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TPS650864: Inquiry about the TPS6508640 efficiency test results

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Replies: 3

Views: 41

Part Number: TPS650864


The efficiency test setup for the PMP12004-HE in the user guide is as follows.

     1. My customer believe that the efficiency test data in the user guide has been tested under the following conditions. Is that right?

           1) Only the measured rail was active, all other rails were disabled and there was no load

           2) The drive voltage of the BUCK1,2,6 was supplied from the external input Pin

       2. Could you please provide efficiency test data measued with all rails of the TPS6508640 working?

       3. Is there a difference in the BUCK efficiency of the TPS6508640 when the load is on only one rail versus on multiple rails?

Thank you.


  • Hi JH,

    1. My interpretation of those lines is that all of the other regulators on TPS6508640 were disabled and inactive. For the buck controllers the power required for the drive source was also accounted for in the efficiency measurements. 

    2. The only additional efficiency data I have available is going to be located in the TPS650864 datasheet or in the User's Guide for the TIDA-01393 reference design

    3. There may be some efficiency differences depending on loading conditions in the final application as heat dissipation and ambient temperature do factor in to efficiency results. At room temperature and 50% loading for every rail I expect this impact to be minimal but I would recommend testing this during while validating your final system to ensure it meets your specific use case.

    Best regards,

    Layne J

  • In reply to Layne J:

    Hi Layne J,

    Thank you for your reply.

    The figure below is the result of my customer testing the efficiency of the TPS6508640 BUCK2.

      - Blue & Brown : Only one rail was active and loaded, all other rails were disabled.

      - Gray : One rail was active and loaded, all other rails were active and  no loaded

    The efficiency was reduced by about 10% for the buck converters and about 5% for the regulators.

    Is this normal? Why does activation alone significantly reduce efficiency even though the other rails are no load?

    Thank you.


  • In reply to JH Shin:

    Hi JH,

    Every regulator dissipates current when enabled so if you do not account for the additional current draw from enabling all of the regulators the efficiency plot will look different. You will notice that the efficiency difference with those regulators enabled decreases as the load on the tested rail increases, this is because the current draw for the enabled regulators with no load does not change much (if at all) as the current draw on the tested rail increases. Enabling those rails does not impact the efficiency of the tested rail as long as you take in to account the power dissipated in the rails that are not being tested.

    Best regards,

    Layne J