Controller for DC-DC converters and related systems and methods

Abstract

The invention relates to a controller for DC-DC converters and related systems and methods. A method for controlling a direct current-direct current (DC-DC) converter includes (a) operating the DC-DC converter in a constant frequency operating mode, (b) determining that a duty cycle of a first switching device of the DC-DC converter has exceeded a first threshold, and (c) controlling the DC-DC converter in response to the duty cycle of the first switching device of the DC-DC converter having exceeded the first threshold. The DC-DC converter is caused to reduce the switching frequency and operate the switch from the constant frequency operating mode to a constant off-time operating mode.

Description

Background Art

[0001] Switching power converters are widely used in electronic devices, for example to provide regulated power supplies. A switching power converter is configured so that its solid-state power switching devices do not continuously operate in their linear state; instead, the switching devices repeatedly switch between their on and off states. One type of switching power converter is a direct current to direct current (DC to DC) converter, which converts one direct current (DC) voltage to another DC voltage or one DC current to another DC current. Summary of the invention

[0002] In one embodiment, a method for controlling a direct current (DC-DC) converter includes: in a first switching cycle of the DC-DC converter, (i) operating the DC-DC converter in a constant frequency operation mode, (ii) determining that a duty cycle of a first switching device of the DC-DC converter has exceeded a first threshold, and (iii) in response to the duty cycle of the first switching device of the DC-DC converter exceeding the first threshold, operating the DC-DC converter from operating a switch in the constant frequency operation mode to operating in a constant off-time operation mode.

[0003] In one embodiment, a controller for a direct current to direct current (DC-DC) converter includes: (i) an oscillator configured to generate an oscillator signal, a clock signal, and a duty cycle signal, the duty cycle signal indicating that a maximum allowable duty cycle of a first switching device of the DC-DC converter has been exceeded, (ii) a slope compensation module configured to generate a slope compensation signal based at least in part on the oscillator signal, (iii) a switch control module configured to generate a control signal to control the first switching device based at least in part on the slope compensation signal and the clock signal, and (iv) a mode change module configured to change the operation of each of the oscillator and the slope compensation module in response to the duty cycle signal being asserted while the control signal is asserted.

[0004] In one embodiment, a direct current to direct current (DC to DC) converter includes: a power stage including a first switching device; and a controller communicatively coupled to the power stage. The controller is configured to: (i) operate the DC-DC converter in a constant frequency operating mode, (ii) determine that a duty cycle of the first switching device has exceeded a first threshold, and (iii) in response to the duty cycle of the first switching device exceeding the first threshold, cause the DC-DC converter to switch from operating in the constant frequency operating mode to operating in a constant off-time operating mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1is a graph showing an example of a duty ratio in a DC-DC converter.

[0006] Figure 2 is a graph showing one example of a constant frequency operation mode of a DC-DC converter.

[0007] Figure 3 is a graph showing one example of a constant off-time operating mode of a DC-DC converter.

[0008] Figure 4 is a schematic diagram of an electrical system including a DC-DC converter having a controller configured to automatically switch the DC-DC converter between a constant frequency operating mode and a constant off-time operating mode according to one embodiment.

[0009] Figure 5 It is shown Figure 4 A graph of switching frequency versus duty cycle of an example of the operation of a controller.

[0010] Figure 6 It is shown Figure 4 A state diagram of another example of the operation of a controller.

[0011] Figure 7 yes Figure 4 A schematic diagram of an embodiment of an electrical system in which a power stage of a DC-DC converter has a boost topology.

[0012] Figure 8 Including showing Figure 7 Three graphs of an example of the operation of a DC-DC converter.

[0013] Fig. 9 yes Figure 4 Schematic diagram of one embodiment of an electrical system in which a power stage of a DC-DC converter has a buck-boost topology.

[0014] Fig.10 Including showing Fig. 9 Three graphs of an example of the operation of a DC-DC converter.

[0015] Fig.11 yes Figure 4 Schematic diagram of one embodiment of an electrical system in which a power stage of a DC-DC converter has a buck topology.

[0016] Fig.12 Including showing Fig.11 Three graphs of an example of the operation of a DC-DC converter.

[0017] Fig.13 yes Figure 4A block diagram of one embodiment of a controller.

[0018] Fig.14 Included is a diagram showing Fig.13 Embodiment of the controller Figure 4 Seven graphs of one example of the operation of a DC-DC converter.

[0019] Fig.15 Included is a diagram showing Fig.13 Embodiment of the controller Figure 4 Seven graphs of another example of the operation of a DC-DC converter.

[0020] Fig.16 yes Fig.13 Schematic diagram of one possible embodiment of an oscillator of a controller.

[0021] Fig.17 Including showing Fig.16 Six graphs of an example of the operation of an oscillator.

[0022] Fig.18 Including showing Fig.16 Six graphs of another example of the operation of an oscillator.

[0023] Fig.19 yes Fig.13 Schematic diagram of one possible embodiment of a voltage control module of a controller. DETAILED DESCRIPTION

[0024] One direct current (DC-DC) converter parameter is the duty cycle (D), which refers to the portion of the switching cycle during which the controlled switching device (sometimes referred to as the active switching device) is in the on state (conducting state). The controlled switching device of a DC-DC converter is the switching device of the DC-DC converter, where the duty cycle of the switching device can be modulated to adjust one or more parameters of the DC-DC converter, such as input voltage amplitude, input current amplitude, output voltage amplitude and / or output current amplitude. As an example of the duty cycle of a DC-DC converter, consider Figure 1 , which is a graph 100 of the amplitude of the control signal Φ versus time during a DC-DC converter switching cycle 102. Figure 1In the example of , a control signal Φ drives a control switching device of a DC-DC converter (not shown), and when the control signal Φ is asserted, the control switching device operates in its conducting state. Conversely, when the control signal Φ is de-asserted, the control switching device operates in its off state (non-conducting state). The switching cycle 102 has a period T1, which is equal to the inverse of the switching frequency F1 of the DC-DC converter in the switching cycle 102. In the switching cycle 102, the control signal Φ is asserted for a duration w1, and the control signal Φ is de-asserted for a duration o1. Therefore, the control switching device is continuously turned on for a time w1 in the switching cycle 102, and the control switching device is continuously turned off for a time o1 in the switching cycle 102. In this way, Figure 1 The duty cycle D1 of the controlled switching device in the example is given by the following formula 1.

[0025]

[0026] The constant frequency operation mode of the DC-DC converter is an operation mode in which the switching frequency of the DC-DC converter is fixed. As mentioned above, since the switching period is the inverse of the switching frequency, the period of each switching period of the DC-DC converter must also be fixed in the constant frequency operation mode. By modulating the control switch on time within each switching period, the duty cycle can be modulated in the constant frequency operation mode to adjust one or more parameters of the DC-DC converter. Therefore, in the constant frequency operation mode, the control switch device on time and the control switch device off time can be changed between switching cycles.

[0027] Figure 2 is a graph 200 of control signal Φ amplitude versus time, illustrating an example of a DC-DC converter operating in a constant frequency operating mode. Figure 2 In the example, a control signal Φ drives a control switching device of a DC-DC converter (not shown), and (a) when the control signal Φ is asserted, the control switching device operates in its on-state, and (b) when the control signal Φ is de-asserted, the control switching device operates in its off-state. Figure 2 Several example consecutive switching cycles 202 of a DC-DC converter operating in a constant frequency operating mode are shown. In this document, specific instances of items may be referred to by using numbers in parentheses (e.g., switching cycle 202(1)), while numbers without parentheses refer to any such item (e.g., switching cycle 202). The switching power converter operates at a constant switching frequency F 2a operation, so each switching cycle 202 has a constant switching frequency F 2a The reciprocal period T 2aHowever, the on-time and off-time of the switching device are controlled to vary between some switching cycles 202, for example, to maintain a desired regulation of one or more DC-DC converter parameters as DC-DC converter operating conditions change.

