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MSP430G2403 operation with 16 MHz DCO

Nuno Romao
Prodigy 200 points
Other Parts Discussed in Thread: MSP430G2403

I want to know if the MSP430G2403 is factory tested or guaranteed to operate off the DCO at 16 MHz at all four temperature and VCC corners. The spec sheet allows operation up to 16 MHz but over all temperature and VCC variations of the DCO using the calibrated 16 MHz settings has a +/- 6% maximum spread that could push MCLK up to 16.96 MHz.

  • 0
    Guru 227245 points

    Not only that. The 16MHz is an average frequency, build by modulating between the next lower and next higher frequency. The next higher one is problematic even if the average is exactly 16MHz.
    For a different MSP with 25MHz specified max clock speed, I once calculated that the maximum safe DCO frequency setting (worst case) is ~23,5MHz. Anything above may cause single clock pulses exceeding 25Mhz, depending on each individual MSP. By considering the maximum DCO modulation step size and the DCO tolerances.

    However, usually, the maximum clock speed has its own tolerance range above this value. It is just not guaranteed to always work. If you need to be safe, don’t go that high. If not, try your luck.

  • 0 in reply to Jens-Michael Gross
    Prodigy 200 points

    Seems like the calibrated 16 MHz setting is useless. I wonder why TI even bothers with it.

  • 0 in reply to Jens-Michael Gross
    Prodigy 200 points

    The part can only be tested at 16 MHz with the DCO because there is no external HF clock source option on this part. So either the 16 MHz data sheet specification isn't tested or it's tested with the DCO, which is why I asked the question.

  • 0 in reply to Nuno Romao
    Guru 227245 points

    The specs only guarantee 16MHz core clock. However, there is some safety margin. If a device fails during 16MHz calibration (with clock pulses above 16MHz), it won’t be sold. However, this does not mean that the MSP will run under all conditions (full temperature and supply range) with 16MHz DCO. You might need to give it 0.1V more than minimum or keep it cool.

    As for the external clock, tests have revealed that these MSPs, while not supporting an HF crystal, can take 16MHz square-wave digital clock on the XT1 pin with up to 16MHz. So if you have an external oscillator with TTL output, you can run the MSP on precise 16MHz. At the cost of additional oscillator operating current.

  • 0 in reply to Nuno Romao
    Guru 46710 points

    Nuno Romao said:
    The part can only be tested at 16 MHz with the DCO because there is no external HF clock source option on this part. So either the 16 MHz data sheet specification isn't tested or it's tested with the DCO, which is why I asked the question.

    Presence of DCO calibration values means that part indeed did run at the calibrated frequencies during manufacturing. Most likely room temperature only.

  • 0 in reply to Jens-Michael Gross
    Prodigy 200 points

    Thank you both, this is useful information.

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