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TLC555: Frequency offset issue

Jiaqi Wang
Intellectual 2220 points
Part Number: TLC555
Other Parts Discussed in Thread: TLC3555-Q1, ,

Tool/software:

Hi team,

My customer is using TLC555DR in their project. And they want the output frequency to keep from 155KHz to 220KHz. Customer wants to know how to keep the frequency in this limitation and would like to know the frequency offset of this device because they didn't find this spec in datasheet. Thanks!

BR,

Jiaqi 

  • 0
    TI__Guru**** 165396 points

    Hello Jiaqi,

    Previous to latest TLC555 PCN, this would be a very easy task. For TLC555-Q1 and TLC3555-Q1 it is still an easy task.

    What is the desired supply voltage and output duty cycle? Do they prefer TLC555-Q1 or TLC3555-Q1?

    Jiaqi Wang said:
    because they didn't find this spec in datasheet.

    Yes, true. This is why it is now hard to keep this window. 

  • 0 in reply to Ron Michallick
    TI__Intellectual 2220 points

    Hi Ron,

    Do you mean customer needs to move to TLC555-Q1 to make sure the frequency range? Do we have a file to describe the details of this? 

    Br,

    Jiaqi

  • 0 in reply to Jiaqi Wang
    TI__Guru**** 165396 points

    Jiaqi,

    Ideal a-stable frequency is based on these low and high time formulas

    If the frequency needed matches these formulas then everything is good with no worries. 150kHz and up is well into the range where this simple formula is not accurate anymore

    A more complicated formula includes factors for propagation delay and the larger ramp voltage that results. 

    So Ra, Rb, C can be tuned to get right frequency with samples that have a specific propagation delays. 

    Later (actually it is already happening now) PCN changes the values for those propagation delays. The fine tuning no long works for new samples. Because PCN is new, inventory can ship with either version. So the application would need two set of tuned value for Ra, Rb, C. I expect you can see the problem with that.

    TLC555-Q1 and TLC3555-Q1 do not have a PCN in play (propagation delays are less variole), so these option would need just one set of tuned values for Ra, Rb, C