JP2010279128A - Dc-dc converter and start control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten time until a target output voltage is output by a simple constitution. <P>SOLUTION: The DC-DC converter which outputs an output voltage obtained by stepping up or stepping down an input voltage includes a first resistor which accommodates a target voltage value of the output voltage, a second resistor which accommodates an initial voltage value of the output voltage which is lower than a preset minimum voltage value of the input voltage, and a voltage conversion unit which sets the output voltage to the initial voltage value by stepping down the input voltage until a fixed time elapses after the start time of the DC-DC converter, and sets the output voltage to the target voltage value by stepping up or stepping down the input voltage after the fixed time elapses. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a DCDC converter that outputs an output voltage obtained by stepping up or down an input voltage, and a startup control method thereof.

  In recent years, a cellular phone device often uses a step-up / step-down DCDC converter that boosts or steps down an input voltage input from a power source such as a battery and outputs an output voltage of a target voltage value set from the outside.

  By using the step-up / step-down DCDC converter, for example, for a power amplifier unit that amplifies the power of the transmission signal transmitted from the mobile phone device, the input voltage input from the power source is set to a voltage that matches the power of the transmission signal. The voltage can be boosted or lowered and heat generation in the power amplifier unit can be avoided.

  In general, a step-up / step-down DCDC converter includes an input terminal to which an input voltage is input from a power supply, an output terminal for outputting an output voltage, and a plurality of FETs (Field Effect Transistors) connected between the input terminal and the output terminal. A switching element, a transmitter for generating a PWM (Pulse Width Modulation) waveform for turning the switching element ON / OFF, and an output smoothing capacitor having one end connected to the output terminal and the other end grounded. Yes.

  Then, the step-up / step-down DCDC converter boosts or steps down the input voltage by turning on / off the switching element according to the generated PWM waveform, and smoothes and outputs the output voltage by the output smoothing capacitor.

  In the following description, an operation state where the step-up / step-down DCDC converter boosts the input voltage is referred to as a boost mode, and an operation state where the input voltage is stepped down is referred to as a step-down mode.

  By the way, in a radio communication system based on LTE (Long Term Evolution) which is a next-generation radio communication standard, signal transmission of a mobile phone device is intermittently performed.

  Therefore, by frequently starting / stopping the step-up / step-down DCDC converter in accordance with the signal transmission of the mobile phone device, it occurs in a transmitter or the like inside the step-up / step-down DCDC converter as compared with the case where the step-up / step-down DCDC converter is always started Current consumption can be suppressed.

  Here, when the step-up / step-down DCDC converter is started, the output smoothing capacitor is charged with electric charges.

  Further, even after the operation of the step-up / step-down DCDC converter is stopped, the electric charge charged in the output smoothing capacitor flows due to the load of another device connected to the step-up / step-down DCDC converter. Therefore, when the step-up / step-down DCDC converter is started, the charge charged in the output smoothing capacitor is often almost empty.

  Therefore, every time the step-up / step-down DCDC converter is started, a large inrush current flows from the power source to the output smoothing capacitor to charge the output smoothing capacitor. Then, the instantaneous drop of the power supply voltage caused by the inrush current adversely affects other devices using the same power supply on the substrate of the mobile phone device.

  Patent Document 1 describes a step-up / step-down DCDC converter that reduces a rush current that flows when the step-up / step-down DCDC converter starts by performing a soft start.

  Here, soft start means that at the start of startup, the duty value indicating the ON / OFF ratio of the switching element is set to a small value, and the duty value is controlled in accordance with the passage of time from the startup. This refers to starting up the step-up / step-down DCDC converter by reducing the flowing inrush current.

  The step-up / step-down DCDC converter described in Patent Document 1 stores in advance a table in which an input voltage is associated with a duty value and a length of a soft start period for driving the switching element with the duty value. At the time of start-up, the duty value and soft start period corresponding to the input voltage are extracted from the table, and in the extracted soft start period, ON / OFF of the switching element is controlled with a small duty value, so that the smoothing capacitor is supplied. Charging is performed gradually to reduce the inrush current that flows during startup.

