HIGH EFFICIENCY PFM CONTROL FOR BUCK-BOOST CONVERTER

• US 20120229110A1
• Filed: 12/30/2011
• Published: 09/13/2012
• Est. Priority Date: 03/08/2011
• Status: Active Grant

• Current Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Original Assignee: Intersil Americas LLC (Renesas Electronics Corporation)
• Inventors: HUANG, CONGZHONG, PETRICEK, SHEA
• Granted Patent: US 8,981,737 B2
• Time in Patent Office: Days
• US Class Current: 323/282
• CPC Class Codes: H02M 3/1582 Buck-boost converters H02M3/1584 takes precedence

Abstract

A buck/boost voltage regulator generates a regulated output voltage responsive to an input voltage and a plurality of control signals. The buck/boost voltage regulator includes a plurality of switching transistors responsive to the plurality of control signals. Control circuitry monitors the regulated output voltage and generates the plurality of control signals responsive thereto. The control circuitry controls the operation of the plurality of switching transistors to enable a charging phase in a first mode of operation, a pass through phase in a second mode of operation and a discharge phase in a third mode of operation within the buck/boost voltage regulator to eliminate occurrence of a four switch switching condition.

Claims

1. A DC-DC converter, comprising:

an input terminal for receiving an input voltage from an input voltage source disposed at an input voltage level;

an output terminal for providing an output voltage at an output voltage level different than the input voltage level to a load connected to the output terminal;

a charge storage element for receiving and storing charge from the input voltage source on an input side thereof via the input terminal and transferring at least a portion of the stored charge to the load from an output side thereof; and

a control system for controlling the storage of charge to and transfer of charge from the charge storage element in at least three recurring phases to attain a desired level for the output voltage level, the three phases comprising a charge storage phase for storing charge from the input terminal in the charge storage element, a first charge transfer phase for transferring only a portion of the stored charge from the charge storage element to the load and a second charge transfer phase to transfer substantially all of the charge to the load.

2. The converter of claim 1, wherein the charge storage element comprises an inductor.

3. The converter of claim 1, and further comprising a clock circuit having a fixed frequency and wherein the charge storage phase and the first charge transfer phase are controlled by the control system to occur in a single period of the clock, with the end of the first charge storage phase occurring at the end of the clock period.

4. The converter of claim 3, wherein the second charge transfer phase occurs in response to an external condition of the output voltage independent of the clock.

5. The converter of claim 4, wherein the external condition is determined with a comparator determining that the output voltage equals or exceeds the desired level for the output voltage.

6. The converter of claim 4, wherein the control system sequences the operation of the charge phase followed by the first transfer phase during sequential periods of the clock until the external condition occurs, such that at the end of a preceding period of the clock, there will be a non zero energy level in the charge storage element and the charge phase of a current period will charge the charge storage element from the non zero energy level until the occurrence of the external condition.

7. The converter of claim 3, wherein the charge storage phase stores charge in the charge storage element until a predetermined amount of energy is stored therein, such that the length of time for reaching the predetermined amount of energy varies as a function of the initial amount of energy stored therein at the beginning of the charge transfer phase and the length of time for the first charge transfer phase will change accordingly.

8. The converter of claim 7, wherein the charge storage element comprises an inductor and the predetermined amount of energy is defined by a current limit of the current through the inductor during charging thereof in the charge storage phase.

9. The converter of claim 1, wherein the desired level of the output voltage is higher than the input voltage to provide a boost DC-DC conversion operation.

10. The converter of claim 1, wherein the charge storage element comprises an inductor and the control system comprises:

an switching bridge having first and second switching nodes, each connected to opposite sides of the inductor with a set of first and second input switches for connecting the first switching node to the input terminal with the first input switch and to a reference voltage with the second input switch and a set of first and second output switches for connecting the second switching node to the output terminal with the first output switch and to a reference voltage with the second output switch; and

a switch controller controlling the first and second input switches and first and second output switches to connect the inductor between the input terminal and the reference voltage and, in the first charge transfer phase, to connect the inductor between the input and output terminals and, in the second charge transfer phase, to connect the inductor between the reference voltage and the output terminal.

11. A buck-boost DC-DC converter, comprising:

an input terminal connected to an input voltage source operating at an input voltage level;

an output terminal connected to a load;

a reference node disposed at a reference voltage level;

a buck-boost conversion circuit, including;

an inductor,

a buck switching section for transferring charge to the inductor and subsequently transferring charge to the load on the output terminal in a voltage buck conversion operation, and

a boost switching section for transferring charge to the inductor and subsequently transferring charge to the load on the output terminal in a voltage boost conversion operation; and

a buck-boost controller for controlling at least the boost switching section to operate in a Pulse Frequency Modulation (PFM) boost mode of operation, the controller including;

a clock operating at a fixed frequency, and

a phase controller to control the first and second output switches to operate in a charging phase initiated at an edge of the clock to connect the inductor between the input terminal and the reference voltage node to charge the inductor to a predetermined charge level and then operate in a first charge transfer phase to connect the inductor between the input terminal and the output terminal to transfer charge from the inductor and the input terminal to the output terminal until the occurrence of the next clock edge, wherein the inductor will be at a non zero stored energy level.

