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Hybrid OPP

bandini
Intellectual 630 points
Other Parts Discussed in Thread: DM3725, DM3730

I have two questions :

Is it possible to run dm3725 at and hybrid opp for instance with ARM @ OPP130 and DSP @ OPP100, or the opposite : ARM@OPP100 and DSP@OPP130. VMPU is set to the required OPP130 voltage.

Is it possible to lift the Tj < 90 °C constraint by running  such an hybrid OPP ? In other word, can I for instance run the DSP at 520 MHz, the ARM at 800 MHz, and let the junction temperature go up to 105 ?

  • 0
    TI__Guru 65405 points

    Hi Bandini,

    It is not possible both DSP and ARM to operate on different (hybrid) OPP levels. The DM3725 can operate only on standard fixed OPP levels as: OPP50, OPP100, OPP130 and OPP1G.

    About the junction temperature you can calculate and it keep it under 90 °C as you measure the power supply or current to DM3725 and consider thermal resistance junction-ambient constant θJA . You can obtain information about it from the DM3730, DM3725 Digital Media Processors document section 7.1 Package Thermal Characteristics at the link:

    http://www.ti.com/lit/ds/symlink/dm3730.pdf

    Also should be useful to look at the AM/DM37x Power Estimation Spreadsheet at the link:

    http://processors.wiki.ti.com/index.php/AM/DM37x_Power_Estimation_Spreadsheet

    BR

    Tsvetolin Shulev

  • 0 in reply to Cvetolin Shulev-XID
    Intellectual 630 points

    Could you be more specific about not possible ? Does it mean not tested, tested and guaranteed to fail ? I have a board that runs just fine with the following setup :

    - ARM Freq is 800 MHz, DSP Freq is 520 MHz, VDD_MPU is 1.33

    What risk am I taking by running in such conditions ?

    I am using the internal temperature sensor to measure junction temperature. Is that a reliable measurement method ?

  • 0 in reply to bandini
    Prodigy 10 points
    I know this is a old thread but I would like to get information about this as well since I am running into the similar situation. the application requires the DM3725 to run in OPP130 or even OPP1G. We don't use the DSP, only use the ARM processor.

    - What will happen if junction temperature higher than 90 °C? Is there a de-rating factor for the part reliability?

    - Is using the internal temperature sensor to measure junction temperature possible and reliable?

    Any help on these questions from any member of this forum is highly appreciated.
    Thanks,
    Josh
  • 0 in reply to joshua zhu
    TI__Guru*** 125430 points

    joshua zhu said:

    - What will happen if junction temperature higher than 90 °C? Is there a de-rating factor for the part reliability?

    I don't have data to quantify the lifetime impact, but it will be substantial.  That's why it is not allowed, i.e. it would make the lifetime far too short.

    joshua zhu said:
    - Is using the internal temperature sensor to measure junction temperature possible and reliable?

    It's certainly better than nothing!  My recollection is that the temperature sensor can be off by as much as 11C.  Therefore if you go this route you should make your "throttling threshold" 79C (or even lower) to account for accuracy issues.