The test report contains information about the output voltage and ripple characteristics of a Buck-Boost converter under different input conditions and with a consistent load of 500mA. It also includes a measurement of the ADC reference voltage. Let's analyze the results:
Buck Boost 1 output with a 2.8V source:
Result: 3.32 VDC mean, 250 mVpp ripple
Observation: The oscilloscope trace shows a significant transient spike upon load application, which settles to a steady-state after some time.
Buck Boost 1 output with a 3.3V source:
Result: 3.28 VDC mean, 50 mVpp ripple
Observation: The oscilloscope trace shows a transient response with less overshoot compared to the 2.8V input condition.
Buck Boost 1 output with a 4.2V source:
Result: 3.32 VDC mean, 150 mVpp ripple
Observation: The oscilloscope trace indicates a transient with more pronounced overshoot than with a 3.3V input, but less than with a 2.8V input.
ADC reference voltage:
Result: 1.11 VDC mean, 10 mVpp ripple
Observation: The ADC reference voltage is stable and has a very low ripple.
Considering that the ADC reference voltage is stable and with low ripple, the inaccuracies in battery voltage readings may not stem from the reference voltage itself. However, there appear to be marked transients and varying levels of ripple on the Buck Boost output depending on the input voltage.
This could affect the accuracy of ADC readings in the following ways:
Transient spikes: When the ADC samples during a transient spike, this could lead to significant inaccuracies in the reading. It's important to ensure that the ADC samples once the voltage has stabilized.
Ripple voltage: High ripple can introduce AC noise into the ADC readings, leading to variance and inaccuracies. It may be beneficial to add filtering, such as a low-pass filter, to reduce the effect of the ripple on ADC readings.
Load regulation: The change in output ripple across different input voltages suggests that the Buck Boost converter's load regulation may be a factor in the observed ADC inaccuracies. If the load changes dynamically during microcontroller operation, this could further influence ADC accuracy.
In summary, the inaccuracies in ADC readings could be due to the transient spikes and the ripple present in the power supply voltage which is being measured. Recommendations to address this may include:
Implementing adequate filtering for the ADC input to smooth out the ripple.
Ensuring the ADC samples are taken during a stable period of the voltage (i.e., not during transients).
Checking the ADC setup, including the sampling rate and resolution, to ensure it's configured correctly for the task.
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