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TPS56C215: Switching Frequency drop during FCCM

Shuhei Goto
Expert 4910 points
Part Number: TPS56C215

Tool/software:

Hi team,

Datasheet Fig.5-25 shows that Fsw is lower than set value in case of FCCM.

Under the following condition, the Fsw diviation from setting value is within expected range?
[Condition]
Vin:12V
Vout: 5.1V
Fsw(setting): 800kHz
Fsw(measured): 675kHz

Also, how did you measure the Fsw (setup) for the datasheet plot. 

Best regards,
Goto

  • 0
    TI__Mastermind 26800 points

    Hi Goto-san,

    That figure should be based on actual data. At higher VOUTs there can be a dip in frequency from the setpoint so these numbers look fine. However, you need to check is if the design is as per datasheet guidelines and if the SW waveform looks stable and also the overall design itself should be stable - can check this with a load transient for example.

    Thanks,

    Amod

  • 0 in reply to Amod Vaze
    TI__Expert 4910 points

    Hi Amod,

    Thank you for reply.

    Is it possible to calculate FSW from specific input/output conditions?
    If so, could you provide me the equation.

    Best regards,
    Goto

  • 0 in reply to Shuhei Goto
    TI__Mastermind 26800 points

    Hi Goto-san,

    You can try WEBENCH as an option to get calculated values though it may not capture all the effects of silicon.

    Thanks,

    Amod

  • 0 in reply to Amod Vaze
    TI__Expert 4910 points

    Hi Amod,

    Thank you for proposing but it is seems that WEBENCH doesn't reflect the effect of Fsw drop during light load.

    Goto

  • 0 in reply to Shuhei Goto
    TI__Genius 11405 points

    Hi Goto-san,

    Amod is out today. TPS56C215 also has a PSPICE model that should also simulate frequency. Can you try this and share your results to see if it reflects what you are expecting? On occasion, Webench may not be as accurate as other simulation tools or EVM bench application. As Amod mentioned earlier, FSW fluctuation will mostly depend on your design, so main thing is to ensure it is a stable design by following the datasheet recommendations. Although some FSW fluctuation is normal for this device. Please let us know what you find.

    Thank you!

    Calan

  • 0 in reply to Calan Elaya
    TI__Expert 4910 points

    Hi Calan,

    The result of PSPICE simulation shows doesn't reflect the effect of Fsw drop during light load same as WEBENCH.

    Are there any TIPS to simulate the frequency response closer to the actual characteristics?


    Thank you,
    Goto

  • 0 in reply to Shuhei Goto
    TI__Mastermind 26800 points

    Hi Goto-san,

    Yeah these are secondary effects that are probably not modeled in the tools. My recommendation would be to use an EVM to measure the use case and make sure it works for your requirements.

    Thanks,

    Amod