Inductor current based mode control for converter circuits

Abstract

A converter circuit includes a pull-up component, a pull-down component, and a controller configured to operate the pull-up component and the pull-down component to deliver power to a load. The controller is configured to operate the pull-up component and the pull-down component in first and second operating modes based on an average current delivered to the load. The converter circuit also includes a mode control circuit for generating a mode control signal based in part on a representation of a peak current received from the pull-up component at a switch node.

Description

Technical Field

[0001] The present application relates generally to converter circuits, and more particularly to converter circuits that switch between a pulse frequency modulation (PFM) operating mode and a continuous conduction mode (CCM) operating mode. Background Art

[0002] Some data converters operate in a pulse frequency modulation (PFM) mode of operation or a continuous conduction mode (CCM) mode of operation. The PFM mode of operation may be preferred for relatively low current load conditions, while the CCM mode of operation may be preferred for relatively high load conditions. Techniques for determining the current load conditions are needed to effectively control the operating mode. Summary of the invention

[0003] One aspect is a converter circuit. The converter circuit includes: a pull-up component that causes a voltage at a switch node to be substantially equal to a voltage at a positive power supply; a pull-down component that causes a voltage at a switch node to be substantially equal to a voltage at a negative power supply; and a controller configured to operate the pull-up component and the pull-down component to deliver power to a load. The controller is configured to operate the pull-up component and the pull-down component in either of a first and a second operating mode, wherein the first operating mode is preferred if an average current delivered to the load is greater than a current threshold, and the second operating mode is preferred if the average current delivered to the load is less than the current threshold. The converter circuit also includes: a mode control circuit for generating a mode control signal based in part on a representation of a peak current received from the pull-up component at the switch node, wherein the controller is configured to operate the pull-up component and the pull-down component in either of the first and second operating modes based on the mode control signal.

[0004] Another inventive aspect is a method of operating a converter circuit, the converter circuit including a switch node, a pull-up component, a pull-down component, a controller, and a mode control circuit. The method includes: using the pull-up component, making the voltage at the switch node substantially equal to the voltage at the positive power supply, wherein closing the pull-up component causes the voltage at the switch node to decrease with the pull-down component. The method also includes making the voltage at the switch node substantially equal to the voltage at the negative power supply, wherein closing the pull-down component causes the voltage at the switch node to increase. The method also includes: using the controller, operating the pull-up component and the pull-down component to deliver power to the load. The method also includes: using the controller. Operating the pull-up component and the pull-down component in either of a first and a second operating mode, wherein if the average current delivered to the load is greater than a current threshold, the first operating mode is preferred, and if the average current delivered to the load is less than the current threshold, the second operating mode is preferred. The method also includes: using the mode control circuit, generating a mode control signal based in part on a representation of a peak current received from the pull-up component at the switch node, and, using the controller, operating the pull-up component and the pull-down component in either of the first and second operating modes based on the mode control signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 is a schematic diagram of a converter circuit configured to operate in a pulse frequency modulation (PFM) mode of operation or a continuous conduction mode (CCM).

[0006] Figure 2 Is an indication during which Figure 1 The pull-up component of the converter circuit is turned on and during its Figure 1 Schematic diagram of the time period during which the pull-down component of the converter circuit is disconnected.

[0007] Figure 3 Is an indication during which Figure 1 The pull-up components of the converter circuit are disconnected and during Figure 1 Schematic diagram of the time period during which the pull-down component of the converter circuit is turned on.

[0008] Figure 4 Is an indication during which Figure 1 The pull-up components of the converter circuit are disconnected and during Figure 1 Schematic diagram of the time period during which the pull-down component of the converter circuit is disconnected.

[0009] Figure 5 yes Figure 1 Schematic diagram of the current flowing in the inductor of the converter circuit.

[0010] Figure 6 is a schematic diagram of an embodiment of a mode control circuit configured to control the Figure 1 operating mode of the converter circuit. DETAILED DESCRIPTION

[0011] Specific embodiments of the present invention are described herein with reference to the accompanying drawings.

[0012] Various details related to certain embodiments are described herein. However, the present invention may also be implemented in a manner different from those described herein. Without departing from the present invention, those skilled in the art may modify the embodiments discussed. Therefore, the present invention is not limited to the specific embodiments disclosed herein.

