Patent Publication Number: US-2022224219-A1

Title: Mitigation of battery output voltage ripple under pulse load

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 63/137,485, filed Jan. 14, 2021, entitled “Mitigation of Battery Output Voltage Ripple Under Pulse Load,” the disclosure of which is incorporated by reference in its entirety for all purposes. 
    
    
     BACKGROUND 
     Battery powered electronic devices may take a variety of forms, such as a smartphone, tablet computer, laptop computer, smart watch, etc. Such devices may include various electronic subsystems, including processing subsystems, communication subsystems, display sub systems, etc. Such devices may be powered by a battery. One or more loads corresponding to one or more of the various subsystems may be subject to intermittent current draws having relatively short rise and fall times and varying pulse widths and amplitudes. The intermittent load changes may result in voltage transients appearing across the main/battery bus that may cause various undesirable effects. As one example, ceramic capacitors may be used for energy storage in relatively small and thin portable devices. If the load current changes take place in the audio range of frequencies, such ceramic capacitors may experience mechanical resonance that leads to undesirable audible noise. In other cases, the magnitude of the voltage changes may cause undesirable disruption to other loads or may require more complex, expensive, and/or space-consuming regulators to be provided to protect such other loads from these transients. 
     SUMMARY 
     Thus, what is needed in the art are improved power system designs for battery powered electronic devices that can be used to mitigate battery output voltage ripple caused by pulsed loads within the device. 
     A battery powered electronic device can include a power bus configured to receive power from a battery, one or more loads connected to the power bus, a first DC-DC converter having an input coupled to the power bus and an output, and a second DC-DC converter cascaded with the first DC-DC converter and coupled to a second load, wherein the second load experiences pulsed operation. The second DC-DC converter may have a higher bandwidth than the first DC-DC converter so as to isolate the one or more loads from transients associated with the pulsed operation of the second load. The second DC-DC converter may have an input coupled to the output of the first DC-DC converter and an output coupled to the second load. The second DC-DC converter may be a bidirectional converter having first terminals coupled to the output of the first DC-DC converter and second terminals coupled to an energy storage capacitor, wherein the second load is coupled to the first terminals of the second DC-DC converter. The second DC-DC converter may be a bidirectional buck-boost converter. The second DC-DC converter may be a bidirectional charge pump. The second load may be a part of a display subsystem of the battery powered electronic device, a part of a processing subsystem of the battery powered electronic device, or a part of a communication subsystem of the battery powered electronic device. The bandwidth of the second DC-DC converter may be between  10 x and  100 x higher than the bandwidth of the first DC-DC converter. 
     A battery powered electronic device can include a battery, one or more loads coupled to and configured to draw power from the battery, a first DC-DC converter having an input coupled to the battery and an output, and a second DC-DC converter cascaded with the first DC-DC converter having an input coupled to the output of the first DC-DC converter and an output coupled to a second load, wherein the second load experiences pulsed operation. The first and second DC-DC converters may be configured so that the first DC-DC converter supplies an average power requirement of the second load and the second bidirectional DC-DC converter supplies a transient energy requirement of the second load. The first DC-DC converter may be a boost converter. The second load may be a part of a display subsystem of the battery powered electronic device, a part of a processing subsystem of the battery powered electronic device, or a part of a communication subsystem of the battery powered electronic device. The bandwidth of the second DC-DC converter may be between  10 x and  100 x higher than the bandwidth of the first DC-DC converter. 
     A battery powered electronic device can include a battery, one or more loads coupled to and configured to draw power from the battery, a first DC-DC converter having an input coupled to the battery and an output, an a second bidirectional DC-DC converter cascaded with the first DC-DC converter having a first terminal coupled to the output of the first DC-DC converter and a second terminal coupled to an energy storage device, and a second load coupled to the output of the first DC-DC converter, wherein the second load experiences pulsed operation. 
