Multilevel switching driver and operation

Abstract

This application describes methods and apparatus for controlling a switching driver to drive a load with a differential drive signal, where the switching driver includes a DC-DC converter configured to generate a boosted voltage. A switching network is configured such that a first output node and a second output node are connectable to either a first supply voltage and a second supply voltage or the boosted voltage. A controller controls the switching network in at least a first mode and a second mode. In the first mode, each of the first output node and the second output node is modulated between the first supply voltage and the second supply voltage with a respective controlled duty cycle. In the second mode, one of the first output node and the second output node is modulated between the first supply voltage and the boosted voltage with a controlled duty cycle, and the other of the first output node and the second output node is maintained at the second supply voltage.

Description

[0001] The field of representative embodiments of this disclosure relates to methods, apparatus and / or implementations of switching drivers, such as Class D amplifiers, etc., which can operate with three or more switching voltages.

[0002] Many electronic devices include transducer driver circuitry systems for driving transducers with appropriate drive signals, such as for driving a host device or an audio output transducer via a connected accessory with an audio drive signal.

[0003] In some applications, the drive circuitry may include a switching amplifier, such as a Class D amplifier, for generating the drive signal. The switching amplifier can be relatively power efficient and is therefore advantageously suited for some applications. The switching amplifier generally operates to switch at least one output node between defined switching voltages, its duty cycle providing the desired average output voltage over the duty cycle of the drive signal. Typically, the switching amplifier can be configured to drive a load in a bridged-load (BTL) configuration, and thus the load can be connected between two output nodes, each of which can be appropriately modulated across the load to generate the desired differential drive signal.

[0004] In some switching amplifiers, each output node can be modulated between two defined switching voltages, such as a positive supply voltage and ground. However, in some cases, at least one additional voltage may be available as a switching voltage, and the switching amplifier can operate to modulate each output node between selected switching voltages. For example, to provide an extended output range for the switching amplifier, a boost voltage can be generated from the supply voltage using a suitable DC-DC converter. When a relatively high amplitude output signal is required, the switching amplifier can operate to modulate the output node between the boost voltage and ground. However, when a lower amplitude output signal is required, the switching amplifier can operate to modulate the output node between the supply voltage and ground, as this reduces the degree of voltage modulation at the output node, which is beneficial for EMI (electromagnetic interference).

[0005] This type of multilevel switching amplifier operates well; however, there may be power losses associated with the boost voltage generated by the DC-DC converter.

[0006] The embodiments disclosed herein relate to switching drivers and operating methods that can provide advantages in power efficiency.

[0007] According to an aspect of the invention, a switching driver device is provided, configured to drive a load connected between a first output node and a second output node using a drive signal based on an input signal. The switching driver device includes a first power node and a second power node configured to receive a first power supply voltage and a second power supply voltage, respectively, and a DC-DC converter configured to generate a boost voltage. A switching network is configured to selectively connect each of the first output node and the second output node to any one of the first power supply voltage, the second power supply voltage, and the boost voltage. A controller is configured to control the switching network, operable to selectively control the switching network in at least a first mode and a second mode. In the first mode, each of the first output node and the second output node is modulated between the first power supply voltage and the second power supply voltage with a corresponding controlled duty cycle. In the second mode, one of the first output node and the second output node is modulated between the first power supply voltage and the boost voltage with a controlled duty cycle, and the other of the first output node and the second output node remains at the second power supply voltage.

[0008] In some examples, the first power supply voltage is a positive power supply voltage, and the second voltage is ground. In some examples, the boost voltage is a positive voltage with an amplitude greater than the first power supply voltage.

[0009] In some examples, the controller may be configured to operate in a first mode for the amplitude of the drive signal in a first range, and in a second mode for the amplitude of the drive signal in a second, higher range. The controller may further operate to control the switching network in a third mode, in which each of the first and second output nodes is modulated between the boost voltage and the second supply voltage with a corresponding controlled duty cycle. The controller may be configured to operate in the third mode for the amplitude of the drive signal in an intermediate range between the first and second ranges.

[0010] In some examples, the controller may be configured in a first mode to selectively operate in each of the first, second, and third modes, and may also be configured in a second mode to selectively operate in the first and third modes without using the second mode.

[0011] In some examples, the controller may be configured to operate in the first mode at a first cycle frequency to modulate the first output node and the second output node, and in the second mode at a second higher cycle frequency to modulate one of the first output node and the second output node.

[0012] In some examples, the controller may be configured to determine which mode to operate in on a cycle-by-cycle basis. The controller may include a modulator configured to generate a modulator output signal for controlling the switching of the switching network based on an input signal, and the controller may be configured to determine which mode to operate in based on the modulator output signal. The modulator may include a quantizer for generating the modulator output signal.

[0013] In some examples, the DC-DC converter may be an inductor boost converter. In some examples, the load may be an audio output transducer, and the input signal may be an audio input signal.

[0014] The switching driver device can be implemented as an integrated circuit.