[0013] Figure 1 1 is a schematic diagram of a converter circuit 100 configured to operate in a pulse frequency modulation (PFM) operating mode or a continuous conduction mode (CCM). The circuit shown is only an example. As will be appreciated by those skilled in the art, the principles and aspects discussed herein may be applied to other converter circuits.

[0014] The converter circuit 100 includes a controller 110 , a pull-up component 120 , a pull-down component 130 , an inductor 140 , and a capacitor 150 .

[0015] The converter circuit 100 generates a substantially DC voltage at the output node OUT by controlling the switching operation of the pull-up component 120 and the pull-down component 130. As will be appreciated by those skilled in the art, the pull-up component 120 makes the voltage at the node SW substantially equal to the voltage at the positive power supply, and turning off the pull-up component 120 causes the voltage at the node SW to decrease due to the continuous current in the inductor 140. Similarly, the pull-down component 130 makes the voltage at the node SW substantially equal to the voltage at the negative power supply, and turning off the pull-down component 130 causes the voltage at the node SW to increase due to the continuous current in the inductor 140.

[0016] While operating in the PFM mode, during each cycle period, the controller 110 makes the voltage at the node SW substantially or approximately equal to the voltage of the positive power supply within the first duration T1, and substantially or approximately equal to the voltage of the negative power supply within the second duration T2. ​​During the third duration T3, the voltage at the node SW is not made substantially or approximately equal to the voltage of the positive power supply or substantially or approximately equal to the voltage of the negative power supply. The first and second durations T1 and T2 have substantially fixed lengths, and the converter circuit 100 affects the voltage at the output node OUT by controlling and adjusting the third duration T3. For example, in response to an indication that the voltage at the output node OUT is too low, the controller 110 can reduce the third duration T3. Similarly, in response to an indication that the voltage at the output node OUT is too high, the controller 110 can increase the third duration T3. Therefore, the frequency associated with the cycle period is adjusted to cause the target voltage value at the output node OUT.

[0017] While operating in CCM mode, during each cycle period, the controller 110 causes the voltage at the node SW to be substantially or approximately equal to the voltage of the positive power supply within a first duration T1, and substantially or approximately equal to the voltage of the negative power supply within a second duration T2. ​​The sum of the first duration T1 and the second duration T2 is fixed. The converter circuit 100 affects the voltage at the output node OUT by controlling and adjusting the first and second durations T1 and T2 without changing the sum of the first and second durations T1 and T2. For example, in response to an indication that the voltage at the output node OUT is too low, the controller 110 increases the first duration T1 and decreases the second duration T2. ​​Similarly, in response to an indication that the voltage at the output node OUT is too high, the controller 110 decreases the first duration T1 and increases the second duration T2. ​​Therefore, the frequency associated with the cycle period during CCM operation is fixed, and the duty cycle is adjusted to cause the target voltage value at the output node OUT.

[0018] The PFM mode of operation may be preferred for relatively low current load conditions, while the CCM mode of operation may be preferred for relatively high load conditions.Thus, a measurement of the load current may be used to determine in which mode the converter circuit 100 is to operate.

[0019] However, the load current may be difficult or impractical to determine. Instead, the average inductor current can be used as a proxy for the load current. And as shown below, other circuit signals can be used as an indication of the average inductor current.

[0020] Figures 2 to 5are schematic diagrams that are referenced to establish, using geometric principles, that other circuit signals can be used as an indication of average inductor current. In this example, converter 100 operates in PFM mode.

[0021] Figure 2 is a diagram indicating a time period during which the pull-up member 120 is turned on and during which the pull-down member 130 is turned off.

[0022] Figure 3 is a diagram indicating a time period during which the pull-up member 120 is turned off and during which the pull-down member 130 is turned on.

[0023] Figure 4 is a diagram indicating a time period during which the pull-up member 120 is disconnected and during which the pull-down member 130 is disconnected.

[0024] Figure 5 is based on Figure 2 , Figure 3 and Figure 4 Schematic diagram of the current of the inductor 140 derived for the various time periods indicated in FIG.

[0025] exist Figure 2 During the time period shown in , the pull-up component 120 is turned on and the pull-down component 130 is turned off, and the voltage at the node SW is substantially or approximately equal to the voltage at the positive power supply. Because the voltage at the output node OUT can be considered as DC, the current of the inductor 140 increases substantially or approximately linearly from the minimum value or zero to the peak value Ipeak.

