JP5956748B2 - Switching regulator - Google Patents

Description

  The present invention relates to a switching regulator that generates an output voltage by stepping up or down an input voltage.

  7A and 7B are circuit diagrams showing a conventional example of a step-up / step-down switching regulator, respectively. In the switching regulator 100 of this conventional example, the first phase (FIG. 7A) for turning on both the switching elements 101 and 102 and the switching elements 101 and 102 are both turned off regardless of the magnitude relationship between the input voltage IN and the output voltage OUT. By periodically repeating the second phase (FIG. 7B), the input voltage IN is boosted or lowered to generate the output voltage OUT.

  As an example of the prior art related to the present invention, Patent Document 1 disclosed by the present applicant can be cited.

JP 2005-33862 A

  However, in the switching regulator 100, the switching element 101 and the switching element 102 are always turned on / off in synchronism regardless of the magnitude relationship between the input voltage IN and the output voltage OUT. Therefore, the longer the first phase during which both the switching elements 101 and 102 are turned on, the longer the average coil current IL (average of the coil current flowing through the coil 103) per switching cycle T is, as the average output current Io (the output current flowing through the load 107) is. The amount of heat generation (loss) of the switching regulator 100 increases.

  The above problem will be described in detail. In the first phase in which both of the switching elements 101 and 102 are turned on, current flows from the application end of the input voltage IN through the switching element 101, the coil 103, and the switching element 102, as indicated by the broken-line arrows in FIG. 7A. . That is, in the first phase of the switching regulator 100, current flows only through the coil 103 and no current flows through the load 107.

  On the other hand, in the second phase in which both of the switching elements 101 and 102 are turned off, current flows from the ground end via the diode 104, the coil 103, the diode 105, and the load 107, as indicated by the broken-line arrows in FIG. 7B. That is, in the second phase of the switching regulator 100, a current flows through both the coil 103 and the load 107.

  Thus, the period during which the current flowing through the coil 103 flows through the load 107 in the switching period T is limited to the second phase of FIG. 7B. Therefore, the average coil current IL for each switching period T is larger than the average output current Io.

The on-time ton1 of the switching element 101 is expressed by the following equation (1).
ton1 = {OUT / (IN + OUT)} × T (1)

When the off time of the switching element 102 is toff2, the average coil current IL for each switching period T is expressed by the following equation (2).
IL = (T / toff2) × Io (2)

Further, the following equation (3) is obtained from the relationship of the above equations (1), (2), ton2 + toff2 = T, and ton1 = ton2.
IL = {1+ (OUT / IN)} × Io (3)

  As can be seen from the above equation (3), the lower the input voltage IN, the greater the difference between the average coil current IL and the average output current Io, and the greater the amount of heat generated (loss) of the switching regulator 100. I understand.

  In view of the above-described problems, an object of the present invention is to provide a step-up / step-down switching regulator that generates a small amount of heat (loss).

  In order to achieve the above object, a switching regulator according to the present invention includes a first switching element and a second switching element that are turned on / off to increase or decrease an input voltage to generate an output voltage; An error signal generation circuit that generates an error signal according to a difference between a feedback voltage corresponding to the predetermined voltage and a predetermined reference voltage; and a signal inversion that generates an inverted error signal obtained by inverting the error signal with reference to a predetermined inverted reference voltage A circuit; an oscillation circuit that generates a rectangular wave signal of a predetermined frequency; a slope signal generation circuit that generates a slope signal from the rectangular wave signal; a first comparison signal is generated by comparing the error signal and the slope signal A first comparison circuit; a second comparison circuit that compares the inverted error signal and the slope signal to generate a second comparison signal; and the first comparison signal and the second ratio. Signal, and, on the basis of the rectangular wave signal, and a control circuit for controlling the on / off timing of the first switching element and the second switching element; has a configuration having a (first configuration).

  In the switching regulator having the first configuration, the control circuit simultaneously performs the on transition of the first switching element and the off transition of the second switching element based on the rectangular wave voltage, while the first switching element Based on the comparison signal and the second comparison signal, the first control signal and the second control signal are generated so that the off transition of the first switching element and the on transition of the second switching element are performed independently of each other. It is preferable to adopt a configuration (second configuration).

  In the switching regulator having the second configuration, when the inversion error signal is larger than the maximum value of the slope signal, the first switching element is turned on / off with a duty corresponding to the first comparison signal. When the step-down mode in which the second switching element is steadily turned off and both the error signal and the inverted error signal are smaller than the maximum value of the slope signal, the first switching element is made to respond to the first comparison signal. When the error signal is larger than the maximum value of the slope signal, the second switching element is turned on / off at a predetermined duty, and the second switching element is turned on / off at a duty corresponding to the second comparison signal. One switching element is steadily turned on, and the second switching element is responsive to the second comparison signal. Configuration turned on / off boost mode Yuti better to (third configuration).

