Patent Publication Number: US-RE38371-E

Title: DC-to-DC controller having a multi-phase synchronous buck regulator

Description:
FIELD 
     The invention generally relates to voltage regulators and in particular to multi-phase pulse width modulated (PWM) direct-current (DC) to DC voltage regulators. 
     BACKGROUND 
     Most electronic circuits, from simple transistors and op-amp circuits up to elaborate digital and microprocessor systems, require one or more sources of stable DC voltage. DC-to-DC converters are well-known in the art. Such circuitry or devices are typically employed to convert from one DC voltage signal level to another DC voltage signal level. This may be useful in a variety of environments. 
     Today&#39;s sophisticated processing units (PUs) have made the job of the power supply designer more difficult. These PUs continue to demand every higher currents and lower voltages. One problem is providing a desired, highly regulated, voltage which may vary in a range, such as, for example, from 0.96 volts to 1.04 volts, and that may depend, at least in part, on clock speed. Another challenge is to provide this voltage at relatively high currents that may vary from several hundred milliamps, up to, for example, 120 amps, and back again, in a clock cycle, for example. Furthermore, yet a third challenge is to provide a scalable design that meets these higher current requirements by using multiple instances of a common building block connected together in parallel. Therefore, a need exists for a DC-to-DC regulator circuit that is at least closer to accomplishing these objectives, or at least one of them, than state-of-the-art circuitry. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and a better understanding of the present invention will become apparent from the following detailed description of example embodiments and the claims when read in connection with the accompanying drawings, all forming a part of the disclosure of this invention. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. While the foregoing and following written and illustrated disclosure focuses on disclosing example embodiments of the invention, it should be clearly understood that the same is by way of illustration and example only and the invention is not limited thereto. The spirit and scope of the present invention are limited only by the terms of the appended claims. 
     The following represents brief descriptions of the drawings, wherein: 
     FIG. 1 is a block diagram illustrating a multi-phase synchronous buck regulator implemented on a motherboard according to an example embodiment of the present invention; 
     FIG. 2 is a block diagram illustrating the multi-phase synchronous buck regulator in greater detail according to an example embodiment of the current invention; 
     FIG. 3 represents an overall circuit layout for combining the circuit parts of FIGS. 3A-3F, such circuit illustrating a four-phase synchronous buck regulator according to an example embodiment of the present invention, where the regulator is implemented on a PU; 
     FIG. 4 represents an overall circuit layout for combining the circuit parts of FIGS. 4A-4D, such circuit illustrating a four-phase synchronous buck regulator according to an example embodiment of the present invention, where the regulator is implemented on an interposer; and 
     FIGS. 5A and 5B are circuit diagrams illustrating a first and second over-voltage protection circuit according to example embodiments of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Before beginning a detailed description of the subject invention, mention of the following is in order. When appropriate, like reference numerals and characters may be used to designate identical, corresponding or similar components in differing figure drawings. Further, in the detailed description to follow, example sizes/models/values/ranges may be given, although the present invention is not limited to the same. Well known power/ground connections to integrated circuits (ICs) and other components may not be shown within the figures for simplicity of illustration and discussion, and so as not to obscure the invention. Further, arrangements may be shown in block diagram form in order to avoid obscuring the invention, and also in view of the fact that specifics with respect to implementation of such block diagram arrangements is highly dependent upon the platform within which the present invention is to be implemented, i.e., specifics should be well within purview of one skilled in the art. Where specific details (e.g., circuit diagrams) are set forth in order to describe example embodiments of the invention, it should be apparent to one skilled in the art that the invention can be practiced without these specific details. 
     Reference in the specification to “one example embodiment” 0  or “an example embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearance of the phase “in one example embodiment” in various places in the specification are not necessarily all referring to the same embodiment. 
