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TL594: Oscillation frequency

Kenji Ohno1
Genius 5095 points
Part Number: TL594

Hi Team,

I got a question from the customer.

The calculation formula of fosc is described in the data sheet below.

  fosc = 1 / Rt × Ct

However, I found a post that "fosc = 1.2 / Rt × Ct "is correct.

 https://e2e.ti.com/support/power_management/isolated_controllers/f/188/t/639470?tisearch=e2e-quicksearch&keymatch=TL494

(Datasheet P19)

It is written that fosc = 20 kHz can be obtained with Ct = 0.001 uF and Rt = 50 kΩ.

I am confused which is right.

With information from customers,

Oscillation frequency (Used with Push-pull)

 Rt: 6.2 kΩ ,Ct: 1000 pF ,Fosc = 1.2 / 2 (Rt * Ct)

Theoretical value: 96.77 kHz

Actual measurement value: 83.45 kHz

There was a big error.

I have been asked by the customer about the cause.

I appreciate your support.

Best rgards,

Kenji

  • 0
    TI__Expert 6080 points

    Hello Kenji,

    According to the datasheet TL594, the Fosc is calculated as 1/(Rt*Ct) following this equation if Rt= 6.2kohm and Ct = 1000pf the Fosc = 161.3kHz.

    But for push-pull applications the frequency is halved the calculated value which is also suggested in the datasheet section attached below: so your actual oscillator frequency will be around 81kHz.  

    I hope this answers your question.

    Regards,

    Sonal

  • 0 in reply to Sonal Singh
    Genius 5095 points
    Sonal-san,

    Thanks for your answer.
    I appreciate your support !

    Regards,
    Kenji