How to optimize the auxiliary power supply filtering of a smart controller (PAC)?

The auxiliary power supply (such as 5V/3.3V for sensors and communication modules) of the intelligent controller PAC needs to be optimized for filtering based on the load characteristics. For noise-sensitive analog sensor power supplies, a two-stage filtering method is used: the first stage uses a PWRA6045 power inductor (6.8μH) and a 10μF tantalum capacitor for low-frequency ripple suppression; the second stage uses a PBZ1608A-102Z0T ferrite bead (1000Ω) and a 0.1μF ceramic capacitor to filter out high-frequency noise. For digital communication modules, a CMZ20 can be added at the power input. A 12A-900T common-mode inductor is used to suppress common-mode interference.

In terms of layout, the auxiliary power supply filter circuit should be independent of the main power supply area, and a star-shaped trace should be used to reduce coupling. At the same time, a low-noise LDO (such as output voltage ripple <10μVrms) is selected as the regulator. Tests show that after optimization, the ripple noise of the auxiliary power supply is reduced from 100mVpp to below 20mVpp, and the noise spectral density in the 10Hz-100MHz frequency band is below -80dBm/Hz, which meets the voltage fluctuation immunity requirements of IEC61000-4-17.