JP 2007-288879 A

  However, the step-up / step-down DCDC converter described in Patent Document 1 requires a special configuration for controlling the duty value in order to perform soft start, and there is a problem that the configuration becomes complicated.

  Further, the step-up / step-down DCDC converter described in Patent Document 1 extracts a duty value and a soft start period corresponding to an input voltage from a stored table from the table, and a time for performing a soft start such as control of the duty value. There is a problem that it takes time until the target output voltage is output after the step-up / step-down DCDC converter is started.

  An object of the present invention is to provide a DCDC converter and a start control method thereof that can reduce the time required for starting the DCDC converter with a simple configuration.

In order to achieve the above object, the DCDC converter of the present invention provides:
A DCDC converter that outputs an output voltage obtained by stepping up or down an input voltage,
A first register for storing a target voltage value of the output voltage;
A second register that stores an initial voltage value of the output voltage that is lower than a predetermined minimum voltage value of the input voltage;
The input voltage is stepped down to the initial voltage value until a predetermined time has elapsed from the start of the DCDC converter, and after the predetermined time has passed, the input voltage is stepped up or stepped down. A voltage converter that sets the output voltage to the target voltage value.

In order to achieve the above object, a start-up control method for a DCDC converter according to the present invention includes:
A start-up control method applied to a DCDC converter having a voltage conversion unit that outputs an output voltage obtained by stepping up or stepping down an input voltage,
A first storing step of storing a target voltage value of the output voltage in a first register;
A second storage step of storing an initial voltage value of the output voltage that is lower than a predetermined minimum voltage value of the input voltage in a second register;
The voltage conversion unit steps down the input voltage to set the output voltage to the initial voltage value until a predetermined time elapses from when the DCDC converter starts up, and after the predetermined time elapses, the input voltage And a voltage conversion step of raising or lowering the voltage to make the output voltage the target voltage value.

  According to the present invention, the DCDC converter includes a first register that stores a target voltage value of the output voltage, and an initial voltage value of the output voltage that is lower than a predetermined minimum voltage value of the input voltage. The second register to be stored and the input voltage are stepped down to the initial voltage value until a certain time has elapsed from the start of the DCDC converter, and the input voltage is stepped up or stepped down after the certain time has elapsed. And a voltage converter that sets the input voltage to a target voltage value.

  Therefore, the DCDC converter can have a simple configuration that does not require a special configuration for performing soft start.

  Further, the DCDC converter can reduce the time required for starting the DCDC converter by stepping down the input voltage and setting the output voltage to the initial voltage value until a certain time has elapsed since the start.

It is a block diagram which shows the structure of the buck-boost DCDC converter of one Embodiment of this invention. It is a flowchart which shows an example of operation | movement of the buck-boost DCDC converter shown in FIG. It is a figure explaining the flow of the electric current immediately after starting of the buck-boost DCDC converter shown in FIG. It is a figure explaining the flow of an electric current immediately after starting of a step-down DCDC converter. It is a graph which shows the simulation result of the time change of the voltage value of an output voltage of the buck-boost DCDC converter and the buck-boost DCDC converter which perform soft start shown in FIG. It is a graph which shows the simulation result of the electric current value which flows into the coil of the buck-boost DCDC converter shown in FIG. 1, and the buck-boost DCDC converter which performs soft start.

  EMBODIMENT OF THE INVENTION Below, the form for implementing this invention is demonstrated with reference to drawings.

  FIG. 1 is a block diagram showing a configuration of a step-up / step-down DCDC converter 10 of the present embodiment.

  A step-up / step-down DCDC converter 10 shown in FIG. 1 includes a normal control register 11, a start-up register 12, a timer 13, a register selection switch 14, a DAC (DA converter) 15, an error amplifier 16, and a pre-driver 17. And transistors Q1 to Q4 such as FETs that are switching elements, a coil L1, and an output smoothing capacitor C1.

  The transistor Q1 has a drain terminal connected to a power source that is an input source of the input voltage (VDD), and a source terminal connected to one end of the coil L1.

  The transistor Q2 has a drain terminal connected to one end of the coil L1, and a source terminal grounded.

