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LM2842

ou gareth
Intellectual 340 points
Other Parts Discussed in Thread: LM2842

Please see below questions and kindly clarify it for me.


1.The voltage is 0.765v in Vfb, but I found the votagle in fsw is o.5v as LM2842 SPEC page4
  Could you please let me know why ther are different? Thanks.

2.inductor selection
the condition is based on vin=42v~4.5v vout=3.3v iout=0.6A fw=550khz
 snva377c data recommend 15u for inductor, but webench is 47u
Please kindly let me know which data is correct.

  • 0
    TI__Genius 15810 points

    Hello,

    Here are the answers:

    1) The spec in the datasheet indicates that the Fsw was measured on an automated test system and that the FB node was set to 0.5V. During normal switching and proper regulation the FB voltage would always be 765mV.

    2) The reason that they are different is that probably the datasheet calculates the inductance using an optimum input voltage (E.g. 12V) instead of the max voltage of 42V. The Webench inductor value is calculated to give a 30% ripple current through the inductor. Both the results should be stable. 

    I hope this helps.

    Regards,
    Akshay 

  • 0 in reply to Akshay Mehta
    Intellectual 340 points

     

     

    question1

    I found out the voltage have a little bit overshoot when I using the LM2842XEVM.

    Actually I setting the voltage with 3.3v, but  it will overshoot to 3.48v.

     

    Please kindly let me know what the cause and how to improve on this. Thanks a lot.

  • 0 in reply to ou gareth
    TI__Genius 16025 points

    Hi Ou,

    It's possible to add additional soft start to this application by bridging the upper feedback resistor with either a capacitor or other passives that disconnect following the soft start.

    See attached scan.4527.E2E Simple Switcher - Ou Garth.pdf

    Thanks,

    Anston

  • 0 in reply to Anston Lobo
    Intellectual 340 points

     

    Hi

    We have a customer has a LM2842X. We know the voltage is 4.5V to 42V as datasheet.

    But they want to know if it could works with 4V.  Could you please confirm it and send me the related document on this. Thanks a lot.