How to measure accurate ADC voltage values?

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a_ziliu
Posts: 207
Joined: 20 Mar 2017, 10:52

31 May 2021, 15:48

The ADC (Analog-to-Digital Converter) architecture of Nuvoton’s microcontroller (MCU) is mostly equipped with SAR ADC (Successive approximation ADC), which needs to store the charge in the sample-and-hold capacitor inside the ADC in use. User needs to make sure that the sample-and-hold capacitor after charging is equal to the external measurement voltage before starting the analog-digital conversion to obtain an accurate voltage value. When a longer charge time is required, the user can set a longer sampling time by using the SMPTSEL (EADC_CTL [18:16]) & EXTSMPT (EADC_SCTLn [31:24]) to make the capacitor voltage equal to the external voltage.

For example, SMPTSEL = 8, EXTSMPT = 200, then the sampling time is 200 + 2 + 8 = 210 (ADC Clock), the ADC clock is 10MHz, 21μs time for the sample and hold capacitor to charge. This ensures that the external measurement voltage is equal to obtain accurate voltage values.

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