10
Figure 12. Recommended Non-Isolated Active Receiver with HCPL-4100 Isolated Transmitter for Simplex Point to Point
20 mA Current Loop.
The cable used contained five
pairs of unshielded, twisted, 22
AWG wire (Dearborn #862205).
Loop current is 20 mA nominal.
Input and output logic supply
voltages are 5 V dc.
a four wire system to provide
simultaneous, bidirectional data
communication between local
and remote 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.
25% distortion data rate at
different VCC values. 25%
distortion data rate is defined as
that rate at which 25% distortion
occurs to output bit interval with
respect to the input bit interval.
Maximum data rate (dotted line)
is restricted by device character-
istics. An input Non-Return-to-
Zero (NRZ) test waveform of 16
bits (0000001011111101) was
used for data rate distortion
measurements. Enhanced speed
performance of the loop system
can be obtained with lower VCC
supply levels, as illustrated in
Figure 14. In addition, when loop
current is supplied through a
resistor instead of by a current
source, an additional series
termination resistance equal to
the characteristic line impedance
can be used at the HCPL-4100
transmitter end to enhance speed
of response by approximately
20%.
Full Duplex
The full duplex point-to-point
communication of Figure 15 uses
40
36
32
V
V
= 0.00212 — (L) + 5.7 V
m
CC
R
I
= 0.05296 Ω/m
CABLE
= 20 mA
LOOP
28
24
20
16
12
V
V
T
= 2.7 Vdc (HCPL-4100)
= 1.5 Vdc (CURRENT SOURCE)
MARK
SAT
= 25 °C
A
8
4
0
0
100
1000
10000
L – LOOP LENGTH (ONE DIRECTION) METERS
Figure 13. Minimum Required Supply
Voltage, VCC, vs. Loop Length for
Current Loop Circuit of Figure 13.
Figure 14. Typical Data Rate vs.
Distance and Supply Voltage.
AGILENT [ AGILENT TECHNOLOGIES, LTD. ]
