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Factors that Affect ASC12OSC in the MPS430F2419

Darren Beckwith
Expert 1010 points
Other Parts Discussed in Thread: MSP430F2419

I was wondering if you could find out what factors affect the frequency of the internal ADC12OSC in the MSP430F2419.  The datasheet (page 67 of SLAS514F) states the range is 3.7 to 6.3 MHz with 5 MHz being the typical value.

I was looking for data (a graph) that would show how the range varied with temperature and with voltage.  I basically want to know how stable this will be during the operating life of the product.

 

  • 0
    Guru 227245 points

    Consider it free-running.

    Individual variations between devices may be larger than the effects of temperature and operating voltage.

    It is even difficult to measure it.

    If you want a stable, known  frequency, use SMCLK or ACLK as clock source.

     

  • 0 in reply to Jens-Michael Gross
    TI__Genius 12770 points

    Darren,

    I agree with Jens-Michael; what would stand in your way of using ACLK or SMCLK as the clock source for the ADC12?

    Best regards,

    Austin Miller

  • 0 in reply to Austin Miller
    Expert 1010 points

    Jens-Michael, Austin,

    Thanks for the quick reply.

    I am working on porting an existing application from the 149 to the 2419.  The existing application used SMCLK as the ADC12 clock source.  Unfortunately the existing application did not sleep and I have been tasked with lowering the quiescent current of the port.  I have the port running at LPM1 but I was trying to move to LPM3.  If I use the LPM3 with the SMCLK as ADC12 clock source then the conversions will stop when the system enters LPM3 and I can not have that.  I need the conversions running in the background (during sleep) so that when the conversion complete interrupt fires the CPU can wake up and process the result. This is why I switched to using the ADC12OSC to drive the conversion.

    We have used the ADC12OSC in other products without any issues but I was surprised to see the variability in the frequency and wanted to know how supply voltage and temperature affected the frequency.

    Cheers,

    Darren

  • 0 in reply to Darren Beckwith
    Guru 227245 points

    Darren Beckwith said:
    If I use the LPM3 with the SMCLK as ADC12 clock source then the conversions will stop when the system enters LPM3 and I can not have that.

    Sure, but why entering LPM3? It makes almost no difference if you shut down SMCLK but activate ADC12OSC or if you do ot use ADC12OSC (which then is shut off) and continue using SMCLK. The difference would be negligible.

    The most energy is saved by putting the MSP into LPM0, thus disabling the CPU if it has nothing to do. How much more you can save depends on many parameters. There is no 'reduce the power consumption' switch that will automatically drop the power usage, else it would be active all the time.
    Whether the different LPMs bring you any benefits or maybe even disadvantages depends on their 'effect' and your application.

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