DC-DC converter, integrated circuit and target voltage generation circuit

Abstract

To provide a DCDC converter capable of outputting a highly accurate power supply voltage.SOLUTION: A DCDC converter, for controlling an output voltage Vout by an error signal between a feedback voltage VFB and a target voltage VREF, includes: a temperature sensor 18; a BG circuit 12 for generating a reference voltage VBG; a compensation calculator 24 for calculating a compensation value from a detected temperature of the temperature sensor 18 using a quadratic function of temperature T; a subtractor 25 for generating a target value DREF by compensating the target initial value DREF0 with the compensation value; and a DAC 22 for converting the target value DREF to the target voltage VREF using the reference voltage VBG.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a DC-DC converter that uses a reference voltage source. [Background technology]

[0002] DCDC converters generally use a bandgap reference circuit as the reference voltage to generate a stable reference voltage. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5590240 Summary of the Invention [Problem to be solved by the invention]

[0004] However, bandgap reference circuits have slight temperature characteristics, which causes the output voltage of DC-DC converters to be temperature dependent. In recent years, DC-DC converters are required to provide highly accurate power supply voltages to loads such as SoCs and FPGAs. Therefore, the slight temperature dependency of DC-DC converters makes it difficult to meet the accuracy requirements of loads that require highly accurate power supply voltages.

[0005] As a technology for improving temperature characteristics, there is disclosed a technology for improving the temperature dependency of output current by controlling it according to the value of a temperature sensor based on a coefficient stored in advance in a flash memory (see, for example, Patent Document 1).

[0006] Patent Document 1 cannot perform optimal temperature compensation when the temperature characteristics themselves vary. Since Patent Document 1 is limited to the output current source, it cannot improve the temperature characteristics of the output voltage of the DC-DC converter.

[0007] The present invention has been made in view of the above problems, and an object of the present invention is to provide a DC-DC converter that can output a highly accurate power supply voltage. [Means for solving the problem]

[0008] In order to achieve the above object, the DC-DC converter and the target voltage generating circuit according to the present invention are configured as follows. The DC-DC converter according to the present invention is a DC-DC converter that controls the output voltage based on an error signal between a feedback voltage and a target voltage, and is characterized by comprising: a temperature sensor; a reference voltage generation circuit that generates a reference voltage; a compensation calculator that calculates a compensation value from the temperature detected by the temperature sensor using a quadratic function of temperature; a corrector that corrects a target initial value using the compensation value to generate a target value; and a digital-to-analog converter that converts the target value into the target voltage using the reference voltage. The integrated circuit according to the present invention is an integrated circuit that controls the output voltage of a DC-DC converter using an error signal between a feedback voltage and a target voltage, and is characterized by comprising: a temperature sensor; a reference voltage generation circuit that generates a reference voltage; a compensation calculator that calculates a compensation value from the temperature detected by the temperature sensor using a quadratic function of temperature; a corrector that corrects a target initial value using the compensation value to generate a target value; and a digital-to-analog converter that converts the target value into the target voltage using the reference voltage. The target voltage generation circuit according to the present invention is a target voltage generation circuit that generates a target voltage to be compared with a feedback voltage, and is characterized by comprising: a reference voltage generation circuit that generates a reference voltage; a compensation calculator that calculates a compensation value from a detected temperature input from a temperature sensor using a quadratic function of temperature; a corrector that corrects a target initial value with the compensation value to generate a target value; and a digital-to-analog converter that converts the target value into the target voltage. [Effects of the Invention]

[0009] The DC-DC converter of the present invention corrects the target voltage used to generate an error signal with the feedback voltage with a compensation value calculated using a quadratic function of temperature, so that the output voltage can be output as a highly accurate power supply voltage for SoCs, FPGAs, etc. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram showing a configuration of an embodiment of a DC-DC converter according to the present invention; [Figure 2] FIG. 10 is a diagram illustrating variations in output voltage. [Figure 3] 2 is a flowchart illustrating the operation of the target voltage generating circuit shown in FIG. [Figure 4] 10 is a flowchart illustrating an IC inspection configuration. [Figure 5] FIG. 10 is a diagram comparing the output voltage of conventional control with the output voltage of the control of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings.

[0012] Referring to FIG. 1, the DC-DC converter of this embodiment includes a control circuit 1, a reactor L, a capacitor C1, and resistors R1 and R2, and converts an input voltage Vin into an output voltage Vout and outputs it to a load PL.

[0013] The control circuit 1 is configured with an integrated circuit such as a switching regulator IC incorporating a switching element such as a power MOSFET, and includes an input terminal IN, a ground terminal GND, a switching output terminal SW, a feedback voltage input terminal VO, and a data input terminal D.

