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Multiphase synchronous boost converter suits portable apps

Posted: 06 Feb 2004 ?? ?Print Version ?Bookmark and Share

Keywords:mobile phones? digital cameras? portable devices? converters? linear technology?

Growing features in handheld devices, such as mobile phones, digital cameras and other portable devices demand higher load current and circuit density. Applications such as disk drives or mobile phone amplifiers require peak current from boost regulators. There are also point-of-load applications, wherein a local 5V output is generated from a 3.3V bus, or a 3.3V from a 2.5V bus.

Traditional boost converters have a direct path from input to output. An external Schottky diode or an internal body diode of the synchronous rectifier connects the input supply through the inductor to the load. Large surge currents during initial plug-in are undesirable; in battery-powered applications, they can cause sufficient input voltage drop to trigger the low-battery detector. The direct path construction also leaves the load connected to the input after the boost converter has been shut down, causing additional power loss due to leakage current. Maintaining a minimum input voltage as low as 1V is also important to enable the accommodation into a variety of batteries, including fuel cells.

High-current and high-efficiency boost converters are therefore required to prolong battery life and control thermal dissipation. However, high-density construction leaves little space for additional filters between the switching regulators and other noise-sensitive circuits.

The solution is a multiphase control scheme. A multiphase converter interleaves the clock signals of the paralleled power stages, reducing the output ripple voltage without increasing the switching frequency. The size of the input and output capacitors are significantly reduced due to the ripple current cancellation, and instead of a bulky single inductor, the converter uses several compact inductors, which are easier to fit on high density boards.

An integrated solution, such as the one discussed in the conference paper will be presented in this year's IIC-China, ESC-China and EDA&T events. The paper will talk about control circuitry and power switches inside a single IC to simplify the design. Designing a multiphase synchronous boost converter using the highly integrated part is just as simple as building a single phase boost converter. Besides discussing the implementation and benefits of a multiphase synchronous boost converter, this paper will also address the most common concerns in boost applications, including controlling inrush current during startup, disconnecting the output load from input source while the converter is shut down, and short circuit protection.

- Dongyan Zhou

Linear Technology Corp.

* Linear Technology will participate in this year's IIC-China, ESC-China and EDA&T-China events.

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