DC-DC converter and semiconductor integrated circuit for power source

Abstract

To reduce the number of large-capacity ceramic capacitors used that make up the bypass capacitor of a DC-DC converter and to reduce the total capacitance value of the large-capacity ceramic capacitors.SOLUTION: In a DC-DC converter equipped with a high-side switch and its on / off control circuit, a switch element is connected between a voltage input terminal and the high-side switch, at least one capacitor constituting a first bypass capacitor is connected to the voltage input terminal, one capacitor constituting a second bypass capacitor is connected to a connection node between the high-side switch and the switch element, and an abnormality detection circuit is provided which monitors the current flowing through the high-side switch or the voltage at the connection node to detect whether the second bypass capacitor is short-circuited, and the switch element is turned off in response to the abnormality detection circuit detecting a short-circuit in the second bypass capacitor.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a DC-DC converter and a power supply semiconductor integrated circuit (power supply IC) that converts and supplies DC voltage, and relates to technology that is effective when used, for example, in an in-vehicle step-down DC-DC converter and the power supply IC that constitutes it. [Background technology]

[0002] Some in-vehicle power supply devices use a DC-DC converter that steps down and outputs a direct current voltage from a battery (see, for example, Patent Document 1). Some DC-DC converters use an IC (power supply IC) that incorporates a switching element connected between a voltage input terminal and a voltage output terminal, and a control circuit that controls the on / off of this switching element, and is configured to convert and output the input voltage by turning the switching element on and off. In addition, bypass capacitors are connected to the voltage input terminals of power supply devices and power supply ICs connected to the battery to reduce noise in the power supply line and suppress power supply fluctuations.

[0003] Meanwhile, lead-acid batteries are generally used in vehicles (excluding electric vehicles), and surge protection is required when the power is cut off. The voltage of an automotive battery using lead-acid batteries is usually 12 to 14 V, but when considering surge protection, bypass capacitors may need to be able to withstand a voltage of around 40 V. Furthermore, surface-mount ceramic capacitors have generally been used as bypass capacitors in automotive power supplies, but the higher the withstand voltage and capacity of these surface-mount ceramic capacitors, the larger their cost and size become.

[0004] Furthermore, a technique is known in which two ceramic capacitors are connected in series to compensate for the withstand voltage of the bypass capacitor and to prevent short circuits, since the possibility of two capacitors shorting out at the same time is extremely low. For example, Patent Document 2 shows in FIG. 1 a power supply device in which two ceramic capacitors are connected in series as a countermeasure against short circuits. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-205295 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-55634 Summary of the Invention [Problem to be solved by the invention]

[0006] When two capacitors are connected in series to form a bypass capacitor, the capacitance required is twice that of a single capacitor. Also, a single series connection cannot handle open circuit faults where the capacitors become disconnected. For this reason, as shown in Figure 2, two series capacitors are sometimes connected as bypass capacitors between the voltage input terminal VIN of the power supply IC10 that makes up the DC-DC converter and the ground point.

[0007] However, if two rows of capacitors are connected in series as shown in Figure 2, a total of four capacitors are required. Moreover, since the original purpose of bypass capacitors requires each capacitor to have a large capacitance value of around 10 μF, there are issues with significantly increasing component costs and mounting area. Furthermore, if the bypass capacitor shorts out, a large current will flow between the voltage input terminal VIN and the ground terminal GND of IC10, which could damage the IC.

[0008] The above-mentioned Patent Document 2 describes an invention that eliminates the need for a series capacitor as a bypass capacitor by preventing overcurrent from flowing when a ceramic capacitor connected to the voltage input terminal of an IC is short-circuited. However, this invention prevents overcurrent from flowing to the output terminal, so it requires a resistive element for overcurrent detection, and does not completely cut off the current supplied to the downstream regulator.

[0009] The present invention has been made in light of the above-mentioned background, and its object is to provide a DC-DC converter and a power supply semiconductor integrated circuit that can reduce the number of large-capacity ceramic capacitors used in bypass capacitors and the total capacitance value, thereby preventing increases in cost and mounting area. Another object of the present invention is to provide a DC-DC converter and a power supply semiconductor integrated circuit that can prevent damage to electronic components due to a large current flow when a short circuit occurs in one of the ceramic capacitors that make up the bypass capacitor. [Means for solving the problem]

