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

DCLK_{MIN} = 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.

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