ADM485JNZ [ADI]
5 V, Low Power, 5 Mbps, Half Duplex EIA RS-485 Transceiver;
| 型号： | ADM485JNZ |
| 厂家： | 
ADI |
| 描述： | 5 V, Low Power, 5 Mbps, Half Duplex EIA RS-485 Transceiver |
| 文件： | 总8页 (文件大小：135K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
+5 V Low Power
EIA RS-485 Transceiver
a
ADM485
FUNCTIONAL BLOCK DIAGRAM
FEATURES
Meets EIA RS-485 Standard
5 Mb/s Data Rate
Single +5 V Supply
ADM485
–7 V to +12 V Bus Common-Mode Range
High Speed, Low Power BiCMOS
Thermal Shutdown Protection
Short Circuit Protection
RO
RE
DE
DI
1
2
3
4
R
8
7
6
5
V
B
A
CC
Zero Skew Driver
Driver Propagation Delay: 10 ns
Receiver Propagation Delay: 25 ns
High Z Outputs with Power Off
Superior Upgrade for LTC485
APPLICATIONS
D
GND
Low Power RS-485 Systems
DTE-DCE Interface
Packet Switching
Local Area Networks
Data Concentration
Data Multiplexers
Integrated Services Digital Network (ISDN)
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.
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 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 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.
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.
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.
The part is fully specified over the commercial and industrial
temperature range and is available in an 8-lead DIL/SOIC package.
REV. A
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
Fax: 781/326-8703
World Wide Web Site: http://www.analog.com
© Analog Devices, Inc., 2000
(VCC = +5 V ؎ 5%. All specifications TMIN to TMAX unless otherwise noted)
ADM485–SPECIFICATIONS
Parameter
Min
Typ Max Units Test Conditions/Comments
DRIVER
Differential Output Voltage, VOD
5.0
5.0
5.0
5.0
0.2
3
0.2
250
250
0.8
V
V
V
V
V
V
V
mA
mA
V
R = ∞, Figure 1
2.0
1.5
1.5
VCC = 5 V, R = 50 Ω (RS-422), Figure 1
R = 27 Ω (RS-485), Figure 1
VTST = –7 V to +12 V, Figure 2
R = 27 Ω or 50 Ω, Figure 1
R = 27 Ω or 50 Ω, Figure 1
R = 27 Ω or 50 Ω
VOD3
∆|VOD| for Complementary Output States
Common-Mode Output Voltage VOC
∆|VOC| for Complementary Output States
Output Short Circuit Current (VOUT = High) 35
Output Short Circuit Current (VOUT = Low) 35
CMOS Input Logic Threshold Low, VINL
–7 V ≤ VO ≤ +12 V
–7 V ≤ VO ≤ +12 V
CMOS Input Logic Threshold High, VINH
Logic Input Current (DE, DI)
2.0
V
1.0 µA
RECEIVER
Differential Input Threshold Voltage, VTH
Input Voltage Hysteresis, ∆VTH
Input Resistance
–0.2
12
+0.2
V
–7 V ≤ VCM ≤ +12 V
VCM = 0 V
–7 V ≤ VCM ≤ +12 V
VIN = 12 V
70
mV
kΩ
mA
mA
µA
V
Input Current (A, B)
+1
–0.8
1
VIN = –7 V
Logic Enable Input Current (RE)
CMOS Output Voltage Low, VOL
CMOS Output Voltage High, VOH
Short Circuit Output Current
0.4
IOUT = +4.0 mA
IOUT = –4.0 mA
VOUT = GND or VCC
4.0
7
V
mA
85
Tristate Output Leakage Current
1.0 µA
0.4 V ≤ VOUT ≤ +2.4 V
POWER SUPPLY CURRENT
ICC (Outputs Enabled)
ICC (Outputs Disabled)
1.35 2.2
0.7
mA
mA
Outputs Unloaded, Digital Inputs = GND or VCC
Outputs Unloaded, Digital Inputs = GND or VCC
1
Specifications subject to change without notice.
