (V)
I
RO
= -8mA
0
40
20
80
60
140
120
100
160
0
4
2
6
8
10
12
14
DRIVER OUTPUT CURRENT
vs. DRIVER OUTPUT LOW VOLTAGE
MAX3157toc07
OUTPUT VOLTAGE (V)
OUTPUT CURRENT (mA)
-120
-90
-110
-100
-60
-80
-70
-10
-30
-20
-40
-50
0
-8
-4
-6
-2
0
2
4
6
DRIVER OUTPUT CURRENT
vs. DRIVER OUTPUT HIGH VOLTAGE
MAX3157toc08
OUTPUT HIGH VOLTAGE (V)
OUTPUT CURRENT (mA)
100
0.01
0
1
3
2
5
4
6
DRIVER OUTPUT CURRENT
vs. DIFFERENTIAL OUTPUT VOLTAGE
0.1
MAX3157toc09
DIFFERENTIAL OUTPUT VOLTAGE (V)
OUTPUT
CURRENT
(
m
A)
1
10
Typical Operating Characteristics
(V
CC
= +5V, YR = ZR = AR = BR = ISOCOM, C1 = C2 = 0.047F, C3 = 1F, C4 = 10nF, T
A
= +25C, unless otherwise noted.)
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