LPV7215 datasheet(16/28 Pages) TI1

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VIN

VCC

LPV7215

SNOSAI6I – SEPTEMBER 2005 – REVISED APRIL 2013

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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 VREF 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 R1 and R2 set the bias point at

the comparator’s non-inverting input. Resistors, R3 and R4 and capacitor C1 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 RD. When this voltage level crosses

the voltage applied by the voltage divider to the inverting input, the output transitions.

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