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TMS320F280049C: need Design support for Decoupling of VDD pins

Jens G
Expert 3485 points

Part Number: TMS320F280049C

Hi team,

please can you provide some support on this question:

  1. In the first approach I want to use the internal 1.2V switching regulator of the controller. The data sheet recommends in chapter 6.3.3 that there must be at least 20uF of capacitance at each VDD pin. In Figure 7-6 and Table 7-2 and in the schematic for the evaluation board the 20uF are only present once:

    This looks contradictory to me. Which configuration counts and should be used for my new design?

  2. ESR question of 10uF for Cvdd or Cvddio:
    According to the BOM, the type GRM188R61A106ME69D from Murata is used on the EVM board for C1 and C2.
    According to the data sheet, this type has a dissipation factor of 0.1@1kHz. A conversion with the formula tan(Delta) = ESR * 2*Pi*f*C results in an ESR of approx. 1.6Ohm, which still means 800mOhm with a parallel connection of two capacitors. However, <10mOhm is required (see Table 7-2 above).

https://search.murata.co.jp/Ceramy/image/img/A01X/G101/ENG/GRM188R61A106ME69-01A.pdf


Can a 10uF/10V with an ESR of approx. 1.6Ohm also be used for our design or which type do you suggest?

Thanks

Jens



  • +1
    TI__Mastermind 28275 points

    Hi Jens,

    Jens G said:
    In the first approach I want to use the internal 1.2V switching regulator of the controller. The data sheet recommends in chapter 6.3.3 that there must be at least 20uF of capacitance at each VDD pin. In Figure 7-6 and Table 7-2 and in the schematic for the evaluation board the 20uF are only present once:

    The requirement is total cap of 20uF and it is recommended to install two 10uF in parallel. See table below:

    Jens G said:
    ESR question of 10uF for Cvdd or Cvddio:
    According to the BOM, the type GRM188R61A106ME69D from Murata is used on the EVM board for C1 and C2.
    According to the data sheet, this type has a dissipation factor of 0.1@1kHz. A conversion with the formula tan(Delta) = ESR * 2*Pi*f*C results in an ESR of approx. 1.6Ohm, which still means 800mOhm with a parallel connection of two capacitors. However, <10mOhm is required (see Table 7-2 above).

    The ESR spec in the datasheet is specified around the switching frequency of the DCDC, i.e about 1MHz. Hence the calculated ESR at the frequency of interest is about 1.6mOhm, well within the specification.

    Let us know if you have more questions.