Soft start method for single-inductor multiple-output power supply

Abstract

A method for soft starting a single-inductor multiple-output (SIMO) power supply is provided. The method includes selecting operation in a pulse-width modulation (PWM) mode. A first pulse frequency modulation (PFM) mode is enabled to supply a first voltage to a first load, and the power supply begins ramping up an output voltage. After the output voltage has reached a desired value in the PFM mode, the PFM mode is disabled. Operation is then enabled in the PWM mode. The SIMO power supply then supplies current to one or more loads in the PWM mode.

Description

Technical Field

[0001] This disclosure generally relates to electronic circuits, and more specifically, to a soft-start method for a single inductor multiple output (SIMO) power supply. Background Technology

[0002] Integrated circuits require at least one DC voltage source, and typically more than one. Single Inductor Multiple Output (SIMO) is a switch-mode power supply that uses only one inductor and feedback control circuitry to generate two or more regulated DC output voltages. Various modulation techniques are used in the design of switch-mode power supplies. One approach uses pulse width modulation (PWM). PWM schemes use a clock with a fixed frequency applied to the switching of the switch-mode power supply to power the load. Typically, PWM converters are used in applications requiring high efficiency under heavy loads.

[0003] During the SIMO startup sequence, the inrush current can be high enough to cause overcurrent or overvoltage conditions and damage components powered by the SIMO power supply. To prevent the high inrush current during SIMO power supply startup, various soft-start circuits are used. These soft-start circuits require additional components to limit the inrush current, prevent overcurrent in the inductor, and prevent overvoltage on the output. These additional components increase the complexity of the integrated circuit implementation of the PWM switch-mode power supply, raise its cost, and increase its area.

[0004] Therefore, a soft-start technology for PWM switching mode power supplies that does not require additional components is needed. Summary of the Invention

[0005] According to a first aspect of the present invention, a method for a soft-start single-inductor multiple-output (SIMO) power supply is provided, the method comprising:

[0006] Select the pulse width modulation (PWM) mode;

[0007] The first pulse frequency modulation (PFM) mode is enabled in the SIMO power supply;

[0008] In the first PFM mode, a first voltage is supplied to the first load;

[0009] Deactivate the first PFM mode;

[0010] Enable the PWM mode in the SIMO power supply; and

[0011] The SIMO power supply is operated in the PWM mode.

[0012] In one or more embodiments, the method further includes using a finite state machine to control the SIMO power supply.

[0013] In one or more embodiments, operating the SIMO power supply in the PWM mode further includes:

[0014] After disabling the first PFM mode and before operating the SIMO power supply in the PWM mode, select the second PFM mode; and

[0015] In the second PFM mode, the first voltage is supplied to the first load and the second voltage is supplied to the second load.

[0016] In one or more embodiments, the method further includes: simultaneously supplying the first voltage to the first load and supplying the second voltage to the second load in the first PFM mode, further including charging a single inductor through the first load and the second load.

[0017] In one or more embodiments, supplying the first voltage to the first load and supplying the second voltage to the second load in the second PFM mode further includes:

[0018] The single inductor is charged in the second PFM mode;

[0019] The single inductor is discharged through the first load in the second PFM mode;

[0020] Recharge the single inductor in the second PFM mode; and

[0021] The single inductor is discharged through the second load in the second PFM mode.

[0022] In one or more embodiments, the second voltage is higher than the first voltage.

[0023] In one or more embodiments, the second voltage is higher than the supply voltage provided to the SIMO power supply, and the first voltage is lower than the supply voltage.

[0024] In one or more embodiments, the method further includes providing the power supply voltage from the battery.

[0025] In one or more embodiments, operating the SIMO power supply in the PWM mode further includes providing a clock in the PWM mode.

[0026] According to a second aspect of the present invention, a method for soft-starting a single-inductor multiple-output (SIMO) power supply is provided, the method comprising:

[0027] Select the pulse width modulation (PWM) mode;

[0028] Charging a single inductor in the first pulse frequency modulation (PFM) mode;

[0029] The single inductor is discharged through the first load in the first PFM mode;

[0030] The single inductor is recharged in the first PFM mode;

[0031] The single inductor is discharged through a second load in the first PFM mode;

[0032] Deactivate the first PFM mode;

[0033] Enable the PWM mode after disabling the first PFM mode; and

[0034] The SIMO power supply is operated in the PWM mode.

