3.3 V , Full Duplex, 840 mA
R
D
RE
DE
DI
A
B
Z
Y
ADM3491
RO
a
FEATURES
Operates with +3.3 V Supply
EIA RS-422 and RS-485 Compliant Over Full CM Range
19 kV Input Impedance
Up to 50 Transceivers on Bus
20 Mbps Data Rate
Short Circuit Protection
Specified Over Full Temperature Range
Thermal Shutdown
Interoperable with 5 V Logic
840 mA Supply Current
2 nA Shutdown Current
Also Available in TSSOP Package
Meets IEC1000-4-4 (>1 kV)
8 ns Skew
Upgrade for MAX 3491, SN75ALS180
APPLICATIONS
Telecommunications
DTE-DCE Interface
Packet Switching
Local Area Networks
Data Concentration
Data Multiplexers
Integrated Services Digital Network (ISDN)
AppleTalk
Industrial Controls
GENERAL DESCRIPTION
The ADM3491 is a low power differential line transceiver
designed to operate using a single +3.3 V power supply. Low
power consumption coupled with a shutdown mode make it
ideal for power sensitive applications. It is suitable for communication on multipoint bus transmission lines.
It is intended for balanced data transmission and complies with
both EIA Standards RS-485 and RS-422. It contains a differential line driver and a differential line receiver, making it suitable
for full duplex data transfer.
The input impedance is 19 kΩ allowing up to 50 transceivers to
be connected on the bus.
Excessive power dissipation caused by bus contention or by
output shorting is prevented by a thermal shutdown circuit.
This feature forces the driver output into a high impedance state
if, during fault conditions, a significant temperature increase is
detected in the internal driver circuitry.
20 Mbps, EIA RS-485 Transceiver
ADM3491
FUNCTIONAL BLOCK DIAGRAM
The receiver contains a fail-safe feature that results in a
logic high output state if the inputs are unconnected
(floating).
The ADM3491 is fabricated on BiCMOS, an advanced
mixed technology process combining low power CMOS
with fast switching bipolar technology.
The ADM3491 is fully specified over the industrial temperature range and is available in DIP and SOIC packages
as well as a new space saving TSSOP package.
REV. 0
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703 © Analog Devices, Inc., 1998
ADM3491–SPECIFICA TIONS
(VCC = +3.3 V 6 0.3 V. All specifications T
MIN
to T
unless otherwise noted.)
MAX
Parameter Min Typ Max Units Test Conditions/Comments
DRIVER
Differential Output Voltage, V
∆|V
| for Complementary Output States 0.2 V R = 54 Ω or 100 Ω, Figure 1
OD
Common-Mode Output Voltage V
∆|V
| for Complementary Output States 0.2 V R = 54 Ω or 100 Ω, Figure 1
OC
CMOS Input Logic Threshold Low, V
OD
OC
INL
CMOS Input Logic Threshold High, V
2.0 V RL = 100 Ω, Figure 1, VCC > 3.1 V
1.5 V R
1.5 V R
= 54 Ω, Figure 1
L
= 60 Ω, Figure 2, –7 V < V
L
3 V R = 54 Ω or 100 Ω, Figure 1
0.8 V
2.0 V
INH
TST
Logic Input Current (DE, DI, RE) ±1.0 µA
Output Leakage (Y, Z) Current ±3 µAV
= –7 V or +12 V, VCC = 0 V or 3.6 V
O
Output Short Circuit Current ±250 mA VO = –7 V or +12 V
RECEIVER
Differential Input Threshold Voltage, V
Input Voltage Hysteresis, ∆V
TH
Input Resistance 12 19 kΩ –7 V < V
Input Current (A, B) +1 mA V
–0.2 +0.2 V –7 V < VCM < +12 V
TH
50 mV VCM = 0 V
= +12 V
–0.8 mA V
IN
= –7 V
IN
< +12 V
CM
Logic Enable Input Current (RE) ±1 µA
Output Voltage Low, V
Output Voltage High, V
OL
OH
VCC –0.4 V V I
Short Circuit Output Current ±60 mA V
Three-State Output Leakage Current ±1.0 µAV
0.4 V I
= +2.5 mA
OUT
= –1.5 mA
OUT
= GND or V
OUT
= 3.6 V, 0 V < V
CC
CC
OUT
< V
CC
POWER SUPPLY CURRENT
I
CC
0.84 1.2 mA DE = V
Outputs Unloaded,
, RE = 0 V
CC
0.84 1.2 mA DE = 0 V, RE = 0 V
Supply Current in Shutdown 0.002 1 µA DE = 0 V, RE = V
Specifications subject to change without notice.
