Figure 1 shows an example of output ripple and switching transients. Their amplitude, expressed as a maximum peak-to-peak voltage, is difficult to measure accurately since it is highly dependent on the test setup. Switching transients are high-frequency oscillations that occur during switching transitions. Its fundamental frequency is the same as the regulator’s switching frequency. Output ripple is a residual ac output voltage that is coherently related to the switching operation of the regulator. Output ripple and switching transients depend on the regulator’s topology, as well as the values and characteristics of the external components. This buck regulator provides high efficiency and operates at switching frequencies up to 2 MHz.

Here, the ADP2114 dual 2-A/single 4-A synchronous step-down dc-to-dc converter is used to demonstrate techniques for measuring output ripple and switching noise. This increases the amplitude of the transients associated with fast switching transitions, so short connections, good techniques, and wide bandwidth must be maintained. 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 article describes effective techniques for measuring output ripple and switching transients in switching regulators. Understanding these artifacts will allow designers to successfully integrate switching regulators in a wider range of high-performance, noise-sensitive applications.

To avoid degrading the signal-to-noise ratio (SNR) and spurious-free dynamic range (SFDR), the switching regulator is often replaced with a low-dropout regulator (LDO), trading the high efficiency of the switching regulator for the cleaner output of the LDO. Minimizing output ripple and transients from a switching regulator can be important, especially when powering noise-sensitive devices such as high-resolution ADCs, where the output ripple can appear as a distinct spur on the ADC’s output spectrum. Understanding Switching Regulator Output Artifacts Expedites Power Supply DesignĪldrick Limjoco Download PDF Introduction

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