• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 63 subscribers
  • Views 463 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS53355: Difference in Inductor values suggested by Webench and theoretical calculation

Madhu Sharma
Expert 2915 points
Part Number: TPS53355

Hi,

I am using TPS53355 in my design to generate 1.1 V from 12V , at 28A max.

Please clarify below points related to this: 

1) For 250Khz switching frequency, the Webench suggests to use 330nH , but calculation using datasheet formula ( equation 8) gives  about 430nH. Please let me know which value can be selected for better performance.

2) As per equation 8 of the datasheet, Inductor value is inversely proportional to current. So inductor value for large current will be smaller and smaller current will be larger. Whether inductor value selected at Imax will cause any performance degradation when current is lesser than that? 

( For example, in above case, inductor value for 28A is 430nH. But for 16A, inductor value comes to be 750nH. But as per datasheet, we have to select 430nH, by considering Imax. Whether this inductor will cause any functional issues when current is 16A?)

Thanks in advance.

Regards,

Madhu.

  • 0
    TI__Mastermind 23845 points
    Hi,

    1) Normally webench will give you a conservative value, therefore in this case i would use the 330nH inductor based on webench
    2) I believe the more important aspect is the ripple current on the inductor. The rule of thumb is the peak to peak ripple current on the inductor is around 20% - 40% of maximum load current. Smaller inductor gives you a higher peak to peak ripple whereas a larger inductor will give you a smaller peak to peak ripple current.

    Let's say you pick 430nH inductor for your 28A design, it will be ok when the current is 16A. The ripple current on the inductor changes with your frequency selection, VIN and VOUT.

    Thanks
    -Arief