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PCM2704C: The crystal oscillator.

Kengo.Y
Guru 10575 points
Part Number: PCM2704C
Other Parts Discussed in Thread: PCM2706C,

Hi team,

Could you tell me how to connect the crystal oscillator?
Also, could you tell me how to calculate R1?

I think the crystal resonator was the only one in the datasheet.


Sincerely.
Kengo.

  • 0
    TI__Mastermind 21300 points

    Hello Kengo, Usually the resistor R1 is a huge resistor ( typically a 1Mohm resistor) and it is connected in parallels to crystal osc.  to  XT1 and XT0 as shown below.

     Regards,

    Arash

  • 0 in reply to Arash Loloee
    Guru 10575 points

    Hi Arash,

    Thank you for your reply.
    Is Crystal resonator and oscillator same connection?
    Does that mean you don't have to change the circuit between the oscillator and the resonator?

    Sincerely.
    Kengo.

  • +1 in reply to Kengo.Y
    TI__Mastermind 21300 points

    Please read this part of the data sheet that explains what you need.

    9.3 Feature Description

    9.3.1 Clock and Reset

    For both USB and audio functions, the PCM2704C/5C/6C/7C require a 12-MHz (±500 ppm) clock that can be generated by the onboard oscillator using a 12-MHz crystal resonator. The 12-MHz crystal resonator must be connected to the XTI pin (pin 28 for the PCM2704C/5C, pin 12 for the PCM2706C/7C) and the XTO pin (pin 1 for the PCM2704C/5C, pin 13 for the PCM2706C/7C) with one large (1-MΩ) resistor and two small capacitors; the capacitance of these components depends on the specified load capacitance of the crystal resonator. An external clock can be supplied from XTI (pin 28 for the PCM2704C/5C, pin 12 for the PCM2706C/7C). If an external clock is supplied, XTO (pin 1 for the PCM2704C/5C, pin 13 for the PCM2706C/7C) must be left open. No clock disabling pin is provided; therefore, TI does not recommend to use the external clock supply. SSPND (pin 27 for the PCM2704C/5C, pin 11 for the PCM2706C/7C) cannot use clock disabling. The PCM2704C/5C/6C/7C have an internal power-on reset circuit, which works automatically when VDD (pin 7 for the PCM2704C/5C, pin 21 for the PCM2706C/7C) exceeds 2-V typical (1.6 to 2.4 V), which is equivalent to VBUS (pin 10 for the PCM2704C/5C, pin 24 for the PCM2706C/7C) exceeding 3-V typical for bus-powered applications. Approximately 700 μs is required until an internal reset release occurs.

    regards,

    Arash

  • 0 in reply to Arash Loloee
    Guru 10575 points

    Hi Arash,

    If I use an oscillator, can I make the following connections?
    Oscillator: https://docs.rs-online.com/1da8/0900766b814e16db.pdf



    And, could you tell me how to calculate this resistance value.
    What resistance value do you recommend?

    Sincerely.
    Kengo.

  • 0 in reply to Kengo.Y
    TI__Mastermind 21300 points

    Hi Kengo,  I don't know the internal circuitry that is connected  to XT0 and XT1 but  I would not leave one pin NC and just use one pin. I have not seen it used they way you want, also I am not familiar with the clock oscillator  that  you want to use to make any suggestions to you. 

    Regards,

    Arash

  • 0 in reply to Arash Loloee
    Guru 10575 points

    Hi Arash,

    The oscillator has an oscillator circuit.
    The resonator doesn't have an oscillator circuit.

    So, PCM2704C has an oscillator circuit for resonator.


    I want to use the osillator, so it does not need an oscillator circuit in PCM2704C.
    Could you tell me how to connect an oscillator?

    Sincerely.
    Kengo.

  • +1 in reply to Kengo.Y
    TI__Mastermind 21300 points

    Kengo, the functional diagram you showed here is a  Pierce Oscillator.  Even though an external clock can be supplied from XTI  as you desired   but no clock disabling pin is provided; therefore, TI does not recommend to use the external clock supply and leave the other pin NC.   As i said I have not seen anybody use it in this fashion- probably  for the above reason. 

  • 0 in reply to Arash Loloee
    Guru 10575 points

    Arash,

    When using an external clock, what is the resistance value of the below?

  • +1 in reply to Kengo.Y
    TI__Mastermind 21300 points

    I have seen oscillators on some EVMs for XMOS and a 33 Ohm resistor was used . I do not know of any equation and may be the best is to contact the manufacturer of the oscillator you want to use and see if they have any recommendation to use with it. 

    Regards,

    Arash