TLC551, TLC551Y

LinCMOS

™ TIMERS

SLFS044B – FEBRUARY 1984 – REVISED SEPTEMBER 1997

11

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

APPLICATION INFORMATION

The equations below provide better agreement with measured values.

t

c(H) +

C

T

(R

A )

R

B

)In 3– exp

–t

PLH

C

T

(R

B )

ron)

) t

PHL

t

c(L) +

C

T

(R

B )

ron)In 3–exp

–t

PHL

C

T

(R

A )

R

B

)

) t

PLH

These equations and those given earlier are similar in that a time constant is multiplied by the logarithm of a number

or function. The limit values of the logarithmic terms must be between In 2 at low frequencies and In 3 at extremely

high frequencies. For a duty cycle close to 50%, an appropriate constant for the logarithmic terms can be substituted

with good results. Duty cycles less than 50%

t

c(H)

t

c(H) )

t

c(L)

require that

t

c(H)

t

c(L)

<1 and possibly RA ≤ ron. These

conditions can be difficult to obtain.

In monostable applications, the trip point of the trigger input can be set by a voltage applied to CONT. An input voltage

between 10% and 80% of the supply voltage from a resistor divider with at least 500-

µA bias provides good results.