Buck converter and drive circuit and bootstrap power supply circuit thereof

Abstract

The invention discloses a buck converter and a driving circuit and a bootstrap power supply circuit thereof, the buck converter comprises a main switch tube connected between an input end and a switch node and a driving unit connected with a control end of the main switch tube, and the bootstrap power supply circuit comprises a bootstrap capacitor. The bootstrap unit is connected between a bootstrap node and the switch node, and the bootstrap node is used for supplying power to the driving unit; the charge pump circuit is connected with the bootstrap node, the charge pump circuit comprises a first pumping unit and a second pumping unit, the first pumping unit comprises a first charge pump capacitor, and the second pumping unit comprises a second charge pump capacitor; and the first pumping unit and the second pumping unit are alternately in a pumping state for charging the bootstrap capacitor and a charging state for charging the charge pump capacitor of the first pumping unit and the second pumping unit, so that the voltage of the bootstrap node is maintained at a preset value, and the light load efficiency of the buck converter is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated circuits, and in particular to a buck converter and a drive circuit and a bootstrap power supply circuit thereof. Background Art

[0002] For a buck converter in which both the main switch tube and the synchronous switch tube use NMOS tubes, a bootstrap capacitor is usually required to form a bootstrap voltage to power the main switch tube.

[0003] In order to make the buck converter work normally when the input voltage Vin is close to the output voltage Vout, it is necessary to integrate a charge pump circuit inside the buck converter to charge the bootstrap capacitor when the voltage difference between the two plates of the bootstrap capacitor is lower than a preset value or the main switch tube is normally open. When the bootstrap capacitor is charged to the preset value, the charge pump circuit will enter a dormant state. However, the buck converter of the prior art needs to frequently turn off the main switch tube to start the charge pump circuit to charge the bootstrap capacitor when the input voltage Vin is low, in no-load or light-load mode, especially when the high-temperature leakage is large, resulting in large losses and affecting the light-load efficiency. In addition, the voltage detection circuit that detects the voltage difference between the two plates of the bootstrap capacitor also needs to work all the time, which will also cause certain losses.

[0004] Therefore, a new buck converter is needed to solve the above problems. Summary of the invention

[0005] In view of the above problems, an object of the present invention is to provide a buck converter and a driving circuit and a bootstrap power supply circuit thereof, so as to improve the light-load efficiency of the buck converter.

[0006] According to one aspect of the present invention, a bootstrap power supply circuit for a buck converter is provided, the buck converter comprising a main switch tube connected between an input end and a switch node, and a drive unit connected to a control end of the main switch tube, the bootstrap power supply circuit comprising a bootstrap capacitor connected between a bootstrap node and the switch node, the bootstrap node being used to power the drive unit; a charge pump circuit connected to the bootstrap node, the charge pump circuit comprising a first pumping unit and a second pumping unit, the first pumping unit comprising a first charge pump capacitor, the second pumping unit comprising a second charge pump capacitor, wherein when the main switch tube is turned on, the first pumping unit and the second pumping unit are alternately in a pumping state for charging the bootstrap capacitor and a charging state for charging their own charge pump capacitors.

[0007] Optionally, when the main switch tube is turned off, one of the first pumping unit and the second pumping unit is in a pumping state to charge the bootstrap capacitor, and the other is in a charging state to charge its own charge pump capacitor.

[0008] Optionally, the first pumping unit also includes a first diode and a first switching network, the anode of the first diode is connected to the second plate of the first charge pump capacitor, and the cathode of the first diode is connected to the bootstrap node; the second pumping unit also includes a second diode and a second switching network, the anode of the second diode is connected to the second plate of the second charge pump capacitor, and the cathode of the second diode is connected to the bootstrap node, wherein the first switching network is configured to connect the first plate of the first charge pump capacitor to the ground terminal and the second plate to the power supply voltage in the charging state of the first pumping unit, and to connect the first plate of the first charge pump capacitor to the power supply voltage and the second plate to the bootstrap node via the first diode in the pumping state of the first pumping unit; the second switching network is configured to connect the first plate of the second charge pump capacitor to the ground terminal and the second plate to the power supply voltage in the charging state of the second pumping unit, and to connect the first plate of the second charge pump capacitor to the power supply voltage and the second plate to the bootstrap node via the second diode in the pumping state of the second pumping unit.

