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SLUU995A question about KI_ADDER_MODE

jun yin
Intellectual 875 points

In SLUU995A, on page 64, it's said "This will only occur at the lowest gain setting of the Error ADC. So if the lowest gain setting of the EADC

is to be used, trapezoidal approximation may cause premature saturation on the input."

what's the gain setting of the EADC here? is it AFE GAIN(front end gain)? how to calculate gain setting of the EADC?

  • 0
    TI__Genius 17090 points

    The EADC gain setting and the AFE gain setting mean the same thing.  The both refer to the gain on the amplifier that takes the EADCDAC as one input, and the EADC pins as the other input.   It's output goes to the EADC.  With 20-20 hindsight, we should  have called it AFE input amplifier gain.  I'll make a note that we should clean up our nomenclature in the next version.  

    It's a bit confusing, because the EADC itself and the AFE as a whole actually have fixed gain.  The gain change on the input amplifier is offset by the change in the shift of the EADC output before it goes to the register.

    The actual effect of changing the input amplifier gain is that the resolution and range of the output change.  With the lowest gain, you can go about +- 255 mV, and with the highest gain you can only go +- 31 mV.  

  • 0 in reply to Ian Bower
    Intellectual 875 points

    Hi Ian:

    thanks a lot;

    if it's AFE GAIN,and lowest gain means +/-255mV, and highest gain means +/-31mV, then the description of"So if the lowest gain setting of the EADC is to be used, trapezoidal approximation may cause premature saturation on the input" couldn't be right; for the same input signal(output change) , +/-31mV(highest gain) should be much easier for EADC to be saturated than +/-255mV(lowest gain);

    it should be "So if the highest gain setting of the EADC is to be used, trapezoidal approximation may cause premature saturation on the input",right?