ad7927 conversion rate

The datasheet specifies a maximum conversion rate of 200 kHz (5 µs) for the ad7927 converter although the conversion time is as low as 800 ns with a serial clock of 20 MHz.

What happens if the converter is operated with a faster conversion rate?  Will there be crosstalk between the inputs, degraded accuracy, or will the device simply blow up :-) ?

  • 0
    •  Analog Employees 
    on Apr 15, 2016 5:18 AM

    Hi,

    As stated in the Modes of Operation section of the datasheet, “For specified performance, the throughput rate should not exceed 200 kSPS, which means there should be no less than 5 us between consecutive falling edges of CS when converting.” We cannot guarantee performance outside of datasheet specs.

    Regards,

    Karen

  • Generally, when an analog-to-digital converter is clocked to fast, the internal capacitors can not charge and discharge sufficiently to provide accurate conversions. Smaller capacitors can provide faster conversion times, but this requires considerations to compensate for problems encountered when smaller capacitors are used, resulting in a more expensive converter. The problems relate to matching accuracy and are beyond the scope of this note.