Introduction For portable power applications, to fully utilize the advantages of advanced battery technology, such as small size and high energy density, efficient operation across the entire battery discharge voltage range is essential. This poses a significant challenge to lithium-ion battery power systems requiring a 3.3V bus voltage. While standard buck converters are highly efficient at converting 4.2–3.0V lithium-ion battery voltages to lower output voltages such as 1.8V, and standard boost converters are highly efficient at converting lithium-ion battery voltages to higher output voltages such as 5V, neither of these is the optimal solution for generating the commonly used 3.3V bus voltage. SEPIC and traditional buck-boost converters, while fully utilizing battery power, suffer from low efficiency, high cost, large board area, and numerous components. The TPS6300x, employing three configurations, addresses these issues. The TPS63000 offers an adjustable output range from 1.2V to 5.5V. The TPS63001 and TPS63002 have fixed output voltages of 3.3V and 5.0V, respectively. All of the above products are packaged in a space-saving 10-pin QFN (DRC) package. The TPS63001 from TI features a minimal component count, small board area, and low cost, and efficiently converts lithium-ion battery input voltage to a 3.3V bus voltage. In addition to buck and boost functions, it integrates switching FETs, compensation, and protection functions within a 3x3 mm QFN package. Only three external components are required for operation: input and output capacitors and an inductor. The converter has a peak efficiency of 96% (see Figure 1) and a peak output current of 800mA, sufficient to power most portable loads. The wide input voltage range of 1.8–5.5V allows it to operate with many common power supplies, such as two or three alkaline batteries, NiMH batteries, and 3.3V and 5V buses. [img=420,306]http://cms.cn50hz.com/files/RemoteFiles/20081225/833138001.gif[/img] Figure 1: TPS63001 efficiency graph from 1.8 to 5.5V [320mA load (VOUT=3.3V)] Figure 2 shows a typical 3.3V power supply that can be powered by a single lithium-ion battery. The 1.5MHz switching frequency allows for the use of a small 2.2μH inductor and small ceramic input and output capacitors of size 0603. High efficiency, coupled with a small number of external components, reduces the overall solution size to only 6x6 mm (see Figure 3). [img=489,257]http://cms.cn50hz.com/files/RemoteFiles/20081225/833138002.gif[/img]Figure 2 Typical application circuit [img=340,356]http://cms.cn50hz.com/files/RemoteFiles/20081225/833138003.gif[/img]Figure 3 Typical layout in 6x6 mm board space. Advanced control topology maximizes efficiency. The TPS6300x is based on the standard H-bridge buck-boost power stage shown in Figure 4, and includes both buck and boost switching FET configurations connected to a single inductor. Unlike the standard buck-boost mode that continuously switches four FETs simultaneously, the TPS6300x uses a proprietary modulator design that switches only two FETs at a time. This control mechanism significantly reduces unnecessary switching losses. The TPS6300x operates more efficiently in buck or boost modes than traditional buck-boost modes, further reducing power loss. [img=460,349]http://cms.cn50hz.com/files/RemoteFiles/20081225/833138004.gif[/img] Figure 4 shows the power supply section. When the lithium-ion battery discharges to below 3.3V, the buck-boost converter must switch from buck mode to boost mode. At this switching point, many buck-boost control mechanisms experience efficiency degradation, power jitter, or output voltage instability. The TPS6300x can seamlessly switch between buck and boost modes as needed in a pulse-by-pulse manner, thus providing constant PWM switching across both buck and boost ranges without superposition or stall time between the two modes. Further features of the TPS6300x include other integrated features that enhance the user experience in portable applications, such as extremely low quiescent current (less than 50μA), a user-selectable power-saving (PS) mode that maintains high efficiency under light loads, and external synchronization that helps minimize system noise. The average current-mode control topology provides fast transient response and low output ripple in both buck and boost modes. Output regulation tolerance is ±1% across the input and load range. Internal compensation is optimized for external inductors of 2.2–4.7μH with output capacitors ranging from 10 to 22μF. Short-circuit protection acts as a feedback current limiter, reducing the maximum output current limit from 1.7A to 800mA when the output voltage drops by 3%. This reduces device power consumption under output overload conditions. Normal operation resumes after overload clearance. This approach allows for the charging of large output capacitors, such as ultra-large capacitors. The PS mode characteristics maintain very high efficiency even under light loads below 300mA. In PS mode, the switching time only guarantees to raise the output voltage slightly above the setpoint, then stops switching until the output voltage drops below the setpoint again. This "on-then-off" switching mode provides extremely high efficiency under light loads. Other applications : The TPS6300x can also drive white LEDs (WLEDs) in current regulation mode, replacing the output voltage divider network with resistors in the WLED circuit. Since the typical forward voltage drop of WLEDs is 4.2–3.5V, powering them with lithium-ion batteries is problematic in most power supply topologies because the power supply needs to both buck and boost its output voltage simultaneously. The TPS6300x's buck-boost function solves this problem well and can easily provide 500mA of current for lighting or flash applications. Conclusion: The TPS6300x is an ideal solution for converting lithium-ion battery voltage to a 3.3V bus voltage. Its high efficiency, small board area, low cost, and seamless transition from buck to boost modes make it an ideal choice for design engineers to achieve high-performance, rapid designs.