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MSP430FR6920: Very slow rising Vcc and BOR - Continued (RESET Hold Time Spec?)

Part Number: MSP430FR6920

TI Family,

This thread builds off of this one -->(+) Very slow rising Vcc and BOR - MSP low-power microcontroller forum - MSP low-power microcontrollers - TI E2E support forums

However, it adds an extra question as follows:

Assuming a user had a very slow ramp (3V/sec or LONGER) up for Vcc to reach 1.8V (again in the order of seconds) would the MSP430 maintain a reset condition until it reached or exceeded 1.8V?  The answer per the DS up to <3V/sec ramp, is a resounding Yes.  

However it goes a bit further where the user needs to ensure that a very slow ramp up does not cause improper operation of the control nor causes the MCU to lock-up.  

Therefore, will the BOR circuit hold reset for (X # of msec) after Vcc reaches it’s threshold?

Now, realizing that any MSP430 device with BOR circuitry does what it is meant to do:  Protect the part by holding it in reset in case of a brownout.  The BOR circuitry, however, is not 100% fine-tuned in silicon to trigger at exactly 1.799999xxxV and therefore has some level of tolerance associated with it. This of course presents us with the question: what if I am just at that gap in spec? 

To that, per the aforementioned e2e post, consider a case where the BOR releases early e.g. at 1.6V;  the part is rated to work only from 1.8V onwards...In this case code execution will proceed as expected provided MCLK stays at the default DCO.  This is also mentioned in a note in the DS.

BUT I’m not sure we explicitly spec the “BOR circuit hold reset for X msec after Vcc reaches its threshold” value itself?

ULTIMATELY it would be very helpful to know the Reset hold time for the BOR after Vcc reached the threshold voltage.  Knowing this and the tolerance on the threshold would imply a minimum ramp time for a user to avoid operating in this no man’s land.  It’s safe to say that during testing and possible during some odd “real life” operation a user could get into a condition in which the Vcc ramp could be slower than 3V/s.

Comments welcomed and appreciated!

TY,

CY

  • Hi Chris,

    First I have to ask, what is this application that has such a very long ramp time?

    According to the DS, the SVSH will allow the device to come out of BOR some where between 1.77(min) to 1.99(max).  It mentions releasing the BOR after a "short delay".  This tells me there is probably no characterization data for this value and is most likely a "by design" value.  I'll see if I can track down a designer who might know.

    Also, minimum operating voltage is controlled by the SVSH thresholds, so 1.77v to 1.99v.  So if the CPU starting to run depends on SVSH (min), and the device does not come out of BOR until sometime after, there doesn't seem to be a risk of the CPU executing before the VCC voltage reaches it's recommended operating voltage.

    Does this answer the question?

  • Hey Dennis,

    Thanks much for the quick reply.  This is for a thermostat.  We did review that portion of the DS as well and - to your point - if characterization data for this value were available (maybe from the design team) that would be very helpful.

    Now your 2nd point is even more appropriate..."if the device does not come out of BOR until sometime after, there doesn't seem to be a risk of the CPU executing before the VCC voltage reaches it's recommended operating voltage".  I agree with that.

    And further, what they are really after is this ... if the device experiences a SUPER SLOW ramp up perhaps even >3v/sec...snail's pace ... what is the MAX Reset hold time for the corresponding BOR after Vcc reaches the desired threshold voltage.  And not in voltage but in TIME. ?

    Does that spec or characterization data exist?

    TY,

    Chris

  • Hi Chis,

    what is the MAX Reset hold time for the corresponding BOR after Vcc reaches the desired threshold voltage

    Ok, let me make sure I have this correct before I approach the design team.

    We want to know what t(max) is at very, very slow VCC ramp time - correct?

  • Yes, sorry for the delay Dennis.  That's it exactly.  Let me know what you can find out please.

    Thank you!

    -Chris

  • Hi Chris,

    Just to let you know I'm waiting to here back from someone in the design team in India on this.

  • Hi Chris,

    I have ping'd our guy in India again today as a reminder.

  • Thank you Dennis , appreciate it.

  • Hi Chris,

    This is getting in incredibly frustrating.  The India team is apparently out until Monday.  I'm looking for other sources that might be able to help.

    Do me a favor and send Tim Claycomb (my manager) an email asking to escalate this issue.

  • Hi Dennis,

    I hear ya loud and clear and certainly appreciate your help.  I know that you are trying to squeeze in PTO as well so thanks for following up on this.  I will reach out to Tim as you suggested.

    Thank you,

    Chris

  • Dennis & Team,

    From customer...

    "What I need to ensure is that under a very slow Vcc ramp the micro stays in reset until Vcc is above the minimum operating voltage for the core.

     If the maximum threshold voltage of the BOR is greater than the minimum operating voltage then I need to know what the max. threshold voltage is, the minimum operating voltage of the core, and the minimum time that BOR will be held. Given that information we can then determine how fast we must transition through this “no man’s land”.

     In other micros that I have worked with the Power on Reset / Brown Out Reset circuitry guaranteed that Vcc was above the min core voltage when reset was released."

    COMMENTS WELCOMED.

    TY,

    Chris

  • Hi Chris,

    There is no spec on the BOR release time and this time does not matter.

    All the data which is needed in in the SVS specification:

    Based on the VSVS- data point the 1.75V listed as MIN value. This is the voltage the device is designed and qualified for.

    Every voltage above 1.75V will operate the device in the specified parameters. However there may be some variation over process and temperature.

    When the SVS releases the reset, the device is in a stable condition.

    Thank you,

    Tim Claycomb

  • Thank you, Tim.  I will discuss with the customer and advise of any additional outcomes.

    Appreciate you running this down for us.

    TY,
    Chris