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PCM1861-Q1: PCM1861-Q1 ADC Oscilator or Cyrstal usage

Jaydon Chae
Prodigy 60 points
Part Number: PCM1861-Q1
Other Parts Discussed in Thread: PCM1861, PCM1821-Q1, PCM1821,

Tool/software:

Hi All,

I'm using PCM1861 ADC with H/W conorl mode and I2S format by connection 12.88MHz OSC as below to make a default 48KHz Fs rather than 24.576MHz Crystal. It's located close enought to IC

But sometimes, there is not working situation so when putting a few pFg(18pF) to C22, C25 wihout Crystal,  this situation has been disappeared..

Previoulsy, I used 24.576MHz crystal with this 18pF and I never encoutered this one.. 

In PCM1861, is it having some weak point when using 12.288MHz OSC? If so, is it OK to put a few pF like above without crystal? Help to get your advice

By the way, I'm using alos PCM1821-Q1 together with putting 12.288MHz OSC but in PCM1821, it's working well without such an issue.

Help to get your suppotting to identify it

Thanks 

Best regards,

Jaydon 

Best regards,

Jaydon 

  • 0
    TI__Mastermind 25360 points

    Hi Jaydon,

    The capacitors to ground is recommended when using a XTAL as an external clock source, typically 15pF. Additionally, 12.288MHz is below the recommended frequency limits on our hardware controlled devices and is likely why you're experiencing this issue.

  • 0 in reply to Daveon Douglas
    Prodigy 60 points

    Hi Daveon,

    Thanks for your reply.. I can see a min fs of XTAL with over 15MHz.. So in the EVM of PCM1861-Q1, there is 24.576MHz crystal 

    But I'd like to use 12.288MHz fs  to make a default 48KHz and in the table, there is that 3.3V CMOS MCLK is possible from 1MHz to 50MHz so I added this 12.288MHz OSC with not using 24.576MHz crystal.. So help to get your advicde on the below questions 

    -. PCM1861-Q1 is not recommending to use the external OSC?

    -. If possible to use the external OSC(like 12.288MHz OSC), how to implement the connection of it?

    -. Will it be better to use crystal(from 15MHz) with 15pF rather than the exteral OSC? 

    Help to get your advice again.

    Thanks 

    Best regards,

    Jaydon 

  • 0 in reply to Jaydon Chae
    TI__Mastermind 25360 points

    Hi,

    You can input 12.228MHz directly into SCKI pin and configure the MDx pins for your desired clock ratios. Please see section 9.3.9 of the datasheet for more details.

  • 0 in reply to Daveon Douglas
    Prodigy 60 points

    Hi Daven,

    Thanks for your reply again and I'd like to get your advice as well..  

    1.  Even though using 12.288MHz OSC directly into SCKI without crystal, the capacitors(15pF) of XTAL should be used instead of leaving N.C of these 15pF to protect any not working issue which I'm encountering now?

    2.  There is no XTAL connection and just OSC connetion way in PCM1821-Q1.. I used the same 12.288MHz OSC as below but in PCM1821-Q1, there is no such an issue.  Could you help to inform what is the difference in btw PCM1861-Q1 and PCM1821-Q1 when connection of the external OSC like 12.288MHz?

      

    I have to finalize ADC part and your advice on the above questions will be highly appreciated..

    Thanks 

    Best regards,

    Jaydon  

  • 0 in reply to Jaydon Chae
    TI__Mastermind 25360 points

    Hi Jaydon, 

    Osc clocks typically provides clock signals directly without needing to add external components. Passive XTAL clock generators typically rely on external circuitry to oscillate.

    If you provide the oscillator clock directly to SCKI of PCM186x there shouldn't be an issue (Same with PCM182x BCLK/CCLK input), however the X0/XI pins of PCM186x are designed for passive quartz crystal components which do require that external circuitry mentioned earlier.