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

Figure 22. Half Duplex Current Loop System Configurations for (a) Point-to-Point, (b) Multidrop.

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AV02-2353EN - February 8, 2010

of common mode influences, elimination of ground

potential differences and reduction of power supply re-

quirements. With this combination of HCPL-4100/-4200

optocouplers, specific current loop noise immunity is

provided, i.e., minimum SPACE state current noise im-

munity 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 loop current to conduct when input V

CC

power

is off. Consult the HCPL-4100 transmitter optocoupler

data sheet for specified device performance.

For more information about the HCPL-4100/-4200 opto-

couplers, consult Application Note 1018.