Datasheet

Table Of Contents

Voltage − 2 V/div

Time − 0.5 ms/div

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Capacitor Voltage

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Output Voltage

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Clock Input Voltage

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= 3 kΩ

C = 0.02 µF

= 1 kΩ

See Figure 18

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Modulation Input Voltage

NA555

NE555

SA555

SE555

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SLFS022I –SEPTEMBER 1973–REVISED SEPTEMBER 2014

Typical Applications (continued)

9.2.2.1 Design Requirements

Clock input must have V

and V

levels that are less than and greater than 1/3 VCC. Modulation input can

vary from ground to VCC. The application must be tolerant of a nonlinear transfer function; the relationship

between modulation input and pulse width is not linear because the capacitor charge is based RC on an negative

exponential curve.

9.2.2.2 Detailed Design Procedure

Choose R

and C so that R

× C = 1/4 [clock input period]. R

improves V

, but it is not required for TTL

compatibility.

9.2.2.3 Application Curves

Figure 19. Pulse-Width-Modulation Waveforms

9.2.3 Pulse-Position Modulation

As shown in Figure 20, any of these timers can be used as a pulse-position modulator. This application

modulates the threshold voltage and, thereby, the time delay, of a free-running oscillator. Figure 21 shows a

triangular-wave modulation signal for such a circuit; however, any wave shape could be used.

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