Linear scalable group operation converter

Abstract

The invention discloses a linear scalable group operation converter. The converter comprises an SC stage comprising one or more SC units stacked in series; the Buck stage is coupled with the SC stage and comprises one or more M-phase Buck units connected in parallel, and M is an integer larger than or equal to 1; and the converter control unit is configured to be used for controlling one or more Buck units in the Buck units to be turned on or turned off based on the input voltage or the output current of the converter.

Description

Technical Field

[0001] Embodiments of the present disclosure relate generally to hybrid converters, and in particular to a dynamically scalable Linear Scalable Group Operation (LEGO) converter. Background Art

[0002] In a typical hybrid converter for high conversion ratio applications, a pair of "coupled" capacitors and inductors form an energy storage reservoir to deliver power. The use of capacitive energy storage devices provides high power density and efficiency. However, these converters usually have limited output power scalability, making them less suitable for many applications. Summary of the invention

[0003] One aspect of the present disclosure provides a converter, comprising: a switched capacitor (SC) stage, comprising one or more SC cells stacked in series; a step-down (Buck) stage, coupled to the SC stage and comprising one or more M-phase Buck cells connected in parallel, where M is an integer greater than or equal to 1; and a converter control unit, configured to control one or more Buck cells in the Buck cells to turn on or off based on an input voltage or an output current of the converter.

[0004] Another aspect of the present disclosure provides a method for a converter, wherein the converter includes: an SC stage, including one or more SC cells stacked in series; and a Buck stage, coupled to the SC stage and including one or more M-phase Buck cells connected in parallel, wherein M is an integer greater than or equal to 1, and the method includes: controlling one or more of the Buck cells to turn on or off based on an input voltage or an output current of the converter.

[0005] Yet another aspect of the present disclosure provides a method for a converter, wherein the converter comprises: an SC stage comprising one or more SC cells stacked in series; and a Buck stage coupled to the SC stage and comprising one or more M-phase Buck cells connected in parallel, wherein M is an integer greater than or equal to 1, and the method comprises: when an input voltage increases in a ramped manner during startup of the converter, controlling the converter to undergo a plurality of states in which flying capacitors in the SC cells are successively disconnected from the input voltage until the voltage of the flying capacitors reaches its steady-state voltage and the input voltage reaches a nominal voltage; and when the voltage of the flying capacitors reaches its steady-state voltage and the input voltage reaches the nominal voltage, generating an enable signal to instruct the converter to start a voltage conversion operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Embodiments of the present disclosure will be illustrated by way of example and not limitation in the figures of the accompanying drawings in which like reference numerals refer to similar elements.

[0007] Figure 1 A typical LEGO converter comprising N hybrid cells with a merged two-level LEGO point-of-load (LEGO-PoL) architecture is shown.

[0008] Figure 2 An example LEGO-PoL CPU voltage regulator is shown that can achieve 48V to 1V voltage conversion and 780A output current.

[0009] Figure 3 An example basic hybrid cell having a merged two-stage LEGO-PoL architecture including a 2:1 switched capacitor (SC) cell and a single-phase buck (Buck) cell according to one or more example embodiments of the present disclosure is shown.

[0010] Figure 4 An example hybrid cell having a merged two-stage LEGO-PoL architecture including a 2:1 SC cell and a multi-phase Buck cell according to one or more example embodiments of the present disclosure is shown.

[0011] Figure 5 An example hybrid cell having a merged two-stage LEGO-PoL architecture including a 2:1 SC cell and multiple multi-phase Buck cells according to one or more example embodiments of the present disclosure is shown.

[0012] Figure 6 An example hybrid cell with a merged two-stage LEGO-PoL architecture is shown in which some Buck cells are turned off or some phases in the active Buck cells are turned off to support low power mode operation according to one or more example embodiments of the present disclosure.

[0013] Figure 7 A LEGO converter including five stacked 12V to 1V hybrid cells to support applications with an input voltage of 60V and 60V to 1V conversion is shown according to one or more example embodiments of the present disclosure.

[0014] Figure 8 An optimized LEGO converter according to one or more example embodiments of the present disclosure is shown, which is composed of a Buck unit in the top hybrid unit by turning off the Buck unit in the top hybrid unit. Figure 7 The LEGO converter shown is obtained, thus supporting applications with 48V input voltage and 48V to 1V conversion.

[0015] Figures 9a to 9h 1 shows a plurality of states that an exemplary five-layer LEGO converter goes through during a flying capacitor pre-charging startup process for the converter according to one or more example embodiments of the present disclosure.

[0016] Fig.10 A state diagram illustrating a flying capacitor pre-charging startup process of an exemplary five-layer LEGO converter according to one or more exemplary embodiments of the present disclosure. DETAILED DESCRIPTION

[0017] The various aspects of the illustrative embodiments will be described using terms commonly used by those skilled in the art to convey the essence of the present disclosure to other persons skilled in the art. However, it will be readily understood by those skilled in the art that many alternative embodiments may be practiced using portions of the described aspects. For purposes of explanation, specific numbers, materials, and configurations are set forth to provide a thorough understanding of the illustrative embodiments. However, it will be readily understood by those skilled in the art that alternative embodiments may be practiced without these specific details. In other cases, well-known features may be omitted or simplified to avoid blurring the illustrative embodiments.

[0018] Furthermore, various operations will be described as multiple discrete operations in a manner that is most helpful for understanding the illustrative embodiments; however, the order of description should not be construed as implying that these operations are necessarily order dependent. In particular, these operations do not need to be performed in the order presented.

[0019] The phrases "in an embodiment," "in one embodiment," and "in some embodiments" are used repeatedly herein. The phrase generally does not refer to the same embodiment; however, it may. The terms "comprising," "having," and "including" are synonymous unless the context dictates otherwise. The phrases "A or B" and "A / B" mean "(A), (B), or (A and B)."

[0020] A power transmission architecture with high efficiency, high power density, and high bandwidth is needed to support future high-performance computing systems (such as CPUs, GPUs, and TPUs). In a typical hybrid converter for large conversion ratio applications, a pair of "coupled" capacitors and inductors form an energy storage reservoir to deliver power outward. The use of capacitive energy storage devices provides high power density and efficiency. However, these converters typically have limited output power scalability, making them less suitable for many applications.

[0021] Recently, a linearly scalable group-operated point-of-load (LEGO-PoL) architecture has been proposed to build a LEGO converter that can achieve a high voltage conversion ratio and provide very high output current. The LEGO-PoL architecture can be linearly scalable and group-operated to cover a wide operating range of input voltage and output current domains.