[0035] In one or more embodiments, the method further includes controlling the SIMO power supply using a finite state machine.

[0036] In one or more embodiments, operating the SIMO power supply in the PWM mode further includes:

[0037] In the PWM mode, the single inductor is charged to a first voltage; and

[0038] The single inductor is discharged from the first voltage to the second voltage sequentially through the first load and then through the second load.

[0039] In one or more embodiments, the method further includes enabling a second PFM mode before selecting the first PFM mode during the soft boot of the SIMO power supply, wherein the second PFM mode includes:

[0040] Simultaneously, the single inductor is charged through the first load and the second load; and

[0041] Simultaneously, the single inductor is discharged through the first load and the second load.

[0042] In one or more embodiments, the method further includes providing a supply voltage from a battery to the SIMO power source.

[0043] In one or more embodiments, the steps of charging the single inductor in the first PFM mode and discharging the single inductor through the first load in the first PFM mode further include the steps of repeated charging and discharging until a first voltage is reached.

[0044] These and other aspects of the invention will become apparent from the embodiments described below, and will be illustrated with reference to these embodiments. Attached Figure Description

[0045] The invention is illustrated by way of example and is not limited to the accompanying drawings, in which similar reference numerals indicate similar elements. The elements in the figures are shown for simplicity and clarity and are not necessarily drawn to scale.

[0046] Figure 1 A SIMO switch-mode power supply according to an embodiment is shown.

[0047] Figure 2 An example is shown. Figure 1 The power stage.

[0048] Figure 3 It shows Figure 2 Waveform of VBUCK PFM mode of SIMO power stage.

[0049] Figure 4 It shows Figure 2 The waveform of the SIMO power stage in VBOOST PFM mode.

[0050] Figure 5 It shows Figure 2 The waveform of the PWM mode of the SIMO power stage.

[0051] Figure 6 An example is shown. Figure 2 The switching position of the power stage in its idle state.

[0052] Figure 7-15 An example is shown. Figure 2 The stage or state of the soft-start sequence of the power level.

[0053] Figure 16 This is a flowchart of a method according to an embodiment.

[0054] Figure 17 Waveforms of various signals, according to an embodiment, are shown that can be used to illustrate a soft-start method for operation in PWM mode.

[0055] Figure 18 Waveforms of various signals, according to another embodiment, are shown that can be used to illustrate a soft-start method operating in PWM mode. Detailed Implementation

[0056] Generally, a method is provided for soft-starting a single-inductor multi-output (SIMO) power supply for operation in PWM mode. SIMO can operate in both Pulse Frequency Modulation (PFM) mode and PWM mode. PFM mode is more efficient at light load currents than PWM mode, which is more efficient at high load currents. In one embodiment, the power supply provides two different DC output voltages: a buck output voltage and a boost output voltage. A battery can be used to power the input power supply. The buck output voltage is lower than the battery voltage, and the boost output voltage is higher than the battery voltage. PFM operation can include two operating modes: a PFM mode referred to as VBUCK PFM mode and another PFM mode referred to as VBOOST PFM mode. In one embodiment, the method for soft-starting the SIMO power supply in PWM mode includes powering on the power supply in one of the two PFM modes and then transitioning to PWM mode. In another embodiment, the power supply is first powered on in VBUCK PFM mode, then transitions to VBOOST PFM mode, and finally moves to PWM mode. VBUCK PFM mode is as follows: Figure 3 The single-charge, single-discharge inductor current power supply scheme is shown. VBOOST PFM mode is as follows: Figure 4 The diagram shows a current supply scheme for an inductor that can be charged and discharged multiple times.

[0057] The startup method used for operation in PWM mode causes the current in the inductor to rise more gradually and limits inrush current, thus reducing the likelihood of overcurrent, overvoltage, or overstress conditions in the two regulated outputs of the SIMO power supply. Furthermore, startup in PFM mode does not require a clock signal or error amplifier as needed in PWM mode. Additionally, startup in PFM mode reduces potential instability issues. Moreover, power efficiency is optimized under relatively light loads during startup in PFM mode to gradually transition the state to PWM mode for operation at maximum output power.

