Step-down DC/DC converter input ripple and noise

When a step-down converter shares a common input voltage with other devices, the input noise generated by the step-down converter may be sufficient to cause interference with the other devices. Simple filter methods can be used to reduce the input noise, and simple models can be developed characterize the circuit. Two circuit models—one for the fundamental switching frequency ripple component and one for the high frequency noise— simplify the analyses. In most cases, a ceramic bypass capacitor placed close to devices that share the common input voltage is sufficient. A ferrite bead placed between the converter input and other devices powered from the same source further attenuates the converter input noise.

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