초록 ▼

A control circuit for a switching regulator implements constant on-time control scheme with synchronous rectification and applies an integrated standard and light load control loop to improve light load efficiency and enhance transient response. In one embodiment, the control circuit includes a refe

A control circuit for a switching regulator implements constant on-time control scheme with synchronous rectification and applies an integrated standard and light load control loop to improve light load efficiency and enhance transient response. In one embodiment, the control circuit includes a reference voltage selection circuit configured to select, based on a low-side current signal, a first reference voltage for standard load condition and a second reference voltage for light load condition as a selected reference voltage. The second reference voltage is greater than the first reference voltage. The control circuit further includes a control loop configured to generate a control signal to turn on the main switch when the feedback voltage is below the selected reference voltage and the minimum off-time duration has expired.

대표청구항 ▼

1. A control circuit for a switching regulator receiving an input voltage, the control circuit controlling a main switch and a low-side switch using a constant on-time control scheme to drive a switch output node for generating a switching output voltage, the switch output node being coupled to an L

1. A control circuit for a switching regulator receiving an input voltage, the control circuit controlling a main switch and a low-side switch using a constant on-time control scheme to drive a switch output node for generating a switching output voltage, the switch output node being coupled to an LC filter circuit to generate a regulated output voltage having a substantially constant magnitude on an output node, the regulated output voltage being fed back to the control circuit as a feedback voltage, the control circuit comprising: a first one-shot timer configured to generate a control signal indicative of a fixed on-time duration of the main switch, the control signal being applied to turn on the main switch while turning off the low-side switch and to turn off the main switch after the fixed on-time duration has expired while turning on the low-side switch;a minimum off-time timer configured to generate a minimum off-time signal having a first state when the main switch has been turned off for a minimum off-time duration;a reference voltage selection circuit configured to select, based on a low-side current signal, a first reference voltage for standard load condition and a second reference voltage for light load condition as a selected reference voltage, the low-side current signal having a first state indicative of a light load condition at the output node and the second reference voltage being greater than the first reference voltage; anda control loop configured to control the first one-shot timer to generate the control signal to turn on the main switch when the feedback voltage is below the selected reference voltage and the minimum off-time signal has the first state, the selected reference voltage being selected from the first reference voltage and the second reference voltage,wherein the control loop regulates the regulated output voltage based on the selected reference voltage and the regulated output voltage during light load conditions is maintained at a voltage level greater than the regulated output voltage maintained during normal or heavy load conditions. 2. The control circuit of claim 1, further comprising: a switching control circuit configured to drive the main switch and the low-side switch in response to the control signal from the first one-shot timer, the switching control circuit generating a drive signal to turn on the main switch while turning off the low-side switch and to turn off the main switch while turning on the low-side switch. 3. The control circuit of claim 1, wherein the control loop comprises: a voltage comparator having a first input terminal coupled to receive the feedback voltage, a second input terminal coupled to receive the selected reference voltage and an output terminal generating a comparator output voltage having a first state when the feedback voltage is less than the selected reference voltage; anda logical AND gate having a first input terminal coupled to receive the comparator output voltage of the voltage comparator and a second input terminal coupled to receive the minimum off-time signal of the minimum off-time timer, the logical AND gate generating an output signal having a first state when the comparator output voltage and the minimum off-time signal both have the first state,wherein the first one-shot timer generates the control signal to turn on the main switch when the output signal of the logical AND gate has the first state. 4. The control circuit of claim 1, wherein the reference voltage selection circuit comprises: a second one-shot timer configured to generate a second control signal having a first state for a predetermined duration as triggered by the low-side current signal having the first state indicative of a light load condition at the output node and having a second state otherwise; anda switch controlled by the second control signal, the switch having a first position selecting the first reference voltage as the selected reference voltage when the second control signal has the second state, and the switch having a second position selecting the second reference voltage as the selected reference voltage when the second control signal has the first state. 