N555 datasheet(10/27 Pages) TI

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C − Capacitance −

µF

10−1

10−2

10−3

10−4

100

0.1

0.01

10−5

0.001

RA = 10 MΩ

RA = 10 kΩ

RA = 1 kΩ

RA = 100 kΩ

RA = 1 MΩ

Time − 0.1 ms/div

Capacitor Voltage

Output Voltage

Input Voltage

RA = 9.1 kΩ

CL = 0.01 µF

RL = 1 kΩ

See Figure 9

Astable Operation

Time − 0.5 ms/div

Capacitor Voltage

Output Voltage

RA = 5 kW

RL = 1 kW

RB = 3 kW

See Figure 12

C = 0.15

µF

GND

OUT

VCC

CONT

RESET

DISCH

THRES

TRIG

Output

0.01

µF

VCC

(5 V to 15 V)

(see Note A)

NOTE A: Decoupling CONT voltage to ground with a capacitor can

improve operation. This should be evaluated for individual

applications.

Open

Pin numbers shown are for the D, JG, P, PS, and PW packages.

NA555, NE555, SA555, SE555

PRECISION TIMERS

SLFS022F – SEPTEMBER 1973 – REVISED JUNE 2006

APPLICATION INFORMATION (continued)

Figure 10. Typical Monostable Waveforms

Figure 11. Output Pulse Duration vs Capacitance

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 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 × V

CC) 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.

Figure 12. Circuit for Astable Operation

Figure 13. Typical Astable Waveforms

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