DC / DC converter control circuits and power supply circuits

Abstract

In the present invention, a main comparator 308 compares a feedback voltage VFB according to an output voltage VOUT of a DC / DC converter 100 with a reference voltage VREF, and asserts a turn-on signal S1 when the feedback voltage VFB falls below the reference voltage VREF. A timer circuit 320 generates a turn-off signal S2 subject to level transition after an ON time TON proportional to (VOUT-VIN) / VOUT has elapsed from the assertion of the turn-on signal S1.

Description

[Technical field]

[0001] The present disclosure relates to a DC / DC converter. [Background technology]

[0002] DC / DC converters are used when converting a DC voltage of one voltage value to a DC voltage of another voltage value. Ripple control is known as a control method for DC / DC converters. With ripple control, the output voltage of the DC / DC converter is compared with a threshold voltage, and when the output voltage exceeds (or falls below) the threshold voltage, this is used as a trigger to switch the switching transistor on and off. Compared to voltage mode control and current mode control using an error amplifier, the ripple control has the advantages of faster response speed and reduced power consumption. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-110530 A [Patent Document 2] JP 2017-169259 A Summary of the Invention [Problem to be solved by the invention]

[0004] The present inventors have investigated the application of bottom detection and constant on-time (COT) ripple control to a boost converter.

[0005] This method is easy to design because it does not require phase compensation, and has the advantage of being excellent in fast transient response. However, if the on-time is fixed, there is a problem that the switching frequency fluctuates significantly.

[0006] An aspect of the present disclosure has been made in view of the above-mentioned problems, and one of its exemplary objectives is to provide a control circuit for a step-up DC / DC converter capable of stabilizing a switching frequency.

[0007] Another exemplary object of an embodiment of the present disclosure is to provide a DC / DC converter and a control circuit thereof that are capable of reducing the output voltage in an overcurrent state. [Means for solving the problem]

[0008] 1. An embodiment of the present disclosure relates to an input voltage V IN The output voltage V OUT The control circuit compares a feedback voltage corresponding to the output voltage of the DC / DC converter with a reference voltage, and when the feedback voltage falls below the reference voltage, it asserts a turn-on signal. The control circuit includes a main comparator that asserts a turn-on signal and a control circuit that outputs a voltage (V OUT -V IN ) / V OUT and a timer circuit that generates a turn-off signal that transitions in level after an on-time proportional to the on-time has elapsed.

[0009] 2. A control circuit according to an embodiment of the present disclosure relates to a control circuit for a DC / DC converter having a switching transistor. The control circuit includes a main comparator that compares a feedback voltage corresponding to the output voltage of the DC / DC converter with a reference voltage and asserts a turn-on signal when the feedback voltage falls below the reference voltage, an on-time generating circuit that asserts a turn-off signal after an on-time has elapsed since the switching transistor is turned on, an overcurrent detection circuit that asserts an overcurrent detection signal when a current flowing through the switching transistor exceeds an overcurrent threshold during the on-time of the switching transistor, a turn-on inhibition circuit that generates a turn-on inhibition signal that is asserted during a period from the turning on of the switching transistor until a predetermined time has elapsed, a logic circuit that generates a pulse signal that transitions to an on level when the turn-on signal is asserted during a period in which the turn-on inhibition signal is negated and transitions to an off level when the turn-off signal or the overcurrent detection signal is asserted, and a driver that drives the switching transistor in response to the pulse signal.

[0010] Any combination of the above components or mutual substitution of the components or expressions of the present invention between methods, devices, systems, etc. are also valid as aspects of the present invention. Effect of the Invention

[0011] According to an aspect of the present disclosure, it is possible to stabilize the switching frequency of a step-up DC / DC converter. According to an aspect of the present disclosure, it is possible to reduce the output voltage in an overcurrent state of the DC / DC converter. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a circuit diagram of a DC / DC converter according to a first embodiment. [Diagram 2] FIG. 2 is an equivalent circuit diagram of the output circuit of the DC / DC converter. [Diagram 3] FIG. 3 is a circuit diagram showing the basic configuration of a timer circuit. [Figure 4] FIG. 4 is an operation waveform diagram of the timer circuit of FIG. [Diagram 5] FIG. 5 is a circuit diagram of a timer circuit according to Example 1.1. [Figure 6] FIG. 6 is an operation waveform diagram of the timer circuit of FIG. [Figure 7] FIG. 7 is a circuit diagram of a timer circuit according to Example 1.2. [Figure 8] FIG. 8 is an operation waveform diagram of the timer circuit of FIG. [Figure 9] FIG. 9 is a circuit diagram of a timer circuit according to the embodiment 1.3. [Figure 10] FIG. 10 is a circuit diagram of a timer circuit according to Example 1.4. [Figure 11] FIG. 11 is a circuit diagram of a DC / DC converter according to the second embodiment. [Figure 12] FIG. 12 is an operation waveform diagram of the DC / DC converter of FIG. 11 in a normal state (non-overcurrent state). [Figure 13] FIG. 13 is an operational waveform diagram of the DC / DC converter of FIG. 11 in an overcurrent state. [Figure 14] FIG. 14 is an equivalent circuit diagram of the output circuit of the DC / DC converter. [Figure 15] FIG. 15 is a circuit diagram showing a basic configuration of an on-time generating circuit. [Figure 16] FIG. 16 is an operation waveform diagram of the on-time generating circuit of FIG. [Figure 17] FIG. 17 is a circuit diagram of an on-time generating circuit according to the embodiment 2.1. [Figure 18] FIG. 18 is an operation waveform diagram of the on-time generating circuit of FIG. [Figure 19] FIG. 19 is a circuit diagram of an on-time generating circuit according to embodiment 2.2. [Figure 20] FIG. 20 is an operation waveform diagram of the on-time generating circuit of FIG. [Figure 21] FIG. 21 is a circuit diagram of an on-time generating circuit according to embodiment 2.3. [Figure 22]FIG. 22 is a circuit diagram of an on-time generating circuit according to embodiment 2.4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] (Overview of the embodiment) A summary of some exemplary embodiments of the present disclosure will be described. This summary is intended to provide a simplified summary of some concepts of one or more embodiments in order to provide a basic understanding of the embodiments as a prelude to the detailed description that follows, and is not intended to limit the scope of the invention or disclosure. Furthermore, this summary is not intended to be a comprehensive overview of all possible embodiments, nor is it intended to limit essential components of the embodiments. For convenience, the term "one embodiment" may be used to refer to one embodiment (example or variant) or multiple embodiments (examples or variants) disclosed in this specification.

[0014] 1. One embodiment disclosed herein is a power supply for an input voltage V IN The output voltage V OUT The control circuit compares a feedback voltage corresponding to the output voltage of the DC / DC converter with a reference voltage, and when the feedback voltage falls below the reference voltage, it asserts a turn-on signal. The control circuit includes a main comparator that asserts a turn-on signal and a control circuit that outputs a voltage (V OUT -V IN ) / V OUT and a timer circuit that generates a turn-off signal that transitions in level after an on-time proportional to the on-time has elapsed.

[0015] According to this embodiment, the on-time is adaptively changed in response to the input voltage and the output voltage, thereby making it possible to stabilize the switching frequency.