[0009] Optionally, the charge pump circuit further includes a switch control unit, configured to generate a clock signal according to a first control signal for controlling the main switch tube to be turned on and off, so as to control the first switch network and the second switch network.

[0010] Optionally, the first switch network includes: a first switch, connected between the ground terminal and the first plate of the first charge pump capacitor; a second switch, connected between the first plate of the first charge pump capacitor and the power supply voltage; a third switch, connected between the second plate of the first charge pump capacitor and the power supply voltage; the second switch network includes: a fourth switch, connected between the ground terminal and the first plate of the second charge pump capacitor; a fifth switch, connected between the first plate of the second charge pump capacitor and the power supply voltage; and a sixth switch, connected between the second plate of the second charge pump capacitor and the power supply voltage.

[0011] Optionally, the first switch and the fourth switch are implemented by NMOS tubes, and the second switch, the third switch, the fifth switch and the sixth switch are implemented by PMOS tubes.

[0012] Optionally, the bootstrap power supply circuit also includes a voltage detection circuit for detecting a voltage difference between the bootstrap node and the switch node, and comparing the voltage difference with a first threshold voltage to output a detection signal based on the comparison result, wherein when the voltage difference decreases to less than the first threshold voltage, the detection signal turns off the main switch tube, and the voltage detection circuit is turned on when the main switch tube is turned on, and is turned off when the main switch tube is turned off.

[0013] According to a second aspect of the present invention, there is provided a driving circuit of a buck converter, wherein the buck converter comprises a main switch tube connected between an input terminal and a switch node, and the driving circuit comprises a comparator for comparing a feedback voltage of an output voltage of the buck converter with a reference voltage to obtain a pulse width modulation signal; a logic control circuit for generating a first control signal according to the pulse width modulation signal, wherein the first control signal is used to control the on and off of the main switch tube; a driving unit connected to a bootstrap node, and used to drive the on and off of the main switch tube; and a bootstrap power supply circuit as described above, used to power the driving unit.

[0014] Optionally, the bootstrap power supply circuit also includes a voltage detection circuit for detecting a voltage difference between the bootstrap node and the switch node, and comparing the voltage difference with a first threshold voltage to output a detection signal according to the comparison result, wherein when the voltage difference decreases to less than the first threshold voltage, the detection signal turns off the main switch tube, and the voltage detection circuit is turned on when the main switch tube is turned on, and is turned off when the main switch tube is turned off; the drive circuit also includes a logic unit for performing an AND operation on the first control signal and the detection signal, and outputting a second control signal, wherein the drive unit receives the second control signal, and drives the main switch tube to be turned on and off according to the second control signal.

[0015] According to a third aspect of the present invention, a buck converter is provided, comprising a main switch connected between an input terminal and a switch node; a synchronous switch connected between the switch node and a ground terminal; an inductor connected between the switch node and an output terminal; and a drive circuit as described above.

[0016] The present invention provides a buck converter, a driving circuit and a bootstrap power supply circuit, wherein the bootstrap power supply circuit includes a bootstrap capacitor and a charge pump circuit, wherein the bootstrap capacitor is connected between a bootstrap node and a switch node, and the charge pump circuit includes a first pumping unit and a second pumping unit. When the main switch tube is turned on, the first pumping unit and the second pumping unit alternately charge the bootstrap capacitor to maintain the voltage of the bootstrap node at a preset value, thereby improving the light-load efficiency of the buck converter.

[0017] In a preferred embodiment, the bootstrap power supply circuit further includes a voltage detection circuit, which can detect the voltage difference between the bootstrap node and the switch node when the main switch tube is turned on, and output a second level detection signal when the voltage difference is reduced to less than the first threshold voltage, so as to timely control the main switch tube to be turned off through the logic unit or the logic control circuit, and the charge pump circuit charges the bootstrap capacitor, which can improve the reliability of the buck converter. In addition, the voltage detection circuit only works when the main switch tube is turned on, which can reduce the power consumption of the buck converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0019] Figure 1 A schematic structural diagram of a buck converter is shown;

[0020] Figure 2 Shows Figure 1 The circuit diagram of the buck converter shown;

[0021] Figure 3 A schematic structural diagram of a buck converter according to a first embodiment of the present invention is shown;

[0022] Figure 4a-4b shows an equivalent circuit diagram of a charge pump circuit according to a first embodiment of the present invention;

[0023] Figure 5 A circuit diagram of a charge pump circuit according to a first embodiment of the present invention is shown;

[0024] Figure 6 Shows Figure 5 The timing diagram of the charge pump circuit shown;

[0025] Figure 7 FIG. 4 is a circuit diagram of a buck converter according to a second embodiment of the present invention. DETAILED DESCRIPTION

[0026] Various embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. In each of the accompanying drawings, the same elements or modules are represented by the same or similar reference numerals. For the sake of clarity, the various parts in the accompanying drawings are not drawn to scale.