[0028] For example, in each of the switching cycles 202(1) and 202(2), the switching device is controlled to be at w 2a The switch device is in its on state for a duration of o 2a Therefore, in each of the switching cycles 202(1) and 202(2), the duty cycle of the control switching device is w 2a / T 2a However, in each of the switching cycles 202(3) and 202(4), the switching device is controlled to be at w 2b The duration of the switch is in its conducting state, controlling the switching device to be in o 2b is in its off state for the duration of w, and the control switching device thus has w 2b / T 2a Duty cycle. Duration w 2b Greater than duration w 2a , and the duty cycle of the controlled switching device in switching cycles 202(3) and 202(4) is therefore greater than the duty cycle of the controlled switching device in switching cycles 202(1) and 202(2). In switching cycle 202(5), the controlled switching device is at w 2c The duration of the switch is in its conducting state, controlling the switching device to be in o 2c The duration of the off state, and the duty cycle of the control switching device is w 2c / T 2a Duration w 2c Greater than duration w 2a and w 2b , and the duty cycle of the controlled switching device in switching period 202(5) is therefore greater than the duty cycle of the controlled switching device in any of switching periods 202(1)-202(4). In contrast, the duty cycle of the controlled switching device in switching period 202(6) is less than the duty cycle of the controlled switching device in any of switching periods 202(1)-202(5). Specifically, in switching period 202(6), the controlled switching device is on for a relatively short duration w. 2d is in its conducting state for a relatively long duration o 2d is in its off state, and the duty cycle of the control switching device is w 2d / T 2a .

[0029] The constant off-time operation mode of the DC-DC converter is an operation mode in which the off-time of the control switch device of the DC-DC converter is fixed, wherein the off-time refers to the duration of each switching cycle in which the control switch device is in its off state. By modulating the on-time of the control switch device in each switching cycle, the duty cycle can be modulated in the constant off-time operation mode to adjust one or more parameters of the DC-DC converter. Therefore, in the constant off-time operation mode, the switching frequency of the DC-DC converter can be changed between switching cycles.

[0030] Figure 3 is a graph 300 of the amplitude of the control signal Φ versus time, illustrating an example of a DC-DC converter operating in a constant off-time operating mode. Figure 2 For example, Figure 3 In the example of , a control signal Φ drives a control switching device of a DC-DC converter (not shown), and (a) when the control signal Φ is asserted, the control switching device operates in its on-state, and (b) when the control signal Φ is de-asserted, the control switching device operates in its off-state. Figure 3 1 shows several example consecutive switching cycles 302 of a switching power converter in a constant off-time operation mode. The switching power converter utilizes a switching cycle 302 having a duration of o in each switching cycle 302. 3a However, the on-time of the controlled switching device and the switching frequency of the DC-DC converter are varied between some switching cycles 302 in order to maintain the desired regulation of one or more DC-DC converter parameters as the DC-DC operating conditions change.

[0031] For example, in each of the switching cycles 302(1), 302(2), 302(5), and 302(6), the switching device is controlled at w 3a The duration is in its on state, the period is T 3a , and the switching power converter has F 3a The switching frequency, F 3a The switching frequency is the period T 3a Therefore, the duty cycle of the control switching device is w in each of the switching cycles 302(1), 302(2), 302(5) and 302(6). 3a / T 3a However, in the switching cycle 302 (3), the switching device is controlled to be in a relatively long w 3b duration in its on state to achieve w 3b / T 3bThe switching cycle 302 (3) has a relatively large period T. 3b and a relatively small switching frequency F 3b In contrast, in switching cycle 302(4), the switch device is controlled to be in its on state for w 3c of relatively short duration to achieve w 3c / T 3c The switching cycle 302 (4) has a relatively small period T. 3c and a relatively large switching frequency F 3c .

[0032] The output voltage of the DC-DC converter is V out With input voltage V in The ratio of the output voltage V is usually a function of the duty cycle D. For example, Equations 2, 3, and 4 convert the output voltage V out With input voltage V in The ratio of is specified as a function of the duty cycle of the step-up DC-DC converter, the buck-boost DC / DC converter, and the buck DC-DC converter, assuming continuous conduction operation.

[0033]

[0034] It is obvious from Equation 2-4 that the duty cycle D must be large to obtain an output voltage V out With input voltage V in However, in a DC-DC converter operating in a constant frequency operation mode, the maximum value of the duty cycle D is limited to allow time for the switching device to change state and time for the controller of the DC-DC converter to obtain and process data. Therefore, the output voltage V of the DC-DC converter operating in a constant frequency operation mode is out With input voltage V in The ratio is limited by the maximum permissible value of the duty cycle D. This limitation is required when a large V out / V in ratio may be problematic in applications such as V in Since the input voltage V in In applications where the power supply has a large load and an unusually low input voltage V in Low temperature of the battery, etc.

[0035] In contrast, in a DC-DC converter operating in a constant off-time operation mode, the duty cycle can be essentially unlimited, which enables the DC-DC converter to achieve large V out / V inHowever, the switching frequency can vary significantly in the constant off-time operation mode, such as the above Figure 3 As discussed. Potential variations in switching frequency may be undesirable, for example, because it may require large inductors and large filtering components to ensure acceptable operation at low switching frequencies. In addition, variations in the switching frequency of the DC-DC converter may complicate efforts to achieve electromagnetic compatibility (EMC) of the DC-DC converter with other equipment.

[0036] This article discloses a new controller for a DC-DC converter and an associated system and method that at least partially alleviate the above-mentioned problems. Certain embodiments of the new controller, system and method are based at least in part on the duty cycle of the control switch device of the DC-DC converter, such as automatically switching the operation mode of the DC-DC converter between a constant frequency operation mode and a constant off-time operation mode in response to the duty cycle of the control switch device exceeding a threshold. For example, certain embodiments are configured to (a) operate the DC-DC converter in a fixed frequency operation mode when the duty cycle of the control switch device of the DC-DC converter does not exceed the maximum allowed duty cycle in the constant frequency operation mode, and (b) operate the DC-DC converter in a constant off-time operation mode when the duty cycle of the control switch device in the constant frequency operation mode exceeds the maximum allowed constant duty cycle. Therefore, certain embodiments cause the DC-DC converter to operate in a constant frequency operation mode, unless it is necessary to operate in a constant off-time operation mode to achieve adjustment of one or more DC-DC converter parameters, thereby promoting stability associated with constant frequency operation, while enabling a large ratio of output voltage to input voltage to be achieved when needed.

[0037] In addition, some embodiments of the new controller, system and method support current mode control, such as peak current mode control to promote high performance line and load regulation. In these embodiments, the slope compensation signal is optionally provided in a constant frequency operating mode to achieve stable operation, such as operation without subharmonic oscillations, with a duty cycle greater than 50%. In addition, some embodiments change the generation of the slope compensation signal in response to the duty cycle of the control switching device exceeding a threshold, such as by maintaining the slope compensation signal at a constant value, so that when the DC-DC converter is operated in a fixed off-time operating mode, the slope compensation signal does not affect the operation of the DC-DC converter.

[0038] Figure 44 is a schematic diagram of an electrical system 400 including a power source 402, a DC-DC converter 404, and an electrical load 406. The DC-DC converter 404 includes a power stage 408 and a controller 410, wherein the controller 410 is an embodiment of the novel controller disclosed herein. The controller 410 is communicatively coupled 412 to the power stage 408, and the controller 410 controls the operation of the power stage 408 as described below. The power stage 408 includes a first input port 414, a second input port 416, a first output port 418, and a second output port 420. In some embodiments, the first input port 414, the second input port 416, the first output port 418, and the second output port 420 are discrete components, such as integrated circuit pins, integrated circuit solder balls or pads, electrical terminals, etc. In some other embodiments, the first input port 414, the second input port 416, the first output port 418, and the second output port 420 are corresponding electrical nodes that optionally surround a plurality of electrical conductors. The power stage 408 also includes a control switch device 422, which is configured to control the power stage 408 to operate in a controlled manner. Figure 4 This is symbolically illustrated by a switch formed by a dotted line.

[0039] The power source 402 is electrically coupled between the first input port 414 and the second input port 416, and the electrical load 406 is electrically coupled between the first output port 418 and the second output port 420. The power stage 408 is configured to, in response to a control signal (not shown) from the controller 410, increase the input voltage V between the first input port 414 and the second input port 416. in Converted into an output voltage V between the first output port 418 and the second output port 420 out (and vice versa). In addition, the power stage 408 is configured to, in response to a control signal (not shown) from the controller 410, flow an input current I between the first input port 414 and the second input port 416. in Converted into an output current I flowing between the first output port 418 and the second output port 420 out (vice versa).

