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C6678 VCNTL

yong zhang3
Prodigy 140 points
Other Parts Discussed in Thread: LM10011, CSD87351Q5D, TPS56221, TPS56121

hello,everybody,I have a question.

1.I want to know that  how much  the VCNTL lines of c6678 output  corresponding to which condition dsp operate in?

  • 0
    TI__Mastermind 42545 points

    The VCNTL outputs are used to set the needed CVDD voltage level. The C6678 will output the six bit code for the needed voltage level after the part exits reset. The power supply must accept that code and set the CVDD to the requested voltage level. This is referred to as a smart reflex power supply design. It is a requirement that the CVDD voltage be set to the level requested using the VCNTL interface.

    Regards, Bill

  • 0 in reply to Bill Taboada
    Prodigy 140 points

    thank you!Bill,I have other two questions,can you answer my question？

    1.when c6678 work full load,how much the current can achieve? if the c6678 have a current pulse, the pulse can beyond 20A or even 30A? somebody say  that the current of c6678 full load can achieve 16A?But the max output current of pmp7256 power plan is 15A, this power can drive c6678 absolutely?

    2.I have two power plans of c6678,one is TPS56221DQP+LM10011,the other is LM27402MHX+CSD87351Q5D.I want to which plan is more fit for me,I  want to know what are the advantages of the two plans respectively? 

    [ed: Please note the similar thread RE: c6678 sudden power down.]

  • 0 in reply to yong zhang3
    TI__Mastermind 42545 points

    Hi Yong Zhang,

    1) If you have entered the loading values into the power consumption model, it should give you the maximum power needed for your design. Be sure to select the correct temperature since that can cause much higher current consumption. It is best to design for the max temperature. It is also best to add some margin to the results from the spreadsheet to act as you power supply design targets. 

    2) The power supplies that you have selected are not the supplies that we have recommended as solutions. You will have to discuss these designs with the power supply support team. I will say that the TPS56221 solution may not generate enough current for the C6678. The LM27402MHX+CSD87351Q5D doesn't appear to support the smart reflex VCNTL signals. How would you modify the output for that solution?

    Regards, Bill

  • 0 in reply to Bill Taboada
    Prodigy 140 points

    Bill，I think LM27402MHX+CSD87351Q5D+LM10011 can support smartreflext.what's more, it'sefficiency can achieve 95%.load curreent is 25A.you say that tps56221 can not generate enough current?it's load current is 25A.but it's efficiency is about 87%,

  • 0 in reply to yong zhang3
    TI__Mastermind 42545 points

    Hi Yong Zhang,

    Sorry, I was looking at the numbers for the TPS56121. I'm not an expert in power supplies, so you will have to ask the detailed questions on the power supply forum. As long as your supply can handle the power and stability requirements and can support Smart Reflex, it should work for the KeyStone devices, but we have only tested the devices with the power supplies recommended in the Hardware Design Guide.

    Regards, Bill