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TMS320C6678: Increased power consumption

Nancy Wang
Expert 8210 points
Part Number: TMS320C6678

Customer did test on over 20 TMS320C6678 boards and found that 2 out of the 20 boards consumed more 10 w than the others. After investigation, they found major power consumption was by core. CVDD power current of normal board is 8.5A but abnormal CVDD power current is 14.3A, as 6.3w more than normal board. Abnormal board CVDD1 consums 1.2w than normal ones. Could you please check and tell why this happened?

 

Since there are many bulk capacitor in switching power supply system, it takes time to shut down power. This is a relatively slow process. And DSP CVDD power and CVDD1 power can experience a temporary restart. Dose this phenomenon casue the current increase in the core ? Reference the attachment please.

 

The yellow lone is CVDD and the blue one is 5v to the board.

  • 0
    TI__Guru**** 161600 points
    Hi,

    DId they follow the Hardware design guide? Specifically Chapter 2 Power Supplies.
    Also did they use the Power Consumption model for TMS320C6678 devices:
    www.ti.com/.../sprm545
    to determine the correct results for their power supplies.

    This is present in the product folder under Tools & Software tab:
    www.ti.com/.../toolssoftware

    Best Regards,
    Yordan
  • 0 in reply to Yordan Kovachev
    Prodigy 160 points

    Hi  Yordan,

    Thanks for your reply. We do follow the guide except using a fixed voltage (1.09V) to supply the CVDD power. According to our experience, it is not the reason. The supply circuit schematic is in the attachment.

    There are two TMS320C6678 on each board.  At the begining, the power dissipation of all boards is about  23 watts running the same program.  All boards are normal. But after a series of experiments, we found the power dissipation of some boards became abnormal.  For instance, one board's power dissipation became 33 watts, one board's power dissipation became 29 watts, one board's power dissipation became 27 watts,and so on. The DSP's CVDD power current and CVDD1 power current of these abnormal boards became larger. The normal board's power dissipation is still about 23 watts.

    So, what might be the reason? Could the temporary restart of CVDD power and CVDD1 power when power down be the reason?

    Best regards

    Lin

    power_part.pdf

  • 0 in reply to user1683887
    TI__Guru**** 161600 points
    I'll have a look at this and update.

    Best Regards,
    Yordan
  • 0 in reply to Yordan Kovachev
    TI__Guru**** 161600 points

    Hi,

    I've asked the factory team for help on this one.
    When you say "There are two TMS320C6678 on each board" , are you using exactly the same devices (same speed grades)?
    Also I am not sure if the temporary restart of CVDD power and CVDD1 power when power down is normal. 

    Best Regards,
    Yordan

  • 0 in reply to Yordan Kovachev
    TI__Mastermind 46460 points

    Nancy,

    Use of AVS power solution is mandatory.  We will not support designs that do not use it.  It is known that power consumption on some chips can be significantly higher than the rated limits when AVS is not used.  Also, due to this higher power consumption, the devices may get hotter than expected and that in turn causes the power consumption to further increase.  Operating the device outside of its rated limits will severely impact device reliability.

    You also mention that during slow power supply decay that the device "tries to restart".  How can this occur when the device is supposed to be in reset with PORz low during the power down sequence?

    Tom

  • 0 in reply to Yordan Kovachev
    Prodigy 160 points
    Hi,
    The two DSPs are exactly the same devices(both TMS320C6678ACYPA25). The temporary restart of cvdd power and cvdd1 power when power down is certainly abnormal. And we have fixed it. But we are not sure if it is the reason of Increased power consumption.
    Best Regards,
    Lin
  • 0 in reply to Tom Johnson 16214
    Prodigy 160 points
    Hi TOM,

    Thanks for your reply. So the reason of increased power consumption is that AVS power solution is not used?
    During slow power supply decay, it is the CVDD and CVDD1 power chips trying to restart. The CVDD power chip is TPS56221DQPT. The CVDD1 power chip is TPS548A20RVER.
    Best Regards,
    Lin
  • 0 in reply to user1683887
    TI__Mastermind 46460 points

    Lin,

    Lack of AVS is definitely a possible cause of increased power consumption.  Over-temp is another possibility.

    Please provide some specific data for both a 'good device' and a 'high current device'.  Please include:

    1. CVDD and CVDD1 voltage measured across a cap right at the C6678
    2. CVDD and CVDD1 current measured across a Kelvin resistor in-series with the load
    3. Steady-state case temperature of the C6678
    4. Operating condition of the C6678 during the previous measurements - i.e. out of reset with all 8 cores running an RTOS application executing matrix multiplies with code stored in DDR3 memory with the core clock running at 1000MHz
    5. Completed power estimation spreadsheet for your use case

    Tom