[0015] In another aspect, a switching driver device is provided, configured to drive a load connected between a first output node and a second output node using a drive signal based on an input signal. The switching driver device includes a first power node and a second power node configured to receive a first power supply voltage and a second power supply voltage, respectively, and a DC-DC converter configured to generate a boost voltage. A switching network is configured to selectively connect each of the first output node and the second output node to any one of the first power supply voltage, the second power supply voltage, and the boost voltage. A controller is configured to control the switching network, the controller being operable in a first mode in which one of the first output node and the second output node is modulated between the first power supply voltage and the boost voltage with a controlled duty cycle, and the other of the first output node and the second output node is maintained at the second power supply voltage.

[0016] The controller can further operate in a second mode, wherein each of the first output node and the second output node is modulated between the first supply voltage and the second supply voltage with a corresponding controlled duty cycle. The controller can further operate in a third mode, wherein each of the first output node and the second output node is modulated between the boost voltage and the second supply voltage with a corresponding controlled duty cycle. The controller can be configured to operate selectively in one of the first mode, the second mode, or the third mode on a cycle-by-cycle basis.

[0017] In another aspect, a switching driver device is provided, configured to drive a load using a drive signal based on an input signal, the switching driver device comprising: a DC-DC converter configured to receive a first power supply voltage from a first voltage source and generate a generated voltage; an output stage having at least a first output node for outputting the drive signal; and a controller configured to operate in a first mode to control the output stage to modulate the first output node between the generated voltage and the first power supply voltage with a controlled duty cycle, such that at least a portion of the load current is drawn from the first power supply voltage via a path not including the DC-DC converter.

[0018] According to another aspect of this disclosure, a switching driver device is provided, configured to drive a load connected between a first output node and a second output node using a drive signal based on an input signal. The switching driver device includes a DC-DC converter configured to generate a boost voltage from a first supply voltage and a second supply voltage, and a switching network configured to selectively connect each of the first output node and the second output node to any one of the first supply voltage, the second supply voltage, and the boost voltage. A controller is configured to control the switching network, operable to selectively control the switching network in multiple modes. In a first mode of the multiple modes, one of the first output node and the second output node is modulated between the first supply voltage and the boost voltage with a controlled duty cycle, and the other of the first output node and the second output node is maintained at the second supply voltage. In the first mode, the controller is configured to dynamically control the average current limit of the DC-DC converter.

[0019] In some examples, the controller may be configured to dynamically control the average current limit of the DC-DC converter based on a first current draw indication. The first current draw indication may be an indication of the load current drawn from a source of the first supply voltage via a path not involving the DC-DC converter. The first current draw indication may be determined based on the average load current indication and the controlled modulation duty cycle. The first current draw indication may be determined as a fraction of the average load current, which is equal to a fraction of a switching cycle in which one of the first and second output nodes is modulated to the first supply voltage. In some examples, the controller may be configured to receive a monitored current signal as the indication of the average load current.

[0020] In some examples, the controller may include a modulator configured to generate a modulator output signal based on an input signal for controlling the switching of the switching network. The controller may be configured to determine the controlled duty cycle from the modulator output signal.

[0021] In some examples, the controller may be configured to dynamically control the average current limit of the DC-DC converter such that the average current limit is lower than or equal to the amount indicated by the first current draw.

[0022] In some examples, the first power supply voltage may be a positive power supply voltage, and the second voltage may be ground. The boost voltage may be a positive voltage with an amplitude greater than the first power supply voltage.

[0023] In some implementations, in a second mode of the multiple modes, each of the first and second output nodes may have its duty cycle modulated between the first and second supply voltages, respectively. In some implementations, in a third mode of the multiple modes, each of the first and second output nodes may have its duty cycle modulated between the boost voltage and the second supply voltage, respectively. The controller may be configured to operate in the first mode with respect to the amplitude of the drive signal in a first range, in the second mode with respect to the amplitude of the drive signal in a second lower range, and in the third mode with respect to the amplitude of the drive signal in an intermediate range between the first and second ranges. The controller may be configured to control the average current limit of the DC-DC converter to a defined fixed value when operating in the second and third modes.

[0024] The controller may be configured to determine whether the mode operates on a cycle-by-cycle basis. The controller may include a modulator configured to generate a modulator output signal for controlling the switching of the switching network based on an input signal, and the controller may be configured to determine which mode to operate in based on the modulator output signal.

[0025] In some examples, the DC-DC converter may be an inductor boost converter. In some examples, the load may be an audio output transducer, and the input signal may be an audio input signal.

[0026] In another aspect, a switching driver device is provided, configured to drive a load using a drive signal based on an input signal. The switching driver device includes a DC-DC converter configured to receive a first supply voltage from a first voltage source and generate a generated voltage, and an output stage having at least a first output node. A controller is configured to operate in a first mode to control the output stage to modulate the first output node between the generated voltage and the first supply voltage, such that at least a portion of the load current is drawn from the first supply voltage via a path excluding the DC-DC converter. In the first mode, the controller is configured to dynamically control the average current limit of the DC-DC converter.

[0027] In another aspect, a switching driver device is provided, configured to drive a load connected between a first output node and a second output node using a drive signal based on an input signal. The switching driver device includes a DC-DC converter and a controller, the DC-DC converter being configured to generate a generated voltage from at least a first supply voltage, and the controller being configured to control an output stage to control voltage modulation of the first and second output nodes. The controller is configured to modulate one of the first and second output nodes with a controlled duty cycle between the generated voltage and the first supply voltage for a first range of the amplitude of the drive signal, while the other of the first and second output nodes remains at a constant voltage, and to dynamically control the average current limit of the DC-DC converter based on the controlled duty cycle.

