JP5567432B2 - DCDC converter - Google Patents

Description

  The present invention relates to a power supply circuit, particularly a DCDC converter, and more particularly to a DCDC converter having an inductor.

  With the miniaturization of LSIs, the input voltage of LSIs is decreasing. Therefore, applications for generating a low output voltage are increasing in DCDC converters that output the input voltage of LSI. FIG. 1 shows a conventional switching step-down DCDC converter. When the first switching device SW1 is on, the slope of the current change of the inductor L1 is

It is represented by When the input voltage V _IN to the DCDC converter is high and the output voltage V _OUT is low, the inductor current i _L rises rapidly. For example, it is conceivable that the input voltage V _IN is 5V, 12V, 48V, etc., and the output voltage V _OUT is 1V or less. On the other hand, when the first switching device SW1 is off and the second switching device SW2 is energized, the slope of the current change in the inductor L1 is

Since the output voltage V _OUT is low, the slope at which the inductor current i _L decreases is gentle.

Consider a case where the load current i _LOAD flowing through the load to which the output voltage V _OUT of the step-down DCDC converter using such an inductor is applied is rapidly reduced. For example, when the load current i _LOAD decreases from 1 A to 100 mA, if the inductor current i _L does not decrease, extra charge is supplied to the capacitor C _OUT , and the output voltage V _OUT exceeds the predetermined overvoltage determination voltage. Ascending overshoot occurs. Even when the first switching device SW1 is turned off, the inductor current i _L decreases only slowly as described in connection with the equation (2). Therefore, it is necessary to use a capacitor having a large capacity so that the increase of the output voltage _VOUT due to the inflow of the inductor current i _L falls within a predetermined range. Here, the rapid decrease of the load current i _LOAD is the fastest case where the load current i _LOAD decreases almost simultaneously when a circuit such as an LSI connected as a load is turned off. The slower case is when the decrease in load current i _LOAD is at least faster than the decrease in inductor current i _{L in} equation (2). In such a case, an extra charge is supplied to the capacitor C _OUT and an overshoot may occur.

  A DCDC converter capable of responding to a decrease in load current at high speed is disclosed in Patent Document 1 and is shown in FIG. The DC-DC converter 1 includes a DC-DC converter control circuit 10a and a converter unit 20a. The converter unit 20a includes an output transistor Q1, which is an N-channel MOS transistor, a diode D1, a choke coil L1, and a smoothing capacitor C1. With. By turning on / off the output transistor Q1 based on the output signal SG1 from the control circuit 10a, the input voltage Vin is stepped down and output to the load connected to the output terminal To as the output voltage Vo. The output voltage Vo is controlled to a predetermined target value by changing the ratio of the on time and the off time of the output transistor Q1.

The output terminal To is connected to the input terminal T1 of the control circuit 10a. The input terminal T1 is connected to the ground via resistors R1 and R2. The connection point between the resistor R1 and the resistor R2 is connected to the inverting input terminal of the comparator 11, so that the output voltage Vo is divided by the resistors R1 and R2, and the divided voltage V1 is compared as a feedback signal. Is input to the inverting input terminal of the device 11. In the comparator 11, the feedback signal and the reference voltage Vr are compared, and the output transistor Q1 is on / off controlled according to the result. In the present technology, the reference voltage Vr to be compared with the feedback signal is sloped to the reference voltage Vref in order to suppress the occurrence of subharmonic oscillation that tends to occur when the ON time or OFF time of the switching element becomes extremely long. The voltage is the sum of the signals. As a result, it is possible to shorten the time until the output voltage Vo converges to the target value based on the reference voltage Vref after a sudden load change, and thus it is possible to suppress the occurrence of overshoot. Here, the reference voltage Vref is set to coincide with the divided voltage V1 by the resistors R1 and R2 when the output voltage Vo reaches the standard value.

  In addition, as control of a switching type DCDC converter, it is generally known that an output voltage is compared with a predetermined voltage and a switching device is turned on when the output voltage is equal to or lower than the predetermined voltage. There are various specific control modes including those of the prior art.

