PATENT DOCUMENT

Publication Number: US-8610423-B2
Application Number: US-201213451358-A
Country: US
Kind Code: B2

Title: Low noise external enable switcher control signal using on-chip switcher

Abstract:
A method and system is disclosed for powering device sub-circuitry of an electronic device. The sub-circuitry may be used to provide control signals to a direct current switcher on a main system board, thus eliminating passive circuitry typically associated with the sub-circuitry. Furthermore, by actively generating the control signals for the direct current switcher, explicit timing control circuitry is not required to synchronize the transmitted power to the sub-circuitry.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 a first circuit board comprising a power management unit, the power management unit comprising a dc/dc converter, wherein the dc/dc converter comprises a slave power controller coupled to passive circuit components configured to convert a first dc voltage to a second dc voltage; and 
 a second circuit board comprising a sub-circuit and a master power controller, the sub-circuit being configured to receive the second dc voltage, the master power controller being operably coupled to the slave power controller, wherein the master power controller is configured to generate a control signal to instruct the slave power controller to switch the first dc voltage relative to the passive circuit components to generate the second dc voltage, wherein the control signal is a power controller switcher activation control signal. 
 
     
     
       2. The electronic device of  claim 1 , wherein the slave power controller comprises a slave switcher coupled to a slave switch, and wherein the master power controller comprises a master switcher coupled to a master switch, the master switch being operably coupled to the slave switcher; and
 wherein the master switcher is operable to switch the master switch on and off to alternatively enable and disable the slave switcher to cause the slave switcher to switch the slave switch on and off to cause the first dc voltage to be switched relative to the passive circuit components to generate the second dc voltage. 
 
     
     
       3. The electronic device of  claim 1 , wherein the first circuit board is separate from the second circuit board. 
     
     
       4. The electronic device of  claim 1 , wherein the slave power controller is arranged relative to the passive components and an input for the first dc voltage to form one of a buck dc/dc voltage converter, a boost dc/dc voltage converter, or a flyback dc/dc voltage converter. 
     
     
       5. The electronic device of  claim 1 , wherein the sub-circuit comprises display logic. 
     
     
       6. The electronic device of  claim 1 , wherein the master power controller circuit controls the slave power controller based at least in part on the power requirements of the sub-circuit. 
     
     
       7. The electronic device of  claim 6 , wherein the master power controller receives from the sub-circuit a signal indicative of the power requirement of the sub-circuit and receives the second dc voltage as a feedback signal, and wherein the master power controller controls the slave power controller based at least in part on a comparison of the power requirement signal and the feedback signal. 
     
     
       8. The electronic device of  claim 1 , wherein the power management unit comprises filtering circuitry coupled between the master power controller and the slave power controller. 
     
     
       9. The electronic device of  claim 1 , wherein the power controller switcher activation control signal generated by the master controller comprises a series of clock pulses. 
     
     
       10. A handheld electronic device comprising:
 a power management unit physically located on a first circuit board and comprising a dc/dc converter, wherein the dc/dc converter comprises a slave power controller coupled to passive circuit components configured to convert a first dc voltage to a second dc voltage; 
 a display configured to provide a user interface; and 
 a display controller coupled to the display, wherein the display controller is physically located on a second circuit board, the display controller comprising a master power controller and a display logic circuit, the display logic circuit being configured to control the display and being configured to receive the second dc voltage, the master power controller being operably coupled to the slave power controller to cause the slave power controller to switch the first dc voltage relative to the passive circuit components to generate the second dc voltage based at least in part on power requirements of the display logic circuit, wherein the master power controller receives from the display logic circuit a signal indicative of the power requirement of the display logic circuit and receives the second dc voltage as a feedback signal. 
 