[0028] It should be noted that, unless expressly stated to the contrary or otherwise clearly incompatible herein, any feature described herein may be implemented in combination with any one or more other described features.

[0029] To better understand the examples of this disclosure, and to more clearly illustrate how the examples can be implemented, reference will now be made to the following figures by way of example only, in which: Figure 1 The illustration shows an example of a switching driver device with a DC-DC converter; Figure 2 A more detailed illustration of an example of a switching drive device with a DC-DC converter; Figure 3a and 3b The diagram illustrates an exemplary switching waveform operating in the first and second modes; Figure 4 The figure illustrates an exemplary switching waveform of a switching driver device that can operate in a first mode and a second mode; Figure 5The diagram illustrates an exemplary switching waveform operating in the third mode; Figure 6 The diagram illustrates exemplary switching waveforms of a switching driver device operable in a first mode, a second mode, and a third mode; and Figure 7 An example of a suitable controller is shown.

[0030] The following description sets forth exemplary embodiments according to this disclosure. Further exemplary embodiments and implementations will be apparent to those skilled in the art. Furthermore, those skilled in the art will recognize that various equivalent techniques may be applied in place of or in combination with the embodiments discussed below, and all such equivalent techniques should be considered to be covered by this disclosure.

[0031] Embodiments of this disclosure relate to driver circuit systems for driving transducers, and more particularly to switching driver circuit systems in which output nodes can be switched between different switching voltages having controlled duty cycles. Embodiments of this disclosure also relate to methods of operating the driver circuit system.

[0032] Figure 1 An example of a driver device 100 for driving a load 101 according to an embodiment is shown. In this example, the load 101 is illustrated as an audio output transducer, such as a speaker, but it should be understood that in other examples, the driver device may be implemented to drive other types of output transducers. The driver device 100 is configured to drive the load 101 in a BTL configuration, and thus the load 101 is connected between a first output node 102p and a second output node 102m. In some embodiments, an output filter may be present in the corresponding output path between each output node 102p and 102m and the load. Figure 1 (not shown in the image), for example, an inductor-capacitor (LC) filter.

[0033] The driver device 100 receives a first power supply voltage and a second power supply voltage, which in this example are positive power supply voltages VP from a first power supply and ground. The driver device 100 also includes a DC-DC converter 103 for generating an additional voltage from the first power supply voltage and the second power supply voltage, which in this example is a boost voltage Vbst.

[0034] In some examples, the DC-DC converter 103 may be an inductor boost converter and therefore may operate in conjunction with an inductor Lbst, as illustrated. In examples where the driver device 100 is implemented as an integrated circuit, the inductor Lbst may be implemented as an external (i.e., off-chip) component. Figure 1The diagram also illustrates the presence of additional capacitors Cbst to maintain the boost voltage Vbst generated by the DC-DC converter 103, which can also be implemented at least in part by one or more external (i.e., off-chip) components. However, it should be understood that other arrangements are possible, and the DC-DC converter 103 can be implemented, for example, as a charge pump for providing the boost output voltage.

[0035] The first and second supply voltages (VP ​​and ground in this example) are provided to driver 104 together with the boost voltage Vbst to be used as switching voltages. Because driver 104 is operable to selectively connect each of the output nodes 102p and 102m to any one of these three switching voltages, driver 104 may be referred to as a Y-bridge driver (sometimes also as a T-bridge driver), although it will be understood that this is merely a convenient label and does not imply the physical layout of the driver.

[0036] Figure 2 An exemplary implementation of the driver device 100 is illustrated in more detail.

[0037] Driver 104 includes a switching output stage, which in this example includes switches S1p, S2p, and S3p for connecting a first output node 102p to ground, a power supply voltage VP, or a boost voltage Vbst, respectively. Similarly, switches S1m, S2m, and S3m selectively connect a second output node 102m to ground, a power supply voltage VP, or a boost voltage Vbst, respectively. The operation of switches S1p, S2p, S3p, S1m, S2m, and S3m is controlled by a switching control signal Scon generated by controller 201 based on the input signal Sin, as will be described in more detail below. Controller 201 may include a modulator, which may be implemented as an analog modulator, a digital modulator, or a hybrid modulator (partially analog and partially digital).

[0038] In this example, DC-DC converter 103 is a conventional inductor boost converter. In use, inductor node NL is connected to one end of inductor Lbst, and the other end of inductor Lbst is connected to the supply voltage VP. Switch SW_L of DC-DC converter 103 selectively connects inductor node NL to a defined voltage, in this example, ground, and selectively connects inductor node NL to the output of DC-DC converter 103. As those skilled in the art will understand, DC-DC converter 103 will operate repeatedly in switching cycles comprising a charging phase and an output phase, in which switch SW_L is closed (where SW_H is open) to ramp up the current in inductor Lbst, and in the output phase, switch SW_H is closed (where SW_L is open) to output a boost voltage Vbst maintained by capacitor Cbst. The switching of switches SW_H and SW_L can also be controlled by controller 201, as will be discussed below.

[0039] In some implementations, controller 201 may be configured to control driver 104 to operate selectively in any of at least two modes.