CC
< +12 V
–2–
REV. 0
ADM3491
TIMING SPECIFICATIONS
(VCC = +3.3 V, TA = +258C)
Parameter Min Typ Max Units Test Conditions/ Comments
DRIVER
Differential Output Delay T
DD
Differential Output Transition Time 1 8 15 ns R
Propagation Delay Input to Output T
Driver O/P to O/P T
SKEW
PLH
, T
PHL
135nsR
72235nsR
8nsR
= 60 Ω, CL1 = CL2 = 15 pF, Figure 5
L
= 60 Ω, CL1 = CL2 = 15 pF, Figure 5
L
= 27 Ω, CL1 = CL2 = 15 pF, Figure 6
L
= 54 Ω, CL1 = CL2 = 15 pF, Figure 6
L
ENABLE/DISABLE
Driver Enable to Output Valid 45 90 ns R
Driver Disable Timing 40 80 ns R
= 110 Ω, CL = 50 pF, Figure 3
L
= 110 Ω, CL = 50 pF, Figure 3
L
Driver Enable from Shutdown 650 110 ns RL = 110 Ω, CL = 15 pF, Figure 3
RECEIVER
Time to Shutdown 80 190 300 ns
Propagation Delay Input to Output T
Skew T
PLH–TPHL
Receiver Enable T
Receiver Disable T
EN
DEN
PLH
, T
PHL
25 65 90 ns CL = 15 pF, Figure 8
10 ns CL = 15 pF, Figure 8
25 50 ns CL = 15 pF, Figure 4
25 45 ns CL = 15 pF, Figure 4
Receiver Enable from Shutdown 500 ns CL = 15 pF, Figure 4
TIMING SPECIFICATIONS
(VCC = +3.3 V 6 0.3 V, TA = T
MIN
to T
MAX
)
Parameter Min Typ Max Units Test Conditions/ Comments
DRIVER
Differential Output Delay T
DD
Differential Output Transition Time 2 8 15 ns R
Propagation Delay Input to Output T
Driver O/P to O/P T
SKEW
PLH
, T
PHL
170nsR
72270nsR
= 60 Ω, CL1 = CL2 = 15 pF, Figure 5
L
= 60 Ω, CL1 = CL2 = 15 pF, Figure 5
L
= 27 Ω, CL1 = CL2 = 15 pF, Figure 6
L
10 ns RL = 54 Ω, CL1 = CL2 = 15 pF, Figure 6
ENABLE/DISABLE
Driver Enable to Output Valid 45 110 ns R
Driver Disable Timing 40 110 ns R
= 110 Ω, CL = 50 pF, Figure 3
L
= 110 Ω, CL = 50 pF, Figure 3
L
Driver Enable from Shutdown 650 110 ns RL = 110 Ω, CL = 15 pF, Figure 3
RECEIVER
Time to Shutdown 50 190 500 ns
Propagation Delay Input to Output T
Skew T
PLH–TPHL
Receiver Enable T
Receiver Disable T
EN
DEN
PLH
, T
PHL
25 65 115 ns CL = 15 pF, Figure 8
20 ns CL = 15 pF, Figure 8
25 50 ns CL = 15 pF, Figure 4
25 50 ns CL = 15 pF, Figure 4
Receiver Enable from Shutdown 600 ns CL = 15 pF, Figure 4
–3–REV. 0
ADM3491
ABSOLUTE MAXIMUM RATINGS*
(TA = +25°C unless otherwise noted)
VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +7 V
Inputs
Driver Input (DI) . . . . . . . . . . . . . . . .–0.3 V to V
Control Inputs (DE, RE) . . . . . . . . . .–0.3 V to V
+ 0.3 V
CC
+ 0.3 V
CC
Receiver Inputs (A, B) . . . . . . . . . . . . . . .–7.5 V to +12.5 V
Outputs
Driver Outputs . . . . . . . . . . . . . . . . . . . . .–7.5 V to +12.5 V
Receiver Output . . . . . . . . . . . . . . . . . –0.5 V to V
+0.5 V
CC
Power Dissipation 14-Lead DIP . . . . . . . . . . . . . . . . 800 mW
θ
, Thermal Impedance . . . . . . . . . . . . . . . . . . . 140°C/W
JA
Power Dissipation 14-Lead SOIC . . . . . . . . . . . . . . . 650 mW
θ
, Thermal Impedance . . . . . . . . . . . . . . . . . . . 115°C/W
JA
ORDERING GUIDE
Power Dissipation 16-Lead TSSOP . . . . . . . . . . . . . . 500 mW
θ
, Thermal Impedance . . . . . . . . . . . . . . . . . . . 158 °C/W
JA
Operating Temperature Range
Industrial (A Version) . . . . . . . . . . . . . . . . –40°C to +85°C
Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C
Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . .+300°C
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . .+215°C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . .+220°C
ESD Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . >2 kV
EFT Rating (IEC1000-4-4) . . . . . . . . . . . . . . . . . . . . . . >1 kV
*Stresses above those listed under Absolute Maximum Ratings may cause perma-
nent damage to the device. This is a stress rating only; functional operation of the
device at these or any other conditions above those listed in the operational
sections of this specification is not implied. Exposure to absolute maximum
ratings for extended periods of time may affect device reliability.
