ANALOG DEVICES ADM3485E Service Manual

±15 kV ESD-Protected, 3.3 V,12 Mbps,
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FEATURES

TIA/EIA RS-485/RS-422 compliant ±15 kV ESD protection on RS-485 input/output pins 12 Mbps data rate Half-duplex transceiver Up to 32 nodes on the bus Receiver open-circuit, fail-safe design Low power shutdown current Outputs high-Z when disabled or powered off Common-mode input range: −7 V to +12 V Thermal shutdown and short-circuit protection Industry-standard 75176 pinout 8-lead narrow SOIC package

APPLICATIONS

Power/energy metering Telecommunications EMI-sensitive systems Industrial control Local area networks
EIA RS-485/RS-422 Transceiver
ADM3485E

FUNCTIONAL BLOCK DIAGRAM

ADM3485E
RO
RE
DE
DI
R
D
Figure 1.
B
A
03338-001

GENERAL DESCRIPTION

The ADM3485E is a 3.3 V, low power data transceiver with ±15 kV ESD protection, suitable for half-duplex communi­cation on multipoint bus transmission lines. The ADM3485E is designed for balanced data transmission and complies with TIA/EIA standards RS485 and RS-422. The ADM3485E is a half-duplex transceiver that shares differential lines and has separate enable inputs for the driver and the receiver.
The devices have a 12 kΩ receiver input impedance,
h allows up to 32 transceivers on a bus. Because only
whic one driver should be enabled at any time, the output of a
disabled or powered-down driver is tristated to avoid overloading the bus.
The receiver has a fail-safe feature that ensures a logic high o
utput when the inputs are floating. Excessive power dissipation caused by bus contention or by output shorting is prevented with a thermal shutdown circuit.
The part is fully specified over the industrial temperature range a
nd is available in an 8-lead narrow SOIC package.
Rev. C
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Anal og Devices for its use, nor for any infringements of patents or ot her rights of third parties that may result from its use. Specifications subject to change without notice. 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 ©2006 Analog Devices, Inc. All rights reserved.
ADM3485E
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TABLE OF CONTENTS

Features .............................................................................................. 1
Applications....................................................................................... 1
Functional Block Diagram .............................................................. 1
General Description......................................................................... 1
Revision History ............................................................................... 2
Specifications..................................................................................... 3
Timing Specifications....................................................................... 4
Absolute Maximum Ratings............................................................ 5
Thermal Resistance ...................................................................... 5
ESD Caution.................................................................................. 5
Pin Configuration and Pin Function Descriptions...................... 6

REVISION HISTORY

12/06—Rev. B to Rev. C
Updated Format..................................................................Universal
Removed PDIP Model ....................................................... Universal
Changes to Features, Applications, and General Description .... 1
Changes to Specifications................................................................ 3
Changes to Timing Specifications.................................................. 4
Changes to Absolute Maximum Ratings....................................... 5
Reorganized Test Circuits and Switching C
haracteristics Section..................................................................... 7
Replaced Figure 3 to Figure 11 ....................................................... 7
Deleted Figure 12 to Figure 14........................................................ 8
Changes to Figure 15 to Figure 20.................................................. 9
Changes to Figure 21 and Figure 22............................................. 10
Changes to Table 9.......................................................................... 11
Deleted Figure 24............................................................................ 11
Removed Fast Transient Burst Immunity (IEC1000-4-4) S
Updated Outline Dimensions....................................................... 13
Changes to Ordering Guide.......................................................... 13
10/04—Rev. A to Rev. B
Updated Format..................................................................Universal
Changes to Power-Supply Current, Table 1 .................................. 3
Updated Outline Dimensions....................................................... 14
Changes to Ordering Guide.......................................................... 14
5/00—Rev. 0 to Rev. A
ection ................................................................... 12
Test Circuits and Switching Characteristics...................................7
Typical Perf or m an c e Charac t e r istics ..............................................9
Standards and Testing .................................................................... 11
ESD Testing ................................................................................. 11
Applications Information.............................................................. 12
Differential Data Transmission ................................................ 12
Cable and Data Rate................................................................... 12
Receiver Open-Circuit Fail-Safe............................................... 12
Outline Dimensions ....................................................................... 13
Ordering Guide .......................................................................... 13
Rev. C | Page 2 of 16
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SPECIFICATIONS