JP 2010-051073 A

However, the prior art of Patent Document 1 is attempting to suppress the occurrence of overshoot in the DC-DC converter control circuit 10a is a controller, only the controller can not respond to fast load current decreases than the decrease of the inductor current i _L Even the suppression of the resulting overshoot is not considered.

  The present invention has been made in view of such problems, and its purpose is to avoid overshoot in response to a rapid decrease in load current or overshoot caused by the load current. An object of the present invention is to provide a DCDC converter capable of suppressing the above.

  In order to achieve such an object, a first aspect of the present invention includes an inductor, a first switching device connected between an input voltage terminal to which an input voltage is applied, and the inductor, and the first A switching point between the switching device and the inductor, a second switching device connected between the ground terminal, a capacitor between the output voltage terminal from which an output voltage is output and the ground terminal, and the first A third switching device inserted in a path from the ground terminal to the output voltage terminal, which is a current path when one switching device is turned off, for interrupting the path in response to a load current. It is a DCDC converter characterized by the above.

  According to a second aspect of the present invention, in the first aspect, the third switching device is disposed between the inductor and the output voltage terminal.

  According to a third aspect of the present invention, in the second aspect, the fourth switching device is disposed between a connection point of the inductor and the third switching device and the input voltage terminal. The current flowing from the input voltage terminal toward the connection point can be cut off, and the inductor current cut off by the third switching device when the third switching device is turned off can flow to the input voltage terminal. A fourth switching device is further provided.

  According to a fourth aspect of the present invention, in the second aspect, the fourth aspect is arranged between a connection point of the inductor and the third switching device and another voltage terminal different from the input voltage terminal. 4, the current flowing from the other voltage terminal toward the connection point is cut off, and the inductor current cut off by the third switching device when the third switching device is turned off is A fourth switching device that can flow to another voltage terminal is further provided, and a voltage applied to the other voltage terminal is higher than a target value of the output voltage.

  According to a fifth aspect of the present invention, in the second aspect, the fifth aspect further comprises a resistor arranged in parallel with the third switching device, and the third switching device causes the third switching device to turn off when the third switching device is off. The interrupted inductor current flows to the output voltage terminal through the resistor.

  According to a sixth aspect of the present invention, in the third or fourth aspect, the sixth aspect further includes a resistor arranged in parallel with the third switching device, and the third switching device is turned off when the third switching device is turned off. The inductor current interrupted by the switching device flows through the resistor to the output voltage terminal.

  According to a seventh aspect of the present invention, in the first aspect, the third switching device is disposed between the second switching device and the ground terminal.

  According to an eighth aspect of the present invention, in the seventh aspect, the eighth aspect further includes a resistor arranged in parallel with the third switching device, and the third switching device causes the third switching device to turn off when the third switching device is off. The interrupted inductor current flows to the output voltage terminal through the resistor.

  According to a ninth aspect of the present invention, in the eighth aspect, the third switching device has a parasitic element, and the parasitic element is arranged in a direction to cut off a current flowing in a direction flowing out from the ground terminal. It is characterized by being.

  According to a tenth aspect of the present invention, in the fifth, sixth, or eighth aspect, the resistor is replaced with a non-linear resistance element.

  The eleventh aspect of the present invention is that, in any one of the first to tenth aspects, when the output voltage is detected to be in an overvoltage state, the third switching device is turned off. Features.

  According to a twelfth aspect of the present invention, in the eleventh aspect, the third switching device is turned off for a predetermined time when it is detected that the output voltage is in an overvoltage state. .

  In addition, in a thirteenth aspect of the present invention, in the eleventh aspect, the third switching device is connected between the inductor and the output voltage terminal, and the third switching device is turned off. The determination voltage for performing and the determination voltage for canceling are respectively set.

  According to a fourteenth aspect of the present invention, in the thirteenth aspect, the condition for turning off the third switching device is an on signal of the first switching device.

  According to a fifteenth aspect of the present invention, in the thirteenth aspect, a determination voltage for turning off the third switching device is provided, and the determination voltage for turning on is set at the bottom of the constant on-time DCDC converter. The output of the detection comparator is used.