     An example embodiment of the present invention is directed to a DC-to-DC regulator that includes a multi-phase synchronous buck regulator having a pulse width modulator to generate a plurality of switching signals, a plurality of drivers, each coupled to receive one of the switching signals, and a plurality of switching voltage converters, each coupled to receive an output from one of the drivers and an input voltage, wherein the outputs of the switching voltage converters are combined to form an output voltage. The multi-phase synchronous buck regulator can be implemented on a motherboard, such as on an interposer board or directly on a PU chip. 
     FIG. 1 is a block diagram illustrating a multi-phase synchronous buck regulator  130  implemented on a computer motherboard  108  according to an example embodiment of the present invention. An alternating current (AC) wall socket  102  provides an AC current to a power supply  104 . Power supply  104  converts the AC signal into one or more DC voltages (where the number of DC voltages is given by N). For example, power supply  104  can convert the AC signal into two DC voltages, 12 volts and 5 volts. A distribution board  106  distributes the DC voltages to various loads, including regulator  130 . Distribution board  106  provides a low impedance, low inductance path to the load (e.g., memory, chip sets, PU). 
     Regulator  130  is implemented on a motherboard  108  (sometimes alternatively referred to, for example, as a processor host board). Motherboard  108  includes an interposer  122  that plugs into a processor socket  120 , one or more Organic LAN Grid Arrays (OLGAs)  124  (shown as  124 A and  124 B), and one or more PUs  126 . Regulator  130  converts the one or more input DC voltages received from distribution board  106  to an output voltage that is used by PU  126 . Regulator  130  therefore provides the complex, highly regulated voltages required by PU  126 . Regulator  130  converts any of the N input DC voltages to an output DC voltage that can range, for example, from 0.9 volts to 1.6 volts, depending on the clock speed of PU  126 . Acceptable tolerances in the output voltage signal are often expressed as a percentage of the mean output voltage. According to an example embodiment of the present invention, regulator  130  provides an output voltage of 1 volt±4% (i.e., the output voltage can range from 0.96 volts to 1.04 volts). Further, regulator  130  provides an output voltage even where the current load varies from 0 amps (e.g., where PU  126  is in stand-by) to 200 amps and above, and back again in a single clock cycle. 
     Prior voltage regulators were implemented on a card separate from motherboard  108 . These voltage regulator cards were therefore plugged into a socket separate from the processor socket. These plug-in voltage regulators require that many decoupling capacitors be implemented on motherboard  108 , interposer  122 , and OLGA  124  to handle the dynamic response requirements of PU  126 . Decoupling capacitors require a significant amount of real estate on motherboard  108 , increase cost, block air flow through the system and contribute to system heating. Further, the distributed impedance associated with the distribution and interconnect between the plug-in voltage regulator and motherboard  108  limits the performance of plug-in voltage regulators. 
     According to the present invention, regulator  130  is implemented on motherboard  108 , rather than as a separate plug-in module, minimizing the distributed impedance between regulator  130  and PU  126 . According to an example embodiment, as depicted in FIG. 1, regulator  130  can be implemented on interposer board  122 . In this first example embodiment, regulator  130  can provide an output DC voltage to one or more PUs  126 . According to another example embodiment, regulator  130  can alternatively be implemented directly on PU  126 . In this second example embodiment, regulator  130  provides an output DC voltage to the PU on which regulator  130  is implemented. These example embodiments are described in greater detail below. 
     According to an example embodiment of the present invention, regulator  130  is implemented using surface mount technology (SMT) output inductors and capacitors, and a number of low inductance, low capacitance, low on-resistance surface mount packages 8-pin package (S 08 ). As a result, the dynamic response of regulator  130  is greatly improved due to its low output impedance path. The number of required output capacitors within regulator  130  is reduced, freeing up more space on interposer  122 . 
