HCPL-4100 Datasheet, PDF (11/12 Pages) Agilent(Hewlett-Packard) – Optically Coupled 20 mA Optically Coupled 20 mA

As Figure 16 illustrates, the combination of Avago current
loop optocouplers, HCPL-4100 transmitter and HCPL-4200
receiver, can be used at the isolated end of current loops.
Cross talk and common mode coupling are greatly reduced
when optical isolation is implemented at the same end of
both loops, as shown. Full duplex data rate is limited by the
non-isolated active transmitter current loop. Comments
mentioned under simplex configuration apply to the full
duplex case. Consult the HCPL-4200 receiver optocoupler
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 transmitters shown in Figures 17a and
17b.This configuration allows the use of two wires to carry
data back and forth between local and remote units. How-
ever, 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 configuration section.
Figures 17a and 17b 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 isola-
tion at one end of the current loop is easily accomplished,
which results in substantial removal of common mode
influences, elimination of ground potential differences
and reduction of power supply requirements. With this
combination of HCPL-4100/-4200 optocouplers, specific
current loop noise immunity is provided, i.e., minimum
SPACE state current noise immunity is 1 mA, MARK state
noise immunity is 8 mA.
Voltage compliance of the current source must be of an
adequate level for operating all units in the loop while
not exceeding 27 V dc, the maximum breakdown voltage
for the HCPL-4100. Note that the HCPL-4100 transmitter
will allow output loop current to conduct when input V
CC
power is off. Consult the HCPL-4200 receiver optocoupler
data sheet for specified device performance.
For more information about the HCPL-4100/-4200 opto-
couplers, consult Application Note 1018.
Figure 16. Full Duplex Point to Point Current Loop System Configuration.
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