[0040] The power stage 408 can have a non-isolated topology or an isolated topology. In some embodiments where the power stage 408 has a non-isolated topology, the first input port 414 and the first output port 418 are part of a common electrical node. In some other embodiments where the power stage 408 has a non-isolated topology, the second input port 416 and the second output port 420 are part of a common electrical node. In certain embodiments, the power stage 408 has one of a boost topology, a buck-boost topology, or a buck topology, as described below with reference to Figure 7-12However, it should be understood that the power stage 408 is not limited to having one of the above topologies. For example, the power stage 408 may alternately have a flyback topology, a forward topology, a Chuck topology, a SEPIC topology, a Zeta topology, etc.

[0041] Controller 410 is formed, for example, by analog electronic circuits and / or digital electronic circuits. Although controller 410 is described as a single element, controller 410 may be formed by multiple sub-elements that do not need to be packaged together. In addition, controller 410 may be partially or completely integrated with one or more other elements, such as integrated with power stage 408. In addition, in some alternative embodiments, controller 410 is at least partially located outside of DC-DC converter 404. For example, in a specific alternative embodiment, controller 410 is divided into a local part and a remote part, wherein the local part is within DC-DC converter 404 and the remote part is outside DC-DC converter 404.

[0042] Certain embodiments of the controller 410 are configured to generate one or more control signals (not shown) to control the duty cycle of the control switch device 422 of the power stage 408, thereby adjusting one or more parameters of the DC-DC converter 404. Examples of such parameters that may be adjusted include, but are not limited to, the input voltage V in The amplitude and output voltage V out The amplitude of the input current I in The amplitude and output current I out Importantly, the controller 410 is also configured to automatically switch the operating mode of the DC-DC converter 404 between the constant frequency operating mode and the constant off-time operating mode based at least in part on the duty cycle of the control switch device 422, for example in response to the duty cycle of the control switch device 422 exceeding a threshold. In some embodiments, the controller 410 is configured to automatically switch the operating mode of the DC-DC converter 404 between the constant frequency operating mode and the constant off-time operating mode based at least in part on the duty cycle of the control switch device 422. Figure 4 The operation mode of the DC-DC converter 404 is switched between the constant frequency operation mode and the constant off-time operation mode, for example by suspending the operation of the oscillator, during a period (not shown).

[0043] For example, Figure 5 is the switching frequency F of the DC-DC converter 404 s A graph 500 of the duty cycle D of the control switching device 422 shows one example of possible operation of the controller 410. Three values ​​of the duty cycle D are labeled along the X-axis of the graph 500, i.e., D=D min 、D=D max and D = 1. min is the minimum allowed value of D, for example, the minimum value of D required for the DC-DC converter 404 to operate reliably.max is the maximum allowed value of D when the DC-DC converter 404 operates in the constant frequency operation mode, and D=1 corresponds to a 100% duty cycle of the control switch device 422. The controller 410 is configured to operate the DC-DC converter 404 in the constant frequency operation mode 502, such as the switching frequency F s As long as D is at least min The same size and D does not exceed D max In addition, the controller 410 is configured to max When Figure 5 As shown, through the switching frequency F s As the D value increases in D max The above increase decreases, causing the DC-DC converter 404 to operate in the constant off-time operation mode 504 .

[0044] Figure 6 6 is a state diagram 600 that illustrates another example of possible operation of the controller 410. The state diagram includes a state 602 and a state 604. In the state 602, the controller 410 generates a control signal to operate the DC-DC converter 404 in a constant frequency operation mode, and in the state 604, the controller 410 generates a control signal to operate the DC-DC converter 404 in a constant off-time operation mode. Figure 6 As shown, when D is less than or equal to D max , the controller 410 operates in state 602. In addition, the controller 410 responds to D rising to D max The above switches from state 602 to state 604, and as long as D remains greater than D max , the controller 410 remains in state 604. In response to D decreasing to D max Or below and switch from state 604 to state 602.

[0045] Figure 7 is a schematic diagram of an electrical system 700, which is an electrical system 400 ( Figure 4 ), wherein the DC-DC converter 404 is implemented by a DC-DC converter 704. The power stage 408 of the DC-DC converter 404 is implemented by a power stage 708 in the DC-DC converter 704. The power stage 708 has a boost topology. Specifically, the power stage 708 includes a control switch device 722, a freewheeling switch device 724, and an inductor 726. The second input port 416 and the second output port 420 are part of a common electrical node 728 in the power stage 708. As the control switch device 422 ( Figure 4) is electrically coupled between a switch electrical node 730 and a common electrical node 728. An inductor 726 is electrically coupled between the first input port 414 and the switch electrical node 730, and a freewheeling switch device 724 is electrically coupled between the switch electrical node 730 and the first output port 418. Each of the control switch device 722 and the freewheeling switch device 724 includes, for example, one or more transistors and a driver circuit for driving the transistors. The control switch device 722 is controlled by a control signal Φ1, and the freewheeling switch device 724 is controlled by a control signal Φ2. The power stage 708 optionally also includes a current sensing circuit 732, which is configured to generate a current I indicative of a current flowing through the inductor 726. L The amplitude of the signal I L_s .

[0046] The controller 410 is implemented by a controller 710 in the DC-DC converter 704, and the controller 710 is configured to generate control signals Φ1 and Φ2. The controller 710 is configured to generate the control signal Φ1 to control the switch of the control switch device 722, thereby adjusting one or more parameters of the DC-DC converter 704. In some embodiments, as Figure 7 As shown, the controller 710 receives the output voltage V out and signal I L_s The controller 710 is configured to generate a control signal Φ2 when the control switch device 722 is in its off state, so that the freewheeling switch device 724 is a current I flowing through the inductor 726. L Provide a path. In some alternative embodiments, the freewheeling switch device 724 is replaced by a diode and the control signal Φ2 is omitted. The controller 710 is configured to cross a threshold based at least in part on the duty cycle of the control switch device 722, for example, in response to the duty cycle of the control switch device 722, for example, as described above with respect to Figure 5 or Figure 6 In the manner discussed, the operating mode of the DC-DC converter 704 is automatically switched between a constant frequency operating mode and a constant off-time operating mode.

[0047] Figure 8 The present invention includes three graphs 800, 802, and 804 that collectively illustrate an example of the operation of the DC-DC converter 704. Graph 800 is a graph of the relationship between the control signal Φ1 and time, graph 802 is a graph of the change of the control signal Φ2 and time, and graph 804 is a graph of the inductor current I L Graphs versus time. All three graphs 800, 802, and 804 have a common time base. Figure 8Assume that (a) when the control signal Φ1 is asserted, the control switch device 722 operates in its on-state, and (b) when the control signal Φ1 is de-asserted, the control device 722 operates in its off-state. In addition, Figure 8 Assume that (a) when the control signal Φ2 is asserted, the free-flow switch device 724 operates in its on-state, and (b) when the control signal Φ2 is de-asserted, the free-flow switch device 724 operates in its off-state. However, the control switch device 722 and the free-flow switch device 724 may respond to the respective control signals Φ1 and Φ2 in different ways. In addition, the control signals Φ1 and Φ2 may have different Figure 8 The polarities shown are of different polarities.

[0048] Figure 8 Several exemplary consecutive switching cycles 806 of the DC-DC converter 704 are depicted. The controller 710 generates the control signal Φ1 such that the DC-DC converter 704 operates in a constant frequency operation mode in the switching cycles 806(1) and 806(2). Thus, in the switching cycles 806(1) and 806(2), the DC-DC converter 704 has a constant switching frequency F 8a , which is equal to the period T 8a However, the corresponding on-time w of the control switch device 722 in the switching cycles 806 ( 1 ) and 806 ( 2 ) is 8a and w 8b Different, for example, in response to operating conditions of DC-DC converter 704 changing between switching cycles 806 ( 1 ) and 806 ( 2 ).