12. The converter of claim 11, wherein the buck-boost controller includes a comparator for comparing the voltage level on the output terminal to a desired reference voltage and, when the voltage level on the output terminal equals or exceeds the reference voltage, the phase controller operates the boost switching section and the buck switching section in a second charge transfer phase to connect the inductor between the reference node and the output terminal to transfer substantially all of the energy stored in the inductor to the output terminal to reduce the energy therein to a substantially zero value.

13. The converter of claim 12, wherein the buck-boost controller controls the boost switching section and the buck switching section to disconnect the inductor from the input and output terminals and the reference node at the end of the second charge transfer phase.

14. The convertor of claim 11, wherein the buck-boost controller controls the buck switching section to operate in a PFM buck mode of operation.

15. The converter of claim 14, and further comprising a mode comparator to compare the voltage levels on the input and output terminals and switching between buck and boost modes of operation when the two voltages are within a predetermined voltage.

16. The converter of claim 11, wherein the buck-boost controller further includes a current limit detector to detect the flow of current into the inductor and change phase from the charge phase to the first charge transfer phase when a predetermined inductor current is detected in the charge phase.

17. A boost regulator, comprising:

an inductor;

a charging circuit for charging the inductor to a predetermined current level from an input voltage source;

a charge transfer circuit for transferring energy from the inductor and voltage source to a load;

a clock for defining a fixed recurring period for a charge/transfer operation; and

a controller for controlling the charging circuit to charge the inductor to the predetermined current level from an initial current level at the beginning of a given period followed by control of the charge transfer circuit to transfer energy for the remaining portion of the period to less than a zero inductor current level.

19. The method of claim 17, wherein the generating further comprises:

generating a voltage limit signal indicating when a regulated output voltage exceeds a reference voltage;

generating a current limit signal indicating when an input current to the charge storage element during the charge phase the buck/boost voltage regulator exceeds a predetermined current limit reference signal;

generating a first portion of a plurality of control signals to control a pair of boost switching transistors of a plurality of switching transistors that switch one side of the charge storage element to a reference voltage during the charge phase and to the output node during the pass-through phase and discharge phase associated with the buck/boost regulator that switch one side of the charge storage element to a reference voltage during the charge phase and to the output node during the pass-through phase and discharge phase responsive to the voltage limit reference signal, the current limit signal and a clock signal; and

generating a second portion of the plurality of control signals to control a pair of buck switching transistors of the plurality of switching transistor associated with the buck/boost regulator that connect on other side of the charge storage element to either the reference voltage during the discharge phase or the input node during the pass-through phase responsive to the voltage limit signal.

20. The method of claim 17 further including:

generating a regulated output voltage responsive to an input voltage and the plurality of control signals at the buck/boost regulator; and

operating the buck/boost regulator according the plurality of control signals in one of the first, second or third modes of operation.

21. The method of claim 19, wherein the operating further comprises:

controlling a plurality of switching transistors in the buck/boost regulator to enable a charging phase in the first mode of operation responsive to a clock signal and a current limit signal to charge an inductor to the current responding to the current limit signal; and

controlling the plurality of switching transistors in the buck/boost regulator to enable a pass through phase in the second mode of operation responsive to the clock signal and the current limit signal to both transfer energy stored in the inductor to the output node and transfer current from the input node to the output such that only a portion of the stored energy in the inductor is transferred to the output.

22. The method of claim 20, wherein the operating further comprises controlling the plurality of switching transistors to enable a discharge phase in the third mode of operation responsive to a voltage limit signal to fully transfer the energy stored in the inductor to the output with no energy transferred to the output from the input node.

18. A method for controlling operation of a buck/boost regulator, comprising:

generating a regulated output voltage or an output responsive to an input voltage received on an input and a plurality of control signals;

monitoring the regulated output voltage; and

generating a plurality of control signals responsive to the output voltage, wherein the plurality of control signals include a first mode of operation controlling a charge phase of the buck/boost regulator to charge a charge storage element from the input voltage on the input, a second mode of operation controlling a pass through phase of the buck/boost regulator to both transfer stored charge from the charge storage element to the output and transfer charge from the input to the output and a third mode of operation controlling a discharge phase of the buck/boost regulator to fully transfer the stored charge in the charge storage element to the output;

wherein the plurality of control signals control the buck/boost regulator to eliminate occurrence of a four switch switching condition.

23. A system, comprising:

a buck/boost voltage regulator for generating a regulated output voltage on an output responsive to an input voltage received on an input node and drive control signals, the buck/boost voltage regulator including a plurality of switching transistors;

control circuitry for monitoring the regulated output voltage and generating the plurality of drive control signals responsive thereto, wherein the control circuitry controls the operation of the plurality of switching transistors to enable a charging phase in a first mode of operation to store charge in an inductor from the input node, a pass through phase in a second mode of operation to transfer only a portion of the charge stored in the inductor to the output node and transfer charge from the input node to the output node and a discharge phase in a third mode of operation where the charge in the inductor is fully transferred to the output node within the buck/boost voltage regulator to eliminate occurrence of a four switch switching condition; and

a load coupled to the output of the buck/boost voltage regulator.

24. The system of claim 23, wherein the load is selected from a group consisting of a processor, a memory, an input device, an output device and a storage device.