a
FEATURES
Meets EIA RS-485 Standard
30 Mbps 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
Driver Propagation Delay: 10 ns
Receiver Propagation Delay: 15 ns
High-Z Outputs with Power Off
Superior Upgrade for LTC1485
APPLICATIONS
Low Power RS-485 Systems
DTE-DCE Interface
Packet Switching
Local Area Networks
Data Concentration
Data Multiplexers
Integrated Services Digital Network (ISDN)
GENERAL DESCRIPTION
5 V Low Power
EIA RS-485 Transceiver
ADM1485
FUNCTIONAL BLOCK DIAGRAM
8-Lead
ADM1485
RO
R
V
CC
RE
B
DE
A
DI
D
GND
The ADM1485 is a differential line transceiver suitable for high
speed bidirectional data communication on multipoint bus trans-
mission lines. It is designed for balanced data transmission and
complies with both RS-485 and RS-422 EIA Standards. The part
contains a differential line driver and a differential line receiver.
Both the driver and the receiver may be enabled independently.
When disabled, the outputs are three-stated.
The ADM1485 operates from a single 5 V power supply. 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 condi-
tions, 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 important,
therefore, that the remaining disabled drivers do not load the bus.
To ensure this, the ADM1485 driver features high output
impedance when disabled and also when powered down.
This minimizes the loading effect when the transceiver is not being
used. 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 that results in a logic
high output state if the inputs are unconnected (floating).
The ADM1485 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 ADM1485 features extremely fast switching speeds. Minimal
driver propagation delays permit transmission at typical data rates
of 30 Mbps while low skew minimizes EMI interference.
The part is fully specified over the commercial and industrial
temperature range and is available in PDIP, SOIC, and small
MSOP packages.
REV.
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 that
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
www.analog.com
Fax:
781/461-3113
©
2012
Analog Devices, Inc. All rights reserved.
ADM1485–SPECIFICATIONS
(V
Parameter
DRIVER
Differential Output Voltage, V
OD
V
OD3
Δ|V
OD
| for Complementary Output States
Common-Mode Output Voltage V
OC
Δ|V
OD
| for Complementary Output States
Output Short-Circuit Current (V
OUT
= High)
Output Short-Circuit Current (V
OUT
= Low)
CMOS Input Logic Threshold Low, V
INL
CMOS Input Logic Threshold High, V
INH
Logic Input Current (DE, DI)
RECEIVER
Differential Input Threshold Voltage, V
TH
Input Voltage Hysteresis,
ΔV
TH
Input Resistance
Input Current (A, B)
CMOS Input Logic Threshold Low, V
INL
CMOS Input Logic Threshold High, V
INH
Logic Enable Input Current (RE)
CMOS Output Voltage Low, V
OL
CMOS Output Voltage High, V
OH
Short-Circuit Output Current
Three-State Output Leakage Current
POWER SUPPLY CURRENT
I
CC
(Outputs Enabled)
I
CC
(Outputs Disabled)
Specifications subject to change without notice.
CC
=5V
5%. All specifications T
MIN
to T
MAX
, unless otherwise noted.)
Unit Test Conditions/Comments
V
V
V
V
V
V
V
mA
mA
V
V
μA
V
mV
kΩ
mA
mA
V
V
μA
V
V
mA
μA
mA
mA
R =
∞,
Test Circuit 1
V
CC
= 5 V, R = 50
Ω
(RS-422), Test Circuit 1
R = 27
Ω
(RS-485), Test Circuit 1
V
TST
= –7 V to +12 V, Test Circuit 2
R = 27
Ω
or 50
Ω,
Test Circuit 1
R = 27
Ω
or 50
Ω,
Test Circuit 1
R = 27
Ω
or 50
Ω
–7 V
≤
V
O
≤
+12 V
–7 V
≤
V
O
≤
+12 V
Min
Typ
Max
5.0
5.0
5.0
5.0
0.2
3
0.2
250
250
0.8
±
1.0
2.0
1.5
1.5
35
35
2.0
–0.2
70
12
+0.2
1
–0.8
0.8
2.0
±
1
0.4
4.0
7
85
±
1.0
1.0
0.6
2.2
1
–7 V
≤
V
CM
≤
+12 V
V
CM
= 0 V
–7 V
≤
V
CM
≤
+12 V
V
IN
= +12 V
V
IN
= –7 V
I
OUT
= +4.0 mA
I
OUT
= –4.0 mA
V
OUT
= GND or V
CC
0.4 V
≤
V
OUT
≤
2.4 V
Digital Inputs = GND or V
CC
Digital Inputs = GND or V
CC
TIMING SPECIFICATIONS
(V
Parameter
CC
=5V
5%. All specifications T
MIN
to T
MAX
, unless otherwise noted.)