[0049] The controller 710 generates the control signal Φ1 to cause the DC-DC converter 704 to operate in a constant off-time operation mode in the switching cycles 806(3) and 806(4), for example in response to the duty cycle of the control switch device 722 increasing to exceed the maximum allowable duty cycle value in the constant frequency operation mode. Therefore, the control switch device 722 has a constant off-time o in the switching cycles 806(3) and 806(4). 8a However, the corresponding on-time w of the control switch device 722 in the switching cycles 806 ( 3 ) and 806 ( 4 ) is 8c and w 8d The switching frequencies F of the DC-DC converter 704 may be different, for example, in response to the operating conditions of the DC-DC converter 704 changing between the switching cycles 806(3) and 806(4). Therefore, the switching cycles 806(3) and 806(4) may have different switching frequencies F. 8b and F 8c , they are respectively period T 8b and T 8cWhen comparing switching periods 806(3) and 806(4) with switching periods 806(1) and 806(2), it is apparent that the switching frequency in the constant off-time mode of operation is less than the switching frequency in the constant frequency mode of operation.

[0050] Fig. 9 is a schematic diagram of an electrical system 900, which is an electrical system 400 ( Figure 4 ) embodiment, wherein the DC-DC converter 404 is implemented by a DC-DC converter 904. The power stage 408 of the DC-DC converter 404 is implemented by a power stage 908 in the DC-DC converter 904. The power stage 908 has a buck-boost topology. Specifically, the power stage 908 includes a control switch device 922, a freewheeling switch device 924, and an inductor 926. The second input port 416 and the second output port 420 are part of a common electrical node 928 in the power stage 908. As the control switch device 422 ( Figure 4 ) of an embodiment of the power stage 908 is electrically coupled between the first input port 414 and the switch electrical node 930. The inductor 926 is electrically coupled between the switch electrical node 930 and the common electrical node 928, and the freewheeling switch device 924 is electrically coupled between the switch electrical node 930 and the first output port 418. Each of the control switch device 922 and the freewheeling switch device 924 includes, for example, one or more transistors and a driver circuit for driving the transistors. The control switch device 922 is controlled by a control signal Φ1, and the freewheeling switch device 924 is controlled by a control signal Φ2. The power stage 908 optionally also includes a current sensing circuit 932, which is configured to generate a current I indicative of a current flowing through the inductor 926. L The amplitude of the signal I L s .

[0051] The controller 410 is implemented by a controller 910 in the DC-DC converter 904, and the controller 910 is configured to generate control signals Φ1 and Φ2. The controller 910 is configured to generate the control signal Φ1 to control the switch of the control switch device 922, thereby adjusting one or more parameters of the DC-DC converter 904. In some embodiments, as Fig. 9 As shown, the controller 910 receives the output voltage V out and signal I L_s The controller 910 is configured to generate a control signal Φ2 when the control switch device 922 is in its off state, so that the freewheeling switch device 924 is a current I flowing through the inductor 926. LProvide a path. In some alternative embodiments, the freewheeling switch device 924 is replaced by a diode and the control signal Φ2 is omitted. The controller 910 is configured to cross a threshold based at least in part on the duty cycle of the control switch device 922, for example, in response to the duty cycle of the control switch device 922, for example, as described above with respect to Figure 5 or Figure 6 In the manner discussed, the operating mode of the DC-DC converter 904 is automatically switched between a constant frequency operating mode and a constant off-time operating mode. The output voltage V out The polarity will be different from the input voltage V in The polarity is opposite.

[0052] Fig.10 The three graphs 1000, 1002 and 1004 collectively show the output voltage V out The amplitude is greater than the input voltage V in An example of the operation of the DC-DC converter 904 in an application with an amplitude of . Figure 1000 is a graph of the relationship between the control signal Φ1 and time, Figure 1002 is a graph of the control signal Φ2 and time, and Figure 1004 is a graph of the inductor current I L Graphs as a function of time. All three graphs 1000, 1002 and 1004 have a common time base. Fig.10 Assume that (a) when the control signal Φ1 is asserted, the control switch device 922 operates in its on-state, and (b) when the control signal Φ1 is de-asserted, the control device 922 operates in its off-state. In addition, Fig.10 Assume that (a) when control signal Φ2 is asserted, free-flow switch device 924 operates in its on-state, and (b) when control signal Φ2 is de-asserted, free-flow switch device 924 operates in its off-state. However, control switch device 922 and free-flow switch device 924 may respond to respective control signals Φ1 and Φ2 in different ways. In addition, control signals Φ1 and Φ2 may have different Fig.10 The polarities shown are of different polarities.

[0053] Fig.10 Several exemplary consecutive switching cycles 1006 of the DC-DC converter 904 are depicted. The controller 910 generates the control signal Φ1 such that the DC-DC converter 904 operates in a constant frequency operation mode in the switching cycles 1006(1) and 1006(2). Thus, in the switching cycles 1006(1) and 1006(2), the DC-DC converter 904 has a constant switching frequency F 10a , which is equal to the period T 10a However, the corresponding on-time w of the control switch device 922 in the switching cycles 1006 ( 1 ) and 1006 ( 2 ) is10a and w 10b Different, for example, in response to operating conditions of the DC-DC converter 904 changing between switching cycles 1006 ( 1 ) and 1006 ( 2 ).

[0054] Controller 910 generates control signal Φ1 to cause DC-DC converter 904 to operate in a constant off-time operating mode in switching cycles 1006(3) and 1006(4), e.g., in response to the duty cycle of controlled switching device 922 increasing to exceed a maximum allowable duty cycle value in the constant frequency operating mode. Thus, controlled switching device 922 has a constant off-time o in switching cycles 1006(3) and 1006(4). 10a However, the corresponding on-time w of the control switch device 922 in the switching cycles 1006 ( 3 ) and 1006 ( 4 ) is 10c and w 10d The switching frequencies F of the DC-DC converter 904 are different, for example, in response to the operating conditions of the DC-DC converter 904 changing between the switching cycles 906 ( 3 ) and 906 ( 4 ). Therefore, the switching cycles 906 ( 3 ) and 906 ( 4 ) have different switching frequencies F . 10b and F 10c , they are respectively period T 10b and T 10c When comparing switching periods 1006(3) and 1006(4) with switching periods 1006(1) and 1006(2), it is apparent that the switching frequency in the constant off-time mode of operation is less than the switching frequency in the constant frequency mode of operation.

[0055] Fig.11 is a schematic diagram of an electrical system 1100, which is a schematic diagram of an electrical system 400 ( Figure 4 ), wherein the DC-DC converter 404 is implemented by the DC-DC converter 1104. The power stage 408 of the DC-DC converter 404 is implemented by the power stage 1108 in the DC-DC converter 1104. The power stage 1108 has a buck topology. Specifically, the power stage 1108 includes a control switch device 1122, a freewheeling switch device 1124, and an inductor 1126. The second input port 416 and the second output port 420 are part of the common electrical node 1128 in the power stage 1108. The control switch device 1122 is a control switch device 422 ( Figure 4), electrically coupled between the first input port 414 and the switching electrical node 1130. The inductor 1126 is electrically coupled between the switching electrical node 1130 and the first output port 418, and the freewheeling switch device 1124 is electrically coupled between the switching electrical node 1130 and the common electrical node 1128. Each of the control switch device 1122 and the freewheeling switch device 1124 includes, for example, one or more transistors and a driver circuit for driving the transistors. The control switch device 1122 is controlled by a control signal Φ1, and the freewheeling switch device 1124 is controlled by a control signal Φ2. The power stage 1108 optionally also includes a current sensing circuit 1132, which is configured to generate a current I indicative of a current flowing through the inductor 1126. L The amplitude of the signal I L_s .

