The TPS51220 is a dual peak-current mode, synchronous step-down controller with three low-dropout (LDO) regulators. It is optimized for 5 V/3.3 V notebook system power supplies. A 99% duty cycle operation enables designers to complete Li-ion battery applications from 2-cells to 4-cells cost effectively. The TPS51220 supports high-efficiency, fast transient response and 99% duty cycle operation. DCR current sensing provides lossless current sensing and free MOSFET selection; resistor sensing supports accurate current-sensing operation. It supports supply input voltages ranging from 4.5 V to 30 V and output voltages from 1 V to 12 V. High-current, 5 V at 100 am, 3.3 V at 10 am, onboard linear regulators have glitch-free switchover function to SMPS, and the 2 V reference has a 100 mA capability.