Cross-coupled charge pump for driving a bootstrap switch

A DC-DC converter, comprising:

• a high-side transistor of an n-channel type, a drain terminal of the high-side transistor coupled to an input supply voltage;
• a low-side transistor of the n-channel type, a drain terminal of the low-side transistor coupled to a source terminal of the high-side transistor to provide an output voltage, a source terminal of the low-side transistor coupled to reference ground;
• a bootstrap switch;
• a bootstrap capacitor coupled to the bootstrap switch;
• and
• a bootstrap drive circuit for driving the bootstrap switch, the bootstrap drive circuit comprising:
• a non-overlapping circuit configured to:
• receive an input signal, the input signal being a function of a pulse width modulated (PWM) signal, wherein the input signal and the PWM signal are characterized by a first logic level;
• generate a first control signal from the input signal at a first output terminal of the non-overlapping circuit, the first control signal having the first logic level;
• and
• generate a second control signal from the input signal at a second output terminal of the non-overlapping circuit, the second control signal being characterized by a second logic level different from the first logic level,
• a first capacitor coupled to the first output terminal of the non-overlapping circuit,
• a second capacitor coupled to the second output terminal of the non-overlapping circuit,
• a first n-channel transistor having a control terminal coupled to the second output terminal of the non-overlapping circuit through the second capacitor, a drain terminal of the first n-channel transistor coupled to a control terminal of the bootstrap switch, a source terminal of the first n-channel transistor coupled to a source terminal of the bootstrap switch, and
• a second n-channel transistor having a control terminal coupled to the first output terminal of the non-overlapping circuit through the first capacitor and the drain terminal of the first n-channel transistor, a drain terminal of the second n-channel transistor coupled to the control terminal of the first n-channel transistor, a source terminal of the second n-channel transistor coupled to the source terminal of the bootstrap switch.

A method for driving a bootstrap switch in a DC-DC converter using a bootstrap drive circuit, the method comprising:

• receiving, by a non-overlapping circuit of the bootstrap drive circuit, an input signal, the input signal being a function of a pulse width modulated (PWM) signal, wherein the input signal and the PWM signal are characterized by a first logic level;
• generating, by the non-overlapping circuit, a first control signal from the input signal at a first output terminal of the non-overlapping circuit, the first control signal having the first logic level;
• generating, by the non-overlapping circuit, a second control signal from the input signal at a second output terminal of the non-overlapping circuit, the second control signal being characterized by a second logic level different from the first logic level;
• charging a first capacitor of the bootstrap drive circuit to a regulated voltage during an ON phase of the DC-DC converter in accordance with the second control signal, the first capacitor coupled to the first output terminal of the non-overlapping circuit;
• turning ON a first n-channel transistor of the bootstrap drive circuit during the ON phase of the DC-DC converter, the first n-channel transistor having a control terminal coupled to the second output terminal of the non-overlapping circuit through a second capacitor of the bootstrap drive circuit, a drain terminal of the first n-channel transistor coupled to a control terminal of the bootstrap switch, a source terminal of the first n-channel transistor coupled to a source terminal of the bootstrap switch;
• turning OFF a second n-channel transistor of the bootstrap drive circuit during the ON phase of the DC-DC converter, the second n-channel transistor having a control terminal coupled to the first output terminal of the non-overlapping circuit through the first capacitor and the drain terminal of the first n-channel transistor, a drain terminal of the second n-channel transistor coupled to the control terminal of the first n-channel transistor, a source terminal of the second n-channel transistor coupled to the source terminal of the bootstrap switch;
• turning OFF the first n-channel transistor during the OFF phase of the DC-DC converter, the control terminal of the bootstrap switch receiving twice the regulated voltage during the OFF phase of the DC-DC converter;
• and
• turning ON the second n-channel transistor during the OFF phase of the DC-DC converter.