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Original question:

TPS61099: Input capacitors selection.

TPS61099: TPS61099

Dawei
Intellectual 280 points
Part Number: TPS61099

Hi,

I use TPS61099 to boost a minimum 3.4V (VCC) supply from Li-SOCL2 battery to 4.3V/15mA, in order to maximize life of battery and reduce ripple voltage of VCC as small as possible, I want to have smaller input and output ripple voltage.

From DS of TPS61099, 2.2uH inductor is fixed to have better stability performance, so I can't use larger inductor to get that, only have one more bulk capacitor just as what WEBENCH gives.

1% output ripple voltage, is it possible to implement with only adding one more 150uF bulk capacitor with low ESR?

My current design has about 1.2mA input ripple current and about 2% ~ 2.5% * 4.3V output ripple voltage.

Or any other good practices can be taken to get smaller input ripple voltage/current to extend battery life.

Thanks.

Regards,

Ma Dawei

  • 0
    TI__Mastermind 21565 points

    Hi Dawei:

    May I know why you need 1% Vout ripple? It's so critical for a switch power. I think adding an filter or low Iq LDO is a good way. (If you do need such low ripple.) 

    For extend the battery life, TPS61099 is suitable as it has low quiescent current, low min input voltage and high efficiency with light load. TI also has low Iq LDO devices. And for such load condition, you can further decrease the input voltage. 

  • 0 in reply to Minqiu Xie
    Intellectual 280 points

    Hi Minqiu,

    Could you tell me how to reduce the input supply ripple current or what's the best performance TPS61099 can hit in terms of input supply ripple current? Just to add one more 150uF bulk capacitor? Not only quiescent current but also input ripple current are both critical to extend battery life, especially when we add a switching regulator after battery directly. Limited information found in DS and fixed inductor value recommended by DS, so no other methods to reduce input ripple current.

    Below picture shows out circuits.

    Regards,

    Ma Dawei

  • 0 in reply to Dawei
    TI__Mastermind 21565 points

    Hi Dawei:

    Sorry that I can't see the picture, may you upload it again?

    And for reducing the input current ripple, an input filter can do some help, like π filter. But I'm not sure the exact value to achieve 1.2mA.

    If needed, I can help to do a simulation next week, after receiving the schematic successfully.

  • 0 in reply to Minqiu Xie
    Intellectual 280 points

    Minqiu,

    Insert file again, if you don't get it again, leave me your email address.

    7215.tps61099.docx

    Regards,

    Ma Dawei

  • 0 in reply to Dawei
    TI__Mastermind 21565 points

    Hi Dawei:

    It's OK now. But I'm sorry that full schedule today. Please allow me check your post tomorrow. Thanks for your kind understanding. 

  • 0 in reply to Minqiu Xie
    TI__Mastermind 21565 points

    Hi Dawei:

    I afraid you can't measure current ripple through a multi-meter. The TPS61099 has burst mode for such light load. The device will switched several pulses, and ramp up the Vout, then it will sleep some time. It makes the input current not so smooth. The ripple of the input current is much larger than what you observed in multi-meter. (As the multi-meter has some filter inside.)

  • 0 in reply to Minqiu Xie
    TI__Mastermind 21565 points

    Hi Dawei:

    If you don't have a current probe in hand, you can series a resistance in input cables. Then you can test its voltage drop to estimate the current.

    Add a small inductance in series the input side may do some help to reduce the ripple.