[0016] The timer circuit is connected to the first capacitor and V OUT A current source that generates a current proportional to OUT -V INand a comparator that detects the occurrence of a voltage change proportional to the input voltage. The current generated by the current source is I=α×V OUT The first capacitor is connected to the OUT -V IN ) proportional to the voltage change ΔV=β×(V OUT -V IN ) occurs. ON teeth, T ON =ΔV / I=β×(V OUT -V IN ) / (α×V OUT ) =(β / α)×(V OUT -V IN ) / V OUT Then, (V OUT -V IN ) / V OUT It is possible to generate an on-time proportional to

[0017] One end of the first capacitor may be grounded. OUT -V IN The comparator may further include a threshold voltage generating circuit that generates a threshold voltage according to the first capacitor.

[0018] The threshold voltage generating circuit may include a second capacitor. The threshold voltage generating circuit may be configured to, when the switching transistor is in an off state, set the second capacitor to (V OUT -V IN ), and during the ON period of the switching transistor, a switching voltage at the connection node between the inductor and the switching transistor is applied to one end of the second capacitor, and the voltage at the other end of the second capacitor may be set as the threshold voltage. The switching voltage during the ON period is I×R ON1 I is the current flowing through the switching transistor, R ON1 is the on-resistance of the switching transistor. Therefore, according to this configuration, it is possible to generate an on-time that takes into account the on-resistance of the switching transistor.

[0019] The threshold voltage generating circuit includes a second capacitor and an input voltage V IN a first selector that connects one end of the second capacitor to a connection node between the inductor and the switching transistor of the DC / DC converter during an on-period of the switching transistor, and an output voltage V OUT and a second selector that applies the voltage to the second capacitor and connects the other end of the second capacitor to the comparator during an on-period of the switching transistor. With this configuration, an on-time can be generated taking into account the on-resistance of the switching transistor.

[0020] The threshold voltage generating circuit may include an inverter that inverts a switching voltage generated at a connection node between an inductor and a switching transistor of the DC / DC converter, and a filter that smoothes the output of the inverter to generate a threshold voltage. With this configuration, it is possible to generate an on-time that takes into account the effects of the on-resistance of the switching transistor and the synchronous rectifier transistor, and the equivalent series resistance of the inductor.

[0021] The filter may be an RC filter. The threshold voltage generating circuitry, while operating in discontinuous current mode, drives a capacitor of the RC filter at V OUT -V IN According to this configuration, when returning from the discontinuous current mode to the continuous current mode, the operation can be resumed from an appropriate on-time.

[0022] The filter may be an RC filter including a resistor and a capacitor. The threshold voltage generating circuit applies the output voltage of the inverter to one end of the resistor during the continuous current mode, and applies the output voltage V OUT a third selector for applying a ground voltage to the other end of the capacitor during the continuous current mode and an input voltage V INand a fourth selector that applies the second selector to the first selector. With this configuration, when returning from the discontinuous current mode to the continuous current mode, operation can be resumed from an appropriate on-time.

[0023] One end of the first capacitor is connected to the input voltage V IN The comparator may be configured to convert the voltage at the other end of the first capacitor into an output voltage V OUT Since the on-resistance of the transistor and the equivalent series resistance of the inductor are ignored, the frequency becomes faster under heavy loads, but the on-time can be generated with a simple configuration.

[0024] The control circuit may be monolithically integrated on a single semiconductor substrate. "Monolithic integration" includes cases where all of the circuit components are formed on a semiconductor substrate, and cases where the main components of the circuit are monolithically integrated, and some resistors and capacitors for adjusting the circuit constants may be provided outside the semiconductor substrate. By integrating the circuit on a single chip, the circuit area can be reduced and the characteristics of the circuit elements can be kept uniform.

[0025] 2. One embodiment disclosed in this specification relates to a control circuit for a DC / DC converter having a switching transistor. The control circuit includes a main comparator that compares a feedback voltage corresponding to an output voltage of the DC / DC converter with a reference voltage and asserts a turn-on signal when the feedback voltage falls below the reference voltage, an on-time generating circuit that asserts a turn-off signal after an on-time has elapsed since the assertion of the turn-on signal, an overcurrent detection circuit that asserts an overcurrent detection signal when a current flowing through the switching transistor exceeds an overcurrent threshold during an on-period of the switching transistor, a turn-on inhibition circuit that generates a turn-on inhibition signal that is asserted during a period from the turning on of the switching transistor until a predetermined time has elapsed, a logic circuit that generates a pulse signal that transitions to an on level when the turn-on signal is asserted during a period in which the turn-on inhibition signal is negated and transitions to an off level when the turn-off signal or the overcurrent detection signal is asserted, and a driver that drives the switching transistor in response to the pulse signal.

[0026] According to this embodiment, the output voltage can be reduced in an overcurrent state.

[0027] The DC / DC converter operates on an input voltage V IN The output voltage V OUT It may be a boost type that generates

[0028] On time is (V OUT -V IN ) / V OUT The switching frequency can be stabilized by adaptively changing the on-time according to the input voltage and the output voltage.

[0029] The on-time generating circuit is connected to the first capacitor and V OUT A current source that generates a current proportional to OUT -V IN and a comparator that detects the occurrence of a voltage change proportional to the input voltage. The current generated by the current source is I=α×V OUT The first capacitor is connected to the OUT -V IN ) proportional to the voltage change ΔV=β×(V OUT -V IN ) occurs. ON teeth, T ON =ΔV / I=β×(V OUT -V IN ) / (α×V OUT ) =(β / α)×(V OUT -V IN ) / V OUT Then, (V OUT -V IN ) / V OUT It is possible to generate an on-time proportional to

[0030] One end of the first capacitor may be grounded. The on-time generating circuit includes: OUT -V IN The comparator may further include a threshold voltage generating circuit that generates a threshold voltage according to the first capacitor.

[0031] The threshold voltage generating circuit may include a second capacitor. The threshold voltage generating circuit may be configured to, when the switching transistor is in an off state, set the second capacitor to (V OUT -V IN ), and during the ON period of the switching transistor, a switching voltage at the connection node between the inductor and the switching transistor is applied to one end of the second capacitor, and the voltage at the other end of the second capacitor may be set as the threshold voltage. The switching voltage during the ON period is I×R ON1 I is the current flowing through the switching transistor, R ON1 is the on-resistance of the switching transistor. Therefore, according to this configuration, it is possible to generate an on-time that takes into account the on-resistance of the switching transistor.

[0032] The threshold voltage generating circuit includes a second capacitor and an input voltage V IN a first selector that connects one end of the second capacitor to a connection node between the inductor and the switching transistor of the DC / DC converter during an on-period of the switching transistor, and an output voltage V OUT and a second selector that applies the voltage to the second capacitor and connects the other end of the second capacitor to the comparator during an on-period of the switching transistor. With this configuration, an on-time can be generated taking into account the on-resistance of the switching transistor.

[0033] The threshold voltage generating circuit may include an inverter that inverts a switching voltage generated at a connection node between an inductor and a switching transistor of the DC / DC converter, and a filter that smoothes the output of the inverter to generate a threshold voltage. With this configuration, it is possible to generate an on-time that takes into account the effects of the on-resistance of the switching transistor and the synchronous rectifier transistor, and the equivalent series resistance of the inductor.

[0034] The filter may be an RC filter. The threshold voltage generating circuitry, while operating in discontinuous current mode, drives a capacitor of the RC filter at V OUT -V IN According to this configuration, when returning from the discontinuous current mode to the continuous current mode, the operation can be resumed from an appropriate on-time.

