LM339LVDR datasheet(28/63 Pages) TI1

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• Cstray (not shown) from VA TO GND = 10 pF

Figure 8-11. Square-Wave Oscillator Output Waveform

8.2.3 Adjustable Pulse Width Generator

Figure 8-12 is a variation on the square wave oscillator that allows adjusting the pulse widths.

R4 and R5 provide separate charge and discharge paths for the capacitor C depending on the output state.

100 kŸ

100 pF

100 kŸ

VCC

100 kŸ

OUT

1 MŸ

100 kŸ

Figure 8-12. Adjustable Pulse Width Generator

The charge path is set through R5 and D2 when the output is high. Similarly, the discharge path for the capacitor

is set by R4 and D1 when the output is low.

The pulse width t1 is determined by the RC time constant of R5 and C. Thus, the time t2 between the pulses

can be changed by varying R4, and the pulse width can be altered by R5. The frequency of the output can be

changed by varying both R4 and R5. At low voltages, the effects of the diode forward drop (0.8 V, or 0.15 V for

Shottky) must be taken into account by altering output high and low voltages in the calculations. RPU should be

at least 10x less than the smallest value of R4 or R5.

8.2.4 Time Delay Generator

The circuit shown in Figure 8-13 provides output signals at a prescribed time interval from a time reference and

automatically resets the output low when the input returns to 0V. This is useful for sequencing a "power on"

signal to trigger a controlled start-up of power supplies.

TL331LV, TL391LV, LM393LV, LM339LV

SNOSDA4C – JUNE 2020 – REVISED MARCH 2023

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LM339LVDR Datasheet(PDF) 28 Page - Texas Instruments