[0022] Figure 1A typical LEGO converter comprising N hybrid cells with a combined two-stage LEGO-PoL architecture is shown. Figure 1 As shown, the LEGO converter includes two stages: a switched capacitor stage and a multi-phase step-down (Buck) stage, and from a different perspective, the LEGO converter contains multiple hybrid cells, each of which contains two building blocks: a 2:1 switched capacitor cell and an M-phase Buck cell. The 2:1 switched capacitor cell can be operated at a fixed complementary 50% duty cycle, and can be operated at a low switching frequency to reduce switching losses and achieve high efficiency. The Buck cell can utilize interleaved operation at a higher switching frequency to achieve a high control bandwidth. There is no resonant inductor in the switched capacitor cell, and there is no large DC decoupling capacitor between the two stages. The two stages are functionally integrated, that is, the Buck cell acts as a current source to softly charge the switched capacitor.

[0023] Figure 1 The topology shown in the figure stacks N 2:1 switched capacitor (SC) cells in series and connects N multi-phase Buck cells in parallel. The input voltage of each 2:1 SC cell is the input voltage V of the LEGO converter. IN The virtual intermediate bus voltage (without decoupling capacitors) is the input voltage V IN 1 / (2N). N Buck units connected in parallel will output a current of I o Divided into N current paths, the output current of each multi-phase Buck unit is the output current I of the LEGO converter o 1 / N of the current, and each individual phase of the Buck unit only provides an output current of I o 1 / (M×N).

[0024] The LEGO-PoL architecture eliminates the resonant inductor and decoupling capacitor in a two-stage hybrid switched capacitor design and merges the operations of the switched capacitor stage and the Buck stage to create mutual advantages. For example, the LEGO-PoL architecture can automatically distribute the voltage burden and current burden, cope with high bandwidth requirements, and achieve voltage balancing, current sharing, soft charging, and soft switching.

[0025] As described above, the LEGO-PoL architecture is highly modular and scalable. This means that the number of hybrid cells included in the LEGO converter can be expanded to cover a wide operating range in the input voltage and output current domains. For example, a LEGO-PoL CPU voltage regulator with three stacked hybrid cells is described in J. Baek et al., "Vertical Stacked LEGO-PoL CPU Voltage Regulator," IEEE Transactions on Power Electronics, June 2022, Vol. 37, No. 6, pp. 6305-6322, which is incorporated herein by reference.

[0026] Figure 2 The topology of the LEGO-PoL CPU voltage regulator is shown, which can achieve a voltage conversion of 48V to 1V and an output current of 780A. Each hybrid unit in the voltage regulator includes a switching frequency f of 286kHz. SC The 2:1 SC cell is operated at a switching frequency of 1MHz. buck Due to the interleaving and magnetic coupling, each phase in the Buck unit provides 65A peak current at an effective current ripple frequency of 4MHz.

[0027] Typically, the LEGO-PoL architecture automatically distributes the voltage and current burdens to all the hybrid cells in the converter, but current balance between the hybrid cells can be an issue for the converter. Since the LEGO-PoL architecture removes the large DC decoupling capacitors between the two stages of the converter, the virtual intermediate bus voltage (V BUS ) may contain larger ripple, which may cause phase current mismatch in the Buck cell. There are several ways to balance the phase currents in the presence of such ripple, including current mode control. The duty cycle of the Buck cell switches can be actively modulated to compensate for the input voltage ripple and balance the phase currents. Another possible way is to use a passive phase rotation scheme to balance the phase currents. The phase currents of each hybrid cell can be balanced by coordinating the selection of the switching frequencies of the SC stage and the Buck stage.

[0028] As described in "Vertical Stacked LEGO-PoL CPU Voltage Regulator" by J. Baek et al., when the switching frequency of the Buck stage is selected according to the following formula (1), all phases in each Buck unit can share a balanced phase current.

[0029]

[0030] where fsw-buck and f sw-SC are the switching frequencies of the Buck stage and the switched capacitor stage, respectively, and k is any positive integer greater than 0. Note that the switching frequency of the Buck stage refers to the switching frequency of each power switch in each Buck unit, and the switching frequency of the SC stage refers to the switching frequency of each power switch in each SC unit.

[0031] By selecting the switching frequencies of the SC and Buck stages according to equation (1), an odd number of (e.g., seven) Buck switches occur during half a switching cycle of the switched capacitor stage. This results in a rotation through different Buck switches in the Buck cell, each Buck switch in turn acting as the highest V BUS The switches turned on under the ripple result in the same average input voltage on all Buck switch nodes, resulting in balanced currents in all phases in each Buck cell. Therefore, according to this formula, the designer of the LEGO converter can select the switching frequency of the SC cell and the Buck cell within the range where the SC stage and the Buck stage operate in the most efficient mode by setting the appropriate "k" value, while maintaining current balance.

[0032] As mentioned above, the number of hybrid cells included in the LEGO converter can be expanded to cover a wide operating range in the input voltage and output current domains, and the switching frequencies of the SC cell and the Buck cell in each hybrid cell can be selected according to the predefined formula (1) to achieve current balance in each hybrid cell.

[0033] However, it is worth noting that although the number of hybrid cells in a LEGO converter can be selected when designing the LEGO converter, once designed and put into use, the LEGO converter has a fixed structure including a fixed number of hybrid cells. In addition, the above formula (1) for determining the switching frequency of the Buck stage and the switched capacitor stage is only applicable to LEGO converters with a fixed stacking structure, such as a LEGO converter with four phases in each Buck cell. The Buck cells in the Buck stage of the LEGO converter or the phases of each Buck cell cannot be dynamically turned on or off based on changes in the input voltage or output current of the LEGO converter, so the LEGO converter can no longer operate at its optimal design point at certain input voltages or output currents.

[0034] According to some embodiments of the present application, a design scheme is proposed that can dynamically add or remove Buck phases or cells to scale the output current of the LEGO converter while maintaining current balance between all Buck phases in the converter.

[0035] Figure 3An example basic hybrid cell with a merged two-stage LEGO-PoL architecture according to one or more example embodiments of the present disclosure is shown. The basic hybrid cell may include a 2:1 SC cell and a single-phase Buck cell. Figure 4 An example hybrid cell having a merged two-stage LEGO-PoL architecture including a 2:1 SC cell and a multi-phase Buck cell according to one or more example embodiments of the present disclosure is shown. Figure 5 An example hybrid cell having a merged two-stage LEGO-PoL architecture including a 2:1 SC cell and multiple multi-phase Buck cells according to one or more example embodiments of the present disclosure is shown.