  According to a sixteenth aspect of the present invention, in the fifteenth aspect, there is provided a function of resetting an on-time when a determination voltage for turning off the third switching device is exceeded. .

  In addition, in a seventeenth aspect of the present invention, in any one of the first to tenth aspects, when it is detected that a load current to which the output voltage is applied is suddenly reduced, the third switching device The inductor current flowing through is cut off.

  Further, an eighteenth aspect of the present invention is that, in the seventeenth aspect, the inductor current flowing through the third switching device is cut off for a certain period of time when it is detected that the load current suddenly decreases. It is characterized by.

  According to a nineteenth aspect of the present invention, in the seventeenth aspect, when it is detected that the load current suddenly decreases, the inductor current flowing through the third switching device is interrupted, and the output voltage When the voltage drops below the release voltage, the third switching device is turned on.

  According to the present invention, an inductor, a first switching device connected between an input voltage terminal to which an input voltage is applied and the inductor, a connection point between the first switching device and the inductor, and a ground terminal In a DCDC converter including a second switching device connected in between and a capacitor between an output voltage terminal from which an output voltage is output and a ground terminal, this is a current path when the first switching device SW1 is off. And a third switching device inserted in a path from the ground terminal to the output voltage terminal for interrupting the path in response to the load current, thereby causing a rapid decrease in the load current or due to this. It is possible to respond to the overshoot generated at a high speed.

It is a figure which shows the conventional step-down DCDC converter of a switching system. It is a figure which shows the conventional DCDC converter which can respond to the reduction | decrease of load current at high speed. It is a figure which shows the DCDC converter which concerns on 1st Embodiment. It is a figure for demonstrating the operation | movement of the conventional DCDC converter shown in FIG. 1 as a comparison. It is a figure for demonstrating operation | movement of the DCDC converter 300 which concerns on 1st Embodiment. It is a figure which shows the insertion location of 3rd switching device SW3. It is a figure which shows the DCDC converter which concerns on 2nd Embodiment. It is a figure which shows the modification of 2 embodiment. It is a figure which shows the DCDC converter which concerns on 3rd Embodiment. It is a figure which shows the DCDC converter which concerns on 4th Embodiment. It is a figure for demonstrating operation | movement of the DCDC converter 1000 which concerns on 4th Embodiment. It is a figure which shows the modification of 4th Embodiment. It is a figure which shows the DCDC converter which concerns on 5th Embodiment. FIG. 14 is a diagram showing a circuit in which a resistor R1 is connected in parallel with a third switching device SW3 in the DCDC converter 1300 of FIG. It is a figure which shows the specific example of 3rd switching device SW3 of FIG. It is a figure which shows the DCDC converter which concerns on 6th Embodiment. It is a figure which shows the DCDC converter which concerns on 7th Embodiment. It is a figure which shows the modification of 7th Embodiment. It is a figure which shows the DCDC converter which concerns on 8th Embodiment. It is a figure which shows the DCDC converter which concerns on 9th Embodiment. It is a figure which shows the DCDC converter which concerns on 10th Embodiment. It is a figure which shows the DCDC converter which concerns on 11th Embodiment. It is a figure which shows the DCDC converter which concerns on 12th Embodiment. It is a figure which shows the modification of 12th Embodiment. It is a figure which shows the DCDC converter which concerns on 13th Embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 3 shows a DCDC converter according to the first embodiment. The DCDC converter 300 includes an inductor L1, a first switching device SW1 connected between an input voltage terminal to which an input voltage V _IN is applied, and the inductor L1, and a connection point between the first switching device SW1 and the inductor L1. The second switching device SW2 connected between the first terminal and the ground terminal GND, the capacitor C _OUT between the output voltage terminal from which the output voltage V _OUT is output and the ground terminal GND, the inductor 1 and the output voltage terminal, And a third switching device SW3 connected between the two. For the sake of explanation, the load is also shown.

The third switching device SW3 is turned off when a sudden decrease in the load current or an overshoot caused by this is detected. As a result, the inductor current i _L flowing from the inductor L1 to the capacitor C _OUT is cut off or reduced, and overshoot can be avoided or suppressed.