[0058] In one embodiment, a method for soft-starting a single-inductor multiple-output (SIMO) power supply is provided, the method comprising: selecting a pulse width modulation (PWM) mode; enabling a first pulse frequency modulation (PFM) mode in the SIMO power supply; supplying a first voltage to a first load while in the first PFM mode; disabling the first PFM mode; enabling the PWM mode in the SIMO power supply; and operating the SIMO power supply in the PWM mode. This embodiment represents a solution to the problem of how to facilitate the implementation of soft-start techniques for PWM switching mode power supplies that do not require additional components. The method may further include controlling the SIMO power supply using a finite state machine. Operating the SIMO power supply in PWM mode may further include: selecting a second PFM mode after disabling the first PFM mode and before operating the SIMO power supply in PWM mode; and supplying a first voltage to the first load and a second voltage to a second load while in the second PFM mode. The method may further include: simultaneously supplying the first voltage to the first load and the second voltage to the second load while in the first PFM mode further comprising charging the single inductor through the first load and the second load. Supplying a first voltage to a first load and a second voltage to a second load in the second PFM mode may further include: charging a single inductor in the second PFM mode; discharging the single inductor through the first load in the second PFM mode; recharging the single inductor in the second PFM mode; and discharging the single inductor through the second load in the second PFM mode. The second voltage may be higher than the first voltage. The second voltage may be higher than the supply voltage provided to the SIMO power supply, and the first voltage may be lower than the supply voltage. The method may further include providing the supply voltage from a battery. Operating the SIMO power supply in PWM mode may further include providing a clock in PWM mode.

[0059] In another embodiment, a method for soft-starting a single-inductor multiple-output (SIMO) power supply is provided, the method comprising: selecting a pulse width modulation (PWM) mode; charging a single inductor in a first pulse frequency modulation (PFM) mode; discharging the single inductor through a first load in the first PFM mode; recharging the single inductor in the first PFM mode; discharging the single inductor through a second load in the first PFM mode; deactivating the first PFM mode; enabling the PWM mode after deactivating the first PFM mode; and operating the SIMO power supply in the PWM mode. This embodiment represents an alternative solution to the problem of how to facilitate the implementation of soft-start techniques for PWM switching mode power supplies that do not require additional components. The method may further include controlling the SIMO power supply using a finite state machine. Operating the SIMO power supply in PWM mode may further include: charging the single inductor to a first voltage in the PWM mode; and discharging the single inductor from the first voltage to a second voltage sequentially through a first load and subsequently through a second load. The method may further include enabling a second PFM mode before selecting a first PFM mode during the soft-start of the SIMO power supply, wherein the second PFM mode includes: simultaneously charging a single inductor through a first load and a second load; and simultaneously discharging the single inductor through the first load and the second load. The method may further include providing a supply voltage from a battery to the SIMO power supply. Operating the SIMO power supply in PWM mode may further include providing a clock in PWM mode. The steps of charging the single inductor in the first PFM mode and discharging the single inductor through the first load in the first PFM mode may further include repeating the charging and discharging steps until a first voltage is reached.

[0060] In another embodiment, a method for soft-starting a single-inductor multiple-output (SIMO) power supply is provided, the method comprising: selecting a pulse width modulation (PWM) mode; enabling a first pulse frequency modulation (PFM) mode in the SIMO power supply; simultaneously charging a single inductor of the SIMO power supply through a first load and a second load in the first PFM mode; simultaneously discharging the single inductor through the first load and the second load in the first PFM mode; enabling a second PFM mode in the SIMO power supply after disabling the first PFM mode; charging the single inductor in the second PFM mode; discharging the single inductor through the first load in the second PFM mode; charging the single inductor in the second PFM mode; discharging the single inductor through the second load in the first PFM mode; enabling the PFM mode after disabling the second PFM mode; and operating the SIMO power supply in the PFM mode. The charging and discharging steps in the first PFM mode may further include repeating the steps until a first voltage is reached. Enabling a first pulse frequency modulation (PFM) mode in a SIMO power supply may further include: simultaneously charging a single inductor of the SIMO power supply through a first load and a second load while in the first PFM mode; and simultaneously discharging the single inductor through the first load and the second load while in the first PFM mode. Enabling a second PFM mode in a SIMO power supply after disabling the first PFM mode may further include: charging the single inductor in the second PFM mode; discharging the single inductor through the first load while in the second PFM mode; charging the single inductor in the second PFM mode; and discharging the single inductor through the second load while in the first PFM mode.

