JP6254874B2 - Step-down converter circuit and test method thereof - Google Patents

Description

The present invention relates to a step-down converter circuit, and in particular, converts an input voltage into an output voltage by complementarily switching a high-voltage side switching element and a low-voltage side switching element based on a voltage divided by a pair of feedback resistors. The present invention relates to a step-down converter circuit.
The present invention also relates to a method for testing such a step-down converter circuit.

Conventionally, various step-down converter circuits have been devised and used.
For example, in the DC-DC converter disclosed in Patent Document 1, a pair of switching elements connected in series between an input voltage and a ground potential are complementarily switched, and the voltage output to the coupling portion of the pair of switching elements Is smoothed by an inductor and a capacitor to obtain an output voltage. The output voltage is controlled by detecting the current flowing through the inductor and adjusting the on / off time of the pair of switching elements according to the detected current.

JP 2006-149056 A

  Here, FIG. 4 shows a schematic configuration of a general voltage mode control type step-down converter circuit. A high-voltage side switching element TH and a low-voltage side switching element TL are connected in series between the input voltage Vin and the ground potential, and an inductor Lout and a capacitor Cout are connected to a joint A of the high-voltage side switching element TH and the low-voltage side switching element TL. The output terminal OUT is connected to the inductor Lout and the capacitor Cout.

  A pair of feedback resistors R1 and R2 are connected in series between the output terminal OUT and the ground potential, and the negative input terminal of the amplifier 1 is connected to the coupling portion B of the feedback resistors R1 and R2. A reference voltage generating circuit 2 is connected to the positive input terminal of the amplifier 1, and an RC circuit 3 is connected between the negative input terminal and the output terminal of the amplifier 1. The negative input terminal of the comparator 4 is connected to the output terminal of the amplifier 1, and the oscillator 5 is connected to the positive input terminal of the comparator 4. Further, the control circuit 6 is connected to the output terminal of the comparator 4, and the gate of the high-voltage side switching element TH is connected to the control circuit 6 via the pre-driver 7, and the low-voltage side switching is connected via the pre-driver 8. The gate of the element TL is connected.

  The high voltage side switching element TH and the low voltage side switching element TL are complementarily switched by the control circuit 6, and the voltage output to the coupling portion A of the high voltage side switching element TH and the low voltage side switching element TL is smoothed by the inductor Lout and the capacitor Cout. Into the output voltage Vout.

  The output voltage Vout is divided by the pair of feedback resistors R1 and R2, and the difference between the divided voltage Vdiv and the reference voltage Vref generated by the reference voltage generation circuit 2 is amplified by the amplifier 1 to become a difference signal Vdif. Further, in the comparator 4, the differential signal Vdif is compared with the triangular wave signal Vosc emitted from the oscillator 5 to form a PWM signal Spwm. The side switching element TL is switched.

When forming such a step-down converter circuit using a semiconductor integrated circuit, an external element 9 including an inductor Lout and a capacitor Cout is connected to the coupling portion A of the high-voltage side switching element TH and the low-voltage side switching element TL. The voltage smoothed by the external element 9 is used as the output voltage Vout.
Therefore, in the test for inspecting the defect of the step-down converter circuit, the external element 9 is usually mounted on the test board and the operation of the output voltage Vout is measured.

However, in a probe test performed before a large number of integrated circuit chips formed on a semiconductor wafer are separated from each other in a manufacturing process of a semiconductor integrated circuit, an integrated circuit chip and an inspection device on the semiconductor wafer are probed using a probe card. Therefore, it is difficult to perform a test in a state where the external element 9 is connected to the coupling portion A of the high voltage side switching element TH and the low voltage side switching element TL.
For this reason, in the probe test, a test as a step-down converter circuit cannot be performed, and the test must be performed by setting inspection items for each circuit element constituting the step-down converter circuit.

The present invention has been made to solve such a conventional problem, and provides a step-down converter circuit capable of simultaneously performing a probe test on a plurality of elements in a circuit without connecting external elements. With the goal.
Another object of the present invention is to provide a method for testing a step-down converter circuit for testing such a step-down converter circuit.

