ADAU1777/ADAU1772/ADA1372 initialization when an external oscillator is used

I am confirming how to start and initialize the ADAU1777, ADAU1772 or ADA1372 when an external oscillator is used.

In each data sheet, I can find following description. Regarding it, please let me ask below.

 

ADAU1772 data sheet (rev.C)

Page 30 CLOCK INITIALIZATION

When a crystal oscillator is used, it is desirable to use a 12.288 MHz crystal, and the crystal oscillator function must be enabled in the COREN bit (Address 0x0000).

 

Question 1.

The crystal oscillator can be enabled/disabled by the XTAL_DIS bit in the CLK_CONTROL register (Address 0x0000).

Is this understanding correct?

 

Question 2.

When the external oscillator is connected to the MCLKIN(XTALI),

can the XTAL_DIS be disable (set to 1) to reduce power consumption.

Or must the XTAL_DIS be disabled?

 

Question 3.

Immediately after power-up, the external oscillator may already provide the MCLK

Then the XTAL_DIS bit is 0 (the internal crystal oscillator is enabled) by default.

Could it cause any problems? After setting the XTAL_DIS into 1, should the MCLK start to be provided?

  • 0
    •  Analog Employees 
    on Jun 15, 2021 2:36 PM

    Hello Euglena,

    Question 1:

    Yes, the XTAL_DIS bit is used to enable and disable the crystal osc. 

    Question 2:

    Yes, you can disable the crystal oscillator when using an external clock source instead of a crystal. It will still function fine if the crystal oscillator is enabled but it is a good idea to disable it to save power and to remove any slight DC offsets that will be there for the crystal oscillator. The pull ups are very weak so it will not damage the part if left on.

    Question 3:

    This was partially answered in the last answer. It is not a problem that the MCLK is present and the part has powered up with the crystal oscillator enabled. Simply disable it when initializing the part and there will not be a problem. It is not  problem to have the MCLK be present from the start. 

    I do need to mention that you should not provide MCLK when the part is powered down. Providing any clock or GPIO input to the part when the part is powered down will violate the MAX voltage on the pins. The MAX is calculated using IOVDD. So if IOVDD = 0 then the max voltage in 0.3V.

    If the system requires that the part be shutdown while other parts of the system is still operating then use level translators to translate to the power domain of the 1777/1772/1372.

    Dave T

  • Hi Dave,

    Thank you very much for your quick reply.

    I clearly understand.

    I will check boards and Sigma Studio configurations as per your suggestions.