LMV715MF NSC [National Semiconductor], LMV715MF Datasheet - Page 13

• Manufacturer Part Number: LMV715MF
• Description: Low Power, RRIO Operational Amplifiers with High Output Current Drive and Shutdown Option
• Manufacturer: NSC [National Semiconductor]

Application Note
The capacitor C
pulse to the reset transistor. When a positive voltage V
applied to the input, the input voltage is higher than the
voltage across C
forward biases the diode D
V
voltage, the output of the op amp A1 goes low and the diode
D
the charge equivalent to the peak of the input voltage. The
follower prevents unintentional discharging of C
from the following circuit.
R
charged rapidly to V
tor slowly discharge through C
and the reverse-biased diode, or op amp bias currents. In
any cases the discharging time constant is much larger than
the charge time constant. And the capacitor can hold its
voltage long enough to minimize the output ripple.
Resistors R
of A1 and the non-inverting input of A2 when power is
disconnected from the circuit. The discharging current from
C
amps.
IN
1
5
1
. When the input becomes less than the current capacitor
during power off may damage the input circuitry of the op
is reverse biased. This isolates the C
and C
1
2
are properly selected so that the capacitor is
and R
FIGURE 7. Peak Detector
1
1
. The output of the op amp goes high and
is first discharged by applying a positive
3
IN
limit the current into the inverting input
. During the holding period, the capaci-
1
. The capacitor C
1
(Continued)
, via leakage of the capacitor
1
and leaves it with
1
is charged to
1
by loading
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IN
is
13
The peak detector can be reset by applying a positive pulse
to the reset transistor. The charge on the capacitor is
dumped into ground, and the detector is ready for another
cycle.
The maximum input voltage to this detector should be less
than (V
diode. Otherwise, the input voltage should be scaled down
before applying to the circuit.
HIGH SIDE CURRENT SENSING
The high side current sensing circuit (Figure 8) is commonly
used in a battery charger to monitor charging current to
prevent over-charging. A sense resistor R
to the battery directly. This system requires an op amp with
rail-to-rail input. The LMV710/711/715 are ideal for this ap-
plication because its common mode input range can go
beyond the positive rail.
+
- V
FIGURE 8. High Side Current Sensing
D
), where V
D
is the forward voltage drop of the
sense
is connected
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