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LMZM23600: About Startup with Pre-Biased Output

Hide
Guru 21045 points
Part Number: LMZM23600
Other Parts Discussed in Thread: TPS560430

Hi Team,

 

Our customer are evaluating LMZM23600V3SILT at the following conditions.

However, it can’t be started if the output voltage remains 1V.

 

I guess that LMZM23600V3SILT can’t support Startup with Pre-Biased Output.

Is my understanding correct?

 

<Conditions>

VIN=24V

VOUT=3.3V (1V remains at startup)

 

And, I understand that TPS560430 can support Startup with Pre-Biased Output.

So, it can be started even if the output voltage remains 1V.

Is my understanding correct?

 

Regards,

Hide

  • 0
    TI__Mastermind 30820 points

    Hello Hide,

    I think the module could be able to support pre biased startup. What is the output capacitance being used in this design?

    Is the mode/sync configured for auto mode?

    I think he device maybe hitting current limit. I would suggest minimizing the amount of output capacitance and setting the device for auto mode.

    In addition, please share the schematic for my review, as well, the physical oscilloscope captures.

  • 0 in reply to Marshall_Beck
    Guru 21045 points

    Marshall-san,

     

    Thank you for your response.

     

    -What is the output capacitance being used in this design?

    =>47uF

     

    -Is the mode/sync configured for auto mode?

    =>Auto mode(MODE/SYNC pin is connected to GND)

     

    -please share the schematic for my review, as well, the physical oscilloscope captures.

    =>Checking

     

    And, I have one more question.

    I found the following comment in the datasheet.

    > Don't: Allow the output voltage to exceed the input voltage, nor go below ground.

     

    So, I guess that LMZM23600V3SILT can’t support Startup at VOUT=around 1V.

    If no, could you please let us know the meaning of this comment?

     

    Regards,

    Hide

  • 0 in reply to Hide
    TI__Mastermind 30820 points

    Hello Hide,

    The comment you are referencing can be said to exclude a startup, as the worry is when the input voltage is at steady state, where their could be continuous current conduction through the high-side body diode, in the case where input voltage is below output voltage.

    I would like to review the oscilloscope captures when made available. 

  • 0 in reply to Marshall_Beck
    Guru 21045 points

    Marshall-san,

     

    I got new information.

    Could you please let us know this cause and workaround?

     

    [Our customer comment]

    -There are individual differences in fail reproduction.

     (So, some unit do not have problems.)

    -When the output voltage is 1V, the rate of occurrence is high.

     

    [Circuit]

     

    [Waveform]

     

    Regards,

    Hide

  • 0 in reply to Hide
    TI__Mastermind 30820 points

    Hello Hide,

    The last thing I would like to confirm is the load current, during the pre-biased startup.

    If they are testing with a high load current, I would consider retesting without any load on the output.

    To me, it seems like the device is hitting current limit. 

    In the case we need to replicate on the bench this information will be useful.

  • 0 in reply to Marshall_Beck
    Guru 21045 points

    Hi Marshall-san,

    Thank you for the information.

    I will contact you again after I get new information.

    Regards,

    Hide

  • 0 in reply to Hide
    TI__Mastermind 30820 points

    Hello Hide-san,

    Thanks for the information.