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LMC555 astable frequency question

Peter Chen(ICP_FAE)
Intellectual 2480 points
Other Parts Discussed in Thread: LMC555

the formula in LMC555 astable condition is not matching. I put the parameters as figure2 of LMC555 datasheet, the maximum frequency is around 9MHz and not matching to datasheet describe(3Mhz maximum in astable mode). Is there anything i miss?

  • 0
    TI__Genius 16890 points

    Hi Peter,

    Formula 4 in the datasheet works best in the range as shown in Figure 8 of the datasheet.  As the operation is placed into the higher frequencies that are not shown in the graph it gets inaccurate.  This is caused by the LMC555 itself, along with the parasitics in the circuit.  In the higher frequencies the formula will need to be used as a staring point and then the parts adjusted to get the performance needed.


    Mike