DC-DC converter, control circuit and semiconductor device

Abstract

To provide a DC-DC converter capable of determining deterioration at a soldering part of a capacitor.SOLUTION: A DC-DC converter 1 includes switching elements 2, 3, an inductor 4 connected to the switching elements 2, 3, a capacitor 5 connected to the inductor 4, and a control circuit 10 for performing on-off control of the switching elements 2, 3 based on a PWM signal. The control circuit 10 includes: a digital filter for calculating a duty command value for controlling a duty of the PWM signal based on an error value between a target voltage and an output voltage Vout; an initial data storage part for storing transition of the duty command value at initial state as initial data; and a comparing part for determining deterioration for at least one of the switching elements 2, 3, the inductor 4, and the capacitor 5, by comparing the initial data and comparison data.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present disclosure relate to a DC-DC converter, a control circuit, and a semiconductor device.

Background Art

[0002] A DC-DC converter that supplies a stable output voltage to a load circuit includes switching elements, inductors, capacitors, etc. as components. Therefore, when the DC-DC converter repeats temperature cycles, cracks occur in the solder joints of the components that make it up, the conduction resistance increases, and eventually it fails. If the DC-DC converter fails, there is a risk that damage will spread, such as destroying the load circuit. For this reason, it is desirable for the DC-DC converter to have a failure prediction function that notifies the user of the precursors of failure before the failure occurs and perform preventive maintenance.

[0003] As a method for predicting the failure of a DC-DC converter, a technique has been proposed in which the theoretical value of the duty of the PWM signal for driving the switching element is compared with the actual duty, and when the error between the theoretical value and the actual value is large, it is determined as abnormal and a FAULT signal is output (see, for example, Patent Document 1). In Patent Document 1, when the solder joints of the switching element or the inductor deteriorate, a change in the direction in which the duty increases is detected to predict the precursor of failure.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the conventional technology has a problem that it cannot predict the precursor of failure when the solder of the capacitor part deteriorates.

[0006] The present disclosure provides a DC-DC converter, a control circuit, and a semiconductor device that can predict a precursor of a failure even when the soldered portion of a capacitor deteriorates.

Means for Solving the Problems

[0007] The DC-DC converter of the present disclosure is a DC-DC converter including a switching element, an inductor connected to the switching element, a capacitor connected to the inductor, and a control circuit that controls on / off of the switching element based on a PWM signal, and includes a duty calculation unit that calculates a duty command value for controlling the duty of the PWM signal based on an error value between a target voltage and an output voltage, an initial data storage unit that stores a transition of the duty command value in an initial state as initial data, a comparison data collection unit that collects a transition of the duty command value calculated by the duty calculation unit as comparison data, and a comparison unit that determines deterioration of a soldered portion of the capacitor by comparing a jitter of the duty command value with respect to a theoretical value with the initial data and the comparison data.

Effects of the Invention

[0008] The DC-DC converter of the present disclosure can detect a change in jitter with respect to a theoretical value of a Duty command value caused by unstable feedback control even when the solder of the capacitor portion deteriorates, can predict a precursor of a failure, and can perform preventive maintenance.

Brief Description of the Drawings

[0009]

Figure 1

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Mode for Carrying Out the Invention

[0010] Hereinafter, preferred embodiments of the present invention will be described based on the accompanying drawings.

[0011] (First Embodiment) The DCDC converter 1 of the first embodiment is a buck converter that controls power by PWM (Pulse Width Modulation). The DCDC converter 1 steps down the input voltage Vin and supplies an output voltage Vout that is feedback-controlled to be equal to the target voltage value to a load circuit (Load) 6.

[0012] Referring to FIG. 1, the DCDC converter 1 includes a high-side switching element 2, a low-side switching element 3, an inductor 4, a capacitor 5, and a control circuit 10. Hereinafter, the switching element 2 and the switching element 3 will be described as MOS-FETs, but the present invention is not limited thereto.

