PATENT DOCUMENT

Publication Number: US-10581330-B2
Application Number: US-201816002551-A
Country: US
Kind Code: B2

Title: Metered charge transfer assisted switching regulators

Abstract:
A power conversion circuit providing a regulated output voltage to a load can include a switching regulator with an input configured to be coupled to an input voltage source and an output configured to be coupled to the load. The power conversion circuit can further include a metered charge transfer converter, such as a charge pump or a switched or pulsed current source, having an input configured to be coupled to an input voltage source and having an output configured to be coupled to the load. A controller coupled to the metered charge transfer converter can be configured to operate the metered charge transfer converter to deliver energy to the load responsive to a dip of the regulated output voltage below a threshold caused by an increase in current drawn by the load. The metered charge transfer converter may be located closer to the load than the switching regulator.

Claims:
The invention claimed is: 
     
       1. A power conversion circuit comprising:
 a switching regulator having an input configured to be coupled to a switching regulator input voltage source and an output configured to be coupled to a load and provide a regulated output voltage to the load; 
 a metered charge transfer converter including a switched or pulsed current source or a charge pump having an input configured to be coupled to a metered charge transfer converter input voltage source and having an output configured to be coupled to the load; 
 a metered charge transfer converter controller coupled to the metered charge transfer converter and configured to operate the metered charge transfer converter to deliver energy to the load responsive to an increase in current drawn by the load. 
 
     
     
       2. The power conversion circuit of  claim 1  wherein the switching regulator comprises a magnetic element. 
     
     
       3. The power conversion circuit of  claim 2  wherein the magnetic element is an inductor. 
     
     
       4. The power conversion circuit of  claim 1  wherein the metered charge transfer converter is a non-magnetic converter. 
     
     
       5. The power conversion circuit of  claim 1  wherein the metered charge transfer converter controller is configured to operate the metered charge transfer converter to deliver energy to the load responsive to a dip of the regulated output voltage below a threshold. 
     
     
       6. The power conversion circuit of  claim 5  wherein the threshold is selected to prevent the regulated output voltage from decreasing below a minimum voltage specified for the load. 
     
     
       7. The power conversion circuit of  claim 1  wherein the metered charge transfer converter controller is configured to operate the metered charge transfer converter to deliver energy to the load responsive to a slew rate of the regulated output voltage above a slew rate threshold. 
     
     
       8. The power conversion circuit of  claim 1  wherein the load is a CPU or GPU. 
     
     
       9. The power conversion circuit of  claim 1  wherein the load is an SoC. 
     
     
       10. The power conversion circuit of  claim 1  wherein the switching regulator input voltage source and the metered charge transfer converter input voltage source are different voltage sources. 
     
     
       11. The power conversion circuit of  claim 10  wherein the metered charge transfer converter input voltage source is an output of a second switching regulator. 
     
     
       12. An integrated circuit comprising:
 an input configured to receive power from a regulated power source; 
 one or more metered charge transfer converter components, including at least a switched or pulsed current source or a charge pump, configured to receive power from the regulated power source and deliver power to at least one load within the integrated circuit responsive to an increase in current drawn by the load. 
 
     
     
       13. The integrated circuit of  claim 12  wherein the one or more metered charge transfer components are configured to deliver power to the load responsive to a voltage dip below a threshold. 
     
     
       14. The integrated circuit of  claim 13  wherein the threshold is selected to prevent the regulated output voltage from decreasing below a minimum voltage. 
     
     
       15. The integrated circuit of  claim 12  wherein the one or more metered charge transfer converter components are configured to deliver power to the load responsive to a slew rate of a regulated output voltage above a slew rate threshold. 
     
     
       16. The integrated circuit of  claim 12  wherein the one or more metered charge transfer converter components comprise one or more charge pump power switches and one or more charge pump control circuit elements. 
     
     
       17. The integrated circuit of  claim 16  wherein the one or more metered charge transfer converter components further comprise one or more charge pump capacitors. 
     
     
       18. The integrated circuit of  claim 12  wherein the one or more metered charge transfer converter components comprise a plurality of charge pumps, each charge pump dedicated to one of the at least one loads within the integrated circuit. 
     
     
       19. The integrated circuit of  claim 18  wherein the load is a CPU core or GPU core of the integrated circuit. 
     
     
       20. A power supply circuit comprising:
 a buck converter configured to receive power from a buck converter input power source and deliver a regulated output voltage to a load; 
 a charge pump configured to receive power from a charge pump input power source and deliver energy to the load responsive to an increase in current drawn by the load; 
 wherein the charge pump is located closer to the load than the buck converter. 
 
     
     
       21. The power supply circuit of  claim 20  wherein the charge pump is configured to deliver energy to the load responsive to a dip of the regulated output voltage below a threshold. 
     
     
       22. The power supply circuit of  claim 21  wherein the threshold is selected to prevent the regulated output voltage from decreasing below a minimum voltage specified for the load. 
     
     
       23. The power supply circuit of  claim 20  wherein the charge pump is configured to deliver energy to the load responsive to a slew rate of the regulated output voltage above a slew rate threshold. 
     