(V = +5 V ؎ 5%. All specifications TMIN to TMAX unless otherwise noted.)
TIMING SPECIFICATIONS
CC
Parameter
Min Typ Max Units Test Conditions/Comments
DRIVER
Propagation Delay Input to Output TPLH, TPHL
Driver O/P to O/P TSKEW
Driver Rise/Fall Time TR, TF
Driver Enable to Output Valid
Driver Disable Timing
2
10
0
2
10
10
15
5
10
25
25
ns
ns
ns
ns
ns
RL Diff = 54 Ω CL1 = CL2 = 100 pF, Figure 3
RL Diff = 54 Ω CL1 = CL2 = 100 pF, Figure 3
RL Diff = 54 Ω CL1 = CL2 = 100 pF, Figure 3
RECEIVER
Propagation Delay Input to Output TPLH, TPHL
18
25
0
15
15
40
5
25
25
ns
ns
ns
ns
CL = 15 pF, Figure 5
Skew |TPLH–TPHL
|
Receiver Enable TEN1
Receiver Disable TEN2
Figure 6
Figure 6
Specifications subject to change without notice.
–2–
REV. A
ADM485
ABSOLUTE MAXIMUM RATINGS*
(TA = +25°C unless otherwise noted)
PIN FUNCTION DESCRIPTION
Pin Mnemonic Function
VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +7 V
Inputs
1
2
3
4
RO
RE
DE
DI
Receiver Output. When enabled if A > B by
200 mV, then RO = High. If A < B by
200 mV, then RO = Low.
Driver Input (DI) . . . . . . . . . . . . . . . . –0.3 V to VCC + 0.3 V
Control Inputs (DE, RE) . . . . . . . . . . –0.3 V to VCC + 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 VCC +0.5 V
Power Dissipation 8-Pin DIP . . . . . . . . . . . . . . . . . . . 500 mW
θJA, Thermal Impedance . . . . . . . . . . . . . . . . . . +130°C/W
Power Dissipation 8-Pin SOIC . . . . . . . . . . . . . . . . . 450 mW
θJA, Thermal Impedance . . . . . . . . . . . . . . . . . . +170°C/W
Power Dissipation 8-Pin Cerdip . . . . . . . . . . . . . . . . 500 mW
θJA, 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 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 indicated in the operational
sections of this specification is not implied. Exposure to absolute maximum ratings
for extended periods may affect device reliability.
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.
5
6
GND
A
Ground Connection, 0 V.
Noninverting Receiver Input A/Driver
Output A.
7
8
B
Inverting Receiver Input B/Driver Output B.
Power Supply, 5 V 5%.
VCC
PIN CONFIGURATION
Table I. Transmitting
1
2
3
4
8
7
6
5
V
CC
RO
RE
DE
DI
B
A
ADM485
TOP VIEW
(Not to Scale)
INPUTS
DE
OUTPUT
RE
DI
B
A
GND
X
X
X
1
1
0
1
0
X
0
1
Z
1
0
Z
ORDERING GUIDE
Model
Temperature Range
Package Option
Table II. Receiving
ADM485JN
ADM485JR
ADM485AN
ADM485AR
ADM485AQ
0°C to +70°C
N-8
SO-8
N-8
SO-8
Q-8
INPUTS
OUTPUT
RO
0°C to +70°C
RE
DE
A-B
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
0
0
0
1
0
0
0
0
≥ +0.2 V
≤ –0.2 V
Inputs Open
X
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 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.
WARNING!