[0056] The controller 410 is implemented by a controller 1110 in the DC-DC converter 1104, and the controller 1110 is configured to generate control signals Φ1 and Φ2. The controller 1110 is configured to generate the control signal Φ1 to control the switch of the control switch device 1122, thereby adjusting one or more parameters of the DC-DC converter 1104. In some embodiments, as Fig.11 As shown, the controller 1110 receives the output voltage V out and signal I L_s The controller 1110 is configured to generate a control signal Φ2 when the control switch device 1122 is in its off state, so that the freewheeling switch device 1124 is a current I flowing through the inductor 1126. L In some alternative embodiments, the freewheeling switch device 1124 is replaced by a diode and the control signal Φ2 is omitted. The controller 1110 is configured to cross a threshold based at least in part on the duty cycle of the control switch device 1122, for example, in response to the duty cycle of the control switch device 1122, for example, as described above with respect to Figure 5 or Figure 6 In the manner discussed, the operating mode of the DC-DC converter 1104 is automatically switched between a constant frequency operating mode and a constant off-time operating mode.

[0057] Fig.12 The present invention includes three graphs 1200, 1202, and 1204 that collectively illustrate one example of the operation of the DC-DC converter 1104. Graph 1200 is a graph of the relationship between the control signal Φ1 and time, graph 1202 is a graph of the control signal Φ2 and time, and graph 1204 is a graph of the inductor current I L Graphs as a function of time. All three graphs 1200, 1202, and 1204 have a common time base. Fig.12Assume that (a) when the control signal Φ1 is asserted, the control switch device 1122 operates in its on-state, and (b) when the control signal Φ1 is de-asserted, the control device 1122 operates in its off-state. In addition, Fig.12 Assume that (a) when control signal Φ2 is asserted, free-flow switch device 1124 operates in its on-state, and (b) when control signal Φ2 is de-asserted, free-flow switch device 1124 operates in its off-state. However, control switch device 1122 and free-flow switch device 1124 may respond to respective control signals Φ1 and Φ2 in different ways. In addition, control signals Φ1 and Φ2 may have different Fig.12 The polarities shown in the figure are different polarities.

[0058] Fig.12 Several exemplary consecutive switching cycles 1206 of the DC-DC converter 1104 are depicted. The controller 1110 generates a control signal Φ1 such that the DC-DC converter 1104 operates in a constant frequency operation mode in the switching cycles 1206(1) and 1206(2). Thus, in the switching cycles 1206(1) and 1206(2), the DC-DC converter 1104 has a constant switching frequency F 12a , which is equal to the period T 12a However, the corresponding on-time w of the control switch device 1122 in the switching cycles 1206 (1) and 1206 (2) is 12a and w 12b Different, for example, in response to operating conditions of the DC-DC converter 1104 changing between switching cycles 1206 ( 1 ) and 1206 ( 2 ).

[0059] The controller 1110 generates the control signal Φ1 such that the DC-DC converter 1104 operates in a constant off-time operation mode in the switching cycles 1206(3) and 1206(4), e.g., in response to the duty cycle of the control switch device 1122 increasing to exceed the maximum allowable constant frequency duty cycle value in the constant frequency operation mode. Thus, the control switch device 1122 has a constant off-time o in the switching cycles 1206(3) and 1206(4). 12a However, the corresponding on-time w of the control switch device 1122 in the switching cycles 1206 ( 3 ) and 1206 ( 4 ) is 12c and w 12d The switching frequencies F of the DC-DC converter 1104 may be different, for example, in response to the operating conditions of the DC-DC converter 1104 changing between the switching cycles 1206 ( 3 ) and 1206 ( 4 ). Therefore, the switching cycles 1206 ( 3 ) and 1206 ( 4 ) may have different switching frequencies F. 12b and F 12c , they are respectively period T 12b and T12c When comparing switching periods 1206(3) and 1206(4) with switching periods 1206(1) and 1206(2), it is apparent that the switching frequency in the constant off-time mode of operation is less than the switching frequency in the constant frequency mode of operation.

[0060] Reference again Figure 4 , some embodiments of the controller 410 are configured to support current mode control, i.e., based at least in part on the magnitude of the current flowing through the inductor of the power stage 408, e.g. Figure 7 , 9 or the inductor current I of 11 L The controller 410 may control the switching of the control switch device 422 according to the magnitude of the current flowing through the inductor of the power stage 408. For example, in some embodiments, in response to the magnitude of the current flowing through the inductor of the power stage 408 reaching a threshold, the control switch device 422 is operated in its off state. In these embodiments, the controller 410 may optionally include a slope compensation module ( Figure 4 404 ), which is configured to generate a slope compensation signal in a constant frequency operation mode of the DC-DC converter 404 when the duty cycle of the control switch device 422 exceeds 50%, so that the DC-DC converter 404 can operate stably. When the DC-DC converter 404 operates in a constant off-time operation mode, no slope compensation is required to achieve stable operation. Therefore, a specific embodiment of the controller 410 is configured to change the operation of the slope compensation module when the DC-DC converter 404 switches from a constant frequency operation mode to a constant off-time operation mode. For example, some embodiments of the controller 410 are configured to suspend the operation of the slope generation module when the DC-DC converter 404 switches from a constant frequency operation mode to a constant off-time operation mode, thereby maintaining the slope compensation signal at a constant value when the DC-DC converter 404 operates in its constant off-time working mode. The constant value of the slope compensation signal is, for example, the latest value of the slope compensation signal before the DC-DC converter 404 switches from its constant frequency operation mode to its constant off-time operation mode.

[0061] Fig.13 13 is a block diagram of a controller 1300, which is one possible embodiment of a controller 410 of a DC-DC converter 404, which generates control signals Φ1 and Φ2, such as for power stage 708 ( Figure 7 )、Power Level 908( Fig. 9 ) or power stage 1108( Fig.11 ) is used. However, it should be understood that the controller 410 can be implemented in other ways without departing from the scope of this document. In addition, the controller 410 does not need to be able to support all features of the controller 1300.

[0062] The controller 1300 includes an oscillator 1302, a slope compensation module 1304, a voltage control module 1306, a switch control module 1308, and a mode change module 1310. The oscillator 1302 is configured to generate an oscillator signal OSC and a clock signal CLK, wherein the clock signal CLK is optionally derived from the oscillator signal OSC. In addition, the oscillator 1302 is configured to assert a duty cycle signal DMAX in each switching cycle in response to a maximum allowable duty cycle of the controlled switching device 422 having been exceeded. The oscillator signal OSC is, for example, a ramp signal, and the slope compensation module 1304 is configured to generate a slope compensation signal SLOPE in response to the oscillator signal OSC and Φ1. The slope compensation signal SLOPE is, for example, a linear or nonlinear slope signal, such as a ramp signal. The voltage control module 1306 is configured to generate an error signal ERR, for example, the error signal is proportional to the output voltage V out The difference between the amplitude and the reference voltage is proportional or integrally proportional, where the reference voltage is, for example, the output voltage V out Expected value or output voltage V out The scaled value of the expected value.

[0063] The switch control module 1308 includes an amplifier 1312, a comparator 1314, a flip-flop 1316, and an inverter 1318. The output of the flip-flop 1316 is a control signal Φ1, and the flip-flop 1316 is set by the assertion of the clock signal CLK by the oscillator 1302. Therefore, in response to the assertion of the clock signal CLK, the control signal Φ1 is asserted. The inverter 1318 generates a control signal Φ2 by inverting the control signal Φ1, so that the control signal Φ2 is complementary to the control signal Φ1. Some embodiments of the switch control module 1308 also include one or more components (not shown) for inserting a dead time between the consecutive assertions of the control signals Φ1 and Φ2 to ensure that there is no shoot-through, that is, the control switch device 422 and the freewheeling switch device (such as the freewheeling switch device 724, 924 or 1124) are turned on at the same time.

[0064] The amplifier 1312 is configured to generate a command signal CMD proportional to the difference between the error signal ERR and the slope compensation signal SLOPE. The comparator 1314 receives the command signal CMD and the signal I L_s As input, the signal I L_s represents the magnitude current flowing through the inductor of the power stage 408. In some embodiments where the power stage 408 has a boost topology, a buck-boost topology, or a buck topology, the signal I L_s The current sensing circuit 732 ( Figure 7 ), current sensing circuit 932 ( Fig. 9 ) or current sensing loop 1132 ( Fig.11 ) is generated. The comparator 1314 responds to the signal IL_s The command signal CMD arrives and the signal TRIP is asserted, and the assertion of the signal TRIP resets the flip-flop 1316, thereby deasserting the control signal Φ1. Therefore, in a given switching cycle of the DC-DC converter 404, the inductor current I L Reaching the amplitude of the command signal CMD terminates the on-time of the control switching device 422 in the switching cycle.