[0035] The filter may be an RC filter including a resistor and a capacitor. The threshold voltage generating circuit applies the output voltage of the inverter to one end of the resistor during the continuous current mode, and applies the output voltage V OUT a third selector for applying a ground voltage to the other end of the capacitor during the continuous current mode and an input voltage V INand a fourth selector that applies the second selector to the first selector. With this configuration, when returning from the discontinuous current mode to the continuous current mode, operation can be resumed from an appropriate on-time.

[0036] One end of the first capacitor is connected to the input voltage V IN The comparator may be configured to convert the voltage at the other end of the first capacitor into an output voltage V OUT Since the on-resistance of the transistor and the equivalent series resistance of the inductor are ignored, the frequency becomes faster under heavy loads, but the on-time can be generated with a simple configuration.

[0037] The control circuit may be monolithically integrated on a single semiconductor substrate. "Monolithic integration" includes cases where all of the circuit components are formed on a semiconductor substrate, and cases where the main components of the circuit are monolithically integrated, and some resistors and capacitors for adjusting the circuit constants may be provided outside the semiconductor substrate. By integrating the circuit on a single chip, the circuit area can be reduced and the characteristics of the circuit elements can be kept uniform.

[0038] (Embodiment) Hereinafter, the present disclosure will be described with reference to the drawings based on preferred embodiments. The same or equivalent components, parts, and processes shown in each drawing will be given the same reference numerals, and duplicated descriptions will be omitted as appropriate. In addition, the embodiments are illustrative and do not limit the invention, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention or disclosure.

[0039] In this specification, "a state in which component A is connected to component B" includes not only a case in which component A and component B are directly physically connected to each other, but also a case in which component A and component B are indirectly connected to each other via other components that do not substantially affect the electrical connection state between them or that do not impair the function or effect achieved by their combination.

[0040] Similarly, "a state in which component C is provided between components A and B" includes not only the case in which components A and C, or components B and C, are directly connected to each other, but also the case in which they are indirectly connected to each other via other components that do not substantially affect the electrical connection between them or that do not impair the functions or effects achieved by their combination.

[0041] Furthermore, "signal A (voltage, current) corresponds to signal B (voltage, current)" means that signal A has a correlation with signal B, specifically meaning (i) when signal A is signal B, (ii) when signal A is proportional to signal B, (iii) when signal A is obtained by level-shifting signal B, (iv) when signal A is obtained by amplifying signal B, (v) when signal A is obtained by inverting signal B, (vi) or any combination thereof. Those skilled in the art will understand that the scope of "corresponding to" is determined according to the types and applications of signals A and B.

[0042] The vertical and horizontal axes of the waveform diagrams and time charts referred to in this specification have been appropriately enlarged or reduced to facilitate understanding, and each waveform shown has been simplified or exaggerated or emphasized to facilitate understanding.

[0043] 1 is a circuit diagram of a DC / DC converter 100 according to a first embodiment. The DC / DC converter 100 is a boost converter, and receives an input voltage V IN The voltage is boosted and stabilized to a predetermined voltage level, and then supplied to a load 4 connected to an output line (output terminal) 104.

[0044] The DC / DC converter 100 includes an output circuit 110 and a control circuit 300. The output circuit 110 includes an inductor L1, a switching transistor (low-side transistor) M1, a synchronous rectifier transistor (high-side transistor) M2, and an output capacitor C1.

[0045] The control circuit 300 is a ripple control type, more specifically, a bottom detection type, controller, and includes a switching pin SW and an output pin OUT. An external inductor L1 is connected to the switching pin SW, and an external output capacitor C1 and an output line 104 are connected to the output pin OUT.

[0046] The control circuit 300 includes a voltage divider circuit 302, a main comparator 308, a logic circuit 312, a first driver 314, a second driver 316, a timer circuit 320, a switching transistor M1, and a synchronous rectifier transistor M2, and is an IC (Integrated Circuit) integrated on a single semiconductor substrate.

[0047] The voltage divider circuit 302 includes resistors R11 and R12, and outputs an output voltage V OUT is divided and the feedback voltage V FB Generate.

[0048] The main comparator 308 detects the output voltage V OUT Feedback voltage V according to FB is the reference voltage V REF Compared to the feedback voltage V FB is the reference voltage V REF When the voltage VFB falls below VREF, the turn-on signal S1 is asserted. The turn-on signal S1 is a pulse signal that indicates the magnitude relationship between VFB and VREF, and either the positive edge or the negative edge can be associated with assertion.

[0049] The logic circuit 312 generates pulse signals Sp1 and Sp2 that instruct the switching transistor M1 and the synchronous rectifier transistor M2 to be on and off, based on the turn-on signal S1.

[0050] The logic circuit 312 uses the assertion of the turn-on signal S1 as a trigger to change the start signal STARTX and operate the timer circuit 320. The timer circuit 320 starts the timer circuit 320 after the assertion of the turn-on signal S1. OUT -V IN) / V OUT On time T proportional to ON The turn-off signal S2 indicates the timing of turning off the switching transistor M1.

[0051] The first pulse signal Sp1 is an on-time T from the assertion of the turn-on signal S1 to the assertion of the turn-off signal S2. ON and is at an off level (for example, low) until the next assertion of the turn-on signal S1.

[0052] In the continuous current mode (CCM), the logic circuit 312 changes the second pulse signal Sp2 complementarily to the first pulse signal Sp1. In the discontinuous current mode (DCM), the logic circuit 312 detects a zero cross of the current flowing through the synchronous rectifier transistor M2, and maintains both the first pulse signal Sp1 and the second pulse signal Sp2 at the off level from the current zero cross to the next assertion of the turn-on signal S1.

[0053] FIG. 2 is an equivalent circuit diagram of the output circuit 110 of the DC / DC converter 100. DC is the equivalent series resistance of the inductor L1 and the wiring, etc. R ON1 is the on-resistance of the switching transistor M1, R ON2 represents the on-resistance of the synchronous rectifier transistor M2.

[0054] The switching period is T. The on-state φ of the switching transistor M1 ON In I L =I M1 and the voltage across the inductor L1 is {V IN -(R ON1 +R DC )×I L Therefore, in the on state φ ON Inductor current I L Increase in ΔI ON is expressed by equation (1). ON is the length of the on-state, which is called the on-time. ΔION =T ON / L×{V IN -(R ON1 +R DC )×I L} …(1)

[0055] The off state φ of the switching transistor M1 OFF In I L =I M2 and the voltage across the inductor L1 is {V OUT +(R ON1 +R DC )×I L -V IN Therefore, in the off state φ OFF Inductor current I L Decrease in ΔI OFF is expressed by equation (2). ΔI OFF =(TT ON ) / L×{V OUT +(R ON2 +R DC )×I L -V IN} …(2)

[0056] In continuous current mode, the output voltage V OUT When is stabilized, ΔI ON = ΔI OFF Therefore, the duty cycle d is expressed by equation (3). d=T ON / T ={V OUT -V IN +(R ON2 +R DC )×I L} / {V OUT -(R ON1 -R ON2 )×I L} …(3)

[0057] R ON1 =R ON2 =R DC If we assume that =0, we obtain equation (4). d=T ON / T ={V OUT -V IN} / V OUT …(4)

[0058] According to the control circuit 300 of FIG. 1, in a boost converter, an input voltage V IN and the output voltage V OUT According to the above, the on-time T ON By adaptively changing, it is possible to keep the switching frequency constant.

[0059] The present disclosure covers various devices and methods that can be understood as the block diagram or circuit diagram of Fig. 1 or derived from the above description, and is not limited to a specific configuration. Below, more specific configuration examples and examples will be described in order to aid in understanding and clarify the essence and operation of the invention, not to narrow the scope of the present invention.

