TLC555CPWR datasheet(16/42 Pages) TI

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Low-to-high ratio

Output waveform duty cycle

= -

Output driver duty cycle

(

)

1.44

frequency

(

)

period

0.693 R

(

)

0.693 R

(

)

0.693 R

Time − 0.5 ms/div

Capacitor Voltage

Output Voltage

GND

OUT

VDD

CONT

RESET

DISCH

THRES

TRIG

Output

0.01

VDD

(5 V t o 15 V)

(see Note A)

Open

TLC555

SLFS043I – SEPTEMBER 1983 – REVISED JULY 2019

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Product Folder Links: TLC555

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Feature Description (continued)

7.3.2 Astable Operation

As shown in Figure 12, adding a second resistor, RB, to the circuit of Figure 9 and connecting the trigger input to

the threshold input causes the timer to self-trigger and run as a multi-vibrator. The capacitor C charges through

RA and RB and then discharges through RB only. Therefore, the duty cycle is controlled by the values of RA and

RB.

This astable connection results in capacitor C charging and discharging between the threshold-voltage level

(

≈ 0.67 × VCC) and the trigger-voltage level (≈ 0.33 × VCC). As in the monostable circuit, charge and discharge

times (and, therefore, the frequency and duty cycle) are independent of the supply voltage.

Decoupling CONT voltage to ground with a capacitor can improve

operation. This should be evaluated for individual applications.

Figure 12. Circuit for Astable Operation

RA = 5 kΩ

RB = 3 kΩ

C = 0.15 µF

See Figure 12

Figure 13. Typical Astable Waveforms

Figure 13 shows typical waveforms generated during astable operation. The output high-level duration tH and

low-level duration tL for frequencies below 100 kHz can be calculated as follows:

(1)

(2)

Other useful relationships are shown below:

(3)

(4)

(5)

(6)

(7)

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