ADM489ANZ [ADI]
5 V, Slew-Rate Limited, Low Power, 250 kbps, Full Duplex EIA RS-485 Transceiver (with DE/RE);
| 型号： | ADM489ANZ |
| 厂家： | 
ADI |
| 描述： | 5 V, Slew-Rate Limited, Low Power, 250 kbps, Full Duplex EIA RS-485 Transceiver (with DE/RE) |
| 文件： | 总12页 (文件大小：215K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
Full-Duplex, Low Power,
Slew Rate Limited, EIA RS-485 Transceivers
a
ADM488/ADM489
FEATURES
FUNCTIO NAL BLO CK D IAGRAMS
Meets EIA RS-485 Standard
250 kbps Data Rate
Single +5 V ؎ 10% Supply
–7 V to +12 V Bus Com m on-Mode Range
12 k⍀ Input Im pedance
2 kV EFT Protection Meets IEC1000-4-4
High EM Im m unity Meets IEC1000-4-3
Reduced Slew Rate for Low EM Interference
Short Circuit Protection
ADM488
A
R
RO
DI
B
Z
Y
D
Excellent Noise Im m unity
30 A Supply Current
APPLICATIONS
Low Pow er RS-485 System s
DTE-DCE Interface
ADM489
Packet Sw itching
Local Area Netw orks
Data Concentration
Data Multiplexers
Integrated Services Digital Netw ork (ISDN)
A
B
R
RO
RE
DE
Z
Y
DI
D
GENERAL D ESCRIP TIO N
T he ADM488 and ADM489 are low power differential line
transceiver suitable for communication on multipoint bus trans-
mission lines.
T he receiver contains a fail-safe feature that results in a logic
high output state if the inputs are unconnected (floating).
T he ADM488/ADM489 is fabricated on BiCMOS, an ad-
vanced mixed technology process combining low power CMOS
with fast switching bipolar technology.
T hey are intended for balanced data transmission and comply
with both EIA Standards RS-485 and RS-422. Both products
contains a single differential line driver and a single differential
line receiver making them suitable for full duplex data transfer.
T he ADM488/ADM489 is fully specified over the industrial
temperature range and is available in DIP, SOIC and T SSOP
packages.
T he ADM489 contains an additional receiver and driver enable
control.
T he input impedance is 12 kΩ, allowing 32 transceivers to be
connected on the bus.
T he ADM488/ADM489 operates from a single +5 V ± 10%
power supply. Excessive power dissipation caused by bus con-
tention or by output shorting is prevented by a thermal shut-
down circuit. T his feature forces the driver output into a high
impedance state if during fault conditions a significant tempera-
ture increase is detected in the internal driver circuitry.
REV. 0
Inform ation furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assum ed by Analog Devices for its
use, nor for any infringem ents of patents or other rights of third parties
which m ay result from its use. No license is granted by im plication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norw ood, MA 02062-9106, U.S.A.
Tel: 617/ 329-4700
Fax: 617/ 326-8703
World Wide Web Site: http:/ / w w w .analog.com
© Analog Devices, Inc., 1997
(V = +5 V ؎ 10%. All specifications TMIN to TMAX unless
CC
otherwise noted)
ADM488/ADM489–SPECIFICATIONS
P aram eter
Min
Typ Max
Units
Test Conditions/Com m ents
DRIVER
Differential Output Voltage, VOD
5.0
5.0
5.0
5.0
0.2
3
0.2
250
250
V
V
V
V
V
V
V
mA
mA
V
V
µA
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
VT ST = –7 V to +12 V, Figure 2, VCC = 5 V ± 5%
R = 27 Ω or 50 Ω, Figure 1
R = 27 Ω or 50 Ω, Figure 1
R = 27 Ω or 50 Ω
∆| VOD| for Complementary Output States
Common-Mode Output Voltage VOC
∆| VOC| for Complementary Output States
Output Short Circuit Current (VOUT = High)
Output Short Circuit Current (VOUT = Low)
CMOS Input Logic T hreshold Low, VINL
CMOS Input Logic T hreshold High, VINH
Logic Input Current (DE, DI)
–7 V ≤ VO ≤ +12 V
–7 V ≤ VO ≤ +12 V
1.4
1.4
0.8
2.0
±1.0
RECEIVER
Differential Input T hreshold Voltage, VT H
Input Voltage Hysteresis, ∆VT H
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
V
mA
µA
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
0.4 V ≤ VOUT ≤ +2.4 V
4.0
7
85
±1.0
T hree-State Output Leakage Current
POWER SUPPLY CURRENT
ICC
Outputs Unloaded, Receivers Enabled
DE = 0 V (Disabled)
DE = 5 V (Enabled)
30
37
60
74
µA
µA
Specifications subject to change without notice.