  FIG. 5 is a diagram for explaining an operation example of the DCDC converter according to the present embodiment. FIG. 4 is a diagram for explaining the operation of the conventional DCDC converter shown in FIG. 1 as a comparison. The first switching device SW1 is turned on for a predetermined time and then turned off until the output voltage falls to the reference voltage. When it falls to the reference voltage, it turns on again for a certain time. We are under such control. This is common in FIGS. However, in FIG. 6 according to the present embodiment, the third switching device SW3 is turned off when a sudden decrease in the load current or an overshoot caused by this is detected, and the output voltage is peaked at this point. It decreases, and overshoot can be avoided or suppressed. When the output voltage reaches the reference voltage, the first switching device SW1 is turned on for a certain time. At this time, the third switching device SW3 is turned on simultaneously with the first switching device SW1.

When the third switching device SW3 is off and the first switching device SW1 is off, the third switching device SW3 is connected from the ground terminal GND to the output voltage terminal when the first switching device SW1 is off. Is inserted into the current path. When the voltage applied to the third switching device SW3 when the third switching device SW3 is off is V _SW3 , the current change of the inductor current i _L is expressed by the following equation.

The higher the voltage applied to the third switching device SW3, the faster the inductor current i _L decreases. The timing at which the third switching device SW3 is turned on varies, but in the DCDC converter 300 according to the present embodiment in which the inductor current i _L decreases rapidly, overshoot is unlikely to occur when the third switching device SW3 is turned on. That is, it is possible to respond rapidly to a sudden decrease in load current or overshoot caused by this.

  Although the third switching device SW3 is arranged between the inductor L1 and the output voltage terminal in FIG. 3, the above-described effect is obtained when the third switching device SW3 is turned off and the first switching device SW1 is turned off. Note that it can be obtained if it is inserted between the ground terminal GND, which is the current path, and the output voltage terminal (see FIG. 6). The third switching device SW3 blocks a path from the ground terminal to the output voltage terminal, which is a current path when the first switching device SW1 is turned off, in response to the load current.

(Second Embodiment)
FIG. 7 shows a DCDC converter according to the second embodiment. DCDC converter 7 00, almost identical to the DCDC converter 300 according to the first embodiment, but an inductor L1 and a connection point of the third switching device SW3, the fourth switching device SW4 between the input voltage terminal The difference is that the parasitic diodes D1 and D3 of the first and third switching devices SW1 and SW3 are shown together.

As the fourth switching device SW4, a device that can cut off the current flowing from the input power supply terminal toward the connection point between the inductor L1 and the third switching device SW3 is used. With such a configuration, the inductor current i _L that is cut off when the third switching device SW3 is turned off can be regenerated to the input voltage terminal through the fourth switching device SW4.

When the first switching device SW1 is off and current flows from the ground terminal GND to the output voltage terminal via the second switching device SW2, the inductor L1, and the third switching device SW3, the third switching device When SW3 is turned off, the potential at the connection point between the inductor L1 and the third switching device SW3 becomes higher than V _IN due to the back electromotive force. For example, when a diode is used as the fourth switching device SW4, the inductor current i _L flows to the input voltage terminal through the diode. As a result, the voltage applied to the third switching device SW3 can be clamped by the input voltage V _IN , and the third switching device SW3 can be protected. Further, since the inductor current i _L is returned to the power source, the loss can be reduced.

  7 shows an example using diodes as the second and fourth switching devices SW2 and SW4, FIG. 8 shows an example using MOSFETs. By turning on the fourth switching device SW4 when the third switching device SW3 is turned off, it is possible to reduce the loss as compared with the case where a diode is used because the on-voltage is low.

(Third embodiment)
FIG. 9 shows a DCDC converter according to the third embodiment. The DCDC converter 900 is substantially the same as the DCDC converter 700 according to the second embodiment shown in FIG. 7, but the fourth switching device SW4 is connected to another voltage terminal different from the input voltage terminal. Different. Here, it is assumed that the voltage V _H applied to the voltage terminal is larger than the target value of the output voltage V _OUT .

