A Compact Constant On-time Buck Converter with Analog Transient-optimized On-time Control and Body Diode Control

A constant on-time buck converter with analog transient-optimized on-time control (OTC) and body diode control (BDC) are proposed in this paper to achieve fast transient response for high slew-rate loads such as system-on-chip (SOC) and microprocessor. The two proposed controls occupy small chip area and can be applied to any type of constant on-time converter. The OTC, which achieves time-optimized control with compact analog circuit and capacitor current sensor, is proposed for load current step-up. Body diode control (BDC), which minimizes overshoot with a simple logic, is proposed for load current step-down. These proposed controls are implemented into integrated circuit (IC) by using 0.18um CMOS process with a chip area of 1.423mm(2). The OTC only occupies 0.054mm(2), 3.8% of the chip. The simulation results show 53.2% and 55.5% reduction of voltage deviation after enabling proposed control functions at load step-up and step-down, respectively. Measurement results show that, for a 1A load transient, the undershoot of output voltage improves 55% with OTC. Moreover, 86.5% peak efficiency is measured at 1W output power