JP5639829B2 - DC-DC converter - Google Patents

Description

  The present invention relates to a DC-DC converter, and relates to a DC-DC converter of a step-down type, step-up / step-down type, or step-up type switching type DC-DC converter that steps down, step-up or step-down or step-up a DC voltage by an on / off operation of a switch element. It is related with the protection function which protects GND short circuit.

  Conventionally, in battery-driven electric devices such as mobile phones, it is necessary to convert the voltage of the battery to a voltage required by various circuit units constituting the electric device. For such DC voltage conversion, for example, a switching type DC -DC converters are used, and DC-DC converters are also used for efficient voltage conversion in electrical devices other than battery-powered devices.

  In such a DC-DC converter, when the DC-DC converter operates in a state where the output node or a component connected to the output node is GND short-circuited, an overcurrent flows from the input power source to the component connected to the GND short-circuited path. If the current value exceeds the rating of the component, the component may be damaged by this overcurrent, or smoke or fire may be generated by overheating.

  Therefore, in these DC-DC converters, when the output node or a component connected to the output node (for example, a transistor, a coil, a Schottky diode, an output capacitor, etc.) is short-circuited to GND, a protection function for protecting these components. It is equipped with.

  FIG. 9 is a block diagram for explaining a conventional buck-boost type DC-DC converter equipped with such a protection function.

  The DC-DC converter 10 includes a DC-DC converter unit 1000 that converts the first power supply voltage VIN into a desired target voltage, and the voltage of the output node VOUT of the DC-DC converter unit 1000 as a reference voltage of the reference power supply 21a. It has a comparator (COMP2) 22a that compares with Vref2a, and a resistance divider circuit 30 that sets the target voltage.

  The DC-DC converter 10 is a DC-DC converter control circuit (hereinafter simply referred to as a control circuit) that controls the DC-DC converter unit 1000 based on the output of the comparator 22a and the output of the resistance divider circuit 30. 200), a level shifter 400 for level-shifting and boosting the first control voltage from the control circuit 200, and the second power supply voltage VDD having a lower voltage than the first power supply voltage VIN are generated. And a series regulator 300.

  Here, the level shifter 400 is supplied with both the first power supply voltage VIN and the second power supply voltage VDD, and outputs a gate voltage for controlling the transistor Q1 constituting the DC-DC converter unit 1000 from these power supply voltages. It is configured. A load circuit 3000 is connected to the output node VOUT of the DC-DC converter 10.

  Here, the DC-DC converter unit 1000 includes a resistor Rs1, a first switching transistor Q1, and a first diode D1 connected in series between the first power supply voltage VIN and the ground potential. Connected to the power supply VIN side, the first diode D1 is connected to the ground side, and the first switching transistor Q1 is connected between them. The DC-DC converter unit 1000 includes a coil L1 connected in series between the connection node (first internal node) LX1 between the transistor Q1 and the first diode D1, and the output node VOUT. The coil L1 is connected to the connection node LX1 side, and the second diode D2 is connected to the output node VOUT side. Further, the DC-DC converter unit 1000 includes a second switching transistor Q2 connected between a connection node (second internal node) LX2 between the coil L1 and the second diode D2, and the output node VOUT. An output capacitor COUT connected to ground. Here, the first switching transistor Q1 is a PMOS transistor, the second switching transistor Q2 is an NMOS transistor, and the first switch transistor Q1 is formed such that the terminal on the node LX1 side has a high breakdown voltage, and the second switch transistor Q2 is formed so that the node LX2 side terminal has a high breakdown voltage.

  The resistor divider circuit 30 includes first and second voltage dividing resistors RFB1 and RFB2 connected in series between the ground and the output node VOUT, and the potential at the connection point FB of these voltage dividing resistors is A feedback voltage is output to the DC-DC converter control circuit 200. Here, the second voltage dividing resistor RFB2 is connected to the output node side, and the first voltage dividing resistor RFB1 is connected to the ground side. A load circuit 3000 is connected to the output node VOUT.

  In the switching-type DC-DC converter 10 having such a configuration, when the first power supply voltage VIN is supplied, the first power supply voltage VIN is supplied to the series regulator 300 and the DC-DC converter 1000. One power supply voltage VIN is converted to a second power supply voltage VDD, and this second power supply voltage VDD is supplied to the DC-DC converter control circuit 200 and the level shifter 400.

  In the step-down operation mode, a control signal from the DC-DC converter control circuit 200 (a drive pulse that is duty-controlled at a constant period) is applied to the gate of the first switching transistor Q1 via the level shifter 400, When the switching transistor Q1 is turned on / off, a desired voltage set by the resistance dividing circuit 30 is output to the output capacitor COUT. That is, in the DC-DC converter control circuit 200, the duty (duty) of the drive pulse of the first switching transistor Q1 is adjusted based on the feedback voltage VFB from the resistance dividing circuit 30. In the step-down operation mode, the second switching transistor Q2 is held in the off state by the control voltage from the DC-DC converter control circuit 200.

  In the step-up operation mode, the control voltage from the DC-DC converter control circuit 200 (a drive pulse that is duty-controlled at a constant period) is applied to the gate of the second switching transistor Q2, and the second switching transistor Q2 is turned on / off. As a result, a desired voltage set by the resistance dividing circuit 30 is output to the output capacitor COUT. That is, in the DC-DC converter control circuit 200, the duty (duty) of the driving pulse of the second switching transistor Q2 is adjusted based on the feedback voltage VFB from the resistance dividing circuit 30. In the step-up operation mode, the first switching transistor Q1 is held in the on state by the control voltage from the DC-DC converter control circuit 200.

  Further, at the time of starting the operation of the DC-DC converter 1000, the DC-DC converter control circuit 200 is based on the comparison output from the comparator 22a until the set time set in advance from the start of the operation. It is determined whether or not the voltage of the output node VOUT becomes higher than the reference voltage Vref2a. Further, if the voltage of the output node VOUT does not become higher than the reference voltage Vref2a even after the set time has elapsed, the DC-DC converter control circuit 200 determines that a GND short circuit has occurred, If the voltage of the output node VOUT becomes larger than the reference voltage Vref2 before the time elapses, it is determined that the GND short circuit has not occurred. When it is determined that the GND short circuit has occurred, the DC-DC converter control circuit 200 stops supplying the power supply voltage to the DC-DC converter unit (turns off the transistor Q1), for example.

  As described above, in the conventional DC-DC converter 10, in order to detect that the output node VOUT of the DC-DC converter is short-circuited to the GND, the output is performed when a certain time has elapsed after the DC-DC converter is started once. In general, a GND short circuit is confirmed based on whether the voltage at the node VOUT exceeds or does not exceed a predetermined voltage.