     
       24. The power supply circuit of  claim 20  wherein a switched capacitor of the charge pump has a value that is substantially less than an output capacitance of the buck converter. 
     
     
       25. The power supply circuit of  claim 24  wherein the switched capacitor of the charge pump has a value of about 1/200th the output capacitance of the buck converter.

Description:
BACKGROUND 
     Modern computing systems, particularly as used with mobile computing devices such as smartphones, tablet computers, laptop computers, etc. may operate in what may be characterized as a “bursty” mode. A bursty mode of operation means that computing element such as a central processing unit (CPU), graphics processing units (GPU), system on a chip (SoC), network adaptors, radios, and/or other components alternate between an idle state in which they draw very little power and a full load state in which they draw relatively high amounts of power. As a consequence of these rapid swings in power requirements, the currents drawn by processors may also experience large transients. These large transient currents can result in significant voltage dips in the power supplies that regulate the voltage delivered to such components. 
     For example, a buck converter is a commonly used switching power supply. In its simplest form, a buck converter steps down an input DC voltage to a lower, regulated level delivered to a load using a switch, a diode, an inductor, and an output capacitor. Large transient currents like those discussed above can significantly discharge the output capacitor of the buck converter, reducing the output voltage, more quickly than the switch can ramp up the current through the inductor to meet the instantaneous current demand of the load. As a result, the output voltage can dip below a minimum acceptable level for the load. 
     To mitigate or reduce this voltage dip, system designers have historically been forced to choose from among various power supply design techniques that have the undesirable side effect of reducing the overall efficiency of the power supply. For example, the voltage dip may be mitigated by selecting a steady state operating voltage that is sufficiently high that even a worst case voltage dip will still result in an output voltage that is above the minimum requirement for the load. However, many losses in such systems are proportional to the square of the voltage, so even a small increase in steady state operating voltage can have a significant increase on overall losses and overall system efficiency. Another alternative is to reduce the inductance of the converter. However, all else being equal, a reduced inductance may require that the inductor be operated at a higher frequency to achieve the same net energy transfer to the load. This higher operating frequency can undesirably impact switching losses, again reducing overall system efficiency. 
     Thus, what is needed in the art is a way to reduce the transient voltage dip associated with large changes in load on an inductor-based (i.e., magnetic) switching converter without causing an undesirable reduction in the system&#39;s efficiency. 
     SUMMARY 
     A power conversion circuit can include a switching regulator with an input configured to be coupled to a switching regulator input voltage source and an output configured to be coupled to a load and provide a regulated output voltage to the load. The power conversion circuit can further include a metered charge transfer converter having an input configured to be coupled to an input voltage source and having an output configured to be coupled to the load. A metered charge transfer converter controller can be coupled to the metered charge transfer converter and configured to operate the converter to deliver energy to the load responsive to a dip of the regulated output voltage below a threshold caused by an increase in current drawn by the load. The metered charge transfer converter may be located closer to the load than the switching regulator. In some embodiments the metered charge transfer converter may be a charge pump. In other embodiments, it may be a pulsed or switched current source. 
     The power conversion circuit may be a buck converter, a boost converter, or other type of switching regulator. The threshold may be selected to prevent the regulated output voltage from decreasing below a minimum voltage specified for the load. The load can be any type of electrical circuit, including a processing circuit such as a CPU or GPU or a system on a chip (“SoC”). The switching regulator input voltage source and the metered charge transfer converter input voltage source may be the same or different voltage sources, and the metered charge transfer converter input voltage source may be an output of a second switching regulator. In charge pump based embodiments, a switching capacitor of the charge pump may be selected so as to have a value that is substantially less than an output capacitance of the switching regulator, for example about 1/200th the output capacitance of the switching regulator. 
     In other embodiments, an integrated circuit can include an input configured to receive power from a regulated power source and one or more metered charge transfer converter components configured to receive power from the regulated power source and deliver power to a load within the integrated circuit responsive to a voltage dip of a power distribution network internal to the integrated circuit caused by an increase in current drawn by the load. The one or more metered charge transfer converter components can include one or more power switches, one or more control circuit elements, and may optionally further include one or more capacitors. In the case of multiple metered charge transfer converters, each converter may be dedicated to a load within the integrated circuit, for example, a CPU core or GPU core of the integrated circuit. The integrated circuit may be a CPU, GPU, or SoC. The metered charge transfer converter may be a charge pump or a switched or pulsed current source. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a switching regulator (buck converter) configured to deliver power to a load. 
         FIG. 2  depicts a series of current and voltage waveforms corresponding to certain operations of the load and switching regulator depicted in  FIG. 1 . 
         FIG. 3A  depicts a metered charge transfer converter assisted switching regulator (buck converter) configured to deliver power to a load in which the metered charge transfer converter is a pulsed current source. 