[0014] The control circuit 1 includes a series circuit 11 in which a switch element Q1 and a switch element Q2 are connected in series. The switch elements Q1 and Q2 are switching elements such as power MOSFETs. The series circuit 11 is connected between an input terminal IN to which an input voltage Vin is input and a ground terminal GND connected to a ground potential (ground: GND). The switch element Q1 is arranged on the input terminal IN side (high potential side), and the switch element Q2 is arranged on the ground terminal GND side (low potential side). The connection point between the switch elements Q1 and Q2 is connected to a switching output terminal SW.

[0015] A switching output terminal SW of the control circuit 1 is connected to the ground potential via a reactor L and a capacitor C1, and the connection point between the reactor L and the capacitor C1 serves as an output terminal of the output voltage Vout.

[0016] Resistors R1 and R2 are connected between the connection point of reactor L and capacitor C1 and ground potential. The connection point of resistors R1 and R2 is connected to feedback voltage input terminal VO of control circuit 1, and the voltage obtained by dividing output voltage Vout by resistors R1 and R2 is the feedback voltage V FB is input to the feedback voltage input terminal VO.

[0017] The control circuit 1 includes a flip-flop 12, an oscillator circuit (OSC) 13, a drive circuit (DRV) 14, an amplifier 15, a comparator 16, a current detection circuit (CS) 17, a temperature sensor 18, and a target voltage generation circuit 2.

[0018] The flip-flop 12 is an RS type. The output (output terminal Q) of the flip-flop 12 is input to a drive circuit 14, and the drive circuit 14 controls the on / off of the switch elements Q1 and Q2 in accordance with the output of the flip-flop 12.

[0019] A clock signal from an oscillation circuit 13 is input to a set terminal S of the flip-flop 12. The clock signal generated by the oscillation circuit 13 is a signal that determines a switching period. When the flip-flop 12 is set by the clock signal from the oscillation circuit 13, a drive circuit 14 controls the switch element Q1 to be on and the switch element Q2 to be off.

[0020] The feedback voltage V input to the feedback voltage input terminal VO FB is input to the inverting input terminal of the amplifier 15 via a resistor R4. The amplifier 15 is a differential amplifier whose output is negatively fed back via a capacitor C2 and a resistor R3. The amplifier 15 generates a feedback voltage V FB and the target voltage V of the non-inverting input terminal REF and outputs an error amplified signal.

[0021] Feedback voltage V FB and the target voltage V REF The error amplified signal is input to the inverting input terminal of comparator 16. A current signal detected by current detection circuit 17 is input to the non-inverting input terminal of comparator 16. Current detection circuit 17 detects the current flowing through switch element Q1 on the high side and inputs it to the non-inverting input terminal of comparator 16 as a current signal.

[0022] The flip-flop 12 is reset when the output of the comparator 16 is input to the reset terminal R and the current signal exceeds the error amplification signal. When the flip-flop 12 is reset, the drive circuit 14 turns off the switch element Q1 and turns on the switch element Q2. This causes the DC-DC converter to operate in peak current mode control.

[0023] The target voltage generating circuit 2 generates a target voltage to be input to the non-inverting input terminal of the amplifier 15. VREF The target voltage generating circuit 2 includes a BG circuit (bandgap reference circuit) 21, a DAC (digital-analog conversion circuit) 22, a memory 23, a compensation calculator 24, and a subtractor 25.

[0024] The DAC 22 outputs the reference voltage V BG Using the target value D REF target voltage V REF and input to the non-inverting input terminal of the amplifier 15.

[0025] The BG circuit 21 utilizes the temperature characteristics of the pn junction of a transistor to generate a stable reference voltage V BG This is a reference voltage generating circuit that generates a voltage, but it has a slight temperature characteristic.

[0026] The DC-DC converter corrects the slight temperature characteristic of the BG circuit 21 with a compensation value to obtain a target value D REF The compensation value is generated by a compensation calculator 24 based on the temperature T detected by the temperature sensor 18.

[0027] Temperature sensor 18 is a sensor circuit that detects temperature. Temperature sensor 18 generates a temperature detection voltage (such as the base-emitter voltage of a bipolar transistor) using a circuit element that has temperature dependency, and outputs the temperature detection voltage to compensation calculator 24. Temperature sensor 18 is disposed in control circuit 1 at a position where it can accurately detect the temperature of BG circuit 21.