  A step-down converter circuit according to the present invention has a high-voltage side switching element and a low-voltage side switching element connected in series between an input voltage and a ground potential, and is output to a coupling portion between the high-voltage side switching element and the low-voltage side switching element. Obtained by dividing the voltage with a pair of feedback resistors and amplifying the difference signal between the divided voltage and the reference voltage with an amplifier and comparing the amplified difference signal with a predetermined oscillation signal with a comparator. In a step-down converter circuit that complementarily switches a high-voltage side switching element and a low-voltage side switching element based on a PWM signal, a first pad connected to a coupling portion between the high-voltage side switching element and the low-voltage side switching element, and a pair of feedback A second pad connected to the high voltage side end of the resistor, a predetermined oscillation signal and a differential signal amplified by an amplifier; A first selector that selects and inputs the first signal to the first input of the comparator; and a first selector that selects one of the differential signal amplified by the amplifier and the output signal of the comparator and inputs the selected signal to the second input of the comparator. A second switch that opens and closes between the output of the comparator and the control terminal of the low-voltage side switching element, and a second switch that opens and closes between the output of the comparator and the control terminal of the low-voltage side switching element. A switch, and a short circuit between the first pad and the second pad, and a differential signal amplified by the amplifier by the first selector is input to the first input of the comparator and the second selector In the state where the output signal of the comparator is input to the second input of the comparator, a test is performed in which the high-voltage side switching element is driven by closing the first switch and opening the second switch, By opening the first switch and closing the second switch, In which test was driven ring element is carried out.

An external element is connected between the first pad and the second pad, and a predetermined oscillation signal is input to the first input of the comparator by the first selector and amplified by the amplifier by the second selector. The differential signal is input to the second input of the comparator, and the first switch and the second switch are both opened, so that the voltage output to the coupling portion of the high-voltage side switching element and the low-voltage side switching element is externally connected. To smooth the output voltage.
In addition, a third switch that opens and closes between the first pad and the second pad can be further provided.
In addition, a first current path securing element connected in parallel with the high voltage side switching element, a second current path securing element connected in parallel with the low voltage side switching element, and a reference voltage generation for generating a reference voltage A bias voltage generating circuit for generating a bias voltage to be supplied to the control terminals of the first current path securing element and the second current path securing element based on the reference voltage generated by the reference voltage generating circuit; Can also be provided.

  A test method for a step-down converter circuit according to the present invention includes a high-voltage side switching element and a low-voltage side switching element connected in series between an input voltage and a ground potential. By dividing the output voltage with a pair of feedback resistors and amplifying the difference signal between the divided voltage and the reference voltage with an amplifier, and comparing the amplified difference signal with a predetermined oscillation signal with a comparator A method for testing a step-down converter circuit that complementarily switches a high-voltage side switching element and a low-voltage side switching element based on an obtained PWM signal, the test method being connected to a coupling portion between the high-voltage side switching element and the low-voltage side switching element. The first pad and the second pad connected to the high-voltage side ends of the pair of feedback resistors are short-circuited to obtain a predetermined oscillation signal. Instead of inputting the differential signal amplified by the amplifier to the comparator, the differential signal amplified by the amplifier and the output signal of the comparator are input to the comparator, and the high-voltage side switching element between the high-voltage side switching element and the low-voltage side switching element is switched. The test is performed by driving the high voltage side switching element by inputting the output of the comparator only to the control terminal of the element, and the low voltage side switching element is input by inputting the output of the comparator only to the control terminal of the low voltage side switching element. This is a method for performing a driven test.

  According to the present invention, the first pad connected to the coupling portion of the high voltage side switching element and the low voltage side switching element, the second pad connected to the high voltage side end of the pair of feedback resistors, and the predetermined oscillation A first selector for selecting one of the signal and the differential signal amplified by the amplifier and inputting the selected signal to the first input of the comparator; and selecting either the differential signal amplified by the amplifier or the output signal of the comparator A second selector to be input to the second input of the comparator, a first switch for switching between the output of the comparator and the control terminal of the high voltage side switching element, the output of the comparator and the low voltage side switching element A second switch that opens and closes between the control terminals, so that the first pad and the second pad are short-circuited and the differential signal amplified by the amplifier by the first selector is a comparator To the first input and by the second selector With the output signal of the comparator being input to the second input of the comparator, the first switch and the second switch are opened and closed, so that a plurality of elements in the circuit can be connected without connecting external elements. The probe test can be performed simultaneously.