     The first and second DC-DC converters may be configured so that the first DC-DC converter supplies an average power requirement of the second load and the second bidirectional DC-DC converter supplies a transient energy requirement of the second load. The second DC-DC converter may supply the transient energy requirement of the second load from the energy storage device. The second load may be a part of a display subsystem of the battery powered electronic device, a part of a processing subsystem of the battery powered electronic device, or a part of a communication subsystem of the battery powered electronic device. The bandwidth of the second DC-DC converter may be between  10 x and  100 x higher than the bandwidth of the first DC-DC converter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a high level block diagram of the power system of a battery powered electronic device. 
         FIG. 2  illustrates various voltage and current waveform of the device of  FIG. 1 . 
         FIG. 3  illustrates a high-level block diagram of the power system of an improved battery powered electronic device including a first and second DC-DC converters configured to mitigate battery output voltage ripple in response to a pulsed load. 
         FIG. 4  illustrates various voltage and current waveforms of the device of  FIG. 3 . 
         FIG. 5  illustrates a high-level block diagram of the power system of an alternative improved battery powered electronic device including a first and second DC-DC converters configured to mitigate battery output voltage ripple in response to a pulsed load. 
         FIG. 6  illustrates various voltage and current waveforms of the device of  FIG. 5 . 
     
    
    
     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 a high-level block diagram of a battery powered electronic device  100 . Battery powered electronic device  100  may take a variety of forms, such as a smartphone, tablet computer, laptop computer, smart watch, etc. Such devices may include various electronic subsystems, such as processing subsystems, communication subsystems, display subsystems, etc. The processing subsystems may include various embodiments of processing devices, such as central processing units (CPUs), graphics processing units (GPUs), neural processing units (NPUs), as well as ancillary components to support these devices such as memory (e.g., random access memory/RAM) and storage (e.g., flash memory, etc.) The communication subsystems may include various embodiments of wired and/or wireless communication systems, including external ports for wired communication via USB, Ethernet, or other wired communication technologies as well as radio modules and associated processing systems for implementing various wireless communication techniques, such as WiFi, Bluetooth, NFC communications, and the like. The display subsystem may include various display elements for providing visual information to a user, such as an LCD, OLED, or other display technology. Electronic device  100  may include other systems as well, including I/O subsystems for touch-sensing, etc. 
     Electronic device  100  may be powered by a battery  102 , which may be represented by its Thevenin equivalent including voltage source Vbattery and series resistance Rbattery. Battery  102  provides power to a power bus  103 , which may deliver a load current I 1  to a load  106  via a first DC-DC converter  108 . DC-DC converter  108  may be any suitable converter type for converting the battery voltage to an appropriate level for load  106 . For example, if load  106  requires a higher voltage than the battery voltage, DC-DC converter may be a boost converter. Alternatively, if load  106  requires a lower voltage than the battery voltage, DC-DC converter may be a buck converter. Charge pumps, buck-boost converters, and other converter types may also be used in a given embodiment, depending on the particular requirements, objectives, and constraints of the system. Power bus  103  may be supported by a capacitor C 1 , which can provide some amount of energy storage allowing the bus voltage to remain relatively stable in the presence of transients associated with changes in operating current of the various loads. Power bus  103  may also deliver power to other loads  104  (which may be powered directly by bus  103  or which may have their own intervening DC-DC converters (not shown). 
     Load  106  may be a load that experiences intermittent current draws, as illustrated by curve  212  in  FIG. 2 , in which the load current alternates between a small or even zero value  212   a  and a peak value  212   b . The rise and fall times of the current may be relatively short, and the pulse width and pulse amplitude may vary from cycle to cycle. In some cases, this change in load current may be relatively large. An example of such a load may be a backlight for an LED display, which draws a relatively higher current when the display is on but draws little or no current when the display is off (which is typical in many portable devices, such as smart phones, tablet computers, smartwatches, etc.). 
