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LMC555: Should we need pull high LMC555 output pin?

Shu-Cheng LIN
Guru 11785 points
Part Number: LMC555


Hi Sirs,

Sorry to bother you.

As title, should we need pull high the LMC555 output pin?
Because if we follow datasheet page 8 fig3 to design, the output will be always high, even if i manually to trigger low.

But if we pull high output pin, the function is normal.

We don't saw any output state description on datasheet, could you help share your experience for us?
Thanks for your reply.

  • 0
    TI__Guru**** 165566 points
    Shu-Cheng,

    If TRIGGER held low (and ~RESET high) then output will always be high.
    If TRIGGER is high long enough for RC time constant then output will go low.

    The TRIGGER negative pulse width needs to be shorter the the output positive pulse width.