[0061] Figure 1 A simplified view of a SIMO switch-mode power supply 40 according to an embodiment is shown. The switch-mode power supply uses switches to power the system for turning current on and off to charge and discharge storage components such as inductors and capacitors. The supply voltage can be AC ​​or DC to provide a regulated DC output voltage. A battery can be used to provide the supply voltage. In one embodiment, the SIMO power supply 40 includes a SIMO power stage 10, a finite state machine (FSM) and driver 42, a PFM controller 44, and a PWM controller 46. The power stage 10 is supplied with two output voltages, labeled VBUCK and VBOOST, from a battery power supply voltage labeled VBAT. Another embodiment may provide more than two regulated output voltages.

[0062] Regulated output voltages VBUCK and VBOOST are provided at different voltage levels. In one embodiment, the output voltage VBUCK is a buck voltage and below the battery voltage VBAT, while the output voltage VBOOST is boosted to above the battery voltage VBAT. In another embodiment, the output voltages may be different. Furthermore, in another embodiment, the power supply voltage may be supplied from different sources. In the illustrated embodiment, power supply 40 acts as a DC-DC converter. Power stage 10 is controlled by an FSM and a driver 42, which receives feedback signals through a feedback path including a PFM controller 44 and a PWM controller 46. When power supply 40 operates in PFM mode, the PFM controller 44 operates, and when power supply 40 operates in PWM mode, the PWM controller 46 operates.

[0063] The finite state machine and driver 42 include various circuits and functions to control the switch control signals SWVBAT, SWGNDB, SWVBOOST, SWVBUCK, and SWGNDA to the power stage 10 for both PFM and PWM modes. For example, the FSM and driver 42 may include a driver for regulating the switch control signals. Furthermore, the FSM and driver 42 may include timing circuitry for timing operation in PFM mode. The FSM may be implemented in hardware, software, or a combination of both. The FSM and driver 42 has an input signal for receiving a clock signal labeled CLOCK. The clock signal can be used to generate a PWM clock signal for timing the switch in PWM mode. The FSM and driver 42 has a mode input labeled MODE for controlling whether the power supply 40 operates in VBUCK PFM mode, VBOOST PFM mode, or PWM mode. Figure 2 Power stage 10 is shown in more detail and will be discussed later. PFM controller 44 includes a timer and comparator in the feedback path from the output of power stage 10 to the FSM and driver 42 to control the voltage levels of VBUCK and VBOOST during operation in one of the two PFM modes. Similarly, PWM controller 46 includes a comparator in the feedback path from the output of power stage 10 to the FSM and driver 42 to control the voltage levels of VBUCK and VBOOST during operation in PWM mode.

[0064] Figure 2 An example is shown. Figure 1 Power stage 10. Power stage 10 includes inductors 18, switches 14, 16, 20, 22 and 28, and capacitors 12, 26 and 30. All switches 14, 16, 20, 22 and 28 are shown in the position of... Figure 2The open position corresponds to the initial off state. Capacitor 12 has a first terminal connected to a power supply terminal marked VBAT and a second terminal connected to ground. Switch 14 has a first terminal connected to VBAT, a second terminal connected to a node marked LX1, and is controlled by the switch control signal SWVBAT. Inductor 18 has a first terminal connected to the second terminal of switch 14 and a second terminal at node LX2. Switch 16 has a first terminal connected to the first terminal of inductor 18 at node LX1, a second terminal connected to ground, and is controlled by the switch control signal SWGNDB. Switch 28 has a first terminal connected to the second terminal of inductor 18 at node LX2, a second terminal connected to ground, and is controlled by the switch control signal SWGNDA. Switch 20 has a first terminal connected to node LX2 and a second terminal for providing the output voltage VBOOST, and switch 20 is controlled by the switch control signal SWVBOOST. Capacitor 26 has a first terminal connected to the second terminal of switch 20 and a second terminal connected to ground. Load 24 is connected to receive the output voltage VBOOST. Load 24 will have its current, labeled ILOAD VBOOST, stored to ground. Switch 22 has a first terminal connected to node LX2, a second terminal for providing the output voltage VBUCK, and switch 22 is controlled by the switch control signal SWVBUCK. Capacitor 30 has a first terminal connected to the second terminal of switch 22, and a second terminal connected to ground. Load 32 is connected to receive the output voltage VBUCK. Load 32 will have its current, labeled ILOAD VBUCK, stored to ground.