         FIG. 3B  depicts a metered charge transfer converter assisted switching regulator (buck converter) configured to deliver power to a load in which the metered charge transfer converter is a charge pump. 
         FIG. 4  depicts a series of current and voltage waveforms corresponding to certain operations of the charge pump assisted switching regulator depicted in  FIG. 1 . 
         FIG. 5  schematically depicts a charge pump controller of a charge pump assisted switching regulator like that illustrated in  FIG. 3 . 
         FIG. 6A  depicts a PCB layout. 
         FIG. 6B  depicts a PCB layout with a metered charge transfer converter assisted switching regulator located near the load in which the metered charge transfer converter is a charge pump. 
         FIG. 7A  depicts a metered charge transfer converter assisted switching regulator in which the metered charge transfer converter is a charge pump integrated with the load. 
         FIG. 7B  depicts a metered charge transfer converter assisted switching regulator in which a plurality of charge pumps are integrated with individual point loads within a SoC. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the disclosed concepts. As part of this description, some of this disclosure&#39;s drawings represent structures and devices in block diagram form for sake of simplicity. In the interest of clarity, not all features of an actual implementation are described in this disclosure. Moreover, the language used in this disclosure has been selected for readability and instructional purposes, has not been selected to delineate or circumscribe the disclosed subject matter. Rather the appended claims are intended for such purpose. 
     Various embodiments of the disclosed concepts are illustrated by way of example and not by way of limitation in the accompanying drawings in which like references indicate similar elements. For simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the implementations described herein. In other instances, methods, procedures and components have not been described in detail so as not to obscure the related relevant function being described. References to “an,” “one,” or “another” embodiment in this disclosure are not necessarily to the same or different embodiment, and they mean at least one. A given figure may be used to illustrate the features of more than one embodiment, or more than one species of the disclosure, and not all elements in the figure may be required for a given embodiment or species. A reference number, when provided in a given drawing, refers to the same element throughout the several drawings, though it may not be repeated in every drawing. The drawings are not to scale unless otherwise indicated, and the proportions of certain parts may be exaggerated to better illustrate details and features of the present disclosure. 
       FIG. 1  illustrates an exemplary system in which a switching converter  101  delivers power to a load  102  via leads  103 . Illustrated switching converter  101  is a buck converter, but other switching converter types may be used. In some embodiments, switching converter may be a magnetic-based switching converter, i.e., a converter in which there is a magnetic energy storage element such as an inductor, transformer, etc. For example, switching converter  101  may be a boost converter, a buck-boost converter, a Cuk converter, a forward converter, a flyback converter, etc. The buck converter receives input voltage Vin and operates switch Q 1  to deliver current through inductor L 1  to output capacitor Cout and load  102 . 
     More specifically, when switch Q 1  is closed, current flows from input voltage Vin, through inductor L 1 , to output capacitor Cout and load  102 . This current delivers energy to load  102  and also charges output capacitor Cout. While switch Q 1  is closed, diode D 1  is reverse biased by input voltage Vin. When switch Q 1  is opened, the current through inductor L 1  cannot change instantaneously, and thus current continues to flow through L 1  to load  102 . However, this current will decay as energy is drawn from inductor L 1 . If the decaying inductor current is insufficient to provide the energy required by the load, output capacitor Cout will also discharge into load  102 , reducing the output voltage. The return current path to inductor L 1  passes through diode D 1 , which is no longer reverse biased once switch Q 1  opens. 
     Controller  104  monitors output voltage Vout and controls switch Q 1  accordingly, using any of a variety of known control techniques. For example, controller may monitor output voltage Vout and compare it to a reference voltage Vref. If Vout&lt;Vref, controller  104  may operate switch such that more energy is transferred from input voltage source Vin to load  102 , e.g., by increasing a duty cycle or switching frequency of switch Q 1 . Conversely, if Vout&gt;Vref, controller  104  may operate switch such that less energy is transferred from input voltage source Vin to load  102 , e.g., by decreasing a duty cycle or switching frequency of switch Q 1 . Various control strategies to accomplish this type of operation are known. In fact, one may purchase a variety of ready-made buck converter controllers from a variety of silicon vendors. 
       FIG. 2  illustrates various waveforms associated with a step load current increase of load  102  in the system of  FIG. 1 . More specifically, waveform  202  represents the current flowing through inductor L 1  (denoted I(L 1 )). The centerline of the illustrated waveform illustrates the average load current, which starts at a current I 0  and increases to I 1  shortly after time t 1  due to a load step. Shortly before time t 4 , the load current decreases from I 1  back to current I 0 . The oscillating portion of inductor current I(L 1 ) is a function of the switching of main switch Q 1  as described above. 