[0013] The drain terminal of the switching element 2 is connected to the positive electrode of the input voltage Vin, and the source terminal of the switching element 2 is connected to one end of the inductor 4 and the drain terminal of the switching element 3. The other end of the inductor 4 is connected to the positive electrode side terminal of the capacitor 5. The source terminal of the switching element 3 and the negative electrode side input terminal of the capacitor 5 are connected to a common line having the same potential as the negative electrode of the input voltage Vin.

[0014] The control circuit 10 is an information processing circuit such as a microcomputer including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc. A control program for controlling the operation of the DCDC converter 1 is stored in the ROM. The control circuit 10 reads out the control program stored in the ROM and expands the control program in the RAM to control the entire apparatus.

[0015] The control circuit 10 ― outputs drive signals SW, SW based on the generated PWM signal to the gate terminals of the switching element 2 and the switching element 3, respectively, and exclusively controls the on / off of the switching element 2 and the switching element 3. By controlling the on / off of the switching element 2 and the switching element 3, the current passing through the inductor 4 is supplied to the capacitor 5 and the load circuit 6, generating a stable output voltage Vout.

[0016] The control circuit 10 includes an ADC (Analog-to-Digital Converter) 11, a subtractor 12, a digital filter 13, a PWM generation unit 14, an initial data collection and storage unit 15, and a determination unit 16. Part or all of the control circuit 10 can be configured as a control IC which is a semiconductor device integrated on a substrate.

[0017] The ADC 11 converts the output voltage Vout into a digital value of a predetermined number of bits and outputs the digital conversion value of the output voltage Vout to the subtractor 12.

[0018] The subtractor 12 generates an error value between the target voltage value, which is the digital conversion value of the target voltage, and the digital conversion value input from the ADC 11, and outputs the generated error value to the digital filter 13.

[0019] Based on the error value input from the subtractor 12 and the preset response characteristics (such as proportional gain, derivative gain, integral gain, etc.), the digital filter 13 performs PI or PID calculations, calculates a Duty command value for bringing the output voltage Vout closer to the target voltage, and outputs it to the PWM generation unit 14.

[0020] The PWM generation unit 14 generates a PWM signal with a time ratio (duty ratio) based on the Duty command value input from the digital filter 13.

[0021] The initial data collection and storage unit 15 stores the transition of the Duty command value calculated by the digital filter 13 as initial data during a preset learning period after the first power-on.

[0022] After the learning period ends, the determination unit 16 performs a degradation determination based on the initial data in the initial data collection and storage unit 15 using the Duty command value calculated by the digital filter 13 as comparison data, and outputs a degradation signal FAULT when it determines that degradation has progressed.

[0023] The resistors R2 to R5 shown in FIG. 1 indicate the conduction losses of the switching element 2, the switching element 3, the inductor 4, and the capacitor 5, respectively. When the temperature cycle is repeated, cracks occur in the solder joints of the components, increasing the conduction loss.

[0024] Figure 2(a) shows the operation waveforms (load current Iout, PWM signal) when the conduction losses of resistors R2 to R5 are normal (initial state before power supply startup). Since the control circuit 10 employs digital control, quantization error occurs in the conversion value of the ADC11. Due to this quantization error, the Duty (Duty command value) of the PWM signal, as shown in Figure 3(a), exhibits some jitter (fluctuation) with respect to the theoretical value determined by the ratio of the input voltage Vin to the output voltage Vout (Vout / Vin), even when the load is constant. The PWM signal increases in Duty during heavy load (when the load current Iout rapidly increases) and decreases in Duty during light load (when the load current Iout rapidly decreases).

[0025] Figure 2(b) shows the operation waveforms (load current Iout, PWM signal) when the soldering part of capacitor 5 deteriorates and the conduction loss of resistor R5 increases. When the conduction loss of resistor R5 increases, the zero point Fz = 1 / (2×π×R1×C) determined by R5 and C (the capacitance of capacitor 5) moves to the low-frequency side. As a result, the frequency band becomes wider, the phase margin decreases, and the feedback control in the control circuit 10 becomes unstable. Consequently, the jitter of the Duty (Duty command value) of the PWM signal with respect to the theoretical value becomes larger than the normal jitter shown in Figure 3(a), as shown in Figure 3(b).