[0036] In other words, according to an embodiment, a converter may include: an SC stage and a Buck stage, the SC stage including one or more SC cells stacked in series, the Buck stage coupled to the SC stage and including one or more M-phase Buck cells connected in parallel, where M is an integer greater than or equal to 1. In the converter, the SC cells may be coupled to the Buck cells in a one-to-one correspondence, that is, one SC cell and one corresponding Buck cell with one or more phases constitute a hybrid unit in the converter, such as Figure 3 and Figure 4 Alternatively, in the converter, the SC units can be coupled to the Buck units in a one-to-many correspondence, that is, one SC unit and multiple corresponding Buck units constitute a hybrid unit in the converter, as shown in Figure 5 shown.

[0037] Specifically, to support higher output currents, multiple phases in the Buck unit of each hybrid unit can be turned on, or even multiple Buck units can be connected in parallel in each hybrid unit. Conversely, to support lower output currents (e.g., in low power modes for applications such as laptop platforms), some Buck units or some Buck phases in the converter can be turned off to maintain optimized and efficient operation of the converter.

[0038] Figure 6 An example hybrid cell with a merged two-stage LEGO-PoL architecture is shown in which some Buck cells are turned off or some phases in the active Buck cells are turned off to support low power mode operation according to one or more example embodiments of the present disclosure. Figure 6 As shown, only one Buck cell (with a bold border) is coupled to the SC cell, and the Buck cell includes two active phases (i.e., two inductors) to support low power mode operation and lower output current. Note that in this disclosure, an active phase means that the phase is turned on, and an activated Buck cell means that the Buck cell is turned on.

[0039] According to an embodiment of the present application, in order to dynamically control the on / off state of the Buck unit, the converter may include a converter control unit (not shown in the figure). The converter control unit may be configured to dynamically control one or more Buck units in the Buck unit to be turned on or off based on the output current of the converter. For example, in the case where an SC unit and a plurality of corresponding Buck units constitute a hybrid unit in the converter, the converter control unit may be configured to control a portion of the Buck units in each hybrid unit to be turned on in response to an increase in the output current or to control a portion of the Buck units in each hybrid unit to be turned off in response to a decrease in the output current, so as to maintain the optimal conversion efficiency of the converter. In addition, the converter control unit may also be configured to control a predetermined number of phases in each activated Buck unit to be turned on in response to an increase in the output current or to control a predetermined number of phases in each activated Buck unit to be turned off in response to a decrease in the output current, so as to maintain the optimal conversion efficiency of the converter.

[0040] In addition, according to some embodiments of the present application, in order to maintain the current balance of all Buck phases in the converter, the switching frequency of the switched capacitor stage and the Buck stage can be selected according to the following formula (2):

[0041]

[0042] Among them, f sw-buck Indicates the switching frequency of the Buck stage, f sw-SC represents the switching frequency of the switched capacitor stage, N is the number of active phases in each Buck unit, and d is an odd number that is relatively prime to N. Preferably, d may be greater than 1.

[0043] It is worth noting that formula (2) is actually a more general form of formula (1) above, which allows the operation of the converter to be extended over a wide range of output currents. For example, when each Buck cell has four active phases (i.e., four phases in the Buck cell are turned on), N is 4 and d can be selected to be 3. In this case, formula (2) is the same as formula (1), where k=1.

[0044] According to formula (2), since d is a relatively prime odd number of N, it can be guaranteed that an odd number of Buck switches occur during half a switching cycle of the switched capacitor stage. This can result in a different Buck switch in the Buck unit being passed in turn, with each Buck switch acting as the highest V BUSThe switches turned on under the ripple result in the same average input voltage on all Buck switch nodes, resulting in balanced currents in all phases in each Buck unit. Therefore, according to formula (2), as N changes, d can be set to different numbers, so the Buck stage can be operated at different switching frequencies while maintaining self-balancing of all phase currents.

[0045] Therefore, according to an embodiment of the present application, in response to changes in the output current of the converter, the converter control unit can be configured to control a portion of the Buck units in each hybrid unit to be turned on or off, or to control a predetermined number of phases in each activated Buck unit to be turned on or off, and to control the SC stage and the Buck stage to operate at the corresponding switching frequency selected according to formula (2). In this way, the optimal conversion efficiency and phase current balance of the converter can be maintained at various output currents.

[0046] In addition to the output current, it may be necessary to dynamically adapt the structure of the converter to different input voltages of the converter. LEGO converters are usually optimized at specific input voltages and output voltages, that is, the LEGO converter may only maintain optimized high conversion efficiency in a narrow range of input voltages around the optimal design point. However, the input voltage of the converter may exceed the voltage range where the converter can maintain optimized high conversion efficiency.

[0047] For example, a 48V nominal power line in a data center may have an increased input voltage range, possibly as low as 36V and as high as 60V. To support an input voltage range of 36V to 60V in a data center, a five-layer LEGO converter based on a merged two-stage LEGO-PoL architecture is required to distribute the voltage burden and current burden to avoid the overload problem. As an example, Figure 7 A LEGO converter comprising five layers of 12V to 1V hybrid cells is shown to support applications with an input voltage of 60V and 60V to 1V conversion.

[0048] for Figure 7 In the converter structure shown, when the input voltage is 60 V, the converter can operate at its optimal design point with optimized high conversion efficiency because the input voltage is 5 times that of 12 V. Since each 12 V to 1 V hybrid unit is well optimized at the required output power level, the five-layer converter can perform 60 V to 1 V conversion with almost the same efficiency as the 12 V to 1 V hybrid unit.

[0049] However, when the input voltage is reduced to lower voltage levels, such as 48V or 36V, the converter may no longer operate at its optimal design point, and each layer of the converter only performs a 9.6V to 1V or 7.2V to 1V conversion.

[0050] According to this observation, it is proposed to detect the input voltage of the converter and determine how many hybrid cells in the converter need to be turned off so as to keep close to the optimal conversion at each hybrid cell to achieve the optimal conversion efficiency.

