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ADCRESEXT resistor value

Albert WOROU
Prodigy 140 points

Other Parts Discussed in Thread: TMS320F28335

I'm using the TMS320F28335 and the datasaheet recommends a 22k resistor on the ADCRESEXT pin. How critical is that resistor value? Would a 20k resistor work and how would the ADC performance be affected?

 

  • 0
    TI__Expert 7845 points

    ADCRESEXT sets the internal bias currents for the ADC, and should be connected through a 22kOhm resistor to ground. ADCREFP/REFM also need to be connected through 2.2uF caps to ground, these are the internally generated reference for the ADC and the caps are there to buffer them during sampling.

    The ADC is not guaranteed to operate within the Datasheet limits without these connections.

    What is the ADC clock value and what sampling speed are we talking about here? Although I don't think that a lower value resistor on that pin should be a problem (especially 20 k), using a different/higher value resistor at this speed may reduce the DNL of the device, giving some greater non-linearities in the transfer function than listed in the Datasheet.