A 95.2% Efficiency DC-DC Boost Converter Using Peak Current Fast Feedback Control (PFFC) for Improved Load Transient Response

Handheld devices and personal laptops are becoming compact and complex every year with a demand to have higher power density, efficiency, and fast transient response. DC-DC boost converters are used in display and haptic drivers where the output voltage needs to be boosted higher than input voltage. The load transient response and unity gain bandwidth (UGB) of DC-DC boost converters are restricted by the presence of a right half plane zero (RHPZ). In this paper, a control scheme termed peak current fast feedback control (PFFC) is proposed to improve the load transient response without the need for additional power switches or passive components. The fast feedback (FFB) path is designed to achieve low output voltage change and fast settling time with the same UGB when compared to the conventional peak current mode control (CPCM). In the proposed PFFC method, the closed loop output impedance (ZOCL) is improved by reducing the DC value and by increasing the bandwidth of ZOCL as compared to conventional peak current mode control (CPCM), thus improving the steady state and transient performance. The fast feedback (FFB) path is implemented within the error amplifier (EA) with an increase of only 2% in the active area as compared to CPCM. The boost converter is designed for VOUT=5V, VIN=2.5V-4.4V and ILOAD=10mA-1A operating at a frequency of 2MHz. Measurement results show that with PFFC enabled, the settling time reduces by ~2.6X and the undershoot reduces by 62% to 12μs and 41mV respectively when compared to CPCM for 10mA to 1A load step at 2A/μs. The PFFC approach improves the settling time by 12X to 26us and reduces the overshoot by 56% to 56mV when compared to CPCM for 1A to 10mA load step at 2A/μs. The converter achieves a peak efficiency of 95.2% at 0.5W output power with VIN=4.4V and load regulation of 9mV/A at VIN=2.5V. The line transient response at VOUT=5V, ILOAD=700mA for VIN=3V ↔ 4V which is repeated at 280μs time period is 235mV and 245mV for CPCM and PFFC respectively.