[0026] Figure 2(c) shows the operation waveforms (load current Iout, PWM signal) when the soldering parts of the switching element 2, switching element 3, and inductor 4 deteriorate and the conduction losses of resistors R2 to R4 increase. When at least one of the conduction losses of the conduction resistors R2 to R4 increases, the Duty (Duty command value) of the PWM signal is controlled to have a wider Duty than the theoretical value. As a result, the error amount of the Duty (Duty command value) of the PWM signal with respect to the theoretical value becomes larger than the normal error amount shown in Figure 3(a), as shown in Figure 3(c).

[0027] Referring to Fig. 4(a), the initial data collection and storage unit 15 includes an initial data collection unit 151, an initial data temporary storage unit 152, and an initial data storage unit 153. The initial data collection unit 151 collects the Duty command value calculated by the digital filter 13 at each time during a preset learning period after the first power-on, and stores the collected Duty command value as initial data in the initial data temporary storage unit 152 and the initial data storage unit 153. The initial data is array data including a time concept showing the transition of the Duty command value as shown in Fig. 2. The initial data temporary storage unit 152 is composed of registers whose data is erased when the power is turned off, and the initial data storage unit 153 is composed of a non-volatile memory whose data is not erased when the power is turned off. When the power is turned on after being turned off once, the initial data is loaded from the initial data storage unit 153 to the initial data temporary storage unit 152.

[0028] Referring to Fig. 4(b), the determination unit 16 includes a comparison data collection unit 161, a comparison data temporary storage unit 162, and a comparison unit 163. The comparison data collection unit 161 collects the Duty command value calculated by the digital filter 13 at each time during a predetermined period, and stores the collected Duty command value as comparison data in the comparison data temporary storage unit 162. The comparison data is array data including a time concept showing the transition of the Duty command value as shown in Fig. 2. The comparison data temporary storage unit 162 is composed of registers whose data is erased when the power is turned off. The timing at which the comparison data collection unit 161 collects the comparison data can be appropriately set according to the power-on time, power-on duration, etc.

[0029] The comparison unit 163 determines whether there is deterioration by comparing the comparison data stored in the comparison data temporary storage unit 162 with the initial data stored in the initial data temporary storage unit 152. The comparison unit 163 determines whether there is deterioration by comparing the jitter and error amount of the Duty (Duty command value) of the PWM signal with the comparison data and the initial data. Note that the theoretical value of the Duty (Duty command value) is determined by the ratio of the input voltage Vin to the output voltage Vout (Vout / Vin), but it can be set as a fixed value when the changes in the input voltage Vin and the output voltage Vout are negligible.

[0030] Next, the operation of collecting the initial data and the comparison data will be described in detail with reference to FIG. When the power is turned on, the control circuit 10 determines whether or not the power is turned on for the first time (step S101). If the power is turned on for the initial state in step S101, the initial data collection unit 151 of the initial data collection and storage unit 15 performs an operation of collecting initial data.

[0031] The initial data collection unit 151 sets a variable n to 1 (step S102), collects the duty command values calculated by the digital filter 13, and stores the collected duty command values in the initial data temporary storage unit 152 and the initial data storage unit 153 as the n-th initial data (step S103).

[0032] The initial data collection unit 151 increments the variable n (step S104) and determines whether the variable n has reached a preset number N of initial data collections (step S105). If the variable n is less than the number N of initial data collections in step S105, the initial data collection unit 151 returns to step S103 and collects the next duty command value calculated by the digital filter 13.

[0033] Collection of duty command values is repeated until the variable n reaches the number of initial data collections N. When the variable n reaches the number of initial data collections N in step S105, the initial data is stored in the initial data temporary storage unit 152 and the initial data storage unit 153 as array data, which is the transition of N duty command values collected during a preset learning period after the first power-on.

[0034] If the power is not turned on in the initial state in step S101, or if the variable n reaches the initial data collection number N in step S105, the comparison data collection unit 161 of the determination unit 16 waits for a preset comparison data collection timing (step S106). When the comparison data collection timing is reached in step S106, the comparison data collection unit 161 executes an operation of collecting comparison data.