[0060] Next, the configuration of the timer circuit 320 will be described based on several embodiments.

[0061] 3 is a circuit diagram showing a basic configuration of the timer circuit 320. The timer circuit 320 includes a first capacitor C11, a current source CS1, a comparator 322, and a threshold voltage generating circuit 330.

[0062] The current source CS1 is connected to the first capacitor C11 and V OUT Current I(∝V OUT For example, the current source CS1 may be a V / I conversion circuit. The comparator 322 generates a voltage V across the first capacitor C11. C11 Monitor (V OUT -V IN ) is detected as a voltage change proportional to the

[0063] 3, one end of the first capacitor C11 is grounded. The threshold voltage generating circuit 330 is OUT -V IN ) proportional to the threshold voltage V TH∝(V OUT -V IN The comparator 322 generates a voltage V C11 , the threshold voltage V TH The switch SW1 is connected in parallel with the first capacitor C11 and is controlled in response to the start signal STARTX.

[0064] 4 is an operation waveform diagram of the timer circuit 320 of FIG. 3. Before time t0, the start signal STARTX is high, and the voltage V C11 When the start signal STARTX transitions from high to low at time t0, the first capacitor C11 is charged by the current I generated by the current source CS1, and the voltage V of the first capacitor C11 C11 increases with a slope proportional to the current I. I=αV OUT

[0065] The voltage V of the capacitor after time t has elapsed from time t0 C11 is expressed by equation (5). V C11 = αV OUT ×t / C11 …(5)

[0066] Threshold voltage V TH But, V TH =β×(V OUT -V IN ) The capacitor voltage V C11 is the threshold voltage V TH If the time it takes to reach this is τ, then equation (6) holds. αV OUT ×τ / C11=β×(V OUT -V IN ) …(6) Solving this for τ gives us equation (7). τ = α / β × C11 × (V OUT -V IN ) / V OUT …(7)

[0067] Therefore, according to the timer circuit 320 of FIG. 2, after the start signal STARTX changes, (V OUT -V IN ) / V OUT A turn-off signal S2 can be generated that changes after a time τ that is proportional to the on-time T ON By driving the DC / DC converter 100 as the inverter, the switching frequency can be stabilized.

[0068] Example 1.1 5 is a circuit diagram of a timer circuit 320A according to Example 1.1. The threshold voltage generating circuit 330A includes a second capacitor C12.

[0069] The threshold voltage generating circuit 330A generates a threshold voltage φ OFF In this case, the second capacitor C12 is (V OUT -V IN ) The threshold voltage generating circuit 330A also charges the switching transistor M1 at an on-state φ ON In this case, the voltage (switching voltage) V of the switching pin SW, which is the connection node between the inductor L1 and the switching transistor M1, is applied to one end of the second capacitor C12. SW is applied, and the voltage at the other end of the second capacitor C12 is set to the threshold voltage V TH to the comparator 322.

[0070] For example, the threshold voltage generating circuit 330 includes a first selector 332 and a second selector 334 in addition to the second capacitor C12. The first selector 332 selects the off state φ OFF In this case, the input voltage V IN When the switching transistor M1 is turned on, ON 1, one end of the second capacitor C12 is connected to the switching pin SW of the DC / DC converter 100.

[0071] When the switching transistor M1 is in an off state, the second selector 334 supplies the output voltage V OUT When the switching transistor M1 is turned on, ON , the other end of the second capacitor C12 is connected to the comparator 322.

[0072] The above is the configuration of the timer circuit 320A. Fig. 6 is a waveform diagram showing the operation of the timer circuit 320A shown in Fig. 5. Before time t0, the timer circuit 320A is in an off state φ OFF and the second capacitor C12 is (V OUT -V IN ) is charged.

[0073] At time t0, the on state φ ON When the switch SW1 is turned off in response to the start signal STARTX, charging of the first capacitor C11 starts, and the capacitor voltage V C11 is the output voltage V OUT It rises with a slope proportional to

[0074] On state φ ON During this time, the potential difference of the second capacitor C12 is maintained, so that the threshold voltage V TH teeth, V TH =(V OUT -V IN )+V SW =(V OUT -V IN )+R ON1 I L …(8) It becomes.

[0075] Therefore, the on-time T generated by the timer circuit 320A ON teeth, T ON =C11 / α×{(V OUT -V IN )+R ON1 I L} / V OUT …(9) It becomes.

[0076] In this way, according to the timer circuit 320A of FIG. 5, the coil current I L (i.e., the load current) and the on-resistance R of the switching transistor M1 ON1 On time T ON can be generated.

[0077] Moreover, since a low-pass filter is not required as in the later-described embodiments 1.2 and 1.3, the circuit can be implemented in a small area.

[0078] Example 1.2 7 is a circuit diagram of a timer circuit 320B according to the embodiment 1.2. In this timer circuit 320B, the configuration of a threshold voltage generating circuit 330B is different from that of the threshold voltage generating circuit 330A in FIG.

[0079] The threshold voltage generating circuit 330B includes an inverter 336 and a low-pass filter 338. The inverter 336 converts the switching voltage V SW The power supply terminal of the inverter 336 is connected to the output voltage V OUT is supplied, and therefore the amplitude of the output signal of the inverter 336 is equal to the output voltage V OUT is equal to.

[0080] A low-pass filter 338 smoothes the output of the inverter 336 and reduces the threshold voltage V TH For example, the low pass filter 338 may be implemented as an RC filter.

[0081] Fig. 8 is an operation waveform diagram of the timer circuit 320B of Fig. 7. The output of the low-pass filter 338 is given by equation (10). V TH =V OUT ×d …(10) where d is the duty cycle of the first pulse signal Sp1. Since equation (4) holds in the steady state of the current continuous mode, equation (11) is obtained from equations (4) and (10). V TH =V OUT ×{VOUT -V IN} / V OUT =V OUT -V IN That is, V OUT -V IN The threshold voltage V is proportional to TH can be generated.

[0082] (Example 1.3) In Example 1.2, during the continuous current mode, equation (4) holds. However, in the discontinuous current mode where equation (4) does not hold, the threshold voltage V TH However, the voltage level deviates from the appropriate level. Therefore, immediately after the transition from the discontinuous current mode to the continuous current mode, the frequency fluctuation becomes large. In the embodiment 1.3, a configuration for solving this problem will be described.

[0083] 9 is a circuit diagram of a timer circuit 320C according to Example 1.3. The threshold voltage generating circuit 330C drives the capacitor C of the RC filter 338 to V OUT -V IN Specifically, during the discontinuous current mode, one end of the capacitor C is charged with V OUT At the other end, the input voltage V IN For example, the threshold voltage generating circuit 330C includes an inverter 336, a low-pass filter 338, a third selector 340, and a fourth selector 342.

[0084] The third selector 340 selects the continuous current mode φ CCM During this period, the output voltage of the inverter 336 is applied to one end of the resistor R, and the current discontinuous mode φ DCM During this time, the output voltage V OUT The fourth selector 342 applies a continuous current mode φ CCM During this period, the ground voltage of 0V is applied to the other end of the capacitor C, and the current discontinuous mode φ DCM During this time, the other end of the capacitor C is connected to the input voltage V IN is applied.

[0085] This results in a discontinuous current mode φDCM During this time, the voltage across the capacitor C becomes V OUT -V IN Then, the continuous current mode φ CCM When the transition to TH Then you can resume operation.

