Circuit and method for adaptive leading edge blanking in pulse width modulated current mode switching power supply controllers

摘要

A current sensing device incorporated into the gate charge current path of the power transistor in a typical pulse-width modulated current mode switching power supply controller provides adaptive leading edge blanking of the current-sense waveform present in the feedback signal to prevent erroneous response in the feedback control circuitry and improve regulation of the power supply output voltage. A serial switch located within the current-sense feedback signal path is directly controlled by the current sensing device to open and close the signal path and generate a blanking interval which is optimally aligned to blank out or remove the leading edge spike in the current-sense waveform which corresponds to the gate charge current pulse that occurs during the turn-on transition of the power transistor. The optimal alignment of the blanking interval is an inherent feature of the current sensing device since the device utilizes the gate charge current pulse to define the timing of the opening and closing of the serial switch. Furthermore, the current sensing device is inherently responsive to variables such as the transistor's Miller capacitance or other manufacturing process and temperature related variations in gate-source capacitance which act to alter the width of the gate charge current pulse, and thus provides a blanking interval which adapts to or is independent of these variables. The width of the blanking interval automatically and dynamically adjusts to accommodate for changes in the leading edge spike of the current-sense waveform that result from the changing width in the gate charge current pulse.