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quartz internal capacity 12.5

chouban
Prodigy 130 points

i using an internal capacitor for watch quartz  32k, i have recive this with my 64/msp430 debuging kit

i see that there are not 12.5 internal capa,

i have test all the case 10 - 12 - 14 and i see a randam clock : (see via a timer that count the sec)

some time it take 1 or 2 min for the clock to stablize it's too long and strange ...

can we help me on this

  • 0
    Prodigy 130 points

    do i need in this case to use a external capa 12.5

    using the internal capa 12 or 14 ... give a randum clock

  • 0
    Guru 227245 points

    Normally, the internal capacitor of 12pF on each pin is good for a standard 32.768kHz watch quartz. No external capacitors should be applied and wiring should be as short as possible. Also, by package and printed board, additional 2pF are added (or more, depending on the PCB layout)

    The 1xx family datasheet also adds a note that a 5.1MOhm resistor should be applied from XOUT to VSS when VCC<2.5V. But this note is missing in the 54xx family guide.

    In any case, the LFXT1 should be stable withing several milliseconds.

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