VCC = +3.3 V ± 0.3 V. All specifications T
Table 1.
Parameter Symbol Min Typ Max Unit Test Conditions/Comments
DRIVER
Differential Outputs
Differential Output Voltage V
1.5 V RL = 54 Ω (RS-485) (see Figure 3)
1.5 V RL = 60 Ω (RS-485) (see Figure 4) ∆|VOD| for Complementary Output States1∆V Common-Mode Output Voltage V ∆|VOC| for Complementary Output States1∆V Short-Circuit Output Current I 250 mA V
Logic Inputs
Input High Voltage V Input Low Voltage V Logic Input Current I
RECEIVER
Differential Inputs
Differential Input Threshold Voltage V Input Voltage Hysteresis ∆V Input Resistance (A, B) R Input Current (A, B) I –0.8 mA DE = 0 V, VCC = 0 V or 3.6 V, VIN = –7 V
RO Logic Output
Output Voltage High V Output Voltage Low V Short-Circuit Output Current I Tristate Output Leakage Current I
POWER SUPPLY CURRENT
Voltage Range V Supply Current I
Shutdown Current I
ESD PROTECTION
A, B Pins ±15 kV Human body model All Pins Except A, B ±4 kV Human body model
1
Δ|VOD| and Δ|VOC| are the changes in VOD and VOC, respectively, when DI input changes state.
MIN
to T
, unless otherwise noted.
MAX
OD
OD
OC
OC
OSD
IH
IL
IN1
TH
TH
IN
IN2
OH
OL
OSR
OZR
CC
CC
2.0 V RL = 100 Ω (RS-422) (see Figure 3)
0.2 V RL = 54 Ω or 100 Ω (see Figure 3) 3 V RL = 54 Ω or 100 Ω ( see Figure 3)
0.2 V RL = 54 Ω or 100 Ω (see Figure 3) –250 mA V
0.8 V
2.0 V ±2 μA
–0.2 +0.2 V –7 V < VCM < +12 V 50 mV VCM = 0 V 12 –7 V < VCM < +12 V
1.0 mA DE = 0 V, VCC = 0 V or 3.6 V, VIN = 12 V
VCC – 0.4 V V I
0.4 V I ±8 ±60 mA 0 V < VRO < V ±1 μA VCC = 3.6 V, 0 V < V
3.0 3.6 V
1.1 2.2 mA
0.95 1.9 mA
SHDN
0.002 1 μA
= –7 V
OUT
= 12 V
OUT
DE, DI, RE DE, DI, RE DE, DI, RE
= –1.5 mA, VID = 200 mV (see Figure 5)
OUT
= 2.5 mA, VID = 200 mV (see Figure 5)
OUT
CC
< V
OUT
CC
No load, DI = 0 V or V
= 0 V or V
RE
CC
No load, DI = 0 V or V
= 0 V
RE DE = 0 V, RE
= VCC, DI = 0 V or V
, DE = VCC,
CC
, DE = 0 V,
CC
CC
Rev. C | Page 3 of 16
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TIMING SPECIFICATIONS

