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Original question:

TLV62585: Ask for 3D CAD file of VQFN-HR package

TLV62585: feed forward capacitor

Shunsuke Nagata
Genius 12340 points
Part Number: TLV62585
Other Parts Discussed in Thread: TPS61081,

Hi,

TLV62585 datasheet shows a feed forward capacitor is required if Output cap is larger than 47uF.

I could not find the explanation how to calculate the feed forward cap. Could you please give me advice how to calculate it?

Regards,
Nagata.

  • 0
    TI__Mastermind 20500 points

    Hi Nagata,

    I would like to share an interesting application note that explains how to choose the feed forward capacitor value (Cff) of internally compensated dc-dc power supplies. I hope this helps.

    https://www.ti.com/lit/an/slva289b/slva289b.pdf 

    Please let me know if you may require further support.

    Regards,

    Febin

  • 0 in reply to Febin
    TI__Genius 12340 points

    Febin,

    The application note use boost converter. I'm not sure it can useful for buck,too. Or should user cut & try to adjust phase / gain margin on his board? for instance, user use 22-pF as default and adjust gain/phase margin by changing feed forward cap.

    Is it possible to adjust the cap in Webench? I could not change Webench schematics.

    Regards,
    Nagata.

  • 0 in reply to Shunsuke Nagata
    TI__Mastermind 20500 points

    Hi Nagata,

    The application note is intended for internally compensated dc-dc converters and TPS61081 was used as an example. We do not  have any equation to calculate Cff in buck converters specifically.

    However, I would suggest to follow the datasheet recommendations in any case. As you said, they could work around with Cff and check for stability with their BOM.

    Unfortunately, the Webench model does not have an option to add Cff but you can change the Cout. Thanks again for your feedback.

    Regards,

    Febin

  • 0 in reply to Febin
    TI__Genius 12340 points

    Febin,

    Could you please share gain or phase margin of your experiment data in TI recommend setting (L= 1uH, Cout=22uF)?

    -> TLV62585EVM-824 use 1uH and 22uF. Could you please share the gain / phase margin test result?

    Regards,
    Nagata.

  • 0 in reply to Shunsuke Nagata
    TI__Mastermind 20500 points

    Hi Nagata,

    Please find below the bode plot measurement taken on a standard EVM with L= 1uH, Cout=22uF and without Cff.

    Vin=3.3V, Vout= 1.8V, Iout=1A

    Vin=3.3V, Vout= 1.8V, Iout=3A

    Regards,

    Febin

  • 0 in reply to Febin
    TI__Mastermind 20500 points

    Hi Nagata,

    I hope I could solve your problem.

    I would like to close this thread, if you do not have any further questions. Please reach out to us for any further support.

    Regards,

    Febin