FUNCTIONAL BLOCK DIAGRAM
R
A
B
DI
DE
RE
RO
ADM485
D
2
3
45
6
7
8
1V
CC
GND
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.
a
+5 V Low Power
EIA RS-485 Transceiver
ADM485
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700 Fax: 617/326-8703
FEATURES
Meets EIA RS-485 Standard
5 Mb/s Data Rate
Single +5 V Supply
–7 V to +12 V Bus Common-Mode Range
High Speed, Low Power BiCMOS
Thermal Shutdown Protection
Short Circuit Protection
Zero Skew Driver
Driver Propagation Delay: 10 ns
Receiver Propagation Delay: 25 ns
High Z Outputs with Power Off
Superior Upgrade for LTC485
APPLICATIONS
Low Power RS-485 Systems
DTE-DCE Interface
Packet Switching
Local Area Networks
Data Concentration
Data Multiplexers
Integrated Services Digital Network (ISDN)
PRODUCT DESCRIPTION
The ADM485 is a differential line transceiver suitable for high
speed bidirectional data communication on multipoint bus
transmission lines. It is designed for balanced data transmission
and complies with both EIA Standards RS-485 and RS-422.
The part contains a differential line driver and a differential line
receiver. Both the driver and the receiver may be enabled inde-
pendently. When disabled, the outputs are tristated.
The ADM485 operates from a single +5 V power supply.
Excessive power dissipation caused by bus contention or by out-
put 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.
Up to 32 transceivers may be connected simultaneously on a
bus, but only one driver should be enabled at any time. It is im-
portant, therefore, that the remaining disabled drivers do not
load the bus. To ensure this, the ADM485 driver features high
output impedance when disabled and also when powered down.
This minimizes the loading effect when the transceiver is not
being utilized. The high impedance driver output is maintained
over the entire common-mode voltage range from –7 V to +12 V.
The receiver contains a fail safe feature which results in a logic
high output state if the inputs are unconnected (floating).
The ADM485 is fabricated on BiCMOS, an advanced mixed
technology process combining low power CMOS with fast
switching bipolar technology. All inputs and outputs contain
protection against ESD; all driver outputs feature high source
and sink current capability. An epitaxial layer is used to guard
against latch-up.
The ADM485 features extremely fast switching speeds. Minimal
driver propagation delays permit transmission at data rates up to
5 Mbits/s while low skew minimizes EMI interference.
The part is fully specified over the commercial and industrial
temperature range and is available in an 8-pin DIL/SOIC package.
ADM485–SPECIFICATIONS
Parameter Min Typ Max Units Test Conditions/Comments
DRIVER
Differential Output Voltage, V
OD
5.0 V R = ∞, Figure 1
2.0 5.0 V V
CC
= 5 V, R = 50 Ω (RS-422), Figure 1
1.5 5.0 V R = 27 Ω (RS-485), Figure 1
V
OD3
1.5 5.0 V V
TST
= –7 V to +12 V, Figure 2
∆|V
OD
| for Complementary Output States 0.2 V R = 27 Ω or 50 Ω, Figure 1
Common-Mode Output Voltage V
OC
3 V R = 27 Ω or 50 Ω, Figure 1
∆|V
OC
| for Complementary Output States 0.2 V R = 27 Ω or 50 Ω
Output Short Circuit Current (V
OUT
= High) 35 250 mA –7 V ≤ V
O
≤ +12 V
Output Short Circuit Current (V
OUT
= Low) 35 250 mA –7 V ≤ V
O
≤ +12 V
CMOS Input Logic Threshold Low, V
INL
0.8 V
CMOS Input Logic Threshold High, V
INH
2.0 V
Logic Input Current (DE, DI) ±1.0 µA
RECEIVER
Differential Input Threshold Voltage, V
TH
–0.2 +0.2 V –7 V ≤ V
CM
≤ +12 V
Input Voltage Hysteresis, ∆V
TH
70 mV V
CM
= 0 V
Input Resistance 12 kΩ–7 V ≤ V
CM
≤ +12 V
Input Current (A, B) +1 mA V
IN
= 12 V
–0.8 mA V
IN
= –7 V
Logic Enable Input Current (RE)±1µA
CMOS Output Voltage Low, V
OL
0.4 V I
OUT
= +4.0 mA
CMOS Output Voltage High, V
OH
4.0 V I
OUT
= –4.0 mA
Short Circuit Output Current 7 85 mA V
OUT
= GND or V
CC
Tristate Output Leakage Current ±1.0 µA 0.4 V ≤ V
OUT
≤ +2.4 V
POWER SUPPLY CURRENT
I
CC
(Outputs Enabled) 1.35 2.2 mA Outputs Unloaded, Digital Inputs = GND or V
CC
I
CC
(Outputs Disabled) 0.7 1 mA Outputs Unloaded, Digital Inputs = GND or V
CC
Specifications subject to change without notice.
