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MSP430FR2355: SAC -- LPM3

steve wenner
Expert 2355 points
Part Number: MSP430FR2355


Good evening.....

I am using a ramp function with the SAC package on the MSP....I am using the internal reference generator, DAC and Internal OpAmp....Can someone tell me when I go into LPM3 what is the minimum I need to keep power supplied to for the DAC to hold it's last known value and produce it at the output pin?  I would like the lowest possible power solution for LPM3....

thank you

Steve

  • 0
    TI__Genius 13215 points

    Hi Steve,

    What do you mean for "the mininum I need to keep power supplied to for the DAC"? You just power the MCU not only the DAC, so that you should follow the MCU power supply spec as described in Datasheet. 

  • 0 in reply to Wei.Jetim Zhao
    Expert 2355 points

    Hi Wei....

    What I mean is I want to set the DAC value at an output pin via the OA buffer, then I want to go into LPM3.  At this point can I turn off the reference or OpAmp or DAC and still retain the value at the output and get the low current savings of not operating the reference buffer or OpAmp or DAC?  These hardware pieces all consume current and I was hoping that after I set the value I can turn hardware pieces off to save on battery current.......As I am writing this I am thinking that once I turn off these devices the output will drop to zero

    Thanks

    Steve

  • 0 in reply to steve wenner
    Guru 100565 points

    User Guide (SLAU445I) doesn't say anything about the SAC (DAC) switching itself off in LPM3. As a Continuous-Time thing, I suspect it doesn't. I don't see any detail on what "Low Power" mode is, but I suspect that isn't it.

    I expect that if you turn off the reference, that will drop to 0 and thence the DAC output will as well. DACSREF=0 is Vcc,so I suppose that won't stop.

    I've seen "Sample and Hold" DACs, which are effectively capacitors backed by refresh circuits. Even they eventually have to go back to an "authority" to know what level to target.

    That said, I imagine this is an easy experiment to set up.

  • 0 in reply to Bruce McKenney
    Expert 2355 points

    thanks Bruce....

    Yea I pretty much tried those experiments and I was hopeful for some wishful magic sauce that maybe I was missing......Thinking maybe they would be like the A/Ds.

    Steve

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