[0065] Power stage 10 operates as a switch-mode power stage capable of providing two different DC output voltages. Specifically, in the illustrated embodiment, power stage 10 is shown for use in a portable device and powered by a battery to provide the supply voltage VBAT. Using feedback, the FSM and driver 42 control the timing and operation of switches 14, 16, 20, 22, and 28 to charge and discharge inductors 18, capacitors 12, 28, and 30, and output loads 24 and 32 at controlled rates to provide two regulated DC output voltages, VBUCK and VBOOST. The DC voltage VBUCK is a buck voltage regulated to be less than the battery voltage VBAT, and the DC voltage VBOOST is a boost voltage regulated to be higher than the battery voltage VBAT. Power stage 10 can be controlled using a PFM switching mode to supply low load current with relatively high efficiency, or using a PWM switching mode to supply high load current with relatively high efficiency. Other embodiments may provide more than two output voltages.

[0066] Starting power stage 10 in PWM mode can generate a large inrush current, which may cause overcurrent conditions in power stage 10. According to an embodiment, the inrush current is limited by soft-starting power stage 10 in one or both of the two PFM modes before transitioning to PWM mode. That is, the soft-start process first enables VBUCK PFM mode until VBUCK PFM mode ramps up, then enables VBOOST PFM mode, followed by PWM mode. Figure 3 It shows Figure 2 The waveform of the power stage 10 in VBUCK PFM mode. VBUCK PFM mode is a single-charge, single-discharge mode that supplies an output with voltage VBUCK. Figure 4 It shows Figure 2 The waveform of the SIMO power stage in VBOOST PFM mode. VBOOST PFM mode is a multiple charge-discharge mode that supplies two outputs: one with voltage VBUCK and the other with voltage VBOOST. Figure 5 It shows Figure 2 The waveform of the SIMO power stage in PWM mode. PWM mode is a single-charge continuous discharge mode that provides maximum output power for both output VBUCK and VBOOST.

[0067] By using a soft-start sequence to enable PWM mode, the current through inductor 18 is allowed to ramp up more slowly, thus reducing the startup current in power stage 10. In another embodiment, either VBUCK PFM mode or VBOOST PFM mode is not used to soft-start power stage 10. For example, VBUCK PFM mode may not be used in the soft-start sequence, such that the soft-start sequence only includes VBOOST PFM mode, followed by PWM mode. Similarly, the soft-start sequence may only include VBUCK PFM mode, followed by PWM mode. When all switches of power stage 10 are as follows... Figure 2 When disconnected as shown, power stage 10 can be in a "shutdown" state. In the illustrated embodiment, the closed switch is a switch with a short circuit between the switch terminals, and the open switch is a switch with an open circuit between the switch terminals.

[0068] Figure 6 The switch positions for the idle state of power stage 10 are shown. In the idle state, switch 16 is closed, connecting node LX1 to ground, and switch 28 is closed, connecting node LX2 to ground. Switches 14, 20, and 22 are open. In one embodiment, the method for soft-starting power stage 10 can begin from idle. In another embodiment, the method for soft-starting power stage 10 starts from... Figure 2 The shutdown state shown has begun.

[0069] Figure 7-15 An embodiment is shown. Figure 2 The soft-start method of power stage 10 involves a series of switching positions in stages or states. When PWM mode is selected, the soft-start sequence of states transitions from the off state of power supply 40 in PWM mode. Figure 6-14 The sequence is shown. In another embodiment, the soft-start sequence may begin with an idle state instead of a shutdown state. The idle state may cause grounding switches SWGNDA and SWGNDB to be closed, while other switches are open (idle state not shown). The states are numbered in a sequence from 1 to 9. Figure 6 and 7 The switch positions and sequences for states 1 and 2 used in VBUCK PFM mode are shown. Figure 7 The switch position of the first state, labeled IND VBUCK PFM STATE 1, is shown. It should be noted that, generally, state names beginning with "IND" indicate the state used for charging inductor 18. Figure 7 As shown, switches 14, 20, and 22 are closed, and switches 16 and 28 are open, to charge inductor 18 through both loads 24 and 32. The voltage at node LX1 increases to VBAT, while node LX2 is at the VBUCK potential (node ​​LX2 was initially at ground). Figure 3 The rise of the current IL of inductor 18 from time T0 to time T1 is shown in IND VBUCK PFM STATE 1.

