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LM25149-Q1: lm25149 constant output 3.3V

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?

  • 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, 


  • 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 ?

  • 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.