Synchronous buck converter with improved transient performance

• US 6,753,723 B2
• Filed: 04/03/2003
• Issued: 06/22/2004
• Est. Priority Date: 04/03/2002
• Status: Expired due to Term

• Current Assignee: Infineon Technologies Americas Corp. (Infineon Technologies AG)
• Original Assignee: International Rectifier Corporation (Infineon Technologies AG)
• Inventors: Zhang, Jason
• Primary Examiner(s): NGUYEN, LONG T
• Application Number:
  US10/407,008
• Publication Number:
  US 20030206425A1
• Time in Patent Office: 446 Days
• Field of Search: 327/427, 327/431, 327/434, 327/581, 327/540, 327/541, 327/544, 327/134, 327/108, 327/379, 323/282-284, 323/288, 323/351, 363/127
• US Class Current: 327/540
• CPC Class Codes: H02M 3/1584 with a plurality of power processing stages connected in parallel
• CPC Class Codes: H02M 3/1588 comprising at least one synchronous rectifier element H02M3/1582, H02M3/1584 take precedence
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A synchronous buck converter having an improved transient response during output current stepdown. The device includes series and shunt MOSFETS, a first driver circuit to turn the series MOSFET on and off according to a variable duty cycle determined by an error signal representing the difference between the voltage output of the converter and a reference voltage, a sensing circuit operative to provide a control signal output when the duty cycle for the series MOSFET is zero; and a second drive circuit responsive to the control signal output of the sensing circuit to turn off the shunt MOSFET. The sensing circuit operates by detecting when the error signal is of a lower amplitude than the minimum value of the ramp waveform used to generate the duty cycle for the series MOSFET.

Claims

1. A synchronous buck converter having an improved transient response during output current stepdown, comprising:

a first switching transistor connected between an input node and a first node;

a second switching transistor connected between the first node and a second node;

a series inductor connected between the first node and an output node;

an output capacitor connected between the output node and the second node;

a first driver circuit operative to turn the first switching transistor on and off according to a variable duty cycle determined by an error signal representing the difference between the voltage output of the converter and a reference voltage;

a sensing circuit operative to provide a control signal output when the duty cycle for the first switching transistor is zero; and

a second drive circuit responsive to the control signal output of the sensing circuit to turn off the second switching transistor.

2. A device as described in claim 1, wherein:

the first driver circuit includes a circuit which generates a repeating ramp waveform having predetermined maximum and minimum values, and generates a signal representing the variable duty cycle by comparing the error signal to the ramp waveform; and

the sensing circuit generates the control signal when the error signal is of a lower amplitude than the minimum value of the ramp waveform.

3. A synchronous buck converter having an improved transient response during output current stepdown, comprising:

a series MOSFET connected between an input node and a first node;

a shunt MOSFET connected between the first node and a second node;

a series inductor connected between the first node and an output node;

an output capacitor connected between the output node and the second node;

a first driver circuit operative to turn the series MOSFET on and off according to a variable duty cycle determined by an error signal representing the difference between the voltage output of the converter and a reference voltage;

a sensing circuit operative to provide a control signal output when the duty cycle for the series MOSFET is zero; and

a second drive circuit responsive to the control signal output of the sensing circuit to turn off the shunt MOSFET.

4. A device as described in claim 3, wherein:

the first driver circuit includes a circuit which generates a repeating ramp waveform having predetermined maximum and minimum values, and generates a signal representing the variable duty cycle by comparing the error signal to the ramp waveform; and

the sensing circuit generates the control signal when the error signal is of a lower amplitude than the minimum value of the ramp waveform.