Say the capacitor six: the application of bypass capacitor

In an embedded design, the MCU is required to enter a low-power idle/sleep mode from a power-intensive, processing-intensive mode of operation. These conversions can easily cause a sharp increase in line loss, which is very high, reaching 20A/ms or even faster.

Bypass capacitors are often used to address load changes caused by high-speed devices in the system to ensure power supply output stability and good transient response. The bypass capacitor is an energy storage device that supplies energy to the local device, which equalizes the output of the regulator and reduces the load requirements. Like a small rechargeable battery, the bypass capacitor can be charged and discharged to the device. To minimize impedance, the bypass capacitor should be as close as possible to the power supply and ground pins of the load device. This can well prevent ground potential elevation and noise caused by excessive input values. The ground bounce is the voltage drop when the ground connection is passed through a large current glitch.

It should be understood that both large and small capacity bypass capacitors may be necessary, and some even have multiple ceramic and tantalum capacitors. Such a combination can solve the problem that the above load current may be caused by a step change, and also provide sufficient decoupling to suppress voltage and current glitch. In the case of very severe load changes, three or more capacitors of different capacities are required to ensure sufficient current before the regulator is regulated. The fast transient process is suppressed by high-frequency small-capacity capacitors. The medium-speed transient process is suppressed by the low-frequency large-capacity, and the rest is left to the regulator.

It should also be remembered that the regulator also requires the capacitor to be as close as possible to the voltage output.