[0070] Figure 8 The switch position for the second state, labeled VBUCK PFM STATE 2, is shown. Figure 8 In the configuration, switches 16, 20, and 22 are closed, while switches 14 and 28 are open. (This is incomplete and requires further context.) Figure 3 As seen from time T1 to time T2, as the charge on inductor 18 discharges through loads 24ILOAD VBOOST and 32ILOAD VBUCK, the current IL of inductor 18 decreases. The voltage at node LX1 drops from VBAT to ground, and the voltage at node LX2 rises from ground to voltage VBUCK. During normal operation in VBUCKPFM mode, the switching positions of states 1 and 2 are repeated to provide the regulated output voltage VBUCK. Furthermore, because switch 20 is closed, voltages VBOOST and VBUCK are equal. This process can be repeated... Figure 7 The first state and Figure 8 The second state provides the DC voltage VBUCK at the VBUCK output of power stage 10.

[0071] Figure 9-12A series of switching positions for operation in VBOOST PFM mode is shown. VBOOST PFM mode is used to provide multiple charge-discharge cycles for inductor 18 and to supply voltages VBUCK and VBOOST at the outputs of power stage 10. As mentioned above, VBOOST PFM mode follows VBUCK PFM mode in one embodiment of the soft-start sequence to enable operation in PWM mode. Alternatively, the soft-start method may begin with VBOOST PFM mode instead of VBUCK PFM mode, where VBUCK PFM mode is not used for startup. In the illustrated soft-start sequence, Figure 9 The switch position for the third state, labeled IND VBOOST PFM STATE 3, is shown. Figure 9 In the middle, switches 14 and 22 are closed, while switches 16, 20 and 28 are open, so that inductor 18 is charged through load 32ILOAD VBUCK. Figure 4 The diagram shows the increase in current of inductor 18 for IND VBOOST PFM STATE 3 between times T0 and T1. Node LX1 is at voltage VBAT, while node LX2 is at ground potential.

[0072] Figure 10 The switch position for the fourth state, labeled VBOOST PFM STATE 4, is shown. Figure 10 In the middle, switches 16 and 22 are closed, while switches 14, 20 and 28 are open to discharge inductor 18 through VBUCK load 32. Figure 4 The diagram shows the decrease in inductor current IL from its maximum current at time T1 to T2. Node LX1 decreases to ground due to the closed switch 16, and node LX2 is at voltage VBUCK.

[0073] Figure 11 The switch position of the fifth state, labeled IND VBOOST PFM STATE 5, for the soft-start method is shown. Figure 11 In this state, switches 14 and 28 are closed, and switches 16, 20, and 22 are open to recharge inductor 18. The switch positions bring the voltage at node LX1 to VBAT and the voltage at node LX2 to ground. The charging current through inductor 18 is progressively higher than the charging current in the previous startup state. Figure 4 The current IL increases from time T2 to time T3.

[0074] Figure 12 The switch position of the sixth state, labeled VBOOST PFM STATE 6, for the soft-start method is shown. Figure 12In the current state, switches 16 and 20 are closed, and switches 14, 22, and 28 are open. The switch positions reduce node LX1 to ground and bring node LX2 to voltage VBOOST, allowing inductor 18 to discharge through load 24 at VBOOST. Current IL is... Figure 4 The sixth state, between times T3 and T4, is shown as decreasing to zero. In VBOOST PFM mode, states 3 through 6 are repeated sequentially to provide regulated voltages VBOOST and VBUCK at the output of power stage 10. The method proceeds until VBOOST PFM mode is disabled and PWM mode is enabled.

[0075] Figure 13 , 14 Figures 1 and 15 show the switching positions in a sequence of multiple charge-discharge cycles for implementing the PWM mode to provide inductor 18. The PWM mode provides regulated output voltages at outputs VBOOST and VBUCK. Figure 13 The switch position for the seventh state, labeled IND PWM STATE 7, is shown. Figure 13 In this configuration, switches 14 and 28 are closed, and switches 16, 20, and 22 are open to charge inductor 18. The switch positions shown cause the voltage at node LX1 to be at voltage VBAT and the voltage at node LX2 to be at ground. The inductor current IL increases from zero at time T0 to its maximum current at time T1, as... Figure 5 As shown. It should be noted that during the initial loop of PWM mode, the current will start at zero at time T0. After the initial loop, and for all subsequent loops, the current will not continue to drop to zero, as shown in... Figure 5 The times T3 and T1 indicate this.