[0065] The mode change module 1310 receives each of the duty cycle signal DMAX and the control signal Φ1 as inputs, and the mode change module 1310 asserts the signal PAUSE in response to each of the above inputs being asserted simultaneously. Therefore, the mode change module 1310 asserts the signal PAUSE in a given switching cycle in response to the control switch device 422 being in its conductive state and when the maximum allowed duty cycle of the control switch device 422 is reached in the switching cycle. The assertion of the signal PAUSE causes the oscillator 1302 to change its operation, such as by extending the cycle of the oscillator 1302, thereby causing the DC-DC converter 404 to change from its constant frequency operating mode to its constant off-time operating mode. For example, in a particular embodiment, the oscillator 1302 suspends its operation in response to the assertion of the signal PAUSE, resulting in (a) the assertion of the clock signal CLK being delayed, and (b) the amplitude of the oscillator signal OSC being maintained at a constant value equal to the last value of the oscillator signal before the assertion of the signal PAUSE. The slope compensation module 1304 also changes its operation in response to the assertion of the signal PAUSE, such as in response to the amplitude of the oscillator signal OSC being maintained at a constant value. For example, in some embodiments, in response to the assertion of the signal PAUSE, the slope compensation signal SLOPE is maintained at a constant value equal to its last value before the assertion of the signal PAUSE. In some alternative embodiments, the slope compensation module 1304 directly receives the signal PAUSE, and the slope compensation module 1304 suspends the generation of the slope compensation signal SLOPE in response to the assertion of the signal PAUSE.

[0066] Fig.14 The present invention includes seven graphs 1400, 1402, 1404, 1406, 1408, 1410 and 1412, which collectively illustrate two consecutive switching cycles 1414 in an operation example of a DC-DC converter 404 including an embodiment of the controller 1300. Graph 1400 is a graph of the relationship between the slope compensation signal SLOPE and time, and graph 1402 is a graph of the change in amplitude over time. Graph 1402 includes a graph representing the command signal CMD, a graph representing the signal I L_s1400 and 1402 show that the command signal CMD is equal to the error signal ERR minus the slope compensation signal SLOPE. Curve 1404 is the relationship between the signal TRIP and time, and curve 1406 is the change of the control signal Φ1 with time. Figure 1408 is a graph of the relationship between the duty cycle signal DMAX and time. It should be noted that the oscillator 1302 sends out the signal duty cycle signal DMAX at the end of each switching cycle 1414. A duration T is inserted between the rising edge of DMAX and the rising edge of CLK. MIN_OFF , which is the minimum allowed off time of the control switch device 422 in each switching cycle 1414. Figure 1410 shows the relationship between the signal PAUSE and time, and Figure 1412 shows the change of the clock signal CLK and time. It should be noted that Fig.14 In the example of FIG. 14 , the duty cycle of the control switch device 422 is less than the maximum allowable duty cycle of the control switch device 422. Specifically, before the duty cycle signal DMAX is asserted in each switching cycle 1414, the signal I L_s The amplitude reaches the amplitude of the command signal CMD. Therefore, in each switching cycle 1414, the current flowing through the inductor of the power stage 408 reaches the threshold defined by the command signal CMD before exceeding the maximum allowable duty cycle of the control switch device 422. Fig.14 In the example of , the control signal Φ1 and the duty cycle signal DMAX are never asserted at the same time, so the signal PAUSE is never asserted. Fig.14 In the example shown, the DC-DC converter 404 operates only in its constant frequency operating mode.

[0067] Fig.15 The seven graphs 1500, 1502, 1504, 1506, 1508, 1510, and 1512 collectively illustrate two consecutive switching cycles 1514 in another example of operation of the DC-DC converter 404 including an embodiment of the controller 1300. The graphs 1500, 1502, 1504, 1506, 1508, 1510, and 1512 are similar to Fig.14 1400, 1402, 1404, 1406, 1408, 1410 and 1412. However, Fig.14 In contrast to the example of , in each switching cycle 1514, the current magnitude flowing through the inductor of the power stage 408 does not reach the threshold defined by the command signal CMD before exceeding the maximum allowed duty cycle of the control switching device 422. Fig.15In the example of , the control signal Φ1 and the duty cycle signal DMAX are simultaneously asserted in each switching cycle 1514, so the signal PAUSE is asserted in each switching cycle 1514. It should be noted that while the signal PAUSE is asserted, the slope compensation signal SLOPE is maintained at a constant value 1516, where the constant value 1516 is equal to the last value of the slope compensation signal SLOPE before the signal PAOSE is asserted. However, it is understood that when the signal PAUSE is asserted, the slope compensation signal SLOPE can alternately have a profile other than a constant value, for example, the assertion of the signal PAUSE can slow down the slope of the slope compensation signal SLOPE instead of keeping the signal at a constant value.

[0068] exist Fig.15 In the example of FIG. 1 , the constant value of the slope compensation signal SLOPE generated by the assertion of the signal PAUSE causes the amplitude of the command signal CMD to remain constant when the signal PAUSE is asserted (assuming that the output voltage V out 14) during a given switching cycle 1514, thereby allowing the control signal Φ1 to remain asserted and control the switching device 422 to maintain its on state until the signal I L_s The amplitude reaches the command signal CMD. Fig.15 In the example of FIG. 1 , the DC-DC converter 404 operates in a constant off-time operation mode, where the duration of the constant off-time is equal to T MIN_OFF Operation in the constant off-time operating mode increases the on-time of the control switch device 422 in each switching cycle, which allows the current magnitude flowing through the inductor of the power stage 408 to reach a threshold defined by the command signal CMD. Operation in the constant off-time operating mode also reduces the switching frequency of the DC-DC converter 404 relative to operation in the constant frequency operating mode.

[0069] Fig.16 is a schematic diagram of an oscillator 1600, which is an oscillator 1302 ( Fig.13 However, it should be understood that the oscillator 1302 may be different from Fig.16 way to achieve it.

[0070] Oscillator 1600 includes current source 1602, p-channel metal oxide field effect transistor (PMOS) 1604, PMOS 1606, PMOS 1608, capacitor 1610, n-channel metal oxide field effect transistor (NMOS) 1612, comparator 1614, delay buffer 1616, AND gate 1618, pulse generator 1620, pulse generator 1622, and inverter 1624. The source (S) of PMOS 1604 is electrically coupled to power rail 1626, and each of the gate (G) and drain (D) of PMOS 1604 is electrically coupled to electrical node 1628. Current source 1602 is electrically coupled between electrical node 1628 and reference electrical node 1630. The source of PMOS 1608 is electrically coupled to power rail 1626, and the drain of PMOS 1608 is electrically coupled to electrical node 1628. The source of PMOS 1606 is electrically coupled to power rail 1626, and the gate of PMOS 1606 is electrically coupled to electrical node 1628. The drain of PMOS 1606 is electrically coupled to oscillator electrical node 1632, and capacitor 1610 is electrically coupled between oscillator electrical node 1632 and reference electrical node 1630. Oscillator electrical node 1632 provides oscillator signal OSC. The drain of NMOS 1612 is electrically coupled to oscillator electrical node 1632, and the source of NMOS 1612 is electrically coupled to reference electrical node 1630.

[0071] The non-inverting input of the comparator 1614 is electrically coupled to the oscillator electrical node 1632, and the inverting input of the comparator 1614 is electrically coupled to the reference voltage V ref_1 . The output of comparator 1614 provides a duty cycle signal DMAX, and the output of comparator 1614 is electrically coupled to the input of delay buffer 1616. The output of the delay buffer provides a signal DMAX_B, which is electrically coupled to the input of AND gate 1618. The input of inverter 1624 receives signal PAUSE, and the output of inverter 1624 provides signal PAUSE_B. Signal PAUSE_B is electrically coupled to each of the gate of PMOS 1608 and the other input of AND gate 1618. The output of AND gate 1618 provides signal DMAX_C, which is electrically coupled to the input (I) of pulse generator 1620. The output (O) of pulse generator 1620 provides signal CLK_B, which is electrically coupled to (a) the gate of NMOS 1612 and (b) the input of pulse generator 1622. The output of pulse generator 1622 provides clock signal CLK.

