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UC3843: About coefficient of fosc equation

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Guru 21045 points
Part Number: UC3843

We understand that 1.72 of fosc equation is typical values.

If correct, could you please let us know the min and max values?

 

<Background>

We calculated fosc, as a result, 95.3kHz at RRT=8.2kohm and CRT=2200pF.

However, actual fosc is 91kHz (lower than calculation result 95.3kHz).

Therefore, we would like to estimate variation of fosc.

(Of cause, we understand that there is RRT and CRT variation.)


 

Regards,

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  • 0
    TI__Mastermind 31580 points

    Hi Hide,

    TI does not provide a min and max value for the 1.72 in the formula above. But f you look at the datasheet, on page 7 you can see that the range given for the Oscillator frequency is 47kHz to 57Khz for a typical value of 52kHz at 25C, which is a little over +/-10% variation around the setpoint. The RC is 10k and 3.3nF and the component tolerance is not part of this variation.

    So if you calculate a value of 95.3kHz then I would expect to values in the range of 85kHz to 105kHz in practice at 25C, plus the variation due to the RC components themselves.

    Regards

    Peter

  • 0 in reply to Peter Meaney
    Guru 21045 points

    Hi Peter-san,

    Thank you for the information.

    I greatly appreciate your cooperation.

    Regards,

    Hide