[0035] The comparison data collection unit 161 sets 1 to the variable m (step S107), collects the Duty command value calculated by the digital filter 13, and stores the collected Duty command value in the comparison data temporary storage unit 162 as the m-th comparison data (step S108).

[0036] The comparison data collection unit 161 increments the variable m (step S109) and determines whether the variable m has reached the preset comparison data collection count M (step S110). If the variable m is less than the comparison data collection count M in step S110, the comparison data collection unit 161 returns to step S108 and then collects the Duty command value calculated by the digital filter 13.

[0037] The collection of the Duty command value is repeated until the variable m reaches the comparison data collection count M. When the variable m reaches the comparison data collection count M in step S105, the comparison data is stored in the comparison data temporary storage unit 162 as array data of the transition of the collected M Duty command values.

[0038] When the comparison data consisting of M Duty command values is stored in the comparison data temporary storage unit 162, the comparison unit 163 of the determination unit 16 performs a degradation determination by comparing with the initial data stored in the initial data temporary storage unit 152 (step S111).

[0039] The comparison unit 163 determines whether there is degradation in the determination result of step S111 (step S112). If the determination result in step S112 indicates degradation, the comparison unit 163 outputs a degradation signal FAULT for notifying the user of the precursor of a failure (step S113). With the degradation signal FAULT, the user can recognize the degradation of the soldering parts of the components (switching element 2, switching element 3, inductor 4, capacitor 5) constituting the DCDC converter 1 and perform preventive maintenance. If the determination result in step S112 indicates no degradation, the comparison data collection unit 161 deletes the comparison data (step S114) and returns to step S106 to wait for the next comparison data collection timing.

[0040] Next, the deterioration determination operation in step S111 will be described in detail with reference to FIG. 6. The comparison unit 163 sets 1 to the variable n (step S201), and calculates the absolute value of the difference between the n-th Duty command value of the initial data and the theoretical value as the error Dref n (step S202). The comparison unit 163 increments the variable n (step S203) and determines whether the variable n has reached the preset initial data collection number N (step S204).

[0041] If the variable n is less than the initial data collection number N in step S204, it returns to step S202 to calculate the error Dref n between the n-th Duty command value of the initial data and the theoretical value.

[0042] If the variable n reaches the initial data collection number N in step S204, the comparison unit 163 calculates the initial error integrated value Dref N obtained by integrating the errors Dref1 to Dref 1-N (step S205).

[0043] Next, the comparison unit 163 sets 1 to the variable m (step S206), and calculates the absolute value of the difference between the m-th Duty command value of the comparison data and the theoretical value as the error Dcmp m (step S202). The comparison unit 163 increments the variable n (step S203) and determines whether the variable n has reached the preset initial data collection number N (step S204).

[0044] If the variable n is less than the initial data collection number N in step S204, it returns to step S202 to calculate the error Dref n between the n-th Duty command value of the learning data and the theoretical value.

[0045] If the variable n reaches less than the initial data collection number N in step S204, the comparison unit 163 calculates the errors Dref1 to Dcmp calculated in step S202m The initial error integrated value Dref obtained by integrating 1-N is calculated (step S205).

[0046] The comparison unit 163 sets 1 to the variable m (step S206), and calculates the absolute value of the difference between the m-th Duty command value of the comparison data and the theoretical value as the error Dcmp m (step S207). The comparison unit 163 increments the variable m (step S208) and determines whether the variable m has reached the preset comparison data collection number M (step S209).

[0047] If the variable m is less than the comparison data collection number M in step S209, it returns to step S207 to calculate the error Dcmp m between the m-th Duty command value of the comparison data and the theoretical value.

[0048] If the variable n reaches the comparison data collection number M in step S209, the comparison unit 163 calculates the comparison error integrated value Dcmp M obtained by integrating the errors Dcmp1 to Dcmp 1-M calculated in step S207 (step S210).

[0049] Next, the comparison unit 163 determines whether the difference between the comparison error integrated value Dcmp 1-M calculated in step S210 and the initial error integrated value Dref 1-N calculated in step S205 is greater than or equal to a preset deterioration threshold (step S211). Note that the initial data collection number N and the comparison data collection number M should be the same so that the initial data and the comparison data can be compared under the same conditions. When the initial data collection number N and the comparison data collection number M are different, it is advisable to compare Dcmp 1-M / M with Dref 1-N / N.

