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TS3V555

3V LOW POWER SINGLE TIMERS

STMicroelectronics 

TS3V555

ASTABLE OPERATION

When the circuit is connected as shown in figure 4

(pin 2 and 6 connected) it triggers itself and free

runs as a multivibrator. The external capacitor

charges through RA an d RB and discharges

through RB only. Thus the duty cycle may be pre-

cisely set by the ratio of these two resistors.

In the astable mode of operation, C charges and

discharges between 1/3 VCC and 2/3 VCC. As in the

triggered mode, the charge and discharge times

and therefore frequency, are independent of the

supply voltage.

Figure 5 shows actual waveforms generated in this

mode of operation.

Figure 4

VCC

Reset

RA

4

8

Out

3

7

TS3V555

RB

The charge time (output HIGH) is given by :

t1 = 0.693 (RA + RB) C

and the discharge time (output LOW) by :

t2 = 0.693 (RB) C

Thus the total period T is given by :

T = t1 + t2 = 0.693 (RA + 2RB) C

The frequency of oscillation is then :

f

=

1

T

=

(RA

1.44

+ 2RB)

C

The

duty

cycle

is

given

by

:

D

=

RA

RB

+ 2RB

Figure 5

t = 0.5 ms / div

OUTPUT VOLTAGE = 5.0V/div

Control

Voltage

0.01 µF

5

1

6

2

C

CAPACITOR VOLTAGE = 1.0V/div

RA = RB = 4.8 kΩ, C = 0.1 µ F , R L = 1.0kΩ

6/8

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