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MC34063A: frequency calculation on inverting design

Alan Chang
Intellectual 2230 points
Part Number: MC34063A

Hi,

  My customer asks how to calculate MC34063A freq. on inverting design? this is -12V output from +12V input, Iout = 0.05A only. 

 From data sheet, CT = 4*10^-5*Ton, following those equation, freq. = 44KHz around, however, 138KHz is measured on real board. so how can we calculate the freq.?

-12V.pdf

  • 0
    TI__Genius 10385 points

    Hi Alan,

    Thank you for using E2E forums, I am not sure if the device is capable of supporting frequency that you are measuring. The maximum Fsw of this device is 100kHz, so I do not know if what you have measured is correct. What is the Ton and Toff you are measuring in the waveform you have attached? I am seeing 4u seconds for Ton and 4u seconds for Toff, am I correct?

    BR,

    Haroon