TLC555-Q1 Datasheet, PDF (10/13 Pages) Texas Instruments – LinCMOS™ TIMER

TLC555-Q1
LinCMOS™ TIMER
SLFS078 – OCTOBER 2006
APPLICATION INFORMATION (continued)
The following equations provide better agreement with measured values.
ƪ ǒ Ǔ ƫ tc(H) + CT (RA ) RB) In
3 –exp
– t _PLH
CT (RB ) ron)
) tPHL
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ƪ ǒ Ǔ ƫ tc(L) + CT (RB ) ron) In
3 –exp
– t _PHL
CT (RA ) RB)
) tPLH
These equations and those given previously 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
tc(H)
tc(H)
can be substituted with good results. Duty cycles less than 50% ^{tc(H) ) tc(L)} require that ^tc(L) < 1 and
possibly R_A ≤ r_on. These conditions can be difficult to obtain.
In monostable applications, the trip point on TRIG 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.
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