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[C6678, Power Consumption Spread Sheet] The lower end of nominal CVDD voltage is being assumed to calculate numbers.

Naoki Kawada
Guru 19890 points

Hi,

This is just a quick conformation about the assumption for using power consumption spread sheet.

The numbers are calculated by using lower end of nominal CVDD voltage. For example, for 1400Mhz device, the nominal CVDD voltage is 0.95-1.15V, and the spread sheet uses 0.95 for the calculation.

Our understanding is this spread sheet would be used to calculate *max* power/current consumption in device point of view under provided conditions.
Here is the related document :

And it says:

            The data found in this document and in the accompanying spreadsheet were measured from devices at the maximum end of the power consumption range for production devices.


Considering this, using higher end of CVDD for the calculation seems to be more likely consequence. Do you have any comments on this ? In fact, my customer is asking me the same question.

Best Regards,
Naoki

  • 0
    TI__Mastermind 43660 points
    Naoki Kawada,

    Yes, the power consumption spreadsheet would be used to calculate worst case power consumption. I do not have full access to the spreadsheet to find the formulas used. I will check with internal team and update. Meanwhile could you please let me know how did you identify the CVDD voltage used for the calculation.

    Regards,
    Senthil
  • 0 in reply to Senthilkumar Srinivasan
    Guru 19890 points

    Hello Senthil,

    Thank you for your quick reply.

    When using the spread sheet with the default parameters (silicon rev = 2.0, case temp = 85*C, Variable=Power, Frequency = 1400, % SP util = 27, % CC Util = 0), you would see 321.33 mW on each CorePac. And if you change the "Variable" to Current,  you would see 338.24 mA.

    Dividing 321.33 mW by 338.24 mA makes 0.950005912961 and it looks the lower end of nominal CVDD.

    Also, you will find the following description in the manual:

    4.3 Current vs. Power Variable Option

               With the variable set to Current - it uses CVDD=0.9V to provide total current estimates in mA

    It looks the lower end of nominal CVDD of 1250MHz version of device.

    Best Regards,
    Naoki

  • 0 in reply to Naoki Kawada
    TI__Expert 6815 points

    Hi Naoki,

    You are right. The current calculation uses Min CVDD to calculate the consumption in mA. This is because for a give max power spec (mW) to which the devices are screened, the min CVDD will give the worst case current consumption (i.e. max mW/min CVDD).

    As you correctly noted from the calculations, for the 1.4GHz device, the power spreadsheet uses 0.95V for current calculation. We will update the Application Report to call out the differences between various devices. Let me know if you have any questions.

  • 0 in reply to Aditya
    Guru 19890 points

    Hi Aditya,

    Thank you for your answers. 
    So this is just short clarifications to conform whether my understanding is correct.
    1. Using lower end of CVDD is supposed/expected for current calculation (max). Not higher end of CVDD. Is this correct ?
    2. The document says SmartReflex voltage is supposed for power calculation (max). What voltage is actually assumed to calculate it ?

    Best Regards,
    Naoki

  • 0 in reply to Naoki Kawada
    TI__Expert 6815 points

    Naoki,

    Naoki Kawada said:
    1. Using lower end of CVDD is supposed/expected for current calculation (max). Not higher end of CVDD. Is this correct ?

    That is correct. To calculate current, the lower end CVDD is used.

    Naoki Kawada said:
    2. The document says SmartReflex voltage is supposed for power calculation (max). What voltage is actually assumed to calculate it ?

    To calculate power, the higher end CVDD is used - 1.15V for 1.4GHz speed grade, 1.1V for the rest.

    Edit: Your measured power will depend on (among other things) the SmartReflex voltage programmed into the device. Measured power will always be less than the power spreadsheet.

  • 0 in reply to Aditya
    Guru 19890 points
    Hi Aditya,

    Thank you for your help. Understood. I close this thread.

    Best Regards,
    Naoki