[0051] According to some embodiments of the present application, each hybrid unit in the converter may have a predetermined optimal voltage conversion ratio, and the number of activated hybrid units included in the converter may be determined based on the ratio of the input voltage to the output voltage of the converter and the optimal voltage conversion ratio of the hybrid unit. For example, when the input voltage is 60V, the output voltage is 1V, and the optimal voltage conversion ratio of each hybrid unit is 12V to 1V, the converter needs to include five activated hybrid units to achieve 60V to 1V conversion; when the input voltage is 48V, the output voltage is 1V, and the optimal voltage conversion ratio of each hybrid unit is 12V to 1V, the converter may include four activated hybrid units to achieve 48V to 1V conversion; when the input voltage is 36V, the output voltage is 1V, and the optimal voltage conversion ratio of each hybrid unit is 12V to 1V, the converter may include three activated hybrid units to achieve 36V to 1V conversion.

[0052] Figure 8 An optimized LEGO converter according to one or more example embodiments of the present disclosure is shown, which is composed of a Buck unit in the top hybrid unit by turning off the Buck unit in the top hybrid unit. Figure 7 The LEGO converter shown is obtained, thus supporting applications with 48V input voltage and 48V to 1V conversion.

[0053] like Figure 8 As shown, the Buck cell in the top hybrid cell is turned off, and the corresponding SC cell is reconfigured so that the two flying capacitors in the SC cell become decoupling capacitors for the input voltage. In this way, each hybrid cell can maintain the optimal 12V to 1V conversion, and the converter can perform 48V to 1V conversion with almost the same efficiency as the converter performs 60V to 1V conversion.

[0054] Similarly, when the input voltage drops to 36 V, the Buck cells in the top two layers of hybrid cells can be turned off, and the corresponding SC cells can be reconfigured so that the flying capacitors in the SC cells become decoupling capacitors for the input voltage. In this case, each hybrid cell can maintain the optimal 12 V to 1 V conversion, and the converter can perform 36 V to 1 V conversion with almost the same efficiency as the converter performs 60 V to 1 V conversion.

[0055] In general, according to some embodiments of the present application, the converter control unit may be configured to control the Buck unit in the hybrid unit starting from the top layer to be turned off in response to the input voltage decreasing and the output voltage remaining unchanged, so that each activated hybrid unit operates at an optimal voltage conversion ratio. At the same time, the converter control unit may be configured to reconfigure the SC unit corresponding to the Buck unit that is controlled to be turned off, so that the flying capacitor in the SC unit is used as a decoupling capacitor for the input voltage.

[0056] As mentioned above, the LEGO-PoL architecture can automatically distribute the voltage burden and current burden and achieve voltage and current balance among multiple stacks of LEGO converters. Indeed, in the steady state, all flying capacitors in the LEGO converter block the input voltage, so the power switches in the converter will not have any voltage burden problem. However, before entering the steady state, it may be necessary to ensure that each power switch will not have an excessive burden problem even during the startup process. This problem is common to most switched capacitor converters.

[0057] In "8.1A 93.8% Peak Efficiency, 5V-Input, 10A Max ILOAD Flying Capacitor Multilevel Converter in 22nm CMOS Featuring Wide Output Voltage Range and Flying Capacitor Precharging" by C. Schaef et al., 2019 IEEE International Solid-State Circuits Conference (ISSCC), February 2019, pages 146–148 (incorporated herein by reference), a flying capacitor precharging technique is proposed to precharge two flying capacitors to their nominal values ​​during startup to ensure that any power switch in the converter will not be overloaded. The flying capacitor precharging method can also be applied to the converter in the present application. During startup, the switched capacitor unit in each hybrid unit can be reconfigured so that all flying capacitors are connected in parallel to the input node of the converter, and then all flying capacitors can be charged to their nominal voltage values.

[0058] According to some embodiments of the present application, when the input voltage increases in a ramped manner during the start-up of the converter, the converter control unit may also be configured to control the converter to undergo a plurality of states in which the flying capacitors in the SC unit are successively disconnected from the input voltage until the voltage of the flying capacitor reaches the steady-state voltage of the flying capacitor and the input voltage reaches the nominal voltage. When the voltage of the flying capacitor reaches its steady-state voltage and the input voltage reaches the nominal voltage, the converter control unit may generate an enable signal to instruct the converter to start a voltage conversion operation.

[0059] Figures 9a to 9h 1 shows a plurality of states that an exemplary five-layer LEGO converter goes through during a flying capacitor pre-charging startup process for the converter according to one or more example embodiments of the present disclosure. Figures 9a to 9h As shown in , in state 1, all flying capacitors in the SC unit are shorted to the input voltage until the voltage of the lowest flying capacitor CF7 reaches the steady-state voltage of the flying capacitor, after which the lowest flying capacitor CF7 is disconnected from the input voltage; in state 2, the remaining flying capacitors except the lowest flying capacitor CF7 remain shorted to the input voltage and continue to be charged until the voltage of the second flying capacitor CF6 from the bottom reaches the steady-state voltage of the flying capacitor, after which the second flying capacitor CF6 from the bottom is disconnected from the input voltage; and so on, until the voltages of all flying capacitors reach the steady-state voltages of all flying capacitors and the input voltage reaches the nominal voltage. During the startup process, the converter passes through a total of eight states.

[0060] Fig.10 A state diagram illustrating a flying capacitor pre-charging startup process of an exemplary five-layer LEGO converter according to one or more exemplary embodiments of the present disclosure.

[0061] like Fig.10 As shown, at the end of state 8, the voltage of all flying capacitors reaches the steady-state voltage of the flying capacitors, and the input voltage reaches the nominal voltage. Once all capacitors have reached their steady-state voltages and the input voltage has reached the nominal value, an enable signal can be generated to instruct the converter to enter the normal state and start the operation of voltage conversion.

[0062] As described above, the present application proposes a dynamically scalable LEGO converter based on a merged two-stage LEGO-PoL architecture. The LEGO converter includes: an SC stage, including one or more SC cells stacked in series; and a Buck stage, coupled to the SC stage and including one or more M-phase Buck cells connected in parallel. The control method for the converter may include controlling one or more Buck cells in the Buck cell to turn on or off based on the input voltage or output current of the converter.

[0063] In some embodiments, the SC units can be coupled to the Buck units in a one-to-one correspondence, and one SC unit and one corresponding Buck unit constitute a hybrid unit in the converter. In addition, in some embodiments, the SC units can be coupled to the Buck units in a one-to-many correspondence, and one SC unit and multiple corresponding Buck units constitute a hybrid unit in the converter.

