Published on:2021-05-28
In embedded design, the MCU is required to go from a processing-intensive work mode that consumes a lot of power to an idle/sleep mode that consumes little power. These conversions can easily cause a sharp increase in line loss, and the rate of increase is very high, reaching 20M/ms or even faster. The bypass capacitor is usually used to solve the load change caused by the high-speed devices in the system by the voltage regulator, so as to ensure the stability of the power supply output and a good transient response. Bypass capacitors provide energy storage devices for local devices, which can equalize the input of the regulator and reduce load requirements. Just like a small rechargeable battery, the bypass capacitor can be charged and discharged to the device. In order to minimize the impedance, the bypass capacitor should be as close as possible to the power supply pin and ground pin of the load device. This can well prevent the ground potential rise and noise caused by the input value being too large. The ground bounce is the voltage drop of the ground connection through the large current burr. It should be understood that both large-capacity and small-capacity bypass capacitors may be necessary, and some are even ceramic capacitors and tantalum capacitors. Such a combination can solve the above-mentioned load current problems that may be caused by step changes, and can also provide sufficient decoupling to suppress voltage and current glitches. In the case of very severe load changes, three or more capacitors with different capacities are required to suppress the transient process by low-frequency and large-capacity, and the rest is done by the regulator. It should also be remembered that the regulator also requires the capacitor to be as close as possible to the voltage output terminal.
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