Overview
A modern system needs several rails, and each rail has its own requirement: a digital rail wants efficiency, an analog rail wants low noise, and a portable node wants a low standby loss. ADI provides the regulators that meet these needs, and BeiLuo supplies them with genuine traceability and FAE support. This page shows how the parts fit together in a power-supply design.
Building the Power Tree
Start from the loads and the noise target. A multichannel regulator such as the ADP5054 provides several rails from one input in a compact package, which shrinks the board and reduces the part count. Phase-shifting the channels spreads the switching noise instead of stacking it at one frequency, which lowers the input ripple and the conducted emissions, and the precision enable, the power-good and the sequencing let the system bring the rails up and down in a controlled order.
Sequencing the Rails
Many devices, from a processor to a converter, require their rails in a defined order, so the sequencing feature of the regulator is used to meet the requirement without extra logic. Confirm the order and the timing against the datasheets of the load devices.
Cleaning the Analog Rail
A switching regulator is efficient but leaves a ripple, and a converter, a reference or a precision amplifier sees that ripple directly. A low-noise LDO such as the ADP7118 placed behind the switcher removes the ripple and delivers a clean rail with a high power-supply rejection, so the analog section keeps its accuracy. Place the LDO close to the analog load and keep its output and noise-reduction capacitors close, because the layout decides the residual noise.
Noise and Power-Supply Rejection
The power-supply rejection of an LDO falls with frequency, so the output capacitor and the placement decide the high-frequency residual. A small, well-placed capacitor close to the load often does more than a much larger one far away.
A Single Efficient Rail
Where one rail is enough, a single synchronous buck such as the ADP2370 delivers it at a high efficiency and a low quiescent current, which suits a battery-powered or an always-on node. The current-mode control gives a fast transient response for a digital load, and the integrated rectifier keeps the part count low. Size the inductor and the output capacitor for the transient you expect and keep the switching loop small.
Getting It Right
A power design succeeds when the efficiency, the noise and the layout are managed together: build the tree from the loads, clean the sensitive rails with a low-noise LDO, sequence the rails correctly and keep every switching loop small. BeiLuo supplies the ADI regulators from stock, with the documentation to prove their origin and an FAE team that will review the power tree and the layout with you.