The STBB2 is a fixed frequency, high efficiency, buck-boost DC-DC converter which provides output voltages from 1.2 V to 4.5 V starting from input voltage from 2.4 V to 5.5 V. The device can operate with input voltages higher than, equal to, or lower than the output voltage making the product suitable for single Li-Ion, multi-cell alkaline or NiMH applications where the output voltage is within the battery voltage range. The low-RDS(on)N-channel and P-channel MOSFET switches are integrated and help to achieve high efficiency. The MODE pin allows the selection between auto mode and forced PWM mode, taking advantage from either lower power consumption or best dynamic performance. The bypass function allows the battery power saving. In this operating mode, the high-side switches are turned on so that the output voltage is equal to the input voltage; in this condition the current consumption is reduced to a maximum of 5 μA. The device also includes soft-start control, thermal shutdown, and current limit. The STBB2 is packaged in Flip Chip 20 bumps with 0.4 mm pitch.