[0028] As shown in Figure 2, the output voltage Vout of a DC-DC converter has absolute value variations due to variations in elements, and each has a different temperature characteristic. Figure 2 is a graph showing the output voltage Vout output by five DC-DC converters measured in the range of -40°C to 150°C. The temperature characteristic of the output voltage Vout shows a tendency to increase in both low and high temperature ranges.

[0029] Therefore, the feedback voltage V FB The relationship between the output voltage Vout and the temperature T is modeled as a quadratic function as shown in the following equation (1). In equation (1), coefficients a and b are temperature characteristic coefficients, and coefficient c is the feedback voltage V FB indicates the extreme value of .

[0030]

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[0031] By transforming equation (1), the temperature characteristic correction equation is given by equation (2).

[0032]

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[0033] Δc is an offset coefficient, which is written as a correction coefficient together with the temperature characteristic coefficients a and b into the memory 23 from the data input terminal D. The correction coefficients a, b, and Δc are values ​​obtained by actual measurements.

[0034] The memory 23 is a storage unit configured with a flash memory or the like, and stores the target initial value D REF0 is stored together with the correction coefficients a, b, and Δc. REF0 The correction coefficients a, b, and Δc may be stored in different locations.

[0035] 3, compensation calculator 24 loads correction coefficients a, b, and Δc when power is turned on (step S01). Next, compensation calculator 24 acquires temperature T input from temperature sensor 18 (step S02), and calculates a compensation value using equation (2) (step S03).

[0036] The subtractor 25 subtracts the target initial value D stored in the memory 23. REF0 Load the target initial value D REF0 The target value D is obtained by subtracting the compensation value calculated by the compensation calculator 24 from REF (Step S04). That is, the subtractor 25 generates the target initial value D REF0 is corrected by the compensation value to obtain the target value D REF It acts as a corrector that generates

[0037]

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[0038] The DAC 22 outputs the reference voltage V BG By multiplying the DA conversion coefficient using REF target voltage V REF (Step S05).

[0039]

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[0040] The compensation calculator 24 monitors the change in the temperature T input from the temperature sensor 18 at predetermined intervals (step S06). If there is a change in the temperature T, the compensation calculator 24 returns to step S03 and calculates a compensation value based on the changed temperature T. As a result, the target voltage V REF is changed to accommodate changes in temperature T during operation.

[0041] The correction coefficients a, b, and Δc are determined in the IC inspection process before shipment and written into the memory 23. The IC inspection process stores the target initial value D REF0 When the DC-DC converter is operated in the IC inspection process, the DAC22 stores the target initial value D REF0 The target initial voltage V REF0 and the DC-DC converter converts it into a feedback voltage V FB and the target initial voltage V REF0 It is controlled by the error amplification signal.

[0042] Referring to Figure 4, the DC-DC converter is operated in a low-temperature environment at temperature T1 (for example, the lower limit of the rated temperature), and the feedback voltage V FB1 is measured (step S11).

[0043] Next, the DC-DC converter is placed in a normal temperature environment (for example, room temperature) at temperature T2 and operated, and the feedback voltage V FB2 is measured (step S12).

[0044] Next, the DC-DC converter is operated in a high-temperature environment at temperature T3 (for example, the upper limit of the rated temperature), and the feedback voltage V FB3 (Step S13). The measurement time can be shortened by performing the measurements in order of increasing temperature, but there is no particular restriction on the order of measurements.

[0045] Next, the feedback voltage V at temperature T1 FB1 , feedback voltage V at temperature T2 FB2 , feedback voltage V at temperature T3 FB3 The correction coefficients a, b, and Δc are calculated using the above formula (step S14). The temperatures T1, T2, and T3 may be values ​​detected by the temperature sensor 18. In this case, by providing the control circuit 1 with a temperature output terminal that outputs the temperature T detected by the temperature sensor 18, the feedback voltage V FB1 , V FB2 , V FB3 The temperatures T1, T2, and T3 can be measured at the same time.

[0046] By solving the simultaneous equations of equation (1), the temperature characteristic coefficients a, b, and c are calculated using the following equations (5), (6), and (7).

[0047]

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[0048]

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[0049]

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[0050] In addition, the offset coefficient Δc is expressed as the feedback voltage V at temperature T2 (normal temperature environment) as shown in equation (8). FB2 and the target initial voltage VREF0 The target initial voltage V REF0 is the target initial value D REF0 is a constant obtained by multiplying by the DA conversion coefficient of the BG circuit 21.

[0051]

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[0052] On the other hand, since the calculation formulas for c and Δc are very complicated, taking into consideration the efficiency of the calculation and the performance of the equipment, c is set as the feedback voltage (V FB2 ) and Δc is the feedback voltage (V FB2 ) and target initial voltage (V REF0 ) can also be used as a difference. In this case, a simplified calculation method for Δc is shown in equation (9). Here, the target initial voltage (V REF0 ) is the target initial value (D REF0 ) by the DA change coefficient of the BG circuit 21.