[0040] In the first mode, each of the first output node 102p and the second output node 102m can be modulated between the power supply voltage VP and ground in each switching cycle with a controlled duty cycle. Figure 3a The diagram illustrates an exemplary voltage waveform for operation of the positive differential drive voltage in the first mode (wherein, for the purposes of this application, the positive differential drive voltage should be understood to mean, on average, that the voltage at the first output node 102p is more positive than the voltage at the second output node 102m during the switching cycle). Therefore... Figure 3a The diagram illustrates the voltages Voutp and Voutm at the first output node 102p and the second output node 102m, respectively, and the resulting differential voltage Vdiff during the switching cycle Tpwm1. The driver 104 can switch in a first mode at a first cycle frequency, which defines the cycle period Tpwm1.

[0041] In this first operating mode, each of the first output node 102p and the second output node 102m is modulated between the supply voltage VP and ground, and for a positive differential drive voltage, the first output node 102p spends a larger proportion of switching cycles than the second output node 102m at the supply voltage VP. This first operating mode can be used to generate differential drive voltages in the range of +VP to -VP.

[0042] In the first operating mode, switches S3p and S3m are therefore off (i.e., off and non-conducting) throughout the entire cycle Tpwm1. Switches S2p ​​and S1p are duty cycle controlled, i.e., switched on and off in opposite phases, to provide the desired duty cycle for the first output node 102p, and switches S2p ​​and S1p are also duty cycle controlled to provide the desired duty cycle for the second output node 102p.

[0043] In the first operating mode, the boost voltage Vbst is not used, and in some embodiments, the DC-DC converter 103 may operate in a relatively low-power burst operating mode. That is, the DC-DC converter 103 may occasionally operate in relatively short bursts to maintain the voltage on capacitor Cbst, for example, taking into account any leakage, so as to be ready for use when needed, but the DC-DC converter 103 may operate discontinuously to reduce power consumption. During abrupt operations that may occur periodically or based on some measurement of the voltage on capacitor Cbst, switches SW_H and SW_L may be switched in opposite phase at the DC-DC converter switching frequency, which will be substantially significantly higher than the switching cycle frequency of the output stage.

[0044] In the second mode, each of the first output node 102p and the second output node 102m can be modulated between the boost voltage Vbst and ground at the same first cycle frequency in each switching cycle with a controlled duty cycle. Figure 3b The illustration shows an exemplary voltage waveform operating in the second mode, which is also a positive differential drive voltage. Therefore, Figure 3b The diagram again illustrates the voltages Voutp and Voutm at the first output node 102p and the second output node 102m, respectively, and the resulting differential voltage Vdiff during the switching cycle Tpwm1. In this second mode, each of the first output node 102p and the second output node 102m is modulated between the boost voltage Vbst and ground, and for a positive differential drive voltage, the first output node 102p spends a larger proportion of the switching cycles than the second output node 102m at the boost voltage Vbst. This second operating mode can be used to generate differential drive voltages in the range of +Vbst to -Vbst.

[0045] In the second operating mode, the boost voltage Vbst is used as the switching voltage, and therefore the DC-DC converter 103 is continuously active, and the switches SW_H and SW_L switch in opposite phase at the DC-DC converter switching frequency.

[0046] In some implementations, controller 201 may be configured to control the operation of the output stage to operate in a first mode or a second mode on a cycle-by-cycle basis. In some implementations, the operating mode may be determined based on comparing a signal indicating the desired output voltage with at least one threshold. In some implementations, the output of the controller's modulator (e.g., the output of a PWM (Pulse Width Modulation) quantizer) may be used in conjunction with at least one threshold to determine the operating mode. In this way, cycle-by-cycle mode transitions can be effectively instantaneous, and cycle-by-cycle signal tracking is achieved. Using the first operating mode for a low-level signal improves power efficiency and may also benefit from reduced EMI compared to continuous operation in the second mode using a boost voltage Vbst.

[0047] Figure 4 The diagram illustrates an example of a switching waveform, showing how driver device 100 can switch between a first mode and a second mode using signal levels. Figure 4 The instantaneous voltages Voutm and Voutp, as well as the differential output voltage Vdiff, are shown again, and the differential drive signal Vdrv, corresponding to the averaged or filtered version of the instantaneous differential output Vdiff, is also illustrated. It will be understood that the individual switching cycles of the modulation cannot be accurately represented on the timescale of the evolution of the output drive signal Vdrv, and therefore... Figure 4 This only indicates the relevant modulation applied. From Figure 4 It can be seen that for low-level signals, in the range of approximately +VP to -VP or less, driver 104 operates in the first mode, while for higher signal levels, driver 104 operates in the second mode.

[0048] While this operation provides the advantages described above, operation in the second mode does result in the load current being drawn essentially through the DC-DC converter 103, i.e., the energy transfer from the first power source to the load is via the DC-DC converter 103, which may involve some inefficiency.

[0049] In some implementations, controller 201 may be configured to control driver 104 to operate in a third operating mode. In the third operating mode, driver 104 may be controlled to drive a load in a single-ended manner by modulating one of the output nodes between the boost voltage Vbst and the supply voltage VP, while the other output node remains grounded throughout the switching cycle. In this third operating mode, the cycle frequency may be varied to a second cycle frequency, which may be substantially twice the first cycle frequency, such that any tones in the differential voltage remain at the same frequency (the output of the signal band of interest).