TIMING SPECIFICATIONS (V = +5 V ؎ 10%. All specifications TMIN to TMAX unless otherwise noted)
CC
P aram eter
Min
Typ Max
Units
Test Conditions/Com m ents
DRIVER
Propagation Delay Input to Output T PLH, T PHL 250
Driver O/P to O/P TSKEW
2000
800
2000
2000
3000
ns
ns
ns
ns
ns
kbps
RL Diff = 54 Ω, CL1 = CL2 = 100 pF, Figure 5
RL Diff = 54 Ω, CL1 = CL2 = 100 pF, Figure 5
RL Diff = 54 Ω, CL1 = CL2 = 100 pF, Figure 5
RL = 500 Ω, CL = 100 pF, Figure 2
100
Driver Rise/Fall T ime T R, T F
Driver Enable to Output Valid
Driver Disable T iming
Data Rate
250
250
300
250
RL = 500 Ω, CL = 15 pF, Figure 2
RECEIVER
Propagation Delay Input to Output T PLH, T PHL 250
Skew | T PLH–T PHL
2000
ns
ns
ns
ns
CL = 15 pF, Figure 5
|
100
10
10
Receiver Enable T EN1
Receiver Disable T EN2
Data Rate
50
50
RL = 1 kΩ, CL = 15 pF, Figure 4
RL = 1 kΩ, CL = 15 pF, Figure 4
250
kbps
Specifications subject to change without notice.
–2–
REV. 0
ADM488/ADM489
Power Dissipation 16-Lead T SSOP . . . . . . . . . . . . . . 800 mW
θJA, T hermal Impedance . . . . . . . . . . . . . . . . . . . 150°C/W
Operating T emperature Range
Industrial (A Version) . . . . . . . . . . . . . . . –40°C to +85°C
Storage T emperature Range . . . . . . . . . . . . –65°C to +150°C
Lead T emperature (Soldering, 10 secs) . . . . . . . . . . . +300°C
Vapor Phase (60 secs) . . . . . . . . . . . . . . . . . . . . . . +215°C
Infrared (15 secs) . . . . . . . . . . . . . . . . . . . . . . . . . . . +220°C
ESD Rating, MIL-ST D-883B . . . . . . . . . . . . . . . . . . . . . 4 kV
EFT Rating, IEC1000-4-4 . . . . . . . . . . . . . . . . . . . . . . . 2 kV
ABSO LUTE MAXIMUM RATINGS*
(T A = +25°C unless otherwise noted)
VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . +7 V
Inputs
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 +12.5 V
Receiver Output . . . . . . . . . . . . . . . . –0.5 V to VCC + 0.5 V
Power Dissipation 8-Lead DIP . . . . . . . . . . . . . . . . . 700 mW
*Stresses above those listed under Absolute Maximum Ratings may cause perma-
nent damage to the device. T his 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.
