ADS8558 - MAX sampling 500kSPS(serial I/F)

Hirotaka-san,

I sincerely apologize for this delay in responding to your query.

For the best throughput, you would have to use all 3 SDO channels for one 32-bit transfer as explained in section 7.3.2.3, with the max SCLK of 36MHz(T=27.8ns).

Based on this, your second calculation is correct.

T_conv = 1090ns
Data transfer time = 27.8*32bits = 889.6ns

CONVST_x low time of t1=min 20ns is required, but need not be added as the data transfer time is greater than that t_acq = 280ns

Total = 1979.6ns = ~500kHz

Regards,
Sandeep

According to the datasheet for this device family, the serial interface outputs data in frames of 16 bits. For this 12-bit device, the first four bits will be all zero. In your calculation above, multiplying the SClk period by 32 bits will give the correct answer. However, you are not using the fastest specified SClk. The datasheet says that the minimum period for SClk is 27.8ns. Also, when you assert CONVST, there is a delay of 20ns (max). Assuming that the interface is quiet during the conversion, then, 20ns (CONVST delay) + 1090ns (conversion time) + (27.8ns * 32bits)(interface time) = 1999.6ns or roughly 500kHz.

If you are using SClk with a period of 33ns, your throughput will be limited to only about 460kHz.