[0026] exist Figure 3 During the time period shown in , the pull-up component 120 is turned off and the pull-down component 130 is turned on, and the voltage at the node SW is substantially or approximately equal to the voltage at the negative power supply. Because the voltage at the output node OUT can be considered as DC, the current of the inductor 140 decreases substantially or approximately linearly from the peak value Ipeak to the minimum value or zero.

[0027] exist Figure 4 During the time period indicated in , during which the pull-up component 120 is disconnected and the pull-down component 130 is disconnected, the voltage at the node SW is substantially or approximately equal to the voltage at the output node OUT. Therefore, the current of the inductor 140 is minimum or zero.

[0028] Using geometric principles known in the art, Figure 2 During the time period indicated in , during which the pull-up component 120 is turned on and the pull-down component 130 is turned off, the average current of the inductor 140 is equal to Ipeak / 2. Similarly, during Figure 3During the time period indicated in , during which the pull-up component 120 is turned off and the pull-down component 130 is turned on, the average current of the inductor 140 is also equal to Ipeak / 2. Figure 4 During the time period shown in , during which the pull-up component 120 is disconnected and the pull-down component 130 is disconnected, the current of the inductor 140 is minimum or zero.

[0029] Therefore, the average current Iavg of the inductor 140 is expressed by the following equation:

[0030] Iavg=Ipeak / 2x(TPUon+TPDon) / (TPUon+TPDon+Toff),

[0031] Where TPUon is equal to Figure 2 The duration of the time period during which the pull-up component 120 is turned on and the pull-down component 130 is turned off is indicated in TPDon, which is equal to Figure 3 The duration of the time period during which the pull-up component 120 is turned off and the pull-down component 130 is turned on is indicated in , and Toff is equal to Figure 4 The duration of the time period indicated in is that the pull-up component 120 is disconnected and the pull-down component 130 is disconnected.

[0032] Figure 6 is a schematic diagram of an embodiment of a mode control circuit 600, which is configured to control the inductor current according to the inductor current. Figure 1 The mode control circuit 600 may be implemented as a part of the controller 110, for example.

[0033] The mode control circuit 600 includes a current source Is1 , a resistor RSW, a switch TPUon, a resistor R1 , a capacitor C1 , a buffer 610 , and a switch Ton, a switch Toff, a resistor R2 , a capacitor C2 , and a comparator 620 .

[0034] In some embodiments, current source Is1 has a current value corresponding to the current of pull-up component 120, which is determined and controlled by a current sensing circuit (such as any current sensing and control circuit known in the art). For example, current source Is1 can have a current value determined by a scaled-down version of pull-up component 120, so that the current of current source Is1 is substantially proportional to the current of pull-up component 120.

[0035] In some embodiments, the current source Is1 is Figure 2, during which the pull-up component 120 is turned on and the pull-down component 130 is turned off (TPUon), and no current is supplied outside those time periods. Thus, in such an embodiment, the mode control circuit 600 is configured to supply current based on only a portion of each inductor current cycle ( Figure 2 The inductor current during the TPUon period (indicated in Figure 1 The operating mode of the converter circuit 100.

[0036] The controller 110 also controls the switch TPUon so that the switch TPUon is Figure 2 , is conductive during the time period indicated in , during which the pull-up component 120 is on and the pull-down component 130 is off (TPUon).

[0037] As a result, the voltage at node A corresponds to the average current of the inductor 140 during the TPUon period, where, as discussed above, the average current of the inductor 140 during the TPUon period is equal to Ipeak / 2. As will be appreciated by those skilled in the art, if Figure 2 As the time period indicated in , during which the pull-up component 120 is turned on and the pull-down component 130 is turned off (TPUon), increases, the voltage at the node A likewise increases. Similarly, if Figure 2 As the time period indicated in , during which the pull-up component 120 is turned on and the pull-down component 130 is turned off (TPUon), decreases, the voltage at the node A also decreases.

[0038] The controller 110 controls the switches Ton and Toff so that the buffer 610 and the switch Ton are Figure 2 and Figure 3 The voltage at the node B is equal to the voltage at the node A during the time period indicated in , during which the pull-up component 120 is turned on or the pull-down component 130 is turned on (Ton=TPUon+TPDon). In addition, the controller 110 controls the switches Ton and Toff so that the switch Toff is Figure 4 The voltage at the node B is made equal to the ground voltage during the time period indicated in , during which the pull-up component 120 is disconnected and the pull-down component 130 is turned off (Toff).