  As a protection circuit for realizing such an output short-circuit protection function, as in the protection function of the DC-DC converter described in FIG. The configuration of the protection circuit is disclosed in which the switching (current supply to the output) is stopped when there is a GND short circuit.

Japanese Unexamined Patent Publication No. 63-274363 JP-A 62-16019 JP-A-11-136853

  However, in the conventional protection circuit system, it is necessary to operate the DC-DC converter for a time until the voltage of the output node VOUT exceeds the predetermined voltage (charges the output node to the predetermined voltage) after the DC-DC converter is started. At this time, if the output node VOUT is short-circuited to GND, the overcurrent continues to flow toward the short-circuit path during that period, so that the components of the DC-DC converter may be damaged.

  In addition, when the output node VOUT is short-circuited to GND during the circuit operation, in order to confirm the determination result of the GND short-circuit, the state where the output node VOUT is the determination voltage or less for a certain period after the voltage becomes the determination voltage or less. It is necessary to confirm that the operation continues with the DC-DC converter operated. For this reason, during that period, overcurrent continues to flow toward the short-circuit path, and the components of the DC-DC converter may be damaged.

  In addition, the time for which the operation of the DC-DC converter is continued needs to be changed depending on the circuit conditions (input voltage, oscillation frequency, circuit constant of the DC-DC converter section). In the case where it is longer than the appropriate value, there is a problem that the time for which the parts are damaged is extended.

  The present invention has been made to solve the above problems, and can detect a GND short circuit of an output node or a component connected to the output node without operating a DC-DC converter unit. An object of the present invention is to obtain a DC-DC converter capable of avoiding damage to the components of the DC-DC converter section.

  A DC-DC converter according to the present invention is a DC-DC converter that converts an input DC voltage into a desired DC voltage and outputs the DC voltage to an output node, the smoothing capacitor connected to the output node, and the input DC voltage A DC-DC converter unit that charges the smoothing capacitor so that the smoothing capacitor generates the desired potential, and a current driving capability smaller than the current driving capability of the DC-DC converter unit, And a charging circuit for charging the output node, whereby the above object is achieved.

  In the DC-DC converter, the present invention includes a first comparator that compares the voltage of the output node with a first reference voltage, and the voltage of the output node is equal to or lower than the first reference voltage. It is preferable to stop the DC-DC converter unit and operate the DC-DC converter unit when the voltage of the output node is higher than the first reference voltage.

  In the DC-DC converter according to the present invention, when the voltage of the output node is equal to or lower than the first reference voltage, the output node is charged by the charging circuit, and when the output node is higher than the first reference voltage, The charging of the output node by the charging circuit is preferably stopped.

  In the DC-DC converter according to the present invention, it is preferable that the charging circuit always charges the output node regardless of the voltage of the output node.

  In the DC-DC converter, the present invention has a second comparator that compares the voltage of the output node with a second reference voltage, and the first node is used when the voltage of the output node is equal to or lower than the second reference voltage. It is preferable to output an error signal.

  In the DC-DC converter according to the present invention, it is preferable that the first reference voltage and the second reference voltage are the same voltage.

  In the DC-DC converter, the present invention preferably has a first error output terminal for outputting the first error signal to the outside of the DC-DC converter.

  In the DC-DC converter, the present invention preferably uses a circuit configuration in which the power supply of the charging circuit and the power supply of the DC-DC converter unit are shared.

  Preferably, the DC-DC converter includes a series regulator that adjusts the input power supply voltage, and the power supply voltage of the charging circuit uses a circuit configuration that is supplied from the series regulator.

  In the DC-DC converter according to the present invention, it is preferable that the charging circuit is constituted by a constant current source circuit.

  In the DC-DC converter according to the present invention, it is preferable that the charging circuit is configured by a resistance element.

  In the DC-DC converter according to the present invention, it is preferable that the charging circuit includes a switch for starting or stopping charging of the output node by the charging circuit, and the switch includes only an NMOS transistor.

  The present invention provides the above-described DC-DC converter, wherein the DC-DC converter unit is connected in series between the input power supply voltage and the first internal node, the input power supply voltage side resistance element, and the first The circuit configuration includes a first switch on the internal node side and a coil provided in a charging path from the first internal node to the output capacitor, and the voltage at the connection node between the resistance element and the first switch is It is preferable that a third comparison circuit for comparing with the three reference voltages is further provided, and a short circuit between both ends of the resistance element is determined based on a comparison result of the third comparison circuit.

  In the DC-DC converter, the present invention further includes a fourth comparison circuit that compares the voltage of the first internal node with a fourth reference voltage, and the charging circuit is charged to form the first internal node. It is preferable to determine a short circuit at both ends of the first switch according to the voltage generated at the coil connection side terminal of the first switch.

  According to the present invention, in the DC-DC converter, an operation start condition of the DC-DC converter unit is set such that the voltage at the output node is higher than the first reference voltage, and the first internal node voltage is the fourth voltage. It is preferable that the voltage is lower than the reference voltage, and the operation stop condition of the DC-DC converter unit is a case where the voltage of the output node is lower than the first reference voltage.

  According to the present invention, in the DC-DC converter, a second error signal indicating a short-circuit state at both ends of the first switch is transmitted to the outside according to the output results of the second comparator and the fourth comparator. It is preferable to have two error output terminals.

  In the DC-DC converter, the DC-DC converter unit is charged with a smoothing capacitor connected to the output node by the charging circuit before starting the DC-DC converter unit. It is preferable to suppress an inrush current flowing toward the smoothing capacitor when starting up.

  A control system according to the present invention is a control system for controlling the above-described DC-DC converter according to the present invention, and includes a microcomputer using the first or second error output signal as an input signal. The power supply of the DC-DC converter is shut down by the control signal from the microcomputer when it is detected that the first or second error signal has continued for a certain time or more. Is achieved.

  The control system according to the present invention is a control system for controlling the above-described DC-DC converter according to the present invention, wherein the control signal step according to the present invention has a timer circuit, and the timer circuit allows a certain time or more. When it is detected that the first or second error output continues, the power source of the DC-DC converter is shut down, whereby the above object is achieved.

  The operation of the present invention will be described.

  In the present invention, the charging path for charging the output node of the DC-DC converter has a charging path by the charging circuit separately from the conventional charging path by the DC-DC converter. Until the voltage exceeds the predetermined voltage, the output node, that is, the smoothing capacitor connected to the output node is charged by a separately provided charging circuit instead of the DC-DC converter, and when the voltage of the output node exceeds the predetermined voltage, The charging from the charging circuit is stopped and the DC-DC converter is operated.

