2 MHz buck in a 1.4 mm² footprint
The Texas Instruments LM3671TLX-ADJ/NOPB is a synchronous step-down (buck) regulator delivering up to 600 mA from a 2.7 V to 5.5 V input rail. Its 2 MHz switching frequency lets you use a small inductor and ceramic output capacitor, shrinking the total solution to fit a 5-bump DSBGA package measuring 1.41 mm × 1.08 mm.
