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CCS/UCD3138ALLCEVM150: Minimum Duty Width

Spin Quantum
Prodigy 30 points
Part Number: UCD3138ALLCEVM150
Other Parts Discussed in Thread: UCD3138A, UCD3138

Tool/software: Code Composer Studio

Hi,

We are evaluating the UCD3138a using the UCD3138ALLCEVM150 LLC evaluation board (FW: LLCHBFirmware-1.2). During our evaluation, we have encountered some difficulties in obtaining switching frequency beyond 400kHz (minimum pulse width of ≈1us) using the Fusion Digital Power Studio (Version 3.0.31).

I shall be grateful, if you could shed some light on this matter. If it is necessary to modify the firmware using the code composer studio, I would appreciate if you could start me off by advising the registers to try out first.

Many thanks and best regards,

Spin

  • 0
    TI__Expert 7310 points
    an expert is looking at this.
  • 0
    TI__Mastermind 18370 points

    Hi,

    I am assuming that you are aware of the UCD3138's  "Mode switching" feature in high frequencies. Where the DPWMs stop acting is resonant(frequency modulation) mode and switch to standard pulse width modulation (PWM mode).

    Did you try to change the frequency of the point where it switches from LLC to PWM mode using Digital Power Studio (Version 3.0.31)?

    I am referring to this configuration page in the GUI:

  • 0 in reply to Yitzhak Bolurian
    Prodigy 30 points

    Dear Yitzhak,

    Thank you for your prompt reply.

    To the best of my understanding, the UCD3138A will switch among pulse skipping mode, PWM @ Fmax, PFM, and PFM with SR duration fixed (TSRMAX) according to the DPWMx Filter Duty. While testing, it seems to me that there are no further effect on the frequency and pulse width once the FMAX has been set above 400kHz.

    Please find the attached screenshots of FDPS_GUI and DPWMs waveform for your reference.

    FYI, we are using FDPS (Version: 3.0.33) and LLCHBFirmware (Version: 1.2).

    Thank you in advance for your kind assistance.

    Many thanks and best regards,

    Spin

  • 0 in reply to Spin Quantum
    TI__Mastermind 18370 points

    Hi Spin,

    As you probably know there are two types/points of mode switching.
    One at high frequencies when you switch from LLC/PFM to PWM.
    And one at low frequencies when you switch between regular LLC/PFM to PFM with clamped SR pulse width.
    Adjustment to both mode switching types appear in the same FDPS_GUI above; but only the FMAX/TMIN is relevant to your point of interest at high frequencies.

    Please also note, after changing FMAX you still need to click the button that says write to hardware in order for this to take effect.
    You may also want to save this to DFlash, so it memorizes the new setting even after power cycling the EVM.

    Hope this makes sense.

  • 0 in reply to Yitzhak Bolurian
    Prodigy 30 points

    Hi Yitzhak,

     

    Thank you for your kind advice.

     

    Unfortunately, we are still unable to obtain switching frequency beyond 400kHz with pulse width less than 1us during soft-start, despite adjusting the FMAX/TMIN per your advice. Would you be kind enough to try it out on your side to help us narrow down the root causes of this issue?

     

    In addition, after checking the DPWMAUTOSWHIUPTHRESH, DPWMAUTOSWHILOWTHRESH, DPWMAUTOSWLOUPTHRESH and DPWMAUTOSWLOLOWTHRESH registers, it appears to me that the FDPS_GUI is not setting the Auto Config Mid Threshold properly. Upon adjusting the FDPS_GUI using the settings listed above (and write to hardware and Flash), it seems that the UCD3138A is beginning the soft-start sequence at the middle of the PFM mode, which is highly undesirable.

     

    Thank you in advance for your kind assistance.

     

    Many thanks and best regards,

    Spin

  • 0 in reply to Spin Quantum
    TI__Mastermind 18370 points

    Did you turn-off the light load mode (Burst mode)?

    Please also make sure that your sample trigger is positioned at the beginning of the period, so when the period gets shorter, the sampling can still get triggered.

  • 0 in reply to Yitzhak Bolurian
    TI__Mastermind 18370 points
    Since this post been inactive for a while, I am going to close it.
    I am assuming that you have things under control.
    In case other questions raise, please open a new post.