[0064] The control method for the converter may include: controlling a portion of the Buck units in each hybrid unit to be turned on in response to an increase in the output current or controlling a portion of the Buck units in each hybrid unit to be turned off in response to a decrease in the output current, so as to maintain the optimal conversion efficiency of the converter. The control method may also include: controlling a predetermined number of phases in each activated Buck unit in the converter to be turned on in response to an increase in the output current or controlling a predetermined number of phases in each activated Buck unit to be turned off in response to a decrease in the output current, so as to maintain the optimal conversion efficiency of the converter.

[0065] In some embodiments, the control method may include controlling the SC stage and the Buck stage to operate according to the following switching frequency equation to maintain phase current balance in the converter:

[0066] In some embodiments, each hybrid cell has a predetermined optimal voltage conversion ratio, and the number of activated hybrid cells included in the converter is determined based on the ratio of the input voltage to the output voltage of the converter and the optimal voltage conversion ratio of the hybrid cell. The control method may include: in response to the input voltage decreasing and the output voltage remaining unchanged, controlling the Buck cell in the hybrid cell starting from the top layer to turn off so that each activated hybrid cell operates at the optimal voltage conversion ratio. The control method may also include: reconfiguring the SC cell corresponding to the Buck cell that is controlled to be turned off to use the flying capacitor in the SC cell as a decoupling capacitor for the input voltage.

[0067] In some embodiments, the control method may include: when the input voltage increases in a ramped manner during the start-up of the converter, controlling the converter to go through a plurality of states in which the flying capacitors in the SC unit are successively disconnected from the input voltage until the voltage of the flying capacitor reaches the steady-state voltage of the flying capacitor and the input voltage reaches the nominal voltage; and when the voltage of the flying capacitor reaches the steady-state voltage of the flying capacitor and the input voltage reaches the nominal voltage, generating an enable signal to instruct the converter to start a voltage conversion operation.

[0068] Specifically, in a first state among the multiple states, all flying capacitors in the SC unit are shorted to the input voltage until the voltage of the flying capacitors in the lowest layer reaches the steady-state voltage of the flying capacitors, and then the flying capacitors in the lowest layer are disconnected from the input voltage; in a second state among the multiple states, the remaining flying capacitors except the flying capacitors in the lowest layer remain shorted to the input voltage and continue to be charged until the voltage of the second flying capacitor from the bottom layer reaches the steady-state voltage of the flying capacitor, and then the second flying capacitor from the bottom layer is disconnected from the input voltage; and so on, until the voltages of all flying capacitors reach the steady-state voltages of all flying capacitors and the input voltage reaches the nominal voltage.

[0069] In addition to the above-mentioned control method for the LEGO converter, the present application also proposes a flying capacitor pre-charging startup method for the LEGO converter. The startup method may include: when the input voltage of the converter increases in a ramped manner during the startup of the converter, controlling the converter to undergo multiple states, in which the flying capacitors in the SC unit are successively disconnected from the input voltage until the voltage of the flying capacitor reaches the steady-state voltage of the flying capacitor and the input voltage reaches the nominal voltage; and when the voltage of the flying capacitor reaches the steady-state voltage of the flying capacitor and the input voltage reaches the nominal voltage, generating an enable signal to instruct the converter to start a voltage conversion operation.

[0070] It is worth noting that this flying capacitor pre-charge startup method can be applied to the dynamically scalable LEGO converter discussed in this article or any other LEGO converter currently in use or to be developed in the future.

[0071] The following paragraphs describe examples of various embodiments.

[0072] Example 1 includes a converter, comprising: a switched capacitor (SC) stage, comprising one or more SC cells stacked in series; a step-down (Buck) stage, coupled to the SC stage and comprising one or more M-phase Buck cells connected in parallel, where M is an integer greater than or equal to 1; and a converter control unit, configured to control one or more of the Buck cells to turn on or off based on an input voltage or an output current of the converter.

[0073] Example 2 includes the converter according to Example 1, wherein the SC units are coupled to the Buck units respectively in a one-to-one correspondence, and one SC unit and a corresponding Buck unit constitute a hybrid unit in the converter.

[0074] Example 3 includes the converter according to Example 1, wherein the SC units are coupled to the Buck units respectively in a one-to-many correspondence, and one SC unit and multiple corresponding Buck units constitute a hybrid unit in the converter.

[0075] Example 4 includes a converter according to Example 3, wherein the converter control unit is further configured to: control a portion of the Buck units in each hybrid unit to turn on in response to an increase in the output current or control a portion of the Buck units in each hybrid unit to turn off in response to a decrease in the output current, so as to maintain the optimal conversion efficiency of the converter.

[0076] Example 5 includes a converter according to any one of Examples 1 to 4, wherein the converter control unit is further configured to: control a predetermined number of phases in each activated Buck unit in the converter to be turned on in response to an increase in the output current or control a predetermined number of phases in each activated Buck unit to be turned off in response to a decrease in the output current so as to maintain the optimal conversion efficiency of the converter.

[0077] Example 6 includes the converter according to any one of Examples 1 to 5, wherein the converter control unit is further configured to: control the SC stage and the Buck stage to operate according to the following switching frequency equation to maintain phase current balance in the converter:

[0078]

[0079] Among them, f sw-buck Represents the switching frequency of each power switch in each Buck unit, f sw-SC represents the switching frequency of each power switch in each SC unit, N is the number of active phases in each Buck unit, and d is an odd number greater than 1 that is relatively prime to N.

[0080] Example 7 includes a converter according to Example 2 or 3, wherein each hybrid unit has a predetermined optimal voltage conversion ratio, and the number of activated hybrid units included in the converter is determined based on the ratio of the input voltage to the output voltage of the converter and the optimal voltage conversion ratio of the hybrid unit.

[0081] Example 8 includes a converter according to Example 7, wherein the converter control unit is further configured to: control the Buck cells in the hybrid cells starting from the top layer to turn off in response to the input voltage decreasing and the output voltage remaining unchanged, so that each activated hybrid cell operates at the optimal voltage conversion ratio.

[0082] Example 9 includes the converter according to Example 8, wherein the converter control unit is further configured to: reconfigure the SC unit corresponding to the Buck unit that is controlled to be turned off to use the flying capacitor in the SC unit as a decoupling capacitor for the input voltage.

