HCPL-0370 View Datasheet(PDF) - HP => Agilent Technologies
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HCPL-0370 Datasheet PDF : 13 Pages
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13
Figure 13. External Threshold Voltage Level Selection.
Electrical Considerations
The HCPL-0370/3700/3760
optocouplers have internal
temperature compensated,
predictable voltage and current
threshold points which allow
selection of an external resistor,
RX, to determine larger external
threshold voltage levels. For a
desired external threshold
voltage, V± , a corresponding
typical value of RX can be ob-
tained from Figure 12. Specific
calculation of RX can be obtained
from Equation (1). Specification
of both V+ and V- voltage
threshold levels simultaneously
can be obtained by the use of RX
and RP as shown in Figure 13 and
determined by Equations (2) and
(3).
RX can provide over-current
transient protection by limiting
input current during a transient
condition. For monitoring con-
tacts of a relay or switch, the
HCPL-0370/3700/3760 in
combination with RX and RP 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 1). It is recom-
mended that the low clamp
condition be used when possible.
The low clamp condition in
conjunction with the low input
current feature will ensure
extremely low input power
dissipation.
In applications where dVCM/dt
may be extremely large (such as
static discharge), a series resistor,
RCC, should be connected in
series with VCC and Pin 8 to pro-
tect the detector IC from destruc-
tively high surge currents. See
Note 13 for determination of RCC.
In addition, it is recommended
that a ceramic disc bypass
capacitor of 0.01 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-, RX can be determined
without use of RP via
V+ (--V) TH+(-)
RX =
(1)
I
TH+
(-)
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. If
the denominator of equation (2)
is positive, then
V+ ≥ VTH+ and V+ - VTH+ < ITH+
V-
VTH-
V- - VTH- ITH-
Conversely, if the denominator of
equation (2) is negative, then
V+ ≤ VTH+ and V+ - VTH+ > ITH+
V-
VTH-
V- - VTH- ITH-
VTH- (V+) - VTH+ (V-)
RX =
(2)
ITH+ (VTH-) - ITH- (VTH+)
VTH- (V+) - VTH+ (V-)
RP =
(3)
ITH+(V--VTH-)+ITH-(VTH+-V+)
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distributors, please go to our web site.
For technical assistance call:
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(916) 788-6763
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Data subject to change.
Copyright © 2004 Agilent Technologies, Inc.
Obsoletes 5989-0785EN
December 20, 2004
5989-2101EN
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