Jörg Kirchner

A step-down conversion concept for a PWM-mode boost converter

A new area efficient approach for regulating the output of boost converters even when the input voltage exceeds the output voltage is presented. Down conversion is achieved without using an LDO and does not require an additional inductor coil and capacitor like the SEPIC or other noninverting buck-boost converters. The concept is based on a back-gate control of the PMOS type synchronous rectifier to avoid forward biasing of the substrate diode when the circuit is operating in the so-called down mode. The converter is implemented in a 10 pin MSOP package and requires only one external inductor and capacitor. The output voltage can be regulated between 1.8 V and 5.5 V for output currents up to 200 mA. When working in continuous boost mode, the efficiency is above 85% and goes up to 95%. In down mode efficiency is typical between 55% and 75%. An optional power save or power save mode is implemented to increase efficiency for light loads.