     In another embodiment, such a load might be one or the processing system components, such as a CPU or GPU, that alternates between lower power draw states when there is little processing activity and higher power draw states when there is significant processing activity or a communication system component in which case the radios draw relatively higher power when transmitting versus relatively lower power when not transmitting. In the case of a display, the frequency of the load changes illustrated in plot  212  will be relatively low. For instance, even if the backlight is intermittently powered off in synchronization with the display refresh cycles, such operations may take place at a frequency on the order of 60 Hz to 120 Hz. (Higher, lower, or intermediate display refresh rates, such as 30 Hz, 75 Hz, 90 Hz, 240 Hz, etc.) could also be used. Conversely, in the case of a processing system or communication system, the frequency of the load changes may be substantially higher, in the kilohertz, megahertz, or even gigahertz range. 
     The intermittent load current changes  212  associated with load  106  may result in voltage transients illustrated in plot  214  of  FIG. 2 , which illustrates the load voltage Vload. DC-DC converter  108  may be designed so as to provide a suitably regulated output voltage Vload in the presence of the expected current transients  212 . However, the intermittent load changes of load  106  may also cause transients to occur on the input side of DC-DC converter  108 , i.e., on bus  103 . Such transients are illustrated in plot  216  (current transients) and plot  218  (voltage transients). The current transients correspond to current I 1 , which is the input converter into DC-DC converter  108 . The voltage transients correspond to voltage VC 1 , which is the voltage across the capacitor C 1 . This voltage is also the voltage that is supplied to other loads  104  (corresponding to others of the various systems discussed above). 
     More specifically, an increase in load current to the peak current level  212   b  may result in a corresponding increase in bus/input current I 1  to a corresponding level  216   b . This increased current, being drawn from battery  102  and therefore flowing through the battery&#39;s series resistance Rbattery, may result in a corresponding voltage dip to a level  218   b . Conversely, when the load current drops to lower level  212   a , there will be a corresponding decrease in the input/bus current I 1  corresponding to level  216   a  and a corresponding increase of the bus/capacitor C 1  voltage to a level  218   a.    
     The aforementioned changes in the bus voltage may cause various undesirable effects. As one example, in relatively small and thin portable devices, capacitor C 1  may be implemented as a ceramic capacitor. In the case that load  106  is a display subsystem or other subsystem in which the load current changes take place in the audio range of frequencies, such ceramic capacitors may experience mechanical resonance that leads to undesirable audible noise. In other cases, the magnitude of the voltage changes may cause undesirable disruption to other loads  104  or may require more complex, expensive, and/or space-consuming regulators to be provided to protect such other loads from these transients. 
       FIG. 3  illustrates an improved battery powered electronic device  300 . The components of  FIG. 3  are numbered with like reference numbers to  FIG. 1 . Electronic device  300  may be powered by a battery  302 , which may be represented by its Thevenin equivalent including voltage source Vbattery and series resistance Rbattery. Battery  302  provides power to a power bus  303 , which may deliver a load current I 1  to a load  306  via a first DC-DC converter  308  and a second converter  310 , discussed in greater detail below. Power bus  303  may be supported by a capacitor C 1 , which can provide some amount of energy storage allowing the bus voltage to remain relatively stable in the presence of transients associated with changes in operating current of the various loads. Power bus  303  may also deliver power to other loads  304 , which may be powered directly by bus  303  or which may have their own intervening DC-DC converters (not shown). 
