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TMS320F2809: The Resistor Value for ADC External Current Bias (ADCRESEXT)

Part Number: TMS320F2809

Hi Champs,

I know TI recommends 22Kohm as ADC external current bias resistor for ADC's normal operation.

I want know the maximum tolerance of this resistor. For example, If 20Kohm is applied, are there any side effects?

Thanks,

Steve

  • Steve,

    The requirement on RESEXT is 22kOhm resistor at 10% tolerance(max EIA spec).  So low side of this is 19.8kOhm.  Assuming customer is using same tolerance 20kOhm that would be low of 18kOHm.

    At any rate, this resistor sets the bias current for the ADC subsystem and per the above is out of spec.  I know that the ADC will draw more current/power due to this, I am not able to predict the effect on the linearity(INL/DNL) would be.  I do not believe there will be damage to the internal system due to this.

    If customer is seeing acceptable performance of the ADC in their system with this resistor, I do not believe there is concern.  However, TI cannot guarantee the in spec operation of the ADC across all conditions since this is out of spec to the DS required value.

    Best,

    Matthew