ANALOG DEVICES ADM2481 Service Manual

Isolated RS-485 Transceiver

ADM2481

Rev. A

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ADM2481

DE

GALVANIC ISOLA

TION

TxD

RxD

A
B

RE

GND

1

GND

2

V

DD1

V

DD2

08920-001

Data Sheet

FEATURES

RS-485 transceiver with electrical data isolation
Complies with ANSI TIA/EIA-485-A and ISO 8482: 1987(E)
500 kbps data rate
Slew rate-limited driver outputs
Low power operation: 2.5 mA maximum
Suitable for 5 V or 3.3 V operations (V
High common-mode transient immunity: >25 kV/μs
True fail-safe receiver inputs
Chatter-free power-up/power-down protection
256 nodes on bus
Thermal shutdown protection
Safety and regulatory approvals

UL recognition: 2500 V rms for 1 minute per

UL 1577

VDE certificates of conformity

DIN V VDE V 0884-10 (VDE V 0884-10): 2006-12
V

= 560 V peak

IORM

Operating temperature range: −40°C to +85°C

DD1

)

Half-Duplex, iCoupler

FUNCTIONAL BLOCK DIAGRAM

Figure 1.

APPLICATIONS

Low power RS-485/RS-422 networks
Isolated interfaces
Building control networks
Multipoint data transmission systems

GENERAL DESCRIPTION

The ADM2481 differential bus transceiver is an integrated,
galvanically isolated component designed for bidirectional data
communication on balanced, multipoint bus transmission lines.
It complies with ANSI EIA/TIA-485-A and ISO 8482: 1987(E).
Using iCoupler® technology from Analog Devices, Inc., the
ADM2481 combines a 3-channel isolator, a three-state diffe­rential line driver, and a differential input receiver into a single
package. The logic side of the device is powered with either a
5 V or 3 V supply, and the bus side uses a 5 V supply only.

The ADM2481 is slew-limited to reduce reflections with improp­erly terminated transmission lines. The controlled slew rate
limits the data rate to 500 kbps. The input impedance of the
device is 96 kΩ, allowing up to 256 transceivers on the bus. Its
driver has an active-high enable feature. The driver differential
outputs and receiver differential inputs are connected internally

to form a differential I/O port. When the driver is disabled or
when V

DD1

or V

= 0 V, this imposes minimal loading on

DD2

the bus. An active-high receiver disable feature, which causes
the receiver output to enter a high impedance state, is provided
as well.

The receiver inputs have a true fail-safe feature that ensures a
logic-high receiver output level when the inputs are open or
shorted. This guarantees that the receiver outputs are in a
known state before communication begins and at the point
when communication ends.

Current limiting and thermal shutdown features protect against
output short circuits and bus contention situations that might
cause excessive power dissipation. The part is fully specified
over the industrial temperature range of −40°C to +85°C and is
available in a 16-lead, wide body SOIC package.

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. Specifications subject to change without notice. No
license i s granted by implication or otherwise under any patent or patent rights of Analog Devices.

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Tel: [phone]

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ADM2481 Data Sheet

TABLE OF CONTENTS

Features .............................................................................................. 1

Applications ....................................................................................... 1

Functional Block Diagram .............................................................. 1

General Description ......................................................................... 1

Revision History ............................................................................... 2

Specifications ..................................................................................... 3

Timing Specifications .................................................................. 4

Package Characteristics ............................................................... 4

Regulatory Information ............................................................... 4

Insulation and Safety-Related Specifications ............................ 4

VDE 0884 Insulation Characteristics ........................................ 5

Absolute Maximum Ratings ............................................................ 6

ESD Caution .................................................................................. 6

Pin Configuration and Function Descriptions ............................. 7

Typical Performance Characteristics ..............................................8

Test Circuits ..................................................................................... 11

Switching Characteristics .............................................................. 12

Circuit Description......................................................................... 13

Electrical Isolation ...................................................................... 13

Truth Tables................................................................................. 14

Thermal Shutdown .................................................................... 14

True Fai l -Safe Receiver Inputs .................................................. 14

Magnetic Field Immunity.......................................................... 14

Applications Information .............................................................. 16

Printed Circuit Board (PCB) Layout ....................................... 16

Isolated Power Supply Circuit .................................................. 16

Outline Dimensions ....................................................................... 17

Ordering Guide .......................................................................... 17

REVISION HISTORY

6/12—Rev. 0 to Rev. A

Updated Safety and Regulatory Approvals (Throughout) .......... 1

Updated Outline Dimensions ....................................................... 17

Changes to Ordering Guide .......................................................... 17

7/10—Revision 0: Initial Version

Rev. A | Page 2 of 20

Data Sheet ADM2481

SPECIFICATIONS

3.0 V ≤ V

Table 1.

