Datasheet

12
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 great-
ly reduced when optical isolation is implemented 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 congura-
tion apply to the full duplex case. Consult the HCPL-
4100 transmitter optocoupler data sheet for specied
device performance.
Half Duplex
The half duplex conguration, whether point-to-point
or multidrop, gives non-simultaneous bidirectional data
ow from transmitters to receivers shown in Figures 22a
and 22b. This conguration 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 specic transmitter can operate at any given
time. Maximum data rate for a half duplex system is
limited by the loop current charging time. These con-
siderations were explained in the Simplex conguration
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 benets. For example, total
optical isolation at one end of the current loop is easily
accomplished, which results in substantial removal of
common mode inuences, elimination of ground po-
tential
Figure 19. Minimum Required Supply Voltage, V
CC
, vs.
Loop Length for Current Loop Circuit of Figure 19.
Figure 20. Typical Data Rate vs. Distance.