     
     
       11. The handheld electronic device of  claim 10 , wherein the slave power controller comprises a slave switcher coupled to a slave switch, and wherein the master power controller comprises a master switcher coupled to a master switch, the master switch being operably coupled to the slave switcher; and
 wherein the master switcher is operable to switch the master switch on and off to alternatively enable and disable the slave switcher to cause the slave switcher to switch the slave switch on and off to cause the first dc voltage to be switched relative to the passive circuit components to generate the second dc voltage. 
 
     
     
       12. The handheld electronic device of  claim 10 , wherein the power management unit is located separately from the display within the handheld electronic device. 
     
     
       13. The handheld electronic device of  claim 10 , wherein the slave power controller is arranged relative to the passive components and an input for the first dc voltage to form one of a buck dc/dc voltage converter, a boost dc/dc voltage converter, or a fly back dc/dc voltage converter. 
     
     
       14. The handheld electronic device of  claim 10 , wherein the master power controller controls the slave power controller based at least in part on a comparison of the power requirement signal and the feedback signal. 
     
     
       15. The handheld electronic device of  claim 10 , wherein the power management unit comprises filtering circuitry coupled between the master power controller and the slave power controller. 
     
     
       16. A method of providing power to a sub-circuit, comprising:
 converting a first dc voltage to a second dc voltage using a slave dc/dc converter located on a first circuit board; 
 supplying the second dc voltage to a sub-circuit, the sub-circuit being operably coupled to a master power controller, wherein the sub-circuit and master power controller are located on a second circuit board; 
 generating a control signal on the master power controller; and 
 transmitting the control signal from the master power controller to the slave dc/dc converter to instruct the slave dc/dc converter to convert the first dc voltage to the second dc voltage based at least in part on power requirements of the sub-circuit; 
 wherein the control signal is a power controller switcher activation control signal. 
 
     
     
       17. The method of  claim 16 , wherein converting the first dc voltage to the second dc voltage comprises switching the first dc voltage relative to passive circuit components in the slave dc/dc converter. 
     
     
       18. The method of  claim 16 , wherein generating the control signal comprises:
 transmitting a signal indicative of the power requirements of the sub-circuit to the master power controller; 
 transmitting the second dc voltage as a feedback signal to the master power controller; and 
 generating the control signal by the master power controller based at least in part on a comparison of the signal indicative of the power requirements of the sub-circuit and the feedback signal. 
 
     
     
       19. The method of  claim 16 , comprising filtering the control signal transmitted from the master power controller to the slave dc/dc converter. 
     
     
       20. The method of  claim 16 , wherein transmitting the control signal comprises enabling and disabling the slave dc/dc converter to cause the slave dc/dc converter to cause the first dc voltage to be switched relative to passive components of the slave dc/dc converter. 
     
     
       21. The method of  claim 16 , wherein converting the first dc voltage to the second dc voltage comprises adjusting the first dc voltage upwardly or downwardly. 
     
     
       22. The method of  claim 16 , wherein the power controller switcher activation control signal generated on the master power controller comprises a series of clock pulses.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a Divisional Application of U.S. patent application Ser. No. 12/410,216 filed Mar. 24, 2009 now abandoned and claims the benefit of U.S. Provisional Application No. 61/194,772, filed Sep. 30, 2008. 
    