[0072] When the signal PAUSE is de-asserted, the signal PAUSE_B is asserted, so when the signal PAOSE is de-asserted, the PMOS 1608 is turned off. Therefore, when the signal PAUSE is released, the PMOS 1608 does not affect the operation of the PMOS 1604 or the PMOS 1606. The PMOS 1604 and the PMOS 1606 jointly mirror the current I of the current source 1602. cs , to generate a current I to charge the capacitor 1610 ch The oscillator signal OSC is equal to the voltage V across the capacitor 1610. oc , so when the current I ch As capacitor 1610 is charged, oscillator signal OSC ramps up. oc Reaching the reference voltage V ref_1 When the comparator 1614 asserts the duty cycle signal DMAX, the duty cycle of the transition between the constant frequency operation mode of the DC-DC converter 404 and the constant off-time operation mode of the DC-DC converter 404 is the reference voltage V ref_1 The size of the capacitor 1610 and the current I ch The delay buffer 1616 asserts the signal DMAX_B after the comparator 1614 asserts the signal duty cycle signal DMAX, and the AND gate 1618 asserts the signal DMAX_C when (a) the signal DMAX_B is asserted and the signal PAUSE is deasserted. The pulse generator 1620 asserts the signal CLK_B in response to the signal DMAX_C being asserted, and the asserted signal CLK_B is equal to T MIN_OFF The width of the pulse (as mentioned above Fig.14 and 15 16). The asserted signal CLK_B turns on NMOS 1612, which discharges capacitor 1610, thereby resetting oscillator signal OSC. In addition, the falling edge of signal CLK_B causes pulse generator 1622 to assert clock signal CLK, which is another pulse.

[0073] The assertion of the signal PAUSE turns on PMOS 1608, which causes each of PMOS 1604 and PMOS 1606 to turn off. Therefore, the assertion of the signal PAUSE disables the current I that charges the capacitor. ch , so the voltage V oc Therefore, before the PAUSE signal is asserted, the oscillator signal OSC remains constant at the voltage V ocIn addition, the assertion of the signal PAUSE prevents the AND gate 1618 from asserting the signal DMAX_C, which disables the generation of the clock signals CLK_B and CLK and the discharge of the capacitor 1610 when the signal PAUSE is asserted. Therefore, when the signal PAUSE is asserted, the operation of the oscillator 1600 is suspended.

[0074] Fig.17 The six graphs 1700, 1702, 1704, 1706, 1708, and 1710 collectively illustrate an example of the operation of the oscillator 1600 over two consecutive switching cycles 1712 when the signal PAUSE is not asserted. Graph 1700 is a graph of the voltage V OC (and oscillator signal OSC) versus time, FIG1702 is a graph showing the current I ch The change of charging capacitor 1610 with time, Figure 1704 is a curve of duty cycle signal DMAX with time, Figure 1706 is a function of signal PAUSE with time, Figure 1708 is a relationship between clock signal CLK and time, and Figure 1710 is a relationship between signal CLK_B and time. Fig.17 As shown, in each cycle 1712, the current I ch is constant, resulting in a voltage V c Rising until capacitor 1610 is discharged in response to the assertion of signal CLK_B.

[0075] Fig.18 The six graphs 1800, 1802, 1804, 1806, 1808, and 1810 collectively illustrate an example of the operation of the oscillator 1600 over two consecutive switching cycles 1812 when the signal PAUSE is asserted. Graphs 1800, 1802, 1804, 1806, 1808, and 1810 are similar to Fig.17 Figures 1700, 1702, 1704, 1706, 1708 and 1710. Fig.18 As shown, the assertion of the signal PAUSE disables the current I that charges the capacitor 1610. ch , so the voltage V oc (and oscillator signal OSC) remain constant while signal PAUSE is asserted. Furthermore, it should be noted that assertion of signal PAUSE inhibits assertion of signal CLK_B, thereby inhibiting discharge of capacitor 1610 and assertion of clock signal CLK while signal PAUSE is asserted.

[0076] Fig.19 1900 is a schematic diagram of a voltage control module 1900, which is a voltage control module 1306 ( Fig.13 However, it should be understood that the voltage control module 1306 may be different from Fig.19 way to achieve it.

[0077] The voltage control module 1900 includes a resistor 1902, a resistor 1904, a transconductance amplifier 1906, and a filter circuit 1908. The resistor 1902 and the resistor 1904 are electrically coupled in series to provide an output voltage V out The inverting input of transconductance amplifier 1906 is electrically coupled to a voltage divider electrical node 1912, where resistor 1902 and resistor 1904 are electrically coupled together. The non-inverting input of transconductance amplifier 1906 is electrically coupled to a reference voltage V ref_2 Filter circuit 1908 is electrically coupled between the output of transconductance amplifier 1906 and reference electrical node 1910. Filter circuit 1908 is shown as including resistor 1914 electrically coupled in series with capacitor 1916, although filter circuit 1908 may vary according to design choices, such as to achieve a desired frequency response of voltage control module 1900. Filter circuit 1906 is responsive to current I flowing out of transconductance amplifier 1906. ERR The transconductance amplifier 1906 generates a voltage at the voltage divider electrical node 1912 and a reference voltage V ref_2 The difference between the current I ERR Therefore, the output voltage V out The magnitude of is (a) the voltage divider formed by resistor 1902 and resistor 1904 and (b) the reference voltage V ref_2 function.

[0078] Feature combination

[0079] The above features can be combined in various ways without departing from the scope of this document. The following examples illustrate some possible combinations.

[0080] (A1) A method for controlling a direct current (DC-DC) converter, the method comprising: in a first switching cycle of the DC-DC converter, (1) operating the DC-DC converter in a constant frequency operation mode, (2) determining that a duty cycle of a first switching device of the DC-DC converter has exceeded a first threshold, and (3) in response to the duty cycle of the first switching device of the DC-DC converter exceeding the first threshold, switching the DC-DC converter from operating a switch in the constant frequency operation mode to operating in a constant off-time operation mode.

[0081] (A2) In the method denoted as (A1), the first threshold may be a maximum allowable duty cycle of the first switching device of the DC-DC converter in a constant frequency operation mode of the DC-DC converter.

[0082] (A3) In either of the methods denoted as (A1) and (A2), operating the DC-DC converter in a constant off-time operating mode may include changing the operation of an oscillator of the DC-DC converter.

[0083] (A4) In the method denoted as (A3), changing the operation of an oscillator of the DC-DC converter may include causing the oscillator to maintain an oscillator signal at a constant value while the DC-DC converter operates in a constant off-time operating mode.

[0084] (A5) In any of the methods denoted as (A3) and (A4), changing the operation of an oscillator of the DC-DC converter may include lengthening a period of the oscillator.

[0085] (A6) Any of the methods denoted as (A1) to (A5) may further include, in response to a duty cycle of the first switching device crossing a first threshold, changing an operation of a slope compensation module of the DC-DC converter.

[0086] (A7) In the method denoted as (A6), changing the operation of a slope compensation module of the DC-DC converter may include causing the slope compensation module to maintain a slope compensation signal at a constant value when the DC-DC converter operates in a constant off-time operating mode.

[0087] (A8) Any of the methods denoted as (A1) to (A7) may further include operating the first switching device in its off state in response to the magnitude of the current flowing through the inductor of the DC-DC converter reaching a second threshold.

[0088] (A9) Any of the methods represented as (A1) to (A8) may further include, in a second switching cycle of the DC-DC converter, in response to a duty cycle of the first switch of the DC-DC converter not exceeding a first threshold before the first switching device of the DC-DC converter is switched to its off state, causing the DC-DC converter to operate in a constant frequency operating mode throughout the second switching cycle of the DC-DC converter.

[0089] (B1) A controller for a direct current to direct current (DC-DC) converter, comprising: (1) an oscillator configured to generate an oscillator signal, a clock signal, and a duty cycle signal, the duty cycle signal indicating that a maximum allowable duty cycle of a first switching device of the DC-DC converter has been exceeded, (2) a slope compensation module configured to generate a slope compensation signal based at least in part on the oscillator signal, (3) a switch control module configured to generate a control signal to control the first switching device based at least in part on the slope compensation signal and the clock signal, and (4) a mode change module configured to change the operation of each of the oscillator and the slope compensation module in response to the duty cycle signal being asserted while the control signal is asserted.