[0050] Figure 5 The diagram illustrates an exemplary voltage waveform operating in the third mode, which is also a positive differential drive voltage. Figure 5The diagram again illustrates the voltages Voutp and Voutm at the first output node 102p and the second output node 102m, respectively, and the resulting differential voltage Vdiff, during the switching cycle Tpwm2 (at the second cycle frequency). In this third mode, for the positive differential drive signal Vdrv, the first output node 102p is modulated between the boost voltage Vbst and the power supply voltage VP, while the second output node 102m is connected to ground throughout the switching cycle. For the negative differential drive signal Vdrv, the second output node 102m will be modulated between the boost voltage Vbst and the power supply voltage VP, while the first output node 102p will be connected to ground.

[0051] In the third operating mode, for a positive differential drive voltage, switch S1m will be closed throughout the switching cycle (while switches S2m and S3m will be open). Switch S1p will be open throughout the switching cycle, and switches S3p and S2p will be switched on and off together in opposite phases with a controlled duty cycle at the switching cycle frequency.

[0052] In this third operating mode, the boost voltage Vbst is used as the switching voltage, and therefore the DC-DC converter 103 remains active, and the switches SW_H and SW_L switch in opposite phase at the DC-DC converter switching frequency.

[0053] Operating in this third mode offers advantages in terms of power efficiency because some of the output power is drawn directly from the first power source (i.e., the source of the power supply voltage VP), bypassing the DC-DC converter 103. As mentioned above, in the second mode, all output power is efficiently drawn indirectly from the first power source via the DC-DC converter 103. The DC-DC converter 103 is not 100% efficient, and therefore, powering via the DC-DC converter 103 will inevitably involve some losses. Drawing power directly from the first power source as much as possible reduces the losses associated with the operation of the DC-DC converter 103 and improves efficiency.

[0054] During a portion of the switching cycle in which output node 102p (or 102m) is modulated to the boost voltage Vbst, switch S3p (or S3m, depending on the situation) will close, providing a first current path from the first supply voltage through DC-DC converter 103 to the load and then to ground. During a portion of the switching cycle in which output node 102p (or 102m) is modulated to the supply voltage VP, switch S2p (or S2m, depending on the situation) will close, providing a second current path from the first supply directly to the load and then to ground. At least a portion of the load current will be delivered directly from the first supply to the load, thus avoiding losses associated with DC-DC converter 103. Thus, when operating in the third mode, a given output power can be delivered more efficiently than in the second mode.

[0055] Operation in the third mode can be used to generate positive or negative differential drive voltages with amplitudes ranging from Vbst to VP.

[0056] As described above, controller 201 can be configured to control the operation of the output stage of driver 104 to operate on a cycle-by-cycle basis in a first or third mode, and the operating mode can be determined based on comparing a signal indicating the desired output voltage with at least one threshold, for example by using the output of the quantizer of the controller's modulator.

[0057] In some implementations, controller 201 may be configured to switch directly between the first and third modes. However, it will be understood that the maximum differential drive voltage achievable when operating in the first mode will have an amplitude equal to the supply voltage VP, and this requires one output node to be driven to the supply voltage VP (i.e., 100% duty cycle) for the entire switching cycle, while the other output node is driven to ground for the entire switching cycle. The minimum differential drive voltage achievable when operating in the third mode will also have an amplitude VP, and this again requires the relevant output node to be driven to the supply voltage VP for the entire switching cycle (but this corresponds to a duty cycle of 0% of the time spent at the highest switching voltage in the relevant mode). In at least some modulator designs, it may be difficult to achieve very high duty cycles, i.e., approximately 100% duty cycle, and / or switching the duty cycle between 100% and 0% can cause some distortion in the output signal.

[0058] To avoid these problems, in some implementations, controller 201 may be configured to switch between the first mode and the third mode by using a second mode.

[0059] Figure 6 The diagram illustrates an example of a switching waveform, showing how driver device 100 can switch between a second mode and a third mode using signal levels. Figure 6The instantaneous voltages Voutm and Voutp, as well as the differential output voltage Vdiff, are shown again, and the differential drive signal Vdrv, corresponding to the averaged or filtered version of the instantaneous differential output Vdiff, is also illustrated. From Figure 4 As can be seen, for low-level signals, below a first threshold amplitude (below the amplitude of the power supply voltage VP), driver 104 operates in the first mode. Between this first amplitude threshold and a higher second amplitude threshold (above the amplitude of the power supply voltage VP), driver 104 operates in the second mode. For output amplitudes above the second threshold, for power efficiency, driver 104 operates in the third mode. When operating in the first mode, the first threshold may correspond to the desired upper limit of the duty cycle, and when operating in the first mode, the second threshold may correspond to the desired upper limit of the duty cycle.

[0060] Therefore, with reference Figure 4 Compared to the described operation, using a third mode for signals in a high signal level range above a second threshold amplitude can provide power efficiency, whereas the second mode is used only for signals in this amplitude range.

[0061] However, the operation of drawing some load current directly from the first power supply instead of drawing all load current via DC-DC converter 103 means that the current delivered via DC-DC converter 103 no longer represents the total current drawn from the first power supply voltage during the operation of driver 104.

