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,
Figure 9. Operating Circuit for Burn-In and Steady State Life Tests.
Rx, to determine larger external
threshold voltage levels. For a
desired external threshold
voltage, V , a corresponding
typical value of Rx can be
obtained from Figure 10. Specific
calculation of Rx 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
detector IC from destructively
high surge currents. See note 14
for determination of RCC. 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.
use of Rx and Rp as shown in
Figure 11 and determined by
Equations (2) and (3).
For interfacing ac signals to TTL
systems, output low pass filtering
Figure 10. Typical External Threshold
Characteristic, V vs. Rx.
Rx 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 Rx
and Rp can be used to allow a
specific current to be conducted
through the contacts for cleaning
purposes (wetting current).
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.
For two specifically selected
external threshold voltage levels,
V+ and V-, the use of Rx and Rp
will permit this selection via
equations (2), (3) provided the
following conditions are met:
Either ac (Pins 1, 4) or dc (Pins
2, 3) input can be used to
determine external threshold
levels.
The choice of which input voltage
clamp level to choose depends
upon the application of this
device (see Figure 3). It is
V+ VTH+
––– ≥ ––– and ––+–––––– < ––––
V- VTH- V- - VTH- ITH-
V - VTH+
ITH+
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.
VTH- (V+) - VTH+ (V-)
Rx = –––––––––––––––––––– (2)
ITH+ (VTH-) - ITH- (VTH+
For one specifically selected
external threshold voltage level
V+ or V-, Rx can be determined
without use of Rp via
)
RP =
VTH- (V+) - VTH+ (V-)
–––––––––––––––––––––––––––(3)
ITH+ (V- - VTH-) + ITH- (VTH+ - V+)
V+ - VTH+
In applications where dVCM/dt may
be extremely large (such as static
discharge), a series resistor, RCC,
should be connected in series
(-)
(-)
Rx = –––––––––
(1)
ITH+
(-)
See Application Note 1004 for
more information.
with VCC and Pin 8 to protect the
HP [ HEWLETT-PACKARD ]