  In the switching regulator having the third configuration, the slope signal generation circuit resets the slope signal using the first pulse edge of the rectangular wave signal as a trigger and triggers the second pulse edge of the rectangular wave signal. As a configuration (fourth configuration) for starting the slope generation of the slope signal.

  Further, in the switching regulator having the third configuration, the slope signal generation circuit resets the slope signal with a pulse edge of the rectangular wave signal as a trigger, and when the predetermined delay time has passed thereafter, the slope signal is generated. A configuration (fifth configuration) for starting the slope generation of the signal may be used.

  In the switching regulator having the fourth or fifth configuration, the slope signal has a maximum value set larger than the inverted reference voltage and a minimum value set smaller than the inverted reference voltage ( A sixth configuration) may be used.

  In addition, when the switching regulator having any one of the first to sixth configurations has a configuration (seventh configuration) having a coil connected between the application terminal for the input voltage and the application terminal for the output voltage. Good.

  Further, in the switching regulator having the seventh configuration, the first switching element is connected between an input voltage application end and a first end of the coil, and the second switching element is A configuration in which the coil is connected between the second end and the ground end (eighth configuration) may be used.

  In the switching regulator having the eighth configuration, the first switching element and the second switching element may be transistors (9th configuration).

  The switching regulator having the ninth configuration includes a first rectifying element connected between the first end of the coil and a ground end, a second end of the coil, and an application end of the output voltage. A second rectifying element connected between them may be used (a tenth configuration).

  In the switching regulator having the tenth configuration, the first rectifying device and the second rectifying device may be diodes (11th configuration).

  The switching regulator having the eleventh configuration may be configured to have a capacitor (twelfth configuration) connected between the output voltage application terminal and the ground terminal.

  According to the present invention, it is possible to provide a step-up / step-down switching regulator that generates a small amount of heat (loss).

Block diagram showing the overall configuration of the switching regulator Circuit diagram showing a configuration example of a VL voltage generation circuit Table showing the operation mode of the switching regulator Timing chart showing an example of step-up / step-down operation Timing chart showing a variation of the step-up / step-down operation Table showing correlation between voltages VA and VB and operation mode Table showing average coil current reduction effect Circuit diagram showing a conventional example of a switching regulator (first phase) Circuit diagram showing a conventional example of a switching regulator (second phase)

<Overall configuration>
FIG. 1 is a block diagram showing the overall configuration of the switching regulator. The step-up / step-down switching regulator 1 shown in this configuration example includes a semiconductor device 10 and various discrete components (for example, switching elements M1 and M2, coils (inductors) L1, diodes D1 and D2, capacitors) externally connected thereto. C1-C5 and resistors R1 and R2).

  The switching elements M1 and M2 are respectively a first switching element (step-down switching element) and a second switching element (step-up switching) that are turned on / off to boost or step down the input voltage IN to generate the output voltage OUT. Device). The switching elements M1 and M2 perform a switching operation for switching on / off (conduction / non-conduction between both ends) according to the control voltages G1 and G2, respectively. When MOSFETs (metal oxide semiconductor field effect transistors) are used as the switching elements M1 and M2, the switching operation performs conduction / non-conduction between the source and the drain in accordance with the control voltages G1 and G2 input to the gate. It becomes the operation to switch. In the present configuration example, the switching element M1 is a P-channel MOSFET and the switching element M2 is an N-channel MOSFET, but is not limited thereto.

  The semiconductor device (regulator IC) 10 includes an internal power supply generation circuit 21, a band gap voltage generation circuit 22, a low voltage malfunction prevention circuit 23, a thermal shutdown circuit 24, an oscillation circuit 31, a slope generation circuit 32, a software A start circuit 33, an error amplifier 34, an operational amplifier 35, comparators 36 and 37, resistors 38a and 38b, a short circuit protection comparator 41, an overvoltage protection comparator 42, a control circuit 51, A current detection circuit 52, a driver 53, a VL voltage generation circuit 54, and a driver 55 are included.

  The semiconductor device 10 has terminals T1 to T14 used for connection with the outside. The terminal T1 is an input voltage application terminal. Terminals T2 and T3 are switch current detection terminals. The terminal T4 is a control terminal for the switching element M1. The terminal T5 is a lower drive voltage application terminal of the driver 53. The terminal T6 is an upper drive voltage application terminal of the driver 55. The terminal T7 is a control terminal for the switching element M2. The terminal T8 is a ground terminal. Terminal T9 is a soft start adjustment terminal. The terminal T10 is a feedback voltage application terminal. The terminal T11 is a phase compensation terminal. The terminal T12 is an oscillation frequency adjustment terminal. The terminal T13 is an internal power supply voltage application terminal. The terminal T14 is an enable terminal.

  The terminal T1 is connected to an application terminal (external power source such as a battery) of an input voltage IN (for example, 4 to 40 V). The terminal T1 is also connected to one end of the capacitor C1, one end of the capacitor C2, and one end of the resistor R1.