VCC = 3.3 V, TA = 25°C.
Table 2.
Parameter Symbol Min Typ Max Unit Test Conditions/Comments
DRIVER
Maximum Data Rate 12 15 Differential Output Delay t Differential Output Transition Time t
DD
TD
Propagation Delay
From Low to High Level t From High to Low Level t
|t
− t
PLH
| Propagation Delay Skew t
PHL
PLH
PHL
PDS
Enable/Disable Timing
Enable Time to Low Level t Enable Time to High Level t Disable Time from Low Level t Disable Time from High Level t Enable Time from Shutdown to Low Level t Enable Time from Shutdown to High Level t
PZL
PZH
PLZ
PHZ
PSL
PSH
RECEIVER
Propagation Delay
From Low to High Level t From High to Low Level t
|t
− t
RPLH
| Propagation Delay Skew t
RPHL
RPLH
RPHL
RPDS
Enable/Disable Timing
Enable Time to Low Level t Enable Time to High Level t Disable Time from Low Level t Disable Time from High Level t Enable Time from Shutdown to Low Level t Enable Time from Shutdown to High Level t Time to Shutdown
1
The transceivers are put into shutdown mode by bringing the RE high and the DE low. If the inputs are in this state for less than 80 ns, the parts are guaranteed not to
enter shutdown. If the parts are in this state for 300 ns or more, the parts are guaranteed to enter shutdown.
1
t
RPZL
RPZH
RPLZ
RPHZ
RPSL
RPSH
SHDN
1 22 35 ns RL = 60 Ω, CL1 = CL2 = 15 pF (see Figure 6) 3 11 25 ns RL = 60 Ω, CL1 = CL2 = 15 pF (see Figure 6)
7 23 35 ns RL = 27 Ω (see Figure 7) 7 23 35 ns RL = 27 Ω (see Figure 7) –1.4 ±8 ns RL = 27 Ω (see Figure 7)
42 90 ns RL = 110 Ω (see Figure 9) 42 90 ns RL = 110 Ω (see Figure 8) 35 80 ns RL = 110 Ω (see Figure 9) 35 80 ns RL = 110 Ω (see Figure 8) 650 900 ns RL = 110 Ω (see Figure 9) 650 900 ns RL = 110 Ω (see Figure 8)
25 62 90 ns VID = 0 V to 3.0 V, CL = 15 pF (see Figure 10) 25 62 90 ns VID = 0 V to 3.0 V, CL = 15 pF (see Figure 10) 6 ±10 ns VID = 0 V to 3.0 V, CL = 15 pF (see Figure 10)
25 50 ns CL = 15 pF (see Figure 11) 25 50 ns CL = 15 pF (see Figure 11) 25 45 ns CL = 15 pF (see Figure 11) 25 45 ns CL = 15 pF (see Figure 11) 720 1400 ns CL = 15 pF (see Figure 11) 720 1400 ns CL = 15 pF (see Figure 11) 80 190 300 ns
Rev. C | Page 4 of 16
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ABSOLUTE MAXIMUM RATINGS

TA = 25°C, unless otherwise noted.
Table 3.
Parameter Values
VCC to GND –0.3 V to +6 V Digital Input/Output Voltage (DE, RE, DI) Receiver Output Voltage (RO) –0.3 V to (VCC + 0.3 V) Driver Output (A, B)/
Receiver Input (A, B) Voltage −8 V to +13 V Driver Output Current ±250 mA Power Dissipation (8-Lead SOIC_N) 650 mW Operating Temperature Range –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
Human Body Model (A, B) ±15 kV
Stresses above those listed under Absolute Maximum Ratings may cause permanent 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 section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
–0.3 V to +6 V

THERMAL RESISTANCE

θJA is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages.
Table 4. Thermal Resistance
Package Type θ
8-Lead SOIC_N 158 °C/W
JA
Unit

ESD CAUTION

Rev. C | Page 5 of 16
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PIN CONFIGURATION AND PIN FUNCTION DESCRIPTIONS

