• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 37 subscribers
  • Views 437 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.

WEBENCH® Tools/LMR33620-Q1: Discrepancies

Barry W
Intellectual 910 points

Part Number: LMR33620-Q1

Tool/software: WEBENCH® Design Tools

A:

The Webench model produced for the LMR33620CQ3 reports a switching frequency of 1.66MHz.

The data sheet specifies a switching frequency of 2.5MHz for that part.

B:

The Webbench model recommends inductors over 2.92 µH for my 3.3V output design.

The data sheet recommends a 2.2µH inductor.

Are these issues related?  Which one is more correct?

  • 0
    TI__Expert 8365 points

    Hi Barry,

    Could you please share the WEBENCH design using the 'Share Design' option.

    Thanks & Regards,

    Praveen

  • 0 in reply to Praveen Badiger
    Intellectual 910 points

    Your graphic is outdated.  The interface does not look like that now.

    Anyway, here is the link: webench.ti.com/.../SDP.cgi

  • 0 in reply to Barry W
    TI__Expert 8365 points

    Hi Barry,

    The device has a minimum switch-on time of 68ns 

    For the above condition Vin=30V, Vout=3.3V, Frequency=2.1 MHz  switch-on time is calculated as :

    Duty cycle is calculated as Duty= Vout/Vin=0.11.

    On time= Duty / frequency

    On time =  0.11/2.1 MHz= 53.3ns

    Therefore calculated on time for Frequency=2.1 MHz is below the minimum on-time 68ns and hence frequency is reduced on WEBENCH to achieve the minimum on-time of 68ns

    For Frequency= 1.6 MHz

    on time = 0.11/1.6 MHz= 68.75 ns is achieved

    The minimum inductor on WEBENCH is calculated as 2.29uH as shown below. However, WEBENCH selects the best suitable inductor within given limits. Alternatively, you can change the inductor limits and select the inductor as per your requirement. 

    .

    Thanks & Regards,

    Praveen