     FIG. 2 is a block diagram illustrating an M-phase synchronous buck regulator  130  in greater detail according to an example embodiment of the current invention, where M is the number of phase in the multi-phase regulator. Regulator  130  includes a pulse width modulator  204 , a sequence timing control  206 , a number of drivers  208  equal to the number of phases (shown as  208 - 1  through  208 -M), a similar number of switching voltage converters  210  (shown as  210 - 1  through  210 -M), and a regulation circuit  214 . The input DC voltages  202  (shown as  202 - 1  through  202 -N) from power supply  104  are input to regulator  130 . Regulator  130  converts input voltages  202  to an output voltage  212 . 
     Pulse width modulator  204  generates a number of switching signals  220  equal to the number of phases M (shown as  220 - 1  to  220 -M). The switching signals may be square-wave in shape, and are out of phase from one another. For example, with a four-phase regulator, pulse width modulator  204  generates four switching signals, where the signals from one phase to the next are separated by 90°. For each of the M phases, the switching signal power is boosted by driver  208  (the boosted signals are depicted by lines  224 - 1  through  224 -M). Driver  208  provides the power necessary to drive switching voltage converter  210  at a high frequency. 
     Sequence timing control  206  insures that regulator  130  will operate properly regardless of the sequencing of input DC voltages  202 . Prior voltage regulators required that, whenever multiple input DC voltages were allowed, they were required to follow a particular preset temporal pattern. For example, a prior voltage regulator that received as input a 12 volt and a 5 volt DC signal, the prior voltage regulator might require that the 12 volt and 5 volt signals alternate over time. Deviation from this pattern could potentially result in catastrophic failure for the voltage regulator. Requiring a known pattern of sequencing requires a more complex and expensive system. According to the present invention, sequencing timing control  206  allows the input DC voltages to come up or down at random, in any sequence, by insuring that drivers  208  turn on before pulse width modulator  204 . 
     According to an example embodiment of the present invention, switching voltage converter  210  represents a pulse width modulated (PWM) series-switch step-down converter. PWM converters an be used to obtain a lower voltage from a higher one by using a low-impedance transistor switch that is made to open and close periodically between input and output. The transistor switch is driven by the switching voltage generated by pulse width modulator  204 . As is well known in the art, any desired output voltage lower than the input voltage can be obtained by varying the width of the “on” time switching signal. Example implementations of switching voltage converter  210  are described in greater detail below. 
     Output voltage  212  is formed by combining the outputs of the switching voltage converters  210 . The output capacitance of regulator  130  causes a ripple on output voltage  212 . The output can be modeled as a capacitance in series with an inductance and a resistance. Even under steady-state conditions, the capacitor will charge and then discharge, causing the output ripple. One advantage of the present invention is that the ripple components from each phase cancel one another, which can reduce the total output ripple by a factor of 10 or more. 
     Further, regulation circuit  214  provides the feedback necessary for voltage regulation. The particular implementation of regulation circuit  214  can vary according to whether a voltage mode topology or a current mode topology is used. Example embodiments of regulation circuit  214  are described in greater detail below. 
     FIG. 3 represents an overall circuit layout for combining the circuit parts of FIGS. 3A-3F, such circuit illustrating a four-phase synchronous buck regulator  130 A according to an example embodiment of the present invention, where regulator  130 A is implemented on PU  126 . Interconnectable arrow heads (“&gt;&gt;”) are used to designate conduction paths which should be reconnected between the various circuit parts, while a smaller number of reconnectable conduction paths have been marked with matching encircled letters in neighboring circuit parts to help index and align the conduction paths which should be reconnected. A remainder of this disclosure should be taken as referring to the overall circuit in its assembled form, and the terminology “FIG.  3 ” may hereinafter be used to refer to the assembled overall circuit. Regulator  130 A receives input DC voltage  202 - 1  (+12 volts for the example shown in FIG. 3) and input DC voltage  202 - 2  (+5.6 volts for the examples shown in FIG.  3 ). The output voltage  212  terminal appears on the right-hand side of the overall figure. Example regulator  130 A can provide, for example, 60 amps of current to PU  126 . 
