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UCC28084: About PWM duty and CTRL input voltage

Tao_2199
Genius 5660 points
Part Number: UCC28084

Hello,

 

Regarding to PWM duty on UCC28084D, my customer is asking  some question.　

(Question)

 

(1) When input voltage is changed on CTRL pin, PWM duty width is changed on OUT A/B. (Up to 50%.)

My understanding is correct?

(2) If so, do you have a data of PWM duty width vs CTRL input voltage ?

Or how do we consider about relations of PWM duty and CTRL input voltage ?

 

Regards,

Tao 2199

  • 0
    TI__Expert 3095 points
    Hi Tao 2199,
    UCC28084 is a peak current mode controller. This means that the CTRL pin voltage sets the peak switch current and not directly the duty cycle. Actually the CTRL pin voltage sets the CS pin voltage that will terminate the ON pulse.
    This means that the actual duty cycle will depend CTRL voltage and the inductor current at the start of the ON time, and the voltage across the inductor during the ON time and the value of the inductor.
    If the CS pin voltage does not reach the trip threshold set by the CTRL pin, then the duty cycle will be its maximum value 49% for each output.
    I hope this answers your question.
    Thanks
    Joe Leisten
  • 0 in reply to Joe Leisten
    Genius 5660 points
    Hello Joe,

    Thank you for replay.
    I informed CTRL pin voltage to my customer.

    Regards,
    Tao 2199