HCPL-4200 Datasheet, PDF (11/13 Pages) Agilent(Hewlett-Packard) – Optically Coupled 20 mA Current Loop Receiver

Figure 17. Simplex Current Loop System Configurations for (a) Point-to-Point, (b) Multidrop.
A recommended non-isolated active transmitter circuit
which can be used with the HCPL-4200 in point-to-point
or in multidrop 20 mA current loop applications is given
in Figure 18. The current source is controlled via a stan-
dard TTL 7407 buffer to provide high output impedance
of current source in both the ON
and OFF states. This non-isolated active transmitter pro-
vides a nominal 20 mA loop current for the listed values
of V , R2 and R3 in Figure 18.
CC
Length of current loop (one direction) versus minimum
required DC supply voltage, V_CC, of the circuit in Figure 18
is graphically illustrated in Figure 19. Multidrop configu-
rations will require larger V than Figure 19 predicts in
CC
order to account for additional station terminal voltage
drops.
Typical data rate performance versus distance is illus-
trated in Figure 20 for the combination of a non-isolated
active transmitter and HCPL-4200 optically coupled cur-
rent loop receiver shown in Figure 18. Curves are shown
for 10% and 25% distortion data rate. 10% (25%) distor-
tion data rate is defined as that rate at which 10% (25%)
distortion occurs to output bit interval with respect to
input bit interval. An input Non-Return-to-Zero (NRZ)
test waveform of 16 bits (0000001011111101) was used
for data rate distortion measurements. Data rate is inde-
pendent of current source supply voltage, V .
CC
The cable used contained five pairs of unshielded, twist-
ed, 22 AWG wire (Dearborn #862205). Loop current is 20
mA nominal. Input and output logic supply voltages are
5 V dc.
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