ADC - Problem in sensing voltage

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ADC - Problem in sensing voltage

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padmaashok765
Contributor II

Hi,

In my project I am using all the 16 ADC channels, facing problem in sensing the exact voltage values.

Have checked with voltage variations from 0v - 3.3v , my reference voltage is 3.3v.

My questions is:

while (in ADC Control Register 1 (ADCR1)) using once sequential or once simultaneous mode and triggered sequential and triggered sequential mode I can get the variation from 0v - 3.3v. But while using loop sequential or loop simultaneous mode even if I dint give any voltage input to adc it is automatically producing 1.2v-1.5v. How is this possible? It is not because of the circuit as I have not connected any sensor or input unit to channels.

I have gone through datasheet and user guide but I'm not clear. Can any one explain in detail?

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padmaashok765
Contributor II

Sorry I am using MC56F8367 .

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xiangjun_rong
NXP TechSupport
NXP TechSupport

Hi, Padma,

Anyway, as you know that the ADC analog channel pin is an input pin, I think it does not make sense to test the voltage of ADC analog channel pin when the ADC analog channel pin is float. If you want to convert ADC analog channel, you have to connect a low impedance voltage source to the ADC analog channel pin.

Hope it can help you

BR

XiangJun Rong

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