  The transistor Q3 has a drain terminal connected to the other end of the coil L1, and a source terminal grounded.

  The transistor Q4 has a drain terminal connected to the output terminal of the step-up / step-down DCDC converter 10 and a source terminal connected to the other end of the coil L1.

  The gate terminals of the transistors Q1 to Q4 are connected to the pre-driver 17.

  The output smoothing capacitor C1 has one end connected to the output terminal of the step-up / step-down DCDC converter 10 and the other end grounded.

  The normal control register 11 stores a target set value of the output voltage (Vout) set from the outside.

  The start-up register 12 has an output voltage (Vout) that is lower than a predetermined minimum voltage value of the input voltage (VDD) so that the step-up / step-down DCDC converter 10 operates in the step-down mode when the step-up / step-down DCDC converter 10 starts. Stores the initial voltage value.

  When the step-up / step-down DCDC converter 10 starts to start, the timer 13 receives a start-up signal, measures an elapsed time since the start-up of the step-up / step-down DCDC converter 10, and is a fixed time (Tg) ) Has passed.

  Then, when a predetermined time (Tg) has elapsed since the start of the step-up / step-down DCDC converter 10, the timer 13 outputs a control signal indicating that the predetermined time (Tg) has elapsed since the start-up of the step-up / step-down DCDC converter 10. 14 for output.

  The register selection switch 14 switches between the normal control register 11 and the startup register 12 and connects to the DAC 15.

  Specifically, the register selection switch 14 connects the startup register 12 and the DAC 15 when the step-up / step-down DCDC converter 10 starts to start. When the control signal is output from the timer 13, the register selection switch 14 determines that a certain time has elapsed since the startup of the step-up / step-down DCDC converter, and normally controls the register connected to the DAC 15 from the startup register 12. Switch to register 11.

  The DAC 15 is connected via the register selection switch 14, and the target voltage value of the output voltage (Vout) stored in the normal control register 11 or the initial voltage value of the output voltage (Vout) stored in the start-up register 12. A reference voltage (Vref) obtained by DA conversion is generated, and the generated reference voltage (Vref) is output to the error amplifier 16.

  The error amplifier 16 compares the feedback voltage (Vfb) obtained by feeding back the output voltage (Vout) with the reference voltage (Vref) output from the DAC 15 and outputs the comparison result to the pre-driver 17.

  Specifically, the error amplifier 16 detects a potential difference between the feedback voltage (Vfb) and the reference voltage (Vref), and outputs the detected potential difference to the pre-driver 17.

  The pre-driver 17 selectively turns on / off the transistors Q1 to Q4 based on the comparison result between the feedback voltage (Vfb) output from the error amplifier 16 and the reference voltage (Vref).

  Next, the operation of the step-up / step-down DCDC converter 10 will be described.

  FIG. 2 is a flowchart showing an example of the operation of the step-up / step-down DCDC converter 10.

  First, when the step-up / step-down DCDC converter 10 starts activation (step S21), the register selection switch 14 connects the activation-time register 12 and the DAC 15 (step S22).

  The start-up register 12 includes an initial voltage value of the output voltage (Vout) that is lower than a predetermined minimum voltage value of the input voltage (VDD) so that the step-up / step-down DCDC converter 10 operates in the step-down mode. Therefore, the step-up / step-down DCDC converter 10 is started in the step-down mode when the start-up register 12 and the DAC 15 are connected.

  As described above, immediately after the step-up / step-down DCDC converter 10 is started, an inrush current flows in order to charge the output smoothing capacitor C1.

  FIG. 3A is a diagram for explaining the flow of current immediately after startup of the step-up / step-down DCDC converter 10.

  As shown in FIG. 3A, immediately after the step-up / step-down DCDC converter 10 is activated in the step-down mode, the pre-driver 17 turns on the transistors Q1 and Q4 and turns off the transistors Q2 and Q3. At this time, since the output smoothing capacitor C1 is not charged, the potential difference between the input voltage (VDD) and the output smoothing capacitor C1 and the resistance value between the drain and source of the transistors Q1 and Q4 are ON. An inrush current determined by the resistance flows.

