A monolithic quasi-fixed-frequency DC-DC boost converter with a modified-adaptive-off-time (MAOF) control is presented. To achieve a quasi-fixed-frequency in the whole loading range, the new MAOF control is able to overcome the frequency variation problems naturally exist in traditional adaptive-off-time control in both continuous- and discontinuous-conduction-mode (CCM and DCM) operations. For the CCM operation, three circuits have been designed to implement the proposed control scheme, including the average-sampling method (AS), peak-sampling method (PS) and the average-predicting method (AP). These methods will be discussed in detail and compared with a conventional adaptive-off-time control scheme. For the DCM operation, an adaptive-off-time extension circuit is proposed to stabiliz...[ Read more ]

A monolithic quasi-fixed-frequency DC-DC boost converter with a modified-adaptive-off-time (MAOF) control is presented. To achieve a quasi-fixed-frequency in the whole loading range, the new MAOF control is able to overcome the frequency variation problems naturally exist in traditional adaptive-off-time control in both continuous- and discontinuous-conduction-mode (CCM and DCM) operations. For the CCM operation, three circuits have been designed to implement the proposed control scheme, including the average-sampling method (AS), peak-sampling method (PS) and the average-predicting method (AP). These methods will be discussed in detail and compared with a conventional adaptive-off-time control scheme. For the DCM operation, an adaptive-off-time extension circuit is proposed to stabilize the frequency variation problems. The MAOF control boost converter was implemented with a 0.35μm High Voltage (HV) CMOS process. With 3V - 4.2V input voltage, 10V - 14V output voltage and 30mA - 300mA load current range, measured results show that the switching frequency keeps constant at 1.05MHz to within ±4% across the whole operation range from CCM to DCM operation.