Model Temperature Range Package Description Package Options
ADM3491AN –40°C to +85°C Plastic DIP N-14
ADM3491AR –40°C to +85°C Small Outline (SOIC) R-14
ADM3491ARU –40°C to +85°C Thin Shrink Small Outline (TSSOP) RU-16
–4–
REV. 0
PIN CONFIGURATION
DIP/SOIC
ADM3491
NC
1
RO
2
ADM3491
3
RE
TOP VIEW
(Not to Scale)
4
DE
DI
5
GND
6
GND
7
NC = NO CONNECT
TSSOP
V
1
CC
NC
2
3
RO
ADM3491
4
RE
TOP VIEW
(Not to Scale)
5
DE
6
DI
NC
7
8
GND
NC = NO CONNECT
V
14
CC
V
13
CC
12
A
11
B
10
Z
9
Y
8
NC
16
NC
15
A
14
B
13
NC
12
Z
11
Y
10
NC
9
NC
PIN FUNCTION DESCRIPTIONS
Mnemonic DIP/
Pin SOIC TSSOP Function
NC 1, 8 2, 7, 9, 10,
13, 16 No Connect.
RO 2 3 Receiver Output. High when A > B by 200 mV or Low when A < B by 200 mV.
RE 3 4 Receiver Output Enable. With RE low, the receiver output RO is enabled. With RE high,
the output goes high impedance. If RE is high and DE low, the ADM3491 enters a
shutdown state.
DE 4 5 Driver Output Enable. A high level enables the driver differential outputs, Y and Z. A low
level places it in a high impedance state.
DI 5 6 Driver Input. When the driver is enabled, a logic Low on DI forces Y low and Z high while
a logic high on DI forces Y high and Z low.
GND 6, 7 8 Ground Connection, 0 V.
Y 9 11 Noninverting Driver Output Y.
Z 10 12 Inverting Driver Output Z.
B 11 14 Inverting Receiver Input B.
A 12 15 Noninverting Receiver Input A.
V
CC
13, 14 1 Power Supply, 3.3 V ± 0.3 V.
–5–REV. 0
ADM3491
Test Circuits
R/2
V
OD
V
CC
Figure 1. Driver Voltage Measurement Test Circuit
0V OR 3V
DE IN
DE
S1
Figure 2. Driver Enable/Disable Test Circuit
DI
RL
D
DIFF
Figure 3. Driver Differential Output Delay Test Circuit
DI
RL
C
DIFF
C
V
R/2
OC
V
CC
R
L
L2
L
OUT
V
OUT
S2
RO
RD
RE
C
V
C
L1
C
A
L1
B
L2
375V
R
L
375V
V
TST
V
OD3
Figure 5. Driver Voltage Measurement Test Circuit 2
V
+1.5V
–1.5V
S1
RE
RE IN
CC
R
L
C
V
S2
L
OUT
Figure 6. Receiver Enable/Disable Test Circuit
V
OM
R
L
S1
DE
IN
V
CC
V
C
OUT
L
Figure 7. Driver Propagation Delay Test Circuit
3V
0V
V
ID
+1.5V
RE
V
OUT
C
L
Figure 4. Driver/Receiver Propagation Delay Test Circuit
Figure 8. Receiver Propagation Delay Test Circuit
–6–
REV. 0
Switching Characteristics
ADM3491
3V
0V
0V
–VO
Z
VO
Y
VO
1/2VO
90% POINT
10% POINT
t
1.5V
PLH
t
SKEW
t
R
1.5V
t
PHL
t
SKEW
90% POINT
10% POINT
t
F
Figure 9. Driver Propagation Delay, Rise/Fall Timing
A–B
RO
0V
t
PLH
1.5V
0V
t
PHL
1.5V
V
OH
V
OL
Figure 10. Receiver Propagation Delay
3V
t
t
1.5V
LZ
HZ
0V
V
+ 0.25V
OL
VOH – 0.25V