  However, in the step-up / step-down DCDC converter 10, the coil L1 is inserted between the transistors Q1 and Q4, and a back electromotive force corresponding to the amount of change in the current flowing through the coil L1 is generated.

  Accordingly, the back electromotive force generated in the coil L1 in response to the inrush current that flows when the step-up / step-down DCDC converter 10 is started causes an induced current to flow in a direction that prevents the inrush current, thereby reducing the inrush current.

  FIG. 3B is a diagram for explaining the flow of current immediately after the startup of the step-down DCDC converter.

  As shown in FIG. 3B, when the step-down DCDC converter is activated in the step-down mode, the pre-driver 17 turns on the transistor Q1 and turns off the transistor Q2. At this time, like the step-up / step-down DCDC converter 10, since the output smoothing capacitor C1 is not charged, an inrush current flows from the power source to the capacitor C1 via the transistor Q1.

  And, in the step-down DCDC converter, the induced current does not flow in the direction that prevents the inrush current unlike the step-up / step-down DCDC converter 10, so in order to reduce the inrush current, for example, the ON resistance of the transistor Q1 is temporarily set. Therefore, it is necessary to make the control larger.

  Thus, the inrush current flowing at the time of starting can be reduced by the back electromotive force generated in the coil L1 by starting the step-up / step-down DCDC converter 10 in the step-down mode.

When the output smoothing capacitor C1 is charged, the potential difference between the input voltage (VDD) and the output smoothing capacitor C1 is reduced, and the inrush current flowing through the coil L1 starts to decrease, or the output voltage (Vout ) Starts to rise, the pre-driver 17 turns off the transistor Q1 and turns on the transistor Q2. Immediately after the transistors Q1 and Q2 are turned on / off, an electromotive force in the direction opposite to that in FIG. 3A is generated, and the output voltage (Vout) jumps. However, for example, the response of the error amplifier 16 And by making the ON / OFF switching frequency of the transistors Q1 to Q4 in the pre-driver 17 sufficiently fast with respect to the change of the output voltage (Vout), the occurrence of the jump of the output voltage (Vout) is avoided. can do.

  Returning to FIG. 2, the timer 13 measures the time elapsed since the start of the step-up / step-down DCDC converter 10 (step S23), and determines whether or not a certain time (Tg) has elapsed (step S24).

  Note that the predetermined time (Tg) is set in consideration of the time required for the output voltage (Vout) to stabilize when the step-up / step-down DCDC converter 10 is started in the step-down mode, for example.

  When the fixed time (Tg) has not elapsed since the startup of the step-up / step-down DCDC converter 10 (step S24: NO), the process of step S24 is repeated until the fixed time (Tg) has elapsed.

  On the other hand, when the fixed time (Tg) has elapsed since the startup of the step-up / step-down DCDC converter 10 (step S24: YES), the timer 13 indicates that the fixed time (Tg) has elapsed since the startup of the step-up / step-down DCDC converter 10. The control signal shown is output to the register selection switch 14.

  When the control signal is output from the timer 13, the register selection switch 14 determines that a certain time (Tg) has elapsed since the startup of the step-up / step-down DCDC converter 10, and connects the register connected to the DAC 15 from the startup register 12. Switch to the normal control register 11 (step S25).

  Then, the step-up / step-down DCDC converter 10 turns on / off the transistors Q1 to Q4 by the pre-driver 17 and changes the input voltage (VDD) to the output voltage (Vout) of the target voltage value stored in the normal control register 11. Step up or down.

  For example, the pre-driver 17 first turns on the transistors Q1 and Q3 and turns off the transistors Q2 and Q4. Then, an input voltage (VDD) is applied to the coil L1, and an electromotive force is generated in the coil L1 due to an increase in the current flowing through the coil L1.

  Next, the pre-driver 17 turns off the transistors Q1 and Q3 and turns on the transistors Q2 and Q4. Then, since the coil L1 is connected to the output terminal of the step-up / step-down DCDC converter 10, the electromotive force generated in the coil L1 is charged in the output smoothing capacitor C1.