    
     BACKGROUND 
     The present disclosure relates generally to off-chip control of an integrated circuit via a DC/DC switcher. 
     DESCRIPTION OF THE RELATED ART 
     This section is intended to introduce the reader to various aspects of art that may be related to various aspects that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of these various aspects. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     Direct current to direct current (DC/DC) switchers, also known as DC/DC controllers or converters, are used in consumer electronics to convert voltage from one level to another. The need for this conversion may stem from sub-circuits in an electronic device requiring different voltages than that supplied by a battery or a power supply. By employing DC/DC switchers in an electronic device for converting the voltage from a fixed source, such as a battery or other power source, the electronic device may power multiple types of sub-circuits using only a single fixed source rather than requiring separate power sources for each sub-circuit. 
     One particular type of DC/DC switcher converts a first DC voltage level to a second DC voltage level by temporarily storing input energy and subsequently releasing that energy at a different voltage through the use of passive components such as an inductors or capacitors. However, utilization of these types of components can lead to electronic noise and electromagnetic interference of sub-circuits neighboring the DC/DC switcher. Furthermore, components such as inductors and capacitors increase the overall size of the DC/DC switcher, thus necessitating more space when integrating DC/DC switchers into electronic devices. Accordingly, as demand for smaller electronic devices continues grow, there is a need for smaller DC/DC switchers that may be used in an electronic device without causing interference with the operation of neighboring circuitry. 
     SUMMARY 
     Certain aspects of embodiments disclosed herein by way of example are summarized below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain embodiments and that these aspects are not intended to limit the scope of the claims. Indeed, the disclosure and claims may encompass a variety of aspects that may not be set forth below. 
     An electronic device that includes a power management unit is described below. The power management unit may include a DC/DC converter (i.e. a DC/DC switcher) that may provide switched power to off board circuitry that would normally require its own DC/DC converter. The DC/DC converter of the power management unit may be treated as a slave unit in that it may be enabled and disabled by a master power controller associated with the off board circuitry via master power controller circuitry. In this manner, the off board circuitry may control the operation of the DC/DC converter, thereby controlling the power generated by the DC/DC converter and provided to the off board circuitry. Moreover, because the power management unit may generate the switched power based, in part, on a control signal from the master power controller, there may be no need to provide an additional timing signal to the off board circuitry. Accordingly, the passive circuitry, such as inductors and capacitors, typically used in conjunction with a power controller as part of a DC/DC converter in the off board circuitry for the generation of power may be removed. Through removal of the passive circuitry, the space utilized by the off board circuitry may be reduced. Additionally, the master power controller may emit less electronic noise and EMI than a DC/DC converter, due to the elimination of the capacitors and inductors, as well as the magnetic and electric fields caused by the switching currents on the off board circuitry. Accordingly, the master power controller may be placed in a closer proximity to other integrated circuits in the electronic device with a reduced risk of inductive crosstalk. These factors, when applied to a plurality of sub-circuits in an electronic device, may combine to allow for a reduction in overall size and ease of packaging of the electronic device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain embodiments may be understood reading the following detailed description and upon reference to the drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is a front view of an electronic device, such as a portable media player, in accordance with one embodiment; 
         FIG. 2  is a block diagram of certain components of the electronic device of  FIG. 1 ; 
         FIG. 3  is a simplified block diagram of the power delivery unit of  FIG. 2  operating in conjunction with a controlled integrated circuit. 
     