[0010] In order to achieve the above object, the present invention provides a first switch element and a second switch element or a rectifier element connected in series between a voltage input terminal to which a DC voltage from a battery is input and a ground potential point; an inductor having one terminal connected to a first connection node between the first switch element and the second switch element or the rectifier element; and a control circuit that controls the on / off of the first switch element or the first switch element and the second switch element in accordance with a feedback voltage of a voltage output via the inductor, wherein the DC-DC converter converts and outputs a voltage input to the voltage input terminal, a third switch element is connected between the voltage input terminal and the first switch element; At least one capacitor constituting a first bypass capacitor is connected to the voltage input terminal; a capacitor constituting a second bypass capacitor is connected to a second connection node between the first switch element and the third switch element; an abnormality detection circuit that monitors the current flowing through the first switch element or the voltage of the second connection node to detect whether a capacitor constituting the second bypass capacitor is short-circuited; The third switch element is configured to be turned off in response to the abnormality detection circuit detecting a short circuit in a capacitor that constitutes the second bypass capacitor.

[0011] A DC-DC converter having the above configuration includes a first bypass capacitor consisting of at least one capacitor and a second bypass capacitor consisting of one capacitor, so the capacitance value of the ceramic capacitor that constitutes the first bypass capacitor can be reduced, thereby reducing the number of large-capacity ceramic capacitors used and the total capacitance value, and suppressing increases in cost and mounting area.

[0012] Furthermore, although the second bypass capacitor consists of a single capacitor, a switch element is provided between the voltage input terminal and the output transistor, and this switch element turns off when a short circuit in the second bypass capacitor is detected, so even if the second bypass capacitor shorts out, it is possible to prevent a large current from flowing and damaging the components that make up the DC-DC converter.On the other hand, the first bypass capacitor is configured as a series capacitor, which provides short circuit protection, so even if one of the capacitors shorts out, a large current will not flow.

[0013] Furthermore, because the second bypass capacitor can be configured with a single ceramic capacitor, when the parts other than the bypass capacitor are configured as an IC, the internal ESR (equivalent series resistance) of the capacitor is smaller than when two are connected in series. This reduces the impedance of the hot loop that passes through the second bypass capacitor and the first switch element in the IC, improving the operational stability of the IC and reducing high-frequency noise that enters from the power supply line connected to the battery. [Effects of the Invention]

[0014] The DC-DC converter and power supply IC of the present invention can reduce the number of large-capacity ceramic capacitors used in the bypass capacitor and the total capacitance value, thereby suppressing cost increases. Furthermore, if a short circuit occurs in one of the ceramic capacitors that make up the bypass capacitor, it is possible to prevent large currents from flowing and damaging electronic components. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a circuit diagram showing an embodiment of a power supply IC to which the present invention is applied and an example of a DC-DC converter using the same; [Figure 2] FIG. 1 is a circuit diagram showing an example of a DC-DC converter using a conventional power supply IC. [Figure 3] FIG. 2 is a circuit diagram showing a modified example of the DC-DC converter according to the embodiment of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Figure 1 shows a switching-type step-down DC-DC converter as one embodiment of a DC-DC converter according to the present invention. In Figure 1, the area enclosed by dashed-dotted line A is formed as a semiconductor integrated circuit (power supply IC) 10 on a semiconductor chip such as single-crystal silicon. The DC-DC converter of this embodiment is a power supply device suitable for use in a vehicle that uses a lead battery as the battery, and supplies power to on-board loads such as electrical components and electronic devices (not shown) mounted on the vehicle.

[0017] In the DC-DC converter of this embodiment shown in FIG. 1, a high-side switch S1 and a low-side switch S2 each made of an N-channel MOS transistor are provided within a power supply IC 10, and a filter circuit 30 made of an inductor L1 and a capacitor C0 is connected to an external terminal SW connected to a connection node N1 between the switches S1 and S2, and the external terminal SW is connected to an output terminal OUT via the filter circuit 30.

[0018] Furthermore, two series capacitors C1, C2 and two series capacitors C3, C4 are connected in parallel as bypass capacitors between voltage input terminal VIN, to which DC voltage from battery 20 is input, and ground potential. High-voltage ceramic capacitors are used for capacitors C1, C2; C3, C4. Furthermore, the power supply IC 10 is provided with an external terminal BC for connecting a capacitor C5, which serves as a second bypass capacitor, in addition to the capacitors C1 to C4.

[0019] Furthermore, in the power supply IC 10 of this embodiment, switches S3 and S4 made of N-channel MOS transistors are connected in series between the voltage input terminal VIN and the high-side switch S1, and a circuit 17 is provided for generating signals that control the on / off of these switches S3 and S4. The reason for connecting the two switches S3 and S4 in series is to prevent reverse current flow through parasitic diodes in the substrates of the MOS transistors of the switches S3 and S4 when the voltage at the voltage input terminal VIN becomes relatively lower than the voltage at the output terminal OUT while the switches S3 and S4 are off. In other words, the MOS transistors constituting the switches S3 and S4 are connected so that the respective parasitic diodes are reverse-directed. In principle, a single switch may be used as the switches S3 and S4.

