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MSP430 Flash & SVS

Atul Bhakay
Genius 3205 points


Hi,    We have tried SVS detection using AVCC and SVSIN pins. Once we detect a Power Failure the device start saving data into the MSP430 Flash. 

Case 1: Using AVCC

Using AVCC pin for SVS was somewhat successful. This was tried out by keeping a RC circuit to generate a time constant delay on the 3.3 volt supply to DVCC. Using this circuit the DVCC pin receive 2.4 Volt due to resistor voltage drop across the RC circuit. This circuit works sometimes and sometimes it doesn't. This not a 100 % correct solution to our requirement.

 

Case 2 : Using SVS

Using SVSIN pin detects a below 1.25 volt. A Raw 9 Volt supply cut down to 1.8 Volt using a potential divider circuit was made. On power failure 1.8 Volt drops faster than 3.3V supply to DVCC and the device starts storing data in Flash but never finishes the operation. This causes 0xFF to be written to the .mydata Flash area. This causes all other stored parameters to be erased too. 

 

If you could suggest a full proof circuit for SVS it would be great. Once power failure is detected the controller should remain on for a longer period of time for it to store data in the Flash. Hope to receive a reply soon. This is a urgent requirement from our side. 

 Regards     Atul Bhakay

  • 0
    Intellectual 595 points

    Hello Atul

    Can you not use your second method but simply ensure that the DVCC has enough capacitance to ensure it maintains operation of the micro for as long as needed?  Presumably when the power-out occurs, you can switch off everything that's not required (presumably nothing else is required since it's about to die), saving as much micro power as possible, and do the saving at the best combination of speed/sleep modes that gets the best out of the capacitor?

    It might be helpful to ensure that any voltage regulator that you are providing to power the micro either has enough capacitance of its own to keep it running normally for the duration of the save, or that if the input voltage on it dies, then it doesn't consume current from the DVCC line.  Whether this is likely to occur or not depends on the kind of regulator you are using.

    How long are you needing to do the save?

    Regards

    Tony

  • 0
    Guru 227245 points

    It's not only the absolute voltage but also the amount/speed at whih VCC changes during a flash write. If DVCC changes too much during a write, the operation may fail even if there's enough supply left for running the chip.

    For flash operations VCC has to be stable.

    The suggestion of adding enough capacitance to DVCC is a good one. And of course switching off all other load like LEDs or so immediately.

  • 0 in reply to Tony Payn
    Genius 3205 points

    Hi,   Thanks for the reply.    Our Leds and LCD display is already connected to 3.3 Volt and 5 Volt respectively; The 3.3 V is generated from 5 Volt itself. I have checked the drop in 5 volt on the oscillator and the time constant for it to reach 67 % of it suply value is around 700 to 900 ms. Now in that the flash write should happen but i think the LCD and the LEDs consume the charge left and hence a drop in voltage below that threshold causes the flash it be erased to 0xFF. 

    Would a separate supply to the controller solve the issue? Could also suggest a different voltage regulator if required. 

    Regards     ATul Bhakay

     

  • 0 in reply to Atul Bhakay
    Guru 25210 points

    Atul Bhakay said:
    Would a separate supply to the controller solve the issue? Could also suggest a different voltage regulator if required. 

    Anything you can do to isolate the MSP430 supply from the other loads on the board is helpful. Ideally you would be able to turn off the LCD and LEDs when a power failure event is detected.

    Regardless, if you supply from a separate LDO, and provide sufficient capacitance on the DVcc pin, you should be able to complete your Flash writing routine. You try to minimize the amount of data that really needs to be stored as well, to reduce the time required for the storage process to complete.

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