[0053]

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[0054] Next, the correction coefficients a, b, and Δc calculated in step S14 are written into the memory 23 from the data input terminal D (step S15), and the IC inspection process is completed.

[0055] The equations (5), (6), and (7) can also be executed by the compensation calculator 24. In this case, the temperatures T1, T2, and T3 and the feedback voltage V FB1 , V FB2 , V FB3 and are written into the memory 23 from the data input terminal D, whereby the compensation calculator 24 calculates the correction coefficients a, b, and Δc, and further calculates the compensation value.

[0056] The offset coefficient Δc is calculated by calculating the feedback voltage V FBIn this case, the offset coefficient Δc is calculated by the remeasured feedback voltage V FB and the target initial voltage V REF0 This offset coefficient Δc correction process is performed by adjusting the feedback voltage V FB1 , V FB2 , V FB3 If this is continued into the final measurement process, the work time can be reduced.

[0057] Figure 5 shows the feedback voltage V FB and the target initial voltage V REF0 Conventional control using an error amplified signal with a feedback voltage V FB and the target voltage V corrected by the compensation value REF 5 is a graph comparing the output voltage Vout output by the conventional control and the output voltage Vout output by the control of the present invention using an error amplified signal. In Fig. 5, the output voltage Vout output by the conventional control is shown by a dotted line, and the output voltage Vout output by the control of the present invention is shown by a solid line.

[0058] As shown in Figures 5(a), (b), and (c), even when conventional control results in variations in temperature characteristics, the control of the present invention can cancel the temperature dependency. Furthermore, since it is possible to simultaneously correct variations in absolute value, it is possible to generate an ultra-high-precision output voltage.

[0059] In this embodiment, a peak current mode control DC-DC converter (Buck converter) has been described. However, the target voltage generating circuit 2 is also REF This technology can be applied to various electronic circuits that use current-mode control, voltage-mode control, hysteresis control, and other converters. It can also be applied to various power supply topologies, such as Boost converters, SEPIC converters, CUK converters, and flyback converters.

[0060] In this embodiment, the feedback voltage V FB The correction coefficients a, b, and Δc were calculated by measuring the reference voltage V BG The output terminal of the reference voltage V BGIt is also possible to directly measure the reference voltage V and calculate the correction coefficients a, b, and Δc. BG The temperature dependency of the output voltage Vout can be improved. BG This is effective when the temperature dependency is the main factor of the temperature dependency of the output voltage Vout.

[0061] As described above, in this embodiment, the feedback voltage V FB and the target voltage V REF The DC-DC converter controls the output voltage Vout based on an error signal between the temperature sensor 18 and the reference voltage V BG a BG circuit 21 (reference voltage generating circuit) that generates a reference voltage T; a compensation calculator 24 that calculates a compensation value from the temperature detected by the temperature sensor 18 using a quadratic function of the temperature T; and a target initial value D REF0 is corrected by the compensation value to obtain the target value D REF and a subtractor 25 (corrector) that generates a reference voltage V BG Using the target value D REF target voltage V REF and a DAC22 (digital-to-analog converter) for converting the signal into a digital signal. This configuration allows the feedback voltage V FB The target voltage V is used to generate the error signal between REF is corrected with a compensation value calculated using a quadratic function of temperature T, so the output voltage Vout can be output as a highly accurate power supply voltage for SoCs, FPGAs, etc.

[0062] Furthermore, in this embodiment, a memory 23 is provided in which the coefficients of the quadratic function are written as correction coefficients a, b, and Δc during pre-shipment inspection, and the compensation calculator 24 calculates a compensation value using the correction coefficients a, b, and Δc in the memory 23. With this configuration, the correction coefficients a, b, and Δc can be written according to the temperature characteristics of the product during the IC inspection process. The compensation calculator 24 can calculate the compensation value using the correction coefficients a, b, and Δc for each product, thereby achieving optimal temperature compensation for each product. Furthermore, the compensation value calculated using the correction coefficients a, b, and Δc for each product can simultaneously correct for absolute value variations, thereby improving the accuracy of the total output voltage Vout.

[0063] Furthermore, in this embodiment, the correction coefficients a, b, and Δc are calculated by the DAC 22 under three different temperature environments (temperatures T1, T2, and T3) to obtain the target initial value D REF0 Target initial voltage V converted from REF0 The feedback voltage V FB1 , V FB2 , V FB3 Based on the feedback voltage V FB is calculated by modeling it as a quadratic function of temperature.