  However, if the charging current of the charging circuit is so small that it does not affect the control of the DC-DC converter, or if the voltage limiter is applied to the charging voltage by the charging circuit at a level that does not affect the voltage of the output node, There is no need to stop the charging circuit.

  Further, when the output VOUT becomes a predetermined voltage or lower, the DC-DC converter is stopped and charging from the charging circuit is started.

  In such a configuration, when the output node V has already been short-circuited to GND when the DC-DC converter is started, the voltage of the output node does not rise, so the DC-DC converter unit does not operate, and the output node It is possible to avoid overcurrent flowing in the path leading to.

  Further, even when the output node VOUT is short-circuited during the operation of the DC-DC converter, conventionally, in order to confirm the determination result of the GND short-circuit, the DC-DC converter unit for a certain period after the detection of the GND short-circuit In the present invention, the operation of the DC-DC converter unit is stopped immediately after the determination, and the output node is provided by the separately provided charging circuit 100 having a smaller driving capability than the DC-DC converter unit. Since the determination result is confirmed in this state, the time during which the overcurrent flows can be reduced.

  In addition, it is not necessary to design the time until the GND short-circuit determination is started at the time of starting the circuit and the time for confirming the GND short-circuit determination result during the DC-DC converter operation. As a result, when a timer circuit is conventionally incorporated in a control circuit or the like for counting the determination time, the timer circuit can be reduced.

  In the conventional circuit, the overcurrent can be stopped only by latching the GND short-circuit detection state, that is, by stopping the operation of the DC-DC converter. However, in the present invention, the DC-DC converter -In addition to the DC converter part, a charging circuit with a smaller driving capacity than the DC-DC converter part is provided, so the design to latch the GND short-circuit detection state so that the DC-DC converter stops, and the DC-DC converter operates normally The overcurrent can be stopped by both of the designs that do not latch the GND short-circuit detection state so as to be able to return to

  That is, specifically, in the design that does not latch the GND short-circuit detection state, the operation of the DC-DC converter unit stops when the GND short-circuit is determined to be caused by the GND short-circuit determination. The charging circuit is designed to charge the output node VOUT without stopping the operation, and the operation of the DC-DC converter is not completely stopped even when a GND short circuit is detected.

  On the other hand, in the design for latching the GND short-circuit detection state, when it is determined by the GND short-circuit determination that the GND short-circuit has occurred, the operation of the DC-DC converter unit is stopped, and the operation of the charging circuit is also predetermined. It is designed to stop after a certain time, and when a GND short circuit is detected, the operation of the DC-DC converter is completely stopped.

  And if the GND short circuit is resolved by designing it so that the GND short circuit detection state is not latched, or if the GND short circuit is erroneously determined due to noise, the LSI chip constituting the DC-DC converter is externally connected to the LSI chip. Even without inputting the reset signal, the circuit operation of the DC-DC converter can be automatically returned to the normal state.

  In the DC-DC converter of the present invention, the output smoothing capacitor is charged in advance with a charge exceeding a predetermined voltage from the charging circuit, and then the operation of the DC-DC converter is started. -The amount of inrush current that flows toward the output smoothing capacitor at the start of the operation of the DC converter can be reduced.

  As described above, according to the DC-DC converter of the present invention, it is possible to detect the GND short circuit of the output node or the load connected to the output node without operating the DC-DC converter unit, and the DC-DC converter There is an effect that it is possible to avoid damage to the component parts.

FIG. 1 is a diagram for explaining a DC-DC converter according to Embodiment 1 of the present invention. FIG. 1A shows a circuit configuration of the DC-DC converter, and FIG. An example using a switch is shown, and FIG. 1C shows an example using a current mirror circuit as a charging circuit. FIG. 2 is a diagram for explaining a DC-DC converter according to Embodiment 2 of the present invention. FIG. 2A shows a circuit configuration of the DC-DC converter, and FIG. 2B is a second comparator. The example of a structure is shown. FIG. 3 is a diagram illustrating a DC-DC converter according to Embodiment 3 of the present invention. FIG. 4 is a diagram for explaining a DC-DC converter according to Embodiment 4 of the present invention. FIG. 4 (a) shows a circuit configuration of the DC-DC converter, and FIG. 4 (b) shows a second comparator. The detailed structure is shown. FIG. 5 is a diagram illustrating a startup waveform when there is no short circuit in the DC-DC converter according to the fourth embodiment of the present invention. FIG. 6 is a diagram illustrating a waveform when a GND short circuit occurs during stable operation in the DC-DC converter according to Embodiment 4 of the present invention. FIG. 7 is a diagram illustrating a start-up waveform when the GND is short-circuited in the DC-DC converter according to the fourth embodiment of the present invention. FIG. 8 is a diagram illustrating a startup waveform when the VIN-LX1 is short-circuited in the DC-DC converter according to the fourth embodiment of the present invention. FIG. 9 is a block diagram illustrating a conventional buck-boost type DC-DC converter equipped with a protection function.

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

(Embodiment 1)
FIG. 1 is a diagram for explaining a DC-DC converter according to Embodiment 1 of the present invention. FIG. 1A shows a circuit configuration of the DC-DC converter, and FIG. An example using a switch is shown, and FIG. 1C shows an example using a current mirror circuit as a charging circuit.

  The DC-DC converter 10a according to the first embodiment includes a charging circuit 100 that charges the output node VOUT in addition to the configuration of the conventional DC-DC converter 10 shown in FIG. The resistor Rc and the switch Q3 are connected in series between the output of the series regulator 300 and the first internal node LX1, and the resistor Rc is connected to the output side of the series regulator 300, and the switch Q3 is connected to the connection node LX1. It is connected to the. The switch Q3 is composed of an NMOS transistor whose internal node LX1 side terminal has a high breakdown voltage. Further, the DC-DC converter 10a of the first embodiment includes a first comparator 12 in place of the comparator 22 in the conventional DC-DC converter 10, and the DC-DC converter control circuit 200a of the first embodiment. In addition to the function of the DC-DC converter control circuit 200 in the conventional DC-DC converter 10, the comparison result between the first reference voltage Vref1 of the reference power supply 11 and the output node voltage VOUT in the first comparator 12 is shown in FIG. Accordingly, the charging mode by the charging circuit 100 and the voltage conversion mode by the DC-DC converter unit 1000 are switched.

  Here, in the charging circuit 100, the switch Q3 is composed of an NMOS transistor, but the switch Q3 is formed by connecting a PMOS transistor Q3a and an NMOS transistor Q3b in parallel as shown in FIG. 1B. An analog switch may be used. In this case, the on / off characteristics of the switch can be improved as compared with the case where the switch Q3 is configured by a single NMOS transistor.