RO
1
ADM3485E
RE
2
TOP VIEW
DE
3
(Not to Scale)
4
DI
Figure 2. SOIC_N Pin Configuration (R-8)
Table 5. Pin Function Descriptions
Pin
Mnemonic
Number
Description
RO 1 Receiver Output. When enabled, if A > B by 200 mV, then RO = high. If A < B by 200 mV, then RO = low. RE
2
Receiver Output Enable. With RE
low, the receiver output (RO) is enabled. With RE high, the output goes into a
high impedance state. If RE is high and DE is low, the ADM3485E enters a shutdown state.
DE 3
Driver Output Enable. A high level enables the driver differen impedance state.
DI 4
Driver Input. When the driver is enabled, a logic low on DI forces A low and B high, while a logic high on DI
orces A high and B low.
f GND 5 Ground Connection, 0 V. A 6 Noninverting Receiver Input A/Driver Output A. B 7 Inverting Receiver Input B/Driver Output B. V
CC
8 Power Supply, 3.3 V ± 0.3 V.
V
8
CC
B
7
A
6
5
GND
03338-002
tial outputs A and B. A low level places it in a high
Rev. C | Page 6 of 16
ADM3485E
V
V
2
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TEST CIRCUITS AND SWITCHING CHARACTERISTICS

A
/2
R
V
B
L
OD
RL/2
V
Figure 3. Driver Differential Output Voltage and
Co
mmon-Mode Output Voltage
375
D
V
CC
R
V
L
OD
375
Figure 4. Driver Differential Output Voltage with
V
arying Common-Mode Voltage
R
ID
0
V
OL
Figure 5. Receiver Output Voltag
I
OL (+)
e High and Output Voltage Low
OC
03338-037
VCM = –7V TO +12V
V
OH
S1
D
GENERATOR
1
PPR = 250kHz, 50% DUT Y CYCLE,
2
CL INCLUDES PROBE AND STRAY CAPACITANCE.
03338-038
OUT
I
OH (–)
03338-039
OUT
1
50
V
CC
+ V
V
OH
=
V
OM
t
6.0ns, ZO = 50.
R
IN
A
B
1.5V 1.5V
t
PLH
V
OM
t
PHL
V
OM
Figure 7. Driver Propagation Delays
OM
RL = 27
OUT
2
C
= 15pF
L
OL
1.5V
2
3V
0V
t
PHL
V
V
OM
V
OM
OH
V
OL
t
PLH
V
OH
V
OL
03338-041
C
L
RL =
D
GENERATOR
1
PPR = 250kHz, 50% DUTY CYCLE,
2
CL INCLUDES PROBE AND STRAY CAPACITANCE.
IN
OUT
1
50
V
CC
+1.5V +1.5V
t
DD
t
TD
t
6.0ns, ZO = 50.
R
90%90%
50%50%
10%10%
CL = 15pF
t
DD
t
TD
60
+3V
0V
+2V
–2V
2
OUT
03338-040
Figure 6. Driver Differential Output Delay and Transition Times
OM
D
t
PHZ
S1
C
= 50pF
L
+ V
V
OH
V
=
OM
t
6.0ns, ZO = 50.
R
1.5V1.5V
2
2
0V OR 3V
OUT
1
50
IN
t
PZH
V
GENERATOR
1
PPR = 250kHz, 50% DUTY CYCLE , CL INCLUDES PRO BE AND STRAY CAPACI TANCE.
Figure 8. Driver Enable and Disable Times (t
OL
0.25V
1.5V
PZH
, t
OUT
RL = 110
3V
0V
V
OH
0V
, t
PSH
PHZ
03338-042
)
Rev. C | Page 7 of 16
ADM3485E
V
2
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CC
0V OR 3V
OUT
1
50
IN
1.5V 1.5V
V
OM
GENERATOR
1
PPR = 250kHz, 50% DUT Y CYCLE,
2
CL INCLUDES PROBE AND STRAY CAPACIT ANCE.
S1
D
2
C
= 50pF
L
t
6.0ns, ZO = 50.
R
t
PSL
t
Figure 9. Driver Enable and Disable Times (t
+1.5V
–1.5V
GENERATOR
PLZ
0.25V
RL = 110
, t
PZL
S3
OUT
GENERATOR
1
PPR = 250kHz, 50% DUTY CYCLE, CL INCLUDES PROBE AND STRAY CAPACITANCE.
3V
0V
V
CC
V
OL
PSL
03338-043
, t
)
PLZ
V
R
ID
1
50
1k
2
C
L
OUT
1
1.5V
0V
IN
t
RPLH
Figure 10. Receiver Propagation Delays
S1
S2
50
V
V
V
ID
t
R
1.5V1.5V
OM
CC
OUT
R
C
VOM =
6.0ns, ZO = 50.
t
RPHL
V
OM
= 15pF
L
V
CC
2
3V
0V
V
CC
0V
2
03338-044
1
OUT
OUT
IN
IN
+0.25V
PPR = 250kHz, 50% DUTY CYCLE,
2
CL INCLUDES PROBE AND STRAY CAPACIT ANCE.
+3V
+1.5V
0V
V
0V
+3V
0V
V
0V
OH
OH
+1.5V
t
RPZH
t
RPSH
t
+1.5V
RPHZ
t
R
S1 OPEN S2 CLOSED S3 = +1.5V
S1 OPEN S2 CLOSED S3 = +1.5V
6.0ns, ZO = 50.
IN
OUT
IN
OUT
+0.25V
+1.5V
t
RPLZ
t t
RPZL
RPSL
+1.5V
+1.5V
+3V
0V
V
V
+3V
0V
V
V
CC
OL
CC
OL
S1 CLOSED S2 OPEN S3 = –1.5V
S1 CLOSED S2 OPEN S3 = –1.5V
03338-045
Figure 11. Receiver Enable and Disable Times
Rev. C | Page 8 of 16
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TYPICAL PERFORMANCE CHARACTERISTICS