[0064] Furthermore, in this embodiment, the target initial value D REF0 Target initial voltage V converted from REF0 The feedback voltage V FB1 , V FB2 , V FB3 The compensation calculator 24 calculates the actual measured values ​​(temperatures T1, T2, T3, feedback voltage V FB1 , V FB2 , V FB3 ) based on the feedback voltage V FB is modeled as a quadratic function of temperature to calculate correction coefficients a, b, and Δc, and the calculated correction coefficients a, b, and Δc are used to calculate the compensation value.

[0065] The method of calculating the correction coefficients a, b, and Δc is not limited to the embodiment of the present invention, and they may be calculated by the least squares method or the like. Furthermore, the measurement of the feedback voltage in the IC testing process is not limited to three different temperature environments, but it is also possible to increase the measurement temperature to four or five different environments.

[0066] It is clear that the present invention is not limited to the above-described embodiments, and that each embodiment can be appropriately modified within the scope of the technical concept of the present invention. Furthermore, the number, position, shape, etc. of the above-described components are not limited to the above-described embodiments, and the number, position, shape, etc. can be set to be suitable for implementing the present invention. Note that the same components are denoted by the same reference numerals in each drawing. [Explanation of symbols]

[0067] 1 Control circuit 2 Target voltage generation circuit 11 Series Circuits 12. Flip-Flop 13 Oscillator circuit (OSC) 14 Drive circuit 15 Amps 16 Comparators 17 Current detection circuit (CS) 18 Temperature Sensor 21 BG circuit (bandgap reference circuit) 22 DAC (digital-analog conversion circuit) 23 Memory 24 Compensation calculator 25 Subtractor

Claims

1. A DC-DC converter that controls an output voltage based on an error signal between a feedback voltage and a target voltage, A temperature sensor; a reference voltage generating circuit that generates a reference voltage; a compensation calculator that calculates a compensation value from the temperature detected by the temperature sensor using a quadratic function of temperature; a corrector that corrects a target initial value with the compensation value to generate a target value; a digital-to-analog converter that converts the target value into the target voltage using the reference voltage.

2. a memory in which the coefficients of the quadratic function are written as correction coefficients at the time of pre-shipment inspection; 2. The DC-DC converter according to claim 1, wherein the compensation calculator calculates the compensation value using the correction coefficient stored in the memory.

3. 3. The DC-DC converter according to claim 2, wherein the correction coefficient is calculated by modeling the feedback voltage as the quadratic function based on the feedback voltage actually measured under control using a target initial voltage converted from the target initial value by the digital-to-analog converter under three different temperature environments.

4. a memory in which the feedback voltages actually measured under control using a target initial voltage converted from the target initial value by the digital-to-analog converter under three different temperature environments are written as actual measurement values ​​during a pre-shipment inspection; 2. The DC-DC converter according to claim 1, wherein the compensation calculator models the feedback voltage as the quadratic function based on the actual measured value in the memory, calculates coefficients of the quadratic function as correction coefficients, and calculates the compensation value using the calculated correction coefficients.

5. 3. The DC-DC converter according to claim 2, wherein the correction coefficient is calculated by modeling the feedback voltage based on the feedback voltage actually measured under control using a target initial voltage converted from the target initial value by the digital-to-analog converter under at least three different temperature environments.

6. a memory in which the reference voltages actually measured under control using a target initial voltage converted from the target initial value by the digital-to-analog converter under three different temperature environments are written as actual measurement values ​​at the time of pre-shipment inspection; 2. The DC-DC converter according to claim 1, wherein the compensation calculator models the reference voltage as the quadratic function based on the actual measured value in the memory, calculates coefficients of the quadratic function as correction coefficients, and calculates the compensation value using the calculated correction coefficients.

7. An integrated circuit that controls the output voltage of a DC-DC converter using an error signal between a feedback voltage and a target voltage, A temperature sensor; a reference voltage generating circuit that generates a reference voltage; a compensation calculator that calculates a compensation value from the temperature detected by the temperature sensor using a quadratic function of temperature; a corrector that corrects a target initial value with the compensation value to generate a target value; a digital-to-analog converter that converts the target value into the target voltage using the reference voltage.

8. A target voltage generating circuit that generates a target voltage to be compared with a feedback voltage, a reference voltage generating circuit that generates a reference voltage; a compensation calculator that calculates a compensation value from the detected temperature input from the temperature sensor using a quadratic function of temperature; a corrector that corrects a target initial value with the compensation value to generate a target value; a digital-to-analog converter that converts the target value into the target voltage.

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