[0050] In step S211, the comparison error integrated value Dcmp 1-M and the initial error integrated value Dref 1-NWhen the difference from [a certain value] is equal to or greater than the deterioration threshold value, the comparison unit 163 determines that there is deterioration (step S212). In step S211, the comparison error integrated value Dcmp 1-M and the initial error integrated value Dref 1-N When the difference between them is less than the deterioration threshold value, it is determined that there is no deterioration (step S213).

[0051] Referring to FIG. 7, the comparison error integrated value Dcmp 1-M increases as the deterioration of the soldered parts of the components (switching element 2, switching element 3, inductor 4, capacitor 5) constituting the DC-DC converter 1 progresses. That is, the comparison error integrated value Dcmp 1-M and the initial error integrated value Dref 1-N in the initial state, the difference between them increases as the deterioration of the soldered parts progresses. Therefore, by setting an appropriate deterioration threshold value, the deterioration of the soldered parts of the components (switching element 2, switching element 3, inductor 4, capacitor 5) constituting the DC-DC converter 1 can be detected.

[0052] The initial error integrated value Dref 1-N and the comparison error integrated value Dcmp 1-M Referring to FIGS. 2(a), (b) and FIGS. 3(a), (b), they become values corresponding to the jitter with respect to the theoretical value of the Duty (Duty command value) of the PWM signal. Therefore, the initial error integrated value Dref 1-N and the comparison error integrated value Dcmp 1-M are the initial data conversion value and the comparison data conversion value indicating the magnitude of the jitter with respect to the theoretical value of the Duty (Duty command value).

[0053] The initial error integrated value Dref 1-N and the comparison error integrated value Dcmp 1-M Referring to FIGS. 2(a), (c) and FIGS. 3(a), (c), they become values corresponding to the error amount with respect to the theoretical value of the Duty (Duty command value) of the PWM signal. Therefore, the initial error integrated value Dref 1-N and the comparison error integrated value Dcmp 1-M are also the initial data conversion value and the comparison data conversion value indicating the error amount with respect to the theoretical value of the Duty (Duty command value).

[0054] Initial error integrated value Dref 1-N is calculated when the initial data collection unit 151 collects initial data, and the initial error integrated value Dref 1-N may be stored in the initial data temporary storage unit 152 and the initial data storage unit 153 as initial data. In this case, the storage capacities of the initial data temporary storage unit 152 and the initial data storage unit 153 can be reduced.

[0055] The comparison unit 163 can also perform a deterioration determination of the soldering part by analyzing the change in the Duty command value for each time. For example, as shown in FIG. 8, the comparison unit 163 can detect that a difference in tendency has occurred when the period of the Duty command value change varies between the initial data and the comparison data. By using array data considering the time concept for the initial data and the comparison data, finer changes can be detected, and highly accurate deterioration prediction can be performed. The comparison unit 163 may use artificial intelligence such as machine learning as a means of trend analysis. Also, as a method for quantitatively grasping the change in the Duty command value, fast Fourier transform may be used.

[0056] The initial data stored in the initial data storage unit 153 may be prepared in advance or provided from the outside as data accumulated in the cloud or the like. In this case, since a program for the initial data collection operation is not required, the control of the control circuit 10 can be simplified.

[0057] (Second Embodiment) Referring to FIG. 9, the DCDC converter 1a of the second embodiment includes a temperature detection unit 17 in the control circuit 10a in addition to the configuration of the DCDC converter 1 of the first embodiment. The temperature detection unit 17 detects the ambient temperature. The on-resistances of the switching element 2 and the switching element 3 have temperature characteristics, and the on-resistance increases as the temperature rises. For this reason, even if the deterioration of the soldering part has not progressed, the Duty command value increases in a high-temperature state, and an accurate determination of the presence or absence of deterioration cannot be made.

[0058] Therefore, as shown in FIG. 10, the initial data and the comparison data are array data including the ambient temperature measured by the temperature detection unit 17. The comparison unit 163 compares the initial data with the comparison data in consideration of the change in the on-resistance due to the temperature change, and performs a deterioration determination. Thereby, more accurate deterioration detection can be performed.