In such a circuit configuration, since a voltage other than the input voltage V _IN can be selected, the gradient at which the inductor current i _LOAD decreases can be changed. The point that the voltage applied to the third switching device SW3 can be clamped with the voltage V _H and the point that the loss can be reduced because the inductor current i _L is returned to the power supply are the same as in the second embodiment. .

(Fourth embodiment)
FIG. 10 shows a DCDC converter according to the fourth embodiment. The DCDC converter 1000 is substantially the same as the DCDC converter 300 according to the first embodiment, except that a resistor R1 is provided in parallel with the third switching device SW3.

  In the case of such a circuit configuration, the current from the inductor L1 to the output voltage terminal, which is interrupted by the third switching device SW3 when the third switching device SW3 is turned off, flows to the output voltage terminal through the resistor R1.

When the first switching device SW1 is off and current flows from the ground terminal GND to the output voltage terminal via the second switching device SW2, the inductor L1, and the third switching device SW3, the third switching device SW3 Is turned off, the inductor current i _L flows through the resistor R1 connected in parallel to the third switching device SW3. The voltage generated in the resistor R1, to join the high voltage to the inductor L1 than conventional DCDC converter as shown in FIG. 1, as shown in the following equation, the decrease in inductor current i _L increases. Therefore, residual charge is less likely to flow into the capacitor C _OUT when turned on third switching device SW3, overshoot is less likely to occur.

This means that, as described with reference to the expression (3) in the first embodiment, it is possible to respond rapidly to a sudden decrease in load current or overshoot caused by this. To do.

Compared with the first to third embodiments, in these embodiments, the current from the inductor L1 to the output voltage terminal becomes zero. Therefore, when the load current i _LOAD is reduced but not zero, the charge of the capacitor C _OUT only decreases, so the output voltage V _OUT also decreases. Since the first switching device SW1 is controlled to be turned on when the output voltage V _OUT becomes equal to or lower than a predetermined voltage, the output voltage V _OUT decreases regardless of whether or not the inductor current i _L is sufficiently reduced. When the first switching device SW1 is turned on in response to the fact, excess charge in the capacitor C _OUT flows, there is a possibility that overshooting occurs.

In the DCDC converter 1000 according to the present embodiment, even when the third switching device SW3 is turned off, the current i _L flows to the output voltage terminal through the resistor R1, and the inductor current is antagonized with the decrease in charge due to the load current i _LOAD. An increase in charge due to i _L occurs. However, the inductor current i _L decreases rapidly according to the equation (4), and when the inductor current i _L becomes smaller than the load current i _LOAD , the output voltage V _OUT starts to decrease. Therefore, when the first switching device SW1 is turned on in response to the output voltage V _OUT being lower than the predetermined voltage, the inductor current i _L is sufficiently reduced, and the first switching device SW1 is turned on. There is no overshoot immediately after turning on. Note that the third switching device SW3 is controlled to be turned on simultaneously with the first switching device SW1. FIG. 11 is a diagram for explaining the operation of the DCDC converter 1000 according to the fourth embodiment. The difference from FIG. 5 is that, in the DCDC converter 1000 according to the fourth embodiment, the output voltage _VOUT increases as described above even after the third switching device SW3 is turned off.

FIG. 12 shows a modification of the fourth embodiment. This is a combination of the DCDC converter 1000 of FIG. 10 and the DCDC converter 700 according to the second embodiment shown in FIG. In addition to the effects of the DCDC converter 1000 according to the fourth embodiment described above with reference to FIG. 10, the potential at the point V _A may be higher than the input voltage V _IN depending on the setting of the resistor R1, in which case Since the energy of the inductor L1 is returned to the power source, the loss can be reduced. In addition, the voltage applied to the third switching device SW3 can be limited by V _IN .

(Fifth embodiment)
FIG. 13 shows a DCDC converter according to the fifth embodiment. The DCDC converter 1300 is different from the DCDC converter 300 of FIG. 3 in that the third switching device SW3 is disposed between the ground terminal GND and the second switching device SW2.

In the case of such a circuit configuration, the inductor current i _L does not flow to the third switching device SW3 when the first switching device SW1 is on, so that the loss is reduced as compared with the circuit configuration of FIG. be able to.

