9
Electrical Considerations
The HCPL-5760, HCPL-5761,
HCPL-576K or 5962-89477
optocoupler has internal
temperature compensated,
predictable voltage and current
threshold points which allow
selection of an external resistor,
R
x
, to determine larger external
threshold voltage levels. For a
desired external threshold
voltage, V
±
, a corresponding
typical value of R
x
can be
obtained from Figure 10. Specific
calculation of R
x
can be obtained
from Equation (1) of Figure 11.
Specification of both V
+
and V
-
voltage threshold levels simulta-
neously can be obtained by the
use of R
x
and R
p
as shown in
Figure 11 and determined by
Equations (2) and (3).
R
x
can provide over-current
transient protection by limiting
input current during a transient
condition. For monitoring
contacts with a relay or switch,
the HCPL-5760/1/K, or
5962-89477 combination with R
x
and R
p
can be used to allow a
specific current to be conducted
through the contacts for cleaning
purposes (wetting current).
The choice of which input voltage
clamp level to choose depends
upon the application of this
device (see Figure 3). It is
recommended that the low clamp
condition be used when possible
to lower the input power
dissipation as well as the LED
current, which minimizes LED
degradation over time.
In applications where dV
CM/dt
may
be extremely large (such as static
discharge), a series resistor, R
CC
,
should be connected in series
with V
CC
and Pin 8 to protect the
Figure 9. Operating Circuit for Burn-In and Steady State Life Tests.
detector IC from destructively
high surge currents. See note 14
for determination of R
CC
. In
addition, it is recommended that a
ceramic disc bypass capacitor of
0.01
µF
to 0.1
µF
be placed
between Pins 8 and 5 to reduce
the effect of power supply noise.
For interfacing ac signals to TTL
systems, output low pass filtering
can be performed with a pullup
resistor of 1.5 kΩ and 20
µF
capacitor. This application
requires a Schmitt trigger gate to
avoid slow rise time chatter
problems. For ac input applica-
tions, a filter capacitor can be
placed across the dc input
terminals for either signal or
transient filtering.
Either ac (Pins 1, 4) or dc (Pins
2, 3) input can be used to
determine external threshold
levels.
For one specifically selected
external threshold voltage level
V
+
or V
-
, R
x
can be determined
without use of R
p
via
V
+
- V
TH+
(-)
(-)
R
x
= –––––––––
(1)
I
TH+
(-)
Figure 10. Typical External Threshold
Characteristic, V
±
vs. R
x
.
For two specifically selected
external threshold voltage levels,
V
+
and V
-
, the use of R
x
and R
p
will permit this selection via
equations (2), (3) provided the
following conditions are met:
V
+
V
TH+
V
+
- V
TH+
I
TH+
–––
≥
––– and –––––––– < ––––
V
-
V
TH-
V
-
- V
TH-
I
TH-
V
TH-
(V
+
) - V
TH+
(V
-
)
R
x
= –––––––––––––––––––– (2)
I
TH+
(V
TH-
) - I
TH-
(V
TH+
)
R
P
=
V
TH-
(V
+
) - V
TH+
(V
-
)
––––––––––––––––––––––––––– (3)
I
TH+
(V
-
- V
TH-
) + I
TH-
(V
TH+
- V
+
)
See Application Note 1004 for
more information.
HP [ AGILENT(HEWLETT-PACKARD) ]
