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AD9257: Initialization time

Hello,

I have a question about the AD9257.

I turn on the power supply of ADC in the state to which the clock is steady.

And, the first analog to digital conversion data becomes valid.

I want to know the time until valid conversion data is output after the power supply is turned on.

Please tell me about the time.

Best regards.

Mr.K

  • Dear Mr. K,

    Thanks for your question.

    There is an analog portion and a digital portion to the time after power-up the AD9257 needs to be operational. The analog portion is nominally about 350us. This time interval is dominated by the slew limited charging of the VREF capacitor. As such, the time required for analog wake up is variable and depends on the size of the VREF capacitor.

    After the analog is ready, the digital will go through an initialization sequence that takes about 3 million sample clock cycles. At 65MSPS one sample clock period is about 15.4ns. (3e6 cycles X 15.4e-9 sec/cycle) = 46.2ms .

    The time needed by the digital is by far the major portion of the overall time. At 65MSPS, 50ms is a conservative number to use. If you are sampling at a lower rate than 65MSPS, the sample period will increase, so the overall time necessary after power up will also increase according to the formula above.

    Thank you.

    Doug