  FIG. 14 shows a structure in which a resistor R1 is connected in parallel with the third switching device SW3 in the DCDC converter 1300 of FIG. Although the parasitic elements D1 and D3 of the first switching device SW1 and the third switching device SW3 are shown, the parasitic element D3 of the third switching device SW3 cuts off the current flowing in the direction from the ground terminal GND. It has a function.

When the first switching device SW1 is off and the current flows to the output voltage terminal via the second switching device SW2, the inductor L1, and the third switching device SW3, the third switching device SW3 is turned off. The inductor current i _L flows through the resistor R1 connected in parallel. Thereby, a voltage component generated across the resistor R1 is so applied to the above conventional DCDC converter as shown in FIG. 1, a decrease of the inductor current i _L increases.

  The parasitic element D3 may or may not exist. When the third switching device SW3 has the parasitic element D3, as shown in FIG. 14, the third switching device SW3 is arranged in such a direction that the parasitic element D3 cuts off the current flowing out from the ground terminal GND. There is a need. FIGS. 15A and 15B show examples in the case where an N-channel MOSFET and a P-channel MOSFET are used as the third switching device SW3, respectively. The structure of FIG. 15A provides the third switching device SW3 of FIG.

(Sixth embodiment)
FIG. 16 shows a DCDC converter according to the sixth embodiment. DCDC converter 1 6 00, almost identical to the DCDC converter 300 according to the first embodiment, except that the zener diode ZD1 connected in parallel with the third switching device SW3 is different.

When the first switching device SW1 is off and the current flows to the output voltage terminal via the second switching device SW2, the inductor L1, and the third switching device SW3, the third switching device SW3 is turned off. The inductor current i _L flows through the Zener diode ZD1 connected in parallel. As a result, the Zener voltage of the Zener diode ZD1 is added more than in the conventional DCDC converter as shown in FIG. 1, and the inductor current i _L is rapidly reduced.

  A non-linear resistance element such as a Zener diode ZD1 may be used.

(Seventh embodiment)
FIG. 17 shows a DCDC converter according to the seventh embodiment. The DCDC converter 1700 includes an overvoltage determination circuit for turning off the third switching device SW3 when it is detected that the output voltage V _OUT is in an overvoltage state. Here, the DCDC converter 1000 of FIG. 10 described in the fourth embodiment will be described by adding an overvoltage determination circuit, but it should be noted that this is merely an example. The same applies to FIGS. 18 to 25.

When the output voltage V _OUT becomes larger than the overvoltage determination voltage V _OV , the output of the overvoltage detection comparator OV_COMP becomes Low, and the third switching device SW3 is turned off. Thereby, the inductor current i _L flows through the resistor R1. The overvoltage determination voltage _VOV can be set to a value such as 1.1 times the reference voltage _Vref , for example.

FIG. 18 shows a modification of the seventh embodiment. When the DCDC converter 1800 detects that the output voltage V _OUT is in an overvoltage state, the DCDC converter 1800 turns off the third switching device SW3 using the one-shot circuit ONE SHOT for a certain period of time. When the output voltage V _OUT becomes larger than the overvoltage determination voltage V _OV , the output of the overvoltage detection comparator OV_COMP becomes Low, and the third switching device SW3 is turned off for a certain time. As a result, it is possible to avoid a decrease in which the third switching device SW3 is turned on / off at high speed.

(Eighth embodiment)
FIG. 19 shows a DCDC converter according to an eighth embodiment. The DCDC converter 1900 is a circuit in which a determination voltage V _OVS when turning off the third switching device SW3 connected between the inductor L1 and the output voltage terminal and a determination voltage V _OVR when turning on are set. Is further provided.

When the output voltage V _OUT becomes higher than the overvoltage determination voltage V _OVS , the output of the overvoltage detection comparator OVS_COMP becomes High, the output QB of the reset set flip-flop (RS-FF) becomes Low, and the third switching device SW Turns off. The output QB becomes High when the output voltage V _OUT becomes lower than the overvoltage release voltage V _OVR .