θ
JA, T hermal Impedance . . . . . . . . . . . . . . . . . . . 120°C/W
Power Dissipation 8-Lead SOIC . . . . . . . . . . . . . . . . 520 mW
JA, T hermal Impedance . . . . . . . . . . . . . . . . . . . 110°C/W
Power Dissipation 14-Lead DIP . . . . . . . . . . . . . . . . 800 mW
JA, T hermal Impedance . . . . . . . . . . . . . . . . . . . 140°C/W
Power Dissipation 14-Lead SOIC . . . . . . . . . . . . . . . 800 mW
JA, T hermal Impedance . . . . . . . . . . . . . . . . . . . 120°C/W
θ
θ
θ
O RD ERING GUID E
Model
Tem perature Range
P ackage D escription
P ackage O ption
ADM488AR
ADM488AN
–40°C to +85°C
–40°C to +85°C
8-Lead Narrow Body (SOIC)
8-Lead Plastic DIP
SO-8
N-8
ADM489AN
ADM489AR
ADM489ARU
–40°C to +85°C
–40°C to +85°C
–40°C to +85°C
14-Lead Plastic DIP (Narrow)
14-Lead Narrow Body (SOIC)
16-Lead T hin Shrink Small Outline Package (T SSOP)
N-14
R-14
RU-16
REV. 0
–3–
ADM488/ADM489
AD M488 P IN FUNCTIO N D ESCRIP TIO NS
P IN CO NFIGURATIO NS
8-Lead D IP /SO
P in Mnem onic Function
1
2
VCC
RO
Power Supply, 5 V ± 10%.
Receiver Output. When A > B by 200 mV,
RO = high. If A < B by 200 mV, RO = low.
V
1
2
3
4
8
7
6
5
A
B
Z
CC
ADM488
TOP VIEW
(Not to Scale)
RO
DI
3
DI
Driver Input. A logic Low on DI forces Y low
and Z high while a logic High on DI forces Y
high and Z low.
GND
Y
4
5
6
7
8
GND
Ground Connection, 0 V
Y
Z
Noninverting Driver, Output Y
Inverting Driver, Output Z
Inverting Receiver Input B
Noninverting Receiver Input A
14-Lead D IP /SO
B
A
1
2
3
4
5
6
7
14
13
12
11
10
9
NC
RO
V
CC
NC
A
AD M489 P IN FUNCTIO N D ESCRIP TIO NS
D IP /SO IC TSSO P
RE
ADM489
DE
B
TOP VIEW
(Not to Scale)
Z
DI
P in
P in
Mnem onic Function
Y
GND
GND
1, 8, 13
2, 9, 10, NC
13, 16
No Connect. No connections
are required to this pin.
NC
8
NC = NO CONNECT
2
3
3
RO
Receiver Output. When
enabled if A > B by 200 mV
then RO = high. If A < B by
200 mV then RO = low.
16-Lead TSSO P
4
RE
Receiver Output Enable. A
low level enables the receiver
output, RO. A high level
places it in a high impedance
state.
1
2
3
4
5
6
7
8
16
15
14
V
NC
A
CC
NC
RO
B
ADM489
RE
13 NC
4
5
5
6
DE
DI
Driver Output Enable. A
high level enables the driver
differential outputs, Y and Z.
A low level places it in a high
impedance state.
TOP VIEW
(Not to Scale)
DE
12
11
10
9
Z
Y
DI
NC
NC
GND
GND
Driver Input. When the
NC = NO CONNECT
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.
6, 7
9
7, 8
11
GND
Y
Ground Connection, 0 V
Noninverting Driver
Output Y
10
11
12
12
14
15
Z
B
A
Inverting Driver Output Z
Inverting Receiver Input B
Noninverting Receiver
Input A
14
1
VCC
Power Supply, 5 V ± 10%.