[0090] (B2) In the controller denoted as (B1), the switch control module may be further configured to generate the control signal based at least in part on the error signal.

[0091] (B3) The controller denoted as (B2) may further include a voltage control module configured to generate an error signal based at least in part on a difference between a voltage of the DC-DC converter and a reference voltage.

[0092] (B4) In any one of the controllers denoted as (B1) to (B3), the switch control module may be further configured to generate the control signal based on a magnitude of a current flowing through an inductor of the DC-DC converter.

[0093] (B5) In any one of the controllers represented as (B1) to (B4), the maximum allowable duty cycle of the first switching device of the DC-DC converter can be the maximum allowable duty cycle of the first switching device of the DC-DC converter in a constant frequency operation mode.

[0094] (B6) In any of the controllers denoted as (B1) to (B5), the oscillator may be configured to cause the DC-DC converter to switch from a constant frequency operating mode to a constant off-time operating mode in response to assertion of the duty cycle signal.

[0095] (B7) In any of the controllers denoted as (B1) to (B6), the oscillator may be configured such that a switching frequency of the DC-DC converter decreases in response to assertion of the duty cycle signal.

[0096] (C1) A direct current to direct current (DC to DC) converter comprising: a power stage including a first switching device; and a controller communicatively coupled to the power stage. The controller is configured to: (1) operate the DC-DC converter in a constant frequency operating mode, (2) determine that a duty cycle of the first switching device has exceeded a first threshold, and (3) in response to the duty cycle of the first switching device exceeding the first threshold, cause the DC-DC converter to switch from operating in the constant frequency operating mode to operating in a constant off-time operating mode.

[0097] (C2) In the DC-DC converter denoted as (C1), in a constant frequency operation mode, the first threshold may be a maximum allowable duty cycle of the first switching device.

[0098] (C3) In either of the DC-DC converters denoted as (C1) and (C2), the power stage may have a topology selected from the group consisting of a boost topology, a buck-boost topology, and a buck topology.

[0099] (C4) In any of the DC-DC converters represented as (C1) to (C3), (1) the controller may include an oscillator, and (2) the controller may be further configured to cause the DC-DC converter to operate in a constant off-time operating mode at least in part by changing the operation of the oscillator.

[0100] (C5) In the DC-DC converter denoted as (C4), changing the operation of the oscillator may include disabling a current source that charges the capacitor.

[0101] (C6) In either of the DC-DC converters denoted as (C4) and (C5), changing the operation of the oscillator may include lengthening a period of the oscillator.

[0102] (C7) In any one of the DC-to-DC converters represented as (C1) to (C3), (1) the controller may include a slope compensation module, and (2) the controller may be further configured to change the operation of the slope compensation module in response to a duty cycle of the first switching device exceeding a first threshold.

[0103] (C8) In the DC-to-DC converter represented as (C7), (1) the controller may further include an oscillator that provides an oscillator signal to the slope compensation module, and (2) the controller may be further configured to change the operation of the slope compensation module by changing the operation of the oscillator.

[0104] Changes may be made to the above methods, devices, and systems without departing from the scope of this document. It should therefore be noted that the matter contained in the above description and shown in the accompanying drawings should be interpreted as illustrative and not restrictive. The following claims are intended to cover all statements of the general and specific features described herein, as well as the scope of the present methods and systems, which, as a matter of language, may be considered to fall between them.

Claims

1. A method for controlling a direct current (DC-DC) converter, the method comprising, in a first switching cycle of the DC-DC converter: operating the DC-DC converter in a constant frequency operating mode; determining that a duty cycle of a first switching device of the DC-DC converter has exceeded a first threshold; and In response to a duty cycle of a first switching device of the DC-DC converter exceeding the first threshold, the DC-DC converter is caused to switch from operating in the constant frequency operating mode to operating in a constant off-time operating mode. 2 . The method of claim 1 , wherein the first threshold is a maximum allowed duty cycle of the first switching device of the DC-DC converter in a constant frequency operation mode of the DC-DC converter. 3 . The method of claim 1 , wherein causing the DC-DC converter to operate in the constant off-time operating mode comprises changing operation of an oscillator of the DC-DC converter. 4 . The method of claim 3 , wherein changing the operation of an oscillator of the DC-DC converter comprises causing the oscillator to maintain an oscillator signal at a constant value when the DC-DC converter is operating in the constant off-time operating mode. 5 . The method of claim 3 , wherein changing the operation of an oscillator of the DC-DC converter comprises lengthening a period of the oscillator.

6. The method according to claim 1, further comprising: In response to the duty cycle of the first switching device exceeding the first threshold, operation of a slope compensation module of the DC-DC converter is changed.

7. The method of claim 6, wherein changing the operation of the slope compensation module of the DC-DC converter comprises: The slope compensation module is enabled to maintain a slope compensation signal at a constant value when the DC-DC converter operates in the constant off-time operation mode. 8 . The method of claim 1 , further comprising operating the first switching device in its off state in response to a magnitude of a current flowing through an inductor of the DC-DC converter reaching a second threshold.

9. The method according to claim 1, further comprising: In a second switching cycle of the DC-DC converter, in response to a duty cycle of the first switch of the DC-DC converter not exceeding the first threshold before the first switching device of the DC-DC converter is switched to its off state, the DC-DC converter is operated in the constant frequency operation mode for the entire second switching cycle of the DC-DC converter.

10. A controller for a direct current-to-direct current (DC-DC) converter, the controller comprising: an oscillator configured to generate an oscillator signal, a clock signal, and a duty cycle signal indicating that a maximum allowable duty cycle of a first switching device of the DC-DC converter has been exceeded; a slope compensation module configured to generate a slope compensation signal based at least in part on the oscillator signal; a switch control module configured to generate a control signal to control the first switch device based at least in part on the slope compensation signal and the clock signal; and A mode change module is configured to change the operation of each of the oscillator and the slope compensation module in response to the duty cycle signal being asserted while the control signal is asserted. 11 . The controller of claim 10 , wherein the switch control module is further configured to generate the control signal based at least in part on an error signal. 12 . The controller of claim 11 , further comprising a voltage control module configured to generate the error signal based at least in part on a difference between a voltage of the DC-DC converter and a reference voltage. 13 . The controller of claim 10 , wherein the switch control module is further configured to generate the control signal based on a magnitude of a current flowing through an inductor of the DC-DC converter.

14. The controller of claim 10, wherein the maximum allowable duty cycle of the first switching device of the DC-DC converter is the maximum allowable duty cycle of the first switching device of the DC-DC converter in a constant frequency operation mode of the DC-DC converter. 15 . The controller of claim 10 , wherein the oscillator is configured to cause the DC-DC converter to switch from a constant frequency mode of operation to a constant off-time mode of operation in response to assertion of the duty cycle signal. 16 . The controller of claim 10 , wherein the oscillator is configured such that a switching frequency of the DC-DC converter decreases in response to assertion of the duty cycle signal.

17. A direct current to direct current (DC to DC) converter, comprising: a power stage, the power stage comprising a first switching device; and a controller communicatively coupled to the power stage, the controller being configured to: operating the DC-DC converter in a constant frequency operation mode, determining that the duty cycle of the first switching device has exceeded a first threshold, and In response to the duty cycle of the first switching device exceeding the first threshold, the DC-DC converter is caused to switch from operating in the constant frequency operating mode to operating in a constant off-time operating mode.

18. The DC-DC converter of claim 17, wherein the first threshold is a maximum allowed duty cycle of the first switching device in the constant frequency operation mode.

19. The DC-DC converter of claim 17, wherein the power stage has a topology selected from the group consisting of a boost topology, a buck-boost topology, and a buck topology.

20. The DC-DC converter of claim 17, wherein: The controller includes an oscillator; and The controller is also configured to cause the DC-DC converter to operate in the constant off-time operating mode at least in part by varying operation of the oscillator.

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