[0027] It should be understood that in the following description, a "circuit" may include a single or multiple combined hardware circuits, programmable circuits, state machine circuits, and / or elements capable of storing instructions executed by programmable circuits. When an element or circuit is said to be "connected to" another element or an element or circuit is said to be "connected between" two nodes, it may be directly coupled or connected to another element or there may be an intermediate element, and the connection between the elements may be physical, logical, or a combination thereof. Conversely, when an element is said to be "directly coupled to" or "directly connected to" another element, it means that there is no intermediate element between the two.

[0028] At the same time, certain words are used in this patent specification and claims to refer to specific components. It should be understood by those skilled in the art that hardware manufacturers may use different terms to refer to the same component. This patent specification and claims do not use differences in names as a way to distinguish components, but rather use differences in components' functions as the criteria for distinction.

[0029] In addition, it should be noted that, in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of more restrictions, the elements defined by the statement "comprise one..." do not exclude the existence of other identical elements in the process, method, article or equipment including the elements.

[0030] Figure 1 A schematic diagram of a buck converter circuit is shown. Figure 1 The buck converter 100 includes a power circuit and a drive circuit. The power circuit includes a main switch tube HS and a synchronous switch tube LS connected in series between an input voltage Vin and a ground terminal, an inductor L connected between a common node of the main switch tube HS and the synchronous switch tube LS, that is, a switch node SW and an output terminal, a load RL connected between the output terminal and the ground terminal, and an output capacitor Cout connected in parallel with the load RL. The input terminal of the power circuit receives an input voltage Vin, and the output terminal provides an output voltage Vout.

[0031] In addition, the buck converter 100 further includes a voltage divider network composed of resistors R1 and R2, which is used to obtain a feedback voltage Vfb of the output voltage Vout.

[0032] The driving circuit includes a logic control circuit 110 , a driving unit 120 , a driving unit 130 , a bootstrap capacitor Cbst, a voltage detection circuit 140 , a charge pump circuit 150 and a comparator 160 .

[0033] The comparator 160 is used to compare the feedback voltage Vfb of the output voltage Vout of the buck converter 100 with the reference voltage Vref, so as to obtain the pulse width modulation signal PWM according to the comparison result. The logic control circuit 110 is used to receive the pulse width modulation signal PWM and the detection signal ctrl_bst, and provide the control signal ctrl_hs and the control signal ctrl_ls. The driving unit 120 is connected between the bootstrap node BST and the switch node SW, and is used to generate the driving signal hs_on according to the control signal ctrl_hs to drive the main switch tube HS to be turned on and off. The driving unit 130 is connected between the power supply voltage Vdd and the ground terminal, and is used to generate the driving signal ls_on according to the control signal ctrl_ls to drive the synchronous switch tube LS to be turned on and off. In each switching cycle, the main switch tube HS and the synchronous switch tube LS are alternately turned on and off to charge and discharge the inductor L, thereby providing a DC output voltage Vout at the output terminal.

[0034] The bootstrap capacitor Cbst is connected between the bootstrap node BST and the switch node SW. The voltage detection circuit 140 is used to detect the voltage difference between the bootstrap node BST and the switch node SW, and compare the voltage difference with the first threshold voltage and the second threshold voltage to output a detection signal ctrl_bst according to the comparison result, wherein when the voltage difference between the bootstrap node BST and the switch node SW increases to be greater than the second threshold voltage, the detection signal ctrl_bst flips to the first level, and when the voltage difference between the bootstrap node BST and the switch node SW decreases to be less than the first threshold voltage, the detection signal ctrl_bst flips to the second level, and the second threshold voltage is greater than the first threshold voltage. The logic control circuit 110 is used to output a second-level control signal ctrl_hs to turn off the main switch tube HS when the detection signal ctrl_bst is at the second level, and output a first-level control signal ctrl_ls to turn on the synchronous switch tube LS.