Min
2
Typ
10
1
8
10
10
0
0
Max
15
5
15
25
25
2
2
Unit Test Conditions/Comments
ns
ns
ns
ns
ns
ns
ns
R
LDIFF
= 54
Ω,
C
L1
= C
L2
= 100 pF, Test Circuit 3
R
LDIFF
= 54
Ω,
C
L1
= C
L2
= 100 pF, Test Circuit 3
R
LDIFF
= 54
Ω,
C
L1
= C
L2
= 100 pF, Test Circuit 3
R
L
= 110
Ω,
C
L
= 50 pF, Test Circuit 4
R
L
= 110
Ω,
C
L
= 50 pF, Test Circuit 4
R
L
= 110
Ω,
C
L
= 50 pF, Test Circuit 4*
R
L
= 110
Ω,
C
L
= 50 pF, Test Circuit 4*
DRIVER
Propagation Delay Input to Output t
PLH
, t
PHL
Driver O/P to
O/P
t
SKEW
Driver Rise/Fall Time t
R
, t
F
Driver Enable to Output Valid
Driver Disable Timing
Matched Enable Switching
|t
AZH
–t
BZL
|, |t
BZH
–t
AZL
|
Matched Disable Switching
|t
AHZ
–t
BLZ
|, |t
BHZ
–t
ALZ
|
RECEIVER
Propagation Delay Input to Output t
PLH
, t
PHL
Skew |t
PLH
–t
PHL
|
Receiver Enable t
EN1
Receiver Disable t
EN2
Tx Pulse Width Distortion
Rx Pulse Width Distortion
*Guaranteed
by characterization.
Specifications subject to change without notice.
8
15
5
5
1
1
30
5
20
20
ns
ns
ns
ns
ns
ns
C
L
= 15 pF, Test Circuit 5
C
L
= 15 pF, Test Circuit 5
C
L
= 15 pF, R
L
= 1 kΩ, Test Circuit 6
C
L
= 15 pF, R
L
= 1 kΩ, Test Circuit 6
–2–
REV.
ADM1485
ABSOLUTE MAXIMUM RATINGS*
(T
A
= 25°C, unless otherwise noted.)
PIN FUNCTION DESCRIPTIONS
V
CC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +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) . . . . . . . . . . . . . . . . . . –9 V to +14 V
Outputs
Driver Outputs (A, B) . . . . . . . . . . . . . . . . . . –9 V to +14 V
Receiver Output . . . . . . . . . . . . . . . . .–0.5 V to V
CC
+ 0.5 V
Power Dissipation 8-Lead MSOP . . . . . . . . . . . . . . . 900 mW
θ
JA
, Thermal Impedance . . . . . . . . . . . . . . . . . . . 206°C/W
Power Dissipation 8-Lead PDIP . . . . . . . . . . . . . . . . 500 mW
θ
JA
, Thermal Impedance . . . . . . . . . . . . . . . . . . . 130°C/W
Power Dissipation 8-Lead SOIC . . . . . . . . . . . . . . . . 450 mW
θ
JA
, Thermal Impedance . . . . . . . . . . . . . . . . . . . 170°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
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . . . 215°C
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220°C
*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.
Pin Mnemonic Function
No.
1
RO
Receiver Output. When enabled if A > B
by 200 mV, then RO = High. If A < B by
200 mV, then RO = Low.
Receiver Output Enable. A low level
enables the receiver output, RO. A high
level places it in a high impedance state.
Driver Output Enable. A high level enables
the driver differential outputs, A and B. A low
level places it in a high impedance state.
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.
Ground Connection, 0 V.
Noninverting Receiver Input A/Driver
Output A.
Inverting Receiver Input B/Driver Output B
Power Supply, 5 V
±
5%.