25
20
0.8
0.7
0.6
IRO = 2.5mA
15
10
OUTPUT CURRENT ( mA)
5
0
03
0.5 1.0 1. 5 2 .0 2.5 3. 0
OUTPUT LOW VOLTAGE (V)
Figure 12. Output Current vs. R
18
–16
–14
–12
–10
–8
–6
OUTPUT CURRENT ( mA)
–4
–2
0
03
0.5 1.0 1. 5 2 .0 2.5 3. 0
OUTPUT HIGH VOLT AGE (V)
Figure 13. Output Current vs. R
3.30
3.25
3.20
3.15
3.10
OUTPUT HIGH VOLT AGE (V)
3.05
3.00 –50 –25 0 25 50 75
eceiver Output Low Voltage
eceiver Output High Voltage
IRO = –1.5mA
TEMPERATURE ( °C)
.5
03338-051
.5
03338-052
03338-053
Figure 14. Receiver Output High Voltage vs. Temperature
0.5
0.4
0.3
0.2
OUTPUT LOW VOLTAGE (V)
0.1
0
–40 10 60 85
Figure 15. Receiver Output Low Voltage vs. Temperature
100
90
80
70
60
50
40
30
OUTPUT CURRENT ( mA)
20
10
0
03.5
0.5 1.0 1. 5 2 .0 2.5 3. 0
Figure 16. Driver Output Current vs. Differential Output Voltage
2.6
2.5
2.4
2.3
2.2
2.1
2.0
1.9
1.8
DIFFERENT IAL OUTPUT VOLT AGE (V)
1.7
1.6 –50
–25 0 25 50 75
Figure 17. Driver Differential Output Voltage vs. Temperature
TEMPERATURE (°C)
DIFFERENT IAL OUT PUT VOL TAGE (V)
TEMPERATURE (° C)
RL = 54
03338-054
03338-055
03338-056
Rev. C | Page 9 of 16
ADM3485E
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120
100
80
60
40
OUTPUT CURRENT (mA)
20
0
024681012
OUTPUT LOW VOLTAGE (V)
Figure 18. Output Current vs. Driv
120
100
80
er Output Low Voltage
03338-057
0.9
0.8
0.7
0.6
0.5
0.4
0.3
SHUTDOWN CURRENT (µA)
0.2
0.1
0 –50
–25 0 25 50 75
TEMPERATURE (° C)
03338-060
Figure 21. Shutdown Current vs. Temperature
DI
3
60
40
OUTPUT CURRENT (mA)
20
0
7–6–5–4–3–2–101234
OUTPUT HIG H VOLTAG E (V)
Figure 19. Output Current vs. Driv
1.2
1.1
1.0
0.9
0.8
0.7
SUPPLY CURRENT (mA)
0.6
0.5 –40
–10 20 50 80
TEMPERATURE (° C)
er Output High Voltage
Figure 20. Supply Current vs. Temperature
03338-058
03338-059
A
B
H2
CH1 1.0V CH2 1.0V IT 400ps/pt CH3 2.0V M20ns 1. 25GS/s
Figure 22. Driver Propagation Delay
VA– V
B
M1
RO
3
CH3 2.0V 4ns/ pt
MATH1 2.01V 200ns
M200ns 250MS/ s A CH2 1.24V
Figure 23. Receiver Propagation Delay,
en by External RS-485 Device
Driv
A CH3 1.44V
03338-061
03338-062
Rev. C | Page 10 of 16
ADM3485E
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STANDARDS AND TESTING

