LMC6772AIMMX_NOPB Datasheet, PDF (15/25 Pages) Texas Instruments – Dual Micropower Rail-To-Rail Input CMOS Comparator with Open Drain Output

LMC6772
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SNOS749F – SEPTEMBER 1995 – REVISED MARCH 2013
A bi-stable multivibrator has two stable states. The reference voltage is set up by the voltage divider of R₂ and
R₃. A pulse applied to the SET terminal will switch the output of the comparator high. The resistor divider of R₁,
R₄, and R₅ now clamps the non-inverting input to a voltage greater than the reference voltage. A pulse applied to
RESET will now toggle the output low.
ZERO CROSSING DETECTOR
Figure 35. Zero Crossing Detector
A voltage divider of R₄ and R₅ establishes a reference voltage V₁ at the non-inverting input. By making the series
resistance of R₁ and R₂ equal to R₅, the comparator will switch when V_IN = 0. Diode D₁ insures that V₃ never
drops below −0.7V. The voltage divider of R₂ and R₃ then prevents V₂ from going below ground. A small amount
of hysteresis is setup to ensure rapid output voltage transitions.
OSCILLATOR
Figure 36. Square Wave Generator
Figure 36 shows the application of the LMC6772 in a square wave generator circuit. The total hysteresis of the
loop is set by R₁, R₂ and R₃. R₄ and R₅ provide separate charge and discharge paths for the capacitor C. The
charge path is set through R₄ and D₁. So, the pulse width t₁ is determined by the RC time constant of R₄ and C.
Similarly, the discharge path for the capacitor is set by R₅ and D₂. Thus, the time t₂ between the pulses can be
changed by varying R₅, and the pulse width can be altered by R₄. The frequency of the output can be changed
by varying both R₄ and R₅.
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