Figure 12. Recommended Non-Isolated Active Receiver with HCPL-4100 Isolated Transmitter for Simplex Point to Point
20 mA Current Loop.
25% distortion data rate at
different V
CC
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 V
CC
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%.
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.
Full Duplex
The full duplex point-to-point
communication of Figure 15 uses
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.
40
36
32
28
V
V
CC
= 0.00212 — (L) + 5.7 V
m
R
CABLE
= 0.05296
Ω/m
I
LOOP
= 20 mA
V
MARK
= 2.7 Vdc (HCPL-4100)
V
SAT
= 1.5 Vdc (CURRENT SOURCE)
T
A
= 25 °C
V
CC
– VOLTS
24
20
16
12
8
4
0
0
100
1000
10000
L – LOOP LENGTH (ONE DIRECTION) METERS
Figure 13. Minimum Required Supply
Voltage, V
CC
, vs. Loop Length for
Current Loop Circuit of Figure 13.
Figure 14. Typical Data Rate vs.
Distance and Supply Voltage.
1-370
AGILENT [ AGILENT TECHNOLOGIES, LTD. ]