[0039] In addition, as will be appreciated by one of ordinary skill in the art, because of the filter formed by resistor R2 and capacitor C2, the voltage at node C is substantially equal to the average voltage at node B, where the voltage at node B is substantially equal to the voltage at node A multiplied by (TPUon+TPDon) / (TPUon+TPDon+Toff). Therefore, because the voltage at node A corresponds to Ipeak / 2, the voltage at node C corresponds to Ipeak / 2×(TPUon+TPDon) / (TPUon+TPDon+Toff), which is equal to the average current of inductor 140.

[0040] The comparator 620 is configured to compare the voltage at the node C with the threshold voltage at the node VTH and generate a control signal at the node CTRL. In response to the voltage at the node C being less than the threshold voltage at the node VTH (which indicates that the load current is less than the PFM-CCM current load threshold), the comparator generates a control signal at the node CTRL, which causes the controller 110 to operate the pull-up component 120 and the pull-down component 130 so that the converter functions in the pulse frequency mode (PFM). In response to the voltage at the node C being greater than the threshold voltage at the node VTH (which indicates that the load current is greater than the PFM-CCM current load threshold), the comparator generates a control signal at the node CTRL, which causes the controller 110 to operate the pull-up component 120 and the pull-down component 130 so that the converter functions in the continuous conduction mode (CCM).

[0041] In some embodiments, comparator 620 is hysteretic such that the control signal at node CTRL does not switch between two mode control values ​​in response to small changes in the voltage at node C when the voltage at node C is close to the threshold voltage at node VTH.

[0042] As will be appreciated by those skilled in the art, complementary switching devices such as Figure 1 The pull-up member 120 and the pull-down member 130 and the like Figure 6 The switches Ton and Toff of the complementary switching devices are used to prevent the two complementary switching devices from being turned on at the same time. For the discussion herein, as understood by a person of ordinary skill in the art, the brief period of time (dead time) between the closing of one of the complementary switching devices and the turning on of the other of the complementary switching devices is considered to be in any of the adjacent time periods.

[0043] In reference Figures 2 to 6In the example shown, the converter 100 operates in PFM mode. As will be appreciated by those skilled in the art, when the converter 100 operates in CCM, the mode control function of the mode control circuit 600 will also appropriately control the mode of operation. As will be appreciated by those skilled in the art, during CCM mode, there will be no Toff time. Therefore, Figure 6 The switch Toff will remain open, and Figure 6 The switch Ton will be continuously turned on.

[0044] Although the present invention is disclosed by the specific embodiments described above, these embodiments are not intended to limit the present invention. Based on the methods and technical aspects disclosed herein, those skilled in the art can make changes and modifications to the presented embodiments without departing from the spirit and scope of the present invention.

Claims

1. A converter circuit comprising: Switching nodes; a pull-up component configured to cause a voltage at the switch node to be equal to a voltage at a positive power supply, wherein disconnecting the pull-up component causes the voltage at the switch node to decrease; a pull-down component configured to cause a voltage at the switch node to be equal to a voltage at a negative power supply, wherein disconnecting the pull-down component causes the voltage at the switch node to increase; a controller configured to operate the pull-up component and the pull-down component to deliver power to a load, wherein the controller is configured to operate the pull-up component and the pull-down component in either of a first and a second operation mode, wherein the first operation mode is applied if an average current delivered to the load is greater than a current threshold, and wherein the second operation mode is applied if an average current delivered to the load is less than the current threshold; and a mode control circuit configured to generate a mode control signal based in part on a representation of a peak current received at the switch node from the pull-up component, wherein the controller is configured to operate the pull-up component and the pull-down component in either of the first and second operation modes based on the mode control signal; wherein the mode control circuit comprises a peak current circuit configured to generate a signal at a first node, wherein the signal generated at the first node corresponds to a peak current received from the pull-up component at the switch node; wherein the peak current circuit comprises a current source configured to supply current to the first node while the pull-up component delivers current to the switch node, and wherein a magnitude of the current of the current source is proportional to the current delivered by the pull-up component to the switch node.

2. The converter circuit according to claim 1, wherein: The first operating mode is a continuous conduction mode.

3. The converter circuit according to claim 1, wherein: The second operation mode is a pulse frequency modulation mode.

4. The converter circuit according to claim 1, wherein: The mode control circuit includes a weighting circuit configured to multiply a signal at the first node by a ratio of an on-time to a cycle time to generate a weighted signal at a second node, wherein the on-time is equal to a sum of a duration of a time period during which the pull-up component is on and the pull-down component is off and a duration of a time period during which the pull-up component is off and the pull-down component is on during a cycle period, and wherein the cycle time is equal to a total duration of the cycle period.