Parameter Symbol Min Typ Max Unit Test Conditions/Comments

DRIVER

Differential Outputs

Logic Inputs

RECEIVER

Differential Inputs

RxD Logic Output

POWER SUPPLY CURRENT

Logic Side I

1.3 mA 3.0 V ≤ V

Bus Side I

1.7 mA Outputs unloaded, DE = 0 V

COMMON-MODE TRANSIENT IMMUNITY

1

Common-mode transient immunity is the maximum common-mode voltage slew rate that can be sustained while maintaining specification-compliant operation.

is the common-mode potential difference between the logic and bus sides. The transient magnitude is the range over which the common mode is slewed. The

V

CM

common-mode voltage slew rates apply to both rising and falling common-mode voltage edges.

≤ 5.5 V, 4.75 V ≤ V

DD1

≤ 5.25 V, TA = T

DD2

MIN

to T

, unless otherwise noted.

MAX

Differential Output Voltage 5 V RL = ∞, see Figure 16
V
V
V

2.0 5 V RL = 50 Ω (RS-422), see Figure 16

OD

1.5 5 V RL = 27 Ω (RS-485), see Figure 16

OD

1.5 5 V V

OD3

= −7 V to +12 V, V

TEST

≥ 4.75,

DD1

see Figure 17
Δ |VOD| for Complementary Output States 0.2 V RL = 27 Ω or 50 Ω, see Figure 16
Common-Mode Output Voltage VOC 3 V RL = 27 Ω or 50 Ω, see Figure 16
Δ |VOC| for Complementary Output States 0.2 V RL = 27 Ω or 50 Ω, see Figure 16
Output Short-Circuit Current, ISC

V

= High −250 +250 mA −7 V ≤ V

OUT

V

= Low −250 +250 mA −7 V ≤ V

OUT

Input High Voltage VIH 0.7 V
Input Low Voltage VIL 0.25 V

−10 +0.01 +10 μA

CMOS Logic Input Current (TxD, DE, RE)

I

I

V

DD1

V

DD1

TxD, DE,

TxD, DE,

TxD, DE,

≤ +12 V

OUT

≤ +12 V

OUT

RE
RE
RE

= V

DD1

or 0 V

Differential Input Threshold Voltage VTH −200 −125 −30 mV −7 V ≤ VCM ≤ +12 V
Input Hysteresis V

20 mV −7 V ≤ VCM ≤ +12 V

HYS

Input Resistance (A, B) 96 150 kΩ −7 V ≤ VCM ≤ +12 V
Input Current (A, B)

Output High Voltage VOH V
V
Output Low Voltage VOL 0.1 V I

0.4 V I
Output Short-Circuit Current ISC 7 85 mA V
Three-State Output Leakage Current ±1 μA 0.4 V ≤ V

0.125 mA VIN = 12 V

−0.1 mA VIN = −7 V

− 0.1 V I

DD1

− 0.4 V

DD1

1

2.5 mA 4.5 V ≤ V

DD1

2.0 mA Outputs unloaded, DE = 5 V

DD2

VCM 25 kV/μs TxD = V

− 0.2 V I

DD1

= 20 μA, VA − VB = 0.2 V

OUT

= 4 mA, VA − VB = 0.2 V

OUT

= −20 μA, VA − VB = −0.2 V

OUT

= −4 mA, VA − VB = −0.2 V

OUT

= GND or VCC

OUT

≤ 2.4 V

OUT

≤ 5.5 V, outputs

DD1

RE

unloaded,

unloaded,

= 0 V

≤ 3.6 V, outputs

DD1

RE

= 0 V

or 0 V, VCM = 1 kV,

DD1

transient magnitude = 800 V

Rev. A | Page 3 of 20

ADM2481 Data Sheet

Propagation Delay

t

, t

400 1050

ns

CL = 15 pF, see Figure 20 and Figure 23

Parameter

Symbol

Value

Unit

Conditions

Rated Dielectric Insulation Voltage

2500

V rms

1-minute duration

TIMING SPECIFICATIONS

3.0 V ≤ V

Table 2.

Parameter Symbol Min Typ Max Unit Test Conditions/Comments

DRIVER

Maximum Data Rate 500 kbps
Propagation Delay t
Skew t
Rise/Fall Time tR, tF 200 600 ns RL = 54 Ω, CL1 = CL2 = 100 pF, see Figure 18 and Figure 22
Enable Time 1050 ns RL = 500 Ω, CL = 100 pF, see Figure 19 and Figure 24
Disable Time 1050 ns RL = 500 Ω, CL = 15 pF, see Figure 19 and Figure 24

RECEIVER

Differential Skew t
Enable Time 25 70 ns RL = 1 kΩ, CL = 15 pF, see Figure 21 and Figure 25
Disable Time 40 70 ns RL = 1 kΩ, CL = 15 pF, see Figure 21 and Figure 25

PACKAGE CHARACTERISTICS

Table 3.

