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LM22676 - start up

Hirotaka Matsumoto
Guru 27525 points
Other Parts Discussed in Thread: LM22676

Hi all,

Would you mind if we ask LM22676 start up?
(About detail, please refer to the following file. )
1222.20150817_LM22676.pdf

Kind regards,

Hirotaka Matsumoto

  • 0
    Guru 27525 points

    Hi all,

    We are sorry to hurry you, but if you have some information, could you let us know it?

    Kind regards,

    Hirotaka Matsumoto

  • 0 in reply to Hirotaka Matsumoto
    TI__Genius 10095 points
    Hi,

    I have moved your question to the Simple Switcher forum, and will have someone look into your issue.

    Marc
  • 0
    TI__Mastermind 23815 points
    Hi,

    Sorry for the late reply, but yes i would recommend putting an enable resistor to make sure the part switch when VIN> 12V.
    As for your abnormal startup, i would think that the converter is unstable at that lower VIN.
    A couple of things to try:
    1) Remove C23 and see whether it changes the behavior (Internally they already have 2 zero compensation) Therefore you might not need this anymore.
    2) Is there a way to isolate the load on the 12V? If yes, let's isolate it from the other converter that converts it to 6.6 V and see if the behavior improves.

    Thanks
    -Arief
  • 0 in reply to Arief Hernadi
    Guru 27525 points

    Arief san

    Thank you for your advice!

    1) Remove C23 and see whether it changes the behavior (Internally they already have 2 zero compensation) Therefore you might not need this anymore.
    -->OK, we suggest that our customer try it.

    2) Is there a way to isolate the load on the 12V? If yes, let's isolate it from the other converter that converts it to 6.6 V and see if the behavior improves.
    -->Our customer already has tried it, the behavior did not inprove.

    kind regards,

    Hirotaka Matsumoto

  • 0 in reply to Hirotaka Matsumoto
    TI__Mastermind 23815 points

    Hirotaka san

    Ok, i will wait until the customer remove C23 and see if that improves it. 

    Also, you can double check the stability of the converter by either running a bode plot or maybe a load transient and see if there is a ringing on the step response. 

    As for the slew rate of the load, you can use 1A/us slew as a guideline.

    Thanks

    -Arief

  • 0 in reply to Arief Hernadi
    Guru 27525 points

    Arief san,

    Our customer removed C23, but it did't improve.
    So, our customer uses the following method which you mentioned

    <Method>
    I would recommend putting an enable resistor to make sure the part switch when VIN> 12V.
    As for your abnormal startup, i would think that the converter is unstable at that lower VIN.

    As the result, it seems all OK.

    Kind regards,

    Hirotaka Matsumoto

  • 0 in reply to Hirotaka Matsumoto
    TI__Mastermind 23815 points

    Yes, i think it would be wise to ensure that the VIN is high enough before enabling the part.

    I am glad that it helps to resolve the issue. Just let me know if you have further questions.

    Thanks

    -Arief