  The other end of the capacitor C1 is connected to the ground terminal. The other end of the capacitor C2 is connected to the terminal T5. The other end of the resistor R1 is connected to the source of the switching element M1. Both ends of the resistor R1 are connected to the terminal T2 and the terminal T3, respectively. The drain of the switching element M1 is connected to the cathode of the diode D1 and one end of the coil L1. The anode of the diode D1 is connected to the ground terminal. The diode D1 corresponds to the first rectifying element and can be replaced with a synchronous rectifying transistor.

  Note that a rectangular wave switch voltage SW1 appears at the drain of the switching element M1 in accordance with the on / off state of the switching element M1. When the switching element M1 is on, the switch voltage SW1 is at a high level (almost input voltage IN), and when the switching element M1 is off, the switch voltage SW1 is at a low level (almost ground voltage GND).

  The other end of the coil L1 is connected to the anode of the diode D2 and the drain of the switching element M2. The source of the switching element M2 is connected to the ground terminal. The cathode of the diode D2 is connected to one end of the capacitor C3 and the application end of the output voltage OUT. The other end of the capacitor C3 is connected to the ground terminal. The diode D2 corresponds to a second rectifying element and can be replaced with a synchronous rectifying transistor.

  Note that a rectangular wave switch voltage SW2 appears at the drain of the switching element M2 in accordance with the on / off state of the switching element M2. When the switching element M2 is off, the switch voltage SW2 is at a high level (almost output voltage OUT), and when the switching element M2 is on, the switch voltage SW2 is at a low level (almost ground voltage GND).

  The gate of the switching element M1 is connected to the terminal T4. The gate of the switching element M2 is connected to the terminal T7. The resistor R2 is a resistor used for adjusting the frequency of the rectangular wave voltage CLK generated by the oscillation circuit 31, and has one end connected to the terminal T12 and the other end connected to the ground terminal. The capacitor C4 is a capacitor mainly used for phase compensation of the internal power supply voltage REG, and has one end connected to the terminal T13 and the other end connected to the ground terminal. A feedback voltage FB corresponding to the output voltage OUT is input to the terminal T10. Terminals T10 and T11 are connected via an external phase compensation circuit (resistor and capacitor).

  The internal power supply voltage generation circuit 21 is connected to a terminal T13 to which the internal power supply voltage REG is applied and a terminal T14 to which an enable signal is externally input. The internal power supply voltage used inside the semiconductor device 10 from the input voltage IN. REG is generated. The internal power supply voltage REG is generated so that the accuracy of the voltage value or the like is higher than the input voltage IN. The internal power supply voltage REG is used as a drive voltage for the thermal shutdown circuit 24 and the driver 55.

  The internal power supply voltage generation circuit 21 once sends the generated internal power supply voltage REG to the outside of the semiconductor device 10 through an external line (a transmission line provided outside the semiconductor device 10) connected to the terminal T13. Then, it is pulled into the semiconductor device 10. For example, the internal power supply voltage REG sent to the external line returns to the semiconductor device 10 through the terminal T6 and is input to the power supply terminal of the driver 55. A capacitor C4 for phase compensation is connected to this external line.

  Thus, in the semiconductor device 10, at least a part of the transmission line of the internal power supply voltage REG is provided outside the semiconductor device 10, and the capacitor C 4 for phase compensation is externally attached, thereby saving the space of the semiconductor device 10. It is easy to make it easier.

  The band gap voltage generation circuit 22 generates a band gap voltage using the internal power supply voltage REG supplied from the internal power supply voltage generation circuit 21. The band gap voltage is generated so as to be more stable than the internal power supply voltage REG by using the band gap of the semiconductor, and is used in each part in the semiconductor device 10.

  The low-voltage malfunction prevention circuit 23 is a circuit that exhibits a UVLO [Under Voltage Lock Out] function in the semiconductor device 10. The low voltage malfunction prevention circuit 23 prevents, for example, the semiconductor device 10 from being turned on unless an input voltage IN of a predetermined value or more is input in order to prevent malfunction caused by the input voltage IN being too low.

  The thermal shutdown circuit 24 is a circuit that prevents thermal runaway of the switching regulator 1 due to overheating (excessive temperature rise). The thermal shutdown circuit 24 continuously detects the temperature using, for example, a temperature sensor, and stops the switching operation of the switching elements M1 and M2 when the detected temperature exceeds the upper limit value. From the viewpoint of the operation accuracy of the thermal shutdown circuit 24, the drive voltage of the thermal shutdown circuit 24 is not the input voltage IN but the internal power supply voltage REG with higher accuracy such as a voltage value.

  The oscillation circuit 31 generates a rectangular wave voltage CLK having a predetermined frequency and outputs it to the slope generation circuit 32 and the control circuit 41. The frequency of the rectangular wave voltage CLK can be adjusted using the resistor R2.

