Steven Keeping writes:
Switching DC/DC converters (“regulators”) have become popular because they are highly efficient and able to step-up (boost), step-down (buck), and invert voltages with ease. However, voltage and current ripples generated by high frequency operation can cause operational problems with sensitive chips and electromagnetic interference (EMI) hassles.
One answer is to spend a lot of time and resources ‘tuning’ the PCB design to minimize parasitic inductances and capacitances, and design time consuming filter circuits to minimize voltage and current ripples. Another is to enlist the venerable linear regulator to work in tandem with the switching converter to smooth the output of the latter and provide a stable, reliable voltage output.
This latter technique requires careful design and considered component selection to get the two regulators working in harmony and eliminate those post-regulation filters. This article describes the benefits of a “hybrid” voltage regulator approach, recommends component selection criteria, and describes a low-noise analog power supply example from Texas Instruments.
Hybrid Power Supplies Deliver Noise-Free Voltages for Sensitive Circuitry - [Link]