ESD SENSITIVE DEVICE
REV. A
–3–
ADM485
Test Circuits
V
CC
R
A
B
R
R
L
S2
S1
0V OR 3V
DE IN
V
OD
DE
V
C
OUT
L
V
OC
Figure 1. Driver Voltage Measurement Test Circuit
Figure 4. Driver Enable/Disable Test Circuit
A
375Ω
V
V
V
TST
60Ω
375Ω
OUT
OD3
B
RE
C
L
Figure 2. Driver Voltage Measurement Test Circuit 2
Figure 5. Receiver Propagation Delay Test Circuit
+1.5V
V
CC
A
S1
C
L1
R
L
R
S2
LDIFF
–1.5V
RE IN
RE
C
C
V
OUT
L2
L
B
Figure 3. Driver Propagation Delay Test Circuit
Figure 6. Receiver Enable/Disable Test Circuit
Switching Characteristics
3V
1.5V
PLH
1.5V
0V
0V
T
A–B
0V
B
T
PHL
1/2VO
T
T
PHL
PLH
VO
V
V
OH
A
T
T
SKEW
SKEW
90% POINT
RO
1.5V
1.5V
VO
0V
90% POINT
OL
10% POINT
10% POINT
–VO
T
T
F
R
Figure 9. Receiver Propagation Delay
Figure 7. Driver Propagation Delay, Rise/Fall Timing
3V
3V
1.5V
1.5V
RE
1.5V
1.5V
DE
A, B
A, B
0V
0V
T
T
LZ
ZL
T
T
ZL
LZ
R
R
1.5V
1.5V
2.3V
2.3V
V
+ 0.5V
O/P LOW
O/P HIGH
OL
V
+ 0.5V
OL
V
OL
V
OL
T
T
HZ
T
T
ZH
HZ
ZH
V
V
OH
OH
V
– 0.5V
V
– 0.5V
OH
OH
0V
0V
Figure 8. Driver Enable/Disable Timing
Figure 10. Receiver Enable/Disable Timing
–4–
REV. A
Typical Performance Characteristics–ADM485
40
36
32
28
24
20
16
12
8
0
–2
5.0
I = 8mA
–4
4.9
–6
–8
4.8
4.7
4.6
4.5
–10
–12
–14
–16
–18
–20
4
0
0.0
0.5
1.0
1.5
2.0
3.5
4.0
4.5
5.0
–50 –25
0
25
50
75
100 125
OUTPUT VOLTAGE – Volts
OUTPUT VOLTAGE – Volts
TEMPERATURE –
°C
Figure 11. Receiver Output Low
Voltage vs. Output Current
Figure 12. Receiver Output High
Voltage vs. Output Current
Figure 13. Receiver Output High
Voltage vs. Temperature
0.4
96
84
72
60
48
36
24
12
0
2.4
2.3
I = 8mA
0.3
2.2
0.2
2.1
2.0
0.1
–50 –25
0
25
50
75
100 125
0
1
2
3
4
–50 –25
0
25
50
75
100 125
TEMPERATURE –
°C
OUTPUT VOLTAGE – Volts
TEMPERATURE – °C
Figure 15. Driver Differential Out-
put Voltage vs. Output Current
Figure 14. Receiver Output Low
Voltage vs. Temperature
Figure 16. Driver Differential Output
Voltage vs. Temperature, RL = 54 Ω
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
100
90
80
70
60
50
40
30
20
10
0
1.00
0.95
0.90
0.85
0.80
0.75
0.70
0.65
0.60
DRIVER ENABLED
DRIVER DISABLED
0
1
2
3
4
5
0
1
2
3
4
–50
–25
0
25
50
75
100 125
OUTPUT VOLTAGE – Volts
OUTPUT VOLTAGE – Volts
TEMPERATURE – °C
Figure 18. Driver Output High
Voltage vs. Output Current
Figure 17. Driver Output Low
Voltage vs. Output Current
Figure 19. Supply Current vs.
Temperature
REV. A
–5–
ADM485–Typical Performance Characteristics
5
4
3
2
1
0
1.0
0.9
0.8
0.7
0.6
0.5
0.4
100
90
10
0%
1
V
1
V
5n
s
–50 –25
0
25
50
75
100 125
–50 –25
0
25
50
75
100 125
TEMPERATURE – °C
TEMPERATURE – °C
Figure 22. Unloaded Driver
Differential Outputs
Figure 20. Receiver tPLH–tPHL, vs.
