Buck Regulator, VLDO Combine For High Efficiency, Low Noise

Combining a 500-mA, 2.25-MHz synchronous buck regulator and a 300-mA VLDO in one package, the LTC3541 delivers two high-efficiency voltage rails from a single input requiring only one inductor. The buck regulator provides up to 95% efficiency, while the VLDO offers very low-noise operation. The device can generate outputs as low as 0.8 V from the buck regulator and 0.4 V from the VLDO, enabling it to power the latest generation of microcontrollers. An input voltage range of 2.7 to 5.5 V makes the LTC3541 well-suited for applications using a single Li-ion/polymer cell or multiple alkaline/NiCad/NiMH cells. The buck regulator's high switching speed and the VLDO design allow the use of very small low-cost externals, ensuring a compact total footprint for handheld systems.

All versions of the LTC3541 can be programmed via an external pin to have the synchronous buck regulator power up independently or simultaneously with the VLDO. Additionally, when both the synchronous switcher and the VLDO are enabled, an automatic start-up sequencing feature brings up either the switcher or the VLDO in a specific order. In the LTC3541 and LTC3541-2, the automatic start-up feature brings the buck output into regulation prior to enabling the VLDO regulator. Alternatively, the LTC3541-1 and LTC3541-3 can bring the VLDO into regulation prior to enabling the switching regulator. For maximum efficiency, the VLDO can be operated directly from the output of the switching regulator. It can also run off a separate 0.9- to 4.1-V input. A Burst Mode feature reduces the quiescent current in the switcher to only 85 µA to extend battery runtime. The LTC3541 comes in a 10-lead, 3- by 3-mm DFN package.