–4–
REV. 0
ADM488/ADM489
Test Circuits
V
CC
A
B
R
R
R
L
S1
S2
0V OR 3V
DE IN
V
OD
DE
C
V
L
V
OC
OUT
Figure 1. Driver Voltage Measurem ent Test Circuit
Figure 3. Driver Voltage Measurem ent Test Circuit 2
V
375⍀
CC
+1.5V
R
S1
L
S2
V
60⍀
375⍀
V
TST
OD3
RE
–1.5V
C
V
L
OUT
RE IN
Figure 4. Receiver Enable/Disable Test Circuit
Figure 2. Driver Enable/Disable Test Circuit
+3V
DE
Y
A
C
C
L1
RO
R
DI
D
RL
DIFF
B
L2
RE
Z
Figure 5. Driver/Receiver Propagation Delay Test Circuit
REV. 0
–5–
ADM488/ADM489
Switching Characteristics
3V
3V
0V
1.5V
1.5V
1.5V
LZ
DE
A, B
A, B
1.5V
T
PLH
0V
B
T
PHL
T
ZL
T
T
1/2VO
VO
2.3V
2.3V
A
V
+ 0.5V
OL
T
T
SKEW
SKEW
V
V
OL
+VO
T
90% POINT
ZH
HZ
90% POINT
OH
0V
V
– 0.5V
OH
10% POINT
10% POINT
–VO
T
T
F
0V
R
Figure 6. Driver Propagation Delay, Rise/Fall Tim ing
Figure 8. Driver Enable/Disable Tim ing
3V
1.5V
1.5V
LZ
RE
0V
0V
0V
A–B
T
T
ZL
T
T
PHL
R
1.5V
1.5V
PLH
V
+ 0.5V
O/P LOW
O/P HIGH
OL
V
V
OH
V
OL
T
T
HZ
ZH
RO
1.5V
1.5V
V
OH
V
– 0.5V
OL
OH
R
0V
Figure 7. Receiver Propagation Delay
Figure 9. Receiver Enable/Disable Tim ing
–6–
REV. 0
Typical Performance Characteristics–
ADM488/ADM489
40
35
30
25
20
15
10
5
90
80
70
60
50
40
30
20
10
0
0
–5
–10
–15
–20
0
0
0.5
1.0
1.5
2.0
2.5
0
0.5
1.0
1.5
2.0
2.5
3.0
3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0
OUTPUT VOLTAGE – Volts
OUTPUT VOLTAGE – Volts
OUTPUT VOLTAGE – Volts
Figure 12. Driver Output Low
Voltage vs. Output Current
Figure 10. Receiver Output Low
Voltage vs. Output Current
Figure 11. Receiver Output High
Voltage vs. Output Current
80
70
60
50
40
30
20
10
0
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
T
T
100
90
RO
DI
T
10
0%
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
OUTPUT VOLTAGE – Volts
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
OUTPUT VOLTAGE – Volts
Figure 15. Driving 4000 ft. of Cable
Figure 13. Driver Output High
Voltage vs. Output Current
Figure 14. Driver Differential Output
Voltage vs. Output Current
80
70
80
70
60
50
LIMIT
100
90
60
50
40
30
20
10
0
40
30
20
10
0
LIMIT
10dB/DIV
10
0%
0
500kHz/DIV
5MHz
0.3 0.6
1
3
6
10
30
30
200
FREQUENCY – MHz
LOG FREQUENCY (0.15–30) – MHz
Figure 18. Conducted Em issions
Figure 16. Driver Output Waveform
and FFT Plot Transm itting @ 150 kHz
Figure 17. Radiated Em issions
REV. 0
–7–
ADM488/ADM489
GENERAL INFO RMATIO N
T he ADM488/ADM489 is a ruggedized RS-485 transceiver that
operates from a single +5 V supply.
T ables I and II show the truth tables for transmitting and
receiving.
Table I. Transm itting Truth Table
It contains protection against radiated and conducted interference.
Inputs
D E
O utputs
It is ideally suited for operation in electrically harsh environ-
ments or where cables may be plugged/unplugged. It is also
immune to high RF field strengths without special shielding
precautions. It is intended for balanced data transmission and
complies with both EIA Standards RS-485 and RS-422. It con-
tains a differential line driver and a differential line receiver, and
is suitable for full duplex data transmission.
RE
D I
Z
Y
X
X
0
1
1
0
0
1
0
X
X
0
1
1
0
Hi-Z
Hi-Z
Hi-Z
Hi-Z
1
X = Don’t Care.
T he input impedance on the ADM488/ADM489 is 12 kΩ,
allowing up to 32 transceivers on the differential bus.
Table II. Receiving Truth Table
Inputs
T he ADM488/ADM489 operates from a single +5 V ± 10%
power supply. Excessive power dissipation caused by bus con-
tention or by output shorting is prevented by a thermal shut-
down circuit. T his feature forces the driver output into a high
impedance state if, during fault conditions, a significant tem-
perature increase is detected in the internal driver circuitry.
O utput
RO
RE
D E
A-B
0
0
0
1
0
1
0
0
≥ +0.2 V
≤ +0.2 V
Inputs O/C
X
1
0
1
Hi-Z
T he receiver contains a fail-safe feature that results in a logic
high output state if the inputs are unconnected (floating).
X = Don’t Care.