[0086] Example 1.4 10 is a circuit diagram of a timer circuit 320D according to Example 1.4. The timer circuit 320D includes a comparator 322, a current source CS1, a capacitor C11, and a switch SW1. An input voltage V IN is applied.

[0087] When switch SW1 is on, the capacitor voltage V C11 is the input voltage V IN When the switch SW1 is turned off, the capacitor voltage V C11 is the input voltage V IN is the initial value, and the output voltage V OUT The comparator 322 increases with a slope proportional to the capacitor voltage V C11 The output voltage V OUT The output S2 of the comparator 322 is compared with the capacitor voltage V C11 But, V OUT -V IN When the signal level changes by only this amount, a level transition occurs.

[0088] In this configuration, R ON and R DC Since we ignore I L In heavy load conditions where the load is large, the switching frequency becomes faster, but the switching frequency can be stabilized with a simple configuration.

[0089] A modification related to the first embodiment will be described.

[0090] (Variation 1.1) In the first embodiment, the switching transistor M1 and the synchronous rectification transistor M2 are integrated into the control circuit 300, but this is not limited thereto, and the switching transistor M1 and the synchronous rectification transistor M2 may be external discrete elements. The synchronous rectification transistor M2 may be an N-channel MOSFET, in which case a bootstrap circuit may be added to the second driver 316.

[0091] (Embodiment 2)

[0092] The present inventors have studied overcurrent protection in a converter with bottom detection and constant on-time (COT) ripple control, and have come to recognize the following problems.

[0093] The overcurrent protection monitors the current flowing through the switching transistor (or inductor) while the switching transistor is on, and turns off the switching transistor if the current exceeds an overcurrent threshold.

[0094] Generally, in an overcurrent state, a drooping characteristic that reduces the output voltage is required. However, with the bottom detection COT method, the bottom of the output voltage is maintained at the reference voltage even in an overcurrent state, so a drooping characteristic cannot be obtained.

[0095] In the second embodiment, a DC / DC converter and its control circuit capable of reducing the output voltage in an overcurrent state will be described.

[0096] 11 is a circuit diagram of a DC / DC converter 100 according to embodiment 2. The DC / DC converter 100 is a boost converter, and receives an input voltage V IN The voltage is boosted and stabilized to a predetermined voltage level, and then supplied to a load 4 connected to an output line (output terminal) 104.

[0097] The DC / DC converter 100 includes an output circuit 110 and a control circuit 400. The output circuit 110 includes an inductor L1, a switching transistor (low-side transistor) M1, a synchronous rectifier transistor (high-side transistor) M2, and an output capacitor C1.

[0098] The control circuit 400 is a ripple control type, more specifically, a bottom detection type, controller, and includes a switching pin SW and an output pin OUT. An external inductor L1 is connected to the switching pin SW, and an external output capacitor C1 and an output line 104 are connected to the output pin OUT.

[0099] The control circuit 400 includes a voltage divider circuit 402, a main comparator 408, a logic circuit 412, a first driver 414, a second driver 416, an on-time generating circuit 420, an overcurrent detection circuit 450, a turn-on inhibition circuit 460, a switching transistor M1, and a synchronous rectification transistor M2, and is an IC (Integrated Circuit) integrated on a single semiconductor substrate.

[0100] The voltage divider circuit 402 includes resistors R11 and R12, and outputs an output voltage V OUT is divided and the feedback voltage V FB Generate.

[0101] The main comparator 408 detects the output voltage V OUT Feedback voltage V according to FB is the reference voltage V REF Compared to the feedback voltage V FB is the reference voltage V REF When the voltage drops below V, the turn-on signal TURN_ON is asserted. FB and V REF It is a pulse signal that indicates the magnitude relationship, and either the positive edge or the negative edge can be associated with assertion.

[0102] The on-time generating circuit 420 generates an on-time T ON Generates a turn-off signal TURN_OFF that is asserted after the on-time T ON may be a predetermined constant time, or may be adaptively controlled according to the state of the DC / DC converter 100. The turn-off signal TURN_OFF is a trigger for turning off the switching transistor M1.

[0103] The turn-on inhibition circuit 460 is configured to inhibit the switching transistor M1 from turning on for a predetermined time (called a minimum period) Tp (MIN) The turn-on inhibition signal TURNON_DIS_B is asserted for a period until the elapse of . In this specification, _B represents negative logic, with assertion assigned to low and negation assigned to high. For example, the start signal START is a signal indicating that the first pulse signal Sp1, which instructs the switching transistor M1 to be turned on and off, has transitioned to the on level.

[0104] The on-time generating circuit 420 and the turn-on inhibiting circuit 460 can be configured with a timer circuit. The logic circuit 412 supplies a start signal START, which serves as a trigger for starting operation, to the on-time generating circuit 420 and the turn-on inhibiting circuit 460. The start signal START is a signal indicating the turning on of the switching transistor M1. The start signal START may be a first pulse signal Sp1.

[0105] The overcurrent detection circuit 450 detects whether the current flowing through the switching transistor M1 exceeds an overcurrent threshold I OCP If the current exceeds this limit, the overcurrent detection signal OCP is asserted (for example, high).

[0106] The logic circuit 412 generates pulse signals Sp1 and Sp2 that instruct the switching transistor M1 and the synchronous rectifier transistor M2 to be on or off, based on the turn-on signal TURN_ON, the turn-off signal TURN_OFF, the turn-on inhibition signal TURNON_DIS_B, and the overcurrent detection signal OCP.

[0107] When the turn-on signal TURN_ON is asserted during a period in which the turn-on inhibition signal TURNON_DIS_B is negated (high), the logic circuit 412 transitions the first pulse signal Sp1 to an on level (high). Even if the turn-on signal TURN_ON is asserted during a period in which the turn-on inhibition signal TURNON_DIS_B is asserted (low), the first pulse signal Sp1 maintains an off level (low).

[0108] When the turn-off signal TURN_OFF or the overcurrent detection signal OCP is asserted, the logic circuit 412 transitions the first pulse signal Sp1 to an off level (low).

[0109] In the continuous current mode (CCM), the logic circuit 412 changes the second pulse signal Sp2 complementarily to the first pulse signal Sp1. In the discontinuous current mode (DCM), the logic circuit 412 detects a zero cross of the current flowing through the synchronous rectifier transistor M2, and maintains both the first pulse signal Sp1 and the second pulse signal Sp2 at the off level from the current zero cross to the next assertion of the turn-on signal TURN_ON.

[0110] The above is the configuration of the control circuit 400. Next, the operation of the control circuit 400 will be described.

[0111] 12 is a waveform diagram showing the operation of the DC / DC converter 100 in FIG. 11 in a normal state (non-overcurrent state). Here, the converter is operating in a continuous mode. The on-time T ON is the minimum period Tp generated by the turn-on inhibition circuit 460 in the normal state. (MIN) In Figure 12, the waveforms are shown ignoring the circuit delay.

[0112] At time t0, the feedback voltage V FB is the reference voltage V REF When the voltage drops to 0 V, the turn-on signal TURN_ON is asserted. At this timing, the turn-on inhibition signal TURNON_DIS_B is negated (high), so in response to the assertion of the turn-on signal TURN_ON, the first pulse signal Sp1 transitions to the on level. The second pulse signal Sp2 transitions in a complementary manner to the first pulse signal Sp1.