Timing Specifications
Parameter Min Typ Max Units Test Conditions/Comments
DRIVER
Propagation Delay Input to Output T
PLH
, T
PHL
21015ns R
L
Diff = 54 Ω C
L1
= C
L2
= 100 pF, Figure 3
Driver O/P to O/P T
SKEW
05 ns R
L
Diff = 54 Ω C
L1
= C
L2
= 100 pF, Figure 3
Driver Rise/Fall Time T
R
, T
F
210ns R
L
Diff = 54 Ω C
L1
= C
L2
= 100 pF, Figure 3
Driver Enable to Output Valid 10 25 ns
Driver Disable Timing 10 25 ns
RECEIVER
Propagation Delay Input to Output T
PLH
, T
PHL
18 25 40 ns C
L
= 15 pF, Figure 5
Skew |T
PLH
–T
PHL
|05ns
Receiver Enable T
EN1
15 25 ns Figure 6
Receiver Disable T
EN2
15 25 ns Figure 6
Specifications subject to change without notice.
REV. 0
–2–
(V
CC
= +5 V 6 5%. All specifications T
MIN
to T
MAX
unless otherwise noted)
(VCC = +5 V 6 5%. All specifications TMIN to TMAX unless otherwise noted.)
ADM485
REV. 0 –3–
WARNING!
ESD SENSITIVE DEVICE
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection.
Although the ADM485 features proprietary ESD protection circuitry, permanent damage may
occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD
precautions are recommended to avoid performance degradation or loss of functionality.
ABSOLUTE MAXIMUM RATINGS*
(T
A
= +25°C unless otherwise noted)
V
CC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .+7 V
Inputs
Driver Input (DI) . . . . . . . . . . . . . . . . –0.3 V to V
CC
+ 0.3 V
Control Inputs (DE, RE) . . . . . . . . . . –0.3 V to V
CC
+ 0.3 V
Receiver Inputs (A, B) . . . . . . . . . . . . . . . . . –14 V to +14 V
Outputs
Driver Outputs . . . . . . . . . . . . . . . . . . . . . . . –14 V to +14 V
Receiver Output . . . . . . . . . . . . . . . . . . –0.5 V to V
CC
+0.5 V
Power Dissipation 8-Pin DIP . . . . . . . . . . . . . . . . . . . . 500 mW
θ
JA
, Thermal Impedance . . . . . . . . . . . . . . . . . . . . +130°C/W
Power Dissipation 8-Pin SOIC . . . . . . . . . . . . . . . . . . 450 mW
θ
JA
, Thermal Impedance . . . . . . . . . . . . . . . . . . . . +170°C/W
Power Dissipation 8-Pin Cerdip . . . . . . . . . . . . . . . . . . 500 mW
θ
JA
, Thermal Impedance . . . . . . . . . . . . . . . . . . . . +125°C/W
Operating Temperature Range
Commercial (J Version) . . . . . . . . . . . . . . . . . .0°C to +70°C
Industrial (A Version) . . . . . . . . . . . . . . . . . –40°C to +85°C
Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C
Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . . . +300°C
Vapour Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . +215°C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . . +220°C
*Stresses above those listed under “Absolute Maximum Ratings” may cause
permanent damage to the device. This is a stress rating only and functional
operation of the device at these or any other conditions above those indicated in the
operational sections of this specification is not implied. Exposure to absolute
maximum ratings for extended periods may affect device reliability.
Table I. Transmitting
INPUTS OUTPUT
RE DE DI B A
X 1101
X 1010
X0XZZ
Table II. Receiving
INPUTS OUTPUT
RE DE A-B RO
00 ≥ +0.2 V 1
00 ≤ –0.2 V 0
0 0 Inputs Open 1
10 X Z
PIN FUNCTION DESCRIPTION
Pin Mnemonic Function
1 RO Receiver Output. When enabled if A > B by
200 mV, then RO = High. If A < B by
200 mV, then RO = Low.
2RE Receiver Output Enable. A low level enables
the receiver output, RO. A high level places it
in a high impedance state.
3 DE Driver Output Enable. A high level enables
the driver differential outputs, A and B. A
low level places it in a high impedance state.
4 DI Driver Input. When the driver is enabled a
logic Low on DI forces A low and B high
while a logic High on DI forces A high and B
low.
5 GND Ground Connection, 0 V.
6 A Noninverting Receiver Input A/Driver
Output A.
7 B Inverting Receiver Input B/Driver Output B.
8V
CC
Power Supply, 5 V ± 5%.