  Further, the charging circuit 100 may be constituted by a current mirror circuit 100a as shown in FIG. That is, the current mirror circuit 100a includes the regulator-side PMOS transistor Q31, the ground-side constant current source A, the output of the series regulator 300, and the output of the series regulator 300, which are connected in series between the output of the series regulator 300 and the ground. A regulator side PMOS transistor Q32 and an internal node LX1 side NMOS transistor Q33 are connected in series with one internal node LX1. This NMOS transistor has a high breakdown voltage at the internal node LX1 side terminal.

  Hereinafter, the DC-DC converter 10a of the first embodiment will be described in detail.

  The DC-DC converter 10a of the first embodiment is a switching type DC-DC converter having a short-circuit protection circuit, and the DC-DC converter unit 1000 constituting the DC-DC converter 10a includes a step-down converter, a step-up / step-down converter, The circuit configuration is compatible with all boosting modes.

  As shown in FIG. 1A, the DC-DC converter 1000 includes a current detection resistor Rs1, a first switch Q1 composed of a PMOS transistor, a second switch Q2 composed of an NMOS transistor, a coil L1, and a first Schottky diode D1. , A second Schottky diode D2, and a smoothing capacitor (smoothing capacitor) COUT of the output node VOUT. The current detection resistor Rs1 is connected between the power source VIN of the DC-DC converter and the first switch Q1, and the terminal not connected to the current detection resistor Rs1 of the first switch Q1 is connected to the coil L1 and the first switch Q1. It is connected to the cathode connection node (first internal node LX1) of Schottky diode D1. The anode side of the first Schottky diode D1 is connected to GND. A terminal opposite to the node LX1 of the coil L1 is referred to as a node (second internal node) LX2. The node LX2 is connected to the second switch Q2 and the anode side of the second Schottky diode D2. The terminal on the opposite side of the node LX2 of the second switch Q2 is connected to GND. The cathode side terminal of the second Schottky diode D2 is an output node VOUT of the DC-DC converter unit 1000, and a smoothing capacitor COUT is connected between the output node VOUT and GND.

  The DC-DC converter unit 1000 controls the voltage of the output node VOUT by switching the switches Q1 and Q2 according to a control signal from the DC-DC converter control circuit 200.

  In the step-down mode, only the switch Q1 is switched. In this mode, the switch Q2 is always turned off. In the step-up / step-down mode, the switches Q1 and Q2 are switched. In the boost mode, only the switch Q2 is switched. In this step-up mode, the switch Q1 is always turned on when the DC-DC converter is operating.

  Further, in the DC-DC converter 10a shown in FIG. 1, the output of the DC-DC converter control circuit 200 is the power supply voltage VDD, whereas in the first switch Q1, the highest voltage at the connection destination of the source terminal is the power supply voltage VIN. Since it is composed of a certain PMOS transistor, it is necessary to generate a control signal for completely turning off the PMOS transistor. Therefore, in this DC-DC converter 10a, the switch Q1 is controlled through the level shifter 400 that converts the level of the control signal from the DC-DC converter control circuit 200 from the power supply voltage VDD level to the power supply voltage VIN level. Yes.

  In the DC-DC converter 10a of the first embodiment having such a configuration, the charging circuit 100 that charges the output node VOUT instead of the DC-DC converter unit 1000 and the voltage of the output node VOUT are monitored, and the reference voltage 11 ( Vref1) and a comparator 12 (COMP1) for comparison, and the output of the comparator 12 (COMP1) is input to the DC-DC converter control circuit 200 to control the operation of the charging circuit 100 and the DC-DC circuit 1000. Like to do.

  Therefore, in the DC-DC converter 10a of the first embodiment, if the voltage of the output node VOUT is equal to or lower than the reference voltage 11 (Vref1), the DC-DC converter unit 1000 is stopped, and the charging circuit 100 causes the output node VOUT to be When charging is performed and the voltage of the output node VOUT becomes higher than the reference voltage 11 (Vref1), charging of the output node VOUT by the charging circuit 100 is stopped and the operation of the DC-DC converter circuit 1000 is started.

  In the above embodiment, charging of the output node VOUT by the charging circuit 100 is stopped if the voltage of the output node VOUT is higher than the reference voltage 11 (Vref1). However, the present invention is not limited to this.

  For example, when the charging current of the charging circuit 100 is small enough not to affect the voltage conversion operation by the DC-DC converter unit, or the charging voltage of the output capacitor by the charging circuit 100 is less than or equal to the output voltage of the DC-DC converter. Only when the voltage limit is applied, there is no need to control the charging by the charging circuit 100, and therefore the charging circuit may be always charged. Thereby, there is an effect that a mechanism for controlling the charging circuit and a control signal line can be reduced.

When the output node VOUT is short-circuited to GND and the output node voltage VOUT does not rise, the circuit system of the DC-DC converter 10a does not generate an overcurrent due to the operation of the DC-DC converter unit 1000. In addition, the current of the charging circuit 100 continues to flow until the GND short-circuit state is resolved. Therefore, an embodiment in which a measure for stopping the current consumption in the case of a GND short-circuit is taken will be described below as a second embodiment.
(Embodiment 2)
FIG. 2 is a diagram for explaining a DC-DC converter according to Embodiment 2 of the present invention. FIG. 2A shows a circuit configuration of the DC-DC converter, and FIG. 2B is a second comparator. The detailed structure is shown.

  The DC-DC converter 10b according to the second embodiment includes a second comparator 22 that compares the voltage of the output node VOUT with the voltage (Vref2) of the second reference power supply 21 in the DC-DC converter 10a of the first embodiment. Further, instead of the DC-DC converter control circuit 200a of the first embodiment, in addition to the function of the control circuit 200a, a DC-DC converter that outputs an error signal (ERROR) based on the output of the second comparator 22 A control circuit 200b is provided. The DC-DC converter 10b is provided with an error output terminal for outputting the error signal to the outside of the DC-DC converter configured as an LSI chip. Here, the error signal indicates a GND short circuit abnormality, and the error signal output from the error output terminal is transmitted to an external control unit such as a microcomputer. In this embodiment, the DC-DC converter 10b is configured such that the microcomputer shuts down the power supply of the DC-DC converter when the microcomputer detects that the error signal continues for a predetermined time or more. ing. As a result, the charging operation of the charging circuit 100 is stopped.

