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ADS8691: SPI serial clock frequency for maximum throughput of 1000kSPS?

Patrick Fehlmann
Prodigy 50 points
Part Number: ADS8691

I intend to use the ADS8691 with a throughput rate of 1000kSPS and now checking the requirements to the SPI. I’m confused regarding the serial clock frequency with a maximum of 66.67MHz. As I understand, data transfer time (Data Read Time) is right after conversion time tconv, initiated by pulling CONVST/ \CS low. Since ADC cycle time period is 1us, conversion time 665ns, there’s only 335ns left for data transfer!? During this time 32 bits shall be transferred with a serial clock SCLK of 66.67MHz? In my opinion there are 100MHz needed...

  • 0
    TI__Expert 3775 points

    Hi Patrick,

    The ADS8691 is an 18-bit ADC and hence 18 SCLKs are sufficient for reading all data bits. I have attached the waveform showing data read after conversion (from datasheet) below -

    You will require about 56-MHz SCLK for reading 18-bits using 1-SDO interface.

    Thanks!

  • 0 in reply to RahulVK
    Prodigy 50 points
    Hi Rahul
    Thank you very much for your quick answer.
    Then I will read just these 18 bits and leave more time until the host controller pulls the CONVST/ \CS pin high again for writing registers.

    Regards,
    Patrick