[0020] When the switches S3 and S4 are turned on, the capacitor C5 connected to the external terminal BC is connected in parallel with the capacitors C1, C2, C3, and C4 connected to the voltage input terminal VIN, and therefore functions as a second bypass capacitor. Therefore, in this embodiment, a high-voltage ceramic capacitor is also used for the capacitor C5. However, the capacitance value of the capacitor C5, which is the second bypass capacitor, can be different from the capacitance values ​​of the capacitors C1 to C4, which are the first bypass capacitors.

[0021] Specifically, when realizing in the DC-DC converter of this embodiment a bypass capacitor having characteristics equivalent to the bypass capacitor consisting of four capacitors C1 to C4 in the conventional DC-DC converter shown in FIG. 2, if the capacitance values ​​of the four capacitors C1 to C4 in the DC-DC converter shown in FIG. 2 are each set to 10 μF, then in the DC-DC converter of this embodiment, if the capacitance value of capacitor C5 is set to 10 μF, then capacitors C1 to C4 will only need to have a capacitance value of 1 μF. In the semiconductor market at the time of filing, 1 μF capacitors were available for less than one-tenth the price of 10 μF capacitors. Therefore, in the case of the DC-DC converter of this embodiment, although the number of capacitors used increases by one compared to the conventional converter (FIG. 2), the total cost can be reduced to about one-third. Furthermore, because the size of a 1 μF capacitor is significantly smaller than that of a 10 μF capacitor, the mounting area of ​​the entire bypass capacitors (C1 to C5) can also be reduced.

[0022] Furthermore, the reason for using two series capacitors as bypass capacitors is, as mentioned above, to prevent a large current from continuing to flow if one capacitor is shorted. In the power supply IC 10 of this embodiment, switches S3 and S4 are provided between the voltage input terminal VIN and the high-side switch S1, and if capacitor C5 connected to the newly provided external terminal BC is shorted, simply turning off switches S3 and S4 eliminates the need to connect two bypass capacitors in series. Furthermore, by using a single stage capacitor instead of two in series like capacitor C5, it is possible to reduce the impedance between the external terminal BC and the ground potential point due to the capacitor's internal ESR (equivalent series resistance), which results in a power supply IC with a hot loop with good characteristics, improving the operational stability of the IC and reducing high-frequency noise.

[0023] Next, a description will be given of the configuration of the power supply IC 10 of this embodiment, which includes a circuit that controls the on / off of the switches S3 and S4 connected between the voltage input terminal VIN and the high-side switch S1. As shown in FIG. 1, the power supply IC 10 of this embodiment includes an external terminal VO to which an output voltage Vout is input, an error amplifier 11 that amplifies the potential difference between a feedback voltage VFB divided by resistors R1 and R2 connected in series between the terminal VO and a ground terminal GND and a predetermined reference voltage Vref, a waveform generating circuit 12 that includes an oscillator circuit OSC and generates a triangular wave (sawtooth wave) of a predetermined frequency, and a PWM comparator 13 that receives as input the waveform signal generated by the waveform generating circuit 12 and the output of the error amplifier 11.

[0024] The control IC 10 also includes a switch control circuit (SW control circuit) 14 that generates control signals for controlling the high-side switch S1 and the low-side switch S2 on and off based on the output of the PWM comparator 13, and drive circuits (drivers DRV) 15a and 15b that generate and output on and off drive signals for the switches S1 and S2 in accordance with the on and off control signals generated by the switch control circuit 14.

[0025] Furthermore, the control IC 10 includes an abnormality detection circuit 16 that detects abnormal conditions such as a short circuit state of the capacitor C5 connected to the external terminal BC, an on / off control circuit 17 that generates a signal to control the on / off of switches S3 and S4 connected between the voltage input terminal VIN and the high-side switch S1 when a short circuit is detected, a logic circuit 18 that generates a short detection signal to the on / off control circuit 17 based on the abnormality detection signal from the abnormality detection circuit 16, and an internal power supply circuit 19 that consists of a linear regulator such as a series regulator that generates an internal power supply voltage VDD (e.g., 5 V) for operating the internal circuitry of the IC based on the battery voltage input to the voltage input terminal VIN.

