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TPS61252 – About behavior of output pre-bias function

Guru 21045 points
Other Parts Discussed in Thread: TPS61252

Hi Gene-san,

 

According to the following E2E thread, we understood that this device have “output pre-bias”.

http://e2e.ti.com/support/power_management/non-isolated_dcdc/f/196/p/397299/1405450#1405450

 

Additionally, we would like to know the behavior of output pre-bias function.

 

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[Q1]

When the output voltage is left (for example 5V), the internal Pch MOSFET is OFF and Nch MOSFET is ON.

After that time, when Nch MOSFET is OFF and Pch MOSFET is ON, is the load current sunk?

---

 

[Q2]

Is the device not broken even if this behavior is repeated?

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[Our customer conditions]

-Vin=2.3V to 4.2V (1cell)

-Vout=6.0V

-Iout=Around 570mA (peak current)

-Cout=22uF

-Cload=47uF*2 + 1uF*2 + 0.1uF*2=96.2uF

 

Regards,

Kanemaru

  • Hi Kanemaru,

    The load current won't sink back to Vin because there is a inductor between Vin and Vout. With LS Mos and HS Mos turn on and off, Vout will be boosted to the target voltage. In your case, the converter just behaves as re-starting.

    Here is some waveforms, it can be found that there is no inverse current through the inductor. CH1 Vout, CH2 EN, CH4 IL

    BR

    Gene

  • Hi Gene-san,

     

    Thank you for the information!

    And, I have one more question.

    Could you please let us know the evaluation condition of this waveform?

    -Vin=??V

    -Vout=??V

    -Iout=??A

    -Cout=??uF

    -Did you use TPS61252EVM?

     

    Regards,

    Kanemaru

  • Hi Kanemaru,
    Sorry for my forgetting to post the test condition.
    I used the standard TPS61252 EVM and the test condition is as follows:
    Vin=2.7V
    Vout=5V
    RL=200ohm
    Cout=2*22uF

    BR
    Gene
  • Hi Gene-san,

     

    Thank you for your prompt reply.

    I apologize.. I have following question.

    They are worrying about the following points.

     

    -Is the device not broken even if this behavior is repeated?

    -Is the device not broken if differences between "Vin" and "Bias Vout" are big?

     

    Regards,

    Kanemaru

  • Hi Kanemaru,
    The device works well even if this behavior is repeated.
    It has nothing to do with the difference between Vin and Bias Vout, it can always work well.

    BR
    Gene
  • Hi Gene-san,

     

    I greatly appreciate your cooperation!

    I will report the information to our customer.

     

    Regards,

    Kanemaru