A high level of robustness is achieved using internal protection
circuitry, eliminating the need for external protection compo-
nents such as tranzorbs or surge suppressors.
EFT TRANSIENT P RO TECTIO N SCH EME
T he ADM488/ADM489 uses protective clamping structures on
its inputs and outputs that clamp the voltage to a safe level and
dissipates the energy present in ESD (Electrostatic) and EFT
(Electrical Fast T ransients) discharges.
Low electromagnetic emissions are achieved using slew limited
drivers, minimizing interference both conducted and radiated.
T he ADM488/ADM489 can transmit at data rates up to
250 kbps.
FAST TRANSIENT BURST IMMUNITY (IEC1000-4-4)
IEC1000-4-4 (previously 801-4) covers electrical fast-transient/
burst (EFT ) immunity. Electrical fast transients occur as a
result of arcing contacts in switches and relays. T he tests simu-
late the interference generated when, for example, a power relay
disconnects an inductive load. A spark is generated due to the
well known back EMF effect. In fact, the spark consists of a
burst of sparks as the relay contacts separate. T he voltage ap-
pearing on the line, therefore, consists of a burst of extremely
fast transient impulses. A similar effect occurs when switching
on fluorescent lights.
A typical application for the ADM488/ADM489 is illustrated in
Figure 19. T his shows a full-duplex link where data may be
transferred at rates up to 250 kbps. A terminating resistor is
shown at both ends of the link. T his termination is not critical
since the slew rate is controlled by the ADM488/ADM489 and
reflections are minimized.
T he communications network may be extended to include
multipoint connections as shown in Figure 25. Up to 32 trans-
ceivers may be connected to the bus.
+5V
+5V
0.1F
0.1F
V
V
CC
DE
CC
RE
A
Y
DI
RO
R
D
B
Z
ADM488
RS-485/RS-422 LINK
ADM489
Z
Y
B
DI
RO
R
D
A
RE
DE
GND
GND
Figure 19. ADM488/ADM489 Full-Duplex Data Link
–8–
REV. 0
ADM488/ADM489
T he fast transient burst test, defined in IEC1000-4-4, simulates
this arcing and its waveform is illustrated in Figure 20. It
consists of a burst of 2.5 kH z to 5 kH z transients repeating at
300 ms intervals. It is specified for both power and data lines.
C
L
R
M
D
R
HIGH
VOLTAGE
SOURCE
C
50⍀
OUTPUT
Z
C
S
C
Four severity levels are defined in terms of an open-circuit volt-
age as a function of installation environment. T he installation
environments are defined as
Figure 21. EFT Generator
T est results are classified according to the following:
1. Normal performance within specification limits.
2. T emporary degradation or loss of performance that is self-
recoverable.
3. T emporary degradation or loss of function or performance
that requires operator intervention or system reset.
4. Degradation or loss of function that is not recoverable due to
damage.
1. Well-protected
2. Protected
3. T ypical Industrial
4. Severe Industrial
V
T he ADM488/ADM489 has been tested under worst case con-
ditions using unshielded cables, and meets Classification 2 at
severity Level 4. Data transmission during the transient condi-
tion is corrupted, but it may be resumed immediately following
the EFT event without user intervention.
t
300ms
16ms
V
5ns
RAD IATED IMMUNITY (IEC1000-4-3)
IEC1000-4-3 (previously IEC801-3) describes the measurement
method and defines the levels of immunity to radiated electro-
magnetic fields. It was originally intended to simulate the elec-
tromagnetic fields generated by portable radio transceivers or
any other device that generates continuous wave radiated electro-
magnetic energy. Its scope has since been broadened to include
spurious EM energy, which can be radiated from fluorescent
lights, thyristor drives, inductive loads, etc.
50ns
t
0.2/0.4ms
Figure 20. IEC1000-4-4 Fast Transient Waveform
T able III shows the peak voltages for each of the environments.
T esting for immunity involves irradiating the device with an EM
field. T here are various methods of achieving this including use
of anechoic chamber, stripline cell, T EM cell and GT EM cell.
T hese consist essentially of two parallel plates with an electric
field developed between them. T he device under test is placed
between the plates and exposed to the electric field. T here are
three severity levels having field strengths ranging from 1 V to
10 V/m. Results are classified as follows:
Table III.