Tabl e 6 compares RS-422 and RS-485 interface standards, and Tabl e 7 and Ta b le 8 show transmitting and receiving truth tables.
Table 6.
Specification RS-422 RS-485
Transmission Type Differential Differential Maximum Data Rate 10 Mbps 10 Mbps 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 Number of Drivers/Receivers per Line 1/10 32/32
Table 7. Transmitting Truth Table
Transmitting Inputs Transmitting Outputs
RE
1
X
1
X 0 0 X 1 0 X
1
X = don't care.
2
High-Z = high impedance.
DE DI B A
1 1 0 1 1 0 1 0
1
1
High-Z High-Z
2
2
High-Z High-Z
2
2
Table 8. Receiving Truth Table
Receiving Inputs Receiving Outputs
RE
0 X 0 X 0 X 1 X
1
X = don't care.
2
High-Z = high impedance.
DE A – B RO
1
1
1
1
> +0.2 V 1 < –0.2 V 0 Inputs open 1
1
X
High-Z
2
influenced by humidity, temperature, barometric pressure, distance, and rate of closure of the discharge gun. The contact discharge method, while less realistic, is more repeatable and is gaining acceptance and preference over the air-gap method.
Although very little energy is contained within an ESD pulse, t
he extremely fast rise time, coupled with high voltages, can cause failures in unprotected semiconductors. Catastrophic destruction can occur immediately as a result of arcing or heating. Even if catastrophic failure does not occur immediately, the device can suffer from parametric degradation, which can result in degraded performance. The cumulative effects of continuous exposure can eventually lead to complete failure.
I/O lines are particularly vulnerable to ESD damage. Simply tou
ching or plugging in an I/O cable can result in a static discharge that can damage or completely destroy the interface product connected to the I/O port. It is extremely important, therefore, to have high levels of ESD protection on the I/O lines.
The ESD discharge could induce latch-up in the device under
st, so it is important that ESD testing on the I/O pins be
te carried out while device power is applied. This type of testing is more representative of a real-world I/O discharge, where the equipment is operating normally when the discharge occurs.
Table 9. ESD Test Results
ESD Test Method I/O Pins
Human Body Model ±15 kV
100%
90%
PEAK
I