  Note that the shutdown of the power source of the DC-DC converter is not limited to the case where it is performed by an external microcomputer based on the error signal output from the error output terminal of the control circuit 200b. For example, the DC-DC converter A timer is built in the control circuit 200b, and if an increase in the voltage VOUT at the output node cannot be confirmed for a certain period or longer, the control circuit 200b receiving the error signal from the second comparator 22 causes the DC-DC converter to The power supply may be shut down. As a result, the charging operation of the charging circuit 100 is stopped.

  As described above, when the increase in the voltage of the output node cannot be confirmed for a certain period or longer, the charging circuit 100 is output in a short-circuited state when the GND is short-circuited by adding a function of shutting down the power source of the DC-DC converter. Even charging current flowing through the node can be stopped.

  The voltage (Vref2) of the reference power supply 22 is set to be equal to or higher than the voltage of the reference power supply 21, that is, the reference voltage (Vref1) for mode switching determination, in order to prevent an erroneous shutdown.

  Although not described in detail in the above embodiment, the DC-DC converter control circuits 200a and 200b of Embodiments 1 and 2 are configured to switch the DC-DC converter according to the voltage level input to the input terminal FB. (When the period is fixed), or has a function of controlling the period (when the ON time is fixed). As a signal from the input terminal FB (also referred to as an FB signal), the voltage of the output node VOUT is a resistance. By using the voltage divided by the RFB1 and the resistor RFB2, the output voltage of the output node VOUT can be set by the ratio of RFB1: RFB1 + RFB2. By producing nodes for monitoring the voltage of the output node VOUT (that is, the power supply voltage drop detection voltage node UVP and the feedback voltage node FB) with the resistance voltage division of the output node VOUT, the second comparator 22 is prepared. A further effect is obtained in that (COMP2) and the control circuit 200 can be configured with low-voltage components.

  FIG. 2B shows a configuration for creating a monitor signal (UVP signal) by dividing the voltage of the output node VOUT by resistance, taking the second comparator as an example. In the figure, reference numeral 222 denotes an inverter that inverts the output of the second comparator and outputs an error signal (ERROR).

  By using such a circuit configuration, by adjusting the resistance voltage dividing ratio (RUVP1: RUVP1 + RUVP2, RFB1: RFB1 + RFB2), the voltage setting of the voltage of the output node VOUT or the second comparator 22 can be easily changed to the error output signal ERROR. A further effect is obtained that the reference potential (set voltage) for outputting can be adjusted.

  Further, by setting the reference voltage 21 (Vref2) for determining the ERROR output to the same voltage value as the mode switching determination voltage 11 (Vref1), the GND short-circuit determination comparator 22 (COMP2), RUVP1, and RUVP2 The circuit configuration can be reduced.

  In the first and second embodiments, the DC-DC converter control circuit 200 and the charging circuit 100 are configured to use the output voltage VDD of the series regulator 300 whose power supply voltage is VIN as the power supply voltage. The power supply voltage (VDD) is connected to the current charging resistor Rc, and the other terminal of the resistor Rc is connected to the node LX1 via the connection switch Q3 of the charging circuit 100.

  In the DC-DC converters of the first and second embodiments, the connection switch Q3 of the charging circuit 100 uses a high breakdown voltage NMOS transistor whose terminal on the LX1 side has a high breakdown voltage. The breakdown voltage of the NMOS transistor Q3 is reduced. By setting the voltage higher than the maximum potential of the connection destination, a circuit in which current does not flow backward toward the charging circuit 100 when the charging circuit 100 is stopped (that is, when the DC-DC converter unit is operating) is realized.

  In the first and second embodiments, since the connection destination of the NMOS transistor Q3 is the node LX1, the breakdown voltage of the NMOS transistor Q3 needs to be higher than the power supply voltage VIN that is the highest potential of the node LX1, but the NMOS transistor When the connection destination of Q3 is the node LX2, a breakdown voltage equal to or higher than the maximum potential of the node LX2 (that is, the maximum output voltage of the output node VOUT + the threshold voltage Vf of the Schottky diode D2) is required. However, in the DC-DC converters of the first and second embodiments, since the power supply voltage of the DC-DC converter control circuit 200 is the voltage VDD, the gate voltage for turning on the NMOS transistor Q3 is also the voltage VDD. The maximum voltage value at which the node VOUT can be charged is limited by a voltage indicated by [voltage VDD−threshold voltage Vt of NMOS transistor−threshold voltage Vf of Schottky diode D2], and the reference voltage (Vref1) of the reference power supply 11 is applied. ) Must be set below the above voltage value at the maximum.

  Further, as a technique for extending the limit of the voltage setting value of the reference voltage (Vref1) of the reference power supply 11 to [VIN-threshold voltage Vt of NMOS transistor-Vf of Schottky diode D2], connection switch Q3 of charging circuit 100 is used. Is constituted by an analog switch (see FIG. 1B). However, in this case, when the switch Q3 is turned OFF, as a condition for preventing the backflow of current from the node LX1 to which the switch Q3 is connected to the charging circuit 100, the node LX1 to which the switch Q3 is connected is connected. Since a voltage equal to or higher than the maximum potential (power supply potential VIN) is required as the OFF signal of the switch Q3, a level shifter circuit that converts the voltage level of the control signal (gate signal) of the switch Q3 from the power supply voltage VDD to the power supply voltage VIN is added. Is required.

  In the circuit system according to the second embodiment of the present invention, the current capability of the charging circuit 100, the reference voltage (Vref1), and the capacitance value of the output capacitor COUT are the same as those in the DC-DC converter unit after the DC-DC converter is turned on. This is the main design factor for designing the time until start-up.

When the charging circuit 100 is designed using the current limiting resistor Rc as in the second embodiment, the time T from the power-on of the DC-DC converter to the start of operation of the DC-DC converter unit is the connection of the current limiting resistor Rc. It can be calculated from the ratio between the previous power supply voltage and the reference voltage (Vref1) and the CR time constant. (However, the ON resistance of the mode switch (transistor Q3) and the load current of the load circuit 2000 and the like are not taken into consideration.)
Example 1: If the voltage ratio is 10%, T = 0.1τ = 0.1 × V (COUT) × V (Rcharge)
Example 2: If the voltage ratio is 63%, T = τ = V (COUT) × V (Rcharge)
Example 3: T = 2.3τ = 2.3 × V (COUT) × V (Rcharge) when the voltage ratio is 90%
Here, V (COUT) indicates the capacitance of the output capacitor COUT, and V (Rcharge) indicates the resistance value of the current limiting resistor Rc.

