Switching circuit, dc/dc converter, and control circuit of dc/dc converter

A switching circuit comprising:

• an input terminal;
• a switching terminal;
• a ground terminal;
• a bootstrap terminal;
• a high side transistor connected to the input terminal and the switching terminal;
• a low side transistor connected to the switching terminal and the ground terminal;
• a bootstrap capacitor connected to the switching terminal and the bootstrap terminal;
• a bootstrap switch including a P-channel metal oxide semiconductor transistor connected to a constant voltage line and the bootstrap terminal;
• and
• a driver circuit that turns on the bootstrap switch in a period in which the low side transistor is on and that turns off the bootstrap switch in a period in which the low side transistor is off, wherein
• the driver circuit includes
• a level shifter that shifts a level of a control signal, and
• a buffer that drives the P-channel metal oxide semiconductor transistor according to output of the level shifter, and
• the level shifter includes
• an output line,
• a first resistance connected to the bootstrap terminal and the output line,
• a first transistor including a drain connected to the output line, the first transistor being turned on when the control signal is in an on level,
• a second resistance connected to a source of the first transistor and a ground,
• a third resistance including a first end connected to the bootstrap terminal,
• a second transistor including a drain connected to a second end of the third resistance, the second transistor being turned on when the control signal is in an off level,
• a third transistor connected to a source of the second transistor and the ground and turned on when the control signal is in the on level,
• a first capacitor connected to the third transistor in parallel, and
• a fourth transistor including a source connected to the bootstrap terminal, a drain connected to the output line, and a gate connected to a drain of the second transistor.