[0062] In some implementations, as those skilled in the art will understand, current limits may be applied in the DC-DC converter 103 to limit the current drawn from a first power source (i.e., the source of the power supply voltage VP). Maximum current limits may exist to prevent the drawing of sufficiently high levels of current that could damage components of the driver device, but average current limits may also typically exist to limit the average current drawn from the first power source. For example, for portable devices operable such that the first power source may sometimes be a battery, it is desirable to limit the average current that can be drawn from the battery during use.

[0063] Conventionally, an average current limit can be applied within the DC-DC converter 103 based on a defined current limit. Those skilled in the art will appreciate the various ways to implement an average current limit in a DC-DC converter 103, such as an inductor boost converter.

[0064] If the defined current limit applied in the DC-DC converter 103 is set to be equal to the maximum desired average current drawn from the first power supply, problems may occur in operation in the third mode because the DC-DC converter 103 may be operating to draw a current equal to the defined current limit, but for part of the switching cycle, some additional current will be drawn directly from the first power supply and may therefore exceed the maximum desired average current drawn.

[0065] Purely as an example, consider driver 104 operating in a third operating mode, with an average load current of 1 A. The proportion of this average load current delivered via DC-DC converter 103 will depend on the operating duty cycle (the duty cycle of the relevant output node modulated between Vbst and VP). For example, if the duty cycle is 70%, the average load current drawn from DC-DC converter 103 could be 0.7 A in terms of the proportion of switching cycles spent at the boost voltage Vbst, where 0.3 A is drawn directly from the first power supply on average. If a defined current limit for the DC-DC converter is set at the level of the desired maximum average current draw from the first power supply, such as 2 A, then the operation of DC-DC converter 103 could result in an average current draw of 2 A from the first power supply. In this case, the additional average current draw of 0.3 A directly from the first power supply would result in a total average current draw of 2.3 A, which exceeds the desired maximum average current draw in this example.

[0066] When operating in the third mode, a statically limited current limit can be set for the DC-DC converter 103 based on the expected maximum value of the average current drawn directly from the first power supply. However, such a static limit is therefore too low for other operating conditions (when the current drawn directly from the first power supply is less than the maximum value) and may therefore result in an unnecessary current limit that negatively impacts performance.

[0067] In at least some embodiments, when operating in a third operating mode, the limited current limit (maximum average current draw) of the DC-DC converter 103 can be dynamically varied during use. When operating in the third mode, the limited current limit can be set based on an indication of the current drawn directly from the first power source. In some cases, when operating in the third mode, the indication of the current drawn directly from the first power source can be based on an indication of the load current and the current duty cycle of operation in the third mode.

[0068] In many switching driver implementations, the output current can be monitored for other reasons, and therefore an indication of the load current may already be available. The operating duty cycle is determined by the controller 201 and is therefore known.

[0069] Therefore, for the example discussed above, where the average load current is 1 A and the duty cycle is 70%, the average current drawn directly from the first power supply is 0.3 A. The limited current limit of the DC-DC converter 103 can be set to 1.7 A, such that the maximum average current drawn by the DC-DC converter 103 together with the average current drawn directly from the first power supply does not exceed the expected maximum average current drawn of 2 A in this example.

[0070] Figure 7 The diagram illustrates an example of a possible arrangement of the controller 201 according to the implementation scheme. Figure 7 The illustrated input signal Sin can be supplied to modulator 701, which generates a PWM control signal Spwm to control the switching of the output stage of driver 104. Those skilled in the art will recognize a variety of different modulator designs that can be implemented, but... Figure 7 The example diagram illustrates that the input signal can be combined with the feedback signal Sfb and filtered by the loop filter 702, and supplied to the quantizer 703 to generate a PWM signal Spwm. The PWM signal is supplied to the switching driver 704 to generate a switching control signal Scon. The PWM signal Spwm output from the modulator can also be input to the mode controller 705, which determines the relevant operating mode, allowing for the design of which switches are switched in response to the PWM signal Spwm, and the use of an appropriate carrier for the quantizer 703.

[0071] exist Figure 7 In the example, the mode controller 705 may also receive an indication IMON of the output current, and when operating in the third mode, a dynamic current limit Ilim of the average current for the DC-DC converter 103 may be set, for example, by the limiter 706 of the DC-DC converter 103.

[0072] With the ability to ensure that the average current draw is kept below the desired maximum value, the ability to operate in the third mode and dynamically control the average current limit imposed by the DC-DC converter 103 thus provides the power efficiency benefits of operating in the third mode. However, in some applications, it may be preferable to impose all current limits via the DC-DC converter 103, in which case it is desirable for the switching drive device to operate only in the first and second modes, as referenced. Figure 4 As discussed above. In some implementations, the switching driver can be configured to operate in a two-level mode (switching between a first mode and a second mode) or a three-level mode (switching between a first mode, a second mode, and a third mode).