  In this manner, the input voltage (VDD) can be boosted or lowered by changing the ON / OFF ratio of the transistors Q1 to Q4 and controlling the amount of charge charged in the output smoothing capacitor C1.

  FIG. 4 is a graph showing a simulation result of the time change of the voltage value of the output voltage (Vout) of the step-up / step-down DCDC converter 10 of this embodiment and the step-up / step-down DCDC converter performing soft start.

  In FIG. 4, the horizontal axis represents time, and the vertical axis represents the voltage value of the output voltage (Vout).

  As shown in FIG. 4, the step-up / step-down DCDC converter 10 according to the present embodiment performs soft start by stepping down the input voltage and setting the output voltage to the initial voltage value until a predetermined time elapses from the startup. The time required for outputting the output voltage (Vout) of the target voltage value can be shortened as compared with a step-up / step-down DCDC converter that performs soft start.

  FIG. 5 is a graph showing a simulation result of the current value flowing through the coil of the step-up / step-down DCDC converter 10 of this embodiment and the step-up / step-down DCDC converter performing soft start.

  In FIG. 5, the horizontal axis represents time, and the vertical axis represents the current value.

  As shown in FIG. 5, the step-up / step-down DCDC converter 10 of this embodiment has an increased maximum current flowing through the coil L1 as compared with the step-up / step-down DCDC converter that performs soft start.

  However, since it is activated in the step-down mode, the maximum current flowing through the coil L1 can be suppressed to a small amount of current compared with the inrush current that flows when the step-up / step-down DCDC converter 10 is operated in the step-up mode.

  Note that the time change of the voltage value of the output voltage (Vout) and the current value flowing through the coil L1 vary greatly depending on the performance of each part constituting the step-up / step-down DCDC converter. Therefore, in FIG. 4 and FIG. Only the relative difference between the DCDC converter 10 and the step-up / step-down DCDC converter that performs soft start is shown.

  Thus, according to this embodiment, the step-up / step-down DCDC converter 10 is lower than the normal control register 11 that stores the target voltage value of the output voltage (Vout) and the predetermined minimum voltage value of the input voltage. And a start-up register 12 for storing an initial voltage value of the output voltage (Vout), which is a value, until the fixed time elapses from the start-up of the DCDC converter 10, the output voltage (Vout) ) Is set to the initial voltage value, and after a predetermined time has elapsed, the input voltage is boosted or lowered to set the output voltage (Vout) to the target voltage value.

  Therefore, the step-up / step-down DCDC converter 10 can have a simple configuration that does not require a special configuration for performing soft start.

  Further, the step-up / step-down DCDC converter 10 reduces the input voltage and sets the output voltage to the initial voltage value until a predetermined time has elapsed from the time of startup, until the output voltage (Vout) reaches the target voltage value. The time is shortened, and the time required for starting up the step-up / step-down DCDC converter 10 can be shortened.

  Further, the step-up / step-down DCDC converter 10 can reduce the inrush current flowing at the start-up by the electromotive force generated in the coil L1 by being started in the step-down mode.

  In the present embodiment, the example in which the start-up register 12 and the timer 13 are provided in the step-up / step-down DCDC converter 10 has been described. However, the present invention is not limited to this, and an external device that controls the step-up / step-down DCDC converter 10 is used. It is also possible to provide it.

  In this case, in the external device, before starting the step-up / step-down DCDC converter 10, the initial voltage value of the output voltage (Vout) for operation in the step-down mode is set, or for a certain period of time (from the start-up of the step-up / step-down DCDC converter) It is also possible to perform control to change the setting to the target voltage value after elapse of Tg).

