SWRA679 January   2021 CC3200 , CC3220R , CC3220S , CC3220SF , CC3230S , CC3230SF , CC3235S , CC3235SF

 

  1.   Trademarks
  2. 1Introduction
    1. 1.1 Basics of the SAR ADC Architecture
    2. 1.2 Introduction to the CC32XX ADC
      1. 1.2.1 Main Features
      2. 1.2.2 ADC Sampling Operation
      3. 1.2.3 ADC Additional Information
  3. 2ADC Application Examples
    1. 2.1 Battery Voltage Measurements
      1. 2.1.1 Important Considerations
        1. 2.1.1.1 Extra Current Draw
        2. 2.1.1.2 Droop Correction
        3. 2.1.1.3 Offset Adjustment
        4. 2.1.1.4 Least Squares Fit
        5. 2.1.1.5 Choosing the Capacitor (for droop correction)
        6. 2.1.1.6 First Measurement
        7. 2.1.1.7 Time Between Measurements
  4. 3AC Measurements
  5. 4Useful References
    1. 4.1 Smart Thermostat
    2. 4.2 Measuring Air Quality With the Winsen MP503 Analog Sensor
    3. 4.3 Touch Position Detection With HMI Through Resistive Touchscreen
  6. 5References

2.1.1.5 Choosing the Capacitor (for droop correction)

The capacitor chosen should be linear in the entire operating voltage range, that is, the capacitance should remain constant over the operating voltage range for the voltage droop calculations to hold. It is recommended to use a tantalum or a film type SMT capacitor for this application. Ceramic multilayer capacitors are prone to capacitance change with voltage. (The capacitance can drop up to 50% with only a few volts DC). If the end user is not implementing the DC offset correction using the droop calculation, then any capacitor can be used.

Also derating the capacitance by choosing one with a very high voltage rating is an option. In this case, the max voltage is 1.4V at the ADC input and we can chose a 16 V capacitor. This will reduce the capacitance change with voltage.