[0073] Please note that the examples above have been described in the context of a switching driver operating with three switching voltages, but some principles can be extended to operation with a larger number of switching voltages. For example, a DC-DC converter may operate in different modes to provide different output voltages, and / or there may be more than one DC-DC converter to provide different boost voltages. However, in general, in single-ended modulation schemes, switching between the output voltage provided by the DC-DC converter and the supply voltage allows at least some energy to be transferred directly from the voltage supply, rather than the DC-DC converter having some efficiency advantage. The discussion also focuses on the supply voltage as a positive supply voltage and ground, but at least one of the supply voltages can be a negative supply voltage and / or the DC-DC converter can produce a negative voltage.

[0074] The driver device of the embodiments of this disclosure is suitable for driving an output transducer. In some implementations, the output transducer may be an audio output transducer, such as a loudspeaker. The output transducer may be a haptic output transducer. In some implementations, the output transducer may be driven in series with an inductor, i.e., an inductor may be present in the output path between the output node of the switching driver and the load. In some implementations, the transducer may be a piezoelectric or ceramic transducer.

[0075] The implementation can be implemented as an integrated circuit. The implementation can be implemented in a host device, particularly a portable and / or battery-powered host device, such as a mobile computing device, like a laptop computer, notebook computer, or tablet computer, or a mobile communication device, such as a mobile phone, e.g., a smartphone. The device can be a wearable device such as a smartwatch. The host device can be a game console, remote control, home automation controller, or home appliance, toy, machine such as a robot, audio player, or video player. It should be understood that the implementation can be implemented as part of a system located in a home appliance, vehicle, or interactive display. Further, a host device incorporating the implementation described above is provided.

[0076] Those skilled in the art will recognize that some aspects of the apparatus and methods described above (e.g., aspects of controlling switching control signals to achieve different modes) can be embodied, for example, on a non-volatile carrier medium such as a disc, CD-ROM, or DVD-ROM, a programmable memory such as read-only memory (firmware), or on a data carrier such as an optical or electrical signal carrier, processor control code. For some applications, implementations can be implemented on a DSP (Digital Signal Processor), ASIC (Application-Specific Integrated Circuit), or FPGA (Field-Programmable Gate Array). Therefore, the code can include conventional program code or microcode, or, for example, code for setting or controlling an ASIC or FPGA. The code can also include code for dynamically configuring reconfigurable devices (such as reprogrammable gate arrays). Similarly, the code can include code for hardware description languages ​​(such as Verilog™ or VHDL (Very High Speed ​​Integrated Circuit Hardware Description Language)). As those skilled in the art will understand, the code can be distributed among multiple coupled components that communicate with each other. Where appropriate, implementations can also be implemented using code that runs on a field-programmable (reprogrammable) analog array or similar device to configure analog hardware.

[0077] It should be noted that the above embodiments are illustrative and not limiting of the invention, and those skilled in the art will be able to devise many alternative embodiments without departing from the scope of the appended claims. The word "comprising" does not exclude the presence of elements or steps other than those listed in the claims, "a (or an)" does not exclude a plurality, and a single feature or other unit may perform the function of several units recited in the claims. Any reference numerals or designations in the claims should not be construed as limiting their scope.

Claims

1. A switching driver device configured to drive a load connected between a first output node and a second output node using a drive signal based on an input signal, the switching driver device comprising: A first power node and a second power node are configured to receive a first power supply voltage and a second power supply voltage, respectively. A DC-DC converter configured to generate a boost voltage; A switching network configured to selectively connect each of the first output node and the second output node to any one of the first power supply voltage, the second power supply voltage, and the boost voltage; and A controller configured to control the switching network, the controller being operable to selectively control the switching network in at least a first mode and a second mode. In the first mode, each of the first output node and the second output node is modulated between the first power supply voltage and the second power supply voltage with a corresponding controlled duty cycle. and In the second mode, one of the first output node and the second output node is modulated between the first power supply voltage and the boost voltage with a controlled duty cycle, and the other of the first output node and the second output node is maintained at the second power supply voltage.

2. The switching driver device according to claim 1, wherein the first power supply voltage is a positive power supply voltage, and the second voltage is ground.

3. The switching driver device according to claim 1 or claim 2, wherein the boost voltage is a positive voltage greater than the first power supply voltage.

4. The switching driver device according to any one of claims 1 to 3, wherein the controller is configured to operate in the first mode for the amplitude of the drive signal in a first range, and in the second mode for the amplitude of the drive signal in a second higher range.

5. The switching driver device of claim 4, wherein the controller is further operated to control the switching network in a third mode, wherein each of the first output node and the second output node is modulated between the boost voltage and the second power supply voltage with a corresponding controlled duty cycle.

6. The switching driver device of claim 5, wherein the controller is configured to operate in the third mode for the amplitude of the drive signal in an intermediate range between the first range and the second range.

7. The switching driver device according to claim 5 or claim 6, wherein the controller is configured in a first mode to selectively operate in each of the first mode, the second mode and the third mode, and is also configured in a second mode to selectively operate in the first mode and the third mode without using the second mode.

8. The switching driver device according to any one of claims 1 to 7, wherein the controller is configured to operate at a first cycle frequency in the first mode to modulate the first output node and the second output node, and to operate at a second higher cycle frequency in the second mode to modulate one of the first output node and the second output node.

9. The switching driver device according to any one of claims 1 to 8, wherein the controller is configured to determine in which mode to operate on a cycle-by-cycle basis.

