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LM3489 decrease Vout ripple

LM3489
Prodigy 20 points
Other Parts Discussed in Thread: LM3489

Hi, I want to decrease the Vout ripple of LM3489 by using the external components the same as D-CAP mode controller(not mentioned in datasheet）.I don't kown whether it works or not. Pls help me,thank you.

  • 0
    TI__Intellectual 2320 points

    Hi,

    Have you tried the feedforward capacitor across the high side feedback resistor as mentioned in the DS? This can help you bring down the output voltage ripple considerably.

    What is your output voltage requirement. If possible, can you share a share a schematic?

    Regards,

    Sourav

  • 0 in reply to Sourav.Sen
    Prodigy 20 points

    Hi Sourav,

    I just want to ask does this circuit work in hysteresis mode .(not mentioned in datasheet）.Thank you.

  • 0 in reply to LM3489
    TI__Intellectual 2320 points

    Hello,

    This ripple injection circuit is used for COTs or DCAP parts (as you have mentioned). The LM3489 is a hysteretic controller with NO one shot on-timer block inisde (unlike in COTs or DCAP). The minimum ripple at the output is decided by the FB comparator hysteresis as shown in the DS.

    I think this additional ripple circuit maybe be useful in the this scheme if  you want to stabillize any perceived oscillatory unstable output behaviour (SW node, possible in Hysteretic mode for D>50%). However, this is not a guaranteed solution.

    Do you want to add this circuit for reduced ripple at the output? What is you input and the output voltage? What is the L that you are using?

    Regards,

    Sourav