How to suppress power supply ripple in an electrical power measurement switch (PMS)?

Ripple and switching noise generated by the internal switching power supply (such as a DC/DC module) of the PMS can couple to analog circuits and measurement references, leading to measurement fluctuations and communication errors. Suppression requires a three-pronged approach: addressing the source, the path, and the affected end. At the source, optimize the feedback loop compensation of the switching power supply, increase the ESR of the output capacitor (e.g., using polymer aluminum electrolytic capacitors), or add a Snubber circuit (1nF + 2.2Ω) at the switching node. For path blocking, add a two-stage LC filter after the DC/DC output, using a PBZ1608E600Z0T ferrite bead (60Ω@100MHz) and low-ESR ceramic capacitors (e.g., 22μF/6.3V, X5R).

For particularly sensitive analog power supplies (such as the VREF of an ADC), use a linear regulator (LDO) for post-stage regulation, and place π-type filters before and after it. During PCB layout, the power loop area of the switching power supply should be minimized and located away from the analog area. Actual measurements show that, through comprehensive suppression, the switching ripple on the 5V power supply bus can be reduced from 100mVpp to below 10mVpp, and the high-frequency noise (>1MHz) can be reduced by 30dB, ensuring that the effective number of bits (ENOB) of the 16-bit ADC reaches more than 15 bits.