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Unstable switching frequency LTC3633

Category: Hardware
Product Number: LTC3633

Hi,

Thanks for looking into my question.

I have a circuit that uses 2 LTC3633 to generate 1.0v, 1.2v, 1.8v and 3.3v. Both LTC3633s' switching frequency is set at 4MHz. The voltage output seems ok, but the switching frequency of 1.0v, 1.2v and 1.8v seems to be unstable. The waveform of 3.3v is rather clear and sharp:

But the waveforms of others seems to be quit fuzzy:

 .

My schematic is as follow:

I am wondering whether this issue is important. If so, how can I solve it?

Thanks,

Piao

  • Hello,

    You can adjust the values of ITH1 and ITH2 resistors and/or capacitors to make it stable. It will be helpful if you can see the bode plot of your system. If not, you can adjust the values of ITH components until it is stable.

    Regards,

    Jhun

  • Hi Jhun,

    Thanks for your advice! 

    But I have noticed a more severe unstable frequency. I have designed a board with a schematic and layout almost identical to the DC1347B. The PMIC works fine initially after power up. But after around 2 minutes, its switching frequency suddenly increase to 8Mhz and become unstable, as shown in the video:

    I am wondering whether you can give any suggestion on this?

    Best,

    Piao