VP EAK (kV)
P SU
VP EAK (kV)
I-O
Level
1
2
3
4
0.5
1
2
0.25
0.5
1
1. Normal Operation.
4
2
2. T emporary Degradation or loss of function that is self-
recoverable when the interfering signal is removed.
A simplified circuit diagram of the actual EFT generator is
illustrated in Figure 21.
3. T emporary degradation or loss of function that requires
operator intervention or system reset when the interfering
signal is removed.
T hese transients are coupled onto the signal lines using an EFT
coupling clamp. T he clamp is 1 m long and completely sur-
rounds the cable, providing maximum coupling capacitance
(50 pF to 200 pF typ) between the clamp and the cable. High
energy transients are capacitively coupled onto the signal lines.
Fast rise times (5 ns) as specified by the standard result in very
effective coupling. T his test is very severe since high voltages are
coupled onto the signal lines. T he repetitive transients can often
cause problems, where single pulses do not. Destructive latchup
may be induced due to the high energy content of the transients.
Note that this stress is applied while the interface products are
powered up and are transmitting data. T he EFT test applies
hundreds of pulses with higher energy than ESD. Worst case
transient current on an I-O line can be as high as 40 A.
4. Degradation or loss of function that is not recoverable due to
damage.
REV. 0
–9–
ADM488/ADM489
T he ADM488/ADM489 comfortably meets Classification 1 at
the most stringent (Level 3) requirement. In fact, field strengths
up to 30 V/m showed no performance degradation and error-
free data transmission continued even during irradiation.
CO ND UCTED EMISSIO NS
T his is a measure of noise that is conducted onto the mains
power supply. T he noise is measured using a LISN (Linc Im-
pedance Stabilizing Network) and a spectrum analyzer. T he test
setup is illustrated in Figure 23. T he spectrum analyzer is set to
scan the spectrum from 0 MHz to 30 MHz. Figure 24 shows
that the level of conducted emissions from the ADM488/
ADM489 are well below the allowable limits.
Table IV.
Level
V/m
Field Strength
1
2
3
1
3
10
SPECTRUM
ANALYZER
DUT
LISN
PSU
EMI EMISSIO NS
T he ADM488/ADM489 contains internal slew rate limiting in
order to minimize the level of electromagnetic interference
generated. Figure 22 shows an FFT plot when transmitting a
150 kHz data stream.
Figure 23. Conducted Em issions Test Setup
80
70
LIMIT
60
50
40
30
20
10
0
100
90
10dB/DIV
10
0%
0.3 0.6
1
3
6
10
30
0
500kHz/DIV
5MHz
LOG FREQUENCY (0.15–30) – MHz
Figure 22. Driver Output Waveform and FFT Plot Trans-
m itting @ 150 kHz
Figure 24. Conducted Em issions
As may be seen, the slew limiting attenuates the high frequency
components. EMI is therefore reduced, as are reflections due to
improperly terminated cables.
EN55022, CISPR22 defines the permitted limits of radiated
and conducted interference from Information T echnology
Equipment (IT E).
T he objective is to control the level of emissions, both con-
ducted and radiated.
For ease of measurement and analysis, conducted emissions are
assumed to predominate below 30 MHz, while radiated emis-
sions predominate above this frequency.
–10–
REV. 0
ADM488/ADM489
AP P LICATIO NS INFO RMATIO N
D iffer ential D ata Tr ansm ission
Cable and D ata Rate
T he transmission line of choice for RS-485 communications is a
twisted pair. T wisted 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.
Differential data transmission is used to reliably transmit data
at high rates over long distances and through noisy environ-
ments. Differential transmission nullifies the effects of ground
shifts and noise signals, which appear as common-mode volt-
ages on the line. T wo main standards are approved by the
Electronics Industries Association (EIA), which specify the
electrical characteristics of transceivers used in differential
data transmission.
T he ADM488/ADM489 is designed for bidirectional data com-
munications on multipoint transmission lines. A typical applica-
tion showing a multipoint transmission network is illustrated in
Figure 25. 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 simultaneously
be enabled.