     According to an example embodiment of the present invention, regulator  130 A is implemented around a perimeter of a PU  126  chip. Also, thermal vias and a multiple layer copper plane are used to equally and quickly dissipate heat from the switching MOSFETs (within switching voltage converters  210 ) to the open air. As a result, heat sinks are not required for dissipating heat from the switching MOSFETs. 
     Pulse width modulator  204  can be implemented, for example, using Semtech&#39;s programmable, multi-phase, high performance PWM controller SC1146, and the supporting circuitry shown in FIG.  3 . The four switching signals  222  generated by the SC1146 are shown as pins Drv 0  through Drv 3 . 
     The example sequence timing control circuit  206  depicted in FIG. 3 includes resistors R 46  and R 48 , capacitors C 42  and C 44 , and diodes D 11 A, D 11 B, D 12 A, D 12 B, and D 13 A, configured as shown in FIG.  3 . Example values for the resistors and capacitors included within this example sequence timing control circuit  206  are shown in FIG.  3 . The diodes within this example sequence timing control circuit  206  can be implemented using Phillip Electronics&#39; diodes BAW 56 . For example regulator  130 A, the example sequence timing control circuit depicted in FIG. 3 insures that regulator  130 A operates correctly regardless of the sequence of input voltages  202 - 1  and  202 - 2 . 
     Each of the four drivers  208  can be implemented, for example, using SEMTECH&#39;s high speed synchronous power MOSFET smart driver SC1405, and the supporting circuitry shown in FIG.  3 . Each driver  208  receives a switching signal  222  generated by pulse width modulator  204 , and outputs the boosted signal at the pin labeled TG. 
     Switching voltage converters  210  are each implemented using similar parts. For example, switching voltage converters  210 - 1  includes diode D 3 , capacitors C 19 , C 20 , and C 23 , resistors R 20 , R 21 , and R 22 , MOSFETs Q 1  and Q 2 , and inductor L 1 , configured as shown in FIG.  3 . Example values for the resistors, capacitors, and inductor included within these example switching voltage converters  210  are shown in FIG.  3 . The diodes within these example switching voltage converters  210  can be implemented using MOTOROLA diodes MBRA13OLT3. The MOSFETs Q 1  and Q 2  can be implemented using INTERNATIONAL RECTIFIER&#39;S MOSFETs IRF7809/IRF7811. The inductor L 1  can be implemented using VISHAY&#39;s inductor IHLP 5050FD-01. 
     Note that many of the component depicted in FIG. 3 have a “x” followed by a number in close proximity to the component symbol. This indicates that the component is implemented using the stated number of duplicate components connected in parallel. For example, “x2” appears just above the label for capacitor C 40 . This indicates that C 40  represents two capacitors, each having a value of 1 μF, connected in parallel. 
     The outputs of switching voltage converters  210 - 1  through  210 - 4  are tied together to form output voltage  212 . FIG. 3 depicts an example output capacitance given by capacitors C 10 , C 11 , C 39 , and C 40 . 
     The example regulation circuit  214  depicted in FIG. 3 includes resistors R 69 , R 70 , R 73 , R 29 , and R 63 . The positive terminal of output voltage  212  is fed back to pin FB  14 , whereas the negative terminal is fed back to pin FBG  16 . The example regulation circuit  214  also includes an alternative feedback path indicated by VoSen(+) and VoSen(−), where these terminals represent remote sensing. 
     According to the example embodiment of the present invention, regulator  130 A can also include a droop circuit, an example of which is shown in FIG.  3 . This example droop circuit includes resistors R 43 , R 49 , R 50 , R 53 , R 54 , R 59 , R 55 , and R 56 , capacitor C 47 , op-amp U3A, and N-channel transistor Q 10 , configured as shown in FIG.  3 . Example values for the resistors and the capacitor included within this example droop circuit are shown in FIG.  3 . Op-amp U3A can be implemented, for example, using TEXAS INSTRUMENTS co-amp TL072. N-channel transistor Q 10  can be implemented, for example, using MOTOROLA&#39;s NPN transistor MMBT3904. 