When the charging circuit 100 is designed with a constant current source circuit as shown in FIG. 1C, the time T from the power-on of the DC-DC converter to the start of operation of the DC-DC converter unit is V ( COUT) × Vref1 ÷ V (Icharge). (However, V (Icharge) is a constant current value of the charging circuit, and the calculation condition does not consider the load current of the load circuit 2000 or the like.)
Thus, the power supply voltage to which the current limiting resistor Rc, which is a parameter related to the start-up time, is selected from the power supply voltage VIN and the output voltage VDD of the series regulator 300, and the circuit configuration of the charging circuit 100 includes a resistor. By selecting from the circuit configuration and the constant current source circuit, an effect that the start-up time can be easily designed can be obtained.

  In order to raise (automatically recover) the voltage of the output node VOUT from the state where the voltage VOUT of the output node is lowered, the charging circuit 100 includes a load circuit 2000 connected to the output node VOUT, a feedback input terminal Although the FB and resistors (for example, the resistors RFB1, RFB2, RUVP1, and RUVP2) constituting the resistance dividing circuit draw a current, it is necessary to generate a voltage higher than the reference voltage (Vref1). Depending on the situation, it may be difficult to achieve.

  For example, the current consumption of the load circuit 2000 is larger than the charging current of the charging circuit 100, and automatic recovery design is impossible. As a countermeasure for this case, the load circuit 2000 has a standby terminal. As long as the error signal ERROR for transmitting the voltage drop of the output node VOUT to the outside is input to the standby input terminal of the load circuit 2000, the load circuit 2000 is shut down when the voltage of the output node VOUT drops, By making the load current almost zero, the voltage of the output node VOUT can be automatically restored.

  Further, when the load circuit 2000 is a light emitting diode LED, since the load current does not flow until the voltage of the output node VOUT rises above the voltage represented by [LED threshold Vf × number of series], the mode switching voltage, That is, if the reference voltage (Vref1) is set to about half or less of the above [LED threshold Vf × number of series], it is considered unnecessary to have a mechanism for stopping the load current.

  When the load circuit 2000 is a light emitting diode (LED), the following voltage is used as the feedback voltage. Usually, there are a light emitting diode driving circuit having a constant current circuit connected in series with the light emitting diode and a current driving resistor having a current setting resistor connected in series with the light emitting diode. Therefore, in a drive circuit having a constant current source, a voltage at a terminal connected to the constant current source on the cathode side of the light emitting diode is used as a feedback voltage. In a drive circuit having a resistance element, the voltage at the connection node of the light emitting diode with the current setting resistor is used as the feedback voltage. By returning such a feedback voltage as feedback to the DC-DC converter control circuit, it becomes possible to automatically adjust the power consumption to an optimum state.

  Regarding the design of the resistance values of the resistors (RFB1, RFB2) for generating the feedback voltage VFB, it is better that the current value flowing through the resistance dividing path is sufficiently smaller than the charge current design value. It is desirable to do.

Further, as a condition for changing from the state where the voltage of the output node VOUT is lowered to the normal DC-DC converter operation state, the reference voltage (Vref1) is set lower than the maximum voltage that can be output by the charging circuit 100. It goes without saying that you need to do it.
(Embodiment 3)
FIG. 3 is a diagram illustrating a DC-DC converter according to Embodiment 3 of the present invention.

  The DC-DC converter 10c of the third embodiment is a third circuit that compares the voltage of the connection node between the resistor Rs1 and the switch Q1 with the voltage (Vref3) of the third reference power supply 31 in the DC-DC converter 10b of the second embodiment. In addition to the function of the control circuit 200b in place of the DC-DC converter control circuit 200b of the second embodiment, the switch Q1 is controlled based on the output of the third comparator 32. A DC-DC converter control circuit 300c is provided.

  That is, in the DC-DC converter 10c of the third embodiment, the voltage of the connection node between the current detection resistor Rs1 and the first switch Q1 and the reference voltage (Vref3) of the third reference power supply 31 in the DC-DC converter unit 1000 are used. Are compared by the comparator 32 (COMP3), and the determination result is input to the DC-DC converter control circuit 200c.

  In such a DC-DC converter 10c, when the terminal voltage value generated by the resistance element Rs1 that converts the current value flowing through the DC-DC converter unit 1000 into a voltage value is lower than the set reference voltage 31 (Vref3), When it is determined that a current greater than the set value has flowed into the DC-DC converter unit 1000 and the determination result is notified to the DC-DC converter control circuit 200c, the switch Q1 in the DC-DC converter unit from the control circuit 200c is switched. The pulse signal to be turned on / off is immediately turned off. In other words, within the period in which an overcurrent equal to or greater than the set current flows, it is turned off when an overcurrent is detected regardless of whether the pulse signal is on or off.

  Thereby, it is possible to avoid an overcurrent from flowing through the DC-DC converter.

In the DC-DC converter 10 of the third embodiment, when the node LX1 is short-circuited with the power supply voltage VIN, there is a problem that the built-in overcurrent detection function does not work, and such a problem has been solved. This will be described below as a fourth embodiment.
(Embodiment 4)
FIG. 4 is a diagram for explaining a DC-DC converter according to Embodiment 4 of the present invention.

  The DC-DC converter 10d of Embodiment 4 includes a fourth comparator 42 that compares the voltage of the internal node LX1 with the voltage (Vref4) of the fourth reference power supply 41 in the DC-DC converter 10c of Embodiment 3. Further, in place of the DC-DC converter control circuit 200c of the third embodiment, in addition to the function of the control circuit 200c, a mode from the charging mode to the DC-DC operation mode based on the output of the fourth comparator 42 is used. A DC-DC converter control circuit 200d that performs switching is provided.

  That is, in the DC-DC converter 10d of the fourth embodiment, as a countermeasure against a short circuit between the power supply voltage VIN and the internal node LX1, the voltage (or LX2 terminal voltage) of the internal node LX1 and the reference voltage 41 (Vref4) are used. The comparison is performed by the comparator 42 (COMP4), and the comparison result is input to the DC-DC converter control circuit 200d.

  In the DC-DC converter control circuit 200d, the voltage of the internal node LX1 is less than or equal to the voltage (Vref4) of the fourth reference power supply 41 under the mode switching condition from the charging mode to the DC-DC operation mode from the charging circuit 100. By adding the condition that there is, it is possible to prevent the DC-DC converter unit 1000 from operating without overcurrent detection. However, since the reference voltage 41 (Vref4) of the reference power supply 41 needs to be set within the voltage output possible range of the voltage of the internal node LX1, it is lower than the power supply voltage VIN and higher than the maximum voltage value that can be generated in the charging mode. Must be set to a value.

  Next, the operation of the DC-DC converter of Embodiment 4 will be described.

  First, the starting operation of the DC-DC converter when there is no short circuit will be described.

  FIG. 5 is a diagram illustrating a startup waveform when there is no short circuit in the DC-DC converter according to the fourth embodiment of the present invention.

