How to Control Phase Voltage Ringing in Synchronous Buck Convertors

by Suresh Kariyadan, International Rectifier, El Segundo, Calif., How2Power Today, Jul 30 2010

Focus:
In synchronous buck converters, fast switching of the MOSFETs can cause high-voltage spikes and ringing at the phase node. These effects can cause increased power dissipation, higher voltage stress on the switching devices, higher EMI, and higher peak-to-peak output ripple and noise at higher bandwidth. In this article, an integrated buck converter (the IR3842) is used to study the undesired voltage spikes and ringing at the phase node caused by fast switching. The focus here is mainly on the peak-to-peak output ripple voltage that occurs at higher bandwidth. Experiments are conducted on an IRDC3842 demo board to gauge the impact of two different methods used to control this ringing. One method places a resistor in series with the bootstrap capacitor, while a second method employs an R-C snubber installed from the phase node to ground. Pros and cons of the ringing suppression methods (including their impact on efficiency) are discussed, and advice is given on how to select the suppression components. In addition, PCB design guidelines are presented for minimizing the impact of EMI.

What you’ll learn:

• How to suppress phase-node ringing and peak-to-peak output ripple in fast-switching buck converters

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