     As alluded to above, load  102  may be a computing component such as a CPU, GPU, SoC, etc., or may be another component of an electronic device, such as a display, radio for WiFi, cellular, Bluetooth, or other data communication, etc. A load step such as that illustrated may occur as the result of a user-initiated event, a system-initiated event, or a combination of the two. For example, a user picking up a mobile telephone may be detected by an accelerometer that triggers the display to come on. Clicking on a link in a web browser may cause the radios to be activated to download the requested content and also cause the CPU and GPU to render the content for display. As another example, an incoming notification may trigger activation of the display, a loudspeaker, etc. as well as a CPU/GPU/etc. to communicate the incoming notification to the user. In any case, load  102  may transition from a first, relatively lower power state to a second, relatively higher power state—or vice-versa—as a function of the particular system and its implementation. 
     The lower portion of  FIG. 2  illustrates voltages corresponding to the load step current discussed above. Constant DC voltage  201  is a minimum target voltage that may correspond to a minimum permissible voltage for the load. As an example, CPUs, GPUs, SoCs, etc. often specify a minimum voltage below which the processor will operate erratically or stop operating entirely. Thus, it may be incumbent on a system designer to ensure that even a worst-case transient event does not take the output voltage below this level. 
     Voltage waveform  203  is the output voltage Vout corresponding to the load current  202  discussed above. Thus, when load current  202  increases from I 0  to I 1  just after time t 1 , output voltage  203  experiences a corresponding dip  204  having magnitude ΔV. This voltage dip occurs as buck converter  101  attempts to maintain Vout in regulation, however, the converter&#39;s transient performance is limited by the rate at which inductor current I(L 1 ) can slew. As illustrated, Vout eventually recovers to the nominal V 0  level. However, when the load current drops back from I 1  to I 0  just before time t 4 , voltage  203  experiences an overshoot  205 , again caused by the limited current slew rate of inductor L 1 . 
     Voltage dip  204  may be problematic for some loads, depending on their specification. As can be seen, the ΔV magnitude of voltage  203  takes it below the minimum voltage  201 /Vmin for the load. Depending on the nature of load  102 , this voltage dip might be unacceptable. Thus, a system designer would be forced to somehow modify the implementation of buck converter  101  to prevent this unacceptable voltage dip  204 . As discussed above, one approach would be to shift the steady state operating voltage V 0  upward, so that the voltage drop ΔV resulted in voltage waveform  203  remaining above minimum voltage  201  at all times. This may be undesirable because of an increase in leakage losses, which are proportional to the square of the average voltage. Alternatively, another approach would be to decrease the size of inductor L 1 , so that the current I(L 1 ) can slew faster. However, this would require an increased switching frequency to deliver the same amount of power/energy to the load, and this increased switching frequency would result in increased losses. Both forms of increased losses are undesirable for mains-powered systems, but become even more undesirable in battery-powered systems, in which such increased losses can have a significant adverse impact on device run time available from the battery. 
       FIGS. 3A and 3B  illustrate power supply systems incorporating a switching regulator  101  (in this case a buck converter like that described above) and a metered charge transfer converter  301  configured to power a load  102 . In the embodiment of  FIG. 3A , the metered charge transfer converter is a switched or pulsed current source  301   a . In the embodiment of  FIG. 3B , the metered charge transfer converter is a charge pump  301   b . A desirable characteristic of the metered charge transfer converter is that it be capable of rapidly delivering a precisely controlled (i.e., metered) amount of charge (energy) to the output of the switching regulator. The illustrated power supply system may be used to reduce the transient voltage dip associated with a rapid step increase in load current by load  102 . 
     Although the following description primarily refers to the particular buck topology and charge pump topology illustrated in  FIG. 3B , it will be appreciated that other switching converter types and configurations, as well as other metered charge transfer converter circuit configurations could be used in the same manner. As will become more apparent below, in some embodiments it may be desirable for the metered charge transfer converter to be constructed as a non-magnetic converter (i.e., lacking a magnetic energy storage element such as an inductor, transformer, etc.). One potential advantage of a non-magnetic metered charge transfer converter can be decreased physical volume, as the energy density of capacitive energy storage elements may be higher than the energy density of inductive energy storage elements. Another potential advantage of a non-magnetic metered charge transfer converter is that its components may be built as part of an integrated circuit, and particularly may be built into the integrated circuit of a load, such as a CPU, GPU, SoC, etc. 
     With reference to  FIG. 3A , metered charge transfer converter  300  is embodied as a switched or pulsed current source that includes a current source  303  and a switching device  305  that may selectively couple current source  303  to load  102 . Metered charge transfer converter  300  receives input voltage Vin via input voltage rail  302 . In the illustrated embodiment, charge pump  301  is coupled to the same input source as buck converter  101 , though it could alternatively have its own independent input source. Switch  305  may be selectively operated by a controller  306  to close the switch responsive to a voltage dip, increased current, or a slew rate (i.e., derivative) or integrated output voltage or current at the output of switching converter  101 . Because the current output by current source  303  is substantially constant, the amount of time that switch  305  is closed will determine the amount of charge (energy) that is transferred to the load (and/or switching regulator  101 &#39;s output capacitor Cout). Thus, switch timing (under the direction of controller  306 ) can result in a transfer of a metered amount of charge (energy) to the load and/or output capacitor Cout. 
