200
t
p
– ENABLE PROPAGATION DELAY – ns
t
p
– ENABLE PROPAGATION DELAY – ns
100
C
L
= 15 pF
V
CC
20 V
C
L
= 15 pF
80
t
PLZ
60
V
CC
20 V
150
t
PHZ
4.5 V
100
4.5 V
20 V
40
t
PZL
20
4.5 V
20 V
50
t
PZH
0
-60
4.5 V
-40
-20
0
20
40
60
80
100
0
-60
-40
-20
0
20
40
60
80
100
T
A
– TEMPERATURE –°C
T
A
– TEMPERATURE –°C
Figure 14. Typical Logic High Enable Propagation Delay vs.
Temperature.
Figure 15. Typical Logic Low Enable Propagation Delay vs.
Temperature.
Figure 16. Test Circuit for Common Mode Transient
Immunity.
Applications
Data transfer between equipment
which employs current loop
circuits can be accomplished via
one of three configurations:
simplex, half duplex or full
duplex communication. With
these configurations, point-to-
point and multidrop arrangements
are possible. The appropriate
configuration to use depends
upon data rate, number of
stations, number and length of
lines, direction of data flow,
protocol, current source location
and voltage compliance value,
etc.
Simplex
The simplex configuration,
whether point to point or multi-
drop, gives unidirectional data
flow from transmitter to
receiver(s). This is the simplest
configuration for use in long line
length (two wire), for high data
rate, and low current source
compliance level applications.
Block diagrams of simplex point-
to-point and multidrop
arrangements are given in
Figures 17a and 17b respectively
for the HCPL-4200 receiver
optocoupler.
For the highest data rate per-
formance in a current loop, the
configuration of a non-isolated
active transmitter (containing
current source) transmitting data
to a remote isolated receiver(s)
should be used. When the current
source is located at the trans-
mitter end, the loop is charged
approximately to V
MI
(2.5 V).
Alternatively, when the current
source is located at the receiver
end, the loop is charged to the
full compliance voltage level. The
lower the charged voltage level
the faster the data rate will be. In
the configurations of Figures 17a
and 17b, data rate is independent
of the current source voltage
compliance level. An adequate
compliance level of current
source must be available for
voltage drops across station(s)
during the MARK state in multi-
drop applications or for long line
length. The maximum compliance
level is determined by the trans-
mitter breakdown characteristic.
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
standard TTL 7407 buffer to
provide high output impedance of
current source in both the ON
1-381
AGILENT [ AGILENT TECHNOLOGIES, LTD. ]