[0026] The control IC 10 also has an external terminal CE to which a chip enable signal that is supplied from an external CPU or the like and that instructs the IC to be turned on or off is input, and the internal power supply circuit 19 operates according to the state of the external terminal CE, and also has the function of generating an enable signal EN and supplying it to the logic circuit 18 and the like. The abnormality detection circuit 16 is configured to monitor the voltage Vin2 at the connection node N2 between the newly provided switch S4 and the high-side switch S1 or the current flowing through the high-side switch S1 to detect a short-circuit state of the capacitor C5.

[0027] For example, if capacitor C5 shorts out, the current flowing through the hot loop passing through capacitor C5 and high-side switch S1 increases. Therefore, a current detection amplifier is provided that receives the drain voltage (voltage Vin2 at connection node N2) and source voltage (voltage Vn1 at connection node N1) of high-side switch S1 as inputs. When the current flowing through high-side switch S1 increases by a predetermined value or more, it can be determined that capacitor C5 has shorted out. Alternatively, when capacitor C5 shorts out, the current increases and the voltage Vin2 at connection node N2 decreases. Therefore, when voltage Vin2 falls below a predetermined potential, it can be determined that capacitor C5 has shorted out. Furthermore, both the current flowing through high-side switch S1 and the voltage Vin2 at connection node N2 may be monitored to determine whether capacitor C5 has shorted out.

[0028] Furthermore, the abnormality detection circuit 16 has a function of detecting abnormal states such as an output overvoltage or low voltage based on the feedback voltage VFB divided by resistors R1 and R2 connected to the external terminal VO. Note that an output low voltage state may also be detected by directly monitoring the voltage of the external terminal VO. Furthermore, the control IC 10 has an external terminal FLG for outputting an abnormality flag signal that notifies the outside of the IC that an abnormality has been detected, and an open-drain N-channel MOS transistor Q1 connected to the terminal FLG.

[0029] When the abnormality detection circuit 16 detects a short-circuit state of the capacitor C5, the logic circuit 18 generates a short-circuit detection signal SD and supplies it to the on / off control circuit 17. Upon receiving the short-circuit detection signal SD, the on / off control circuit 17 turns off the switches S3 and S4. Furthermore, when the abnormality detection circuit 16 detects a short-circuit state of the capacitor C5, it turns on the transistor Q1 connected to the external terminal FLG. Although not particularly limited, the abnormality detection circuit 16 has a function of calculating the logical sum of a plurality of abnormality detection results, and also turns on the transistor Q1 when it detects an abnormal state such as an output overvoltage or low voltage.

[0030] A pull-up resistor Rp is connected to the signal line connected to the external terminal FLG. When the transistor Q1 is turned on, current flows through the pull-up resistor Rp, causing the voltage on the signal line to drop, allowing an external device to know that an abnormality has occurred in the control IC 10. In addition, the short detection signal SD generated by the logic circuit 18 is also supplied to the switch control circuit 14, and the switch control circuit 14 is configured to stop the on / off control of the high-side switch S1 and the low-side switch S2 upon receiving the short detection signal SD.

[0031] The abnormality detection circuit 16 may be provided with a temperature detection element to detect when the IC chip temperature rises above a predetermined value or a function to detect overcurrent, so that the operation of the IC can be stopped when an abnormality in the chip temperature or an overcurrent is detected. Also, in order to notify the outside that such an abnormality has been detected, the power supply IC 10 may be configured to have a plurality of external terminals FLG for outputting abnormality flag signals so that the type of abnormality can be distinguished and output. Furthermore, the power supply IC 10 may be provided with a soft start circuit that suppresses inrush current at startup to prevent overshoot of the output voltage.

[0032] In the above embodiment, two sets of bypass capacitors C1, C2; C3, C4 connected in series are connected to the voltage input terminal VIN as a countermeasure against capacitor shorts, but by providing a separate short countermeasure, two bypass capacitors C1, C3 may be connected in parallel to the voltage input terminal VIN as shown in Fig. 3. As described in the aforementioned prior art patent document 2, for example, a technique for countering bypass capacitor shorts is known, which provides a means for detecting current, such as a sense resistor, and a means for limiting or cutting off the current when an abnormal current due to a capacitor short is detected. Therefore, it is conceivable to utilize such a technique.

[0033] Furthermore, since the basic operation of the DC-DC converter is not affected even if the bypass capacitor connected to the voltage input terminal VIN becomes disconnected, a system that allows the bypass capacitor to become disconnected is also possible. Therefore, the bypass capacitor connected to the voltage input terminal VIN can be a set of two series capacitors (C1, C2 or C3, C4) or just one capacitor (C1 or C3). Even when using a set of two series capacitors or just one capacitor, the capacitance of the bypass capacitor connected to the voltage input terminal VIN can be reduced by providing a second bypass capacitor C5 and setting its capacitance value to a large value.