[0076] Figure 14 The switch position for the eighth state, labeled VBOOST PWM STATE 8, is shown. Figure 14 In this configuration, switches 14 and 20 are closed, and switches 16, 22, and 28 are open to begin discharging inductor 18 to load 24 at VBOOST. The shown switch positions result in the voltage at node LX1 being at voltage VBAT and the voltage at node LX2 being at voltage VBOOST. The inductor current IL is as follows: Figure 5 The figure shows a decrease between time T1 and T2.

[0077] Figure 15 The switch position for the ninth state, labeled VBUCK PWM STATE 9, is shown. Figure 15 In the middle, switches 16 and 22 are closed, and switches 14, 20 and 28 are open. Figure 15The shown switching position grounds the voltage at node LX1 and reduces the voltage at node LX2 from VBUCK to ground. In this switching position, inductor 18 continues discharging until the current IL reaches its minimum value. Figure 5 During this process, the current IL drops to its minimum between times T2 and T3. When power stage 10 is in PWM mode, states 7-9 are continuously repeated. It should be noted that the PWM states are changed by... Figure 17 and 18 The clock signal marked PWMCLOCK is used for timing.

[0078] Alternatively, the soft-start method can soft-start power stage 10 using only VBUCK PFM mode or only VBOOST PFM mode before enabling PWM mode. For embodiments that soft-start power stage 10 using only VBOOST PFM mode, no PWM mode is used. Figure 7 and 8 The switch position is shown, and the soft-start method begins with the switch position shown. Figure 9 The switch position for VBOOST PFM mode startup. In another embodiment with a power stage different from the power stage 10 shown, different switching schemes can be provided to cycle through PFM and PWM modes for soft start. Starting power stage 10 using the stage sequence shown results in a lower initial inrush current, thus protecting power stage 10 from overcurrent conditions.

[0079] Figure 16 This is a flowchart of a method 49 for soft-starting a SIMO power supply in PWM mode according to an embodiment. Method 49 begins at step 50 and will be referenced to... Figure 2 The SIMO power stage 10 is discussed here. At step 50, the SIMO power supply is selected for operation in PWM mode. At step 51, PFM mode is enabled in power stage 10, and inductor 18 is charged from voltage VBAT. The PFM mode can correspond to... Figure 4 The flowchart shows the VBOOST PFM mode, and has Figure 9-12 The switch position is shown. Alternatively, the PFM mode can be... Figure 3 The flowchart illustrates the VBUCK PFM mode. At step 52, inductor 18 is discharged through a first load, for example, as shown... Figure 9 The load shown is 32ILOAD VBUCK in VBOOST PFM mode. At step 53, for example, via... Figure 10 The switch position shown recharges inductor 18. At step 54, as... Figure 12The diagram shows inductor 18 being discharged from load 24 to VBOOST via switches 16 and 20. Steps 51-54 are repeated until the output voltage (e.g., VBOOST) is at a predetermined voltage level. When the PFM mode steps are completed, at step 55, the PWM mode is enabled after the first PFM mode is disabled. Steps 51-54 can be repeated multiple times before enabling the PWM mode. Figure 5 The waveforms showing the PWM mode are provided, and Figure 13-15 The sequence of switch positions is shown in the diagram. In another embodiment, the soft-start sequence may include, for example, Figure 17 The VBUCK and VBOOST PFM modes are shown.

[0080] Figure 17 Waveforms of various signals that can be used to illustrate a soft-start method for operation in PWM mode are shown. Figure 17 In this diagram, the operating mode is labeled POWER MODES. Between times T0 and T1, power stage 10 is turned off. At time T1, VBUCK PFM mode is activated. If necessary, the VBUCK PFM mode state can be repeated between times T1 and T2. The time interval between T1 and T2 can be determined to stabilize the output voltage and current, and can be a fixed time or based on monitoring the output voltage VBUCK. At time T2, VBUCK PFM is deactivated, and VBOOST PFM mode is activated. In VBOOST PFM mode, power stage 10 repeatedly cycles through states 3-6 as described above. The voltage VBOOST stabilizes at the maximum boost voltage just before time T3. At time T3, power stage 10 transitions from VBOOST PFM mode to PWM mode. Figure 1 The PWM clock generated by controller 42 is marked as PWM CLOCK, which provides timing based on the received clock signal CLOCK. As shown, when the input PWM mode is active, the output voltage VBOOST is already at its maximum value. PWM mode in Figure 5 and Figures 13-15 As shown in the image.

