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TPS54325: EN internal circuit consult

Lin_Charles
Expert 4260 points
Part Number: TPS54325


Hi team,

My customer is using TPS54325 to converter 12V to 5V. We found below strange phenomenon and may need the team to check TPS54325 internal logic circuit,

When TPS54325 works normally, then suddenly EN drop down to about 0.8V and lasts about 436ms, then the EN signal rise to about 2.1V, the PG signal cannot goes to high when EN>1.6V (this VENH value claimed in our datasheet). At about 1 minute later, the PG will be good again and then the output is ok.

This may relate to the internal EN logic circuit, could you please help share how EN signal controls the switching MOS and why this 0.8V EN signal can lead to such strange phenomenon? Thanks. 

BR,

Charles Lin

  • 0
    TI__Mastermind 32400 points

    Hi,

    When you say EN drop down to 0.8V, the EN is an input pin, it means, you need to drive the EN pin voltage above 1.6V to become a logic High and guaranty below 0.6V for logic Low. The EN pin needs to be driven below 0.6V for the device to operate properly. Anything in between 0.6V and 1.6V has no guaranties for the device to behave as expected.

    The EN pin should hold below 0.6V, the device is disabled and switching is inhibited even if the VIN pin is above the UVLO threshold. The IC quiescent current is reduced in this state. If the EN voltage increases above 1.6V (Typical) while the VIN pin is above the UVLO threshold, the device becomes active. Switching is then enabled and the slow-start sequence is initiated.

    Can you please test with proper voltage levels as in the datasheet and let us know is this help fix the issue?

    Thanks!

    Tahar

  • 0 in reply to Tahar Allag
    TI__Expert 4260 points

    Hi Tahar,

    Thank you for your reply here. As you can see from the waveform, VIN is above UVLO 12V, and the EN is indeed above 1.6V, PG is low. This happens when EN suddenly drop down to 0.8V.This will happen in customer real design and if you think make EN to below 0.6V can solve this problem. What is your suggestions to make our device EN signal lower than 0.6V  and solve this issue?

    Thanks.

    BR,

    CL

  • 0 in reply to Lin_Charles
    TI__Mastermind 32400 points

    Hello Charles,

    What causing the EN to go below 1.6V and not all the way to 0.4V?

    Actually, need to be below 0.4V as shown in the EC table in the datasheet, not 0.6V as I mentioned in the post above.

    Thanks!

    Tahar

  • 0 in reply to Tahar Allag
    TI__Expert 4260 points

    Hi Tahar,

    When EN is below 0.4V, the issue can be solved. But in the customer's real case, the VCC my drop down to 4V for 436ms, which leads EN to be 0.8V (EN has divide resistor to VCC). After that situation, even EN is higher than 1.6V, the PG is LOW, which means switching stops. The 0.8V EN signal will lock our device for about 1 minutes. You can see the result from the waveform. 

    Customer is pushing us to give explanation about this strange phenomenon. Please help take some time to explain it. Thanks.

    BR,

    Charles Lin

  • 0 in reply to Tahar Allag
    TI__Expert 4260 points

    Hi Tahar,

    Do you have any updates about the phenomenon I described here? Thanks.

    BR,

    CL

  • 0 in reply to Lin_Charles
    TI__Mastermind 32400 points

    Hi Charles, 

    let take this one off line. i will close this post 

    thanks 

    Tahar