The TPS51221 is a dual synchronous buck regulator controller with 2 LDOs. It is optimized for 5-V/3.3-V system controller, enabling designers to cost effectively complete 2-cell to 4-cell notebook system power supply. The TPS51221 supports high efficiency, fast transient response and 99% duty cycle operation. It supports supply input voltage ranging from 4.5 V to 28 V, and output voltages from 1 V to 12 V. Peak current mode supports stability operation with lower ESR capacitor and output accuracy. The high duty (99%) operation and wide input/ output voltage range supports flexible design for small mobile PCs and a wide variety of other applications. The fixed frequency can be adjusted from 200 kHz to 1MHz by a resistor, and each channel runs 180° out of phase.