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LM5148-LM25148DESIGN-CALC: Question about Step 7, Compensation Design.

Kazuya Nakai59
Guru 21495 points
Part Number: LM5148-LM25148DESIGN-CALC
Other Parts Discussed in Thread: LM5148

Tool/software:

Hello guys,

One of my customer is designing a power supply using LM5148.

At this moment, they have the following question.
Could you please give me your reply?

Q.
They want to set LM5148 switching frequency to 2.1MHz.

They are using LM5148-LM25148DESIGN-CALC for their power supply design.

Desired Crossover Frequency in Step7 has a comments.
The comment says that the maximum crossover frequency should be up to 100kHz.

Could you please tell me why the maximum crossover frequency should be up to 100kHz?

Your reply would be much appreciated.

Best regards,
Kazuya.

  • 0
    TI__Genius 11235 points

    Hi Kazuya,

    Beyond 100kHz of crossover frequency - the noise attenuation of the control loop is bad. The system becomes very sensitive to noise being picked up leading to instability since there is a large bandwidth. Furthermore, the parasitics introduced by real world passives begin to play a role in the loop response at higher frequencies. For reliable operation. proper attenuation needs to be ensured so as to ensure a stable control loop

    100kHz is generally accepted as a good point for the cross over frequency.

    Hope this helps. 

    Thanks,

    Best Regards,

    Taru