Temperature
Figure 21. Driver Skew vs.
Temperature
100
90
100
100
90
90
10
10
10
0%
0%
0%
1
V
1
V
500m
V
500m
V
1
V
1
V
5
H
5
10ns
5
H
5
10ns
5n
s
O
O
Figure 23. Loaded Driver
Differential Outputs
Figure 24. Driver/Receiver Propa-
gation Delays Low to High
Figure 25. Driver/Receiver Propaga-
tion Delays High to Low
RT
RT
D
D
R
R
R
R
D
D
Figure 26. Typical RS-485 Network
–6–
REV. A
ADM485
APPLICATIONS INFORMATION
ure 26. An RS-485 transmission line can have as many as 32 trans-
ceivers on the bus. Only one driver can transmit at a particular time
but multiple receivers may be enabled simultaneously.
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.
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 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.
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.
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.
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).
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.
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.
The ADM485 is designed for bidirectional data communica-
tions on multipoint transmission lines. A typical application
showing a multipoint transmission network is illustrated in Fig-
Table III. Comparison of RS-422 and RS-485 Interface Standards
Specification
RS-422
RS-485
Transmission Type
Differential
4000 ft.
2 V
Differential
4000 ft.
1.5 V
Maximum Cable Length
Minimum Driver Output Voltage
Driver Load Impedance
100 Ω
54 Ω
Receiver Input Resistance
Receiver Input Sensitivity
Receiver Input Voltage Range
No of Drivers/Receivers Per Line
4 kΩ min
200 mV
–7 V to +7 V
1/10
12 kΩ min
200 mV
–7 V to +12 V
32/32
REV. A
–7–
ADM485
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
8-Lead SOIC (SO-8)
0.1968 (5.00)
0.1890 (4.80)
8
1
5
4
0.2440 (6.20)
0.2284 (5.80)
0.1574 (4.00)
0.1497 (3.80)
PIN 1
0.0196 (0.50)
0.0099 (0.25)
0.0500 (1.27)
BSC
؋
45؇ 0.0688 (1.75)
0.0532 (1.35)
0.0098 (0.25)
0.0040 (0.10)
8؇
0؇
0.0500 (1.27)
0.0160 (0.41)
0.0192 (0.49)
0.0138 (0.35)
0.0098 (0.25)
0.0075 (0.19)
SEATING
PLANE
8-Lead Plastic DIP (N-8)
8
1
5
0.280 (7.11)
0.240 (6.10)
PIN 1
4
0.325 (8.25)
0.300 (7.62)
0.430 (10.92)
0.348 (8.84)
0.060 (1.52)
0.015 (0.38)
0.195 (4.95)
0.115 (2.93)
0.210
(5.33)
MAX
0.130
(3.30)
MIN
0.160 (4.06)
0.115 (2.93)
0.015 (0.381)
0.008 (0.204)
SEATING
PLANE
0.100
(2.54)
BSC
0.070 (1.77)
0.045 (1.15)
0.022 (0.558)
0.014 (0.356)
8-Lead Cerdip (Q-8)
0.055 (1.4) MAX
0.005 (0.13) MIN
8
5
0.310 (7.87)
0.220 (5.59)
PIN 1
1
4
0.320 (8.13)
0.290 (7.37)
0.405 (10.29) MAX
0.060 (1.52)
0.015 (0.38)
0.200
(5.08)
MAX
0.150
(3.81)
MIN
0.015 (0.38)
0.008 (0.20)
0.200 (5.08)
0.125 (3.18)
15°
0°
0.023 (0.58)
0.014 (0.36)
0.100
(2.54)
BSC
0.070 (1.78)
0.030 (0.76)
SEATING
PLANE
–8–
REV. A
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