Broadcom

AV02-0876EN

13

HCPL-0720, HCPL-7720, HCPL-0721,

and HCPL-7721 Data Sheet

40-ns Propagation Delay, CMOS Optocoupler

Optical Isolation for Field Bus Networks

To recognize the full benefits of these networks, Broadcom optocouplers are recommended to provide galvanic isolation. As

network communication is bidirectional (involving receiving data from and transmitting data onto the network), two Broadcom

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 12, some of the node's components are referenced

to a ground other than V– of the network.

These components could include such things as devices with serial ports, parallel ports, RS-232 and RS-485 type ports. As

shown in Figure 12, 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 temperature range of 0°C to +85°C, and power supply voltage range of 4.5V to 5.5V.

Figure 12: Typical DeviceNet Node

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