5. The converter circuit according to claim 4, wherein: The weighting circuit comprises: a buffer configured to drive a third node with a voltage at the first node during an on-time; and A switch is configured to connect the third node to a ground voltage when the buffer is not driving the third node with the voltage at the first node.

6. The converter circuit according to claim 4, wherein: The mode control circuit includes a comparison circuit configured to compare the weighted signal at the second node with a mode control threshold to generate the mode control signal.

7. The converter circuit according to claim 6, wherein: The comparison circuit includes a comparator configured to compare the mode control signal such that if the weighted signal at the second node is greater than the mode control threshold, the mode control signal causes the controller to operate the pull-up component and the pull-down component in the first operating mode.

8. The converter circuit according to claim 6, wherein: The comparison circuit includes a comparator configured to compare the mode control signal such that if the weighted signal at the second node is less than the mode control threshold, the mode control signal causes the controller to operate the pull-up component and the pull-down component in the second operating mode.

9. A method of operating a converter circuit, the converter circuit comprising: Switching nodes; Pull-up components; Drop-down widget; Controller; as well as Mode control circuit, The method comprises: Using the pull-up component, the voltage at the switch node is made equal to the voltage at the positive power supply, wherein disconnecting the pull-up component causes the voltage at the switch node to decrease; utilizing the pull-down component to cause a voltage at the switch node to be equal to a voltage at a negative power supply, wherein disconnecting the pull-down component causes the voltage at the switch node to increase; operating the pull-up component and the pull-down component to transfer power to a load using the controller; operating, with the controller, the pull-up component and the pull-down component in either of a first and a second operating mode, wherein the first operating mode is applied if an average current delivered to the load is greater than a current threshold, and wherein the second operating mode is applied if an average current delivered to the load is less than a current threshold; generating, with the mode control circuit, a mode control signal based in part on a representation of a peak current received at the switch node from the pull-up component: and operating, with the controller, the pull-up component and the pull-down component in either of the first and second operation modes based on the mode control signal; wherein the mode control circuit includes a peak current circuit, and the method further includes: generating a signal at a first node using the peak current circuit, wherein the signal generated at the first node corresponds to a peak current received from the pull-up component at the switch node; Wherein, the peak current circuit comprises a current source, and the method further comprises: The current source supplies current to the first node while the pull-up component delivers current to the switch node, and wherein a magnitude of the current of the current source is proportional to the current delivered by the pull-up component to the switch node.

10. The method according to claim 9, wherein: The first operating mode is a continuous conduction mode.

11. The method according to claim 9, wherein: The second operation mode is a pulse frequency modulation mode.

12. The method according to claim 9, wherein: The mode control circuit includes a weighting circuit, and the method further includes causing the circuit to multiply the signal at the first node by a ratio of an on-time to a cycle time to generate a weighted signal at a second node, wherein the on-time is equal to the sum of a duration of a time period during which the pull-up component is on and the pull-down component is off and a duration of a time period during which the pull-up component is off and the pull-down component is on during a cycle period, and wherein the cycle time is equal to a total duration of the cycle period.

13. The method according to claim 12, wherein: The weighting circuit comprises a buffer and a switch, and wherein the method further comprises: using the buffer to drive a third node with a voltage at the first node during an on-time; and The switch is used to connect the third node to a ground voltage when the buffer is not driving the third node with the voltage at the first node.

14. The method according to claim 12, wherein: The mode control circuit includes a comparison circuit, and the method further includes: using the comparison circuit, comparing the weighted signal at the second node with a mode control threshold to generate the mode control signal.

15. The method according to claim 14, wherein: The comparison circuit includes a comparator, and the method further includes: generating, using the comparator, the mode control signal so that if the weighted signal at the second node is greater than the mode control threshold, the mode control signal causes the controller to operate the pull-up component and the pull-down component in the first operating mode.

16. The method according to claim 14, wherein: The comparison circuit includes a comparator, and the method further includes: generating, using the comparator, the mode control signal so that if the weighted signal at the second node is less than the mode control threshold, the mode control signal causes the controller to operate the pull-up component and the pull-down component in the second operating mode.

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