     With reference to  FIG. 3B , metered charge transfer converter  300  may be implemented as a charge pump  301 . Charge pump  301  includes a charge pump capacitor Cp (i.e., a switched capacitor), four switching devices S 1 -S 4 , and a charge pump controller  304 . The charge pump receives input voltage Vin via input voltage rail  302  coupled to switches S 1  and S 4 . In the illustrated embodiment, charge pump  301  is coupled to the same input source as buck converter  101 , though it could alternatively have its own independent input source. Input voltage rail  302  is coupled to the drain terminals of MOSFET switches S 1  and S 4 , though other switching device types could be used. Charge pump capacitor Cp is coupled between the source terminals of switches S 1  and S 2 . Additionally, drain terminals of switches S 2  and S 3  are coupled to charge pump capacitor Cp and to the source terminals of switches S 1  and S 4 . A source terminal of switch S 2 , which is the output of charge pump  301 , is coupled to the output terminal of buck converter  101  and load  102 . A source terminal of switch S 3  is coupled to ground. Finally, the output voltage terminal of buck converter  101  is coupled to the charge pump controller  304 , which also has gate drive connections to switches S 1 -S 4 . 
     An exemplary embodiment of charge pump controller  304  is discussed in greater detail below with respect to  FIG. 5 . Functionally, charge pump  301  may operate as follows. Switches S 1  and S 3  may be closed, which charge capacitor Cp to a voltage Vin. Switches S 1  and S 3  may then be opened, with charge pump capacitor Cp remaining charged. If load  102  exhibits a step load that causes voltage Vout to drop below a threshold determined by charge pump controller  304 , switches S 2  and S 4  may be closed, which allows charge pump capacitor to discharge into load  102  and/or buck converter output capacitor Cout, minimizing the voltage dip associated with the step load. Waveforms associated with the operation of the system illustrated in  FIG. 3B  are illustrated in  FIG. 4 . The same basic operating principles apply to the controller  306  of  FIG. 3A . 
     In other embodiments, charge pump controller may charge the output based on other parameters instead of or in addition to the dip of output voltage Vout below a threshold. For example, a band pass filtered slope detection on the output voltage may be used to trigger the charge pump. When output voltage Vout slews down too fast (i.e., faster than a predetermined rate threshold), charge pump  301  may be configured to inject charge into the buck converter output capacitor Cout using switches S 2  and S 4 . As the output voltage recovers, and the slope turns shallow, controller  304  may stop firing the charge pump (stopping the charging of the output) by opening the switches S 2  and S 4 . More generally, charge pump  301  may be triggered (by controller  304 ) to charge the output in response to one or more parameters including output voltage, output slew rate, voltage error, and/or an integrated value of one or more of these parameters. In other words, the charge pump may be controlled using any proportional, integral, and/or derivative (PID) controller responding to any parameter characterizing the output of the circuit. Although the following examples focus on the case in which the charge pump is controlled responsive to the output voltage, it is to be understood that any combination of the foregoing parameters could also be used as controller inputs. Again, the same principles may be employed with respect to controller  306  of  FIG. 3A . 
     With reference now to  FIG. 4 , waveform  402  represents the current flowing through inductor L 1  (denoted I(L 1 )). The centerline of the illustrated waveform illustrates the average load current, which starts at a current I 0  and increases to I 1  shortly after time t 1  due to a load step. Shortly before time t 4 , the load current decreases from I 1  back to current I 0 . The oscillating portion of inductor current I(L 1 ) is a function of the switching of main switch Q 1  as described above. Current waveform  402   b  is the load current I(I 1 ), which exhibits the type of step operation described above. 
     The lower portion of  FIG. 4  illustrates voltages corresponding to the load step current discussed above. Constant DC voltage  401  is a minimum target voltage that may correspond to a minimum permissible voltage for the load. Voltage waveform  403  is the output voltage Vout corresponding to the load current  402  discussed above. Thus, when load current  402  increases from I 0  to I 1  just after time t 1 , output voltage  403  experiences a corresponding dip  404  having magnitude ΔV. This voltage dip occurs as buck converter  101  attempts to maintain Vout in regulation. As before, the converter&#39;s transient performance is limited by the rate at which inductor current I(L 1 ) can slew. However, because charge pump  301  detects a dip of output voltage Vout below a predetermined threshold, it can discharge its capacitor Cp (one time or many times) to help support the output voltage. As a result, the voltage dip ΔV is minimized. 
     As illustrated, Vout eventually recovers to the nominal V 1  level. However, when the load current drops back from I 1  to I 0  just before time t 4 , voltage  403  experiences an overshoot  405 , again caused by the limited current slew rate of inductor L 1 . Charge pump  301  may be configured and operated to absorb some of this excess energy from buck converter inductor L 1 , minimizing the voltage overshoot  405 . 
     As can be seen in  FIG. 4 , because charge pump  301  is available to support output voltage Vout, the steady state operating voltage V 1  can be much closer to minimum acceptable output voltage Vmin. This can substantially improve the operating efficiency of a system such as that illustrated in  FIG. 3  as compared to the arrangement illustrated in  FIG. 1 . For example, leakage losses are proportional to the square of the voltage, so a 10% reduction in steady state operation voltage (e.g., from V 0  illustrated in  FIG. 2  to V 1  illustrated in  FIG. 4 ) can result in a 20% improvement in leakage losses. By comparison, substantial engineering efforts, and sometimes also substantially increased costs, are required to provide even a 1% efficiency improvement in conventional inductor-based switching regulators. Thus, providing a charge pump in tandem with an inductor-based switching regulator can provide substantially improved efficiency. 