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     One or more specific embodiments will be described below. In an effort to provide a concise description of these exemplary embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     The present disclosure is directed to techniques and circuitry for conversion and delivery of electrical power from internal circuitry in an electronic device to electronic sub-circuits of the electronic device. In one embodiment, a power management unit includes a DC/DC converter that may be used to accomplish regulation and conversion of voltage for transmission to sub-circuits of the electronic device that would normally include their own DC/DC converters. Rather, a sub-circuit is associated with a master power controller that treats the DC/DC converter of the power management unit as a slave DC/DC converter. By providing switched power to the sub-circuit, passive circuitry, such as inductors and capacitors, typically used in conjunction with the master power controller of the sub-circuit to form a DC/DC converter, may be removed from the sub-circuit. In this manner, the use of passive circuitry in the sub-circuit may be eliminated. Further, because the passive circuitry is confined to the power management unit, the passive circuitry that may otherwise induce inductive crosstalk with other electrical components can be shielded properly in a single location, rather than in multiple locations. Thus, the sub-circuits may be placed in closer proximity to one another with reduced potential for unwanted effects such as inductive crosstalk between the sub-circuits. Additionally, since the master power controller of the sub-circuit provides a control signal to the slave DC/DC converter, the need for independent timing circuitry for controlling the slave DC/DC converter is alleviated. A discussion is presented below of an electronic circuit that utilizes such circuitry. 
     Turning now to the figures,  FIG. 1  illustrates an electronic device  10  that may be a handheld device incorporating the functionality of one or more portable devices, such as a media player, a cellular phone, a personal data organizer, and so forth. Depending, of course, on the functionalities provided by the electronic device  10 , a user may listen to music, play games, record video, take pictures, and place telephone calls, while moving freely with the device  10 . In addition, the electronic device  10  may allow a user to connect to and communicate through the Internet or through other networks, such as local or wide area networks. For example, the electronic device  10  may allow a user to communicate using e-mail, text messaging, instant messaging, or other forms of electronic communication. The electronic device  10  also may communicate with other devices using short-range connections, such as Bluetooth and near field communication. By way of example, the electronic device  10  may be a model of an iPhone® available from Apple Inc. of Cupertino, Calif. 
     In the depicted embodiment, the device  10  includes an enclosure  12  that protects the interior components from physical damage and shields them from electromagnetic interference. The enclosure  12  may be formed from any suitable material such as plastic, metal, or a composite material and may allow certain frequencies of electromagnetic radiation to pass through to wireless communication circuitry within the device  10  to facilitate wireless communication. 
     The enclosure  12  allows access to user input structures  14 ,  16 ,  18 ,  20 , and  22  through which a user may interface with the device. Each user input structure  14 ,  16 ,  18 ,  20 , and  22  may be configured to control a device function when actuated. For example, the input structure  14  may include a button that when pressed causes a “home” screen or menu to be displayed on the device. The input structure  16  may include a button for toggling the device  10  between a sleep mode and a wake mode. The input structure  18  may include a two-position slider that silences a ringer for the cell phone application. The input structures  20  and  22  may include buttons for increasing and decreasing the volume output of the device  10 . In general, the electronic device  10  may include any number of user input structures existing in various forms including buttons, switches, control pads, keys, knobs, scroll wheels, or other suitable forms. 
     The device  10  also includes a display  24  which may display various images generated by the device. For example, the display  24  may show photos, movies, album art, and/or data, such as text documents, spreadsheets, text messages, and email, among other things. The display  24  also may display system indicators  26  that provide feedback to a user, such as power status, signal strength, call status, external device connection, and the like. The display  24  may be any type of display such as a liquid crystal display (LCD), a light emitting diode (LED) display, an organic light emitting diode (OLED) display, or other suitable display. Additionally, the display  24  may include a touch-sensitive element, such as a touch screen. 
