Datasheet

R
2
R
4
V
O
R
5
R
6
R
3
V
2
+
-
R
1
V
IN
D
1
V
CC
V
1
LPV7215
SNOSAI6I –SEPTEMBER 2005–REVISED APRIL 2013 www.ti.com
Figure 37. Zero Crossing Detector with Positive Feedback
THRESHOLD DETECTOR
Instead of tying the inverting input to 0V, the inverting input can be tied to a reference voltage. As the input on
the non-inverting input passes the V
REF
threshold, the comparator’s output changes state. It is important to use a
stable reference voltage to ensure a consistent switching point.
Figure 38. Threshold Detector
CRYSTAL OSCILLATOR
A simple crystal oscillator using the LPV7215Q is shown in Figure 39. Resistors R
1
and R
2
set the bias point at
the comparator’s non-inverting input. Resistors, R
3
and R
4
and capacitor C
1
set the inverting input node at an
appropriate DC average level based on the output. The crystal’s path provides resonant positive feedback and
stable oscillation occurs. The output duty cycle for this circuit is roughly 50%, but it is affected by resistor
tolerances and to a lesser extent by the comparator offset.
Figure 39. Crystal Oscillator
IR RECEIVER
The LPV7215Q can also be used as an infrared receiver. The infrared photo diode creates a current relative to
the amount of infrared light present. The current creates a voltage across R
D
. When this voltage level crosses
the voltage applied by the voltage divider to the inverting input, the output transitions.
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