TPS61178: negative current after soft-start

Mark Huang3

Prodigy 60 points

Part Number: TPS61178

Hi Sir,

I design one 9V to 12V converter by TPS611781.

I was measurement the negative current after soft start at choke, and vout had dropped.

Why does this event happen?

How can I avoid about this event?

Thanks.

over 5 years ago

0 Minqiu Xie over 5 years ago

TI__Mastermind 21565 points

Hi Mark:

TPS611781 is the Force PWM version. It's won't turn off the high side switch even there is reverse current, until the ending of clock cycle.

If you don't expect the reverse current, you could select TPS61178 version, it has PFM, and will turn off the high side switch if there is a reverse current.

0 Mark Huang3 over 5 years ago in reply to Minqiu Xie

Prodigy 60 points

Hi Minqiu,

"until the ending of clock cycle." is meaning soft-start end?

Will the reverse current hurt IC, make IC damage?

0 Minqiu Xie over 5 years ago in reply to Mark Huang3

TI__Mastermind 21565 points

Hi Mark:

I mean every switch cycle. Not only startup.

The reverse current won't hurt IC, but the efficiency is lower than PFM.(TPS61178 use Auto PFM)

0 Mark Huang3 over 5 years ago in reply to Minqiu Xie

Prodigy 60 points

Hi Minqiu,

And I would like to know why is the Vout rise over my setting voltage, and then drop back to setting?

Is the vout drop making the "negative current "(red circle)? not reverse current when converter is been steady state.

0 Minqiu Xie over 5 years ago in reply to Mark Huang3

TI__Mastermind 21565 points

Hi Mark:

It's normal that converter has overshoot during the startup or load transient. Modify the compensation components will change the value in some way.

And there will be still reverse current in steady state if the load is light enough.

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TPS61178: negative current after soft-start