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LMR16030: LMR16030, Cff capacitance and output ripple problem

Prodigy 120 points

Replies: 7

Views: 91

Part Number: LMR16030

Hello! We use LMR16030 to supply 18-30vac after half-wave rectification and then connect it with 2200uF filter to form DC. As the input of LMR16030, the output is the maximum 2A of 5VDC. The Cff capacitance of the output terminal is recommended to be 470pF or 560pF when calculated on the official website. However, in the actual test of each waveform of load 0~2A, it was found that when 470pF was used, the ripple output of 5V was up to 300mV, while when 12pF was used, the ripple output was within 60mV. Why is that?Are we at risk of using 12pF?

7 Replies

  • Hi,

    Could you please tell us what are all 4 waveform channels? Could you please probe SW node and zoom it in for the both conditions? Thanks.

    Best Regards

    Iven

  • In reply to Iven Su:

    turquoise is the input of DC/DC,

    green is the voltage of output  5V,

    pink is the ripple(Vp-p) of output 5V,

    yellow is the load current of output 5V.The waveform is connected to electronic loading 1A and 900mA.

    Can I get your email? I can send you the waveform of each loading with 470pF Vs 12pF.

    My email : rctan@computime.com

  • In reply to user4856666:

    Hi,

    OK, I see, could you please probe SW node and zoom it in for the both conditions? It might cause loop unstable using different Cff.

    Best Regards

    Iven

  • In reply to Iven Su:

    I can paste pictures on here and I have no your email . Can you send an email to my email : rctan@computime.com

    I will send you the waveform of each loading with 470pF Vs 12pF.

    Mybe could your down load the document from the baidu pan : link ,code is n6we.

  • In reply to user4856666:

    Hi,

    I recommend that you upload the files in the post so that other people might have the same question can search for it. Thanks.

    Best Regards

    Iven

  • In reply to Iven Su:

    1, 5V without loading, then add 1A loading(the output voltage ripple Vp-p with 12pF is better than 470pF)

    2、470pF,18VAC input, Electron Loading 0~2A, input VTP94 OK, output 5V OK. the output voltage ripple Vp-p<320mV

    3,change to 12pF

    also 18VAC in ,Electron Loading 0~2A, input VTP94 OK, output 5V OK.And the output voltage ripple Vp-p<50mV

  • In reply to user4856666:

    Hi,

    Could you please Zoom Vout in and also probe SW node, it's helpful to check if the loop is unstable. Thanks.

    Best Regards

    Iven

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