5. The control circuit of claim 4, wherein the reference voltage selection circuit further comprises: first, second and third resistors connected in series between a first voltage and a ground potential, the switch being connected in parallel with the second resistor and the first and second reference voltages being generated at a node between the second and third resistors,wherein the switch is closed at the first position to short out the second resistor and to generate the first reference voltage having a voltage value proportional to the resistances of the first and third resistors; andwherein the switch is open at the second position to generate the second reference voltage having a voltage value proportional to the resistances of the first, second and third resistors. 6. The control circuit of claim 5, wherein the first voltage comprises a bandgap voltage. 7. The control circuit of claim 1, wherein the low-side current signal detects a light load condition at the output node by monitoring a current flow through the low-side switch, the low-side current signal having the first state when the current flow through the low-side switch is below a predetermined threshold level. 8. The control circuit of claim 7, wherein the low-side switch comprises a MOSFET device and the low-side current signal is generated by monitoring a voltage across a drain terminal and a source terminal of the MOSFET device to determine the current flowing through the low-side switch. 9. The control circuit of claim 1, wherein the feedback voltage is a divided down voltage of the regulated output voltage. 10. The control circuit of claim 1, wherein the second reference voltage has a voltage value for regulating the regulated output voltage to a voltage value greater than a voltage value of the regulated output voltage during normal or heavy load conditions. 11. A method in a switching regulator receiving an input voltage and controlling a main switch and a low-side switch using a constant on-time control scheme to drive a switch output node for generating a switching output voltage, the switch output node being coupled to an LC filter circuit to generate a regulated output voltage having a substantially constant magnitude on an output node, the regulated output voltage being fed back to the switching regulator as a feedback voltage, the method comprising: turning on the main switch for a fixed on-time duration and turning off the low-side switch in response to a control signal;turning off the main switch for a minimum off-time duration and turning on the low-side switch in response to the control signal;selecting, based on a low-side current signal, a first reference voltage for standard load condition and a second reference voltage for light load condition as a selected reference voltage, the low-side current signal having a first state indicative of a light load condition at the output node and the second reference voltage being greater than the first reference voltage; andgenerating the control signal to turn on the main switch based on a control loop when the feedback voltage is below the selected reference voltage and the minimum off-time duration has expired, the selected reference voltage being selected from the first reference voltage and the second reference voltage,wherein the control loop regulates the regulated output voltage based on the selected reference voltage and the regulated output voltage during light load conditions is maintained at a voltage level greater than the regulated output voltage maintained during normal or heavy load conditions. 12. The method of claim 11, wherein generating the control signal to turn on the main switch based on a control loop comprises: comparing the feedback voltage to the selected reference voltage;generating a comparator output signal having a first state when the feedback voltage is less than the selected reference voltage; andgenerating the control signal to turn on the main switch when the comparator output signal has the first state and when the minimum off-time duration has expired. 13. The method of claim 11, wherein selecting, based on a low-side current signal, a first reference voltage for standard load condition and a second reference voltage for light load condition as a selected reference voltage comprises: generating a second control signal having a first state for a predetermined duration as triggered by the low-side current signal having the first state indicative of a light load condition at the output node and having a second state otherwise;selecting the first reference voltage as the selected reference voltage when the second control signal has the second state; andselecting the second reference voltage as the selected reference voltage when the second control signal has the first state. 14. The method of claim 11, further comprising: monitoring a current flow through the low-side switch, the low-side current signal having the first state when the current flow through the low-side switch is below a predetermined threshold level. 15. The method of claim 14, wherein the low-side switch comprises a MOSFET device and monitoring a current flow through the low-side switch comprises: monitoring a voltage across a drain terminal and a source terminal of the MOSFET device to determine the current flowing through the low-side switch. 16. The method of claim 11, wherein the feedback voltage is a divided down voltage of the regulated output voltage. 17. The method of claim 11, wherein the second reference voltage has a voltage value for regulating the regulated output voltage to a voltage value greater than a voltage value of the regulated output voltage during normal or heavy load conditions.