Abstract:
A method for operating a voltage regulator controller, for use in a voltage regulator including coupled inductors, is provided as follows. A first signal is generated for driving a first switch of the voltage regulator. A second signal is generated driving a first switch of the voltage regulator. The voltage regulator determines whether a light-load condition exists. Upon determining the existence of a light-load condition, adjusting the phase difference between said first and second signals so that the first and second signals are approximately in-phase.

Description:
CLAIM OF PRIORITY 
     This application is a reissue of U.S. application Ser. No. 12/952,954, filed on Nov. 23, 2010 now U.S. Pat. No. 8,125,207 issued Feb. 28, 2012, which is a continuation of U.S. application Ser. No. 12/192,234, (the &#39;234 application), filed Aug. 15, 2008 now U.S. Pat. No. 7,898,236 issued Mar. 1, 2011, which claims the benefit of priority of U.S. Provisional Applications, each respectively having Ser. Nos. 61/043,790 (filed Apr. 10, 2008) and 61/075,149 (filed Jun. 24, 2008)., both of which are herein incorporated by reference. 
    
    
     RELATED APPLICATIONS 
     This application is related to U.S. Applications, each respectively having Ser. No. 11/519,516 (filed Sep. 12, 2006), Ser. No. 12/136,014 (filed Jun. 9, 2008), Ser. No. 12/136,018 (filed Jun. 9, 2008), and Ser. No. 12/136,023, all of which are incorporated by reference. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One or more embodiments and features and benefits thereof may be understood upon review of the following detailed description together with the accompanying drawings, in which: 
         FIG. 1A  illustrates a schematic of an embodiment of a voltage regulator whose operation varies based upon load conditions. 
         FIG. 1B  illustrates a schematic of an alternate embodiment of a voltage regulator controller whose operation varies based upon load conditions. 
         FIGS. 2A-H  illustrates exemplary signal waveforms generated by the embodiment of the voltage regulator illustrated in  FIG. 1A . 
         FIG. 3  illustrates a system that may incorporate an embodiment of the voltage regulator whose operation varies based upon load conditions. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is presented to enable one of ordinary skill in the art to make and use one or more embodiments of the present invention as provided within the context of a particular application and its requirements. Various modifications to the disclosed embodiment(s) will, however, be apparent to one skilled in the art, and the general principles defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the particular embodiments shown and described herein, but is to be accorded the widest scope consistent with the principles and novel features herein disclosed. 
     Some voltage regulators (‘VRs’) convert a first DC voltage to a higher or lower second DC voltage. Such VRs may enhance conversion efficiency to reduce or eliminate wasted power. 
     It may be important to maintain high VR conversion efficiency under light-load conditions (i.e. when the load consumes relatively low power), e.g. to maintain battery life. VR efficiency under light-load conditions may be enhanced in different ways. 
     One technique for enhancing efficiency under light-load conditions is by ‘phase dropping,’ which is when a VR inactivates one or more phase(s) (i.e., make some phase(s) inactive) during light-load conditions. 
     Another technique to further enhance efficiency under light-load conditions is to implement the VR with a diode-emulation control (also referred to as synchronous rectification, or discontinuous conduction mode, or ‘DCM’, control). A DCM control circuit prevents sinking current, and removing energy, from the VR&#39;s capacitance  143  ( FIG. 1 ), Cout, during light-load conditions. This also may further improve VR conversion efficiency. One technique for implementing DCM control circuitry is illustrated in U.S. Pat. No. 6,643,145 (issued Jul. 26, 2002) which is hereby incorporated by reference. Other DCM control circuitry may be used; known conventional alternatives are not illustrated here for the sake of brevity. 
     To implement a DCM control scheme in a VR, the VR is provided a signal indicating that a light-load condition exists or will exist. In one embodiment, the load, e.g. a microprocessor, generates a power-state indicator (PSI#). For example, this may occur in an implementation of Intel Corporation&#39;s VR11 specification, e.g. VR11.1. The PSI# is provided to the VR controller to signify a light-load condition. The “#” symbol appended to a signal name denotes negative logic in which PSI#=logic 1 (asserted high) for normal operation, and PSI#=logic 0 (asserted low) for light-load conditions. The power-state indicator is analogous to the PSC signal described below. 
     Alternatively, the light-load condition may be determined by measuring the current to the load. The measured current is compared to a threshold current level. If the measured current is below the threshold current level, then an appropriate signal is generated and provided to the VR controller to indicate a light-load condition. 
