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Piccolo 28035 Supply and BOR brownout levels - undefined voltage range?

StephanS
Genius 4087 points

Other Parts Discussed in Thread: TMS320F28035

The TMS320F28035 Piccolo Device supply voltage  VDDIO is  2.97V ~ 3.63 V  (page 93 of sprs584d.pdf).

The VDDIO BOR trip point however is min 2.50V, typ. 2.78V, max. 2.96V.

So if the processor is guaranteed to run from 2.97V and the BOR trip may be at 2.5V, isn't there a gap (undefined behaviour) between 2.5V and 2.97V?

Or am I missing something?

We are running the Piccolo with internal VREG for 1.8/1.9V, but I cannot see any note regarding the min 3.3V supply for a proper 1.8/1.9V VREG.

It should run down to 2.5V, otherwise this undefined voltage range would make the internal BOR pretty useless.

Any clarification is appreciated.

  • 0 in reply to StephanS
    Genius 4087 points

    We would really like to get some clarification on that.

    Is the Piccolo running properly down to 2.5V (other than stated in the datasheet)?

    Or is the BOR simply useless (because of the gap between BOR trip point min supply) and we need an external voltage supervisor that trips at 2.97V?

  • 0 in reply to StephanS
    Genius 4087 points

    Are we the only ones with this question?

  • 0 in reply to StephanS
    Genius 5885 points

     Hi Stephan,

    As far as I understand BOR functionality, it is there only to monitor VDD - core voltage. But it does so through monitoring VDDIO voltage. So if VDDIO goes lower than 2.5 (worst case lowest point when internal regulator still works) BOR puts CPU in reset.

     

    My questions might be a little bit more specific:

    1. Do GPIO buffers work correctly between 2.5V and 2.97V, and core voltage is fixed at 1.8V

    2. Does FLASH have full functionality when VDDIO is between 2.5V and 2.97V, and core voltage is fixed at 1.8V?

    If answer to both question is yes, than BOR functionality is useful otherwise not.

     

    And I agree you should get some feedback from TI (you question probably landed on the same guys/gals desk probably that is supposed to update compiler documantation)

    Regards, Mitja

  • 0 in reply to Mitja Nemec
    Genius 4087 points

    Hi Mitja,

    thanks for your reply - so my thoughts regarding BOR are not totally wrong as you are asking similar questions.

    I am so glad that my question seems to be visible to others and is not located in some black hole or wormhole or whatsoever - or you and me are located in some sort of parallel universe that obviously is not visible to any TI guy who could bring some light into this topic....:-)

    So any TI feedback is still appreciated...

    Regards, Stephan

  • 0 in reply to StephanS
    TI__Expert 8500 points

    Stephan/Mitja,

    TI cannot guarantee anything outside of the datasheet. While devices typically work outside of the recommended operating conditions it cannot be guaranteed that the device will work down to 2.5v when the datasheet does not allow it. This does leave a hole between the minimum operating condition and the minimum BOR trip point. The need for an external supervisor will depend on the reliability/safety requirements of the application. Typically when the supply voltage fails to reach the chip (due to a faulty regulator, or a bad solder joint, etc.), it is usually a catastrophic event, meaning the voltage typically does not sit at 2.7v while the device continues out of spec but not in reset. In this catastrophic case the BOR removes any requirement for an external supervisor to pull reset. If an application must handle the low level DPPM fault of a non-catastrophic supply fault, then yes, they will need an external supervisor. This is in line with competitor's products of this class.

    Hope this helps.

    Regards,
    Dave

     

  • 0 in reply to David Foley
    Genius 4087 points

    Hi David,

    David Foley said:

    This does leave a hole between the minimum operating condition and the minimum BOR trip point.

    Thanks for clarification. I was afraid of that.

    A range with undefined behaviour from 2.5V to 2.97V (worst case) seems to be a danger for ANY application to me.
    So we will have to add an external voltage supervision with additional cost and board space :-(