[0034] The invention made by the inventor has been specifically described above based on embodiments, but the present invention is not limited to the above embodiments. For example, in the above embodiments, an example was described in which the present invention is applied to a synchronous rectification DC-DC converter equipped with a high-side switch and a low-side switch, but the present invention may also be applied to a DC-DC converter that uses a diode instead of the low-side switch and the power supply IC that constitutes it. Furthermore, the present invention is not limited to switching-type DC-DC converters, and can also be applied to DC-DC converters such as linear regulators and the power supply IC that constitutes them.

[0035] In addition, in the above embodiment, the high-side switch S1 and the low-side switch S2 are configured as on-chip elements, but these elements may also be discrete transistors. Similarly, the switches S3 and S4 connected between the voltage input terminal VIN and the high-side switch S1 may also be external discrete transistors. In that case, the power supply IC 10 may be provided with terminals for outputting the on / off control signals for the switches S3 and S4 generated by the on / off control circuit 17 to the outside. Furthermore, in the above embodiment, the functions of the power supply IC 10 are realized by one IC, but may be configured by a plurality of ICs or electronic components. [Explanation of symbols]

[0036] 10...power supply IC, 11...error amplifier, 12...waveform generation circuit, 13...PWM comparator, 14...switch control circuit, 15a, 15b...drive circuit, 16...abnormality detection circuit, 17...on / off control circuit, 18...logic circuit, 19...internal power supply circuit, S1...high-side switch, S2...low-side switch, S3, S4...switch, C1, C2; C3, C4; C5...bypass capacitor, BC...external terminal for connecting bypass capacitor, 20...battery

Claims

1. a first switch element and a second switch element or a rectifier element connected in series between a voltage input terminal to which a DC voltage from a battery is input and a ground potential point; an inductor having one terminal connected to a first connection node between the first switch element and the second switch element or the rectifier element; and a control circuit that controls the on / off of the first switch element or the first switch element and the second switch element in accordance with a feedback voltage of a voltage output via the inductor, wherein the DC-DC converter converts and outputs a voltage input to the voltage input terminal, a third switch element is connected between the voltage input terminal and the first switch element; At least one capacitor constituting a first bypass capacitor is connected to the voltage input terminal; a capacitor constituting a second bypass capacitor is connected to a second connection node between the first switch element and the third switch element; an abnormality detection circuit that monitors the current flowing through the first switch element or the voltage of the second connection node to detect whether a capacitor constituting the second bypass capacitor is short-circuited; a third switch element that is turned off in response to detection by the abnormality detection circuit of a short circuit in a capacitor that constitutes the second bypass capacitor;

2. the battery is a lead-acid battery mounted on a vehicle, 2. The DC-DC converter according to claim 1, wherein a voltage obtained by converting a voltage input to said voltage input terminal is supplied to an on-vehicle load.

3. a voltage input terminal to which a DC voltage from a battery is input; a first external terminal to which one terminal of an external inductor is connected; a ground terminal to which a ground potential is applied; a second external terminal to which the voltage output via the inductor is input; a first switch element connected between the voltage input terminal and the first external terminal; a second switch element or rectifier element connected between the first external terminal and the ground terminal; a control circuit that controls the first switch element or the first switch element and the second switch element to be turned on and off in response to a feedback voltage of a voltage input to the second external terminal; A power supply semiconductor integrated circuit comprising: a third switch element connected between the voltage input terminal and the first switch element; a third external terminal connected to a connection node between the third switch element and the first switch element and to which one terminal of an externally arranged capacitor is connected; an abnormality detection circuit that monitors the current flowing through the first switch element or the voltage of the connection node to detect whether the capacitor connected to the third external terminal is short-circuited, 2. The semiconductor integrated circuit for a power supply, wherein the third switch element is turned off in response to the abnormality detection circuit detecting a short circuit of the capacitor.

4. the third switch element is composed of two MOS transistors connected in series, 4. The power supply semiconductor integrated circuit according to claim 3, wherein the two MOS transistors are connected so that their parasitic diodes face in opposite directions.

5. a power supply semiconductor integrated circuit according to claim 3 or 4; an inductor that is arranged externally and has one terminal connected to the first external terminal and the other terminal connected to an output terminal; a first bypass capacitor comprising at least one ceramic capacitor disposed externally and connected in series between the voltage input terminal and a ground potential point; a second bypass capacitor comprising at least one ceramic capacitor disposed externally and connected between the third external terminal and a ground potential point; A DC-DC converter comprising:

6. 6. The DC-DC converter according to claim 5, wherein the first bypass capacitor is configured by connecting a plurality of pairs of ceramic capacitors in series in parallel.

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