[0035] The charge pump circuit 150 is used to charge the bootstrap capacitor Cbst when the main switch HS is turned off.

[0036] Figure 2 Shows Figure 1 The circuit diagram of the buck converter is shown in Figure 1. Figure 2 The logic control circuit 110 , the resistor R1 , the resistor R2 , and the comparator 160 are not shown.

[0037] See also Figure 2The charge pump circuit 150 includes diodes D1-D2, a charge pump capacitor Cpunp, and switches S1-S2. The anode of the diode D2 is connected to the input voltage Vin, the cathode of the diode D2 is connected to the anode of the diode D1, and the cathode of the diode D1 is connected to the bootstrap node BST. The charge pump capacitor Cpunp and the switch S1 are connected between the cathode of the diode D2 and the ground terminal in sequence, and the switch S2 is connected between the input voltage Vin and the intermediate node between the charge pump capacitor Cpunp and the switch S1.

[0038] When the main switch tube HS is turned off, the switch S1 is turned off and the switch S2 is turned on to pump up the first plate voltage of the charge pump capacitor Cpunp to the input voltage Vin, so that the charge pump capacitor Cpunp charges the bootstrap capacitor Cbst; when the main switch tube HS is turned on, the switch S1 is turned on and the switch S2 is turned off to charge the charge pump capacitor Cpunp through the input voltage Vin.

[0039] When the input voltage Vin of the buck converter 100 is relatively low, in no-load or light-load mode, especially when the high-temperature leakage is large, the main switch tube HS needs to be frequently turned off to start the charge pump circuit 150 to charge the bootstrap capacitor Cbst, resulting in large power consumption of the buck converter 100 and affecting the light-load efficiency. In addition, the voltage detection circuit 140 of the buck converter 100 also needs to work all the time, further increasing the power consumption of the buck converter 100.

[0040] Figure 3 FIG. 4 is a schematic structural diagram of a buck converter according to a first embodiment of the present invention.

[0041] See also Figure 3 The buck converter 200 includes a power circuit and a drive circuit. The power circuit and voltage divider network of the buck converter 200 are the same as those of the buck converter 100, and will not be described in detail here. Figure 3 Only some components of the power circuit are shown.

[0042] The driving circuit includes a logic control circuit, a driving unit 220, a driving unit 230, a bootstrap capacitor Cbst, a charge pump circuit 250 and a comparator. The bootstrap capacitor Cbst and the charge pump circuit 250 constitute a bootstrap power supply circuit of the buck converter 200. For the convenience of explanation, Figure 3 The logic control circuit and the comparator of the driving circuit are not shown.

[0043] The comparator is used to compare the feedback voltage Vfb of the output voltage Vout of the buck converter 200 with the reference voltage Vref, so as to obtain the pulse width modulation signal PWM according to the comparison result. The logic control circuit is used to receive the pulse width modulation signal PWM, and provide the control signal ctrl_hs for controlling the main switch tube HS to be turned on and off and the control signal ctrl_ls for controlling the synchronous switch tube LS to be turned on and off, wherein the control signal ctrl_hs and the control signal ctrl_ls are, for example, pulse width modulation signals. The driving unit 220 is connected between the bootstrap node BST and the switch node SW, and is used to generate the driving signal hs_on according to the control signal ctrl_hs to drive the main switch tube HS to be turned on and off. The driving unit 230 is connected between the power supply voltage Vdd and the ground terminal, and is used to generate the driving signal ls_on according to the control signal ctrl_ls to drive the synchronous switch tube LS to be turned on and off. In each switching cycle, the main switch tube HS and the synchronous switch tube LS are alternately turned on and off, and the inductance in the power circuit is charged and discharged, thereby providing a DC output voltage at the output terminal. The control signal ctrl_hs controls the main switch tube HS to be turned on at the first level, and controls the main switch tube HS to be turned off at the second level. The first level can be a high level or a low level. When the first level is a high level, the second level is a low level. When the first level is a low level, the second level is a high level. In the following, the embodiment of the present invention is described by taking the first level as a high level and the second level as a low level as an example.

[0044] The bootstrap capacitor Cbst is connected between the bootstrap node BST and the switch node SW. The bootstrap node BST is used to supply power to the driving unit 220 .

