On 8/21/2018 4:06 PM, Jason White wrote:
> A footnote (note 2 in attached image) in the STM32F207 datasheet (page 12=
7)
> states that a high capacitance at the ADC input pin can reduce conversion
> accuracy. How exactly should this be interpreted?
>
> Sure, having a R-C lowpass at the ADC input pin will reduce bandwidth. Bu=
t
> will the capacitance affect the internal operation of the ADC?
>
>
>
I think I have seen an explanation of this before (maybe in a PIC=20
datasheet?).

The total input capacitance would be affected by the parasitic=20
capacitance and that would would change the charge time of the ADC=20
capacitor. For any given input voltage, this will change how many counts=20
occur for the same sample rate. Thus, note 2 states that the sampling=20
frequency would have to be reduced to compensate for the difference in=20
charge time. Lower sample frequency gives more time to charge and more=20
counts for a given input voltage.

Richard


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