V
OL
V
OH
RE
0V
1.5V
t
ZL
R
R
1.5V
t
ZH
1.5V
O/P
LOW
O/P HIGH
Figure 11. Driver Enable/Disable Timing
3V
t
LZ
t
1.5V
HZ
0V
V
+ 0.25V
OL
VOH – 0.25V
V
OL
V
OH
RE
0V
1.5V
t
ZL
R
R
1.5V
t
ZH
1.5V
O/P
LOW
O/P HIGH
Figure 12. Receiver Enable/Disable Timing
–7–REV. 0
ADM3491
–Typical Performance Characteristics
14
12
10
8
6
4
OUTPUT CURRENT – mA
2
0
0 3.50.5 1 1.5 2 2.5 3
OUTPUT VOLTAGE – Volts
Figure 13. Receiver Output Low Voltage vs. Output
Current
0.8
0.7
0.6
0.5
0.4
IRO = 2.5mA
14
12
10
8
6
4
OUTPUT CURRENT – mA
2
0
040 1 1.5 2 2.5 3 3.5
.5
OUTPUT HIGH VOLTAGE – Volts
Figure 16. Receiver Output High Voltage vs. Output
Current
3.3
3.25
3.2
3.15
IRO = –1.5mA
0.3
OUTPUT VOLTAGE – V
0.2
0.1
0
–40 100–20 0 20406080
TEMPERATURE – 8C
Figure 14. Receiver Output Low Voltage vs. Temperature
120
100
80
60
40
OUTPUT CURRENT – mA
20
0
030.5 1 1.5 2 2.5
DIFFERENTIAL O/P VOLTAGE – Volts
Figure 15. Driver Differential Output Voltage vs. Output
Current
3.1
OUTPUT VOLTAGE – V
3.05
3
–40 100–200 20406080
TEMPERATURE – 8C
Figure 17. Receiver Output High Voltage vs. Temperature
2.6
2.5
2.4
2.3
2.2
2.1
2.0
1.9
OUTPUT VOLTAGE – V
1.8
1.7
1.6
–40 100–200 204060 80
TEMPERATURE – 8C
Figure 18. Driver Differential Output Voltage vs.
Temperature
–8–
REV. 0
ADM3491
1.2
1.1
1
0.9
SUPPLY CURRENT – mA
0.8
0.7
–40 100–200 20406080
TEMPERATURE – 8C
Figure 19. Supply Current vs. Temperature
[ T ]
T
3
T
T
1
2
T
4
CH1 1.00V CH2 1.00V M40.0ns CH3 640mV
CH3 2.00V CH4 2.00V
100FT
CABLE
Figure 20. Driving 100 ft. Cable L-H Transition
[ T ]
T
3
T
1
2
4
T
T
CH1 1.00V CH2 1.00V M40.0ns CH3 640mV
CH3 2.00V CH4 2.00V
100FT CAT 5
CABLE
Figure 21. Driving 100 ft. Cable H-L Transition
100
90
80
70
60
50
40
30
SHUTDOWN CURRENT – mA
20
10
0
–40 80–20 0 20 40 60
TEMPERATURE – 8C
Figure 22. Shutdown Current vs. Temperature
–9–REV. 0
ADM3491
+3.3V
RE
RO
ADM3491
DI
DE
0.1mF
V
CC
A
R
B
Z
D
Y
GND
RS-485/RS-422 LINK
+3.3V
Y
Z
B
A
V
CC
ADM3491
R
GND
0.1mF
DE
DI
D
RO
RE
Figure 23. ADM3491 Full-Duplex Data Link
Table I. Transmitting Truth Table
Transmitting
Inputs Outputs
RE DE DI Z Y
X11 01
X10 10
0 0 X Hi-Z Hi-Z
1 0 X Hi-Z Hi-Z
Table II. Receiving Truth Table
Receiving
Inputs Outputs
RE DE A–B RO
0 X > +0.2 V 1
0 X < –0.2 V 0
0 X Inputs O/C 1
1 X X Hi-Z
–10–
REV. 0
ADM3491
APPLICATIONS INFORMATION
Differential Data Transmission
Differential data transmission is used to reliably transmit data at
high rates over long distances and through noisy environments.