  The slope generation circuit 32 performs a process of inclining the rising (or falling) of the rectangular wave voltage CLK generated by the oscillation circuit 31 so that the slope voltage SLOPE (sawtooth voltage, triangular wave voltage, or Is generated and output to the non-inverting input terminals of the comparators 36 and 37. The slope voltage SLOPE is set such that the maximum value VMAX is larger than the inversion reference voltage V2, and the minimum value VMIN is smaller than the inversion reference voltage V2.

  The soft start circuit 33 is a circuit that exhibits a soft start function in order to prevent overshoot of the output voltage OUT, generation of an inrush current, and the like. The soft start circuit 33 supplies an appropriate soft start voltage SS to the error amplifier 34 when starting the switching regulator 1 so that the output voltage OUT rises gently. The soft start voltage SS is reset based on an overcurrent detection signal received from the overcurrent detection circuit 52, for example. A capacitor C5 for setting a soft start time is connected to the soft start circuit 33. One end of the capacitor C5 is connected to the soft start circuit 33 via the terminal T9, and the other end is connected to the ground terminal.

  The error amplifier 34 amplifies the difference between the feedback voltage FB (divided voltage of the output voltage OUT) applied to the inverting input terminal and the predetermined reference voltage V1 applied to the non-inverting input terminal to generate the error voltage VA. This corresponds to an error signal generation circuit to be generated. Note that, when the switching regulator 1 is started, the soft start voltage SS is prioritized as the voltage input to the non-inverting input terminal of the error amplifier 34 instead of the reference voltage V1. The output terminal of the error amplifier 34 is connected to the inverting input terminal of the operational amplifier 35 via the resistor 38a, and is connected to the inverting input terminal of the comparator 36 and the terminal T11.

  A predetermined inversion reference voltage V <b> 2 is applied to the non-inverting input terminal of the operational amplifier 35. The output terminal of the operational amplifier 35 is connected to the inverting input terminal of the comparator 37 and is connected to the inverting input terminal of the operational amplifier 35 via the resistor 38b. The resistor 38a, the resistor 38b, and the operational amplifier 35 correspond to a signal inverting circuit (inverting amplifier) that generates an inverted error voltage VB obtained by inverting the error voltage VA using a predetermined inverted reference voltage V2. That is, when the error voltage VA increases, the inversion error voltage VB decreases. Conversely, when the error voltage VA decreases, the inversion error voltage VB increases.

  The comparator 36 corresponds to a first comparison circuit that compares the error voltage VA and the slope voltage SLOPE to generate a comparison voltage CMP1. The comparison voltage CMP1 is at a low level when the error voltage VA is larger than the slope voltage SLOPE, and is at a high level when the error voltage VA is smaller than the slope voltage SLOPE.

  The comparator 37 corresponds to a second comparison circuit that compares the inverted error voltage VB and the slope voltage SLOPE to generate a comparison voltage CMP2. The comparison voltage CMP2 becomes low level when the inversion error voltage VB is larger than the slope voltage SLOPE, and becomes high level when the inversion error voltage VB is smaller than the slope voltage SLOPE.

  The short circuit protection comparator 41 receives a feedback voltage FB at a non-inverting input terminal and a predetermined voltage V3 at an inverting input terminal, and outputs a comparison result of these voltages as a short circuit protection signal SCP. The overvoltage protection comparator 42 receives the feedback voltage FB at the non-inverting input terminal and the predetermined voltage V4 at the inverting input terminal, and outputs a comparison result of these voltages as an overvoltage protection signal OVP.

  The control circuit 51 performs on / off control (PWM [pulse width modulation] control) of the switching elements M1 and M2 based on the comparison voltages CMP1 and CMP2 and the rectangular wave voltage CLK.

  More specifically, the control circuit 51 generates a control voltage G1 for turning on / off the switching element M1 based on the comparison voltage CMP1 and the rectangular wave voltage CLK. The control voltage G1 is input to the gate of the switching element M1 through the driver 53 and the terminal T4. Thus, the driver 53 is provided on the transmission line of the control voltage G1 that connects the control circuit 51 and the switching element M1.

  When the control voltage G1 is at a high level, the switching element M1 is turned off, and when the control voltage G1 is at a low level, the switching element M1 is turned on. Thereby, the switching operation of the switching element M1 is performed according to the duty of the comparison voltage CMP1.

  The control circuit 51 outputs a control voltage G2 for turning on / off the switching element M2 based on the comparison voltage CMP2 and the rectangular wave voltage CLK. The control voltage G2 is input to the gate of the switching element M2 via the driver 55 and the terminal T7. Thus, the driver 55 is provided on the transmission line of the control voltage G2 that connects the control circuit 51 and the switching element M2.

  When the control voltage G2 is high level, the switching element M2 is turned on, and when the control voltage G2 is low level, the switching element M2 is turned off. Thereby, the switching operation of the switching element M2 is performed according to the duty of the comparison voltage CMP2.