     The display  24  may be used to display a graphic user interface (GUI)  28  that allows a user to interact with the device. The GUI  28  may include various layers, windows, screens, templates, elements, or other components that may be displayed in all, or a portion, of the display  24 . Generally, the GUI  28  may include graphical elements that represent applications and functions of the device  10 . The graphical elements may include icons and other images representing buttons, sliders, menu bars, and the like. In certain embodiments, the user input structure  14  may be used to display a home screen of the GUI  28 . For example, in response to actuation of the input structure  14 , the device may display graphical elements, shown here as icons  30 , of the GUI  28 . The icons  30  may correspond to various applications of the device  10  that may open upon selection of an icon  30 . The icons  30  may be selected via a touch screen included in the display  24 , or may be selected by user input structures, such as a wheel or button. 
     The icons  30  may represent various layers, windows, screens, templates, elements, or other components that may be displayed in some or all of the areas of the display  24  upon selection by the user. Furthermore, selection of an icon  30  may lead to a hierarchical navigation process, such that selection of an icon  30  leads to a screen that includes one or more additional icons or other GUI elements. Textual indicators  32  may be displayed on or near the icons  30  to facilitate user interpretation of each icon  30 . It should be appreciated that the GUI  30  may include various components arranged in hierarchical and/or non-hierarchical structures. 
     When an icon  30  is selected, the device  10  may be configured to open an application associated with that icon and display a corresponding screen. For example, when the Weather icon  30  is selected, the device  10  may be configured to open a weather application with a user interface that may provide the current weather conditions to a user. Indeed, for each icon  30 , a corresponding application that may include various GUI elements may be opened and displayed on the display  24 . 
     The electronic device  10  also may include various input and output (I/O) ports  34 ,  36 , and  38  that allow connection of the device  10  to external devices. For example, the I/O port  34  may be a connection port for transmitting and receiving data files, such as media files. Furthermore, the I/O port  34  may be a proprietary port from Apple Inc. The I/O port  36  may be a connection slot for receiving a subscriber identify module (SIM) card. The I/O port  38  may be a headphone jack for connecting audio headphones. In other embodiments, the device  10  may include any number of I/O ports configured to connect to a variety of external devices, including but not limited to a power source, a printer, and a computer. In other embodiments, multiple ports may be included on a device. Additionally, the ports may be any interface type, such as a universal serial bus (USB) port, serial connection port, Firewire port, IEEE-1394 port, or AC/DC power connection port. 
     The electronic device  10  may also include various audio input and output structures  40  and  42 . For example, the audio input structures  40  may include one or more microphones for receiving voice data from a user. The audio output structures  42  may include one or more speakers for outputting audio data, such as data received by the device  10  over a cellular network. Together, the audio input and output structures  40  and  42  may operate to provide telephone functionality. Further, in some embodiments, the audio input structures  40  may include one or more integrated speakers serving as audio output structures for audio data stored on the device  10 . For example, the integrated speakers may be used to play music stored in the device  10 . Additional details of the illustrative device  10  may be better understood through reference to  FIG. 2 , which is a block diagram illustrating various components and features of the device  10  in accordance with one embodiment of the present invention. 
       FIG. 2  is a block diagram that illustrates the components that may be utilized by the electronic device  10  to operate. In the presently illustrated embodiment, the device  10  includes the display  24  discussed above. In addition, as discussed in greater detail below, the electronic device  10  may include includes a central processing unit (CPU)  46 , long-term storage  48 , internal components  50 , a display controller  52 , a power source  54 , and a power management unit (PMU)  56 . 
     As set forth above, the electronic device  10  may include a CPU  46 . The CPU  46  may include a single processor or it may include a plurality of processors. For example, The CPU  46  may also include one or more “general-purpose” microprocessors, a combination of general and special purpose microprocessors, and/or ASICS, as well as one or more reduced instruction set (RISC) processors, graphics processors, video processors, and/or related chip sets. The CPU  46  may provide the processing capability to execute the operating system, programs, the GUI  28 , and any other functions of the device  10 . 