Differential transmission nullifies the effects of ground shifts
and noise signals which appear as common-mode voltages on
the line.
Two main standards are approved by the Electronics Industries
Association (EIA) which specify the electrical characteristics of
transceivers used in differential data transmission. The RS-422
standard specifies data rates up to 10 MBaud and line lengths
up to 4000 ft. A single driver can drive a transmission line with
up to 10 receivers.
The RS-485 standard was defined to cater to true multipoint
communications. This standard meets or exceeds all the requirements of RS-422, but also allows multiple drivers and
receivers to be connected to a single bus. An extended common
mode range of –7 V to +12 V is defined.
The most significant difference between RS-422 and RS-485 is
the fact that the drivers may be disabled thereby allowing more
than one to be connected to a single line. Only one driver should
be enabled at a time, but the RS-485 standard contains additional specifications to guarantee device safety in the event of
line contention.
Cable and Data Rate
The transmission line of choice for RS-485 communications is a
twisted pair. Twisted pair cable tends to cancel common-mode
noise and also causes cancellation of the magnetic fields generated by the current flowing through each wire, thereby reducing
the effective inductance of the pair.
The ADM3491 is designed for bidirectional data communications on multipoint transmission lines. A typical application
showing a multipoint transmission network is illustrated in
Figure 23. Only one driver can transmit at a particular time, but
multiple receivers may be enabled simultaneously.
As with any transmission line, it is important that reflections are
minimized. This may be achieved by terminating the extreme
ends of the line using resistors equal to the characteristic impedance of the line. Stub lengths of the main line should also be
kept as short as possible. A properly terminated transmission
line appears purely resistive to the driver.
Receiver Open-Circuit Fail Safe
The receiver input includes a fail-safe feature that guarantees a
logic high on the receiver when the inputs are open circuit or
floating.
Table III. Comparison of RS-422 and RS-485 Interface Standards
Specification RS-422 RS-485
Transmission Type Differential Differential
Maximum Cable Length 4000 ft. 4000 ft.
Minimum Driver Output Voltage ±2 V ±1.5 V
Driver Load Impedance 100 Ω 54 Ω
Receiver Input Resistance 4 kΩ min 12 kΩ min
Receiver Input Sensitivity ±200 mV ±200 mV
Receiver Input Voltage Range –7 V to +7 V –7 V to +12 V
–11–REV. 0
ADM3491
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
0.210 (5.33)
MAX
0.160 (4.06)
0.115 (2.93)
14-Lead Plastic DIP
(N-14)
0.795 (20.19)
0.725 (18.42)
14
17
PIN 1
0.022 (0.558)
0.014 (0.356)
0.100
(2.54)
BSC
0.070 (1.77)
0.045 (1.15)
8
0.280 (7.11)
0.240 (6.10)
0.060 (1.52)
0.015 (0.38)
0.1574 (4.00)
0.1497 (3.80)
0.0098 (0.25)
0.0040 (0.10)
0.130
(3.30)
MIN
SEATING
PLANE
0.325 (8.25)
0.300 (7.62)
0.015 (0.381)
0.008 (0.204)
0.195 (4.95)
0.115 (2.93)
16-Lead Thin Shrink Small Outline (TSSOP)
(RU-16)
0.201 (5.10)
0.193 (4.90)
16 9
0.177 (4.50)
0.169 (4.30)
1
8
0.256 (6.50)
0.246 (6.25)
14-Lead Narrow Body Small Outline (SOIC)
(R-14)
0.3444 (8.75)
0.3367 (8.55)
SEATING
PLANE
14 8
PIN 1
0.0500
0.0192 (0.49)
(1.27)
0.0138 (0.35)
BSC
0.2440 (6.20)
71
0.2284 (5.80)
0.0688 (1.75)
0.0532 (1.35)
0.0099 (0.25)
0.0075 (0.19)
0.0196 (0.50)
0.0099 (0.25)
8°
0°
0.0500 (1.27)
0.0160 (0.41)
x 45°
C3216–8–1/98
0.006 (0.15)
0.002 (0.05)
SEATING
PLANE
PIN 1
0.0256
(0.65)
BSC
0.0118 (0.30)
0.0075 (0.19)
0.0433
(1.10)
MAX
0.0079 (0.20)
0.0035 (0.090)
8°
0°
0.028 (0.70)
0.020 (0.50)
PRINTED IN U.S.A.
–12–
REV. 0
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