1 is a circuit diagram showing a configuration of a step-down converter circuit according to an embodiment of the present invention. It is a circuit diagram which shows roughly the step-down converter circuit of embodiment at the time of performing the test which driven the high voltage | pressure side switching element. It is a circuit diagram which shows roughly the step-down converter circuit of embodiment at the time of performing the test which driven the low voltage | pressure side switching element. It is a circuit diagram which shows the structure of the conventional step-down converter circuit.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 shows a configuration of a step-down converter circuit according to the embodiment. The step-down converter circuit has a high-voltage side switching element TH and a low-voltage side switching element TL connected in series between the input voltage Vin and the ground potential. The gate of the high-voltage side switching element TH is connected to the input voltage Vin via the switch T1, and the gate of the low-voltage side switching element TL is connected to the ground potential via the switch T3.
The first current path securing element THp is connected in parallel to the high-voltage side switching element TH, and the gate of the first current path securing element THp is connected to the input voltage Vin via the switch T2. It is connected to the bias voltage Pbias via the switch G1. Similarly, a second current path securing element TLp is connected in parallel to the low-voltage side switching element TL, and the gate of the second current path securing element TLp is connected to the ground potential via the switch T4. The bias voltage Nbias is connected via the switch G2.

Further, the first pad P1 is connected to the coupling portion A of the high-voltage side switching element TH and the low-voltage side switching element TL, and the second pad P2 is connected via the switch G3. A pair of feedback resistors R1 and R2 are connected in series between the second pad P2 and the ground potential, and the negative input terminal of the amplifier 1 is connected to the joint B of the feedback resistors R1 and R2. A reference voltage generating circuit 2 is connected to the positive input terminal of the amplifier 1, and an RC circuit 3 is connected between the negative input terminal and the output terminal of the amplifier 1.
The output terminal of the amplifier 1 is connected to the second input terminal of the first selector 11 and the first input terminal of the second selector 12, and a comparator is connected to the output terminal of the first selector 11. 4 positive input terminal (first input) is connected, and the negative input terminal (second input) of the comparator 4 is connected to the output terminal of the second selector 12. The oscillator 5 is connected to the first input terminal of the first selector 11, and the output terminal of the comparator 4 is connected to the second input terminal of the second selector 12.

Furthermore, one end of an oscillation prevention resistor R3 is connected to the output terminal of the comparator 4 via a switch G4, and the other end of the oscillation prevention resistor R3 is connected to the high voltage side via a switch G5 (first switch). The gate of the switching element TH is connected, and the gate of the low voltage side switching element TL is connected via a switch G6 (second switch).
Further, the control circuit 6 is connected to the output terminal of the comparator 4, and the gate of the high-voltage side switching element TH is connected to the control circuit 6 through the pre-driver 7, and the low-voltage side switching is performed through the pre-driver 8. The gate of the element TL is connected.

The amplifier 1 amplifies the difference between the voltage Vdiv at the coupling portion B divided by the pair of feedback resistors R1 and R2 and the reference voltage Vref generated by the reference voltage generation circuit 2, and outputs the difference signal Vdif. .
The oscillator 5 outputs a triangular wave signal as the predetermined oscillation signal Vosc.
A bias voltage generation circuit 9 is connected to the reference voltage generation circuit 2. This bias voltage generation circuit 9 is based on the reference voltage Vref obtained by the reference voltage generation circuit 2 and the bias voltage Pbias input to the gate of the first current path securing element THp via the switch G1 and the switch A bias voltage Nbias input to the gate of the second current path securing element TLp via G2 is generated.