[0059] (Third Embodiment) Referring to FIG. 11, the DCDC converter 1b of the third embodiment includes a current detection unit 18 in the control circuit 10b in addition to the configuration of the DCDC converter 1a of the second embodiment. The current detection unit 18 detects the current flowing through the inductor 4.

[0060] As shown in FIG. 12, the initial data and the comparison data are array data including the current measurement value measured by the current detection unit 18. The comparison unit 163 analyzes the change in the current measurement value and the Duty command value at each time to determine the deterioration of the soldering part. Thereby, the comparison unit 163 can detect a finer change and perform more accurate deterioration detection.

[0061] (Fourth Embodiment) The DCDC converter 1c of the fourth embodiment is different from the DCDC converter 1 of the first embodiment in that it is a boost converter that controls power by PWM (Pulse Width Modulation). The DCDC converter 1c excites energy in the inductor 4 during the period when the switching element 3 is on and the switching element 2 is off, and discharges the energy stored in the inductor 4 to the capacitor 5 and the load circuit 6 during the period when the switching element 3 is off and the switching element 2 is on.

[0062] The DCDC converter 1c shows that the present disclosure can also be applied to a boost converter which is another power supply topology. Thus, the present disclosure can also be applied to various power supply topologies such as a buck-boost converter.

[0063] The following summarizes the key points in the above embodiments. This embodiment is a DC-DC converter 1 including switching elements 2 and 3, an inductor 4 connected to the switching elements 2 and 3, a capacitor 5 connected to the inductor 4, and a control circuit 10 for controlling the on / off of the switching elements 2 and 3 based on a PWM signal. The control circuit 10 includes a digital filter 13 (duty calculation unit) that calculates a duty command value (duty command value) for controlling the duty of the PWM signal based on the error value between the target voltage and the output voltage Vout, an initial data storage unit 153 that stores the transition of the duty command value in the initial state as initial data, a comparison data collection unit 161 that collects the transition of the duty command value calculated by the digital filter 13 as comparison data, and a comparison unit 163 that determines the deterioration of the soldered portion of the capacitor 5 by comparing the jitter of the duty command value with respect to the theoretical value using the initial data and the comparison data. Due to this feature, even when the solder of the capacitor portion deteriorates, the DC-DC converter 1 can detect the change in the jitter of the duty command value with respect to the theoretical value caused by unstable feedback control, predict the precursor of a failure, and perform preventive maintenance.

[0064] Further, according to this embodiment, an initial data collection unit 151 is provided that stores the transition of the duty command value calculated by the digital filter 13 as initial data in the initial data storage unit 153 during the learning period of the initial state. Due to this feature, the initial data can reflect the characteristics of each device.

[0065] Further, according to this embodiment, the initial data is stored in the initial data storage unit 153 as an initial error integrated value Dref obtained by integrating the error between the duty command value and the theoretical value. The comparison unit 163 converts the duty command value in the comparison data into a comparison error integrated value Dcmp obtained by integrating the error with the theoretical value, and determines the deterioration of the soldered portion of the capacitor 5 by comparing the initial error integrated value Dref with the comparison error integrated value Dcmp. 1-N 1-M 1-N 1-M ​​​​Due to this feature, since the control circuit 10 does not require a program for the initial data collection operation, the control can be simplified. The initial error integrated value Dref 1-N and the comparison error integrated value Dcmp 1-M can be used to perform degradation determination through a simple comparison between them.

[0066] Also, according to this embodiment, the initial data and the comparison data are array data of the Duty command value for each time, and the comparison unit 163 performs degradation determination by analyzing the trends of the initial data and the comparison data. Due to this feature, the comparison unit 163 can perform a more accurate degradation determination including the concept of time.

[0067] Also, according to this embodiment, a temperature detection unit 17 for detecting the ambient temperature is provided, and the initial data and the comparison data include the temperature for each time detected by the temperature detection unit 17. Due to this feature, the comparison unit 163 has the advantage of being able to perform degradation detection considering the temperature dependence of the on-resistance of the switching elements 2 and 3.

