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LM25085: how to reduce toff

Hirotaka Matsumoto
Guru 27585 points
Part Number: LM25085

Hi all

Would you mind if we ask LM25085?
This device is COT type, so it is not possible to adjust the toff.
Our customer would like to reduce toff.
We recognize the method for it as follow;

-Increasing the load(to add the resistance, snubber circuit)
-To reduce the vaule of inductor

As our questions, do you have any idea for it?
Especially, our customer uses ripple configuration, using constant of RC, is it possible to improve?

Kind regards,

Hirotaka Matsumoto

  • 0
    TI__Mastermind 23845 points
    Hi,

    It seems like the on time is only inversely proportional to VIN, therefore i do not think you can adjust the time off.
    You can however adjust the frequency through RT, what is the reason for adjusting the toff?

    Thanks
    -Arief
  • 0 in reply to Arief Hernadi
    Guru 27585 points

    Arief san

    Thank you for your reply!

    what is the reason for adjusting the toff?
    ->Our customer would like to reduce the PWM cycle to reduce the ripple.
       Of course, we persuade that COT topology doesn't adjust the toff.

    Kind regards,

    Hirotaka Matsumoto


  • 0 in reply to Hirotaka Matsumoto
    TI__Expert 5745 points

    For reducing the output ripple, you can increase the switch frequency, output cap, so i don't think changing toff will make a big effort for reducing ripple.

    For this IC, you can use the RC circuit to simulate the injection ramp(Refer to figure 24 in the DS), and change the output cap with a small ESR(maybe the ceramic cap is also OK).

    Increase frequency and cap also can be useful for decreasing output ripple.Thank you