TLV62585: feed forward capacitor

Shunsuke Nagata

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.

over 4 years ago

0 Febin over 4 years ago

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 Shunsuke Nagata over 4 years ago 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 Febin over 4 years ago 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 Shunsuke Nagata over 4 years ago 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 Febin over 4 years ago 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 Febin over 4 years ago 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

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TLV62585: feed forward capacitor