     To further improve light-load efficiency, the VR may be implemented with coupled inductors, such as a two (2) phase VR with two (2) coupled inductors. Coupled-inductor VRs may also have the benefit of reducing the space occupied by such VRs in comparison to corresponding, non-coupled-inductor VRs. Coupled inductors are two or more inductors whose windings are magnetically coupled so that current flowing in one inductor affects the current flowing in one or more other inductors. For example, a pair of coupled inductors may be fabricated by winding two inductors about the same magnetic core. A magnetic core, however, is not required. The measure of coupling (or ‘mutual coupling’) between a pair of inductors is known as mutual inductance, M. 
     When a VR having a fixed PWM switching frequency (otherwise known as ‘FSW’) operates in DCM mode in the lightest-load conditions the energy supplied to the capacitance  143 , Cout, may become greater than the energy consumed by the load. In this case the controller will adjust and force the modulator to skip PWM pulses in some switching cycles. 
     In a two (2) phase pulse-width-modulation (‘PWM’) VR using coupled inductors and operating in a light-load condition, the drive signals for the two phases may be interleaved and approximately 180 degrees phase shifted from each other. This interleaving may reduce peak-to-peak current in each inductor, may reduce the magnitude of VR peak-to-peak output ripple current, and, therefore, may reduce the magnitude of VR output voltage ripple, reduce the capacitance  143 , Cout, or some combination of the foregoing. When the VR controller enters DCM and the load current reduces sufficiently to force the modulator to skip PWM pulses, the output ripple voltage may become erratic and increase beyond specified peak-to-peak limits. 
     The two interleaved coupled phases create inductor currents that do not have a singular triangular waveform (in one switching cycle) as is the case for a two-phase implementation using conventional (non-coupled) inductors. Rather, the two interleaved phases generate inductor currents with a wave form that has two peaks and two valleys during one switching cycle. 
     This inductor-current waveform may complicate the implementation of the DCM control circuitry and cause inaccurate zero current detection, in DCM and Continuous Conduction Mode (‘CCM’), and reduce efficiency in DCM operation. 
     The following describes an embodiment of a technique that may solve some or all of the foregoing problems. This embodiment may also reduce the magnitude of output voltage ripple under light-load conditions. 
       FIG. 1A  illustrates an embodiment of a Voltage Regulator (‘VR’)  100 , which includes a VR controller  110 , two driver circuits (‘drivers’)  120 ,  122 , two switches  130 ,  131  and  132 ,  133 , e.g., pairs of field effect transistors (‘FETs’), two inductors (L 1  and L 2 )  141 ,  142  that are coupled, output current sensors  151 ,  152 , a capacitance  143 , Cout, and other conventional components that are omitted for brevity. Each switch, alternatively, may be implemented by one or more of other devices, e.g., bipolar transistors, diodes, or combinations of a variety of devices; known conventional alternatives are not illustrated for the sake of brevity. The switches  131  and  133  are coupled to a DC supply voltage node  135 , Vin. The inductors  141 ,  142  and the capacitance  143  form a filter that may reduce either the magnitude of the Iload ripple in comparison to such ripple in a conventional non-coupled inductor VR or reduce the transient response at Vout in comparison to a conventional non-coupled inductor VR, or a trade off of some lesser reduction of both Iload ripple and the transient response at Vout. The process for designing such a filter and making such a trade-off is not disclosed for the sake of brevity. 
     A load  160  is coupled to the output  137  of the VR  100 . The load  160  may be one or more electrical devices, e.g. a processor, memory, bus, or the combination thereof. 
     The drivers  120 ,  122  provide an interface between the VR controller  110 , operating at relatively low voltage and current levels, and the switches  130 ,  132  operating at relatively high voltages and currents; the drivers  120 ,  122  permit the VR controller  110  to turn the switches  130 ,  132  on and off. The drivers  120 ,  122  also include circuitry to implement CCM and DCM operation based upon receiving the appropriate PWM signals  410 ,  420 , as is subsequently described. Exemplary drivers are Intersil Corporation&#39;s ISL6612, ISL6614, ISL6609, ISL6610, ISL6622, and ISL6620 drivers whose data sheets are herein incorporated by reference. 
     The generator and phase shift controller  114  may include one or more of the following: a signal generator, a phase shifter, and/or a switch. The implementation for the generator and phase shift controller is not illustrated for the sake of brevity. 
     The generator and phase shift controller  114  may generate analog ramp signal(s) provided to each PWM controller and are used to generate PWM signals. The generator and phase shift controller  114  may generate signal(s) other than analog ramp signal(s), e.g. digitized ramp signals; for the sake of brevity alternative signal wave forms are not illustrated herein. 
