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ad777x phase adjustment

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Product Number: AD7770

HI.

I'm testing the AD7770's PHASE ADJUSTMENT function, and it's behaving strangely.

My configuration is like this:

mclk input : 7.68Mhz

SPS : 7680

high resolution mode

SPI control mode

60Hz analog input

According to the data sheet calculation:

(7680Khz/4) / 7680SPS = 250 decimation rate

(7680Khz/4) / 60Hz = 32000

360deg / 32000 = 0.01125deg

I wrote a value of 89 (0x59) to correct the 1deg phase difference.

But it doesn't work the way I want it to.
There is less or more adjustment.
When only one channel is adjusted, when two or more channels are adjusted, the offset is the same, but the adjusted result is different.

What am I doing wrong?

ps. Does phase adjustment adjust the conversion timing?

What am I doing wrong?



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[edited by: PCM at 9:14 AM (GMT -4) on 2 Sep 2022]

Top Replies

  • Hi  ,

    We will look into this. I will contact the product owner and get back to you.

    Regards,

    JC

  • Hi  ,

    As I can see, you have calculated the value of 89 MCLK pulses correctly. Unfortunately, that is not the value to be written into the OFFSET register which is calculated as per the last paragraph…

  • Hi  ,

    We will look into this. I will contact the product owner and get back to you.

    Regards,

    JC

  • Hi  ,

    As I can see, you have calculated the value of 89 MCLK pulses correctly. Unfortunately, that is not the value to be written into the OFFSET register which is calculated as per the last paragraph in phase adjustment section on page 41 of the Datasheet.

    It will be (decimation rate - MCLK pulses calculated)/Phase Adjustment Compensation = (250-89)/1 = 161 (0xA1) in your case.
    please write this into the CHx_SYNC_OFFSET to get 1 degree phase shift. 
    Also, please note that it is effective only after SYNC_IN pulse is given.

    Thanks.

    Vikas J