  The overcurrent detection circuit 52 detects the value of the current flowing through the resistor R1 based on the voltages at the terminals T2 and T3. The overcurrent detection circuit 52 outputs an overcurrent detection signal to the control circuit 51 when the detected value exceeds a predetermined upper limit value (that is, when it is detected that the current flowing through the resistor R1 is in an overcurrent state). Output to. Note that the control circuit 51 performs an operation (overcurrent protection operation) for preventing a problem caused by the overcurrent according to the overcurrent detection signal.

  The first power supply terminal of the driver 53 is connected to the terminal T1 and receives the input voltage IN. The VL voltage generation circuit 54 is connected between the second power supply terminal of the driver 53 and the terminal T5. The VL voltage generation circuit 54 generates a voltage VL obtained by reducing the voltage of the input voltage IN by a constant voltage Vs. Supply to the power terminal. This voltage Vs is a voltage having an appropriate magnitude as the driving voltage of the driver 53 (the difference between the voltage of the first power supply terminal and the voltage of the second power supply terminal).

  FIG. 2 shows the configuration of the VL voltage generation circuit 54. In the VL voltage generation circuit 54, Zener diodes 54a and 54b and a constant current source 54c are provided in series between the input terminal of the input voltage IN and the ground terminal. The sum of the Zener voltages of the Zener diodes 54a and 54b is set to the voltage Vs, and the constant current source 54c is set to flow the current I necessary for generating the voltage VL.

  According to the VL voltage generation circuit 54, the voltage VL (= IN−Vs) is generated between the Zener diodes 54 a and 54 b and the constant current source 54 c and supplied to the second power supply terminal of the driver 53. Note that the configuration of the VL voltage generation circuit 54 is not limited to the above-described configuration, and may be another configuration.

  According to the VL voltage generation circuit 54, an appropriate drive voltage is supplied to the driver 53 regardless of the voltage fluctuation of the input voltage IN, and an excessive voltage is prevented from being applied to the driver 53. Thus, the VL voltage generation circuit 54 serves as a voltage adjustment circuit that keeps the difference between the voltage of the first power supply terminal and the voltage of the second power supply terminal of the driver 53 substantially constant.

<Basic operation of switching regulator>
Next, the basic operation of the switching regulator 1 will be described. The operation mode of the switching regulator 1 is basically the step-up mode in which the step-up operation is performed when the output voltage OUT is smaller than the target voltage, and the step-down mode in which the step-down operation is performed when the output voltage OUT is larger than the target voltage.

  In the boost mode, the error voltage VA is constantly larger than the slope voltage SLOPE. Accordingly, in the boost mode, the comparison voltage CMP1 is constantly at a low level, and the switching element M1 is constantly turned on.

  Here, when the inversion error voltage VB is greater than the slope voltage SLOPE, the comparison voltage CMP2 is at a low level, and when the inversion error voltage VB is less than the slope voltage SLOPE, the comparison voltage CMP2 is at a high level. As described above, the comparison voltage CMP2 varies in level according to the magnitude relationship between the inversion error voltage VB and the slope voltage SLOPE, and the switching element M2 is switched on / off in accordance with the level variation of the comparison voltage CMP2.

  When the switching element M2 is turned on, magnetic energy is accumulated in the coil L1, and when the switching element M2 is turned off, the magnetic energy accumulated in the coil L1 is released. In the step-up mode, the switching and switching of the switching element M2 are repeated, whereby the magnetic energy is repeatedly stored and released in the coil L1. As a result of such a boosting operation, an output voltage OUT obtained by boosting the input voltage IN is generated.

  On the other hand, in the step-down mode, the inversion error voltage VB is constantly larger than the slope voltage SLOPE. Accordingly, in the step-down mode, the comparison voltage CMP2 is constantly at a low level, and the switching element M2 is constantly turned off.

  Here, when the error voltage VA is greater than the slope voltage SLOPE, the comparison voltage CMP1 is at a low level, and when the error voltage VA is less than the slope voltage SLOPE, the comparison voltage CMP1 is at a high level. Thus, the comparison voltage CMP1 changes in level according to the magnitude relationship between the error voltage VA and the slope voltage SLOPE, and the switching element M1 is switched on / off according to the level change of the comparison voltage CMP1.

  When the switching element M1 is turned on, magnetic energy is accumulated in the coil L1, and when the switching element M1 is turned off, the magnetic energy accumulated in the coil L1 is released. In the step-down mode, the switching and switching of the switching element M1 are repeated, whereby the magnetic energy is repeatedly stored and released in the coil L1. As a result of such a step-down operation, an output voltage OUT obtained by stepping down the input voltage IN is generated.

  The switching regulator 1 is in a step-up / step-down mode in which both the switching elements M1 and M2 are repeatedly turned on / off when the input voltage IN and the output voltage OUT are close.

<Details of step-up / step-down operation>
FIG. 3 is a table showing operation modes (step-down mode, step-up / step-down mode, and step-up mode) of the switching regulator 1. This table shows the magnitude relationship between the input voltage IN and the output voltage OUT, the operation mode of the switching regulator 1 corresponding to this, and the on / off states of the switching elements M1 and M2 (the waveforms of the switch voltages SW1 and SW2). It is depicted.