     Rather than directly powering load  306 , DC-DC converter  308  may power an intermediate bus  309 , supported by a capacitor C 2 . This intermediate bus  309  may then power a second DC-DC converter  310 , that can power load  306  via its output bus, which may also be supported by a capacitor C 3 . As above, load  306  may be a load that experiences intermittent current draws, as illustrated by curve  412  in  FIG. 4 , in which the load current alternates between a small or even zero value  412   a  and a peak value  412   b . The intermittent load current changes  412  associated with load  106  may result in voltage transients illustrated in plot  414  of  FIG. 4 , which illustrates the load voltage Vload. DC-DC converter  310  may be designed so as to provide a suitably regulated output voltage Vload in the presence of the expected current transients  412 . This may correspond to a relatively “fast” converter controller, i.e., one with a relatively high bandwidth. DC-DC converter  308  may then be configured with a relatively “slower” controller, i.e., one with a relatively lower bandwidth so as to prevent large transients from appearing on bus  303 . For example, in some embodiments, DC-DC converter  308  may be designed with a controller bandwidth that is 1/10 as fast or even 1/100 as fast as DC-DC converter  310 . In other words, DC-DC converter  310  may be 10× to 100× faster than DC-DC converter  308 . The net result of such a configuration is that DC-DC converter  308  ends up supplying the “average” requirement of load  306 , while DC-DC converter  310  meets the transient demands of load  306 , with intermediate bus  309 /capacitor C 2  being used to store the energy needed for DC-DC converter  310  to meet the transient demand. 
     Thus, as can be seen with reference to curve  416 ,  FIG. 4 , voltage of intermediate bus  309 , which corresponds to the voltage across capacitor VC 2  increases  416   a  during time periods in which load  306  is in its low current mode  412   a  and decreases  416   b  during time periods in which load  306  is in its higher current state  412   b . As before, the intermittent load changes of load  306  may also cause transients to occur on the input side of DC-DC converter  308 , i.e., on bus  303 ; however, the interposition of cascaded DC-DC converter  310  can significantly reduce the magnitude of these transients. Such transients are illustrated in plot  418  (current transients) and plot  420  (voltage transients). The current transients correspond to current I 1 , which is the input converter into DC-DC converter  308 . The voltage transients correspond to voltage VC 1 , which is the voltage across the capacitor C 1 . This voltage is also the voltage that is supplied to other loads  304  (corresponding to others of the various systems discussed above). 
     More specifically, an increase in load current to the peak current level  412   b  may result in a corresponding increase in bus/input current I 1  to a corresponding level  418   b . This increased current, being drawn from battery  302  and therefore flowing through the battery&#39;s series resistance Rbattery, may result in a corresponding voltage dip to a level  420   b . Conversely, when the load current drops to lower level  412   a , there will be a corresponding decrease in the input/bus current I 1  corresponding to level  416   a  and a corresponding increase of the bus/capacitor C 1  voltage to a level  420   a . As can be seen by comparison to  FIG. 2 , the transients appearing on main bus  303  can be substantially smaller than corresponding transients appearing on main bus  103 . 
       FIG. 5  illustrates an alternative improved battery powered electronic device  500 . The components of  FIG. 5  are numbered with like reference numbers to  FIGS. 1 and 3 . Electronic device  500  may be powered by a battery  502 , which may be represented by its Thevenin equivalent including voltage source Vbattery and series resistance Rbattery. Battery  502  provides power to a power bus  503 , which may deliver a load current I 1  to a load  506  via a first DC-DC converter  508 . A second converter  310  may also be provided, as discussed in greater detail below. Power bus  503  may be supported by a capacitor C 1 , which can provide some amount of energy storage allowing the bus voltage to remain relatively stable in the presence of transients associated with changes in operating current of the various loads. Power bus  503  may also deliver power to other loads  504 , which may be powered directly by bus  503  or which may have their own intervening DC-DC converters (not shown). 
