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TM4C1230C3PM - How to set ADC clock source (OSC : 25MHz)

Grace Lai
Intellectual 605 points

Hi Sir,

For our application, we must to use OSC 25MHz not 16MHz. Please help us to tell us How to set ADC clock source is the best. Thanks a lot !!!

  • 0
    TI__Guru**** 244400 points
    Hello Grace

    On TM4C123x devices the maximum conversion rate is 1MSPS (without using the phase shift approach). This results in the maximum clock rate of 16MHz. Any other clock source higher than 16MHz, may result in in-correct conversion results.
  • 0 in reply to Amit Ashara
    TI__Intellectual 1630 points

    Hi Amit,

    Customer would like to use 25MHz crystal as main clock source. Is there any recommendation of how to set the registers? It is only used for battery monitoring so the speed could be lower than 1MSPS.

    Regards,

    Edward

  • 0 in reply to Edward Chang
    TI__Guru**** 244400 points
    Hello Edward

    The TM4C123x device has two settings for clock source in the ADCCC register

    1. PIOSC which is 16MHz
    2. System clock which when the PLL is bypassed is same as the crystal or if the PLL is used then the VCO is divided to get 16MHz.

    Now if the user is using 25MHz crystal, then the PLL must be used so that the resulting clock to the ADC is PLL VCO divided by 25 to get 16MHz. If the PLL is not used then 25MHz is provided to the ADC. In this case we cannot guarantee the result as per the data sheet.