     Accordingly, the electronic device  10  may include long term storage  48 . The long-term storage  48  of electronic device  10  may be used for storing data utilized for the operation of the CPU  46  as well as other data required by the device  10 . For example, the long term storage  48  may store the firmware for the electronic device  10  usable by the CPU  46 , such as an operating system, other programs that enable various functions of the electronic device  10 , user interface functions, and/or processor functions. Additionally, the long term storage  48  may store data files such as media (e.g., music and video files), image data, software, preference information (e.g., media playback preferences), wireless connection information (e.g., information that may enable the device  10  to establish a wireless connection, such as a telephone connection), subscription information (e.g., information that maintains a record of podcasts, television shows or other media to which a user subscribes), telephone information (e.g., telephone numbers), and any other suitable data. The long term storage  48  may be non-volatile memory such as read only memory, flash memory, a hard drive, or any other suitable optical, magnetic, or solid-state storage medium, as well as a combination thereof. Some of the data files stored by the long term storage  48  may be used by additional components of the device, which are designated as internal components  50 . 
     The internal components  50  of electronic device  10  may include sub-circuits that perform specialized functions of the electronic device  10 . These internal components  50  may include phone circuitry, camera circuitry, video circuitry, and audio circuitry. The phone circuitry may allow a user to receive or make a telephone call through user interaction with the audio input and output structures  40  and  42 . The camera circuitry may allow a user to take digital photographs. Additionally, the video circuitry and the audio circuitry may be used to encode and decode video samples taken by the user in conjunction with the camera circuitry or downloaded from an external source such as the internet, and allow for the playing of audio files such as compressed music files, respectively. Moreover, while the display  24  and the display controller  52  and may also be considered a portion of the internal components  50 , they have been illustrated separately to provide an example of the interaction of a given one of the sub-circuits with the power management unit (PMU)  56 . The general operation of the display  24  and the display controller  52  will be described below, followed by a description of their interaction with the PMU  56 . However, it should be noted that the PMU  56  may be used in a similar manner with any of the sub-circuits that make up the internal components  50 . 
     As described above, the electronic device  10  may also include a display controller  52  that operates to generate images for the electronic device  10 . The display controller  52  may be a device which, for example, receives image data from the video circuitry via the CPU  46 . The display controller  52  may determine the pixel values used to create an image corresponding to the image data received and may generate voltage signals corresponding to those pixel values for display on the display  24 . The pixel values may be numerical assignments that correspond to respective pixel intensities of the display  24  from which the display  24  may produce an image corresponding to the received voltage signals. 
     The electronic device  10  also includes a power source  54 . The power source  54  may be used to power the electronic device  10  via, for example, one or more batteries, such as a Li-Ion battery, which may be user-removable or secured to the enclosure  12  and, which may be rechargeable. Additionally, the power source  54  may be connected to an I/O port that alternately allows for the power source  54  to receive power from an external AC or a DC power source, such as an electrical outlet or a car cigarette lighting mechanism. 
     The power source  54  may be coupled to the PMU  56  for translation of power from the power source  54  to power levels required by one or more sub-circuits of the electronic device  10 . For ease of illustration, this discussion will focus on the PMU  56  providing power to the display controller  52 , but it should be understood that the PMU  56  may provide power to any suitable sub-circuit of an electronic device. In this embodiment, the display  24  may include a display controller  52 . The display controller  52  may include a master power controller  62 . The PMU  56  includes a DC/DC converter, as described in detail below, that may be controlled by the master power controller  62  so that a DC voltage generated by the converter may be transmitted the display controller  52 . The master power controller  62  may receive this power from the PMU  56  along the power line  58  as well as transmit control signals to the PMU  56  along the control line  60 . In this manner, the PMU  56  may adjust the power transmitted to the display controller  52 , as determined by the master power controller  62 . For example, the power transmitted to the display controller  52  may be stepped up or stepped down, based on the requirements of the display controller  52 , as determined by the master power controller  62 . The PMU  56  may be on a different circuit board from the display controller  52 . The PMU  56  may also monitor the power connections to an AC power source, as well as the charge of a battery, determine what power should be used to charge the battery, and/or control sleep and on/off functions for the electronic device  10 . 
