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LM43603: Questions about LM43603 webench.

Kazuya Nakai59
Guru 20560 points
Part Number: LM43603

Hello guys,

One of my customers is considering using LM43603 for their next products.
They are simulating LM43603 with Webench.
At this moment, they have the following questions.
Could you please give me your answer to the questions.

Q1.
The webench shows 205kohm as RT when 200kHz is input as the device switching frequency.
LM43603 datasheet table 1 says that RT should be 200kohm when the device switching frequency is 200kHz.
Why is RT value different between Webench and the datasheet?
Is it Webench software bug?

Q2.
Which should RT value be used? In Webench or in the datasheet?

 Your reply would be much appreciated.

Best regards,
Kazuya.

  • 0
    TI__Guru 59395 points

    Hello

    I will assign this to our Webench team and they will get back to you as soon as possible.

    Thanks

  • 0
    TI__Prodigy 490 points

    Hi Kazuya,

    1. When inputting your desired frequency in Webench, the difference in RT value is likely due to the tool rounding up to or using the next standard resistor value. This value should be close to the RT value listed in the LM43603 datasheet.  

    2. Either the datasheet or Webench value for RT can be used since there should only be a small difference between the two. The effect on switching frequency should also be minimal. 

    When using equation (3) from the LM43603 datasheet: RT(kΩ) = 40200 / Freq(kHz) - 0.6 

    • Using an RT value of 200kΩ results in a switching frequency of 200.4kHz
    • Using an RT value of 205kΩ results in a switching frequency of 195.5kHz 

    In your case, difference in switching frequency would be ~5kHz. 

    Regards,
    Carol