PIN CONFIGURATION
2
RE
3
DE
4
DI
5
6
7
8
GND
A
B
V
CC
RO
1
8
V
CC
Table I. Transmitting
RE
2
7
B
TOP VIEW
DE
3
(Not to Scale)
6
A
ADM1485
Inputs
DE
1
1
0
DI
1
0
X
Outputs
B
0
1
Z
A
1
0
Z
DI
4
5
GND
Table II. Receiving
RE
0
0
0
1
Inputs
A-B
≥
+0.2 V
≤
–0.2 V
Inputs Open
X
Outputs
RO
1
0
1
Z
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
ADM1485 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.
REV.
–3–
ADM1485
Test Circuits
V
CC
R
V
OD
R
V
OC
A
R
L
0V OR 3V
DE
B
DE IN
S1
C
L
V
OUT
S2
Test Circuit 1. Driver Voltage Measurement
375
Test Circuit 4. Driver Enable/Disable
A
V
OD3
60
375
V
TST
B
RE
C
L
V
OUT
Test Circuit 2. Driver Voltage Measurement
Test Circuit 5. Receiver Propagation Delay
+1.5V
V
CC
S1
–1.5V
RE
R
L
S2
C
L
V
OUT
A
R
LDIFF
B
C
L1
C
L2
RE
IN
Test Circuit 3. Driver Propagation Delay
Test Circuit 6. Receiver Enable/Disable
Switching Characteristics
3V
1.5V
0V
B
1/2VO
V
O
A
1.5V
t
PLH
t
PHL
A, B
0V
0V
t
PLH
t
PHL
V
OH
t
SKEW
=
t
PLH
–
t
PHL
V
O
0V
–V
O
10% POINT
10% POINT
90% POINT
90% POINT
RO
1.5V
1.5V
t
SKEW
=
t
PLH
–
t
PHL
t
R
t
F
V
OL
Figure 1. Driver Propagation Delay, Rise/Fall Timing
Figure 3. Receiver Propagation Delay
3V
DE
1.5V
1.5V
0V
RE
1.5V
1.5V
3V
0V
t
ZL
t
LZ
t
ZL
t
LZ
A, B
2.3V
V
OL
+ 0.5V
V
OL
R
1.5V
O/P LOW
V
OL
+ 0.5V
V
OL
t
ZH
A, B
2.3V
t
HZ
V
OH
V
OH
– 0.5V
R
t
ZH
O/P HIGH
1.5V
t
HZ
V
OH
V
OH
– 0.5V
0V
0V
Figure 2. Driver Enable/Disable Timing
Figure 4. Receiver Enable/Disable Timing
–4–
REV.
Typical Performance Characteristics–ADM1485
50
45
40
0.35
0.40
I = 8mA
OUTPUT CURRENT – mA
35
30
25
20
15
10
5
0
0
0.25
0.50
0.75
1.25
1.50
1.00
OUTPUT VOLTAGE – V
1.75
2.00
OUTPUT VOLTAGE – V
0.30
0.25
0.20
0.15
–50
–25
0
25
50
TEMPERATURE – C
75
100
125
TPC 1. Output Current vs. Receiver Output Low Voltage
TPC 4. Receiver Output Low Voltage vs. Temperature
0
–2
–4
90
80
70
OUTPUT CURRENT – mA
–6
–8
–10
–12
–14
–16
–18
3.50
OUTPUT CURRENT – mA
3.75
4.00
4.25
4.50
OUTPUT VOLTAGE – V
4.75
5.00
60
50
40
30
20
10
0
0
0.5
1.0
1.5
2.0
2.5
3.0
OUTPUT VOLTAGE – V
3.5
4.0
4.5
TPC 2. Output Current vs. Receiver Output High Voltage
TPC 5. Output Current vs. Driver Differential
Output Voltage
4.55
I = 8mA
4.50
4.45
4.40
4.35
4.30
4.25
4.20
4.15
–50
2.15
DIFFERENTIAL VOLTAGE – V
–25
0
25
50
75
TEMPERATURE – C
100
125
2.10
OUTPUT VOLTAGE – V
2.05
2.00
1.95
1.90
–50
–25
0
25
50
75
TEMPERATURE – C
100
125
TPC 3. Receiver Output High Voltage vs. Temperature
TPC 6. Driver Differential Output
Voltage vs. Temperature, R
L
= 26.8
Ω
REV.
–5–
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