[0083] Example 10 includes a converter according to any one of Examples 1 to 9, wherein the converter control unit is further configured to: when the input voltage increases in a ramped manner during startup of the converter, control the converter to undergo multiple states in which the flying capacitors in the SC units are successively disconnected from the input voltage until the voltage of the flying capacitor reaches the steady-state voltage of the flying capacitor and the input voltage reaches the nominal voltage; and when the voltage of the flying capacitor reaches the steady-state voltage of the flying capacitor and the input voltage reaches the nominal voltage, generate an enable signal to instruct the converter to start a voltage conversion operation.

[0084] Example 11 includes the converter according to Example 10, wherein, in a first state among the plurality of states, all flying capacitors in the SC unit are shorted to the input voltage until a voltage of a flying capacitor in a lowest layer reaches a steady-state voltage of the flying capacitor, after which the flying capacitor in the lowest layer is disconnected from the input voltage; in a second state among the plurality of states, the remaining flying capacitors except the flying capacitor in the lowest layer remain shorted to the input voltage and continue to be charged until a voltage of a second flying capacitor from the lowest layer reaches the steady-state voltage of the flying capacitor, after which the second flying capacitor from the lowest layer is disconnected from the input voltage; and so on, until the voltages of all flying capacitors reach the steady-state voltages of all flying capacitors and the input voltage reaches the nominal voltage.

[0085] Example 12 includes a method for a converter, wherein the converter includes: a switched capacitor (SC) stage, including one or more SC cells stacked in series; and a step-down (Buck) stage, coupled to the SC stage and including one or more M-phase Buck cells connected in parallel, wherein M is an integer greater than or equal to 1, and the method includes: controlling one or more of the Buck cells to turn on or off based on an input voltage or an output current of the converter.

[0086] Example 13 includes the method according to Example 12, wherein the SC cells are coupled to the Buck cells respectively in a one-to-one correspondence, and one SC cell and a corresponding Buck cell constitute a hybrid cell in the converter.

[0087] Example 14 includes the method according to Example 12, wherein the SC units are respectively coupled to the Buck units in a one-to-many correspondence, and one SC unit and multiple corresponding Buck units constitute a hybrid unit in the converter.

[0088] Example 15 includes a method according to Example 14, wherein controlling one or more of the Buck cells to be turned on or off based on the input voltage or output current of the converter includes: controlling a portion of the Buck cells in each hybrid cell to be turned on in response to an increase in the output current or controlling a portion of the Buck cells in each hybrid cell to be turned off in response to a decrease in the output current, so as to maintain the optimal conversion efficiency of the converter.

[0089] Example 16 includes a method according to any one of Examples 12 to 15, further comprising: controlling a predetermined number of phases in each activated Buck unit in the converter to be turned on in response to an increase in the output current or controlling a predetermined number of phases in each activated Buck unit to be turned off in response to a decrease in the output current to maintain the optimal conversion efficiency of the converter.

[0090] Example 17 includes the method of any one of Examples 12 to 16, further comprising: controlling the SC stage and the Buck stage to operate according to the following switching frequency equation to maintain phase current balance in the converter:

[0091]

[0092] Among them, f sw-buck Represents the switching frequency of each power switch in each Buck unit, f sw-SC represents the switching frequency of each power switch in each SC unit, N is the number of active phases in each Buck unit, and d is an odd number greater than 1 that is relatively prime to N.

[0093] Example 18 includes a method according to Example 13 or 14, wherein each hybrid unit has a predetermined optimal voltage conversion ratio, and the number of activated hybrid units included in the converter is determined based on the ratio of the input voltage to the output voltage of the converter and the optimal voltage conversion ratio of the hybrid unit.

[0094] Example 19 includes the method according to Example 18, further comprising: in response to the input voltage decreasing and the output voltage remaining unchanged, controlling the Buck cells in the hybrid cells starting from the top layer to turn off so that each activated hybrid cell operates at the optimal voltage conversion ratio.

[0095] Example 20 includes the method according to Example 19, further comprising: reconfiguring the SC cell corresponding to the Buck cell that is controlled to be turned off to use a flying capacitor in the SC cell as a decoupling capacitor of the input voltage.

[0096] Example 21 includes a method according to any one of Examples 12 to 20, further comprising: when the input voltage increases in a ramped manner during startup of the converter, controlling the converter to undergo multiple states in which the flying capacitors in the SC units are successively disconnected from the input voltage until the voltage of the flying capacitor reaches the steady-state voltage of the flying capacitor and the input voltage reaches the nominal voltage; and when the voltage of the flying capacitor reaches the steady-state voltage of the flying capacitor and the input voltage reaches the nominal voltage, generating an enable signal to instruct the converter to start a voltage conversion operation.

[0097] Example 22 A method according to Example 21, wherein, in a first state among the multiple states, all flying capacitors in the SC unit are shorted to the input voltage until the voltage of the flying capacitors in the lowest layer reaches the steady-state voltage of the flying capacitors, after which the flying capacitors in the lowest layer are disconnected from the input voltage; in a second state among the multiple states, the remaining flying capacitors except the flying capacitors in the lowest layer remain shorted to the input voltage and continue to be charged until the voltage of the second flying capacitor from the bottom layer reaches the steady-state voltage of the flying capacitor, after which the second flying capacitor from the bottom layer is disconnected from the input voltage; and so on, until the voltages of all flying capacitors reach the steady-state voltages of all flying capacitors and the input voltage reaches the nominal voltage.

[0098] Example 23 includes a method for a converter, wherein the converter includes: a switched capacitor (SC) stage, including one or more SC cells stacked in series; and a step-down (Buck) stage, coupled to the SC stage and including one or more M-phase Buck cells connected in parallel, wherein M is an integer greater than or equal to 1, and the method includes: when the input voltage of the converter increases in a ramp manner during startup of the converter, controlling the converter to undergo a plurality of states in which the flying capacitors in the SC cells are successively disconnected from the input voltage until the voltage of the flying capacitor reaches the steady-state voltage of the flying capacitor and the input voltage reaches the nominal voltage; and when the voltage of the flying capacitor reaches the steady-state voltage of the flying capacitor and the input voltage reaches the nominal voltage, generating an enable signal to instruct the converter to start a voltage conversion operation.

