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PCM1820: Specification of AVDD

Taku Murayama
Intellectual 1240 points
Part Number: PCM1820

Could you tell us about the specifications of the PCM1820?

Full scale input is 2Vrms = 5.66Vpp
VREF = 2.75V
This means that the analog signal can be input up to Vpp=5.5V at the center of 2.75V.
The analog input in the specification is rated as AVDD+0.3V.

Since AVDD is MAX=3.9V, it is assumed that 3.3V is assumed, but if the center of 2.75V and the Max side is 3.3V, there is only 0.55V margin on the positive side.
I think it does not make sense if the rating is not about 5.5V or higher, but is it a misstatement in the specification sheet?

  • 0
    TI__Mastermind 23030 points

    We are measuring the signal Differentially.

    The DC Bias internally is set at Vref/2 or 2.75V/2 or 1.375V

    We apply a 1V RMS signal at each of the pins the signals being in Phase Opposition to each other.

    A 1V rms signal is 1.4Vp. At the highest point of the sine wave the pin shall go to 1.375v+1.414v =2.78V  -----(1v*sqrt(2)

    This is lower then 3.3v.

    At this instant the other pin shall gave a Voltage of 1.375V-1.414V  or approximately 0

    The difference between the pins is about 2.8V =Vp. In RMS Terms this is   VRMS=Vp/sqrt(2) or 2.8/ 2V

    On the other cycle of the sine the phase reverses and the first pin goes to zero and the second to 2.78V . Hence we have a Peak to Peak Varistion of 2.78*2V or approx 5.6V