T he 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 to true multipoint communications, the RS-
485 standard was defined. T his standard meets or exceeds all
the requirements of RS-422 and 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. T he 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 a time but the RS-485 standard
contains additional specifications to guarantee device safety in
the event of line contention.
As with any transmission line, it is important that reflections are
minimized. T his 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.
Table V. Com parison of RS-422 and RS-485 Interface Standards
Specification
RS-422
RS-485
T ransmission T ype
Maximum Data Rate
Maximum Cable Length
Minimum Driver Output Voltage
Driver Load Impedance
Differential
10 MB/s
4000 ft.
±2 V
Differential
10 MB/s
4000 ft.
±1.5 V
54 Ω
100 Ω
Receiver Input Resistance
Receiver Input Sensitivity
Receiver Input Voltage Range
Number 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
RT
RT
D
D
R
R
R
R
D
D
Figure 25. Typical RS-485 Network
REV. 0
–11–
ADM488/ADM489
O UTLINE D IMENSIO NS
D imensions shown in inches and (mm).
8-Lead Narrow Body (SO IC)
14-Lead P lastic D IP
(N-14)
(SO -8)
0.1968 (5.00)
0.1890 (4.80)
0.795 (20.19)
0.725 (18.42)
14
1
8
7
0.280 (7.11)
0.240 (6.10)
8
1
5
4
0.1574 (4.00)
0.1497 (3.80)
0.2440 (6.20)
0.2284 (5.80)
0.325 (8.25)
0.300 (7.62)
0.195 (4.95)
0.115 (2.93)
0.060 (1.52)
0.015 (0.38)
PIN 1
PIN 1
0.0688 (1.75)
0.0532 (1.35)
0.210 (5.33)
MAX
0.0196 (0.50)
0.0099 (0.25)
x 45°
0.0098 (0.25)
0.0040 (0.10)
0.130
(3.30)
MIN
0.160 (4.06)
0.115 (2.93)
0.015 (0.381)
0.008 (0.204)
SEATING
PLANE
0.022 (0.558)
0.014 (0.356)
0.100 0.070 (1.77)
8°
0°
0.0500
(1.27)
BSC
0.0192 (0.49)
0.0138 (0.35)
(2.54)
BSC
0.045 (1.15)
SEATING
PLANE
0.0098 (0.25)
0.0075 (0.19)
0.0500 (1.27)
0.0160 (0.41)
8-Lead P lastic D IP
(N-8)
14-Lead Narrow Body (SO IC)
(R-14)
0.3444 (8.75)
0.3367 (8.55)
0.430 (10.92)
0.348 (8.84)
8
5
14
1
8
7
0.280 (7.11)
0.240 (6.10)
0.1574 (4.00)
0.1497 (3.80)
0.2440 (6.20)
0.2284 (5.80)
1
4
0.325 (8.25)
0.300 (7.62)
0.060 (1.52)
0.015 (0.38)
PIN 1
0.0688 (1.75)
0.0532 (1.35)
PIN 1
0.0196 (0.50)
0.195 (4.95)
0.115 (2.93)
x 45°
0.210 (5.33)
0.0098 (0.25)
0.0040 (0.10)
0.0099 (0.25)
MAX
0.130
(3.30)
MIN
0.160 (4.06)
0.115 (2.93)
0.015 (0.381)
0.008 (0.204)
8°
0°
SEATING
PLANE
0.0500
(1.27)
BSC
0.0192 (0.49)
0.0138 (0.35)
0.100
(2.54)
BSC
0.022 (0.558)
0.014 (0.356)
0.070 (1.77)
0.045 (1.15)
SEATING
PLANE
0.0500 (1.27)
0.0160 (0.41)
0.0099 (0.25)
0.0075 (0.19)
16-Lead Thin Shrink Sm all O utline P ackage (TSSO P )
(RU-16)
0.201 (5.10)
0.193 (4.90)
16
9
1
8
PIN 1
0.006 (0.15)
0.002 (0.05)
0.0433
(1.10)
MAX
0.028 (0.70)
0.020 (0.50)
8°
0°
0.0118 (0.30)
0.0075 (0.19)
0.0256
(0.65)
BSC
SEATING
PLANE
0.0079 (0.20)
0.0035 (0.090)
–12–
REV. 0
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