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LM25149-Q1: lm25149 constant output 3.3V

Meng Liu
Intellectual 1765 points
Part Number: LM25149-Q1
Other Parts Discussed in Thread: LM5149-LM25149DESIGN-CALC

Hi support team

I want constant output 3.3V through connect FB to VDDA. but I don't know loop circuit how to control in this situation?

  • 0
    TI__Mastermind 22299 points

    Hi Meng,

    You can use the LM5149-LM25149Design-Calc Quickstart tool to predict the loop response crossover frequency and phase margin when using internal feedback divider. WEBENCH model of LM25149-Q1 will also predict loop response.

    When using internal feedback resistors, the output voltage VOUT pin is shared with the current sense amplifier. You can not inject a signal to measure loop response, it will disturb the peak-current control.

    I recommend using time-domain step response if you need to test.

    Hope this helps, 

    -Orlando

  • 0 in reply to Orlando Murray
    TI__Intellectual 1765 points

    hi orlando

    thanks for you  explain. I need t o test  loop response but I don't know want is time-domain step response. could you give some advice for me ?

  • 0 in reply to Meng Liu
    TI__Guru 63187 points

    Meng,

    You need to use an external feedback divider in order to correctly inject the oscillator signal for bode plot measurement.

    As Orlando recommended, you can take a look at a load transient with the fixed 3.3V setting and check that it is well damped with no ringing during the settling time. The quickstart tool is also helpful from this standpoint.

    Regards,

    Tim