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ADS4246: How to synchronise 2 units of ADS4246 on the same board?

yeow teng toh
Prodigy 60 points
Part Number: ADS4246

I have used 2 units of ADS4246 on the same digital board.

I need them to be synchronised for my application.

However, each time when I power up the board, the output of these 2 ADS4246 may or may not be synchronised.

may I know how I can "set" or "reset" or "program" them to be syncronised?

thanks in advance.

  • 0
    TI__Guru* 91947 points

    Yeow,

    Make sure the clock phase is the same (with no delay if possible) at the input of both parts. Use an external reset for both parts and make sure the delay is the same at both parts. Make sure power and clock is present to both parts before issuing a reset.

    Regards,

    Jim 

  • 0 in reply to jim s
    Prodigy 60 points

    Hi Jim,

    I have measured my

    1) both IC's input clocks are <250ps synchronisation error

    2) Common Power plane and common Ground plane are used to supply to both IC. And they are side by side. 

    3) All control pins are grounded and no possibility to do hardware "reset". 

    However, still have some instances 180 degrees out of phase at data output

    regards,

    YT

  • 0 in reply to yeow teng toh
    TI__Guru* 91947 points

    YT,

    Per the data sheet:

    "A high pulse on the RESET pin is required in the serial interface mode when initialized through a hardware reset. For parallel

    interface operation, RESET must be permanently tied high."

    If you are using serial SPI, are you following this? If using parallel SPI mode, is RESET tied high?

    Are you using LVDS or CMOS outputs? What is your sample rate? Is the clock provided after power?

    Regards,

    Jim 

  • 0 in reply to jim s
    Prodigy 60 points

    Hi Jim,

    If in parallel mode, and the RESET is set to low, what is the consequence?

    LVDS, ~120M, Power on, Clock signal not monitored, but assumed at the same time.

    regards,

     

  • 0 in reply to yeow teng toh
    TI__Guru* 91947 points

    YT,

    The registers will be in an undefined state. Do you have any way to toggle this reset or write to the reset register using the serial SPI interface?

    Regards,

    Jim 

  • 0 in reply to jim s
    Prodigy 60 points

    Hi Jim,

    I tried to Software reset both IC at the same time. Although the Syncronisation become "better", but not totally in "complete sync".

    Each step is (1/120MHz)

    The unsync is about +1 step or -1 step with reference to 1 of the IC.

    I can't get them on complete 0 step sync, or completely in sync.

  • 0 in reply to yeow teng toh
    TI__Guru* 91947 points

    YT,

    Have you tried a hard reset to both parts at the same time? How are you resetting both parts in software at the same time? Are you sure they are getting the register writes at the same time with respect to the sample clock?  

    Regards,

    Jim 

  • 0 in reply to jim s
    Prodigy 60 points

    Hi Jim,

    i am unable to do hard reset as the pin is permanently grounded.

    Ctrl 1,2,3 all grounded.

    i can only do the soft reset, somewhat improved the unsync condition but not completely making it 100% sync

    regards,

    yeow teng

  • 0 in reply to yeow teng toh
    TI__Guru* 91947 points

    Yeow,

    Try turning off the clock just before doing the soft rest then turn the clock on after the reset is complete.

    Regards,

    Jim