ADC Conversion time doesn't change when changing the sampling time
Hello,
at the moment i try to verify the conversion time of the ADC that is described in the datasheet.
I measure one channel in regular conversion mode without interrupt.
To calculate the conversion time i used the equation in the datasheet.
Tconversion = tsampletime + ConversionTime
The resolution is fixed with 14bit -> 17 ADC cycles.
ADC clk = 3682540Hz.
I toggle a pin after starting the ADC and i toggle the pin again when EOS flag bit is set:
GPIOA_NS->BSRR |= GPIO_BSRR_BS0;
while((ADC1->ISR & ADC_ISR_EOC) != (ADC_ISR_EOC))
{
}
GPIOA_NS->BSRR |= GPIO_BSRR_BR0;
I measured the Conversion time with the ocilloscope.
Here are the results ( at the left hand side the measured conversion time and at the right side the calculated):
There is a delay of 6us because of the pin toggling that i have also taken into account for the measurement results!.
| TSmpl [cycles] | Tsar [cycles] | Tconv + PIN Toggle measurement [us] | Tconv + PIN Toggle Theory [us] |
| 5 | 17 | 11.9 | 11.9 |
| 6 | 17 | 11.9 | 12.2 |
| 12 | 17 | 11.9 | 13.8 |
| 20 | 17 | 16.3 | 16 |
| 36 | 17 | 20.6 | 20.4 |
| 68 | 17 | 29.3 | 29.1 |
| 391 | 17 | 116 | 116.8 |
| 814 | 17 | 233 | 231.6 |
My question is: Why stays the conversion time the same for the first 3 sampling time configurations?