SE555CD datasheet(10/15 Pages) TI

10 / 15 page

SLFS022 – D1669, SEPTEMBER 1973—REVISED FEBRUARY 1992

NE555, SA555, SE555, SE555C

PRECISION TIMERS

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

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 multivibrator. The capacitor C will charge

through RA and RB and then discharge through RB only. The duty cycle may be controlled, therefore, 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.

GND

OUT

VCC

CONT

RESET

DISCH

THRES

TRIG

Output

0.01

µF

VCC

(5 V to 15 V)

(see Note A)

Time – 0.5 ms/div

Capacitor Voltage

Output Voltage

RA = 5 kΩ

RL = 1 kΩ

RB = 3 kΩ

See Figure 12

C = 0.15

µF

NOTE A: Decoupling CONT voltage to ground with a

capacitor may improve operation. This should be

evaluated for individual applications.

Open

Pin numbrs shown are for the D, JG, and P packages.

Figure 12. Circuit for Astable Operation

Figure 13. Typical Astable Waveforms

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