     As described above, output voltage  212  for many applications must stay within a well defined range of acceptable values. In the example given above, output voltage  212  can vary from 0.96 volts to 1.85 volts, where 1.6 volts is the mean steady state output voltage, otherwise referred to herein as the voltage identification (V ID ) setting. However, the current requirements of PU  126  vary over time. For example, PU  126  can go from a stand-by mode, requiring from zero to a few hundred milliamps, to a power-on mode requiring 100 amps and above, and back to stand-by mode, all in the span of a single clock cycle. The step-up transition in the current load (i.e., from stand-by to power-on modes) causes a transitory dip in output voltage  212 . Conversely, the step-down transition in the current load (i.e., from power-on to stand-by modes) causes a transitory spike in output voltage  212 . In order to maintain proper operation, regulator  130  should insure that output voltage  212  remains within the defined range of acceptable values, even during dips and spikes due to step-up and step-down transitions. The magnitude of the dips and spikes can be lessened by adding additional output capacitance. 
     The droop circuit allows the circuit designer to program the V ID  setting of output voltage  212 . For the example droop circuit shown in FIG. 3, the V ID  setting is programmed by selecting particular values for resistors R 55  and R 56 . For example, the values shown for resistors R 55  and R 56  result in a droop voltage of 40 millivolts, i.e., the output voltage  212  is increased by 40 millivolts. This makes better use of the available range of output voltage because magnitude of the dip caused by the step-up transition is often larger than the magnitude of the spike caused by the step-down transition. In other words, by increasing the V ID  setting, dips due to the step-up transition are less likely to cross the lower acceptable boundary of output voltage  212 . And because the spikes due to step-up transitions are lower in magnitude relative to the dips, increasing the V ID  setting may not result in increased violations of the upper acceptable boundary of output voltage  212 . 
     By adding droop voltage to increase the V ID  setting, the number of capacitors that are required to control the magnitude of the step-up transition dips can be reduced. For example, where output voltage  212  is constrained to 1 volt±4%, adding a 40 millivolt droop reduces the amount of capacitance by 25 percent. 
     Further, the example droop circuit shown in FIG. 3 has the additional advantage of being very fast, which means that the droop circuit can respond quickly to AC transient load events and can provide the 40 millivolt drop voltage to the circuit. This increased speed results in better dynamic performance for regulator  130 A. 
     According to the example embodiment of the present invention, regulator  130 A can also include a current sharing circuit, an example of which is shown in FIG.  3 . This example current sharing circuit includes resistors R 60 , R 62 , and R 68 , capacitor C 48 , op-amp U 3 B, and diode D 14 A, configured s shown in FIG.  3 . Example values for the resistors and the capacitor included within this example current sharing circuit are shown in FIG.  3 . Op-amp U 3 B can be implemented, for example, using TEXAS INSTRUMENTS co-amp TL072. Diode D 14 A can be implemented, for example, using PHILLIPS ELECTRONICS diode BAW56. 
     The current sharing circuit insures that the current load is distributed evenly between multiple regulators  130 A that are connected together in parallel. The current sharing circuit therefore makes regulator  130 A scalable in the sense that multiple regulator modules can be combined to satisfy larger current requirements. Without the current sharing circuit, there is no guarantee that each regulator module will carry an equal portion of the total current load. This can result in particular modules carrying a load greater than they are designed for, which can damage the module. 