     As shown in  FIG. 1A , the VR controller  110  includes an error amplifier  112 , coupled to two PWM controllers  113 ,  115 . The VR controller  110  also includes a comparator  116  coupled to a generator and phase shift controller  114  and a summer  118 . The comparator  116  generates a PSC signal. The error amplifier  112  compares the voltage at the output  137  of the VR  100  to a reference voltage  145 , Vref. The output of the error amplifier  112 , which provides the COMP signal, is coupled to the two PWM controllers  113 ,  115 . The operation of the foregoing circuitry is described in U.S. patent application Ser. No. 11/318,081 (Filed May 17, 2006), which is hereby incorporated by reference. The VR controller has two outputs  170 ,  171  which respectively provide output signals, e.g. signals PWM 1  and PWM 2 , or just signal PWM 1  as is further discussed herein. The VR controller  110 , for example, may be implemented with Intersil Corporation&#39;s ISL6334 or ISL6336 PWM controllers or incorporate circuitry like that found in such controllers. The datasheets for such controllers are hereby incorporated herein by reference. 
     The output current, I 11  and I 12 , from each coupled inductor  141 ,  142  is measured by respective current sensors  151 ,  152 . The first and second current sensors  151 ,  152  measure the current respectively flowing through the first and second inductors  151 ,  152 . The current sensors  151 ,  152  may be implemented using a conventional DCR current sensing network. DCR current sensing is accomplished by measuring the DC voltage drop across a capacitor in series with a resistor; a series capacitor and resistor network is coupled in parallel with each inductor  140 ,  141 . The capacitor and resistor values are selected so that the voltage across the capacitor is in phase with, and has the same amplitude profile, as the current of the inductor across which the series capacitor and resistor network is in parallel. DCR current sensing, and an alternative current sensing using Rds (On), are further described in Intersil Corporation Data Sheet FN9098.5 (May 12, 2005) which is entitled “Multi-Phase PWM Controller with Precision Rds (On) or DCR Differential Current Sensing for VR 10.X Application,” which is incorporated by reference. 
     A first output current sensor  151  measures a first current flowing through inductor  141 . A second output current sensor  152  measures a second current flowing through inductor L 2   142 . The first and second current measurements are summed by summer  118  that provides a signal, Iout, representative of the current (Iload) flowing through the load  160 . 
     Signal Iout is then compared by comparator  116  with a threshold current level  139 , Ithreshold. During normal VR  100  operation, the level of signal lout is greater then the threshold current level  139  and the comparator  116  generates a phase shift control (PSC) signal waveform, e.g. with a zero volt level. Such PSC signal waveform causes the phase difference between PWM 1   113  and PWM 2   115  to be approximately one hundred and eighty degrees. However, in a light-load condition, the level of signal lout will be less then the threshold current level  139  and the comparator  116  generates a PSC signal waveform that causes the phase difference between PWM 1   113  and PWM 2   115  to change by approximately one hundred and eighty degrees. Hence, the resulting phase difference between PWM 1  signal  170  and PWM 2  signal  171  is approximately zero degrees. 
     Note, the threshold current level  139 , Ithreshold, may correspond to a very light-load condition rather then just a light-load condition. A very light load condition occurs when the value of Iload is less then the value of Iload at the light-load condition. Thus, the other light-load efficiency enhancement techniques mentioned herein may be used at light-load current levels above the threshold current level below which embodiments of the invention provide a benefit. 
       FIG. 2  illustrates exemplary waveforms  200  of signals generated by one embodiment of the multimode Voltage Regulator (“VR”)  100  of  FIG. 1A .  FIG. 2  illustrates the use of dual ramps (e.g. RAMP 1 A and RAMP 1 B  310 ,  312 ) to generate a PWM signal (e.g. PWM  1   410 ). This technique is also illustrated in U.S. patent application Ser. No. 11/318,081 (Filed May 17, 2006). Alternatively, other techniques for using one or more ramps to create a PWM signal may be used; known conventional alternatives are not illustrated for the sake of brevity. 