  In the switching regulator 1, the control circuit 51 independently controls the switching elements M1 and M2 based on the comparison voltages CMP1 and CMP2, thereby switching the operation mode according to the magnitude relationship between the input voltage IN and the output voltage OUT. Duty control of the control voltages G1 and G2 is performed simultaneously and in parallel. This will be specifically described below.

  In a state where the input voltage IN is higher than the output voltage OUT (IN> OUT), the control circuit 51 turns on / off the switching element M1 with a duty corresponding to the comparison voltage CMP1, and steadily turns off the switching element M2. In addition, the control voltages G1 and G2 are generated. This state corresponds to the step-down mode of the switching regulator 1.

  In a state where the input voltage IN is close to the output voltage OUT (IN≈OUT), the control circuit 51 turns on / off the switching element M1 with a duty corresponding to the comparison voltage CMP1, and the switching element M2 according to the comparison voltage CMP2. The control voltages G1 and G2 are generated so as to be turned on / off with a different duty. This state corresponds to the step-up / step-down mode of the switching regulator 1.

  In the state where the input voltage IN is smaller than the output voltage OUT (IN <OUT), the control circuit 51 steadily turns on the switching element M1, and turns on / off the switching element M2 with a duty according to the comparison voltage CMP2. Thus, the control voltages G1 and G2 are generated. This state corresponds to the boost mode of the switching regulator 1.

  Here, an important point for reducing the heat generation amount (loss) of the switching regulator 1 is that in the step-up / step-down mode in which both of the switching elements M1 and M2 are turned on / off, during the ON period of the switching element M1, The switching element M2 is turned off as long as possible, and the switching element M2 is turned on as long as possible during the OFF period of the switching element M1.

  In order to realize the above operation, the control circuit 51 performs timing control for turning off the switching element M2 at the same time as turning on the switching element M1. Hereinafter, the timing control will be described in detail with reference to FIG. 4A.

  FIG. 4A is a timing chart showing an example of the step-up / step-down operation. From the top, the rectangular wave voltage CLK, the slope voltage SLOPE, the control voltages G1 and G2 (equivalent to the comparison voltages CMP1 and CMP2), and the switch voltage SW1 and SW2 is depicted. In FIG. 4A, as an example of a situation where the switching regulator 1 is in the step-up / step-down mode, a situation where the inversion error voltage VB is smaller than the maximum value VMAX of the slope voltage SLOPE and larger than the error voltage VA is illustrated.

  When the rectangular wave voltage CLK rises from the low level to the high level at time t1, the control circuit 51 causes both of the control voltages G1 and G2 to fall from the high level to the low level using the rising edge of the rectangular wave voltage CLK as a trigger. . As a result, at time t1, the switching element M1 is turned on and at the same time the switching element M2 is turned off. At time t1, the slope signal generation circuit 32 resets (discharges) the slope voltage SLOPE to the minimum value VMIN (for example, GND) using the rising edge of the rectangular wave voltage CLK as a trigger.

  When the rectangular wave voltage CLK falls from the high level to the low level at time t2, the slope signal generation circuit 32 starts the slope generation (charging) of the slope voltage SLOPE using the falling edge of the rectangular wave voltage CLK as a trigger. . As a result, after time t2, the slope voltage SLOPE rises with a predetermined slope.

  At time t3, when the slope voltage SLOPE exceeds the error voltage VA and the comparison voltage CMP1 rises from low level to high level, the control circuit 51 raises the control voltage G1 from low level to high level. As a result, at time t3, the switching element M1 is switched from on to off. Note that the smaller the error voltage VA, the earlier the off-timing of the switching element M1, and the larger the error voltage VA, the later the off-timing of the switching element M1. That is, the on-duty of the switching element M1 changes according to the voltage value of the error voltage VA.

  At time t4, when the slope voltage SLOPE exceeds the inversion error voltage VB and the comparison voltage CMP2 rises from the low level to the high level, the control circuit 51 raises the control voltage G2 from the low level to the high level. As a result, at time t4, the switching element M2 is switched from off to on. The smaller the error voltage VB, the earlier the on-timing of the switching element M2, and the larger the error voltage VB, the later the on-timing of the switching element M2. That is, the on-duty of the switching element M2 changes according to the voltage value of the error voltage VB.

  Thereafter, the control circuit 51 repeats the same operation at time t1 to t4, thereby turning on the switching element M1 based on the rectangular wave voltage CLK and simultaneously turning off the switching element M2, while switching based on the comparison signal CMP1. Control signals G1 and G2 are generated so that the element M1 is turned off and the switching element M2 is turned on based on the comparison signal CMP2.

  That is, in the switching regulator 1 of this configuration example, the control circuit 51 simultaneously performs the ON transition of the switching element M1 and the OFF transition of the switching element M2 based on the rectangular wave voltage CLK, while switching based on the comparison signals CMP1 and CMP2. Control signals G1 and G2 are generated so that the off transition of the element M1 and the on transition of the switching element M2 are performed independently of each other.