10. The switching driver device of claim 9, wherein the controller includes a modulator configured to generate a modulator output signal for controlling the switching of the switching network based on an input signal, and the controller is configured to determine, based on the modulator output signal, in which mode to operate.

11. The switching driver device of claim 10, wherein the modulator includes a quantizer for generating the modulator output signal.

12. The switching driver device according to any one of claims 1 to 11, wherein the DC-DC converter is an inductor boost converter.

13. The switching driver device according to any one of claims 1 to 12, wherein the load is an audio output transducer, and wherein the input signal is an audio input signal.

14. The switching driver device according to any one of claims 1 to 13, wherein it is implemented as an integrated circuit.

15. A switching driver device configured to drive a load connected between a first output node and a second output node using a drive signal based on an input signal, the switching driver device comprising: A first power node and a second power node are configured to receive a first power supply voltage and a second power supply voltage, respectively. A DC-DC converter configured to generate a boost voltage; A switching network configured to selectively connect each of the first output node and the second output node to any one of the first power supply voltage, the second power supply voltage, and the boost voltage; and A controller configured to control the switching network, the controller being operable in a first mode in which one of the first output node and the second output node is modulated between the first power supply voltage and the boost voltage with a controlled duty cycle, and the other of the first output node and the second output node is maintained at the second power supply voltage.

16. The switching driver device of claim 15, wherein the controller is further operable in a second mode, wherein each of the first output node and the second output node is modulated between the first power supply voltage and the second power supply voltage with a corresponding controlled duty cycle.

17. The switching driver device of claim 16, wherein the controller is further operable in a third mode in which each of the first output node and the second output node is modulated between the boost voltage and the second power supply voltage with a corresponding controlled duty cycle.

18. The switching driver device of claim 17, wherein the controller is configured to operate selectively in one of the first mode, the second mode, or the third mode on a cycle-by-cycle basis.

19. A switching driver device configured to drive a load using a drive signal based on an input signal, the switching driver device comprising: A DC-DC converter is configured to receive a first power supply voltage from a first voltage source and generate the generated voltage. An output stage having at least a first output node for outputting the drive signal; A controller configured to operate in a first mode to control the output stage to modulate the first output node between the generated voltage and the first supply voltage with a controlled duty cycle, such that at least a portion of the load current is drawn from the first supply voltage via a path that does not include the DC-DC converter.

20. A switching driver device configured to drive a load connected between a first output node and a second output node using a drive signal based on an input signal, the switching driver device comprising: A DC-DC converter configured to generate a boost voltage from the first supply voltage and the second supply voltage; A switching network configured to selectively connect each of the first output node and the second output node to any one of the first power supply voltage, the second power supply voltage, and the boost voltage; and A controller configured to control the switching network, the controller being operable to selectively control the switching network in multiple modes. In the first of the multiple modes, one of the first and second output nodes is modulated between the first power supply voltage and the boost voltage with a controlled duty cycle, and the other of the first and second output nodes remains at the second power supply voltage; and In the first mode, the controller is configured to dynamically control the average current limit of the DC-DC converter.

21. The switching driver device of claim 20, wherein the controller is configured to dynamically control the average current limit of the DC-DC converter based on a first current draw indication, wherein the first current draw indication is an indication of the load current drawn from a source of the first power supply voltage via a path not involving the DC-DC converter.

22. The switching driver device of claim 21, wherein the first current draw indication is determined based on an indication of the average load current and the controlled modulation duty cycle.

23. The switching driver device of claim 22, wherein the first current draw indication is determined as a fraction of the average load current, the fraction being equal to a fraction of a switching cycle in which one of the first output node and the second output node is modulated to the first power supply voltage.

24. The switching driver device of claim 22 or claim 23, wherein the controller is configured to receive a monitored current signal as an indication of the average load current.

25. The switching driver device according to any one of claims 22 to 24, wherein the controller includes a modulator configured to generate a modulator output signal for controlling the switching of the switching network based on an input signal, and the controller is configured to determine the controlled duty cycle from the modulator output signal.

26. The switching driver device of any one of claims 21 to 25, wherein the controller is configured to dynamically control the average current limit of the DC-DC converter such that the average current limit is lower than the maximum average current draw limit by an amount equal to the first current draw indication.

27. A switching driver device configured to drive a load using a drive signal based on an input signal, the switching driver device comprising: A DC-DC converter is configured to receive a first power supply voltage from a first voltage source and generate the generated voltage. An output stage, which has at least a first output node; A controller configured to operate in a first mode to control the output stage to modulate the first output node between the generated voltage and the first supply voltage, such that at least a portion of the load current is drawn from the first supply voltage via a path that does not include the DC-DC converter. In the first mode, the controller is configured to dynamically control the average current limit of the DC-DC converter.

28. A switching driver device configured to drive a load connected between a first output node and a second output node using a drive signal based on an input signal, the switching driver device comprising: A DC-DC converter configured to generate the generated voltage from at least a first supply voltage; A controller is configured to control the output stage to control the voltage modulation of the first output node and the second output node. The controller is configured to modulate one of the first output node and the second output node with a controlled duty cycle between the generated voltage and the first power supply voltage for a first range of the amplitude of the drive signal, while the other of the first output node and the second output node is maintained at a constant voltage, and to dynamically control the average current limit of the DC-DC converter based on the controlled duty cycle.

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