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TPS568215: Deviation for load current-frequency characteristics

Ryotaro Fukui
Intellectual 2345 points
Part Number: TPS568215

Hello team,

We received a question from a customer about TPS568215. I would appreciate it if you could give us some advice.

The data sheet has a "load current-frequency characteristics" graph for each MODE and frequency, but they could not find the deviation for each set frequency.

Could you tell us about the frequency variation range when the following settings are made?
・ DCM mode
・ 400kHz
・ Ioutmax = 5A

Best Regards,

Ryotaro Fukui

  • 0
    TI__Expert 5470 points

    Hi Ryotaro,

    The frequency with DCM mode and 400kHz SW frequency is shown in the Fig.20 of datasheet.

    Do you mean that customer wants to get a SW frequency range upper and lower limits (as xxHz~xxHz) with the given setting? With the DCM mode setting, if the load current is smaller than half of the inductor current ripple, the converter will enter into DCM mode. In this mode, the SW frequency is variable and affected by lots of factors including loading current and output capacitance. So the SW frequency range with DCM mode can only be got for application with certain components and certain loading range.

    For TPS568215, we have Webench tool simulation to help get results.

    If you have any further question, please tell us.

    Regards,

    Andrew

  • 0
    TI__Expert 7500 points

    Hi Fukui,

    When setting at DCM mode, the frequency variation from 0A to 5V will be from several hundred hertz to our target.

    If you are talking about the frequency variation after FCCM mode, the variation is about 10%, even 20% for our DCAP mode part which also applies for TPS568215. DCAP mode is pseudo-fixed frequency operation.

    Thanks,

    Lishuang

  • 0 in reply to Lishuang Zhao
    TI__Intellectual 2345 points

    Hi Lishuang, Andrew,

    Thank you all for your prompt response.

    Lishuang: So, the frequency fluctuation in each mode are as follows?

      DCM mode (0 - 5A): several hundred - target [Hz]

      After FCCM mode: 10%

      DCAP mode: 20%

    Andrew: "Do you mean that customer wants to get a SW frequency range upper and lower limits (as xxHz~xxHz) with the given setting?"

    I understand that way. If it fluctuates due to many factors, I would also like to introduce WEBENCH simulation for them.

    Regards,

    Ryotaro Fukui

  • 0 in reply to Ryotaro Fukui
    TI__Expert 7500 points

    Hi Fukui,

    Below understanding is not correct. I mean for this TPS568215, as long as the system enters CCM mode (load current is higher than half of the inductor current ripple), the frequency will have 10%-20% variation related to target frequency. This is an experienced range.

    Hope it will help.

    ------

    After FCCM mode: 10%

      DCAP mode: 20%

    ------

    Thanks,

    Lishuang

  • 0 in reply to Lishuang Zhao
    TI__Intellectual 2345 points

    Hi Lishuang,

    Sorry I made a mistake in reading.

    I will answer to the customer that the variation of CCM mode is 10-20% related to target frequency. Thank you for your correction.

    Regards,

    Ryotaro

  • 0 in reply to Ryotaro Fukui
    TI__Expert 7500 points

    Hi Ryotaro,

    Hope it will help. I will close this thread. If you have any further question, you can submit a new thread or email to me directly.

    Thanks,

    Lishuang

  • 0 in reply to Lishuang Zhao
    TI__Intellectual 2345 points

    Hi Lishuang, Andrew,

    Thanks for all the help. I will close this case too. I would like to contact you if any other questions arrives.

    Regards,

    Ryotaro

  • 0 in reply to Ryotaro Fukui
    TI__Intellectual 2345 points

    Hi team,

    I received an additional question about the previous answer from the customer.

    In Figure 20 of the data sheet, when set to 400kHz, it appears to be fixed at around 400kHz above 1A.

    Would the frequency's variation range be like that in the previous answer even after reaching the target frequency? Or will the variation become smaller after reaching the target frequency than before?

    Regards,

    Ryotaro

  • 0 in reply to Ryotaro Fukui
    TI__Expert 4795 points

    Hi Ryotaro,

    Andrew will feedback to you tomorrow.

  • +1 in reply to Ryotaro Fukui
    TI__Expert 7500 points

    Hi Ryotaro,

    As Andrew comment before, one is with the DCM mode setting,  before reaching the target frequency, the SW frequency is variable and affected by lots of factors including loading current and output capacitance. So the SW frequency range with DCM mode can only be got for application with certain components and certain loading range.

    The other is with CCM mode setting, after reaching the target frequency, the SW frequency is pseudo-fixed frequency operation. It depends on Vin and Vout. As we can see from the figure 20, it still have some variation to 400KHz, maybe this variation is about 5% from figure 20. But this picture is got from one or two samples when we did validation for this device. Considering process and device variation, the frequency variation can be up to 10%.

    Thanks,

    Lishuang