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TPS54418: External frequency SYNC

Sanjay Pithadia
Genius 12855 points
Part Number: TPS54418
Other Parts Discussed in Thread: LMQ61460-Q1, SN74HC367

Hi,

I am testing TPS54418EVM to achieve external SYNC functionality with the following specs:

Vin = 3.3V, Vout = 0.85V, Iout = 1.6A

Fsync = 500kHz to 2MHz

While synchronizing to external frequency, the output of the device goes unstable. Please find the attached slide deck with observations. Can someone please look at it and retest on the EVM? Or share any thoughts why such behaviour is observed?

Thank you.TPS54418-Sync-Issue.pptx

Regards,

Sanjay R. Pithadia

  • 0
    TI__Genius 14876 points

    Hello Sanjay,

    Can you give us more details on what is the signal generator is producing?
    What is V_low, V_high ? Do you have an on time of at least 75ns as recommended in the datasheet?

    Can you show a scope shot of the square wave used on the RT/CLK pin?
    Thanks a lot!

    Regards,

    Dorian

  • 0 in reply to Dorian Brillet de Cande
    TI__Genius 12855 points

    Hello Dorian,

    Thank you for looking into this.

    The generator is producing square wave with V_low = 0V, V_high = 2V and duty cycle = 50%.

    The waveform is square wave but unfortunately I did not take the scope shot. I will take it when next time I go to lab.

    Can you please test the conditions (I highlighted in the PPT in my last post) and share waveforms?

    Thank you.

    Regards,

    Sanjay R. Pithadia

  • 0 in reply to Sanjay Pithadia
    TI__Genius 14876 points

    Hello Sanjay,

    Do you have any update here?

    Doing some tests on the TPS54418EVM, I reckon it is easy to pickup different source of noise which can come from the probe of the switching and from the external clock.

    The phenomenon you are observing might be coming from your test setup.

    When only probing the output voltage directly at the output capacitor I do not observe anything.

    Please, let me know!

    Thanks,
    Dorian

  • 0 in reply to Dorian Brillet de Cande
    TI__Genius 12855 points

    Hello Dorian,

    Sorry for the delay in replying, as I was on vacation.

    I have not taken the waveforms yet, but to me, it doesn't seem to be a set-up issue. The same set-up is being used for TI's other EVM testing (LMQ61460-Q1) and it works perfectly fine.

    If you can take the exact waveform, VOUT, VSYNC and SW-node for 1MHz/1.5MHz/2MHz - it will be really helpful.

    Appreciate your help. Thank you.

    Regards,

    Sanjay R. Pithadia

  • 0 in reply to Sanjay Pithadia
    TI__Genius 14876 points

    Hello Sanjay,

    Both implementation for LMQ61460-Q1 ad TPS54418 are different.

    I was able to use a setup in the lab to synchronize to the output of an external function generator: TPS54418-Sync-EVM.pptx

     As you can see, the no load condition is influenced by the function generator.

    Also, as you can read in the following E2E posts:

    RT is a very sensitive pin and I would advise to use a common clock buffer like the SN74HC367 to drive this pin.

    I only was able to use a signal generator like you did.

    Thanks a lot!

    Regards,
    Dorian

  • 0 in reply to Dorian Brillet de Cande
    TI__Genius 14876 points

    Hello Sanjay,

    I haven't heard back from you.

    Did you have a look at the proposed solution? Do you see any improvements?

    Let me know if you have any other questions,

    Thanks a lot!
    Dorian