(Ninth embodiment)
FIG. 20 shows a DCDC converter according to the ninth embodiment. The DCDC converter 2000 includes a circuit that uses a condition for turning off the third switching device SW3 connected between the inductor L1 and the output voltage terminal as an ON signal of the first switching device SW1.

When the output voltage V _OUT becomes higher than the overvoltage determination voltage V _OVS, the output of the overvoltage detection comparator OVS_COMP becomes High, the output QB of the reset set flip-flop (RS-FF) becomes Low, and the third switching device SW3 becomes Turn off. With the signal for turning on the first switching device SW1, the output QB becomes High and the third switching device SW3 turns on.

(Tenth embodiment)
FIG. 21 shows a DCDC converter according to the tenth embodiment. The DCDC converter 2100 provides a determination voltage for turning off the third switching device SW3 connected between the inductor L1 and the output voltage terminal, and the determination voltage for turning off the constant switching voltage of the constant on-time DCDC converter. A circuit using the output of the bottom detection comparator is further provided.

When the output voltage V _OUT is less than the reference voltage V _ref, a predetermined time, the constant on-time DCDC converter as the first switching device SW1 is turned on, the output of the comparator for comparing the output voltage V _OUT and the reference voltage V _ref The overvoltage release signal shown in FIG. 19 can be substituted with the above signal. By adopting such a circuit configuration, it is possible to reduce the size of the circuit of FIG.

(Eleventh embodiment)
FIG. 22 shows a DCDC converter according to the eleventh embodiment. The DCDC converter 2200 resets the on-time of the first switching device SW1 when the determination voltage for turning off the third switching device SW3 connected between the inductor L1 and the output voltage terminal is exceeded. A circuit having a function is further provided.

In a constant on-time DCDC converter in which the first switching device SW3 is turned on for a certain period of time when the output voltage V _OUT is equal to or lower than the reference voltage V _ref, a comparator for comparing the output voltage V _OUT with the overvoltage determination voltage V _OVS The amount of increase in output voltage can be reduced by turning off an on signal for a certain period of time with an output signal within a certain period of time. This embodiment is particularly effective when the control described with reference to FIGS. 5 and 6 is performed and an overvoltage state occurs when the first switching device SW1 is turned on.

(Twelfth embodiment)
FIG. 23 shows a DCDC converter according to a twelfth embodiment. The DCDC converter 2300 further includes a circuit that turns off the third switching device SW3 when it is detected that the load current has rapidly decreased. The load current is measured, and it is detected that the load current has suddenly decreased, and the third switching device SW3 is turned off.

Since the phase of the change in the output voltage _VOUT due to the sudden decrease in the load current is delayed by 90 degrees, the response can be made faster by detecting the load current.

  FIG. 24 shows a modification of the eleventh embodiment. The DCDC converter 2400 turns off the third switching device SW3 for a certain period of time when detecting that the load current has sharply decreased.

(13th Embodiment)
FIG. 25 shows a DCDC converter according to a thirteenth embodiment. The DCDC converter 2500 turns off the third switching device SW3 when detecting that the load current has sharply decreased, and turns on the third switching device SW3 when the output voltage falls below the release voltage. The load current is measured, and it is detected that the load current has suddenly decreased, and the third switching device SW3 is turned off. To turn on the third switching device SW3 when the output voltage falls below the release voltage V _R.

Claims (17)

