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TPS544C20: Behavior @ light load

Yi Dou
Intellectual 545 points
Part Number: TPS544C20
Other Parts Discussed in Thread: TPS549D22, TPS549B22, TPS548D22, TPS548B22

Hi E2E,

I don't see any description of light load behaviors of TPS544C20, can it support DCM operation?

As you know, in typical DCAP control, by entering DCM, fsw will drop to very low, how can it avoid acoustic noise below 20kHz? Also, how to reduce ripple and PWM jitter of DCM?

  • 0
    TI__Genius 14455 points

    Hi

       The device operates in CCM mode always even at light load current. Please refer to section 8.4.1 of the data sheet.

    Regards,

    Gerold

  • 0 in reply to Gerold Dhanabalan - Online Design Tools
    Intellectual 545 points

    Well, that means FCCM is adopted as always, seems like light-load efficiency is not a concern for its application.

    Does TI have similar parts that will go into skip-mode or DCM? 

  • 0 in reply to Yi Dou
    TI__Genius 14455 points

    Hi

       Can you please look into the TPS549D22? This has Eco Mode

    What is your VIn, Vout, Iout conditions?

    https://www.ti.com/lit/ds/symlink/tps549d22.pdf

    Regards,

    Gerold

  • 0 in reply to Yi Dou
    TI__Guru 56985 points

     

    It depends on what you mean by "similar"

    As Gerold Dhanabalan notes, the TPS544C20 does not operate in auto-skip mode, running fully synchronous (Forced CCM) at light and even negative load currents.

    The TPS549D22 and TPS549B22 offer a D-CAP3 mode control architecture that can be programmed for AutoSkip to enter into pulse frequency modulation at lighter loads and maintain the PMBus interface and control of VOUT using VOUT_COMMAND, but they do not offer telemetry to report output voltage, current, and temperature.

    If you are looking for a D-CAP3 converter with integrated FETs that does not have PMBus, you can consider the TPS548D22 or TPS548B22, which are similar to the 9D22 and 9B22 respectively, but do not have the PMBus interface.

    We do not offer a PMBus converter with both integrated telemetry and auto-skip.

  • 0 in reply to Peter James Miller
    Intellectual 545 points

    Thanks peter for your info. PMBUS interface will be better for my application.

    However, eco-mode will bring in low-frequency noise issue. For some small-current TI D-CAP3 buck, I have seen a mode named "OOA" to avoid <20k audio noise.

    Among those mid-high current buck in TI, it seems no such functions available. What is the reason?

  • 0 in reply to Yi Dou
    TI__Guru 56985 points

     

    The switching frequency of a COT power converter in DCM is generally giving by Fo x Iload / Icrt

    Where Icrit is the critical conduction load when the inductor ripple current just reaches zero load current and Fo is the CCM switching frequency.

    For a switching converter operating at 500kHz normally, 25kHz frequency is typically observed at 1/20th of the critical conduction current, or less than 1% full load power.  For applications requiring these higher load currents, such as digital processors, their sensitivity to audiable noise when operate at 1% power or less is typically quite low, and the added power dissipation needed to maintain a higher switching frequency in such low power modes is generally not desirable.

    If Out of Audio operating range is needed at moderately lower currents, the inductor can be sized to keep Icri to 10 or even 5% of maximum load current to keep the switching frequency 25kHz below 1% of full load current.

    If you would like PMBus for fault reporting and output voltage control, I would recommend the TPS549D22, or it's 25A version the TPS549B22.