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MSP430FR2000: Using the eComp peripheral in a low-power way to check Vcc..

Newman
Expert 5995 points
Part Number: MSP430FR2000

Hello,

My customer would like to use the eComp peripheral to check when Vcc reaches 2.0VDC.  FR2000 SVS will not work since it is not programmable.  The internal (absolute) eComp reference is 1.15V-1.23V.. making it unusable w/ an input that is higher (Vcc ~3.6VDC-1.8VDC) than the ref.. and Vcc will not work (as the eComp reference).  Also, don't want to use an external divider on Vcc since this would be a constant current drain.  You guys have anything creative or a creative use of the part/peripherals to do this in a low-power way?

Thanks, Merril

  • 0
    TI__Mastermind 39650 points
    Hi Newman

    This application note will help you solve the problem.
    www.ti.com/.../slaa828.pdf

    Best regards
    Gary
  • 0 in reply to Gary Gao
    TI__Expert 5995 points
    Hi Gary,
    Thanks.. but switching to a version of the device w/ the ADC will add to the cost. Any cleverness to solve this w/o adding the ADC?
    Thanks, Merril
  • 0 in reply to Newman
    TI__Mastermind 39650 points

    Hi Newman

    Can you give me more information about the customer's requirement?
    For example, How often to detect the VCC?(Always or just for some time and what's the period) What's the maximum power limit? Why to check 2.0VDC of DVCC ?It will be some risk. Because the minimum supply power voltage is 2.0 V it will be unreliable to use eCOMP at the limited voltage.

    Best regards
    Gary

  • 0 in reply to Gary Gao
    TI__Expert 5995 points

    Hi Gary,

    Thanks.  This is a battery operated system so we want long battery life and we're checking for low battery voltage.  The check does not need to be continuous but often enough to see if the battery is getting low.. say once a minute.. or once every 10 minutes (guessing). 

    The minimum (operating) VCC of the FR2000 is (per datasheet) "Wide Supply Voltage Range (1.8 V to 3.6 V)" but.. it does need a slightly higher voltage (~1.99VDC) to power-up. 

    Once powered up (from the min voltage of ~1.99VDC) it can then run/operate down-to 1.8VDC. 

    So if we can run downto 1.8VDC.. we want to detect when we are getting close (say 2.0VDC) to the minimum (of 1.8VDC).. to warn user of need to replace the battery.

    Thanks, Merril

  • 0 in reply to Newman
    TI__Mastermind 39650 points

    Hi Newman

    What I mean of the limitation of 2.0v is the eCOMP supply voltage.That we can see in the datasheet as below:

    I know what's the application now.

    I have an idea that:

    You can use the P1.7 to output the internal reference 1.2V. Put this REF to eCOMP input channel. And use DAC to another eCOMP channel. The DAC 's reference you should choose the VDD. And you can configue the DAC divided the VDD to (1.2/2.2)*64=34.9≈32=0x10(Suppose the detected voltage is 2.2V). You can use a timer to detect the VCC on and off. This solution will cost two GPIOs. 

    Best regards

    Gary

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