     During normal operation (or “first operating mode”) of the VR  100 , the PSC signal waveform  210  is in a low voltage state. As a result, the generator and phase shift controller  114  generates four ramp signals, RAMP 1 A, RAMP 1 B  310 ,  312  and RAMP 2 A, RAMP 2 B  320 ,  322 , where ramp signals RAMP 1 A and RAMP 2 A, and RAMP 1 B and RAMP 2 B are respectively out-of-phase, having approximately one hundred and eighty (180) degree phase difference. When the voltage level of the two sets of ramp signals  310 ,  312  and  320 ,  322  exceeds the voltage level at the Comp node, then PWM controllers  113 ,  115  generate PWM 1  and PWM 2  signals to have signal waveforms  410 ,  420  that are interleaved, i.e. approximately one hundred and eighty (180) degrees out of phase. The PWM signals  410 ,  420  operate the Drivers  121 ,  122  to turn the switches  131 ,  132  on and off in an alternating fashion. As a result the currents, I 11  and I 12 , flowing through coupled inductors  140  have waveforms  151 ,  152  that are also interleaved. Such interleaving desirably reduces the magnitude of the ripple of Vout as compared to any phase difference other than approximately 180 degrees. 
     In the illustrated embodiment of the invention, the PWM signals  410 ,  420  are tri-level to enable DCM through drivers  120 ,  122 . DCM is enabled through a driver only after the load current I 1 n of the corresponding phase transitions from a positive current to zero current, and the corresponding PWM signal is at its middle level. The zero level (e.g. zero volts) and high level (e.g. five volts) of the tri-level PWM signals  410 ,  420  instruct the drivers  120 ,  122  to operate in CCM. When the PWM 1  signal  410  is at zero level, the lower FET  130  is turned on. When the PWM signal is at a high level, the upper FET  131  is turned on. FETs  132 ,  133  operate in an analogous fashion based upon the level of PWM 1  signal  420 . Other techniques for activating DCM and CCM may be used; known conventional alternatives are not illustrated for the sake of brevity. Embodiments of the invention may also be used in coupled inductor voltage regulators that do not operate in DCM, i.e. that only operate in CCM. 
     Under a light-load condition, the interleaved signals waveforms of I 11   510  and I 12   520  may be undesirable because they create a more complex inductor current waveform (i.e. the signal waveforms of I 11 +I 12 ). Hence, implementation of diode emulation control circuitry and detection of zero current crossings may become more difficult. Also, the magnitude of the ripple on Vout may be undesirably increased. 
     Therefore, when a light-load condition occurs, such as at time T 1   222 , the PSC signal waveform  210  transitions to a high state. The PSC signal waveform  210  is provided to a generator and phase shift controller  114 . 
     Upon the PSC signal waveform  210  transitioning to a high voltage level representative of a light-load condition, the VR  100  enters a second operating mode. The generator and phase shift controller  114  shifts the phase difference between the RAMP 1 A and B, and RAMP 2 A and B waveforms  310 ,  320  by approximately one hundred and eighty (180) degrees. This is illustrated in  FIG. 2  at Time  220  T 1   222 . 
     This causes the PWM signal waveforms to shift by approximately one hundred and eighty (180) degrees so that the PWM signal waveforms  410 ,  420  are in phase, i.e., have a phase difference of approximately zero degrees. This is illustrated in  FIG. 2  at Time  220  T 1   222 . As a result the currents, I 11  and I 12 , flowing through coupled inductors  400  have waveforms  510 ,  520  that are also in-phase (i.e. have approximately zero degree phase difference) at Time  220  T 1   222 . 
     Because the inductor current waveforms  510 ,  520  after Time  220  T 1   222  are similar to those found in VRs employing non-coupled inductors, diode emulation control circuitry used in non-coupled inductor VRs may be used by the VR  100  during light-load operation. Also, detection of zero current crossings can more accurately be detected, in part due to reduced noise because of the more conventional current waveform. This results in enhanced VR efficiency. The magnitude of the ripple at Vout is also reduced under light-load conditions. 
     To further enhance the performance of the VR  100 , the current threshold level  139 , Ithreshold, may be modified to improve efficiency and minimize output voltage ripple. The value of the current threshold level  139 , Ithreshold, may be stored in memory (not shown), e.g. in the VR controller  110 . 
       FIG. 1B  illustrates an alternate embodiment of a multimode voltage regulator (“VR”) controller  110 . In this alternate embodiment, the generator and phase shift controller  114  is replaced by a generator  117 . Like the generator and phase shift controller  114 , the generator  117  generates signal(s), e.g., ramp signal(s). However, unlike a generator and phase shift controller  114 , the generator  117  does not perform phase shifting. Rather, as illustrated in  FIG. 1B , the phase is shifted by the use of a switch  119  coupled between the outputs of the PWM controllers  113 ,  115  and the VR controller outputs  170 ,  171 . 