  With such a configuration, in the step-up / step-down mode in which both switching elements M1 and M2 are turned on / off, switching element M2 is turned off as long as possible while switching element M1 is on, and switching element M1 is turned off. During the period, since the switching element M2 can be turned on as long as possible, the heat generation amount (loss) of the switching regulator 1 can be reduced.

  In view of the downsizing of the slope generation circuit 32, it is desirable to generate a sawtooth voltage rather than a triangular wave voltage as the slope voltage SLOPE. In the case of generating a triangular wave voltage, the slope generation circuit 32 includes not only a first current source circuit that determines a charging rate (eg, rising slope) but also a second current source circuit that determines a discharging rate (eg, falling slope). It is necessary to provide it. On the other hand, when the sawtooth voltage is generated, the second current source circuit is not necessary, and the slope generation circuit 32 can be downsized accordingly.

  In view of prevention of missing pulses, it is desirable to generate a sawtooth voltage rather than a triangular voltage as the slope voltage SLOPE. For example, when comparing the triangular wave voltage and the error voltage VA, if the triangular wave voltage does not fall below the error voltage VA from the start of discharge of the triangular wave voltage (t1) to the next start of charging (t2), the pulse of the comparison voltage CMP1 is missing. Occurs, and the on / off control of the switching element M1 cannot be performed correctly. On the other hand, if it is a sawtooth voltage, the discharge operation is completed almost simultaneously with the start of discharge of the sawtooth voltage (t1), and the sawtooth voltage is surely below the error voltage VA by the start of the next charge (t2). There is no possibility that the pulse of the comparison voltage CMP1 is lost, and the on / off control of the switching element M1 can be performed correctly.

  In FIG. 4A, the description has been given by taking as an example a configuration in which slope generation of the slope voltage SLOPE is started using the falling edge of the rectangular wave voltage CLK as a trigger. However, the configuration of the present invention is not limited to this. For example, as shown in FIG. 4B, the slope voltage SLOPE may be generated at a time when a predetermined delay time τ has elapsed (time t2 ′) from the rising edge (time t1) of the rectangular wave voltage CLK. I do not care.

  FIG. 5 is a table showing the correlation between the error voltage VA and the inverted error voltage VB and the operation mode. In the foregoing, it has been described that the operation mode of the switching regulator 1 is switched according to the magnitude relationship between the input voltage IN and the output voltage OUT. However, when focusing on the operation of the comparators 36 and 37, the switching regulator 1 It can be seen that the operation mode 1 is switched according to the magnitude relationship between the error voltage VA and the inverted error voltage VB and the slope voltage SLOPE.

More specifically, when the inversion error voltage VB is larger than the maximum value VMAX of the slope voltage SLOPE (VB> VMAX), the comparison voltage CMP2 is constantly at a low level, so that the switching element M2 is constantly activated. Turn off. On the other hand, the switching element M1 is in a state where ON / OFF is periodically switched according to the magnitude relationship between the error voltage VA and the slope voltage SLOPE. This state corresponds to the step-down mode of the switching regulator 1. When the switching cycle is T and the ON time of the switching element M1 is Ton1, the output voltage OUT can be calculated by the following equation (A).
OUT = (Ton1 / T) × IN (A)

When both the error voltage VA and the inverted error voltage VB are smaller than the maximum value VMAX of the slope voltage SLOPE (VMAX ≧ (VA, VB)), the magnitude relationship between the error voltages VA and VB and the slope voltage SLOPE is satisfied. Accordingly, both switching elements M1 and M2 are repeatedly turned on / off. This state corresponds to the step-up / step-down mode of the switching regulator 1. When the on time of the switching element M1 is Ton1, and the off time of the switching element M2 is Toff2, the output voltage OUT can be calculated by the following equation (B).
OUT = (Ton1 / Toff2) × IN (B)

When the error voltage VA is larger than the maximum value VMAX of the slope voltage SLOPE (VA> VMAX), the comparison voltage CMP1 is constantly at a low level, so that the switching element M1 is constantly turned on. On the other hand, the switching element M2 is in a state where ON / OFF is periodically switched according to the magnitude relationship between the inversion error voltage VB and the slope voltage SLOPE. This state corresponds to the boost mode of the switching regulator 1. When the switching period is T and the off time of the switching element M2 is Toff2, the output voltage OUT can be calculated by the following equation (C).
OUT = (T / Toff2) × IN (C)

  FIG. 6 is a table showing the effect of reducing the average coil current. Under the conditions of the output voltage OUT = 6V and the average output current Io = 2A, each operation mode (step-down mode (IN = 12V), step-up / down mode (IN = 6V) and the average coil current IL in the boost mode (IN = 3V)) are shown. In addition, the calculation result of the average coil current IL obtained by the conventional configuration (see FIGS. 7A and 7B) is shown in the X line in the table, and the Y line in the table shows the calculation result. The calculation result of the average coil current IL obtained in the configuration example (see FIG. 1) is shown.

