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Power options and power consumption for TMS320C5515.

John Tomson
Prodigy 250 points
Other Parts Discussed in Thread: TMS320C5515, TPS74801, TPS54240, TPS54260

According to SLVA400B(Power for TMS320C5515) manual there are several power options for the processor.

1. Why it is recommended to use for example TPS78401 with 3.3V at 1170mA on the output if the processor core consumption not higher than 250mA at 1.3/1.05V?

2. Why the processor LDO's are powered from different sources as an option instead of using one TPS78401? What are the advantages of those solutions?

3. What minimum power option(minimum current consumption on the output) should I use for a proper device operation if I use Vin=9-36V?

4. If a typical consumption of the device is 0.14mW/MHz-0.22mW/MHz as stated in the data sheet why the recommended power supplies are so powerfull, I mean they designed for a much bigger power consumption. Which normal operation for the processor the consumption will be that high?

  • 0
    TI__Expert 8065 points

    John,

    Please note that there is a max current column on the first page. The power consumption in the datasheet are typical number that you will see most of the time. However, the hardware should be designed to cover maximum (worst) peak current consumption. The numbers in the max current column are the design max peak current (we have not seen those numbers though). The basic idea is that the parts in the SLVA400B were selected to cover the worst possible peak current. For the specific power solutions, let me forward your questions to our power team.

     

    Regards,

    Peter Chung

     

     

  • 0
    TI__Prodigy 280 points

    John,

    1. Why it is recommended to use for example TPS78401 with 3.3V at 1170mA on the output if the processor core consumption not higher than 250mA at 1.3/1.05V?

     >> Answer: In the design using the TPS74801, the TPS74801 is providing power for everthing on the device.  The TPS74801 provides the 3.3V and the C5514/15's internal LDO's convert the voltages for the specific other rails required.

     

    2. Why the processor LDO's are powered from different sources as an option instead of using one TPS78401? What are the advantages of those solutions?

      >> Answer: This is just one option where if the user wanted the simplest possible power solution and didn't care as much about efficiency.

     

    3. What minimum power option(minimum current consumption on the output) should I use for a proper device operation if I use Vin=9-36V?

      >> Answer: We can only recommned the likely maximum current consumption of the C5514/15, which is the number listed in the table.  You can calculate the power requirements for your exact application using the recommendations in the comments column as well as the C5514/15 datasheet.

     

    4. If a typical consumption of the device is 0.14mW/MHz-0.22mW/MHz as stated in the data sheet why the recommended power supplies are so powerfull, I mean they designed for a much bigger power consumption. Which normal operation for the processor the consumption will be that high?

      >> Answer: The numbers are so much higher than the 0.14mW/MHz-0.22mW/MHz because the mW/MHz #'s are typical values.  We have to design the power supply to potential worst case scenarios.

     

  • 0
    TI__Prodigy 280 points

    John,

    i realized there were a couple ways to read your question #3.  If you are looking for a device recommendation for 9-36Vin, start by looking at the TPS54240 (42Vin max) TPS54260 (60Vin max).  These are a non-synchronous device with the top-side FET integrated.  Both device have switcherPro models available ... SwitcherPro is a tool that gives you a design and analysis based on your input/output parameters.  http://focus.ti.com/docs/toolsw/folders/print/switcherpro.html

  • 0 in reply to kstrady
    Prodigy 250 points

    Thank you for your answers.

    But i still cannot figure out why in the datasheet(SPRS645B) on p. 65 it's stated that DSP_LDO shutdown current=250mA but at the same time in SLVA400B is written that CVDD max current is 500mA? How such contradictions are possible?

    I'am concerned about this because I need a power-efficient system, so I should choose a proper Step-Down Regulator with the highest efficiency.

  • 0 in reply to John Tomson
    TI__Prodigy 280 points

    John,

    The 250mA spec you mention is a MIN value.  The 500mA is a MAX value.  If you are designing a power supply, you have to design to worst case.  The 500mA was used to cover 99.999% of applications.  If you want to know what the true max requirement is in your system, you can do the calculations and the C55xx team can help and it may come out to less than 500mA.

    If your input voltage range is 9-36V, your best bet is the TPS54240. 

  • 0 in reply to John Tomson
    TI__Expert 8065 points

    John,

    SLVA400B was made very early before we completed characterized the device. When we created the SLVA400B, we did not know the max LDO current output capability. 500mA was the theoritically possible peak current but you never going to see the number. You can consider the LDO max current as the max current of the core.

    Regards,

    Peter Chung

     

  • 0 in reply to Peter Chung
    Prodigy 250 points

    Ok, thank you for your help. I appreciate it.