[0099] Example 24 includes a method according to Example 23, wherein, in a first state among the multiple states, all flying capacitors in the SC cell are shorted to the input voltage until a voltage of a flying capacitor in a lowest layer reaches a steady-state voltage of the flying capacitor, after which the flying capacitor in the lowest layer is disconnected from the input voltage; in a second state among the multiple states, the remaining flying capacitors except the flying capacitor in the lowest layer remain shorted to the input voltage and continue to be charged until a voltage of a second flying capacitor from the lowest layer reaches the steady-state voltage of the flying capacitor, after which the second flying capacitor from the lowest layer is disconnected from the input voltage; and so on, until the voltages of all flying capacitors reach the steady-state voltages of all flying capacitors and the input voltage reaches the nominal voltage.

[0100] Example 25 includes a circuit system comprising a processor, a power interface for the processor, and a converter according to any one of Examples 1 to 11, wherein the power interface is coupled to the converter to provide power to the processor.

[0101] Embodiments according to the present disclosure are specifically disclosed in the appended claims for methods and devices, wherein any feature mentioned in one claim category (e.g., method) may also be claimed in another claim category (e.g., device). Dependencies or references in the appended claims are selected for formal reasons only. However, any subject matter resulting from intentional tracing back to any previous claim (especially multiple dependencies) may also be claimed, so that any combination of claims and their features is disclosed and may be claimed, regardless of the dependencies selected in the appended claims. The subject matter that may be claimed includes not only the combination of features listed in the appended claims, but also any other combination of features in the claims, wherein each feature mentioned in the claims may be combined with any other feature in the claims or with a combination of other features. In addition, any embodiments and features described or depicted herein may be claimed in separate claims and / or in any combination with any embodiment or feature described or depicted herein or with any feature of the appended claims.

[0102] The foregoing description of one or more embodiments provides illustration and description, but is not intended to be exhaustive or to limit the scope of the embodiments to the precise forms disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from practice of the various embodiments.

[0103] Any term expressed in the form of a plurality without an explicit statement of "plurality" or "multiple" similarly refers to a quantity equal to or greater than one. The terms "group," "set," "subset," and the like refer to a quantity equal to or greater than one. The words "exemplary" or "example" are used herein to mean "serving as an example, instance, demonstration, or illustration." Any aspect, embodiment, or design described herein as "exemplary" or "example" is not necessarily to be construed as preferred or advantageous over other aspects, embodiments, or designs.

[0104] As used herein, unless otherwise indicated, the use of ordinal adjectives "first," "second," "third," etc. to describe common objects simply indicates that different instances of similar objects are referenced and is not intended to imply that the objects so described must be in a given sequence in time, space, ranking, or in any other manner.

[0105] The phrases “at least one” and “one or more” may be understood to include numerical quantities greater than or equal to one, for example, one, two, three, four, [...], etc. The phrase “at least one of” with respect to a group of elements may be used herein to mean at least one element from the group consisting of these elements.

[0106] Conditional language, such as "may" or "might", etc., unless expressly stated otherwise or otherwise understood in the context of use, is generally intended to convey that certain embodiments may include, while other embodiments do not include, certain features, elements, and / or operations. Thus, such conditional language is generally not intended to imply that features, elements, and / or operations are in any way required for one or more embodiments, or that one or more embodiments must include logic for determining, with or without user input or prompting, whether such features, elements, and / or operations are included in any particular embodiment or are to be performed in any particular embodiment.

[0107] Many modifications and other embodiments of the disclosure set forth herein will clearly benefit from the teachings presented in the foregoing description and the associated drawings. Therefore, it should be understood that the disclosure is not limited to the specific embodiments disclosed, and modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are used herein, they are used in a general and descriptive sense only and not for the purpose of limitation.

Claims

1. A converter, comprising: a switched capacitor (SC) stage comprising one or more SC cells stacked in series; a step-down (Buck) stage coupled to the SC stage and comprising one or more M-phase Buck cells connected in parallel, where M is an integer greater than or equal to 1; as well as The converter control unit is configured to control one or more of the Buck cells to turn on or off based on the input voltage or output current of the converter.

2. The converter according to claim 1, wherein: The SC units are coupled to the Buck units in a one-to-one correspondence, and one SC unit and one corresponding Buck unit constitute a hybrid unit in the converter.

3. The converter according to claim 1, wherein: The SC units are coupled to the Buck units in a one-to-many correspondence relationship, and one SC unit and a plurality of corresponding Buck units constitute a hybrid unit in the converter.

4. The converter according to claim 3, wherein: The converter control unit is further configured to control a portion of the Buck units in each hybrid unit to turn on in response to an increase in the output current or to control a portion of the Buck units in each hybrid unit to turn off in response to a decrease in the output current, so as to maintain an optimal conversion efficiency of the converter.

5. The converter according to claim 1, wherein: The converter control unit is further configured to: control a predetermined number of phases in each activated Buck unit in the converter to be turned on in response to an increase in the output current or control a predetermined number of phases in each activated Buck unit to be turned off in response to a decrease in the output current to maintain the optimal conversion efficiency of the converter.

6. The converter according to any one of claims 1 to 5, wherein: The converter control unit is further configured to control the SC stage and the Buck stage to operate according to the following switching frequency equation to maintain phase current balance in the converter: Among them, f sw-buck Represents the switching frequency of each power switch in each Buck unit, f sw-SC represents the switching frequency of each power switch in each SC unit, N is the number of active phases in each Buck unit, and d is an odd number greater than 1 that is relatively prime to N.

7. The converter according to claim 2 or 3, wherein: Each hybrid cell has a predetermined optimal voltage conversion ratio, and the number of activated hybrid cells included in the converter is determined based on a ratio of the input voltage to an output voltage of the converter and the optimal voltage conversion ratio of the hybrid cell.

8. The converter according to claim 7, wherein: The converter control unit is further configured to control the Buck cells in the hybrid cells starting from the top layer to turn off in response to the input voltage decreasing and the output voltage remaining unchanged, so that each activated hybrid cell operates at the optimal voltage conversion ratio.

9. The converter according to claim 8, wherein: The converter control unit is further configured to reconfigure the SC unit corresponding to the Buck unit that is controlled to be turned off, so as to use the flying capacitor in the SC unit as a decoupling capacitor for the input voltage.

10. The converter according to claim 1, wherein: The converter control unit is further configured to: When the input voltage is ramped up during the start-up of the converter, controlling the converter to go through a plurality of states in which the flying capacitors in the SC unit are successively disconnected from the input voltage until the voltage of the flying capacitor reaches a steady-state voltage of the flying capacitor and the input voltage reaches a nominal voltage; and When the voltage of the flying capacitor reaches the steady-state voltage of the flying capacitor and the input voltage reaches the nominal voltage, an enable signal is generated to instruct the converter to start a voltage conversion operation.

