Voltage-Mode Control Scheme Improves Buck Converter Performance At High Frequencies

Focus:

Higher operating frequency combined with jitter-free operation allows synchronous buck converter designs to run at higher closed-loop bandwidth, which results in the use of fewer output capacitors, saving board space and system cost. This article explains the operation of a new pulse-width modulator scheme for achieving jitter-free operation at high frequency and narrow duty cycle using a voltage-mode controller. This modulator scheme has been implemented in International Rectifier’s IR3899 synchronous buck regulator, which also contains built-in features that enhance flexibility in the design of point-of-load regulators. Test results are presented to demonstrate the performance advantages of the new modulator scheme versus a traditional voltage-mode controller. In addition, the special features of the IR3899 are described. The article begins by reviewing operating principles of conventional voltage-mode control, then explains IR’s new technique which changes the timing of the ramp signal to the PWM comparator. The effect of this technique is that the controller intersects the voltage error signal in a more linear region of the ramp signal, thereby reducing jitter and noise.

What you’ll learn:

• How to understand operation and benefits of the voltage-mode control technique used in the IR3899 synchronous buck converter
• How to achieve jitter-free operation at high frequency and narrow duty cycle using a voltage-mode controller
• How to reduce output capacitor requirements for a synchronous buck converter

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Author & Publication:

Suresh Kariyadan and Parviz Parto, International Rectifier, El Segundo, Calif., How2Power Today, Jan 27 2012

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