HCPL-0721 datasheet(13/18 Pages) AVAGO

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Optical Isolation for Field Bus Networks

To recognize the full benefits of these networks, Avago

optocouplers are recommended to provide galvanic iso-

lation. As network communication is bi-directional (in-

volving receiving data from and transmitting data onto

the network), two Avago optocouplers are needed. By

providing galvanic isolation, data integrity is retained

via noise reduction and the elimination of false signals.

In addition, the network receives maximum protection

from power system faults and ground loops.

Within an isolated node, such as the DeviceNet Node

shown in Figure 16, some of the node’s components are

referenced to a ground other than V- of the network.

Figure 16. Typical DeviceNet Node

These components could include such things as devices

with serial ports, parallel ports, RS-232 and RS-485 type

ports. As shown in Figure 16, power from the network is

used only for the transceiver and input (network) side of

the optocouplers.

Isolation of nodes connected to any of the three types of

digital field bus networks is best achieved by using the

HCPL-772X/072X optocouplers. For each network, the

HCPL-772X/072X satisify the critical propagation delay

and pulse width distortion requirements over the tem-

perature range of 0 °C to +85 °C, and power supply volt-

age range of 4.5 V to 5.5V.

NODE/APP SPECIFIC

µP/CAN

HCPL

772x/072x

HCPL

772x/072x

TRANSCEIVER

LOCAL

NODE

SUPPLY

5 V REG.

NETWORK

POWER

SUPPLY

V+ (SIGNAL)

V– (SIGNAL)

V+ (POWER)

V– (POWER)

GALVANIC

ISOLATION

BOUNDARY

AC LINE

DRAIN/SHIELD

SIGNAL

POWER

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