     In addition to directly powering load  506 , DC-DC converter  508  may power an intermediate bus  509 , supported by a capacitor C 2 . This intermediate bus  509  may then power a second DC-DC converter  510 , that can store energy in or retrieve energy from an energy storage capacitor C 3 . To that end, DC-DC converter may be a bidirectional converter of any suitable topology, such as a bidirectional buck-boost converter or a bidirectional charge pump. As above, load  506  may be a load that experiences intermittent current draws, as illustrated by curve  612  in  FIG. 6 , in which the load current alternates between a small or even zero value  612   a  and a peak value  612   b . The intermittent load current changes  612  associated with load  506  may result in voltage transients illustrated in plot  614  of  FIG. 6 , which illustrates the load voltage Vload. DC-DC converters  508  and  510  may be designed so as to, in combination, provide a suitably regulated output voltage Vload in the presence of the expected current transients  612 . This may include DC-DC converter  508  being a relatively “slower” converter, with a corresponding, slower converter controller, and DC-DC converter  510  being a relatively “faster” converter with a relatively faster controller, i.e., one with a relatively high bandwidth. For example, in some embodiments, DC-DC converter  508  may be designed with a controller bandwidth that is 1/10 as fast or even 1/100 as fast as DC-DC converter  510 . In other words, DC-DC converter  510  may be 10× to 100× faster than DC-DC converter  508 . The net result of such a configuration is that, similarly to the arrangement of  FIG. 4  discussed above, DC-DC converter  508  ends up supplying the “average” requirement of load  506 , while DC-DC converter  510  meets the transient demands of load  506 , with capacitor C 3  being used to store the energy needed for DC-DC converter  510  to meet the transient demand. 
     Thus, as can be seen with reference to curve  616 ,  FIG. 6 , the across of capacitor C 3  (and thus the energy stored therein) increases  616   a  during time periods in which load  506  is in its low current mode  612   a  and decreases  616   b  during time periods in which load  506  is in its higher current state  612   b . As before, the intermittent load changes of load  506  may also cause transients to occur on the input side of DC-DC converter  508 , i.e., on bus  503 ; however, the addition of DC-DC converter  510  (and its associated energy storage capacitor C 3 ) can significantly reduce the magnitude of these transients. Such transients are illustrated in plot  618  (current transients) and plot  620  (voltage transients). The current transients correspond to current I 1 , which is the input converter into DC-DC converter  508 . The voltage transients correspond to voltage VC 1 , which is the voltage across the capacitor C 1 . This voltage is also the voltage that is supplied to other loads  504  (corresponding to others of the various systems discussed above). 
     More specifically, an increase in load current to the peak current level  612   b  may result in a corresponding increase in bus/input current I 1  to a corresponding level  618   b . This increased current, being drawn from battery  502  and therefore flowing through the battery&#39;s series resistance Rbattery, may result in a corresponding voltage dip to a level  620   b . Conversely, when the load current drops to lower level  612   a , there will be a corresponding decrease in the input/bus current I 1  corresponding to level  616   a  and a corresponding increase of the bus/capacitor C 1  voltage to a level  620   a . As can be seen by comparison to  FIG. 2 , the transients appearing on main bus  503  can be substantially smaller than corresponding transients appearing on main bus  103 . 
     In each of the embodiments above, the reduction of transient voltages appearing on the bus directly supplied by the battery is accomplished by the presence of a second DC-DC converter that responds to load transients more quickly than the “main” DC-DC converter. As discussed above, for at least some applications, a bandwidth of the faster converter may be 10× to 100× the bandwidth of the slower converter. The faster converter may respond to these transients using energy stored in the mechanism of the converter itself and/or one or more additional energy storage components, such as additional capacitors. The net result is that the slower converter can supply the average power requirement of the load, with the faster converter supplying the transient requirements. Because of its slower response, the “main” converter may not provide as precise a degree of regulation as might otherwise be desired, however, the presence of the second, faster converter can make up for this deficit, allowing for the high draw load to still be sufficiently precisely regulated. 
     Such arrangements may be particularly advantageous when used in conjunction with battery powered portable electronic devices and in particular with high draw, relatively low frequency subsystems of such devices, such as display subsystems. In these cases, it may be impractical to provide other energy storage mechanisms, such as larger capacitors, suitable to meet the required transient performance due to space constraints. Likewise, because they operate at lower frequencies, the energy storage requirements are higher, resulting in much larger energy storage components (e.g., capacitors or inductors), which, again, may run afoul of the space constraints for a given application. 
     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 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.