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MSP430 DCO

Christopher Daily1
Intellectual 400 points

E2E Team,

I’m looking for a spec on the min voltage for the MSP430 that can support DCO of 16MHz.

There is something in the datasheet about 3V, but it doesn’t seem to have a min level.

Do they have a recommended or required way to safely switch to 16MHz on start up from 0V to 3.3V

My understanding is after a PUC it defaults to 1MHz and that is stable within 2uS.

Thanks.

  • 0
    Guru 16361 points

    Which specific chip are you using?

  • 0
    Guru 23000 points

    In which Data Sheet and where dit you read the 'something'?

  • 0
    Guru 34483 points

    If you want to run MSP430 at low (core) voltage at highest possible clock (depending on used peripherals) using external crystal will be a better choice. I am running (for few years) MSP430F550X devices on 26 MHz MCLK with 26 MHz XT2 on 1.8V VCC and default core voltage.

    http://forum.43oh.com/topic/3906-msp430f5xx-overclocking/

  • 0 in reply to zrno soli
    Guru 27285 points

    zrno soli said:

    If you want to run MSP430 at low (core) voltage at highest possible clock (depending on used peripherals) using external crystal will be a better choice. I am running (for few years) MSP430F550X devices on 26 MHz MCLK with 26 MHz XT2 on 1.8V VCC and default core voltage.

    http://forum.43oh.com/topic/3906-msp430f5xx-overclocking/

     Hi Zrno, thank a lot for this report, I was aware of this performance and I never touched vcore, also I am underclocking than overclocking but your test is complete.

     The only parameter I exceeded in the past is MAX vcc, one time was due to a defect on Smart Card socket resulting in a lopp over charge pump powering MSP @6V, none of lot was burn.. but a lot of smart card died.

     The processor run from 3 AA batteries powered on from end of 2006 lasted from october to november, batteries leaked out, processor was 2xxx  20 pin, the simplest with enough Flash.

  • 0 in reply to Roberto Romano
    Intellectual 400 points

    E2E Team,

    Here is some feedback from our customer...

    "That's not very good or specific to my question. I'm running dco at 16MHz from a 3.3 supply. My supply tolerance is 3.1V min. Will I have any issues? There seems to be a couple spots in the data sheet that day 3 volts is enough but another that almost seems to recommend 3.3 volts. The pare we are using is MSP430F2619TPMR."

    Thanks!

     

     

  • 0 in reply to Christopher Daily1
    Guru 23000 points

    Christopher Daily1 said:
    That's not very good or specific to my question.

    I can’t find the ‘something’ about 3V.

    I think the Data Sheet is very clear; Page 30: Vcc equal or greater than 3.3V 16MHz. Also look to the graph in: “Figure 1. Operating Area”.

    3.1V might work but is not recommended.

  • 0 in reply to Leo Bosch
    Intellectual 400 points

    Under the dco section.

    See 3 volts for 16MHz.

  • 0 in reply to Christopher Daily1
    Guru 23000 points
    Ok, now I see the ‘something’, and agree this might look in contradiction and maybe confuses.

    But these are specifying the frequency range and calibration data at a certain voltage level. Your car might be able to drive 300Kmh and the manufacturer can specify the amount of noise at this speed but this doesn’t mean that this speed is recommended (save) to use, for that only the ‘Recommended Operating Conditions’ counts.
  • 0 in reply to Leo Bosch
    Guru 16361 points

    Those two tables aren't contradictory as far as I can tell.

    Page 30 of the datasheet specifies maximum MCLK frequency for various VCC levels. Granted it's a bit vague because it says "recommended operating conditions", and specifies 16 MHz maximum frequency for voltages above 3.3V (but the maximum frequency isn't specified between 2.7V and 3.3V)

    The other table specifies DCO frequency only, as distinct from MCLK. With RSELx =15 and DCOx=7 the DCO frequency could be as high as 26MHz. That doesn't mean you can clock the CPU at 26MHz. If the DCO was running at 26MHz and MCLK was sourced from it, then the MCLK divider would need to be set to 2 so as not to exceed the maximum MCLK frequency specification.

  • 0 in reply to Christopher Daily1
    Guru 227245 points
    As Leo and Robert pointed out, the table for the DCO just lists the typical and min/max frequencies the DCO will have at different supply voltage levels. Since the DCO has a certain voltage drift, it will be slower on lower supply voltage. However, the DCO will operate down to the minimum allowed supply voltage. But while on VCC=3V, it is able to reach at least 16 but not more than 26MHz on its highest setting, it might only reach, say, 15MHz when running on 2.8V. While a different MSP of the same model may reach 25MHz with the same setting.
    So with RSELx=15 and DCOx=7 you can expect at least 16MHz for VCC=3V, but maybe(!) less for a lower VCC. The reason why 2,2V isn't listed on the highest setting sis because it (at first glance) doesn't make sense to run the DCO on >12MHz while the CPU can't run as fast on 2.2V anyway.
    However, as Robert noted, you can run the DCO on 16MHz and use DIVM_2 to run MCLK with 8MHz. And, more important, you can run SMCLK on either 16MHz (as SMCLK and the peripherals are nor as limited by the supply voltage as the CPU core) or on 8Mhz too which would smoothen the DCO clock jitter that is introduced by the modulation.

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