LMV393-SM1-R datasheet(6/11 Pages) UTC

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LMV393

LINEAR INTEGRATED CIRCUIT

UNISONICTECHNOLOGIESCO.,LTD

6 of 11

www.unisonic.com.tw

QW-R104-004,A

APPLICATION CIRCUITS(Cont.)

Square Wave Oscillator

Comparators are suitable for oscillator applications. This application uses the minimum number of external

components. The output frequency is set by the RC time constant which is determined by capacitor C1 and the

resistor in the negative feedback R4 of the comparator. Capacitive load at the output would degrade the output slew

rate and limit the maximum operating frequency.

100k

4.3k

VOUT

100k

75pF

t = 0

Va2

Va1

-Vcc

Vc1

Squarewave Oscillator

VOUT

At first, assume that the output is high, so the voltage at the inverting input VC is less than the voltage at the

non-inverting input Va, the capacitor C1 has to be discharged. When it has charged up to value equal to the positive

input voltage Va1, the comparator output will switch.

Va1 will be given by:

If: R1=R2=R3

Then:

When the output switches to ground, the value of Va is reset by the resistor network:

Then capacitor C1 discharge through a resistor towards ground. The output will return to its high state when the

voltage across the capacitor has discharged to a value equal to Va2.The time to charge the capacitor can be

calculated from:

Where VMAX =2VCC/3 and VC = VCC/3

One period will be given by: 1/freq = 2t or calculating the exponential gives: 1/freq = 2(0.694) R4 C1Resistors R3

and R4 must be at least two times larger than R5 to insure a reasonable VO. The frequency stability of this circuit

should strictly be a function of the external components.

LMV393-SM1-R Datenblatt(PDF) 6 Page - Unisonic Technologies