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TPS65132 using 1uH inductor

Given Ding
Genius 10205 points

In customer application, inductor will decrease to 1uH at some cases which inductor is not so good,  so HW want to know What our IC will behavior at this case.

In my opinion, 1uH will increase current ripple which may bring larger Vout ripple and trigger current limit. I’m wondering if it will make the Vout oscillate since the inductor you recommend should be related with loop stability.   is 1uH can achieve stable loop?

 

Also is there any hidden register or method that can report the issue if using smaller inductor?

 

please kindly add your commends.

  • 0
    TI__Expert 8010 points
    Hello Given,

    Yes you are right smaller inductance means higher ripple current and this can cause the current limit to trigger earlier.
    What is the specified output current for this design? What is the tolerance of this inductor? For the loop stability you should also consider the input and output capacitor. Why do they want to use such a small inductance? How did they decide for 1 uH?
    For a first approach to determine the value of the components I recommend to look at the Application Note (www.ti.com.cn/.../slva372c.pdf).
    What so ever I do not recommend to use such a small inductance for this device as it has been designed to work stable with following components:
    2.2 uH < L < 4.7 uH (+/-30%)
    2.2 uF < CIN < 10 uF (+/-10%)
    4.7 uF < CREG < 10 uF(+/-10%)
    Every value below/above has not been simulated or tested and therefore cannot be determined to work stable or not.
    However I want to point out that the customer either way has to validate its design. If the tests determine that it works as expected and with the performance as expected than it is ok.

    Best Regards,
    Ilona
  • 0 in reply to Ilona
    TI__Expert 8010 points
    Hello Given,

    I have forgot to mention a very important consideration when choosing the inductance. This is the scenario during start-up.
    When the inductance is too small this means that inrush current will increase extremely and this can cause the inductance to get in saturation. If an inductor gets in saturation the inductance will slowly decrease and at some point the component will not act as an inductor anymore but as a piece of wire.

    Best Regards,
    Ilona