[0045] The charge pump circuit 250 receives the control signal ctrl_hs and is connected to the bootstrap node BST. The charge pump circuit 250 includes a pumping unit 251, a pumping unit 252, and a switch control unit 253. When the control signal ctrl_hs is at the second level (the main switch tube HS is turned off), one of the pumping units 251 and 252 charges the bootstrap capacitor Cbst; and when the control signal ctrl_hs is at the first level (the main switch tube HS is turned on), the pumping unit 251 and the pumping unit 252 charge the bootstrap capacitor Cbst alternately.

[0046] The pump-up unit 251 includes a charge pump capacitor C1, a diode D3 and a first switch network. The first switch network includes switches S3-S5. Switch S3 is connected between the ground terminal and the first plate of the charge pump capacitor C1, switch S5 is connected between the power supply voltage Vdd and the second plate of the charge pump capacitor C1, switch S4 is connected between the power supply voltage Vdd and the first plate of the charge pump capacitor C1, the second plate of the charge pump capacitor C1 is also connected to the anode of the diode D3, and the cathode of the diode D3 is connected to the bootstrap node BST. The pump-up unit 252 includes a charge pump capacitor C2, a diode D4 and a second switch network. The second switch network includes switches S6-S8. Switch S6 is connected between the ground terminal and the first plate of the charge pump capacitor C2, switch S7 is connected between the power supply voltage Vdd and the second plate of the charge pump capacitor C2, switch S8 is connected between the power supply voltage Vdd and the first plate of the charge pump capacitor C2, the second plate of the charge pump capacitor C2 is also connected to the anode of the diode D4, and the cathode of the diode D4 is connected to the bootstrap node BST.

[0047] The first switch network is configured such that in the charging state of the pumping unit 251, the first plate of the charge pump capacitor C1 is connected to the ground terminal, and the second plate is connected to the power supply voltage Vdd; and in the pumping state of the pumping unit 251, the first plate of the charge pump capacitor C1 is connected to the power supply voltage Vdd, and the second plate is connected to the bootstrap node BST via the diode D3; the second switch network is configured such that in the charging state of the pumping unit 252, the first plate of the charge pump capacitor C2 is connected to the ground terminal, and the second plate is connected to the power supply voltage Vdd; and in the pumping state of the pumping unit 252, the first plate of the charge pump capacitor C2 is connected to the power supply voltage Vdd, and the second plate is connected to the bootstrap node BST via the diode D4.

[0048] The switch control unit 253 is used to control the first switch network and the second switch network, so that when the main switch tube HS is turned off, one of the pump-up unit 251 and the pump-up unit 252 is in a pumping state and the other is in a charging state, and when the main switch tube HS is turned on, the pump-up unit 251 and the pump-up unit 252 are alternately in a pumping state and a charging state. The pump-up unit 251 and the pump-up unit 252 are alternately in a pumping state and a charging state, which means that the pump-up unit 251 and the pump-up unit 252 switch working states according to a certain rule, and when one of them is in a pumping state, the other is in a charging state. For example, when the main switch tube HS is just turned on, the pump-up unit 251 is in a pumping state, and at this time, the pump-up unit 252 is in a charging state. After reaching a first predetermined time, the pump-up unit 251 switches to a charging state, and the pump-up unit 252 switches to a pumping state. After reaching a second predetermined time, the pump-up unit 251 switches to a pumping state, and the pump-up unit 252 switches to a charging state, and so on.

[0049] The switch control unit 253 controls the first switch network and the second switch network through the clock signals Φ1 and Φ2 generated according to the control signal ctrl_hs, thereby controlling the working state of the pump-up units 251 and 252. Among them, the switch S4, the switch S6-S7 are controlled by the clock signal Φ1, the switch S3, the switch S5, and the switch S8 are controlled by the clock signal Φ2, and the clock signal Φ1 and the clock signal Φ2 are non-overlapping clock signals. The clock signal Φ1 and the clock signal Φ2, for example, control the corresponding switches to be turned on at the first level. The switch control unit 253, for example, includes a charge pump oscillator, which works when the main switch tube HS is turned on, so that the switch control unit 253 can make one of the clock signals Φ1 and the clock signal Φ2 at a high level and the other at a low level in the first half of a cycle, and switch the clock signal at a high level in the first half of the cycle to a low level in the second half of the cycle, and switch the clock signal at a low level in the first half of the cycle to a high level.