[0113] When the switching transistor M1 is turned on at time t0, the on-time generating circuit 420 starts counting, and the on-time T ON At time t1 after the elapse of the time, the turn-off signal TURN_OFF is asserted. This causes the first pulse signal Sp1 to transition to an off level, and the switching transistor M1 is turned off. After that, at time t2, the feedback voltage V FB is the reference voltage V REF When the voltage drops to , the turn-on signal TURN_ON is asserted. This operation is repeated in the normal state.

[0114] 13 is a waveform diagram showing the operation of the DC / DC converter 100 in FIG. 11 in an overcurrent state. At time t0, the feedback voltage V FB is the reference voltage V REF When the voltage Vcc falls below 1 V, the turn-on signal TURN_ON is asserted (low). At this timing, the turn-on inhibition signal TURNON_DIS_B is negated (high), so in response to the assertion of the turn-on signal TURN_ON, the first pulse signal Sp1 transitions to the on level. The second pulse signal Sp2 transitions in a complementary manner to the first pulse signal Sp1.

[0115] When the switching transistor M1 is turned on at time t0, the on-time generating circuit 420 and the turn-on inhibit circuit 460 start timing, and the turn-on inhibit signal TRUNON_DIS_B is asserted (low). ONAt time t1 before the lapse of the time, the overcurrent detection signal OCP is asserted, and in response to the overcurrent detection signal OCP, the first pulse signal Sp1 transitions to the off level, turning off the switching transistor M1. This activates pulse-by-pulse overcurrent protection.

[0116] Feedback voltage V FB rises immediately after the switching transistor M1 is turned off, and then decreases over time. At time t2, the reference voltage V REF When the voltage Vcc falls below t0, the turn-on signal TURN_ON is asserted. However, the time t2 is the minimum period Tp from the time t0 when the previous switching transistor M1 was turned on. (MIN) Since the time period has not elapsed, the turn-on inhibition signal TURNON_DIS_B is asserted, and the first pulse signal Sp1 is maintained at the off level.

[0117] Thereafter, when the turn-on inhibition signal TURNON_DIS_B is negated at time t3, which is the minimum period Tp(MIN) after time t1, the first pulse signal Sp1 transitions to the on level in response to the turn-on signal TURN_ON that is already asserted (low) at that time, and the switching transistor M1 is turned on.

[0118] When the first pulse signal Sp1 transitions to an on level at time t3, the turn-on inhibition signal TURNON_DIS_B is asserted (low), and timing is started by the turn-on inhibition circuit 460. When the overcurrent detection signal OCP is asserted at time t4, the first pulse signal Sp1 transitions to an off level, and the switching transistor M1 is turned off.

[0119] In an overcurrent state, the operations from t1 to t4 are repeated. The above is the operation of the DC / DC converter 100.

[0120] According to this DC / DC converter 100, in an overcurrent state, the switching frequency is reduced to 1 / Tp (MIN)In an overcurrent condition, the feedback voltage V FB That is, the output voltage V OUT can be decreased over time, thereby realizing a drooping characteristic.

[0121] The present invention encompasses various devices and methods that can be understood as the block diagram or cross-sectional diagram of Fig. 11 or that are derived from the above description, and is not limited to a specific configuration. Below, more specific configuration examples and embodiments will be described not to narrow the scope of the present invention, but to aid in understanding and clarify the essence and operation of the invention.

[0122] A specific example of the configuration of the control circuit 400 will be described.

[0123] FIG. 14 is an equivalent circuit diagram of the output circuit 110 of the DC / DC converter 100. DC is the equivalent series resistance of the inductor L1 and the wiring, etc. R ON1 is the on-resistance of the switching transistor M1, R ON2 represents the on-resistance of the synchronous rectifier transistor M2.

[0124] The switching period is T. The on-state φ of the switching transistor M1 ON In I L =I M1 and the voltage across the inductor L1 is {V IN -(R ON1 +R DC )×I L Therefore, in the on state φ ON Inductor current I L Increase in ΔI ON is expressed by equation (1). ON is the length of the on-state, which is called the on-time. ΔI ON =T ON / L×{V IN -(R ON1 +R DC )×I L} …(1)

[0125] The off state φ of the switching transistor M1 OFF In I L =I M2 and the voltage across the inductor L1 is {V OUT +(R ON1 +R DC )×I L -V IN Therefore, in the off state φ OFF Inductor current I L Decrease in ΔI OFF is expressed by equation (2). ΔI OFF =(TT ON ) / L×{V OUT +(R ON2 +R DC )×I L -V IN} …(2)

[0126] In continuous current mode, the output voltage V OUT When is stabilized, ΔI ON = ΔI OFF Therefore, the duty cycle d is expressed by equation (3). d=T ON / T ={V OUT -V IN +(R ON2 +R DC )×I L} / {V OUT -(R ON1 -R ON2 )×I L} …(3)

[0127] R ON1 =R ON2 =R DC If we assume that =0, we obtain equation (4). d=T ON / T ={V OUT -V IN} / V OUT …(4)

[0128] Therefore, the on-time generating circuit 420 of the control circuit 400 sets the target period in the non-overcurrent state as Tp (REF) When T ON ={V OUT -V IN} / V OUT ×T REF On time T ON This makes it possible to keep the switching frequency of the DC / DC converter 100 constant.

[0129] Next, the configuration of the on-time generating circuit 420 will be described based on several embodiments.

[0130] 15 is a circuit diagram showing a basic configuration of the on-time generating circuit 420. The on-time generating circuit 420 includes a first capacitor C11, a current source CS1, a comparator 422, and a threshold voltage generating circuit 430.

[0131] The current source CS1 is connected to the first capacitor C11 and V OUT Current I(∝V OUT For example, the current source CS1 may be a V / I conversion circuit. The comparator 422 generates a voltage V across the first capacitor C11. C11 Monitor (V OUT -V IN ) is detected as a voltage change proportional to the

[0132] 15, one end of the first capacitor C11 is grounded. The threshold voltage generating circuit 430 is OUT -V IN ) proportional to the threshold voltage V TH ∝(V OUT -V IN The comparator 422 generates the voltage V C11 , the threshold voltage V TH The switch SW1 is connected in parallel with the first capacitor C11 and is controlled in response to the start signal START_B.

[0133] 16 is an operation waveform diagram of the on-time generating circuit 420 of FIG. 15. Before time t0, the start signal START_B is high, and the voltage V C11 When the start signal START_B transitions from high to low at time t0, the first capacitor C11 is charged by the current I generated by the current source CS1, and the voltage V of the first capacitor C11 C11 increases with a slope proportional to the current I. I=αV OUT

[0134] The voltage V of the capacitor after time t has elapsed from time t0 C11 is expressed by equation (5). V C11 = αV OUT ×t / C11 …(5)

[0135] Threshold voltage V TH But, V TH =β×(V OUT -V IN ) The capacitor voltage V C11 is the threshold voltage V TH If the time it takes to reach this is τ, then equation (6) holds. αV OUT ×τ / C11=β×(V OUT -V IN ) …(6) Solving this for τ gives us equation (7). τ = α / β × C11 × (V OUT -V IN ) / V OUT …(7)

[0136] Therefore, according to the on-time generating circuit 420 of FIG. 15, after the start signal START_B changes, (V OUT -V IN ) / V OUT A turn-off signal TURN_OFF that changes after a time τ that is proportional to the on-time T ON By driving the DC / DC converter 100 as the inverter, the switching frequency can be stabilized.

