Datasheet

14
Optical Isolation for Field Bus Networks
To recognize the full benets of these networks, each
recommends providing galvanic isolation using Avago
optocouplers. Since network communication is bi-direc-
tional (involving 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 pro-
tection 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.
NODE/APP SPECIFIC
uP/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
HCPL-0710 fig 17
Figure 16. Typical DeviceNet Node.
These components could include such things as devices
with serial ports, parallel ports, RS232 and RS485 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 eld 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 5.5 V.