11. The converter according to claim 10, wherein: In a first state among the plurality of states, all flying capacitors in the SC cell are shorted to the input voltage until the voltage of the flying capacitors in the lowest layer reaches the steady-state voltage of the flying capacitors, after which the flying capacitors in the lowest layer are disconnected from the input voltage; in a second state among the plurality of states, the remaining flying capacitors except the flying capacitors in the lowest layer remain shorted to the input voltage and continue to be charged until the voltage of the second flying capacitor from the lowest layer reaches the steady-state voltage of the flying capacitor, after which the second flying capacitor from the lowest layer is disconnected from the input voltage; and so on, until the voltages of all flying capacitors reach the steady-state voltages of all flying capacitors and the input voltage reaches the nominal voltage.

12. A method for a converter, wherein the converter comprises: a switched capacitor (SC) stage comprising one or more SC cells stacked in series; and a step-down (Buck) stage coupled to the SC stage and comprising one or more M-phase Buck cells connected in parallel, where M is an integer greater than or equal to 1, and the method comprises: One or more Buck units in the Buck unit are controlled to be turned on or off based on the input voltage or output current of the converter.

13. The method according to claim 12, wherein: The SC units are coupled to the Buck units in a one-to-one correspondence, and one SC unit and one corresponding Buck unit constitute a hybrid unit in the converter.

14. The method according to claim 12, wherein: The SC units are coupled to the Buck units in a one-to-many correspondence relationship, and one SC unit and a plurality of corresponding Buck units constitute a hybrid unit in the converter.

15. The method according to claim 14, wherein: Controlling one or more Buck units in the Buck unit to turn on or off based on the input voltage or output current of the converter includes: controlling a portion of the Buck units in each hybrid unit to turn on in response to an increase in the output current or controlling a portion of the Buck units in each hybrid unit to turn off in response to a decrease in the output current, so as to maintain the optimal conversion efficiency of the converter.

16. The method according to claim 12, further comprising: In response to an increase in the output current, a predetermined number of phases in each activated Buck unit in the converter are controlled to be turned on, or in response to a decrease in the output current, a predetermined number of phases in each activated Buck unit are controlled to be turned off to maintain an optimal conversion efficiency of the converter.

17. The method according to any one of claims 12 to 16, further comprising: The SC stage and the Buck stage are controlled to operate according to the following switching frequency equation to maintain phase current balance in the converter: Among them, f sw-buck Represents the switching frequency of each power switch in each Buck unit, f sw-SC represents the switching frequency of each power switch in each SC unit, N is the number of active phases in each Buck unit, and d is an odd number greater than 1 that is relatively prime to N.

18. The method according to claim 13 or 14, wherein: Each hybrid cell has a predetermined optimal voltage conversion ratio, and the number of activated hybrid cells included in the converter is determined based on a ratio of the input voltage to an output voltage of the converter and the optimal voltage conversion ratio of the hybrid cell.

19. The method according to claim 18, further comprising: In response to the input voltage decreasing and the output voltage remaining unchanged, the Buck cells in the hybrid cells starting from the top layer are controlled to be turned off, so that each activated hybrid cell operates at the optimal voltage conversion ratio.

20. The method according to claim 19, further comprising: The SC unit corresponding to the Buck unit that is controlled to be turned off is reconfigured to use the flying capacitor in the SC unit as a decoupling capacitor for the input voltage.

21. The method of claim 12, further comprising: When the input voltage is ramped up during the start-up of the converter, controlling the converter to go through a plurality of states in which the flying capacitors in the SC unit are successively disconnected from the input voltage until the voltage of the flying capacitor reaches a steady-state voltage of the flying capacitor and the input voltage reaches a nominal voltage; and When the voltage of the flying capacitor reaches the steady-state voltage of the flying capacitor and the input voltage reaches the nominal voltage, an enable signal is generated to instruct the converter to start a voltage conversion operation.

22. The method according to claim 21, wherein: In a first state among the plurality of states, all flying capacitors in the SC cell are shorted to the input voltage until the voltage of the flying capacitors in the lowest layer reaches the steady-state voltage of the flying capacitors, after which the flying capacitors in the lowest layer are disconnected from the input voltage; in a second state among the plurality of states, the remaining flying capacitors except the flying capacitors in the lowest layer remain shorted to the input voltage and continue to be charged until the voltage of the second flying capacitor from the lowest layer reaches the steady-state voltage of the flying capacitor, after which the second flying capacitor from the lowest layer is disconnected from the input voltage; and so on, until the voltages of all flying capacitors reach the steady-state voltages of all flying capacitors and the input voltage reaches the nominal voltage.

23. A method for a converter, wherein the converter comprises: a switched capacitor (SC) stage comprising one or more SC cells stacked in series; and a step-down (Buck) stage coupled to the SC stage and comprising one or more M-phase Buck cells connected in parallel, where M is an integer greater than or equal to 1, and the method comprises: When the input voltage of the converter is ramped up during the start-up of the converter, controlling the converter to go through a plurality of states in which the flying capacitors in the SC unit are successively disconnected from the input voltage until the voltage of the flying capacitor reaches a steady-state voltage of the flying capacitor and the input voltage reaches a nominal voltage; and When the voltage of the flying capacitor reaches the steady-state voltage of the flying capacitor and the input voltage reaches the nominal voltage, an enable signal is generated to instruct the converter to start a voltage conversion operation.

24. The method according to claim 23, wherein: In a first state among the plurality of states, all flying capacitors in the SC cell are shorted to the input voltage until the voltage of the flying capacitors in the lowest layer reaches the steady-state voltage of the flying capacitors, after which the flying capacitors in the lowest layer are disconnected from the input voltage; in a second state among the plurality of states, the remaining flying capacitors except the flying capacitors in the lowest layer remain shorted to the input voltage and continue to be charged until the voltage of the second flying capacitor from the lowest layer reaches the steady-state voltage of the flying capacitor, after which the second flying capacitor from the lowest layer is disconnected from the input voltage; and so on, until the voltages of all flying capacitors reach the steady-state voltages of all flying capacitors and the input voltage reaches the nominal voltage.

25. A circuit system comprising a processor, a power interface for the processor, and a converter according to any one of claims 1 to 11, wherein the power interface is coupled to the converter to provide power to the processor.

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