In this step-down converter circuit, the operation state of the step-down converter circuit is controlled using two types of test signals Ptest and Ntest. For example, when performing a test by driving the high-voltage side switching element TH, the test signal Ptest is set to the H level and the test signal Ntest is set to the L level. On the other hand, when a test is performed by driving the low-voltage side switching element TL, the test signal Ptest is set to the L level and the test signal Ntest is set to the H level. Furthermore, when not functioning as a test but functioning as a step-down converter that converts the input voltage Vin into the output voltage Vout, the two test signals Ptest and Ntest are both set to the L level.
Further, inside the step-down converter circuit, a test signal Test obtained by taking the logical sum of two test signals Ptest and Ntest is also used.

The high-voltage side switching element TH and the first current path securing element THp are each composed of a PMOS transistor, and the low-voltage side switching element TL and the second current path securing element TLp are each composed of an NMOS transistor.
The switch T1 is a PMOS transistor controlled by the inverted signal of the test signal Ntest, the switch T2 is a PMOS transistor controlled by the test signal Ntest, the switch T3 is an NMOS transistor controlled by the test signal Ptest, and the switch T4 is an inverted signal of the test signal Ptest. It consists of NMOS transistors controlled by signals.
The switches G1 to G6 are each composed of a transfer gate, the switches G1 and G6 are controlled by the test signal Ntest, the switches G2 and G5 are controlled by the test signal Ptest, and the switches G3 and G4 are controlled by the test signal Test. Is done.

  Each of the first selector 11 and the second selector 12 is composed of an analog multiplexer composed of transfer gates, and is controlled by a test signal Test. Specifically, each of the first selector 11 and the second selector 12 outputs the signal input to the first input terminal to the output terminal when the test signal Test is at the L level, while the test signal Test When the signal Test is at the H level, the signal input to the second input terminal is output to the output terminal.

That is, when the test signal Test is at the H level, the differential signal Vdif output from the amplifier 1 is input to the positive input terminal of the comparator 4 and the output signal from the comparator 4 is input to the negative input terminal of the comparator 4. . As a result, the comparator 4 functions as a buffer having a gain “1”, and the differential signal Vdif output from the amplifier 1 is output from the comparator 4 as it is.
On the other hand, when the test signal Test is at the L level, the oscillation signal Vosc output from the oscillator 5 is input to the positive input terminal of the comparator 4 and the differential signal Vdif output from the amplifier 1 is input to the negative input terminal of the comparator 4. The comparator 4 outputs a PWM signal Spwm generated by inputting and comparing the difference signal Vdif with the oscillation signal Vosc.

  The pre-drivers 7 and 8 are inactivated when the test signal Test is at the H level, and when the test signal Test is at the L level, the pre-drivers 7 and 8 are switched on the high-voltage side switching elements TH and based on the switching signal output from the control circuit 6. Each of the low-voltage side switching elements TL is driven and controlled.

Next, the operation of the step-down converter circuit according to the embodiment will be described.
(1) Operation as a step-down converter First, when functioning as a step-down converter that converts the input voltage Vin to the output voltage Vout, the test signals Ptest and Ntest are both set to L level, and the logical sum of these test signals Ptest and Ntest is obtained. A certain test signal Test also becomes L level.
As a result, the switches T1 and T3 are turned off, the switches G4 to G6 are opened, the pre-drivers 7 and 8 are activated, and the pre-drivers are respectively connected to the gates of the high-voltage switching element TH and the low-voltage switching element TL. A switching signal output from the control circuit 6 is input via the drivers 7 and 8.

Since the switches T2 and T4 are turned on and the switches G1 and G2 are opened, the input voltage Vin is applied to the gate of the first current path securing element THp made of a PMOS transistor, thereby securing the first current path. The element THp is turned off, the ground potential is connected to the gate of the second current path securing element TLp made of an NMOS transistor, and the second current path securing element TLp is also turned off.
Further, when the switch G3 is opened, the first pad P1 and the second pad P2 are disconnected, and the L-level test signal Test is input to the first selector 11 and the second selector 12, respectively. As a result, the oscillation signal Vosc output from the oscillator 5 is input to the positive input terminal of the comparator 4, and the differential signal Vdif output from the amplifier 1 is input to the negative input terminal of the comparator 4, so that the differential signal Vdif Is compared with the oscillation signal Vosc, and the PWM signal Spwm generated by the comparator 4 is output from the comparator 4.