10 Buck-Boost DCDC Converter 11 Normal Control Register 12 Start-up Register 13 Timer 14 Register Select Switch 15 DAC (DA Converter)
16 Error amplifier 17 Pre-driver

Claims (8)

A DCDC converter that outputs an output voltage obtained by stepping up or down an input voltage,
A first register for storing a target voltage value of the output voltage;
A second register that stores an initial voltage value of the output voltage that is lower than a predetermined minimum voltage value of the input voltage;
The input voltage is stepped down to the initial voltage value until a predetermined time has elapsed from the start of the DCDC converter, and after the predetermined time has passed, the input voltage is stepped up or stepped down. A DCDC converter comprising: a voltage converter configured to set the output voltage to the target voltage value. The voltage converter is
A plurality of switching elements connected in series between a power source of the input voltage supply source and an output terminal of the output voltage;
A coil connected in parallel with the plurality of switching elements;
A pre-driver that selectively turns ON / OFF the plurality of switching elements to set the output voltage to the initial voltage value or the target voltage value,
The pre-driver is
The plurality of switching elements are selectively turned ON / OFF so that the input current from the power source flows through the coil until the predetermined time has elapsed from the start of the DCDC converter, and the output voltage is set to the initial voltage. Value,
2. The DCDC converter according to claim 1, wherein the output voltage is set to the target voltage value by selectively turning on and off the plurality of switching elements according to the target voltage value after the predetermined time has elapsed. . A reference obtained by D / A conversion of the target voltage value stored in the first register, or the initial voltage value stored in the second register, connected to the first or second register A DA converter for generating a voltage;
The second register and the DA converter are connected until the predetermined time elapses from the start of the DCDC converter, and after the predetermined time elapses, the first register and the DA converter are connected. A switch part to be connected;
An error amplifier that compares the reference voltage generated by the DA converter and the output voltage of the DCDC converter;
3. The DCDC according to claim 2, wherein the pre-driver selectively turns ON / OFF the plurality of switching elements based on a comparison result by the error amplifier to set the output voltage to the target voltage value or the initial voltage value. converter. A timer that outputs a control signal indicating that the predetermined time has elapsed to the switch unit when the time elapsed since the start of the DCDC converter is measured and the predetermined time has elapsed;
The DCDC converter according to claim 3, wherein the switch unit determines that the predetermined time has elapsed when the control signal is output from the timer. A start-up control method applied to a DCDC converter having a voltage conversion unit that outputs an output voltage obtained by stepping up or stepping down an input voltage,
A first storing step of storing a target voltage value of the output voltage in a first register;
A second storage step of storing an initial voltage value of the output voltage that is lower than a predetermined minimum voltage value of the input voltage in a second register;
The voltage conversion unit steps down the input voltage to set the output voltage to the initial voltage value until a predetermined time elapses from when the DCDC converter starts up, and after the predetermined time elapses, the input voltage And a voltage conversion step of raising or lowering the voltage to bring the output voltage to the target voltage value. The voltage converter is
A plurality of switching elements connected in series between a power source of the input voltage supply source and an output terminal of the output voltage;
A coil connected in parallel with the plurality of switching elements;
A pre-driver that selectively turns ON / OFF the plurality of switching elements to set the output voltage to the initial voltage value or the target voltage value,
In the voltage conversion step,
The pre-driver selectively turns on and off the plurality of switching elements so that an input current from the power source flows through the coil until the predetermined time has elapsed since the DCDC converter is activated. Set the voltage to the initial voltage value,
6. The start-up control according to claim 5, wherein after the predetermined time has elapsed, the plurality of switching elements are selectively turned ON / OFF according to the target voltage value to set the output voltage to the target voltage value. Method. A reference obtained by D / A conversion of the target voltage value stored in the first register, or the initial voltage value stored in the second register, connected to the first or second register Generating the reference voltage by a DA converter for generating a voltage;
The second register and the DA converter are connected until the predetermined time elapses from the start of the DCDC converter, and after the predetermined time elapses, the first register and the DA converter are connected. A connection step to connect;
Comparing the reference voltage generated by the DA converter with the output voltage of the DCDC converter;
In the voltage conversion step, the output voltage is set to the target voltage value or the initial voltage value by selectively turning on / off the plurality of switching elements by the pre-driver based on the comparison result in the comparison step. Item 7. The startup control method according to item 6. Measuring a time elapsed from the start of the DCDC converter, and when the predetermined time has elapsed, including a measurement step of outputting a control signal indicating that the predetermined time has elapsed
The start control method according to claim 7, wherein in the connection step, it is determined that the predetermined time has elapsed when the control signal is output in the measurement step.