8.1 A 94.5%-Peak-Efficiency 3.99W/mm²-Power-Density Single-Inductor Bipolar-Output Converter with a Concise PWM Control for AMOLED Displays

DC-DC converters with bipolar outputs are widely used to drive AMOLED displays in battery-powered electronic devices. To prolong the battery life and meet the demand of increasing display dimensions, these converters should have high efficiency and high driving capability while minimizing PCB footprint. Compared with the solution using one boost converter and one inverting buck-boost converter with two inductors [1], the single-inductor bipolar-output (SIBO) converters [2] only require one inductor to generate both positive output (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OP</inf> ) and negative output (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</inf> ), making them highly desirable for reducing form factor and cost. A flying capacitor is further introduced to the SIBO topology in [3] to reduce voltage stress on power transistors and inductor current for efficiency improvement. However, the three-phase control, which encompasses inductor charging, V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OP</inf> regulation and V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</inf> regulation phases, leads to large output ripple and poor load and line regulation. Two-phase control that simultaneously transfers power to V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</inf> and V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OP</inf> is proposed in [4] to mitigate output voltage ripples. However, regulating V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</inf> relies on adjusting V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OP</inf> regulation loop to change the inductor current, resulting in poor transient responses and severe cross-regulation. The converter with a floating V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</inf> is further proposed in [5] to achieve a clean V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OP</inf> , but the shunt regulator used for V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OP</inf> regulation compromises the efficiency. In addition, as shown in Fig. 8.1.1, the 10-μH inductors employed in [4] [5] must have a saturation current of at least 1.8A (@V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IN</inf> =2.7V) to sustain a 0.5A load, occupying a significant amount of the PCB footprint.