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TM4C1294KCPDT: VCC monitoring for storage while power is lost

Pallav Gandhi
Intellectual 900 points
Part Number: TM4C1294KCPDT


Dear,

We are using TM4C1294KCPDT for one of our product. Now as we have to store some of the parameters while mains supply is gone. So as to restore from those last readings.

Now my question is is there something which monitors VCC of controller? If so can i generate interrupt on degradation of VCC by 25% and store those in my memory.

If so please guide me. Also if is there any other way for doing this please suggest.

Regards.

  • 0
    Guru 117855 points

    Greetings,

    This sounds much like an ideal job for an, 'Analog Voltage Comparator.'    Note that the MCUs here 'include' one or more such 'Analog Comparators' - yet our preference is for an 'External Analog Comparator.'

    Our justification (for external over MCU's internal) follows:

    • Assume that your Main Supply feeds 12V (or above) to your board(s) - which then regulate down to '3V3 for the MCU'  - & pehaps another voltage to satisfy (other) device demands.   Now the MCU's ADC  restricts that input voltage to 3V3 - forcing the implementation of a (near) 4:1 voltage divider network.   (to bring the external supply voltage 'DOWN' - to MCU-Acceptable levels.)   In this process (although 'glossed over' - far too often) is the 'Loss of (near) 75% of the Analog Comparator's 'effective' signal resolution.'     (caused by the voltage divider)    Most external Analog Comparators provide supply ratings which 'accept' the direct application of 12V.   (some devices - even higher!)   You have thus significantly increased the 'sensitivity' of your Voltage Detection circuit - via the external device.
    • Both 'Size & Additional Channels' are accommodated by external analog comparators.   (tiny SOT single channel, dual/quad in soic)   Often it is desirable to monitor 'multiple' voltages - the external, quad channel device is the one my firm most often deploys.    Further - w/those 'additional channels' one can create a (most) useful, 'Window Comparator' - which insures that the monitored signal remains w/in 'adjustable voltage bounds.'    (i.e. by 'bounds' is meant - the signal must remain w/in (both) 'low & high' signal limits - to prevent the 'alerting' interrupt.)
    • Hysteresis (setting the comparator's 'switching points' to reduce/prevent 'oscillation' - as the input signal 'loiters' at/around the 'switching point.'    The pinouts of the external comparators ease & reduce board size by grouping the 3 comparator signal pins in (very) close proximity.   This is 'not too often' the case w/the 'busier pinned' MCU.
    • Finally - 'Re-Use of your IP.'   Choosing the MCU's Analog Comparator places demands upon (both) your hardware & software development.   And - when 'competitive advances' prove 'Too Strong' to resist - and a different MCU is needed - what then?    Most likely - a brand new 'learning curve' arrives - and that new, 'MCU du jour' - may itself require replacement - down the road.    In contrast - the Analog Comparator's Gerber File may be, 'Quickly, Easily, Efficiently' imported to each/every new device - and/or 'Used in multiple' when (many) voltages are to be monitored.

    One or more of the external comparator's outputs will attach (likely aided via pull-ups) to 'close in' MCU GPIO(s) - which 'Interrupt to signal voltage alerts.'

    The 'MCU as Kitchen Sink'  trend continues (here as well as elsewhere) - yet is not always the 'best choice' - as the facts here (rather clearly) reveal...