  When the system operation start signal XSTBY rises and the power supply voltage is supplied to the DC-DC converter (timing Ta1), the output capacitor COUT is charged by the charging circuit 100, and the voltage of the output node VOUT rises. At this time, the switch Q1 of the DC-DC converter unit 1000 is in the OFF state, but the voltage of the internal node LX1 increases as the voltage of the output node VOUT increases.

  Thereafter, when the output node VOUT reaches the first reference voltage Vref1, the output of the first comparator 12 is inverted, and the inverted result is notified to the control circuit 200d. At this time, the comparison result between the voltage of the internal node LX1 and the fourth reference voltage Vref4 is notified to the control circuit 200d. The control circuit 200d supplies a drive pulse to the switch Q1 of the DC-DC converter unit 1000 on the condition that the voltage of the internal node LX1 is equal to or lower than the fourth reference voltage Vref4, thereby shifting from the charging mode to the DCDD operation mode. (Timing Ta2).

  Thereafter, due to the operation of the DC-DC converter unit 1000 having a large driving capability, the voltage of the output node VOUT rises rapidly, and when this voltage reaches the second reference voltage Vref2 (timing Ta3), the output of the second comparator 22 Is inverted, and the inversion of the output is notified to the control circuit 200d. Here, a normal determination is made that there is no GND short circuit. At this time, the control circuit 200d changes the error output (ERROR) from the abnormality detection state to the normal determination state.

  Thereafter, the voltage of the output node VOUT further rises beyond the second reference voltage Vref4 (timing Ta4).

  Next, the operation when a GND short circuit occurs during stable operation will be described.

  FIG. 6 is a diagram showing signal waveforms for explaining the operation when the GND short circuit occurs during the stable operation in the DC-DC converter according to the present embodiment.

  If a GND short circuit occurs during the stable operation of the DC-DC converter 10d (timing Tb1), the voltage of the output node VOUT rapidly decreases and exceeds the fourth reference voltage Vref4 (timing Tb2), and the second reference voltage Vref2 (Timing Tb3).

  At this time, when the output of the second comparator 22 changes from the normal determination level to the GND short-circuit determination level, and this change is notified to the control circuit 200d, the control circuit 200d determines the error output (ERROR) level as normal. This error output is notified to the load circuit 2000 as a standby (STBY) signal. Thereafter, when the voltage of the output node VOUT decreases to the first reference voltage Vref1 or lower, the output of the first comparator 12 changes from the DCDC operation mode determination level to the charge mode determination level, and the operation mode of the DC-DC converter changes to DCDC. The operation mode is switched to the charging mode (timing Tb4).

  Next, the starting operation of the DC-DC converter when the GND is short-circuited will be described.

  FIG. 7 is a diagram showing a startup waveform when the GND is short-circuited in the DC-DC converter according to the present embodiment.

  When the system operation start signal XSTBY rises and the power supply voltage is supplied to the DC-DC converter 10d (timing Ts), the output capacitor COUT is charged by the charging circuit 100, and the voltage of the output node VOUT rises. At this time, the switch Q1 of the DC-DC converter unit 1000 is in the OFF state, but the voltage of the internal node LX1 increases as the voltage of the output node VOUT increases.

  However, in this case, since the GND is short-circuited, the output node VOUT does not reach the first reference voltage Vref1. The output of the first comparator 12 remains at the charge mode determination level, and the output of the second comparator 22 remains at the GND short-circuit determination level. Therefore, the error output of the control circuit 200d is maintained at the abnormality determination level.

  Next, the startup operation when the power supply voltage VIN and the internal node LX1 are short-circuited (when VIN-LX1 is short-circuited) will be described.

  FIG. 8 is a diagram illustrating a startup waveform when the VIN-LX1 is short-circuited in the DC-DC converter according to the present embodiment.

  In this state where the power supply voltage VIN and the internal node LX1 are short-circuited, when the system operation start signal XSTBY rises and the power supply voltage is supplied to the DC-DC converter 10d (timing Ts), the voltage of the internal node LX1 is the power supply. The voltage rises to near the voltage VIN, and the output of the fourth comparator 42 becomes a VIN-LX1 short-circuit determination level indicating that the power supply voltage VIN and the internal node LX1 are short-circuited.

  At this time, the output of the first comparator 12 is a DC-DC operation mode determination level and the output of the second comparator 22 is a normal determination level, but the control circuit 200d changes the operation mode from the charge mode to the DC- Since the condition for switching to the DC operation mode is not satisfied, the charging mode is maintained, and the error signal (ERROR) is maintained at the abnormality determination output.

  As described above, in the DC-DC converter 10d according to the fourth embodiment, the voltage of the output node VOUT does not increase when the output node VOUT is already short-circuited to the GND when the circuit is activated by adopting the above circuit configuration. The DC-DC converter unit does not operate, and it is possible to avoid an overcurrent flowing through a path from the power supply to the output node.

  Further, even when the output node VOUT is short-circuited during the operation of the DC-DC converter, conventionally, in order to confirm the determination result of the GND short-circuit, the DC-DC converter unit for a certain period after the detection of the GND short-circuit However, in the present invention, the operation of the DC-DC converter unit is stopped immediately after the determination, and the output node is set by the charging circuit 100 having a smaller driving ability than the DC-DC converter unit provided separately. Since the battery is charged and the determination result is confirmed in this state, the time during which the overcurrent flows can be reduced.

  In addition, it is not necessary to design the time until the GND short-circuit determination is started at the time of starting the circuit and the time for confirming the GND short-circuit determination result during the DC-DC converter operation. As a result, when a timer circuit is conventionally incorporated in a control circuit or the like for counting the determination time, the timer circuit can be reduced.

  In the conventional circuit, the overcurrent can be stopped only by latching the GND short-circuit detection state, that is, by stopping the operation of the DC-DC converter. However, in the present invention, the DC-DC converter -In addition to the DC converter part, a charging circuit with a smaller driving capacity than the DC-DC converter part is provided, so the design to latch the GND short-circuit detection state so that the DC-DC converter stops, and the DC-DC converter operates normally The overcurrent can be stopped by both of the designs that do not latch the GND short-circuit detection state so as to be able to return to

  Specifically, in the design that does not latch the GND short-circuit detection state, the operation of the DC-DC converter unit 1000 stops when the GND short-circuit is determined to be caused by the GND short-circuit determination, but the charging circuit 100 is designed to charge the output node VOUT by this charging circuit without stopping, and even when a GND short circuit is detected, the operation of the DC-DC converter is not completely stopped.

