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TMS320C6748: Power sequencing using buck DC-DC converters

Part Number: TMS320C6748

Please review the attached schematic.  I want to make sure we aren't going to have issues with the power up sequencing on the DSP.  The TI power guys are saying COUT is too large on VR2, while the C6748 errata says the additional load(C2) is necessary.  Please also verify the PG outputs from the DC-DC converters will power up the rails correctly.

Thanks, Dean

405-030452 for TI review.pdf

  • I'm not familiar with details of the capacitance requirement defined in the errata. Therefore, not qualified to make any other recommendation. You may need to find another power source that can tolerate the higher load capacitance that is recommended in the errata.

    Regards,
    Paul

  • I must have been looked at the wrong errata before posting my previous reply. I now understand what is happening after reading Advisory 2.3.18. The recommended capacitance is producing a short-term load to the1.8V power rail that holds it down until the dual voltage IO cells resolve their operating mode. It is very important that your power supply solution prevents the 1.8V power rail from exceeding the limits defined in the datasheet. The advisory provides other workaround options if you can not make the capacitor option work. In my opinion the more robust solution is defined in option 2.

  • Paul,

    Thanks for taking a look at the schematic and the errata for the DSP.  I've always been confused by option 2 in the DSP errata.  It mentions synchronous buck DC-DC converters.  We are using the TLV62568AP.  Would this DC-DC satisfy the requirement for option 2?  If not, can you recommend a TI DC-DC converter that would?

    - Dean

  • The more common power management device only sources current to the load, where the regulation function monitors its output voltage and changes the amount of current being sourced to the load as necessary to maintain the desired output voltage. Option 2 is describing a power management device that is capable of sourcing or sinking current as necessary to maintain the desired output voltage.

    I'm not familiar with the various power management options. Therefore, you should discuss this topic with someone from the power management via their E2E forum. 

    Regards,
    Paul