Rohm Co., Ltd.

Takeru Matsuki

Koichi Miyanaga

Shinya Karasawa

A pulse generator includes a mode controller that detects a state in which there has been no transition of a pulse signal to the off level for a given cycle (period). When such a state is detected, the pulse generator transits to a skip mode. In the skip mode, the period is repeatedly switched between: (i) a first period in which the pulse signal is maintained at the on level over multiple cycles; and (ii) a second period in which the pulse signal is forcibly switched to the off level so as to charge the bootstrap capacitor by means of a bootstrap circuit.

Step-down DC/DC converter

A bootstrap power supply circuit generates a constant voltage Vfor charging a bootstrap capacitor. An output transistor is configured as an N-channel MOSFET arranged such that its drain is connected to an input line and such that its source is connected to an output line. A constant voltage circuit connected to the gate of the output transistor stabilizes the gate voltage Vto a constant value. A variable impedance circuit is arranged between the input line and the gate of the output transistor, in order to provide a variable impedance. An impedance controller controls the impedance of the variable impedance circuit according to the state of a step-down DC/DC converter.

The present invention relates to improving the reliability of the control IC of DC/DC converters. The present invention provides a control ICof a rectifier diode-type buck DC/DC converter. An N-channel DMOS switch transistor Mis disposed between an input terminal VCC and a switch terminal LX. A first diode Dand an N-channel DMOS low-side transistor Mare connected in series with and disposed between the switch terminal LX and a ground terminal GND.

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Kyoto, Japan

Takeru Matsuki