As a result, by connecting the external element 9 including the inductor Lout and the capacitor Cout between the first pad P1 and the second pad P2, a pair is connected from the coupling portion A of the high-voltage side switching element TH and the low-voltage side switching element TL. The negative feedback returning to the control circuit 6 is formed through the coupling part B of the feedback resistors R1 and R2, the amplifier 1 and the comparator 4, and the step-down converter circuit shown in FIG. 4 is formed.
That is, the control circuit 6 complementarily switches the high-voltage side switching element TH and the low-voltage side switching element TL, and the voltage output to the coupling portion A of the high-voltage side switching element TH and the low-voltage side switching element TL is smoothed by the external element 9 Into the output voltage Vout. The output voltage Vout is divided by the feedback resistors R1 and R2, and the difference between the divided voltage Vdiv and the reference voltage Vref generated by the reference voltage generation circuit 2 is amplified by the amplifier 1 to become a difference signal Vdif. The comparator 4 compares the differential signal Vdif with the triangular wave signal Vosc emitted from the oscillator 5 to form a PWM signal Spwm. Based on the PWM signal Spwm, the control circuit 6 controls the high-voltage side switching element TH and the low-voltage side switching. The element TL is switched.

In this way, the input voltage Vin is converted into the output voltage Vout.
At this time, when the negative feedback gain determined by the power supply voltage, the gain of the amplifier 1 and the amplitude of the triangular wave signal Vosc emitted from the oscillator 5 is sufficiently large, the switching of the high-voltage side switching element TH and the low-voltage side switching element TL is performed. Of the feedback resistors R1 and R2 using the resistance values r1 and r2.
D = r1 / (r1 + r2)
The output voltage Vout is
Vout = Vin × D = Vin × r1 / (r1 + r2)
It can be expressed as.

(2) Test for Driving High Voltage Side Switching Element TH Next, when performing a test for driving the high voltage side switching element TH, the test signal Ptest is set to H level and the test signal Ntest is set to L level. As a result, the test signal Test that is the logical sum of the test signals Ptest and Ntest becomes the H level.
As a result, the switch T1 is turned off, the switches G4 and G5 are closed, the pre-driver 7 is deactivated, the output terminal of the comparator 4 is connected to the gate of the high-voltage side switching element TH, and the switch Since T2 is turned on and the switch G1 is opened, the input voltage Vin is applied to the gate of the first current path securing element THp, and the first current path securing element THp is turned off.

Further, the switch T3 is turned on, the switch G6 is opened, the pre-driver 8 is deactivated, the ground potential is connected to the gate of the low-voltage side switching element TL, and the low-voltage side switching element TL is turned off. At the same time, since the switch T4 is turned off and the switch G2 is closed, the bias voltage Nbias is applied to the gate of the second current path securing element TLp, and the second current path securing element TLp is turned on. That is, the low-voltage side switching element TL that is not subject to the current test is turned off, but the second current path securing element TLp connected in parallel to the low-voltage side switching element TL is turned on. A current path is secured in place of the low-voltage side switching element TL.
Further, when the switch G3 is closed, the first pad P1 and the second pad P2 are short-circuited, and an H-level test signal Test is input to the first selector 11 and the second selector 12, respectively. As a result, the differential signal Vdif output from the amplifier 1 is input to the positive input terminal of the comparator 4 and the output signal from the comparator 4 is input to the negative input terminal of the comparator 4. The differential signal Vdif output from the amplifier 1 is output from the comparator 4 as it is, functioning as a “1” buffer.

  As a result, the linear regulator shown in FIG. 2 is formed. That is, the negative feedback is formed without connecting an external element between the first pad P1 and the second pad P2, and the output output to the coupling portion A of the high-voltage side switching element TH and the low-voltage side switching element TL. The voltage Vout is divided by the pair of feedback resistors R1 and R2, and the difference between the divided voltage Vdiv and the reference voltage Vref generated by the reference voltage generation circuit 2 is amplified by the amplifier 1 to become a difference signal Vdif. Is input to the gate of the high-voltage side switching element TH via the capacitor 4 and the oscillation prevention resistor R3.

