AD7768 DaisyChain Timing

Hi,

I am evaluating the AD7768-4 for an application with multiple, distributed channels using the daisy-chain mode.

There is some confusing info in the Datasheet on how to calculate the Maximum DCLK frequency:

where t8 = 1/(DCLK/2) , so this formula folds back on itself and seems unsolvable.

Is there an example calculation that shows how to use the formula?

In my case I can calculate the minimum frequency for 10kHz sampling rate with 40 channels using two DOUTx as

DCLKMIN = Output Data Rate × Channels per DOUTx × 32 bits = 6.4MHz

but I am stuck at calculating the maximum allowed frequency for daisy chained devices to check if the AD7768 is feasible for my application.

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  • 0
    •  Analog Employees 
    on Dec 21, 2016 7:24 PM

    Hi,

    The formula in the datasheet is incorrect. The correct formula is:

    where:

    FMAX is the maximum usable frequency.

    T11 and T4 are the AD7768/AD7768-4 timing specifications (see Table 3 and Table 5 of the datasheet).

    TP is the maximum propagation delay of the data between successive AD7768/AD7768-4 devices in chain.

    TSKEW is the maximum skew in the MCLK signal seen by any pair of AD7768/AD7768-4 devices in the chain.

    The datasheet revision is ongoing and this will be corrected.

    Thanks,

    Jellenie

Reply
  • 0
    •  Analog Employees 
    on Dec 21, 2016 7:24 PM

    Hi,

    The formula in the datasheet is incorrect. The correct formula is:

    where:

    FMAX is the maximum usable frequency.

    T11 and T4 are the AD7768/AD7768-4 timing specifications (see Table 3 and Table 5 of the datasheet).

    TP is the maximum propagation delay of the data between successive AD7768/AD7768-4 devices in chain.

    TSKEW is the maximum skew in the MCLK signal seen by any pair of AD7768/AD7768-4 devices in the chain.

    The datasheet revision is ongoing and this will be corrected.

    Thanks,

    Jellenie

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