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PMP41006: soft-start

Expert 3570 points
Part Number: PMP41006

Hi Champs,

I have a question about the soft-start routine. It was stated on page 9 of the SW guide that there are 2 modes at which the converter starts its turn-on. It can be VMC or PWM mode. So when at VMC mode, does this mean that there is a voltage controlled-oscillator to determine the turn-on and -off during start up?

Regards,

Kien Nguyen

  • Hi Kien,

    I didn't fully get your question. what does voltage controlled-oscillator mean here? basically, it is the same as the normal voltage control mode(VMC) which the frequency is decided by the voltage loop. 

    does this mean that there is a voltage controlled-oscillator to determine the turn-on and -off during start up?

    Regards,

    Chen

  • Hi Chen, 

    Basically what you are trying to say is that during the start up, the PWM mode is first activated, which means that it is still at fixed frequency operation? And it is the duty that is controlled until it reaches a maximum duty value (is it 50% in this case?).  and then once it reaches a certain threshold, in this case the dead band threshold, it will already be direct frequency control for the remaining of the soft start time.

    Did I get it correctly?

  • Hi Jessica,

    Basically what you are trying to say is that during the start up, the PWM mode is first activated, which means that it is still at fixed frequency operation? And it is the duty that is controlled until it reaches a maximum duty value (is it 50% in this case?).  

    Yes, the freq is clamped to a max value. And yes, it is 50%. 

    and then once it reaches a certain threshold, in this case the dead band threshold, it will already be direct frequency control for the remaining of the soft start time.

    That is correct. 

    Regards,

    Chen

  • Thanks Chen.

    During the PWM mode, am I correct to assume that it is the maximum frequency at which the soft start will begin with? 

    Regards, 

    Jessica