  On the other hand, in the design for latching the GND short-circuit detection state, when it is determined by the GND short-circuit determination that the GND short-circuit has occurred, the operation of the DC-DC converter unit 1000 is stopped, and the operation of the charging circuit 100 is further stopped. Is designed to stop after a predetermined time, and when a GND short circuit is detected, the operation of the DC-DC converter is completely stopped.

  And if the GND short circuit is resolved by designing it so that the GND short circuit detection state is not latched, or if the GND short circuit is erroneously determined due to noise, the LSI chip constituting the DC-DC converter is externally connected to the LSI chip. Even without inputting the reset signal, the circuit operation of the DC-DC converter can be automatically returned to the normal state.

  In the DC-DC converter of the present invention, the charge smoothing capacitor COUT is charged in advance with a charge exceeding a predetermined voltage from the charging circuit, and then the operation of the DC-DC converter is started. There is also an effect of reducing the amount of inrush current flowing toward the output smoothing capacitor COUT when the operation of the DC-DC converter is started.

  As mentioned above, although this invention has been illustrated using preferable embodiment of this invention, this invention should not be limited and limited to this embodiment. It is understood that the scope of the present invention should be construed only by the claims. It is understood that those skilled in the art can implement an equivalent range based on the description of the present invention and the common general technical knowledge from the description of specific preferred embodiments of the present invention. It is understood that the patent documents cited in the present specification should be incorporated by reference into the present specification in the same manner as the content itself is specifically described in the present specification.

  The present invention relates to a DC-DC converter section in the field of a step-down type or step-up / step-down type or step-up type switching type DC-DC converter that steps down, step-up or step-down or step-up a DC voltage by an on / off operation of a switch element. It is possible to obtain a DC-DC converter that can detect an output node or a GND short-circuit of a load connected to the output node without operating, and avoid damage to the components of the DC-DC converter unit. it can.

11 First Reference Power Supply 12 First Comparator (GND Short-Circuit Determination / Mode Switch Determination Comparator) COMP1
21 Second reference power source 22 Second comparator (GND short circuit determination / ERROR output determination comparator) COMP2
31 Third reference power supply 32 Third comparator (overcurrent detection comparator) COMP3
41 Fourth reference power source 42 Fourth comparator (VIN-LX1 short-circuit comparator) COMP4
DESCRIPTION OF SYMBOLS 100 Charging circuit 200a-200d DC-DC converter control circuit 300 Series regulator 400 Level shifter 1000 DC-DC converter part 2000 Standby circuit for load circuits 3000 Load circuit Vref1 1st reference voltage (reference voltage for GND short circuit determination and mode switching determination)
Vref2 Second reference voltage (GND short-circuit determination and ERROR output determination reference voltage)
Vref3 Third reference voltage (reference voltage for overcurrent detection)
Vref4 fourth reference voltage (VIN-LX1 short-circuit determination reference voltage)

Claims (14)

A DC-DC converter that converts an input DC voltage to a desired DC voltage and outputs the DC voltage to an output node,
A smoothing capacitor connected to the output node;
A DC-DC converter unit that uses the input DC voltage as a power supply voltage and charges the smoothing capacitor so that the smoothing capacitor generates the desired potential;
A charging circuit having a current driving capability smaller than that of the DC-DC converter unit and charging the output node ;
E Bei a first comparator for comparing a voltage and a first reference voltage of the output node,
The charging circuit is composed only of a resistance element,
When the voltage of the output node is less than or equal to the first reference voltage, the DC-DC converter unit stops, and when the voltage of the output node is higher than the first reference voltage, the DC-DC converter unit operates. DC-DC converter. The DC-DC converter according to claim 1 ,
A DC-DC converter that always charges the output node by the charging circuit regardless of the voltage of the output node. The DC-DC converter according to claim 1 ,
A second comparator for comparing the voltage with a second reference voltage of said output node, DC-DC converter that outputs an error signal when the voltage of said output node is equal to or less than the second reference voltage. The DC-DC converter according to claim 3 ,
A DC-DC converter in which the first reference voltage and the second reference voltage are the same voltage. The DC-DC converter according to claim 3 ,
DC-DC converter having an error output terminal for outputting the error signal to the outside of the DC-DC converter. The DC-DC converter according to claim 1,
A DC-DC converter using a circuit configuration in which a power source of the charging circuit and a power source of the DC-DC converter unit are shared. The DC-DC converter according to claim 1,
A series regulator for adjusting the input power supply voltage is provided.
A DC-DC converter using a circuit configuration in which the power supply voltage of the charging circuit is supplied from the series regulator. The DC-DC converter according to claim 1,
The DC-DC converter section is
A resistance element on the input power supply voltage side and a first switch on the first internal node side connected in series between the input power supply voltage and the first internal node;
A circuit configuration having a coil provided in a charging path from the first internal node to the output capacitor;
A third comparison circuit for comparing a voltage at a connection node between the resistance element and the first switch with a third reference voltage;
Determining a short circuit across the resistor element of said input supply voltage side based on the comparison result of said third comparator circuit, DC-DC converters. The DC-DC converter according to claim 8 ,
A fourth comparison circuit for comparing the voltage of the first internal node with a fourth reference voltage;
The DC-DC converter which determines the short circuit of the both ends of this 1st switch according to the voltage which generate | occur | produced in the terminal of the coil connection side of said 1st switch which is this 1st internal node by charge of the said charging circuit. The DC-DC converter according to claim 9 ,
The operation start condition of the DC-DC converter unit is a case where the voltage of the output node is higher than the first reference voltage and the first internal node voltage is lower than the fourth reference voltage,
The DC-DC converter, wherein the operation stop condition of the DC-DC converter unit is a case where the voltage of the output node is lower than the first reference voltage. The DC-DC converter according to claim 10 , wherein
In accordance with the output result of the second comparator and the fourth comparator, transmits an error signal indicating a short circuit condition across the series connection of the resistance element and the first switch of the input power source voltage side to the outside DC-DC converter with an error output terminal. The DC-DC converter according to claim 1,
Before starting the DC-DC converter unit, the charging circuit charges the smoothing capacitor connected to the output node, so that the inrush current flows toward the smoothing capacitor when the DC-DC converter unit is started. DC-DC converter that suppresses current. A control system for controlling the DC-DC converter according to claim 5 ,
A microcomputer having the error signal as an input signal;
The microcomputer, a predetermined time or more, when said error signal is detected to be continued, the control signal from the microcomputer, to shut down the power supply of the DC-DC converter, the control system. A control system for controlling the DC-DC converter according to claim 5 ,
Having a timer circuit,
By the timer circuit, a predetermined time or more, when said error signal is detected to be continued, to shut down the power supply of the DC-DC converter, the control system.

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