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LM3150 not stable

Ludwig Schwarzhans
Prodigy 90 points
Other Parts Discussed in Thread: LM3150

Hello,

I have made a design with WEBENCH

The Output is not stable and ~6V instead of 5V

When I remove Cff (560pF) it works well.

What ist the minimum value of Cff ?

 

Best regards,

Ludwig Schwarzhans

 

 

 

  • 0
    TI__Genius 11085 points

    Hi Ludwig,

    From your description, it seems like this LM3150 design has too much output ripple. If the output ripple is too large, the DC value of the output voltage will be shifted up, since the valley of the ripple is regulated. Also OVP could be tripped causing unstable operation.  

    Large output ripple could come from too little capacitance at the output, or too much ESR on the capacitors. The Cout shown in your schematic (4 * 2.2uF) is too small. Maybe you have other Cout that is not shown. If you have more output capacitance, is the ESR of the capacitors you have on your board similar to what Webench recommended?  I'd suggest adding more output capacitors and select capacitors with lower ESR. Then it should work well with Cff.

    Could you measure the output voltage ripple without the Cff?

    -Yang