[0137] Example 2.1 17 is a circuit diagram of an on-time generating circuit 420A according to Example 2.1. The threshold voltage generating circuit 430A includes a second capacitor C12.

[0138] The threshold voltage generating circuit 430A generates a threshold voltage φ OFF In this case, the second capacitor C12 is (V OUT -V IN ) The threshold voltage generating circuit 430A also charges the switching transistor M1 at an on-state φ ON In this case, the voltage (switching voltage) V of the switching pin SW, which is the connection node between the inductor L1 and the switching transistor M1, is applied to one end of the second capacitor C12. SW is applied, and the voltage at the other end of the second capacitor C12 is set to the threshold voltage V TH to the comparator 422.

[0139] For example, the threshold voltage generating circuit 430 includes a first selector 432 and a second selector 434 in addition to the second capacitor C12. The first selector 432 selects the off state φ OFF In this case, the input voltage V IN When the switching transistor M1 is turned on, ON 1, one end of the second capacitor C12 is connected to the switching pin SW of the DC / DC converter 100.

[0140] When the switching transistor M1 is in an off state, the second selector 434 supplies the output voltage V OUT When the switching transistor M1 is turned on, ON 4, the other end of the second capacitor C12 is connected to the comparator 422.

[0141] The above is the configuration of the ON time generating circuit 420A. Fig. 18 is an operation waveform diagram of the ON time generating circuit 420A of Fig. 17. Before time t0, the ON time generating circuit 420A is in the OFF state φ OFF and the second capacitor C12 is (V OUT -V IN ) is charged.

[0142] At time t0, the on state φ ON When the switch SW1 is turned off in response to the start signal START_B, the first capacitor C11 starts to be charged, and the capacitor voltage V C11 is the output voltage V OUT It rises with a slope proportional to

[0143] On state φ ON During this time, the potential difference of the second capacitor C12 is maintained, so that the threshold voltage V TH teeth, V TH =(V OUT -V IN )+V SW =(V OUT -V IN )+R ON1 I L …(8) It becomes.

[0144] Therefore, the on-time T generated by the on-time generating circuit 420A ON teeth, T ON =C11 / α×{(V OUT -V IN )+R ON1 I L} / V OUT …(9) It becomes.

[0145] In this way, according to the on-time generating circuit 420A of FIG. 17, the coil current I L (i.e., the load current) and the on-resistance R of the switching transistor M1 ON1 On time T ON can be generated.

[0146] Moreover, since a low-pass filter is not required as in the later-described embodiments 2.2 and 2.3, the circuit can be implemented in a small area.

[0147] Example 2.2 19 is a circuit diagram of an ON time generating circuit 420B according to embodiment 2.2. In this ON time generating circuit 420B, the configuration of a threshold voltage generating circuit 430B is different from that of the threshold voltage generating circuit 430A in FIG.

[0148] The threshold voltage generating circuit 430B includes an inverter 436 and a low-pass filter 438. The inverter 436 converts the switching voltage V SW The power supply terminal of the inverter 436 is connected to the output voltage V OUT is supplied, and therefore the amplitude of the output signal of the inverter 436 is equal to the output voltage V OUT is equal to.

[0149] A low pass filter 438 smoothes the output of the inverter 436 and reduces the threshold voltage V TH For example, the low pass filter 438 may be implemented as an RC filter.

[0150] Fig. 20 is an operational waveform diagram of the on-time generating circuit 420B of Fig. 19. The output of the low-pass filter 438 is given by equation (10). V TH =V OUT ×d …(10) where d is the duty cycle of the first pulse signal Sp1. Since equation (4) holds in the steady state of the current continuous mode, equation (11) is obtained from equations (4) and (10). V TH =V OUT ×{V OUT -V IN} / V OUT =V OUT -V IN That is, V OUT -V IN The threshold voltage V is proportional to THcan be generated.

[0151] Example 2.3 In Example 2.2, during the continuous current mode, equation (4) holds. However, in the discontinuous current mode, where equation (4) does not hold, the threshold voltage V TH However, the voltage level deviates from the appropriate level. Therefore, immediately after the transition from the discontinuous current mode to the continuous current mode, the frequency fluctuation becomes large. In the embodiment 2.3, a configuration for solving this problem will be described.

[0152] 21 is a circuit diagram of an on-time generating circuit 420C according to Example 2.3. The threshold voltage generating circuit 430C converts the capacitor C of the RC filter 438 to V OUT -V IN Specifically, during the discontinuous current mode, one end of the capacitor C is charged with V OUT At the other end, the input voltage V IN For example, the threshold voltage generating circuit 430C includes an inverter 436, a low-pass filter 438, a third selector 440, and a fourth selector 442.

[0153] The third selector 440 selects the continuous current mode φ CCM During this period, the output voltage of the inverter 436 is applied to one end of the resistor R, and the current discontinuous mode φ DCM During this time, the output voltage V OUT The fourth selector 442 applies a continuous current mode φ CCM During this period, the ground voltage of 0V is applied to the other end of the capacitor C, and the current discontinuous mode φ DCM During this time, the other end of the capacitor C is connected to the input voltage V IN is applied.

[0154] This results in a discontinuous current mode φ DCM During this time, the voltage across the capacitor C becomes V OUT -V IN Then, the continuous current mode φ CCM When the transition to TH Then you can resume operation.

[0155] Example 2.4 22 is a circuit diagram of an on-time generating circuit 420D according to Example 2.4. The on-time generating circuit 420D includes a comparator 422, a current source CS1, a capacitor C11, and a switch SW1. An input voltage V IN is applied.

[0156] When switch SW1 is on, the capacitor voltage V C11 is the input voltage V IN When the switch SW1 is turned off, the capacitor voltage V C11 is the input voltage V IN is the initial value, and the output voltage V OUT The comparator 422 increases with a slope proportional to the capacitor voltage V C11 The output voltage V OUT The output of the comparator 422, TURN_OFF, is compared with the capacitor voltage V C11 But, V OUT -V IN When the signal level changes by only this amount, a level transition occurs.

[0157] In this configuration, R ON and R DC Since we ignore I L In heavy load conditions where the load is large, the switching frequency becomes faster, but the switching frequency can be stabilized with a simple configuration.

[0158] Below, modifications related to the second embodiment will be described.

[0159] (Variation 2.1) In the second embodiment, the switching transistor M1 and the synchronous rectification transistor M2 are integrated into the control circuit 400, but this is not limited thereto, and the switching transistor M1 and the synchronous rectification transistor M2 may be external discrete elements. The synchronous rectification transistor M2 may be an N-channel MOSFET, in which case a bootstrap circuit may be added to the second driver 416.

[0160] (Variation 2.2) Although a boost converter has been described in the second embodiment, the present invention is also applicable to a step-down converter or a step-up / step-down converter.

