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Inquiry regarding TPS54360 behavior on light load

Atsushi Okui
Genius 4015 points
Other Parts Discussed in Thread: TPS54360EVM-182

Hello, all

Now we are evaluating TPS54360EVM-182, then would like to know the behavior when light load adopted.

Please see the enclosed report and feedback us your comment, in order to clarify this root cause.

 4426.Inquiry regarding TPS54360 behavior on light load.doc

Please let us clarify whether we could some adoption on EVM to resolve this behavior on normal operation.

We thank you in advance for your information.

Best regards,

  • 0
    TI__Mastermind 35185 points

    Were there any modifications done to the EVM for this testing?

    The measurements with 0.017A load is likely pulse skipping due to minimum on time. The device switches with the minimum on time charging the output up to greater than the target regulated value. When it gets too high it stops switching to allow the output to discharge some.

    The other two conditions (0.33A and 0.35A load) are probably the internal boot recharge FET activating to charge the BOOT capacitor. When there is not enough charge on the BOOT capacitor, the high-side FET turns off and the internal pull down switch turns on to charge the BOOT capacitor. To confirm, you can measure the BOOT-PH voltage. I expect it to be near the 2.1V typical BOOT UVLO.

  • 0 in reply to Anthony F
    Genius 4015 points

    Hello, thank you for your prompt reply.

    Actually, we haven't had any modification on TPS54360EVM-182.

    I also captured the waveform on BOOT pin, however the measured voltage is higher than 2.1V.

    Please see the enclosed file for the detail.

    I hope this could help us to find the root cause of this issue.

    We thank you once again for your information.

    Best regards,

    0383.TPS54360-BOOTpin.doc

  • 0 in reply to Atsushi Okui
    TI__Mastermind 35185 points

    Thanks for the further testing. Looking at it again I didn't notice the input voltage you are testing at is relatively high (27V and 40V) so I do not think it is BOOT UVLO either. But it is the BOOT minus SW voltage which should be measured for the 2.1V UVLO. In this case it is >5V which also shows this is not the issue.

    The 0.017A case is definitely minimum on time pulse skipping. We will need to look closer at the 330mA and 350mA case and let you know.

  • 0 in reply to Anthony F
    Genius 4015 points

    Hello, thank you for your verification on TPS54360EVM.

    I also have some concerning when comparing the waveform which I updated on this thread.

    When referring the figure 10, 11 and 12 on User's guide (SLVU769B), there seems to have some issue on waveform in case of 0.33A (fig 1.3) and 0.35A (fig 1.5).

    In case of 0.33A, 2nd pulse width from left on BOOT pin is less than other, and it seems to have some effect on output ripple.

    In case of 0.35A, 2nd pulse width from left on BOOT pin is less than other, and it seems to have some effect on output ripple.

    Please let us clarify whether you have any idea to resolve this issue as well.

    We thank you once again for your information.

    Best regards,

  • 0 in reply to Atsushi Okui
    TI__Mastermind 35185 points

    Hi Atsushi,

    I confirmed with the designer the operation with the 0.33A and 0.35A loads is normal and expected.

    Best Regards,
    Anthony