1.1.4 Power Supplies and Brown-Out

Another aspect to examine is the power supply. For the microcontroller to operate correctly, the power supply must be higher than the minimum supply voltage and less than the absolute maximum supply voltage(1). If the brown-out circuit is enabled, the power supply must also be higher than that threshold to exit reset.

Note: On some devices, the maximum operating frequency of the microcontroller is derated from the operating voltage. The lower the operating voltage, the lower the maximum frequency is. The electrical specification section of the device data sheet contains a graph showing the maximum frequency with voltage, if applicable to the device.

One final thing to check in the power supply is ripple. If the ripple in the power supply violates the minimum voltages in the paragraph above, the microcontroller may reset, stop working or lead to undefined behavior. Additionally, if the ripple causes the supply voltage to exceed the absolute maximum rating, the microcontroller may be damaged or destroyed.

An AC-coupled(2) 10x oscilloscope probe(3) can be attached to the power rail to visualize the ripple. Decoupling capacitors close to the microcontroller’s power inputs are required to both reject ripple and provide a near-instantaneous source of current for the fast-switching logic inside the microcontroller. The data sheet of the microcontroller contains the recommended values for decoupling the device.

Note:
  1. The microcontroller may be permanently damaged or destroyed if the absolute maximum supply voltage is exceeded.
  2. DC coupling the probe yields a better low-frequency response. However, the DC offset reduces the resolution of the small AC signals present.
  3. Specialty oscilloscope probes for power line measurements are also available.