  As is clear from comparison between the X-th row and the Y-th row of this table, the switching coil 1 of this configuration example can suppress the average coil current IL for each switching cycle T. It is possible to reduce the amount of heat generation (loss).

<Other variations>
The configuration of the present invention can be variously modified in addition to the above-described embodiment without departing from the gist of the invention. That is, the above-described embodiment is an example in all respects and should not be considered as limiting, and the technical scope of the present invention is not the description of the above-described embodiment, but the claims. It should be understood that all modifications that come within the meaning and range of equivalents of the claims are included.

  The switching regulator according to the present invention is suitable, for example, as an in-vehicle power supply device, and can be widely applied to power supply devices for various electric devices. When applied as an in-vehicle power supply device, the switching regulator according to the present invention is used in a form in which an in-vehicle battery is connected as an external power source and an in-vehicle electric device is connected as a load.

DESCRIPTION OF SYMBOLS 1 Switching regulator 10 Semiconductor device 21 Internal power supply voltage generation circuit 22 Band gap voltage generation circuit 23 Low voltage malfunction prevention circuit 24 Thermal shutdown circuit 31 Oscillation circuit 32 Slope generation circuit 33 Soft start circuit 34 Error amplifier 35 Operational amplifier 36, 37 Comparator 38a , 38b Resistor 41 Short circuit protection comparator 42 Overvoltage protection comparator 51 Control circuit 52 Overcurrent detection circuit 53 Driver 54 VL voltage generation circuit 55 Driver C1 to C5 Capacitor D1, D2 Diode L1 Coil (inductor)
M1 switching element (P-channel MOS field effect transistor)
M2 switching element (N-channel MOS field effect transistor)
R1, R2 resistors T1-T14 terminals

Claims (9)

A coil connected between an input voltage application terminal and an output voltage application terminal;
A first switching element connected between the application end of the input voltage and the first end of the coil and turned on / off in response to a first control signal ;
A second switching element connected between the second end of the coil and the ground end and turned on / off in response to a second control signal ;
An error signal generation circuit that generates an error signal according to a difference between a feedback voltage corresponding to the output voltage and a predetermined reference voltage;
A signal inverting circuit for generating an inverted error signal obtained by inverting the error signal with reference to a predetermined inverted reference voltage;
An oscillation circuit that generates a rectangular wave signal of a predetermined frequency;
A slope signal generating circuit for generating a slope signal from the rectangular wave signal;
A first comparison circuit that compares the error signal and the slope signal to generate a first comparison signal;
A second comparison circuit that compares the inverted error signal with the slope signal to generate a second comparison signal;
A control circuit that generates the first control signal and the second control signal so as to step up or step down the input voltage based on the first comparison signal, the second comparison signal, and the rectangular wave signal;
I have a,
The control circuit simultaneously performs an on transition of the first switching element and an off transition of the second switching element based on the rectangular wave signal, and on the basis of the first comparison signal and the second comparison signal. A switching regulator , wherein the first control signal and the second control signal are generated so that an off transition of one switching element and an on transition of the second switching element are performed independently of each other . When the inverted error signal is larger than the maximum value of the slope signal, the first switching element is turned on / off with a duty corresponding to the first comparison signal, and the second switching element is steadily turned off. And
When the error signal and the inverted error signal are both smaller than the maximum value of the slope signal, the first switching element is turned on / off with a duty corresponding to the first comparison signal, and the second switching element is turned on. The step-up / step-down mode turns on / off at a duty according to the second comparison signal
A step-up mode in which when the error signal is larger than the maximum value of the slope signal, the first switching element is steadily turned on, and the second switching element is turned on / off at a duty according to the second comparison signal; Become,
The switching regulator according to claim 1 . The slope signal generation circuit resets the slope signal using a first pulse edge of the rectangular wave signal as a trigger, and starts generating a slope of the slope signal using a second pulse edge of the rectangular wave signal as a trigger. The switching regulator according to claim 2 . The slope signal generation circuit resets the slope signal with a pulse edge of the rectangular wave signal as a trigger, and starts slope generation of the slope signal when a predetermined delay time elapses thereafter. Item 3. A switching regulator according to Item 2 . The slope signal is greater than the maximum value of the inversion reference voltage, and a switching regulator according to claim 3 or claim 4 minimum characterized in that it is smaller than the inversion reference voltage. The switching regulator according to claim 1, wherein the first switching element and the second switching element are transistors. A first rectifier connected between a first end of the coil and a ground end;
A second rectifying element connected between the second end of the coil and the application end of the output voltage;
The switching regulator according to any one of claims 1 to 6 , characterized by comprising: The switching regulator according to claim 7 , wherein the first rectifying element and the second rectifying element are diodes. The switching regulator according to any one of claims 1 to 8, further comprising a capacitor connected between the output voltage application terminal and a ground terminal.

Images