       FIG. 3  illustrates a configuration of electronic device  10  whereby a sub-circuit, such as the display controller  52 , receives an adjusted voltage V dda  from the PMU  56 . The generation of this adjusted voltage V dda  may be controlled by the power controller  52 , as described below. 
     The PMU  56  may include a DC/DC converter  63 . This DC/DC converter  63  may generally be activated (enabled) by an activation signal from inverter  64 . The DC/DC converter  63  may be utilized to convert voltage from one level to another. The DC/DC converter  63  may include a slave power controller  66  (including a slave switcher  68  and a slave switch  70 ), a diode  72 , as well as passive circuitry such as inductor  74  and capacitor  76 . In the embodiment illustrated in  FIG. 3 , the slave power controller  66 , the diode  72 , the inductor  74 , and the capacitor  76  are in a configuration consistent with a step-up, or boost, DC/DC converter  63 . However, the slave power controller  66 , the diode  72 , the inductor  74 , and the capacitor  76  may alternatively be arranged into other power conversion configurations including a buck, a buck boost, and/or a flyback configuration, based on the adjusted voltage V dda  requirements of a controlling sub-circuit of the electronic device  10 . 
     As noted above, the slave power converter  66  may include a slave switcher  68  and a slave switch  70 . The slave switcher  68  starts or stops switching based on a comparison between a target voltage and the adjusted voltage V dda  received by the slave switcher  68  via a feedback loop. In this manner, the slave power converter  66  regulates the adjusted voltage Vdda to a desired level. The slave switch  70  may be pulsed on and off to charge up an output capacitor  76 . Indeed, the feedback voltage determines whether the slave switch  70 , which may be a metal oxide semiconductor field effect transistor (MOSFET) that may operate as a switch, or any other suitable switch type, is to be pulsed or not pulsed. 
     As described above, the slave switch  70  may be activated and deactivated based on an output of the slave switcher  68 , which, in turn, is controlled by an enable signal received from the inverter  64 . As it switches, the slave switch  70  may alternately provide a path to ground for an input voltage V in . For example, when the slave switch  70  is on, current is allowed to flow through the slave switch  70 , providing a path to ground for the input voltage V in  via the inductor  74 . Conversely, when the slave switch is off, current is prevented from flowing through the slave switch  70 , removing the path to ground for input voltage V in . This input voltage V in  may be a voltage supplied from, for example, the power source  54 . For example, the input voltage V in  may be a high rail voltage from an input voltage rail that may be 3.0 volts. 
     By regulating the amount of time that the path to ground is available for the input voltage V in  to discharge, the value of the adjusted voltage V dda  may be controlled. While slave switch  70  is on, and the path to ground is active, energy may be stored in the inductor  74  as part of a charging phase. Additionally, diode  72  prevents discharge the capacitor  76  to ground. Accordingly, the adjusted voltage V dda  may be equal to the voltage as it discharged from the capacitor  76 . As the capacitor  84  discharges, the adjusted voltage V dda  may begin to drop in value. The value of the dropping adjusted voltage V dda  may be transmitted to the slave switcher  68  via a feedback loop. 
     The value of the adjusted voltage V dda  received via the feedback loop may be compared to a target voltage level required by the display controller  52 . This target level may be, for example, 5.8 volts. As the adjusted voltage V dda  falls below the target level required by the display controller  52 , the slave switcher  68  may cease to provide an activation signal to the slave switch  70 , thus turning the slave switch  70  off and removing the path to ground for input voltage V in . While slave switch  70  is off, and the path to ground is disabled, energy may be released from the inductor  74  as part of a discharge phase. Since the path to ground is disabled, the energy released from the inductor  74  is transmitted to the display controller  52 . As the energy is released, voltage may be provided to the capacitor  76  to charge the capacitor  76 . Additionally, the adjusted voltage V dda  transmitted across power line  58  to the display controller  52  may increase. This increase of the adjusted voltage V dda  may be monitored by the slave switcher  68  via a feedback loop. The adjusted voltage V dda  may be compared to the target voltage in the slave switcher  68 . Once the adjusted voltage V dda  reaches the target voltage, the slave switcher  68  may provide an activation signal to the slave switch  70 , causing the charging phase to begin again. 
     In this manner, the DC/DC converter  63  operates to generate an adjusted voltage V dda , which may be transmitted to the display controller  52  across power line  58 . However, as described above, the DC/DC converter  63  is enabled and disabled (controlled) by an enable signal from inverter  64 . Generation of this enable signal may be performed in the display controller  52 , as described below. 
