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TPS61170: outside inductance confirmation

Adrian Ymeraj
Expert 3750 points
Part Number: TPS61170

Hello team,

About the TPS61170 I  would like to ask you for clarifications regarding the coil.
Based on our requirements:
Vin: 6V - 12V
Vout: about 14V and Iout=140mA.

From calculations it should be around 47uH, but on the excel spreadsheet with this value I get as result the following suggestion: “Inductance outside tested range. User responsible for confirming control loop stability ”.
So I would like to ask you what it actually means, I can still use a 47uH using the stability calculations proposed on the file, or it is better to reduce the value of the coil?
Please let me know your thoughts.
Best regards,
Adrian
  • 0
    TI__Mastermind 40080 points

    Hi Adrian,

    Bigger inductance will form a lower right half plane zero, the lower frequency of the right half plane zero, the more likely results in stability problem.

    In your application, a 22uH inductor is enough.

  • 0 in reply to Helen chen
    TI__Expert 3750 points

    Hi Helen,

    As for the inductance I can also use a 22uH, it will mean that I will have a greater ripple current even though it adds some drawbacks, which is however better than having a low margin of stability.

    Thank you and best regards,

    Adrian

  • 0 in reply to Adrian Ymeraj
    TI__Mastermind 40080 points

    Dear Sir,

    Since your current is not big. So higher inductor current ripple is OK! Infact at the low current application, we generally choose a much higher inductor ripple current ratio,which is  much higher than 20%-40%,  so even 50%-100% ripple current is OK.

    So you needn't worry about the ripple. The output cap can help to filter the output voltage ripple.