[0050] Figure 4a-4b FIG. 2 shows an equivalent circuit diagram of a charge pump circuit according to a first embodiment of the present invention when operating in different states. For the convenience of explanation, Figure 4a-4b The switch control unit 253 is omitted.

[0051] See also Figure 4a When the clock signal Φ1 switches to a high level and the clock signal Φ2 switches to a low level, the pumping unit 251 works in a pumping state to charge the bootstrap capacitor Cbst, and the pumping unit 252 works in a charging state to charge the charge pump capacitor C2. At this time, the switches S4, S6-S7 are turned on, the switches S3, S5, and S8 are turned off, and the first plate of the charge pump capacitor C1 is switched from being connected to the ground terminal to being connected to the power supply voltage Vdd, so that the voltage of the second plate of the charge pump capacitor C1 is pumped up to the power supply voltage Vdd, so that the second plate of the charge pump capacitor C1 charges the bootstrap capacitor Cbst through the diode D3, and at the same time, the second plate of the charge pump capacitor C2 is connected to the power supply voltage Vdd, and the first plate of the charge pump capacitor C2 is connected to the ground terminal, so as to charge the charge pump capacitor C2 through the power supply voltage Vdd.

[0052] See also Figure 4bWhen the clock signal Φ1 switches to a low level and the clock signal Φ2 switches to a high level, the pumping unit 251 works in a charging state to charge the charge pump capacitor C1, and the pumping unit 252 works in a pumping state to charge the bootstrap capacitor Cbst. At this time, the switches S4, S6-S7 are turned off, the switches S3, S5, and S8 are turned on, the first plate of the charge pump capacitor C1 is connected to the ground terminal, and the second plate of the charge pump capacitor C1 is connected to the power supply voltage Vdd to charge the charge pump capacitor C1 through the power supply voltage Vdd. At the same time, the first plate of the charge pump capacitor C2 is switched from being connected to the ground terminal to being connected to the power supply voltage Vdd, so that the voltage of the second plate of the charge pump capacitor C2 is pumped up to the power supply voltage Vdd, so that the second plate of the charge pump capacitor C2 charges the bootstrap capacitor Cbst through the diode D4.

[0053] Figure 5 FIG. 4 is a circuit diagram of a charge pump circuit according to a first embodiment of the present invention.

[0054] See also Figure 5 , the switches S3-S8 of the charge pump circuit 250 can be implemented by MOS tubes, specifically, switches S3 and S6 are implemented by NMOS tubes, and switches S4-S5 and switches S7-S8 are implemented by PMOS tubes. At this time, the switch control unit 253 also needs to output the inverted signal Φ1_b of the clock signal Φ1 and the inverted signal Φ2_b of the clock signal Φ2, wherein the clock signal Φ1 controls the switch S6, the clock signal Φ1_b controls the switches S4 and S7, the clock signal Φ2 controls the switch S3, and the clock signal Φ2_b controls the switches S5 and S8.

[0055] Figure 6 Shows Figure 5 The timing diagram of the charge pump circuit shown.

[0056] See also Figure 6 , the clock signal Φ1 changes synchronously with its inverted signal Φ1_b, and the clock signal Φ2 changes synchronously with its inverted signal Φ2_b. The clock signals Φ1 and Φ2 theoretically change synchronously, but in practice there will be a certain dead time.

[0057] When the control signal ctrl_hs has a rising edge, that is, when the main switch tube HS switches from off to on, the clock signals Φ1 and Φ2 begin to change periodically. In the first sub-period of each cycle, the clock signal Φ1 is low and the clock signal Φ2 is high. In the second sub-period of each cycle, the clock signal Φ1 is high and the clock signal Φ2 is low. It can be understood that in the first sub-period of each cycle, the clock signal Φ1 is high and the clock signal Φ2 is low, and in the second sub-period of each cycle, the clock signal Φ1 is low and the clock signal Φ2 is high. It is also feasible.

[0058] In the buck converter 200 provided in the first embodiment of the present application, when the main switch tube HS is turned on, the charge pump circuit 250 alternately charges the bootstrap capacitor Cbst by the pump-up units 251 and 252, so that the voltage of the bootstrap node BST can be maintained at a preset value, i.e., 2*Vdd-VD-Vin, where VD represents the on-resistance of the diode D3 / D4, so that the main switch tube HS can be kept in the on state when needed, without being turned off in the middle to charge the bootstrap capacitor Cbst, and thus the light-load efficiency of the buck converter 200 can be improved. In addition, in some embodiments, the circuit can be provided without the need to set a voltage detection circuit, which can reduce the power consumption of the buck converter 200 and reduce the chip area.