PIN CONFIGURATION
RO
RE
DE
DI GND
A
B
V
CC
1
2
3
4
8
7
6
5
TOP VIEW
(Not to Scale)
ADM485
ORDERING GUIDE
Model Temperature Range Package Option
ADM485JN 0°C to +70°C N-8
ADM485JR 0°C to +70°C R-8
ADM485AN –40°C to +85°C N-8
ADM485AR –40°C to +85°C R-8
ADM485AQ –40°C to +85°C Q-8
ADM485
REV. 0
–4–
Test Circuits
R
RV
OC
V
OD
Figure 1. Driver Voltage Measurement Test Circuit
375Ω
V
OD3
V
TST
375Ω
60Ω
Figure 2. Driver Voltage Measurement Test Circuit 2
A
B
RLDIFF
CL1
CL2
Figure 3. Driver Propagation Delay Test Circuit
V
OUT
C
L
A
B
V
CC
S2
R
L
S1
0V OR 3V
DE IN
DE
Figure 4. Driver Enable/Disable Test Circuit
C
L
V
OUT
RE
A
B
Figure 5. Receiver Propagation Delay Test Circuit
V
OUT
V
CC
S2
R
L
S1
RE IN
RE C
L
+1.5V
–1.5V
Figure 6. Receiver Enable/Disable Test Circuit
T
PLH
T
PHL
0V 0V
1.5V 1.5V
A–B
RO
V
OL
V
OH
Figure 9. Receiver Propagation Delay
T
ZH
1.5V 1.5V
3V
0V
1.5V
T
HZ
V
OH
V
OH
– 0.5V
0V
R
V
OL
+ 0.5V
T
ZL
1.5V
T
LZ
V
OL
R
RE
O/P LOW
O/P HIGH
Figure 10. Receiver Enable/Disable Timing
Switching Characteristics
–VO
VO 1/2VO
0V
3V
1.5V 1.5V
T
PLH
T
SKEW
VO
0V
90% POINT
10% POINT
90% POINT
10% POINT
T
PHL
B
AT
SKEW
T
R
T
F
Figure 7. Driver Propagation Delay, Rise/Fall Timing
T
ZH
1.5V
DE 1.5V
3V
0V
2.3V
T
HZ
V
OH
V
OH
– 0.5V
0V
A, B
V
OL
+ 0.5V
T
ZL
2.3V
T
LZ
V
OL
A, B
Figure 8. Driver Enable/Disable Timing
Typical Performance Characteristics–ADM485
REV. 0 –5–
40
02.0
12
4
8
0.0
24
16
20
28
32
36
1.00.5 1.5
OUTPUT VOLTAGE – Volts
OUTPUT CURRENT – mA
Figure 11. Receiver Output Low
Voltage vs. Output Current
0.4
0.1–50 125
0.3
0.2
–25 50 10025075
TEMPERATURE –
°
C
OUTPUT VOLTAGE – Volts
I = 8mA
Figure 14. Receiver Output Low
Voltage vs. Temperature
100
04
30
10
20
0
60
40
50
70
80
90
213
OUTPUT VOLTAGE – Volts
OUTPUT CURRENT – mA
Figure 17. Driver Output Low
Voltage vs. Output Current
OUTPUT VOLTAGE – Volts
OUTPUT CURRENT – mA
0
–20 5.0
–14
–18
–16
3.5
–8
–12
–10
–6
–4
–2
4.54.0
Figure 12. Receiver Output High
Voltage vs. Output Current
OUTPUT VOLTAGE – Volts
OUTPUT CURRENT – mA
96
0
24
12
0
48
36
60
72
84
4321
Figure 15. Driver Differential Out-
put Voltage vs. Output Current
0
–100 5
–70
–90
–80
0
–40
–60
–50
–30
–20
–10
3241
OUTPUT VOLTAGE – Volts
OUTPUT CURRENT – mA
Figure 18. Driver Output High
Voltage vs. Output Current
5.0
4.5 125
4.8
4.6
–25
4.7
–50
4.9
1007550250
TEMPERATURE –
°
C
OUTPUT VOLTAGE – Volts
I = 8mA
Figure 13. Receiver Output High
Voltage vs. Temperature
2.4
2.0–50 125
2.3
2.1
–25
2.2
1007550250
TEMPERATURE – °C
DIFFERENTIAL VOLTAGE – Volts
Figure 16. Driver Differential Output
Voltage vs. Temperature, R
L
= 54
Ω
1.00
0.60 125
0.70
0.65
–25–50
0.80
0.75
0.85
0.90
0.95
1007550250
TEMPERATURE – °C
SUPPLY CURRENT – mA
DRIVER ENABLED
DRIVER DISABLED
Figure 19. Supply Current vs.
