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LM46002: LM46002PWP ouput problem while powering up

Thomas Aero
Prodigy 20 points
Part Number: LM46002

Hi,

the Output voltage of the LM4002 is set to +5V. But sometimes in the first 100ms after powering up the output voltage rises up to 11V. Then it slowly comes back to 5V and then it works fine.

The capacitor Cff which is parallel to the upper Feedback resistor is set to 100pF. We figured out, that when we change Cff to 220pF everything is working fine. No 11V spikes anymore.

In chapter 9.2.2.6 is a formular for calculating the capacitor Cff with which we calculated 196pF.

So can it be that with a Cff of 100pF the Regulation is not stable?

The first 200ms the circuit has no load at 5V an we have at least 480µF low ESR capacitors at the output. 

Are we good with 220pF or do we probably get elsewhere Problems because the Cff is too high?

Best regard,

Thomas

  • 0
    TI__Expert 4531 points

    Hi Thomas,

       Is it convenient for you to upload your schematic? I need  the input voltage/inductance/Fsw. Thet are essential to solve this issue.

       You used a very big output capacitor, I guess there may be something wrong  with your Loop stablity. Have you tested the circuit for a bold plot?

    BR,

    Victor