[0161] The embodiments merely illustrate the principles and applications of the present invention, and many modifications and changes in arrangement are permitted to the embodiments without departing from the spirit of the present invention defined in the claims. [Industrial Applicability]

[0162] The present disclosure relates to a DC / DC converter. [Explanation of symbols]

[0163] 100 DC / DC Converter 102 input lines 104 Output Line 110 Output circuit M1 Switching transistor M2 Synchronous rectifier transistor 300 Control circuit 302 Voltage divider circuit 308 Main Comparator 312 Logic Circuits 314 1st Driver 316 2nd Driver 320 Timer Circuit 322 Comparator 330 Threshold voltage generation circuit C11 First capacitor C12 Second capacitor 332 First Selector 334 Second Selector 336 Inverter 338 Low Pass Filter 340 3rd Selector 342 4th Selector S1 Turn-on signal S2 turn off signal Sp1 First pulse signal Sp2 Second pulse signal 400 Control circuit 402 Voltage divider circuit 408 Main Comparator 412 Logic Circuit 414 1st Driver 416 2nd Driver 420 ON-time generation circuit 422 Comparator 430 Threshold voltage generation circuit C11 First capacitor C12 Second capacitor 432 First Selector 434 Second Selector 436 Inverter 438 Low Pass Filter 440 3rd Selector 442 4th Selector TURN_ON Turn-on signal TURN_OFF Turn-off signal

Claims

1. A control circuit for a DC / DC converter that boosts an input voltage V IN and generates an output voltage V OUT , comprising: a main comparator that compares a feedback voltage corresponding to an output voltage of the DC / DC converter with a reference voltage and asserts a turn-on signal when the feedback voltage falls below the reference voltage; a timer circuit that generates a turn-off signal whose level transitions after an on-time proportional to (V OUT -V IN ) / V OUT has elapsed since the assertion of the turn-on signal; Equipped with The timer circuit includes: a first capacitor having one end grounded; a current source coupled to the first capacitor for generating a current proportional to V OUT ; a threshold voltage generating circuit that generates a threshold voltage according to (V OUT -V IN ); a comparator that detects a voltage change proportional to (V OUT -V IN ) occurring in the first capacitor by comparing the voltage at the other end of the first capacitor with the threshold voltage; Including, The threshold voltage generating circuit includes a second capacitor, and during an off period of the switching transistor, the second capacitor is ＯＵＴ -V ＩＮ ), and during an on-period of the switching transistor, applies a switching voltage of a connection node between an inductor and the switching transistor to one end of the second capacitor, and sets the voltage of the other end of the second capacitor to the threshold voltage.

2. A control circuit for a DC / DC converter that boosts an input voltage V IN and generates an output voltage V OUT , comprising: a main comparator that compares a feedback voltage corresponding to an output voltage of the DC / DC converter with a reference voltage and asserts a turn-on signal when the feedback voltage falls below the reference voltage; a timer circuit that generates a turn-off signal whose level transitions after an on-time proportional to (V OUT -V IN ) / V OUT has elapsed since the assertion of the turn-on signal; Equipped with The timer circuit includes: a first capacitor having one end grounded; a current source coupled to the first capacitor for generating a current proportional to V OUT ; a threshold voltage generating circuit that generates a threshold voltage according to (V OUT -V IN ); a comparator that detects a voltage change proportional to (V OUT -V IN ) occurring in the first capacitor by comparing the voltage at the other end of the first capacitor with the threshold voltage; Including, The threshold voltage generating circuit includes: A second capacitor; During the off period of the switching transistor, the input voltage V ＩＮ a first selector that applies a voltage to the first end of the second capacitor and connects the first end of the second capacitor to a connection node between an inductor and a switching transistor of the DC / DC converter during an on-period of the switching transistor; During the off period of the switching transistor, the output voltage V ＯＵＴ a second selector that applies a voltage to the second capacitor and connects the other end of the second capacitor to the comparator during an on-period of the switching transistor; a control circuit.

3. A control circuit for a DC / DC converter that boosts an input voltage V IN and generates an output voltage V OUT , comprising: a main comparator that compares a feedback voltage corresponding to an output voltage of the DC / DC converter with a reference voltage and asserts a turn-on signal when the feedback voltage falls below the reference voltage; a timer circuit that generates a turn-off signal whose level transitions after an on-time proportional to (V OUT -V IN ) / V OUT has elapsed since the assertion of the turn-on signal; Equipped with The timer circuit includes: a first capacitor having one end grounded; a current source coupled to the first capacitor for generating a current proportional to V OUT ; a threshold voltage generating circuit that generates a threshold voltage according to (V OUT -V IN ); a comparator that detects a voltage change proportional to (V OUT -V IN ) occurring in the first capacitor by comparing the voltage at the other end of the first capacitor with the threshold voltage; Including, The threshold voltage generating circuit includes: an inverter that inverts a switching voltage generated at a connection node between an inductor and a switching transistor of the DC / DC converter; a filter that smoothes the output of the inverter and generates a threshold voltage; a control circuit.

4. the filter is an RC filter, The threshold voltage generation circuitry drives the capacitor of the RC filter to V ＯＵＴ -V ＩＮ 4. The control circuit of claim 3, wherein the control circuit charges the battery with

5. the filter is an RC filter including a resistor and a capacitor; The threshold voltage generating circuit includes: During a continuous current mode, the output voltage of the inverter is applied to one end of the resistor, and during a discontinuous current mode, the output voltage V ＯＵＴ a third selector for applying During the current continuous mode, a ground voltage is applied to the other end of the capacitor, and during the current discontinuous mode, the input voltage V ＩＮ a fourth selector for applying The control circuit of claim 3 further comprising:

6. The input voltage V ＩＮ is applied, The comparator converts the voltage at the other end of the first capacitor into the output voltage V ＯＵＴ 4. A control circuit as claimed in claim 1, wherein:

7. A control circuit for a DC / DC converter having a switching transistor, comprising: a main comparator that compares a feedback voltage corresponding to an output voltage of the DC / DC converter with a reference voltage and asserts a turn-on signal when the feedback voltage falls below the reference voltage; an on-time generating circuit that asserts a turn-off signal after an on-time has elapsed since the switching transistor was turned on; an overcurrent detection circuit that asserts an overcurrent detection signal when a current flowing through the switching transistor exceeds an overcurrent threshold during an on-period of the switching transistor; a turn-on inhibition circuit that generates a turn-on inhibition signal that is asserted during a period from when the switching transistor is turned on until a predetermined time has elapsed; a logic circuit that generates a pulse signal that transitions to an on level when the turn-on signal is asserted during a period in which the turn-on inhibition signal is negated, and that transitions to an off level when the turn-off signal or the overcurrent detection signal is asserted; a driver that drives the switching transistor in response to the pulse signal; Equipped with The on-time generating circuit includes: a first capacitor having one end grounded; a current source coupled to the first capacitor for generating a current proportional to V OUT ; a threshold voltage generating circuit that generates a threshold voltage according to (V OUT -V IN ); a comparator that detects a voltage change proportional to (V OUT -V IN ) occurring in the first capacitor by comparing the voltage at the other end of the first capacitor with the threshold voltage; Including, the threshold voltage generation circuit includes a second capacitor, and during an off-period of a switching transistor, the second capacitor is charged with (V OUT -V IN ), and during an on-period of the switching transistor, a switching voltage of a connection node between an inductor and a switching transistor is applied to one end of the second capacitor, and the voltage of the other end of the second capacitor is set to the threshold voltage.

8. The DC / DC converter receives an input voltage V ＩＮ is boosted to output voltage V ＯＵＴ 8. The control circuit of claim 7, which is of the boost type generating:

9. The on-time is (V ＯＵＴ -V ＩＮ ) / V ＯＵＴ 9. The control circuit of claim 8, wherein the control signal is proportional to

10. A control circuit as described in any one of claims 1 to 9, which is monolithically integrated on a single semiconductor substrate.

11. an output circuit of a step-up DC / DC converter; A control circuit according to any one of claims 1 to 6; A power supply circuit comprising:

12. an output circuit of a DC / DC converter; A control circuit according to any one of claims 7 to 10; A power supply circuit comprising:

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