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TPS65131: TPS65131 datasheet Problem

Aaron-s
Prodigy 20 points
Part Number: TPS65131

Hi,

I have some problems with TPS65131 datasheet.

1. According to the datasheet, L1 and L2 are inversely proportional to the required output current. Not the larger the inductance, the more energy storage? Trouble to explain the principle.

2.Do 6.8us and 7.5us have specific meanings in the feed-forward capacitance formula? What effect does C9 and C10 have on the circuit output if they become larger or smaller?

3.According to the datasheet, when the input is 5v , the output efficiency is as high as more than 80 %. however during the actual test(input 5V, output + 15 / - 15),the efficiency is 72 % and the converter is very hot. Where can efficiency be affected? What are the ways to improve efficiency?

4.According to the datasheet, the BSW pin goes low when ENP is set high. But in practice, this pin will output a square wave, what is the case? If the switch MOS is not configured, can this bsw pin be suspended?

5. “the connections of the components connected from CN, CP, FBN and FBP to AGND is important on this component. AGND needs to be a very clean GND directly connected to the power pad to make sure the IC is able to regulate properly.” Do PGND and AGND need to be wired separately and then single - connected?

Thanks

Aaron

  • 0
    TI__Expert 8010 points
    Hello Aaron-s,

    Thanks for your request. We will get back to you asap.

    Best Regards.
    Ilona
  • 0
    TI__Guru 58225 points

    Hello Aaron-s,

    1. I expect you are referring to formulas 5 and 6. The inductance is inversely proportional to the ripple current not the output current according these formulas. The bigger the inductance, the smaller the inductor ripple.

    2. The feedforward capacitor transfers fast load changes directly to the feedback node. For fast output voltage changes, the cap is a short.  For more details on compensation, have a look in this application note:

    3. Efficiency is influenced especially from the used inductor and the used external diode. If you want to improve efficiency you need to use an inductor with low DC and AC losses and diodes with low forward drop and reverse leakage.

    4. The output should not deliver a square wave. This one is pulled low when the converter is enabled. But if you do not want to use an external transistor you can leave this pin floating.

    5. If possible, please review the evaluation module, found here: http://www.ti.com/product/TPS65130/toolssoftware for more details on a good layout.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 20 points

    Hi Brigitte,

    Thanks for your help. I changed the PCB, it finally works. 

    Best regards,
    Aaron

  • 0 in reply to Aaron-s
    TI__Guru 58225 points
    Hello Aaron-s,

    Thank you very much for your feedback. If you want to share your experience it might be helpful for others.

    Best regards,
    Brigitte