     According to the example embodiment of the present invention, regulator  130 A can also include an over-voltage protection circuit, an example of which is shown in FIG.  5 A. The overvoltage protection circuit monitors output voltage  212 , and halts operation of regulator  130 A if the output voltage crosses a certain threshold. This example over-voltage protection circuit includes resistors R 33 , R 34 , R 35 , and R 37 , capacitors C 37  and C 38 , reference Zener diode U 2  and a synchronous controlled rectifier SCR 1 , and P-channel transistor Q 9 , configured as shown in FIG.  5 A. Example values for the resistors and capacitors included within this example overvoltage protection circuit are shown in FIG.  5 A. Reference Zener diode U 2  can be implemented, for example, using Texas Instruments reference regulator TL431. Synchronous controlled rectifier SCR 1  can be implemented, for example, using Motorola rectifier 2N6504. P-channel transistor Q 9  can be implemented, for example, using Motorola P-channel transistor MMBT3906. The output voltage threshold is 2.098 volts for the example over-voltage protection circuit depicted in FIG.  5 A. 
     Very high frequency switching signals  220  can be achieved using the design of regulator  130 A according to the present invention. Prior regulators have achieved switching frequencies of approximately 250 kHz per phase (total of 1 MHz for a four phase design). Regulator  130 A can achieve at least a 1-2 MHz switching rate per phase (total of 4-8 MHz). This increased switching frequency is due, in part, to several factors: (i) the selection of fast drivers  208  with low output impedance and low input capacitance MOSFETs within switching voltage converter  210 , (ii) the decreased loop inductance (and therefore increased speed) resulting from moving regulator  130 A onto PU  126 , and (iii) the selection of high Q and low resistance output inductors within switching voltage converter  210 . The output inductors should be very small and very efficient in order to support the high switching rate of regulator  130 A. 
     Switching at high frequencies results in many benefits for regulator  130 A. As PU  126  power requirements increase, regulator  130 A must either switch faster or use larger components. Faster switching means that smaller capacitors can be used at the output of regulator  130 A, saving chip real estate and costs associated with the additional capacitive components. Also, regulator  130 A can respond more quickly to step-up and step-down transitions by PU  126 . Faster switching reduces the voltage dip associated with the step-up transitions. Another advantage is that regulator  130 A can be implemented using surface mount technology (SMT) rather than through-hole technology which is bulky and more difficult to manufacture. 
     In another example embodiment, the components within an area  1000  in FIG. 3E may be able to be omitted. Further, throughout the drawing pertaining to example circuits, any component having a designation “DNS” associated therewith may be omitted. 
     FIG. 4 represents an overall circuit layout for combining the circuit parts of FIGS. 4A-D, such circuit illustrating a four-phase synchronous buck regulator  130 B according to another example embodiment of the present invention, where regulator  130 B is implemented on interposer  122 . Again, just like with FIG. 3, interconnectable arrow heads and indexing encircled letters are used with respect to reconnectable conduction paths, and the terminology “FIG.  4 ” will hereinafter be used to refer to the assembled overall circuit. Regulator  130 B receives input DC voltage  202 - 1  (+12 volts for the example shown in FIG. 4) and input DC voltage  202 - 2  (+5.0 volts for the example shown in FIG.  4 ). The output voltage  212  terminal appears on the right-hand side of FIG.  4 . 
     According to an example embodiment of the present invention, regulator  130 B can provide output voltage  212  to multiple PUs  126  resident on motherboard  108 . The example regulator  130 B depicted in FIG. 4 is designed to supply a total of 120 amps of current to two PUs  126 . Those skilled in the art will recognize that the design of regulator  130 B can easily be extended to support more than two PUs  126 . 
     According to the example regulator  130 B embodiment, pulse width modular  204  can be implemented, for example, using INTERSIL&#39;s PWM controller HIP6301, in addition to the supporting circuitry shown in FIG.  4 . The HIP6301 has a built-in droop circuit, which operates in a manner similar to the droop circuit described above with respect to FIG.  3 . 
     The example sequence timing control circuit  206  depicted in FIG. 4 includes resistors R 198  and R 223 , capacitor C 101 , and diode CR 18 , configured as shown in FIG.  4 . This example sequence timing control circuit operates in a manner similar to that described above with respect to the example sequence timing control circuit depicted in FIG.  3 . Example values are shown in FIG. 4 for the resistors and capacitor included within this example sequence timing control circuit  206 . Diode CR 18  can be implemented, for example, using MOTOROLA diode IN4148. 