     The alternate embodiment of the VR controller  110  includes a switch  119 , e.g. a single pole, double throw (“SPDT”) switch, coupled to the outputs of both PWM controllers  113 ,  115  and both drivers  120 ,  122 . The SPDT switch  119  may contain buffer and control logic circuitry. The output of comparator  116  is coupled to the SPDT switch  119 . One or more switch(es), e.g. SPDT or other configurations of poles and throws, may be required for VRs having more than two phases. 
     A change in the PSC signal, generated by comparator  116 , toggles the state of switch  119 . Under normal VR  100  operating conditions, the switch  119  couples the PWM 1  signal from the output of PWM controller  113  to the input of driver  120 , and couples the PWM 2  signal from the output of PWM controller  115  to the input of driver  122 . As a result, the PWM signals provided to drivers  120 ,  122  are dissimilar, and thus out-of-phase. 
     However, when the VR  100  operates under light-load conditions, the PSC signal toggles the switch  119  so that the PWM 1  signal from the output of PWM controller  113  is provided to the input of both drivers  120 ,  122 . The output of PWM controller  115  is terminated by a termination, e.g. a resistor, an open circuit or another impedance having resistive, capacitive, and/or inductive components. 
     As a result, the PWM signals provided to drivers  120 ,  122  are the same, and thus in-phase. The benefit of such in-phase signals is further described herein. 
     The PWM 2  signal from the output of PWM controller  115  is provided to neither driver  120 ,  122 . In another embodiment, the output of comparator  116  may also be coupled to PWM controller  115 . When the VR  100  operates under light-load conditions, the PSC signal would disable PWM controller  115 , e.g. turning it off, to further conserve power and reduce noise. 
     An embodiment of the present invention is applicable to VRs with N-coupled inductors, and with PWM VRs having fixed and variable frequencies. To maintain higher efficiency at lower loads, i.e. reduced VR power output, the PWM frequency may be reduced. PWM frequency, for example, may be adjusted by varying the frequency of RAMP 1  and RAMP 2  waveforms in the generator and phase shift controller. 
       FIG. 3  illustrates an exemplary system  300 , e.g. a computer or telecommunications system. An embodiment of the VR  100  of  FIG. 1  may be incorporated into the system  300 . The system  300  includes a power source  301  coupled to the VR  303 . The power source  301  may be a conventional AC to DC power supply or battery; other power sources may be used but are excluded for the sake of brevity. The load  160  may be one or more of a processor  305 , memory  309 , a bus  307 , or a combination of two or more of the foregoing. The processor  305  may be a one or more of a microprocessor, microcontroller, embedded processor, digital signal processor, or a combination of two or more of the foregoing. The processor  305  is coupled by a bus  307  to memory  309 . The memory  309  may be one or more of a static random access memory, dynamic random access memory, read only memory, flash memory, or a combination of two or more of the foregoing. The bus  307  may be one or more of an on chip (or integrated circuit) bus, e.g. an Advanced Microprocessor Bus Architecture (‘AMBA’), an off chip bus, e.g. a Peripheral Component Interface (‘PCI’) bus or PCI Express (‘PCIe’) bus, or some combination of the foregoing. The processor  305 , bus  307 , and memory  309  may be incorporated into one or more integrated circuits and/or other components. 
     Although one or more embodiments of the present invention have been described in considerable detail with reference to certain disclosed versions thereof, other versions and variations are possible and contemplated. For example, an embodiment may be implemented with more than two coupled inductors and phases. The capacitance  143 , Cout, may be implemented with one or more capacitors which, for example, can be leaded, leadless, or a combination thereof. Also, the circuits and/or logic blocks described herein may be implemented as discrete circuitry and/or integrated circuitry and/or software, and/or in alternative configurations. For example, additional components, e.g. the Drivers  120 ,  122  and switches  130 ,  131 ,  132 ,  133  may be integrated with the PWM controller into a single integrated circuits. Alternatively, a driver and a switch may be respectively be integrated into a single integrated circuit or package. Further alternatively, some components illustrated as being part of the VR controller  110  may be implemented discretely, i.e. not part of a PWM controller integrated circuit. The illustrated embodiments show VRs that are buck converters. Other embodiments of the invention may be implemented with other VR topologies, e.g. boost converters or buck-boost converters, a constant on time implementation, and combinations thereof. Finally, those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiments as a basis for designing or modifying other structures for carrying out the same purposes without departing from the spirit and scope of the invention.