(3) Test for driving the low-voltage side switching element TL When performing the test for driving the low-voltage side switching element TL, the test signal Ptest is set to the L level and the test signal Ntest is set to the H level. The test signal Test, which is the logical sum of the test signals Ptest and Ntest, is at the H level.
As a result, the switch T1 is turned on, the switch G5 is opened, the pre-driver 7 is deactivated, the input voltage Vin is applied to the gate of the high voltage side switching element TH, and the high voltage side switching element TH is turned off. Since the switch T2 is turned off and the switch G1 is closed, the bias voltage Pbias is applied to the gate of the first current path securing element THp so that the first current path securing element THp is turned on. Become. That is, the high-voltage side switching element TH that is not subject to the current test is turned off, but the first current path securing element THp connected in parallel to the high-voltage side switching element TH is turned on. A current path is secured in place of the high-voltage side switching element TH.

Further, the switch T3 is turned off, the switches G4 and G6 are closed, the pre-driver 8 is inactivated, the output terminal of the comparator 4 is connected to the gate of the low-voltage side switching element TL, and the switch T4 Is turned on and the switch G2 is opened, so that the ground potential is connected to the gate of the second current path securing element TLp, and the second current path securing element TLp is turned off.
Further, when the switch G3 is closed, the first pad P1 and the second pad P2 are short-circuited, and an H-level test signal Test is input to the first selector 11 and the second selector 12, respectively. As a result, the differential signal Vdif output from the amplifier 1 is input to the positive input terminal of the comparator 4 and the output signal from the comparator 4 is input to the negative input terminal of the comparator 4. The differential signal Vdif output from the amplifier 1 is output from the comparator 4 as it is, functioning as a “1” buffer.

  As a result, the linear regulator shown in FIG. 3 is formed. That is, the negative feedback is formed without connecting an external element between the first pad P1 and the second pad P2, and the output output to the coupling portion A of the high-voltage side switching element TH and the low-voltage side switching element TL. The voltage Vout is divided by the pair of feedback resistors R1 and R2, and the difference between the divided voltage Vdiv and the reference voltage Vref generated by the reference voltage generation circuit 2 is amplified by the amplifier 1 to become a difference signal Vdif. The voltage is input to the gate of the low-voltage side switching element TL via the capacitor 4 and the oscillation prevention resistor R3.

  As described above, by setting the levels of the test signals Ptest and Ntest, respectively, as described in (2) Test for driving the high-voltage side switching element TH and (3) Test for driving the low-voltage side switching element TL. Since the negative feedback can be formed without connecting an external element between the first pad P1 and the second pad P2, and the step-down converter circuit according to the embodiment can be operated as a linear regulator, the probe card Can be used to simultaneously perform a probe test on a plurality of elements in the step-down converter circuit. Specifically, a test can be performed on the feedback resistors R1 and R2, the amplifier 1, the reference voltage generation circuit 2, the comparator 4, the high-voltage side switching element TH, and the low-voltage side switching element TL.

Even when operating as a linear regulator, if the gain of the amplifier 1 is sufficiently large, the output voltage Vout is
Vout = Vin × r1 / (r1 + r2)
And can be considered equivalent to the output voltage Vout when operating as a step-down converter.

  The present invention can also be applied to a step-down converter circuit configured by combining the high-voltage side switching element TH and the low-voltage side switching element TL in multiple stages. In this case, the high-voltage side switching element TH and It becomes possible to test the low voltage side switching element TL.

DESCRIPTION OF SYMBOLS 1 Amplifier, 2 Reference voltage generation circuit, 3 RC circuit, 4 Comparator, 5 Oscillator, 6 Control circuit, 7 and 8 Pre-driver, 9 Bias voltage generation circuit, 11 1st selector, 12 2nd selector, TH high voltage side switching element, TL low voltage side switching element, THp first current path securing element, TLp second current path securing element, T1 to T4 switch, G1 to G6 switch, P1 first pad, P2 Second pad, R1, R2 feedback resistor, R3 oscillation prevention resistor, A, B coupling unit, Vin input voltage, Vout output voltage, Vdiv divided voltage, Vref reference voltage, Vdiff differential signal, Vosc oscillation signal, Spwm PWM signal, Ptest, Ntest, Test Test signal.