[0059] However, the inventors of the present application discovered that, although theoretically when the main switch tube HS is turned on, the voltage of the bootstrap node BST can be maintained at a preset value, i.e., 2*Vdd-VD-Vin, when the frequencies of the clock signals Φ1 and Φ2 are low or there is a circuit failure, the voltage of the bootstrap node BST may also decrease due to leakage of the bootstrap capacitor Cbst, thereby reducing the voltage difference between the bootstrap node BST and the switch node SW to less than the first threshold voltage. Based on this, the invention of the present application improves the buck converter 200 of the first embodiment.

[0060] Figure 7 FIG. 4 is a circuit diagram of a buck converter according to a second embodiment of the present invention.

[0061] The buck converter of the second embodiment of the present invention is an improvement on the buck converter of the first embodiment. The same contents of the buck converter and the first embodiment are not described here. Only the differences between the buck converter and the first embodiment are described below.

[0062] See also Figure 7 The bootstrap power supply circuit of the buck converter 200 further includes a voltage detection circuit 240 .

[0063] The voltage detection circuit 240 is used to detect the voltage difference between the bootstrap node BST and the switch node SW, and compare the voltage difference with the first threshold voltage to output a detection signal ctrl_bst according to the comparison result. The initial level of the detection signal ctrl_bst is the first level. When the voltage detection circuit 240 detects that the voltage difference between the bootstrap node BST and the switch node SW decreases to less than the first threshold voltage, the detection signal ctrl_bst flips to the second level.

[0064] The detection signal ctrl_bst is also provided to the logic control circuit. When the detection signal ctrl_bst is at the second level, the logic control circuit outputs the second level control signal ctrl_hs to control the main switch tube HS to turn off, and outputs the first level control signal ctrl_ls to control the synchronous switch tube LS to turn on.

[0065] Furthermore, the driving circuit of the buck converter 200 further includes a logic unit 260. The logic unit 260 is used to perform an AND operation on the detection signal ctrl_bst and the control signal ctrl_hs to obtain the control signal ctrl_hs_a. The logic unit 260 is implemented, for example, by an AND gate. By setting the logic unit 260, it can be ensured that the main switch tube HS is turned on only after the voltage detection circuit 240 is turned on, thereby improving the reliability of the circuit.

[0066] At this time, the driving unit 220 no longer receives the control signal ctrl_hs, but receives the control signal ctrl_hs_a, that is, the driving unit 220 outputs the driving signal hs_on through the control signal ctrl_hs_a to drive the main switch tube HS to be turned on and off.

[0067] Furthermore, the voltage detection circuit 240 is turned on and off by the control signal ctrl_hs, and is turned on when the control signal ctrl_hs is at the first level, i.e., the main switch tube HS is turned on, and is turned off when the control signal ctrl_hs is at the second level, i.e., the main switch tube HS is turned off, thereby reducing power consumption compared to the buck converter 100. The voltage detection circuit 240 is turned on and off, for example, by a switch.

[0068] According to the embodiments of the present invention as above, these embodiments do not describe all the details in detail, nor do they limit the invention to specific embodiments. Obviously, many modifications and changes can be made based on the above description. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can make good use of the present invention and the modified use based on the present invention. The scope of protection of the present invention shall be based on the scope defined by the claims of the present invention and their equivalents.

Claims

1. A bootstrap power supply circuit for a buck converter, the buck converter comprising a main switch connected between an input terminal and a switch node, and a drive unit connected to a control terminal of the main switch, the bootstrap power supply circuit comprising: A bootstrap capacitor connected between a bootstrap node and the switch node, the bootstrap node being used to supply power to the drive unit; a charge pump circuit connected to the bootstrap node, the charge pump circuit comprising a first pumping unit and a second pumping unit, the first pumping unit comprising a first charge pump capacitor, the second pumping unit comprising a second charge pump capacitor, Wherein, when the main switch tube is turned on, the first pump-up unit and the second pump-up unit are alternately in a pumping state for charging the bootstrap capacitor and a charging state for charging their own charge pump capacitor.

