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TPS62140: The repple at light load

Hirokazu Takahashi
Expert 8420 points
Part Number: TPS62140

Dear Team,

 

Will the ripple range be affected by FSW configuration at light load condition?

If so, please let me know the reason.

 

Best Regards,

Hirokazu Takahashi

  • 0
    TI__Intellectual 1780 points

    Dear Takahashi-san,

    Thank you for your question.

    The output voltage ripple in the power-save mode is explained in the last paragraph of section (9.2.2.2.2.1 Output Capacitor) in page 15 of the datasheet.

    The output voltage ripple under steady-state condition is explained in section (8.3.5 Frequency Selection (FSW)) in page 11 of the datasheet.

    For more information on how to optimize the output filter, please refer to this application note: slva463a

    Best regards

    Omar

  • 0 in reply to Omar Hegazi
    TI__Expert 8420 points

    Hello Omar

     

    Thanks for your advice and support.

    We found below output voltage phenomenon at light load condition with FSW=Low and High

    The condition of Vin, Vout and Load is same for below twice waveform.

     

    The switching frequency at FSW=H is over 2 times slower than one at FSW=L.

    And then, ripple range of output at FSW=H is larger than one at FSW=L.

     

    Is this phenomenon is normal working?

    Best Regards,

    Hirokazu Takahashi

  • 0 in reply to Hirokazu Takahashi
    TI__Intellectual 1780 points
    Hello Takahashi-san,

    The behavior you described matches the datasheet. The option to operate at either frequency is determined based on the application.

    If high power density and a very small solution size are needed, a high switching frequency allows the use of small external components for the output filter. The output voltage ripple should be lower and also the efficiency. Operating at a high switching frequency is achieved by setting FSW=L.

    If efficiency is the key parameter, more than solution size, the switching frequency can be set to half (1.25 MHz typ.) by FSW=H. At this case, the output voltage ripple should be higher. To get low ripple and full output current at the lower switching frequency, it's recommended to use an inductor of at least 2.2uH.

    It is mandatory to start with FSW=L to limit inrush current, which can be done by connecting to VOUT or PG.

    I hope this answers your question.

    Best regards,
    Omar