1-333

Figure 18. Recommended Non-Isolated Active Transmitter with HCPL-4200 Isolated Receiver for Simplex Point-to-Point

20 mA Current Loop.

receiver, can be used at the

isolated end of current loops.

Cross talk and common mode

coupling are greatly reduced

when optical isolation is imple-

mented at the same end of both

loops, as shown. The full duplex

data rate is limited by the non-

isolated active receiver current

loop. Comments mentioned under

simplex configuration apply to

the full duplex case. Consult the

HCPL-4100 transmitter opto-

coupler data sheet for specified

device performance.

Half Duplex

The half duplex configuration,

whether point-to-point or

multidrop, gives non-

simultaneous bidirectional data

flow from transmitters to

receivers shown in Figures 22a

and 22b. This configuration

allows the use of two wires to

carry data back and forth

between local and remote units.

However, protocol must be used

to determine which specific

transmitter can operate at any

given time. Maximum data rate

for a half duplex system is limited

by the loop current charging

time. These considerations were

explained in the Simplex config-

uration section.

Figures 22a and 22b illustrate

half duplex application for the

combination of HCPL-4100/-4200

optocouplers. The unique and

complementary designs of the

HCPL-4100 transmitter and

HCPL-4200 receiver

optocouplers provide many

designed-in benefits. For

example, total optical isolation at

one end of the current loop is

easily accomplished, which

results in substantial removal of

common mode influences,

elimination of ground potential

Figure 19. Minimum Required Supply

Current Loop Circuit of Figure 19.

Figure 20. Typical Data Rate vs.

Distance.

Figure 21. Full Duplex Point-to-Point Current Loop System

Configuration.