An inductor;
A first switching device connected between an input voltage terminal to which an input voltage is applied and the inductor;
A second switching device connected between a connection point between the first switching device and the inductor and a ground terminal;
A capacitor between the output voltage terminal from which the output voltage is output and the ground terminal;
A third switching device inserted in a path from the ground terminal to the output voltage terminal, which is a current path when the first switching device is turned off, for blocking the path in response to a load current; Prepared ,
The third switching device is disposed between the inductor and the output voltage terminal;
A fourth switching device arranged between a connection point of the inductor and the third switching device and the input voltage terminal, wherein a current flowing from the input voltage terminal toward the connection point is cut off; and, the third said at off switching device of the third fourth further comprising DCDC converter according to claim Rukoto switching devices the inductor current is interrupted by the switching device can flow to the input voltage terminal. An inductor;
A first switching device connected between an input voltage terminal to which an input voltage is applied and the inductor;
A second switching device connected between a connection point between the first switching device and the inductor and a ground terminal;
A capacitor between the output voltage terminal from which the output voltage is output and the ground terminal;
A third switching device inserted in a path from the ground terminal to the output voltage terminal, which is a current path when the first switching device is off, for blocking the path in response to a load current;
With
The third switching device is disposed between the inductor and the output voltage terminal;
A fourth switching device disposed between a connection point of the inductor and the third switching device and another voltage terminal different from the input voltage terminal, the connection from the other voltage terminal; A fourth switching device capable of interrupting a current flowing toward the point and allowing an inductor current interrupted by the third switching device to flow to the other voltage terminal when the third switching device is turned off; ,
The other voltage applied to the voltage terminal, D CDC converter you being higher than the target value of the output voltage. An inductor;
A first switching device connected between an input voltage terminal to which an input voltage is applied and the inductor;
A second switching device connected between a connection point between the first switching device and the inductor and a ground terminal;
A capacitor between the output voltage terminal from which the output voltage is output and the ground terminal;
A third switching device inserted in a path from the ground terminal to the output voltage terminal, which is a current path when the first switching device is off, for blocking the path in response to a load current;
With
The third switching device is disposed between the inductor and the output voltage terminal;
A resistor disposed in parallel with the third switching device;
Said third inductor current is interrupted by the third switching device during off switching devices, D CDC converter you characterized in that flowing to the output voltage terminal through the resistor. A resistor disposed in parallel with the third switching device;
Said third inductor current is interrupted by the third switching device during off switching devices, DCDC converter according to claim 1 or 2, characterized in that flowing to the output voltage terminal through the resistor. An inductor;
A first switching device connected between an input voltage terminal to which an input voltage is applied and the inductor;
A second switching device connected between a connection point between the first switching device and the inductor and a ground terminal;
A capacitor between the output voltage terminal from which the output voltage is output and the ground terminal;
A third switching device inserted in a path from the ground terminal to the output voltage terminal, which is a current path when the first switching device is off, for blocking the path in response to a load current;
With
Said third switching device, the second switching device and D CDC converter you characterized in that it is disposed between the ground terminal. A resistor disposed in parallel with the third switching device;
6. The DCDC converter according to claim 5 , wherein an inductor current interrupted by the third switching device when the third switching device is turned off flows to the output voltage terminal through the resistor. The third switching device has a parasitic element;
The DCDC converter according to claim 6, wherein the parasitic element is arranged in a direction to interrupt a current flowing out from the ground terminal. It claims 3, 4 or 6 DCDC converter according to, characterized in that replacing the resistor in the non-linear resistance element. The DCDC converter according to any one of claims 1 to 8 , wherein when the output voltage is detected to be in an overvoltage state, the third switching device is turned off. 10. The DCDC converter according to claim 9 , wherein when the output voltage is detected to be in an overvoltage state, the third switching device is turned off for a predetermined time. The third switching device is connected between the inductor and the output voltage terminal;
DCDC converter according to claim 9, wherein the determination voltage for turning off the third switching device, a determination voltage for turning on the set, respectively. The DCDC converter according to claim 11 , wherein a condition for turning on the third switching device is an on signal of the first switching device. The determination voltage for turning off the third switching device is provided, the determination voltage at the time of turning on, according to claim 11, characterized by using the output of the bottom detection comparator Constant on time DCDC converter DCDC converter. The DCDC converter according to claim 13 , further comprising a function of resetting an on-time when a determination voltage for turning off the third switching device is exceeded. When it is detected that the load current which the output voltage is applied is reduced drastically, according to any one of claims 1 to 8, characterized in that interrupting the inductor current through the third switching device DCDC converter. 16. The DCDC converter according to claim 15 , wherein when detecting that the load current suddenly decreases, the inductor current flowing through the third switching device is cut off for a certain period of time. When it is detected that the load current suddenly decreases, the inductor current flowing through the third switching device is cut off, and when the output voltage falls below the release voltage, the third switching device is turned on. The DCDC converter according to claim 15 , wherein

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