TLC555-Q1 Datasheet, PDF (15/25 Pages) Texas Instruments – LinCMOS™ TIMER

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TLC555-Q1
SLFS078B – OCTOBER 2006 – REVISED OCTOBER 2015
Typical Applications (continued)
9.2.2.1 Design Requirements
Clock input must have V_OL and V_OH levels that are less than and greater than 1/3 VDD. Modulation input can
vary from ground to VDD. 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_A and C so that R_A × C = 1/4 [clock input period]. R_L improves V_OH, but it is not required for TTL
compatibility.
9.2.2.3 Application Curve
R_A = 3 kW
C = 0.02 mF
R_L = 1 kW
See Figure 18
Modulation Input Voltage
Clock Input Voltage
Output Voltage
Capacitor Voltage
Time − 0.5 ms/div
Figure 15. Pulse-Width-Modulation Waveforms
9.2.3 Pulse-Position Modulation
As shown in Figure 16, 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 17 shows a
triangular-wave modulation signal for such a circuit; however, any wave shape could be used.
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