     To understand the synergistic benefits of metered charge transfer converter assisted switching regulators, it is useful to consider the differences between the exemplary magnetic (i.e., inductor-based) switching regulators and the exemplary charge pumps. As compared to charge pumps (or other forms of non-magnetic metered charge transfer converters), magnetic switching regulators may be more efficient for a given power level. However, as discussed above, magnetic switching regulators may have less rapid transient response, unless the inductor sizes are reduced and switching frequencies are increased, which negates some of their efficiency advantage. Conversely, as compared to magnetic switching regulators, charge pumps (or other forms of metered charge transfer converters, including non-magnetic metered charge transfer converters) may be less efficient for a given power level. However, charge pumps can have extremely rapid response times. By providing a magnetic switching regulator and fast operating metered charge transfer converter, such as a charge pump, operating in tandem, the steady-state efficiency advantages of the magnetic switching regulator may be realized in steady state operation. In these steady state conditions, the charge pump (or other metered charge transfer converter) need not be in operation, thus overcoming its efficiency disadvantage. However, when a large load transient necessitates improved transient response, the advantages of the charge pump (or other fast operating metered charge transfer converter) may be realized, without significant efficiency penalty because of the limited amount of time that the charge pump is in operation. 
       FIG. 5  schematically illustrates an embodiment of charge pump controller  304 . Output voltage Vout ( FIG. 3B ) is provided to one input of comparator  501 . A reference voltage source  502  provides a reference voltage Vref to the other input of comparator  501 . This reference voltage is the reference voltage that will trigger discharge of charge pump capacitor Cp to the output terminal of buck converter  101  and load  102 . Thus, Vref should be selected to be sufficiently below the nominal operating output voltage of switching regulator  101  that the charge pump will not fire unnecessarily, i.e., for load transients that are within the ability of switching regulator  101  to maintain sufficient output regulation. However, Vref must be selected to be sufficiently above the minimum operating voltage of the load (Vmin) that the charge pump will have sufficient time and energy delivery capability to prop up output voltage Vout before the load transient causes output voltage Vout to dip below Vmin. 
     Whenever Vout dips below the reference voltage Vref, the output of comparator  501  will transition high, which activates the “set” or S terminal of flip flop  503 . This causes the “output” or Q terminal of flip flop  503  to transition high. The output terminal Q of flip flop  503  may be the signal (Droop) that triggers switches S 4  and S 2  to turn on, allowing charge pump capacitor Cp to discharge, delivering energy to load  102  and/or switching regulator  101 &#39;s output capacitor Cout. The Droop signal may also be provided to inverter  504 , which creates the inverse signal DroopB, which may be the signal used to trigger switches S 1  and S 3  to turn on, charging charge pump capacitor Cp. This DroopB signal may also be passed through delay element  505  and returned to the “reset” terminal R of flip flop  503 . Delay  505  may be configured to allow sufficient time for the discharge of charge pump capacitor Cp before resetting flip flop  503 , which de-asserts the droop signal, causing DroopB to go high, allowing the charge pump to recharge. If Vout is still less than Vref, the cycle will repeat, continuing to charge/discharge charge pump  301  until the output voltage is above Vref. (It should be understood that additional circuit elements, such as additional delays, gate drive circuitry for switches S 1 - 24 , etc., may be required in a given implementation. The selection and/or design of these components is within the abilities of the ordinarily skilled artisan having the benefit of this disclosure.) 
     Additional design considerations may be addressed in the design of charge pump  301 . One such consideration is the size (i.e., capacitance value) of charge pump capacitor Cp. The size of this capacitor, together with, the input voltage Vin supplied to charge pump  301  will determine the amount of energy that can be delivered to load  102  with each firing of the charge pump, as well as the amount of time required to charge and discharge the charge pump. The inventors have determined that capacitor Cp may have a capacitance that is substantially less than the output capacitance of switching regulator/buck converter  101  (Cout). Specifically, in some embodiments Cp may be about 1/200 th  the value of Cout. That said, Cp may, depending on system requirements and desired operation, be in a range of 1/10 th  the value of Cout to 1/1000 th  the value of Cout. In some embodiments, even relatively smaller capacitance values for Cp may be used. 
     Another design consideration, which is related to the capacitance value of charge pump capacitor Cp, is amount of energy that will be transferred with each firing of the charge pump and the number of firings that will be expected for a given transient. To address this consideration, it is useful to further consider that the converter system illustrated in  FIG. 3B  is intended to have the switching regulator/buck converter  101  operate as the primary source of regulation for output voltage Vout, with charge pump  301  only providing assistance with transients as required. Thus, it may be advantageous to avoid a situation in which charge pump  301  delivers sufficient energy to completely meet the transient requirements of load  102 , as this could cause the controller of switching converter/buck regulator  104  to “give up” and allow the charge pump to take over. (This condition could incur a significant efficiency penalty as well as lead to system stability issues.) In an even more severe case, if the charge pump delivered more than the transient requirements of the load, output voltage Vout would go above the setpoint/reference voltage used by controller  104 , causing switching regulator/buck converter  104  to reduce the amount of power delivered to the load. This would be counterproductive, as the switching regulator and charge pump would end up fighting one another. 
