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TPS82130: Supercap application

Part Number: TPS82130
Other Parts Discussed in Thread: LM66100

Hello,

My customer used the TPS82130 to power the supercap charge and buck/boost converter input with the following conditions.

  - VIN = 5.6V, VOUT = 4.2V

When the input voltage of 5.6V is removed and the supercap is activated, a reverse current of about 1A occurs in the TPS82130.

Is this normal? Please let us know if there are any way to prevent the reverse current.

Thank you.

JH

  • Hi JH,

    The reverse current is expected for your application. When Vin 5.6V is removed, the output will get reflected at input with high-side FET body diode. There will be reverse current through the high-side FET body diode and there is no protection scheme built-in for this device. You need to consider the thermal aspect due to power dissipation in HS body diode caused by this reverse current. This power may be quite high. Ensure that the IC junction temperature rating is not exceeded. The diode in series with the input will mitigate the reverse current concerns.

    Hope this helps,

    Thanks,

    Nancy

  • Hi Nancy,

    My customer would like to see a little more clarify for the design.

    1. If they use a diode in series with the input, is it ok to use this design as is?

    2. If so, could you please recommend a diode with the required specifications?

    Thank you.

    JH

  • Hi JH,

    1. Yes, it is ok to use this design. Please refer to apps note in the link.

    Slyt689

    2. The diode required specification depends on your application. Your #1 selection criteria should be forward voltage drop which should obviously be as low as possible. Look at Vf at maximum load (for example 3A). Pick at least 5A continues current rating and about double the reverse voltage. And  also take a look at thermal capabilities of the chosen package. Reverse recovery speed is not critical in this application.

    Hope this helps,

    Thanks,

    Nancy 

  • Hi Nancy,

    Thanks for your kind response.

    My customer found the following application in the LM66100 datasheet.

    Please advise if it is okay to apply the applicaiton below between the output of the TPS82130 and the supercap.

    Thanks,

    JH

  • Hi JH,

    The concept is same as the diode. But for LM66100, the max recommended operating input voltage is 5.5V, Your Vin is 5.6V which is over 5.5V. The input voltage spike may damage the absolute max voltage 6V. Please follow the Apps note slyt689 and select a proper discrete diode.

    Hope this helps,

    Thanks,

    Nancy

  • Hi Nancy,

    My customer wants to use the LM66100 for the output stage of the TPS82130, the VOUT they use is 4.2V.

    Isn't it recommended to use the LM66100 for the output stage?

    Thanks,

    JH

  • Hi JH,

    It is ok to add LM66100 on the output side.

    Thanks,

    Nancy