     The four drivers  208  can be implemented as described above with respect to FIG. 3, for example, using SEMTECH&#39;s high speed synchronous MOSFET smart driver SC1405, and the supporting circuitry shown in FIG.  4 . The switching voltage converter  210  within each phase are each implemented using similar parts. For example, switching voltage converter  210 - 1  as shown in FIG. 4 includes diode CR 3 , capacitors C 77 , C 94 , Cd, and C 227 , resistors R 37 , R 39 , R 77 , R 217 , R 52 , and R 106 , in MOSFETs Q 15  and Q 21 , and inductor L 5 , configured as shown in FIG.  4 . Example values for the resistors, capacitors, and inductor included within these example switching voltage converters  210  are shown in FIG.  4 . The diodes within these example switching voltage converters  210  can be implemented using MOTOROLA diodes MBRA130LT3. The MOSFETs switches can be implemented using INTERNATIONAL RECTIFIER&#39;s MOSFETs IRF7809/IRF7811. The inductors can be implemented using Vishay&#39;s inductor IHLP5050FD-01. 
     The outputs of switching voltage converters  210 - 1  through  210 - 4  are tied together to form output voltage  212 . FIG. 4 depicts an example output capacitance given by capacitors Ci, Cj, Ck, and Cl. 
     The example regulation circuit  214  depicted in FIG. 4 differs from the regulation circuit described above with respect to FIG. 3 in that regulator  130 B is implemented using a current mode topology, whereas regulator  130 A is implemented using a voltage mode topology. Current mode topologies require both voltage and current feedback, where voltage mode topologies require only voltage feedback. As shown in FIG. 4, voltage feedback is achieved by connecting output voltage  212  to the Vsen pin on the HIP6301 via a resistor R 222 . Current feedback is achieved by feeding back a current signal from each phase, shown as Isen 1  through Isen 4 , to the Isen 1  through Isen 4  pins on the HIP6301. 
     Though no current sharing circuit is shown in FIG. 3, such a circuit could be added to regulator  130 A in a manner similar to that described above with respect to regulator  130 B. Adding a current sharing circuit would make regulator  130 A scalable in the sense that multiple regulator modules could then be connected in parallel to support larger current loads. 
     According to the example embodiment of the present invention, regulator  103 B can also include an over-voltage protection circuit, an example of which is shown in FIG.  5 B. The over-voltage protection circuit operates in a manner similar to the circuit described above with respect to FIG.  5 A. This example over-voltage protection circuit includes resistors R 160 , R 161 , R 162 , R 163 , and R 164 , capacitors C 299  and C 303 , a reference Zener diode U 59  and synchronous controlled rectifier SC 26 , and a P-channel transistor Q 25 , configured as shown in FIG.  5 B. Example values for the resistors and capacitors included within this example over-voltage protection circuit are shown in FIG.  5 B. Reference Zener diode U 59  can be implemented, for example, using TEXAS INSTRUMENTS regulator TL431. Synchronous controlled rectifier SC 26  can be implemented, for example, using MOTOROLA rectifier 2N6504. P-channel transistor Q 25  can be implemented, for example, using any P-channel transistor MMBT3906. 
     Although the present invention has been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this invention. More particularly, reasonable variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the foregoing disclosure, the drawings and the appended claims without departing from the spirit of the invention. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art. 
     For example, while the above example discussions describe sequence timing control  206  and drivers  208  as being implemented using separate parts, the sequence timing control may instead be implemented within drivers  208  rather than as a separate circuit. For example, SEMTECH&#39;s multi-phase current mode controller with I-share bus SC 2424  includes a built-in sequence timing control circuit that operates in a manner similar to that described above with respect to FIGS. 3 and 4.