Datasheet

LMV710-N, LMV711-N, LMV715-N
www.ti.com SNOS519J –APRIL 2000–REVISED MARCH 2013
Figure 42. Peak Detector
The capacitor C
1
is first discharged by applying a positive pulse to the reset transistor. When a positive voltage
V
IN
is applied to the input, the input voltage is higher than the voltage across C
1
. The output of the op amp goes
high and forward biases the diode D
1
. The capacitor C
1
is charged to V
IN
. When the input becomes less than the
current capacitor voltage, the output of the op amp A1 goes low and the diode D
1
is reverse biased. This isolates
the C
1
and leaves it with the charge equivalent to the peak of the input voltage. The follower prevents
unintentional discharging of C
1
by loading from the following circuit.
R
5
and C
1
are properly selected so that the capacitor is charged rapidly to V
IN
. During the holding period, the
capacitor slowly discharge through C
1
, via leakage of the capacitor 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
2
and R
3
limit the current into the inverting input of A1 and the non-inverting input of A2 when power
is disconnected from the circuit. The discharging current from C
1
during power off may damage the input circuitry
of the op amps.
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
+
- V
D
), where V
D
is the forward voltage drop
of the 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 43) is commonly used in a battery charger to monitor charging
current to prevent over-charging. A sense resistor R
SENSE
is connected to the battery directly. This system
requires an op amp with rail-to-rail input. The LMV710-N/LMV711/LMV715 are ideal for this application because
its common mode input range can go beyond the positive rail.
Figure 43. High Side Current Sensing
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