HCPL-4200 Datasheet, PDF (12/13 Pages) Agilent(Hewlett-Packard) – Optically Coupled 20 mA Current Loop Receiver

Figure 18. Recommended Non-Isolated Active Transmitter with HCPL-4200 Isolated Receiver for Simplex Point-to-Point 20 mA Current Loop.
Full Duplex
The full duplex point-to-point communication of Figure
21 uses a four wire system to provide simultaneous, bi-
directional data communication between local and re-
mote equipment. The basic application uses two simplex
point-to-point loops which have two separate, active,
non-isolated units at one common end of the loops. The
other end of each loop is isolated.
As Figure 21 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. The full duplex data
rate is limited by the non-isolated active receiver current
loop. Comments mentioned under simplex configura-
tion apply to the full duplex case. Consult the HCPL-4100
transmitter 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 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 configuration 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 eas-
ily accomplished, which results in substantial removal
Figure 19. Minimum Required Supply Voltage, V_CC, vs.
Loop Length for Current Loop Circuit of Figure 19.
12
Figure 20. Typical Data Rate vs. Distance.