2. The bootstrap power supply circuit according to claim 1, wherein: When the main switch tube is turned off, one of the first pumping unit and the second pumping unit is in a pumping state to charge the bootstrap capacitor, and the other is in a charging state to charge its own charge pump capacitor.

3. The bootstrap power supply circuit according to claim 1 or 2, wherein: The first pumping unit further includes a first diode and a first switch network, wherein the anode of the first diode is connected to the second plate of the first charge pump capacitor, and the cathode of the first diode is connected to the bootstrap node; The second pumping unit further includes a second diode and a second switch network, the anode of the second diode is connected to the second plate of the second charge pump capacitor, and the cathode of the second diode is connected to the bootstrap node. wherein the first switch network is configured to connect the first plate of the first charge pump capacitor to the ground terminal and the second plate to the power supply voltage in the charging state of the first pumping unit, and to connect the first plate of the first charge pump capacitor to the power supply voltage and the second plate to the bootstrap node via the first diode in the pumping state of the first pumping unit; The second switching network is configured to connect the first plate of the second charge pump capacitor to the ground terminal and the second plate to the power supply voltage in the charging state of the second pumping unit, and to connect the first plate of the second charge pump capacitor to the power supply voltage and the second plate to the bootstrap node via the second diode in the pumping state of the second pumping unit.

4. The bootstrap power supply circuit according to claim 3, wherein: The charge pump circuit further includes: A switch control unit is used to generate a clock signal according to a first control signal used to control the main switch tube to be turned on and off, so as to control the first switch network and the second switch network.

5. The bootstrap power supply circuit according to claim 3, wherein: The first switch network comprises: A first switch connected between a ground terminal and a first plate of the first charge pump capacitor; a second switch connected between the first plate of the first charge pump capacitor and the power supply voltage; a third switch connected between the second plate of the first charge pump capacitor and the power supply voltage; The second switch network comprises: a fourth switch connected between a ground terminal and a first electrode plate of the second charge pump capacitor; a fifth switch connected between the first plate of the second charge pump capacitor and the power supply voltage; A sixth switch is connected between the second plate of the second charge pump capacitor and the power supply voltage.

6. The bootstrap power supply circuit according to claim 5, wherein: The first switch and the fourth switch are implemented by NMOS tubes, and the second switch, the third switch, the fifth switch and the sixth switch are implemented by PMOS tubes.

7. The bootstrap power supply circuit according to claim 1, further comprising: a voltage detection circuit, configured to detect a voltage difference between the bootstrap node and the switch node, and compare the voltage difference with a first threshold voltage to output a detection signal according to the comparison result, When the voltage difference decreases to less than the first threshold voltage, the detection signal turns off the main switch tube, and the voltage detection circuit is turned on when the main switch tube is turned on, and is turned off when the main switch tube is turned off.

8. A drive circuit for a buck converter, the buck converter comprising a main switch connected between an input terminal and a switch node, the drive circuit comprising: a comparator, for comparing a feedback voltage of the output voltage of the buck converter with a reference voltage to obtain a pulse width modulation signal; A logic control circuit, used for generating a first control signal according to the pulse width modulation signal, wherein the first control signal is used for controlling the on and off of the main switch tube; A driving unit, connected to the bootstrap node, for driving the main switch tube to be turned on and off; The bootstrap power supply circuit according to any one of claims 1 to 6, is used to power the drive unit.

9. The driving circuit according to claim 8, wherein: The bootstrap power supply circuit also includes: a voltage detection circuit, configured to detect a voltage difference between the bootstrap node and the switch node, and compare the voltage difference with a first threshold voltage to output a detection signal according to the comparison result, Wherein, when the voltage difference decreases to less than the first threshold voltage, the detection signal turns off the main switch tube, and the voltage detection circuit is turned on when the main switch tube is turned on, and is turned off when the main switch tube is turned off; The driving circuit further includes: a logic unit, configured to perform an AND operation on the first control signal and the detection signal, and output a second control signal, The driving unit receives the second control signal and drives the main switch tube to be turned on and off according to the second control signal.

10. A buck converter, comprising: A main switch tube connected between the input terminal and the switch node; A synchronous switch tube connected between the switch node and the ground terminal; an inductor connected between the switch node and the output terminal; as well as A drive circuit as claimed in any one of claims 8 to 9.

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