Measure—and Reduce—Output-Voltage Ripple for DC-DC Regulators (.PDF Download)

Many modern servers, as well as telecom and networking equipment, are populated with multiple voltage regulators on the system board to provide power to ICs or subcircuits. These power rails often have very tight voltage tolerances (<1%). Power-integrity measurement, such as measuring ripple voltage in full bandwidth, becomes crucial to meet the system design requirement. This article provides measurement guidelines and ripple-reduction methodology based on implementation of constant-on-time (COT) regulators, with specific results given using the MPQ8633B from Monolithic Power Systems (MPS).

Ripple and Noise Origin

Full-bandwidth output ripple typically includes LF ripple and HF noise. Figure 1 shows that the LF ripple in buck converters is an ac component of the output voltage.