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PLL configuration and limits

Dominique Ignacio

I am trying to make an eval-board MCB2368 work at 19.968MHz. According to the user manual, 275<Fcco<550MHz. However, at the errata sheet version 1.1 for LPC2368 is said that the limit for Fcco is 290MHz. So, I realize we have the range 275<Fcco<290MHz for LPC2368.

The LPC2368 documentation says also that 1<N<256 and 1<M<32768.

To match my needs, I found the values N=125, M=1456 (for these values I got Fcco=279.552MHz), both inside the respect range.

My problem is that for any value of N bigger than 37 the PLL doesn't work.

Some one can explain me if I am doing something wrong or is it really missing information at LPC2300 documentation?

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  • 0 in reply to Suvidh Kankariya

    OK, with this information I see M is out of the range. Thank you.

    But, for 6<M<512, N value is also problematic and in low values.

    For example, using a MCB2368:
    M = 419
    N = 36
    FIN = 12MHz
    I got Cclk = 19.9523MHz and it works.

    But:
    M = 440
    N = 38
    FIN = 12MHz
    I got Cclk = 19.8496MHz and it doesn't work.

    Any reason for that?

Reply
  • 0 in reply to Suvidh Kankariya

    OK, with this information I see M is out of the range. Thank you.

    But, for 6<M<512, N value is also problematic and in low values.

    For example, using a MCB2368:
    M = 419
    N = 36
    FIN = 12MHz
    I got Cclk = 19.9523MHz and it works.

    But:
    M = 440
    N = 38
    FIN = 12MHz
    I got Cclk = 19.8496MHz and it doesn't work.

    Any reason for that?

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