Understanding Switching Regulator Output Artifacts Expedites Power Supply Design
Aldrick S. Limjoco · 2014
This article describes effective techniques for measuring output ripple and switching transients in switching regulators. Measuring these artifacts requires great care, as a poor setup can lead to incorrect readings, with the loops formed by the oscilloscope probe’s signal and ground leads introducing parasitic inductance. This increases the amplitude of the transients associated with fast switching transitions, so short connections, good techniques, and wide bandwidth must be maintained. Here, the ADP2114 dual 2-A/single 4-A synchronous step-down dc-to-dc conv erter is used to demonstrate techniques for measuring output ripple and switching noise. This buck regulator provides high efficiency and operates at switching frequencies up to 2 MHz. Output Ripple and Switching Transients Output ripple and switching transients depend on the regulator’s topology, as well as the values and characteristics of the external components. Output ripple is a residual ac output voltage that is coherently related to the switching operation of the regulator. Its fundamental frequency is the same as the regulator’s switching frequency. Switching transients are high-frequency oscillations that occur during switching transitions. Their amplitude, expressed as a maximum peakto-peak voltage, is difficult to measure accurately since it is highly dependent on the test setup. Figure 1 shows an example of output ripple and switching transients.