TLC556, TLC556Y

DUAL LinCMOS

™ TIMERS

SLFS047B – FEBRUARY 1984 – REVISED SEPTEMBER 1997

10

POST OFFICE BOX 655303

APPLICATION INFORMATION

0.1

µF

0.1

µF

CT

CL

RL

Output

RB

RA

GND

TRIG

THRES

RESET

DISCH

CONT

VDD

OUT

VDD

2/3 VDD

1/3 VDD

GND

tPHL

tPLH

tH

tL

CIRCUIT

TRIGGER AND THRESHOLD VOLTAGE WAVEFORM

TLC556

Figure 3. Astable Operation

Connecting the trigger input to the threshold input, as shown in Figure 3, causes the timer to run as a

tH [ CT (RA ) RB) In 2 (In 2 + 0.693)

tL [ CT RB In 2

Period

+ t

H ) tL [ CT (RA ) 2RB)In 2

Output driver duty cycle

+

tL

tH ) tL

[ 1 *

RB

R

A )

2RB

Output waveform duty cycle

+

tH

tH ) tL

[

RB

R

A )

2RB

The 0.1-

µF capacitor at CONT in Figure 3 decreases the period by about 10%.

The formulas shown above do not allow for any propagation delay from the trigger and threshold inputs to the

discharge output. These delay times add directly to the period and create differences between calculated and

The equations below provide better agreement with measured values.

tH + CT (RA ) RB)In

3

* exp

* t

PLH

CT (RB ) ron)

) t

PHL

tL + CT (RB ) ron)In

3

* exp

* t

PHL

CT (RA ) RB)

) t

PLH