Consistency of DCO parameters across multiple samples of a given part number?

Started by "Dav...@yahoo.com [msp430]" June 20, 2018
I am working on a project that uses MSP430G2452IPW14 (14 pin TSSOP package.)

At initialization, I set MCLK and SMCLK sourced from DCO and set DCO to my chosen clock frequency (I did not rely on Info flash segment D calibration parameters, as those didn't yield the frequency I require.)

I was surprised to find upon building my second prototype of the project that the DCO frequency, using the same parameters as the first prototype, was off considerably (perhaps 5% or so.)

What should I expect in terms of DCO frequency consistency? Should I plan a calibration step for each device I use (i.e., find it's correct parameters to obtain the required frequency?) I do not have a crystal or other primary frequency source in the design -- the DCO is being used stand-alone with no discipline mechanism available.

Thanks,

Dave
w...@yahoo.com

Posted by: David Feldman



Beginning Microcontrollers with the MSP430

The accuracy and repeatability of the DCO  clock for the pre-programmed
values is around 3%. I tested just 20 samples and found that typically
this was closer to 1%. Certainly on a range of 200 shipped units, using
a calibrated DCO for a 460kb UART, no complaints were received regarding
failed communication to a PC based program. But this is a small sample.
For any other value of DCO frequency I would expect much worse, given
that Ti rate some of their calibrated values as worst case +/-6% over
the full temperature range.  What prevents you from using one of the
calibrated frequencies, or even a cheap watch crystal. Not all, but
most, of my designs use a watch crystal, and still achieve very low mean
power consumption, and I design very tiny systems typically 1cm square
or smaller, so size shouldn't be an issue.

Al
On 21/06/2018 9:01 AM, David Feldman w...@yahoo.com [msp430] wrote:
> I am working on a project that uses MSP430G2452IPW14 (14 pin TSSOP package.)
>
> At initialization, I set MCLK and SMCLK sourced from DCO and set DCO to my chosen clock frequency (I did not rely on Info flash segment D calibration parameters, as those didn't yield the frequency I require.)
>
> I was surprised to find upon building my second prototype of the project that the DCO frequency, using the same parameters as the first prototype, was off considerably (perhaps 5% or so.)
>
> What should I expect in terms of DCO frequency consistency? Should I plan a calibration step for each device I use (i.e., find it's correct parameters to obtain the required frequency?) I do not have a crystal or other primary frequency source in the design -- the DCO is being used stand-alone with no discipline mechanism available.
>
> Thanks,
>
> Dave
> w...@yahoo.com
>
> Posted by: David Feldman
>
>
>
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