Decoupling capacitors (also known as bypass capacitors) are use to supply just-in-time energy to circuits during times of elevated load. The reason for this need of additional energy because of the transient response time of voltage regulators. Regulators supply stable voltage at a constant load current, but if that load current suddenly changes there is a finite amount of time that needs to elapse so that the voltage regulator can adjust to the new load. During this transient time, the output voltage of the regulator may exhibit slumps or ringing. In many cases, this is not an issue, but in microprocessor or microcontroller applications this can be an issue. Those devices can exhibit unwanted behavior such as resets during the transient time. A bypass capacitor is implemented to mitigate this issue. The amount of bypass needed depends on the size and duration of the transient.
Saturday, July 25th, 2015