LPV7215 datasheet(15/28 Pages) TI1

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VCC

VREF

VIN

VIN2 =

VREF (R1 + R2) ± VCC R1

R1 + R2

VA = VIN +

(VCC-VIN1) R1

LPV7215

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SNOSAI6I – SEPTEMBER 2005 – REVISED APRIL 2013

To make the comparator switch back to it’s low state, VIN must equal VREF before VA will again equal VREF. VIN2

can be calculated by

The hysteresis of this circuit is the difference between VIN1 and VIN2.

ΔVIN = VCCR1/R2

Figure 35. Non-Inverting Comparator with Hysteresis

ZERO CROSSING DETECTOR

In a zero crossing detector circuit, the inverting input is connected to ground and the non-inverting input is

connected to a 100 mVPP AC signal. As the signal at the non-inverting input crosses 0V, the comparator’s output

changes state.

Figure 36. Zero Crossing Detector

To improve switching times and to center the input threshold to ground a small amount of positive feedback is

added to the circuit. The voltage divider, R4 and R5, establishes a reference voltage, V1, at the positive input. By

making the series resistance, R1 plus R2 equal to R5, the switching condition, V1 = V2, will be satisfied when VIN

= 0. The positive feedback resistor, R6, is made very large with respect to R5 (R6 = 2000 R5). The resultant

hysteresis established by this network is very small (

ΔV1 < 10 mV) but it is sufficient to insure rapid output

voltage transitions. Diode D1 is used to insure that the inverting input terminal of the comparator never goes

below approximately

−100 mV. As the input terminal goes negative, D1 will forward bias, clamping the node

between R1 and R2 to approximately −700 mV. This sets up a voltage divider with R2 and R3 preventing V2 from

going below ground. The maximum negative input overdrive is limited by the current handling ability of D1.

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