Circuit Note

CN-0416

Circuits from the Lab® reference designs are engineered

and testedfor quickandeasysystem integrationtohelpsolve

today’sanalog, mixed-signal, and RF design challenges.

For more informationand/or support, visit

www.analog.com/CN0416.

Devices Connected/Referenced

ADM2682E

16 Mbps, 5 kV rms Signal and Power

Isolated RS-485 Transceiver with ±15 kV

ESD Protection

LTC2865

±60 V Fault Protected 3 V to 5.5 V

RS-485/RS-422 Transceivers

ADP7102

3.3 V, 300 mA, Low Noise, CMOS LDO

Robust, Configurable, Isolated and Nonisolated RS-485 Transceiver

Rev. 0

Circuits from the Lab® reference designs from Analog Devices have been designed and built by

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constructionofeachcircuit,andtheirfunctionandperformancehavebeentestedandverifiedinalab

environment at room temperature. However, you are solely responsible for testing the circuit and

determiningitssuitabilityandapplicabilityforyouruseandapplication.Accordingly,innoeventshall

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EVALUATION AND DESIGN SUPPORT

Circuit Evaluation Boards

CN-0416 Circuit Evaluation Board (EVAL-CN0416-ARDZ)

Arduino Form Factor-Compatible Development Board

(EVAL-ADICUP3029)

Design and Integration Files

Schematics, Layout Files, Bill of Materials

CIRCUIT FUNCTION AND BENEFITS

The TIA/EIA-485-A, the most widely used transmission line

standard of the telecommunication industry, describes the

physical layer of the RS-485 interface and is normally used with

a higher level protocol, such as Profibus, Interbus, Modbus, or

BACnet. Applications include process control networks, industrial

automation, remote terminals, building automation (such as

heating, ventilation, air conditioning (HVAC)), security systems,

motor control, and motion control. The RS-485 interface allows

for robust data transmission over relatively long distances (up

to 1 km).

The circuit shown in Figure 1 is a universal RS-485 communi-

cation platform, implementing both isolated and nonisolated

RS-485 designs. The nonisolated circuit provides an extended

common-mode range of ±25 V, improving on the RS-485 speci-

fication of −7 V to +12 V and avoiding the need for isolation in

many applications, such as the case when all nodes are supplied

and referenced to the same power and ground lines.

The isolated interface, however, allows up to 500 V between the

controller ground and RS-485 signals for large scale systems

requiring robust communications between remote nodes, such

as building-to-building communications. Eliminating common-

mode effects in long haul networks requires nodes or repeaters

to be isolated from one another and the isolated transceiver,

certified in accordance with the UL1577, allows protection and

insulation for up to 5000 V between the controller ground and

RS-485 signals (1 minute, per UL1577).

The circuit is configurable to operate in full-duplex and half-

duplex operations, depending on the application. The

termination for each connection can be open or resistance

terminated, which allows customers to easily add or remove

nodes to the bus lines. Furthermore, the termination resistance

is configurable to support standard RS-485 cables or CAT5

Ethernet cables. Power to the device can be sourced from an

onboard supply or from the bus power lines.

The circuit can be used for point to point systems or multidrop

systems using the onboard address selector. Each circuit can be

set as a master device or slave device, depending on the

particular application and network in which it is used. The on-

board 10-pin connector, compatible with the ADALM-

UARTJTAG, allows the master to act as the gateway between a

host computer and the RS-485 bus via a USB virtual COM port.