[0068] Also, according to this embodiment, a current detection unit 18 for detecting the current flowing through the inductor 4 is provided, and the initial data and the comparison data include the current for each time detected by the current detection unit 18. Due to this feature, the comparison unit 163 can perform a more accurate degradation determination by performing degradation analysis considering the inductor current.

[0069] It should be noted that the present invention is not limited to the above-described embodiments, and it is obvious that each embodiment can be appropriately changed within the scope of the technical idea of the present invention. Also, the number, position, shape, etc. of the above-described components are not limited to the above embodiments, and can be set to appropriate numbers, positions, shapes, etc. for implementing the present invention. Note that the same reference numerals are assigned to the same components in each figure.

Explanation of Reference Numerals

[0070] 1, 1a, 1b, 1c DCDC converter 2, 3 Switching element 4 Inductor 5 Capacitor 6 Load Circuit 10, 10a, 10b Control Circuit 11 ADC 12 Subtractor 13 Digital Filter 14 PWM Generation Unit 15 Initial Data Collection and Storage Unit 16 Judgment Unit 17 Temperature Detection Unit 18 Current Detection Unit 151 Initial Data Collection Unit 152 Initial Data Temporary Storage Unit 153 Initial Data Storage Unit 161 Comparison Data Collection Unit 162 Comparison Data Temporary Storage Unit 163 Comparison Unit

Claims

1. A DC-DC converter comprising a switching element, an inductor connected to the switching element, a capacitor connected to the inductor, and a control circuit for controlling the on / off of the switching element based on a PWM signal, wherein a duty calculation unit that calculates a duty command value for controlling the duty of the PWM signal based on an error value between a target voltage and an output voltage; an initial data storage unit that stores the transition of the duty command value in an initial state as initial data; a comparison data collection unit that collects the transition of the duty command value calculated by the duty calculation unit as comparison data; a comparison unit that compares the jitter of the duty command value with respect to the theoretical value using the initial data and the comparison data to determine the deterioration of the soldered portion of the capacitor. The DC-DC converter is characterized by comprising the comparison unit.

2. The DC-DC converter according to claim 1, further comprising an initial data collection unit that stores, as the initial data, the transition of the duty command value calculated by the duty calculation unit in an initial data storage unit during a learning period in an initial state.

3. The initial data is stored in the initial data storage unit as an initial error integrated value obtained by integrating the error between the duty command value and the theoretical value, The comparison unit converts the duty command value in the comparison data into a comparison error integrated value obtained by integrating the error with the theoretical value, and compares the initial error integrated value with the comparison error integrated value to determine the deterioration of the soldered portion of the capacitor. The DC-DC converter according to claim 1 or 2 is characterized by performing the determination.

4. The initial data and the comparison data are array data of the duty command value at each time, The comparison unit determines the deterioration by trend analysis of the initial data and the comparison data. The DC-DC converter according to claim 1 or 2 is characterized by performing the determination.

5. Comprising a temperature detection unit for detecting the ambient temperature, The initial data and the comparison data include the temperature at each time detected by the temperature detection unit. The DC-DC converter according to claim 4 is characterized by including the temperature.

6. Comprising a current detection unit for detecting the current flowing through the inductor, The initial data and the comparison data include the current at each time detected by the current detection unit. The DC-DC converter according to claim 4 is characterized by including the current.

7. A control circuit for controlling a DC-DC converter including a switching element, an inductor connected to the switching element, and a capacitor connected to the inductor, a PWM generation unit that generates a PWM signal for on / off control of the switching element, a duty calculation unit that calculates a duty command value for controlling the duty of the PWM signal based on an error value between a target voltage and an output voltage, an initial data storage unit that stores the transition of the duty command value in an initial state as initial data, a comparison data collection unit that collects the transition of the duty command value calculated by the duty calculation unit as comparison data, and a comparison unit that determines deterioration of a soldered portion of the capacitor by comparing jitter with respect to a theoretical value of the duty command value using the initial data and the comparison data. A control circuit characterized by comprising:

8. A semiconductor device characterized in that the control circuit according to claim 7 is integrated on a substrate.

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