Temperature
5
0125
3
1
–25
2
–50
4
1007550250
TEMPERATURE – °C
TIME – ns
Figure 20. Receiver t
PLH
–t
PHL
, vs.
Temperature
10
90
100
0%
500m
V5n
s
500m
V
Figure 23. Loaded Driver
Differential Outputs
ADM485–Typical Performance Characteristics
REV. 0
–6–
1.0
0.4
0.7
0.5
0.6
0.9
0.8
125–25–50 1007550250
TEMPERATURE – °C
TIME – ns
Figure 21. Driver Skew vs.
Temperature
10
90
100
0%
1
V5 5 10ns
HO
1
V
Figure 24. Driver/Receiver Propa-
gation Delays Low to High
10
90
100
0%
1
V5n
s
1
V
Figure 22. Unloaded Driver
Differential Outputs
Figure 25. Driver/Receiver Propaga-
tion Delays High to Low
RT RT
D
R
DRDR
R
D
Figure 26. Typical RS-485 Network
ADM485
REV. 0 –7–
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. There are two main standards approved by the
Electronics Industries Association (EIA) which specify the elec-
trical 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 transmis-
sion line with up to 10 receivers.
In order to cater for true multipoint communications, the
RS-485 standard was defined. This standard meets or exceeds
all the requirements of RS-422 but also allows for up to 32
drivers and 32 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 (32 in fact) to be connected to a single line. Only one driver
should be enabled at 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 gener-
ated by the current flowing through each wire, thereby, reducing
the effective inductance of the pair.
The ADM485 is designed for bidirectional data communica-
tions on multipoint transmission lines. A typical application
showing a multipoint transmission network is illustrated in
Figure 26. An RS-485 transmission line can have as many as
32 transceivers on the bus. 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 imped-
ance 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.
Thermal Shutdown
The ADM485 contains thermal shutdown circuitry which pro-
tects the part from excessive power dissipation during fault con-
ditions. Shorting the driver outputs to a low impedance source
can result in high driver currents. The thermal sensing circuitry
detects the increase in die temperature and disables the driver
outputs. The thermal sensing circuitry is designed to disable the
driver outputs when a die temperature of 150°C is reached. As
the device cools, the drivers are reenabled at 140°C.
Propagation Delay
The ADM485 features very low propagation delay ensuring
maximum baud rate operation. The driver is well balanced en-
suring distortion free transmission.
Another important specification is a measure of the skew be-
tween the complementary outputs. Excessive skew impairs the
noise immunity of the system and increases the amount of elec-
tromagnetic interference (EMI).
Receiver Open-Circuit Fail Safe
The receiver input includes a fail-safe feature which 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 Ω54 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
No of Drivers/Receivers Per Line 1/10 32/32
ADM485
REV. 0
–8–
C1817–18–7/93
PRINTED IN U.S.A.
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Lead SOIC (R-8)
0.0098 (0.25)
0.0075 (0.19)
0.0500 (1.27)
0.0160 (0.41)
8
°
0
°
0.0196 (0.50)
0.0099 (0.25) x 45
°
PIN 1
0.1574 (4.00)
0.1497 (3.80)
0.2440 (6.20)
0.2284 (5.80)
4
5
1
8
0.0192 (0.49)
0.0138 (0.35)
0.0500
(1.27)
BSC
0.0098 (0.25)
0.0040 (0.10)
0.1968 (5.00)
0.1890 (4.80)
0.102 (2.59)
0.094 (2.39)
8-Pin Plastic DIP (N-8)
PIN 1 0.280 (7.11)
0.240 (6.10)
4
5
8
1
SEATING
PLANE
0.060 (1.52)
0.015 (0.38)
0.130
(3.30)
MIN
0.210
(5.33)
MAX
0.160 (4.06)
0.115 (2.93)
0.430 (10.92)
0.348 (8.84)
0.022 (0.558)
0.014 (0.356)
0.070 (1.77)
0.045 (1.15)
0.100
(2.54)
BSC
0.325 (8.25)
0.300 (7.62)
0.015 (0.381)
0.008 (0.204)
0.195 (4.95)
0.115 (2.93)
8-Pin Cerdip (Q-8)
0.320 (8.13)
0.290 (7.37)
0.015 (0.38)
0.008 (0.20)
15
°
0
°
0.005 (0.13) MIN 0.055 (1.4) MAX
1
PIN 1
4
5
8
0.310 (7.87)
0.220 (5.59)
0.405 (10.29) MAX
0.200
(5.08)
MAX
SEATING
PLANE
0.023 (0.58)
0.014 (0.36) 0.070 (1.78)
0.030 (0.76)
0.060 (1.52)
0.015 (0.38)
0.150
(3.81)
MIN
0.200 (5.08)
0.125 (3.18)
0.100
(2.54)
BSC