Part Number: TMS320F280049C
Hello,
I am using the ADCA peripheral to sample the output voltage(designated as ADC in the diagram below) from an external board. The external board schematic is shown below:
Setup Details: The 12V comes from a power supply and the 3v3 is fed from the launchpad 3v3. In an ideal case, I expect 3.1V fed to the ADC.
Firmware Setup: I am using the internal 3v3 ADC reference and the sampleWindow parameter is set to 20(SYSCLK cycles). To verify when the ADC is sampling the signal , I placed a function inside the ADC ISR to toggle a test signal high or low when the ISR occurs. In the scope reading below, the DC signal shown in orange dips with ADC sampling shown by the rising and falling edges of the green square wave.
The DC signal has AC Coupling enabled in the scope.
With the scope attached to my setup, I saw digital readings of 3750 (3.02 V) which is close to the expected 3.05V measured by the scope with DC coupling enabled.
This leads me to my inquiries
1) I need to investigate why the DC signal drops suddenly when sampling occurs.
2) Without a scope attached, why do I see digital readings of 3485 (2.81 V)? This is different than the 3.1V input voltage I expected to be fed to the ADC.