     The display controller  52  may include display logic  78  that may control the power requirements for the display  24 . The power requirements may be expressed as a target voltage V target . The display logic  78  may also transmit the target voltage V target  to the master power controller  62 , where it may be utilized as the voltage that the master power controller  62  may attempt to maintain, i.e. insure that the adjusted voltage V dda  is maintained at the same level as the target voltage V target . Thus, based on the target voltage V target , the master power controller  62  may generate a control signal that may be used to generate an adjusted voltage V dda  corresponding to the power requirements of the display  24 . 
     The master power controller  62 , may include a master switcher  82  and a master switch  84 . The master power controller  62  may include similar components to those found in the slave power controller  66 . Accordingly, the master switch  84  may perform as a switching device in conjunction with the master switcher  82 . However, because the master power controller  80  is not connected to passive circuitry, such as inverters or capacitors, in the display controller  52 , the master power controller may act as a control signal generator instead of a typical DC/DC controller. This may reduce the overall size of the display controller  52  due to the absence of the passive circuitry typically associated with the master power controller  62 . 
     In generating the control signal, the master switcher  82  may act as a comparator for comparing the target voltage V target  with the adjusted voltage V dda , which may be received by the master switcher  82  as part of a feedback loop. The result of the comparison of the target voltage V target  and the adjusted voltage V dda  may be output in the form of a series of clock pulses. For example, when the adjusted voltage V dda  is determined to be lower than the target voltage V target , the master switcher  82  may begin switching, i.e. generating a series of clock pulses that may toggle the master switch  84  to generate the activation signal for the slave switcher  68 . 
     In operation, the master switch  84  may toggle on and off at a rate determined by the output of the master switcher  82 . The master switcher  82  may make this determination based, in part, on the voltage transmitted across power line  58  via a feedback loop. In this manner, the voltage transmitted across power line  58  acts both as a power line for the display  24  and as a feedback loop used by the master switcher  82  to determine the rate at which to toggle the master switch  84  on and off. 
     The toggling of the master switch  84  may activate and deactivate a control signal across control line  60  used to control internal circuitry of the PMU  56 , thus insuring proper power (adjusted voltage V dda ) is transmitted to the display controller  52  across power line  58 . Toggling the master switch  84  may provide and disable a discharge path to the capacitor  88  across the control line  60  and through the diode  90 . The discharged capacitor  88  is equivalent to a low voltage which is then inverted, via the inverter  64 , to enable the slave switcher  68 . A suitable resistor  86  is chosen to limit the rise time of the RC circuit formed by the capacitor  88  and the resistor  86 , thus limiting the bandwidth of the control signal to the slave switcher  68 . The time constant of the RC circuit may be chosen to be longer than the period of the pulse from the master switcher  82  to filter out individual pulses so that the slave switcher  68  essentially sees on/off signals as an enable signal. 
     It should be noted that by utilizing the control signal as the basis for the enable signal of the slave switcher  68 , the timing sequencing of the display controller  52 , and specifically the master power controller  62 , is maintained implicitly and without an explicit timing control signal. Accordingly, the display controller  52  may continue to function as if it included both a master power controller  62  as well as its own passive components, i.e. as if an unmodified internal DC/DC controller was present, rather than a master power controller  62  absent the passive components typically associated with a DC/DC converter. 
     In this manner, internal circuitry, such as PMU  56 , may provide switched power to a sub-circuit, such as the display controller  52 . The sub-circuit may include a master power controller  62  without passive circuitry typically associated with a DC/DC converter. Thus, instead of generating its own power on sub-circuit, the master power controller  62  may be utilized to generate a control signal that may control the generation of the switched power on the PMU. 
     Specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the claims are not intended to be limited to the particular forms disclosed. Rather, the claims are to cover all modifications, equivalents, and alternatives falling within their spirit and scope.

Metadata:
Filing Date: 20120419
Publication Date: 20131217
Grant Date: 20131217
Priority Date: 20080930
Inventors: AL-DAHLE AHMAD
TAM JOHN CHING YU
FIENNES HUGO
YAO WEI H.
Assignee: APPLE INC
CPC Classifications: [{"code": "H02M1/36", "inventive": false, "first": false, "tree": "[]"}, {"code": "H02M3/156", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02M3/156", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02M1/36", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 42056716