Claims (5)

A high-voltage side switching element and a low-voltage side switching element connected in series between the input voltage and the ground potential, and the voltage output to the coupling portion of the high-voltage side switching element and the low-voltage side switching element is a pair of feedback resistors After the voltage is divided and the difference signal between the divided voltage and the reference voltage is amplified by an amplifier, the high voltage is obtained based on the PWM signal obtained by comparing the amplified difference signal with a predetermined oscillation signal by a comparator. In the step-down converter circuit for switching the side switching element and the low-voltage side switching element in a complementary manner,
A first pad connected to a coupling portion of the high-voltage side switching element and the low-voltage side switching element;
A second pad connected to the high-voltage side ends of the pair of feedback resistors;
A first selector for selecting one of the predetermined oscillation signal and the differential signal amplified by the amplifier and inputting the selected signal to a first input of the comparator;
A second selector that selects one of the differential signal amplified by the amplifier and the output signal of the comparator and inputs the selected signal to the second input of the comparator;
A first switch for switching between an output of the comparator and a control terminal of the high-voltage side switching element;
A second switch for opening and closing between the output of the comparator and the control terminal of the low-voltage side switching element, and short-circuiting between the first pad and the second pad and the first selection The differential signal amplified by the amplifier by the comparator is input to the first input of the comparator and the output signal of the comparator is input to the second input of the comparator by the second selector. A test is performed in which the high-voltage side switching element is driven by closing the first switch and opening the second switch, and opening the first switch and closing the second switch. The step-down converter circuit is characterized in that a test is performed by driving the low-voltage side switching element.   An external element is connected between the first pad and the second pad, and the first selector inputs the predetermined oscillation signal to the first input of the comparator, and the second selector. The differential signal amplified by the amplifier is input to the second input of the comparator and both the first switch and the second switch are opened, so that the high-voltage side switching element and the low-voltage side switching are opened. The step-down converter circuit according to claim 1, wherein the voltage output to the coupling portion of the elements is smoothed by the external element to become an output voltage.   3. The step-down converter circuit according to claim 1, further comprising a third switch that opens and closes between the first pad and the second pad. A first current path securing element connected in parallel with the high-voltage side switching element;
A second current path securing element connected in parallel with the low-voltage side switching element;
A reference voltage generating circuit for generating the reference voltage;
Bias voltage generation circuit for generating a bias voltage to be supplied to control terminals of the first current path securing element and the second current path securing element based on the reference voltage generated by the reference voltage generation circuit The step-down converter circuit according to any one of claims 1 to 3, further comprising: A high-voltage side switching element and a low-voltage side switching element connected in series between the input voltage and the ground potential, and the voltage output to the coupling portion of the high-voltage side switching element and the low-voltage side switching element is a pair of feedback resistors After the voltage is divided and the difference signal between the divided voltage and the reference voltage is amplified by an amplifier, the high voltage is obtained based on the PWM signal obtained by comparing the amplified difference signal with a predetermined oscillation signal by a comparator. In a test method of a step-down converter circuit that complementarily switches a side switching element and the low-voltage side switching element,
Short-circuiting between the first pad connected to the coupling portion of the high-voltage side switching element and the low-voltage side switching element and the second pad connected to the high-voltage side end of the pair of feedback resistors,
Instead of inputting the predetermined oscillation signal and the differential signal amplified by the amplifier to the comparator, the differential signal amplified by the amplifier and the output signal of the comparator are input to the comparator,
Of the high-voltage side switching element and the low-voltage side switching element, a test is performed by driving the high-voltage side switching element by inputting the output of the comparator only to a control terminal of the high-voltage side switching element and the low-voltage side switching element. A test method for a step-down converter circuit, wherein a test is performed by driving the low-voltage side switching element by inputting the output of the comparator only to a control terminal of the element.

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