ESD TESTING

Two coupling me t hods are us e d for ESD testi n g , cont act discharge and air-gap discharge. Contact discharge calls for a direct connection to the unit being tested. Air-gap discharge uses a higher test voltage but does not make direct contact with the unit under test. With air-gap discharge, the discharge gun is moved toward the unit under test, developing an arc across the air gap, hence the term air-gap discharge. This method is
Rev. C | Page 11 of 16
6.8%
10%
t
RL
Figure 24. Human Body Model Current Waveform
t
DL
TIME
t
03338-023
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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 that appear as common-mode voltages on the line.
Two main standards that specify the electrical characteristics of
nsceivers used in differential data transmission are approved
tra by the Electronics Industries Association (EIA). The RS-422 standard specifies data rates up to 10 Mbps and line lengths up to 4000 feet. 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
e fact that under the RS-485 standard the drivers may be
th 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 ADM3485E is designed for bidirectional data communi-
ations on multipoint transmission lines. A typical application
c showing a multipoint transmission network is illustrated in Figure 25. Only one driver can transmit at a particular time, b
ut multiple receivers may be enabled simultaneously.
As with any transmission line, it is important that reflections are minimize
d. This can be achieved by terminating the extreme ends of the line using resistors equal to the characteristic impe­dance of the line. Stub lengths off the main line must 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 10. 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
ADM3485E
A
B
R
RO
RE
DE
D
DI
03338-027
RO
RE
DE
DI
ADM3485E
R
D
A
B
ADM3485E
R
RO
A
B
D
DE
RE DI
MAXIMUM NUMBER OF TRANSCEIVERS ON BUS: 50
Figure 25. Multipoint Transmission Network
RO
A
R
RE
B
ADM3485E
D
DI
DE
Rev. C | Page 12 of 16
ADM3485E
www.BDTIC.com/ADI

OUTLINE DIMENSIONS

5.00 (0.1968)
4.80 (0.1890)
4.00 (0.1574)
3.80 (0.1497)
0.25 (0.0098)
0.10 (0.0040)
COPLANARIT Y
0.10
CONTROLL ING DIM ENSIONS ARE IN MILL IMETERS; INCH DIME NSIONS (IN PARENTHESES) ARE ROUNDE D-OFF M ILLIMETER EQUIVALENTS FOR REFERENCE ON LY AND ARE NOT APPRO PRIATE FOR US E IN DESIG N.
85
1
1.27 (0.0500)
SEATING
PLANE
COMPLI ANT TO JEDEC STANDARDS MS-012-A A
Figure 26. 8-Lead Standard Small Outline Package [SOIC_N]
BSC
6.20 (0.2440)
5.80 (0.2284)
4
1.75 (0.0688)
1.35 (0.0532)
0.51 (0.0201)
0.31 (0.0122)
Nar
row Body
8° 0°
0.25 (0.0098)
0.17 (0.0067)
0.50 (0.0196)
0.25 (0.0099)
1.27 (0.0500)
0.40 (0.0157)
45°
060506-A
(R-8)
Dimensions shown in millimeters and (inches)

ORDERING GUIDE

Model Temperature Range Package Description Package Option
ADM3485EAR –40°C to +85°C 8-Lead Standard Small Outline Package [SOIC_N] R-8 ADM3485EAR-REEL7 –40°C to +85°C 8-Lead Standard Small Outline Package [SOIC_N] R-8 ADM3485EAR-REEL –40°C to +85°C 8-Lead Standard Small Outline Package [SOIC_N] R-8 ADM3485EARZ ADM3485EARZ-REEL7 ADM3485EARZ-REEL
1
Z = Pb-free part.
1
1
1
–40°C to +85°C 8-Lead Standard Small Outline Package [SOIC_N] R-8 –40°C to +85°C 8-Lead Standard Small Outline Package [SOIC_N] R-8 –40°C to +85°C 8-Lead Standard Small Outline Package [SOIC_N] R-8
Rev. C | Page 13 of 16
ADM3485E
www.BDTIC.com/ADI
NOTES
Rev. C | Page 14 of 16
ADM3485E
www.BDTIC.com/ADI
NOTES
Rev. C | Page 15 of 16
ADM3485E
www.BDTIC.com/ADI
NOTES
©2006 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. C03338-0-12/06(C)
T
Rev. C | Page 16 of 16
TTT
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