     Thus, in some embodiments, it may be desirable to have charge pump  301  deliver relatively small amounts of energy, and fire multiple times in response to a given transient, rather than deliver a single, decisive large pulse in response to such a transient. This consideration, in part, drives the relatively small capacitance values of charge pump capacitor Cp relative to switching regulator/buck converter  101 &#39;s output capacitor Cout as discussed above. In such a system, multiple, rapid operations of charge pump  301  will assist switching regulator  101  with maintaining output regulation, while still allowing controller  104  to see an error signal of sufficient magnitude and correct direction that it continues to “pull the laboring oar” with respect to maintaining output regulation. As a further extension of this idea of providing many rapid but small bursts of energy from the charge pump to assist the switching regulator, it may be desirable to have more than one charge pump assisting a switching regulator. In such an embodiment, the charge pumps may be operated alternately, or even simultaneously to assist in reducing voltage dips as described above. Construction of such multi-charge pump systems follows the basic principles outlined above, and would be within the capabilities of an ordinarily skilled artisan having the benefit of this disclosure. 
     Still another consideration is the source of the input voltage for charge pump  301  (or switched or pulsed current source  300 ). In the embodiments of  FIGS. 3A and 3B , switched or pulsed current source  300  and charge pump  301  are illustrated as receiving the same unregulated input voltage Vin as switching regulator/buck converter  101 . However, it may be desirable for the metered charge transfer converters  300 ,  301  to receive as their input voltage the regulated output voltage of a separate converter. In the charge pump based embodiment of  FIG. 3B , the voltage to which charge pump capacitor Cp is charged, and thus the energy that is delivered to load  102  with each firing of the charge pump, is directly related to this voltage. Similarly, maintaining current source  303  at a constant current is more challenging of it does not receive a well-regulated input voltage. Thus, in either case, control of the system becomes more complex if the input voltage of the metered charge transfer converter is not sufficiently tightly regulated. Thus, providing an additional regulator for the metered charge transfer converter&#39;s input voltage may lead to improved system operation. This additional regulator may be any of a variety of types. For example, a separate buck regulator, boost regulator, buck-boost regulator, or other regulator type may be provided depending on the system design and the ultimate power source of the system. 
     A metered charge transfer assisted switching converter may be advantageously employed as part of a point of load regulator system. Point of load regulators place the converter/regulator components in close physical proximity to the load to be supplied. This arrangement can reduce or eliminate the voltage drop and other undesirable electrical effects caused by the parasitic properties (resistivity and parasitic inductance and/or capacitance) of relatively long electrical connections (wires, PCB traces, etc.) between the converter/regulator and its load. While point of load regulators have been a known solution to provide improved voltage regulation, packaging constraints with many modern compact electronic devices sometimes make it impractical or impossible to locate converter/regulator components near their load. This may be especially true with respect to magnetic components, such as inductors, coupled inductors, transformers, because they may be much larger than other circuit components. However, a metered charge transfer assisted switching converter may overcome this issue by locating the magnetic-based switching converter farther away from the load, but locating the metered charge transfer converter (which may be made up only of relatively more compact switches and capacitors) located nearer the load. 
     A example of such an arrangement, using a charge pump for the metered charge transfer converter, is illustrated in  FIGS. 6A and 6B .  FIG. 6A  is a simplified diagram of a printed circuit board  601 . Disposed on printed circuit board  601  is a switching regulator  602  that powers a load  603  via a power distribution network  604 . Switching regulator  602  may be any of a variety of types of switching regulators, such as a buck converter, boost converter, buck-boost converter, etc. Load  603  may be any of a variety of electronic devices, circuits, processors, etc. In some embodiments Load  603  may be a CPU, GPU, SoC, or other electronic device that exhibits significant step load behaviors. Load  603  may also be connected to external device  605  via connection  608 , which is in turn connected to device  606  via connection  607 . Devices  605  and  606  may also be located on printed circuit board  601 . Interconnections  607  and  608 , as well as power distribution network  604  may take the form of traces on the printed circuit board. In alternative embodiments, these may be wires or other known means for providing electrical connections between electronic devices. 
     As depicted in  FIG. 6A , design considerations for the layout of printed circuit board  601  may result in switching regulator  602  and load  603  being located some distance from one another. These design considerations could include physical arrangement or spatial requirements of the overall electronic device in which printed circuit board  601  is located, electromagnetic interference issues, or other considerations. In any case, the result is that power distribution network  604  requires a longer path than if load  603  and switching regulator  602  were located in closer physical proximity. As a result, the resistance of power distribution network  604  may be increased, and there may be parasitic inductances and/or capacitances associated with the physical structure of power distribution network  604 . These electrical properties may exacerbate a voltage dip associated with a step load increase in the power requirements of load  603 . As a consequence, switching regulator  602  may need to be configured to operate at a higher steady state voltage to prevent the voltage at load  603  from dropping below a specified minimum value. This can have the undesirable efficiency effects described above. 