[0081] Figure 18 Waveforms of various signals, according to another embodiment, are shown that can be used to illustrate a soft-start method operating in PWM mode. Figure 18 In this context, the soft start method only uses VBOOST PFM, instead of the method described above. Figure 17 The diagram shows the use of both VBUCK PFM and VBOOST PFM modes. Between times T0 and T1, power stage 10 is shut down. At time T1, VBOOST PFM mode is activated. If necessary, the VBOOST PFM mode state can be repeated between times T1 and T2. Figure 9-12 The state of VBOOST PFM mode is shown. The time interval between T1 and T2 can be determined to allow the output voltage and current to stabilize, and this time interval can be a fixed time or based on monitoring the output voltage VBOOST. At time T2, power stage 10 transitions from VBOOST PFM mode to PWM mode. Figure 1 The controller 42 generates a PWM clock marked PWM CLOCK to provide timing based on the received clock signal CLOCK. As shown, when entering PWM mode, the output voltage VBOOST is already at its maximum value. Figure 5 and Figure 13-15 The PWM mode is shown in the image.

[0082] The startup method causes the current in the inductor to rise more gradually and limits inrush current, thus reducing the likelihood of overcurrent, overvoltage, or overstress conditions in the two regulated outputs of the SIMO power supply's power stage. Furthermore, startup in PFM mode does not require a clock signal like PWM mode. Startup in PFM mode avoids potential stability issues. Additionally, power efficiency is optimized under relatively light loads during startup in PFM mode to gradually transition the state to PWM mode for operation at maximum output power.

[0083] Since the devices implementing this invention are mostly composed of electronic components and circuits known to those skilled in the art, circuit details will not be explained to any extent deemed necessary as shown above, in order to understand and comprehend the basic concepts of this invention and in order not to obscure or distract from the teachings of this invention.

[0084] Although the invention has been described herein with reference to specific embodiments, various modifications and changes may be made without departing from the scope of the invention as set forth in the appended claims. Therefore, this specification and the accompanying drawings should be considered illustrative rather than restrictive, and all such modifications are intended to be included within the scope of the invention. Any benefits, advantages, or solutions to problems described herein with reference to specific embodiments are not intended to be construed as key, necessary, or essential features or elements of any or all claims.

[0085] As used in this article, the term “coupling” is not intended to be limited to direct coupling or mechanical coupling.

[0086] Furthermore, as used herein, the term "a" is defined as one or more. Additionally, introductory phrases such as "at least one" and "one or more" used in the claims should not be construed as implying that any particular claim containing such an introduced element is limited to an invention containing only one such element, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a". The same applies to the use of definite articles.

[0087] Unless otherwise stated, terms such as "first" and "second" are used to arbitrarily distinguish the elements described by such terms. Therefore, these terms are not necessarily intended to indicate the temporal or other priority order of such elements.

Claims

1. A method for soft-starting a single-inductor multiple-output (SIMO) power supply, comprising: The method includes: Select Pulse Width Modulation (PWM) mode; The first pulse frequency modulation (PFM) mode is enabled in the SIMO power supply; In the first PFM mode, a first voltage is supplied to the first load; Deactivate the first PFM mode; Enable the PWM mode in the SIMO power supply; and The SIMO power supply is operated in the PWM mode. Operating the SIMO power supply in the PWM mode further includes: After disabling the first PFM mode and before operating the SIMO power supply in the PWM mode, select the second PFM mode; and In the second PFM mode, the first voltage is supplied to the first load and the second voltage is supplied to the second load. Furthermore, in the second PFM mode, supplying the first voltage to the first load and supplying the second voltage to the second load further includes: The single inductor is charged in the second PFM mode; The single inductor is discharged through the first load in the second PFM mode; Recharge the single inductor in the second PFM mode; and The single inductor is discharged through the second load in the second PFM mode.

2. The method of claim 1, wherein, Further, it includes using a finite state machine to control the SIMO power supply.

3. The method according to any of the preceding claims, characterized by, The second voltage is higher than the first voltage.

4. The method of claim 3, wherein, The second voltage is higher than the supply voltage provided to the SIMO power supply, and the first voltage is lower than the supply voltage.

5. The method of claim 4, wherein, This further includes providing the power supply voltage from a battery.

6. The method according to any of the preceding claims, characterized by, Operating the SIMO power supply in the PWM mode further includes providing a clock in the PWM mode.

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