Parameter Symbol Min Typ Max Unit Test Conditions

Resistance (Input-Output)1 R
Capacitance (Input-Output)1 C
Input Capacitance2 CI 4 pF

1

Device is considered a 2-terminal device: Pin 1 to Pin 8 are shorted together, and Pin 9 to Pin16 are shorted together.

2

Input capacitance is from any input data pin to ground.

≤ 5.5 V, 4.75 V ≤ V

DD1

≤ 5.25 V, TA = T

DD2

, t

250 620 ns RL = 54 Ω, CL1 = CL2 = 100 pF, see Figure 18 and Figure 22

PLH

PHL

40 ns RL = 54 Ω, CL1 = CL2 = 100 pF, see Figure 18 and Figure 22

SKEW

PLH

PHL

250 ns CL = 15 pF, see Figure 20 and Figure 23

SKEW

1012 Ω

I-O

3 pF f = 1 MHz

I-O

MIN

to T

, unless otherwise noted.

MAX

REGULATORY INFORMATION

Table 4. ADM2481 Approvals

Organization Approval Type Notes

UL Recognized under the Component Recognition

Program of Underwriters Laboratories, Inc.

In accordance with UL 1577, each ADM2481 is proof tested by
applying an insulation test voltage of ≥ 3000 V rms for 1 second
(current leakage detection limit = 5 µA).

VDE Certified according to DIN V VDE V 0884-10

(VDE V 0884-10): 2006-12

In accordance with DIN V VDE V 0884-10, each ADM2481 is proof
tested by applying an insulation test voltage of ≥ 1050 V peak for
1 second (partial discharge detection limit = 5 pC).

INSULATION AND SAFETY-RELATED SPECIFICATIONS

Table 5.

Minimum External Air Gap (Clearance) L(I01) 7.7 mm Measured from input terminals to output

terminals, shortest distance through air

Minimum External Tracking (Creepage) L(I02) 7.6 mm Measured from input terminals to output

terminals, shortest distance along body
Minimum Internal Gap (Internal Clearance) 0.017 min mm Insulation distance through insulation
Tracking Resistance (Comparative Tracking Index) CTI >175 V DIN IEC 112/VDE 0303 Part 1
Isolation Group IIIa Material Group (Table 1 in DIN VDE 0110,1/89)

Rev. A | Page 4 of 20

Data Sheet ADM2481

Input-to-Output Test Voltage, Method a

VDE 0884 INSULATION CHARACTERISTICS

This isolator is suitable for basic electrical isolation only within this safety limit data. Maintenance of this safety data shall be ensured by
means of protective circuits.

Table 6.

Description Symbol Characteristic Unit

Installation Classification per DIN VDE 0110 for Rated Mains Voltage

≤150 V rms I to IV
≤300 V rms I to III

≤400 V rms I to II
Climatic Classification 40/85/21
Pollution Degree (Table 1 in DIN VDE 0110) 2
Maximum Working Insulation Voltage V
Input to Output Test Voltage, Method b1 VPR 1050 V

V

× 1.875 = VPR, 100% Production Tested

IORM

tm = 1 sec, Partial Discharge of < 5 pC

(After Environmental Tests, Subgroup 1)

V

× 1.6 = VPR, tm = 60 sec, Partial Discharge of < 5 pC 896 V

IORM

(After Input and/or Safety Test, Subgroup 2/3)

V

× 1.2 = VPR, tm = 60 sec, Partial Discharge of < 5 pC VPR 672 V

IORM

Highest Allowable Overvoltage
(Transient Overvoltage, tTR = 10 sec) VTR 4000 V
Safety-Limiting Values (Maximum Value Allowed in the Event of a Failure; see Figure 13)

Case Temperature TS 150 °C

Input Current I

Output Current I
Insulation Resistance at TS, VIO = 500 V RS >109 Ω

560 V

IORM

265 mA

S, INPUT

335 mA

S, OUTPUT

PEAK

PEAK

PEAK

PEAK

PEAK

Rev. A | Page 5 of 20

ADM2481 Data Sheet

V

−0.5 V to +7 V

ABSOLUTE MAXIMUM RATINGS

TA = 25°C, unless otherwise noted. All voltages are relative to
their respective ground.

Table 7.

Parameter Rating

DD1

V

−0.5 V to +6 V

DD2

Digital Input Voltage (DE, RE, TxD) −0.5 V to V
Digital Output Voltage (RxD) −0.5 V to V
Driver Output/Receiver Input Voltage −9 V to +14 V

ESD Rating: Contact (Human Body

Model) (A, B Pins)
Operating Temperature Range −40°C to +85°C
Storage Temperature Range −55°C to +150°C
Average Output Current per Pin −35 mA to +35 mA
θJA Thermal Impedance 65°C/W
Lead Temperature

Soldering (10 sec) 260°C

Vapor Phase (60 sec) 215°C

Infrared (15 sec) 220°C

±2 kV

DD1

DD1

+ 0.5 V
+ 0.5 V

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.

ESD CAUTION

Rev. A | Page 6 of 20