       FIG. 6B  illustrates a similar arrangement in which switching regulator  602  is assisted by a charge pump  612 , which is located physically closer to load  603  than switching regulator  602  is. (It will be appreciated that charge pump  612  could alternatively be another type of metered charge transfer controller, such as the switched or pulsed current source discussed above.) Charge pump  612  may be configured to operate in conjunction with switching regulator  602  as described above. Locating charge pump  612  closer to load  603  may be feasible because charge pump  612  may composed of switching devices and capacitors, which tend to be more compact for a given power or energy handling level than inductors or magnetic components. In some cases, EMI considerations may also allow for placing the switching devices and capacitors of charge pump  612  closer to load  603 . In any event, the effect of locating charge pump  612  closer to load  603  than switching regulator  602  is to load  603  is that charge pump  612  can quickly respond to load transients as described above preventing the voltage seen at load  603  from dropping below a specified minimum value. 
     In some embodiments, it may be desirable to integrate a charge pump (or other metered charge transfer converter) configured to assist a switching regulator within a load itself. As an example, charge pumps are made up of switching devices (both for the power switches and control logic) and capacitances. These structures may be readily constructed as part of an integrated circuit that makes up a CPU, GPU, SoC or other integrated circuit load.  FIG. 7A  illustrates such an embodiment, which is similar to that illustrated in  FIG. 6B , except that charge pump  712  has been integrated within load  603 . Depending on the specific requirements and implementation, all of charge pump  712  may be integrated within load  603 , or only the switching components (i.e., the power switches and controller) may be integrated within load  603 , with the charge pump capacitor being external to load  603 . In either case, the charge pump may receive power from an input voltage source, such as a switching regulator, located outside the integrated circuit, via an input power pin of the integrated circuit. The charge pump may be configured to deliver power to one or more circuits within the integrated circuit, including one or more processing circuits, such as a CPU or GPU, or other types of circuits that may experience significant step load changes in operation. Similar principles apply to other types of metered charge transfer converters. 
       FIG. 7B  illustrates a further variation on the embodiment of  FIG. 7A , in which load  603  can have multiple charge pumps (or other metered charge transfer converters) integrated within load  603  to prevent localized dips within the load itself.  FIG. 7B  is a simplified block diagram of an SoC  720 . SoC  720  includes a multi-core CPU  722 , a multi-core GPU  724 , an I/O controller  726 , and cache memory  728  all interconnected by communication busses  730 . It is understood that a real-world SoC implementation may include more components and more complex arrangements, but the foregoing description is simplified for the purposes of illustrating the use of a metered charge transfer assisted switching converter integrated with an SoC. To that end, a number of charge pumps  734  are used to couple the on chip power distribution network  732  to some of the individual loads within the SoC, in the illustrated example each core of CPU  722  and each core of GPU  724 . The charge pumps  734  may cooperate with a switching regulator located off chip (to which SOC  720  is coupled via the off chip PDN). Because a charge pump (or other metered charge transfer converter) is located in close proximity to a number of distinct loads within the SoC, e.g., the CPU cores and the GPU cores, the charge pumps can also help to avoid voltage dips caused by the parasitic impedances of the on chip power distribution network (PDN). This can extend the advantages discussed above to the on chip PDN as well. 
     Described above are various features and embodiments relating to power converters incorporating charge pump assisted switching regulators. Such converters may be used in a variety of applications, but may be particular advantageous when used in conjunction with point of load regulators, on-chip regulators, and/or other power supply solutions for use in conjunction with portable electronic devices such as mobile telephones, smart phones, tablet computers, laptop computers, media players, and the like, as well as the peripherals associated therewith. Such associated peripherals can include input devices (such as keyboards, mice, touchpads, tablets, microphones and the like), output devices (such as headphones or speakers), combination input/output devices (such as combined headphones and microphones), storage devices, or any other peripheral. 
     Additionally, although numerous specific features and various embodiments have been described, it is to be understood that, unless otherwise noted as being mutually exclusive, the various features and embodiments may be combined in any of the various permutations in a particular implementation. Thus, the various embodiments described above are provided by way of illustration only and should not be constructed to limit the scope of the disclosure. Various modifications and changes can be made to the principles and embodiments herein without departing from the scope of the disclosure and without departing from the scope of the claims.

Metadata:
Filing Date: 20180607
Publication Date: 20200303
Grant Date: 20200303
Priority Date: 20180307
Inventors: LEE, DAMON
LANGLINAIS, JAMIE L.
AUDY, JONATHAN M.
YOSHIMOTO, MARK A.
PAUL, RAJARSHI
HOUK, TALBOTT M.
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F1/26", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/156", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/07", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/16", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02M3/156", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/28", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02M3/07", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/16", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02M3/07", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02M3/1566", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02M3/1566", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 67842112