A flying capacitor pre-charge circuit for a multi-mode DC-DC converter

Abstract

The present application belongs to the technical field of DC-DC converter control, and particularly relates to a flying capacitor pre-charging method for a multi-modal DC-DC converter. The flying capacitor pre-charging method makes the flying capacitor charging current controllable, and avoids damage to devices caused by a large pulse current. Meanwhile, the control mode of the flying capacitor pre-charging method is relatively simple, and no obvious additional loss is generated when the DC-DC converter is normally working.

Description

Technical Field

[0001] This invention belongs to the field of DC-DC converter control technology, and specifically relates to a flying capacitor pre-charging method for a multi-mode DC-DC converter. Background Technology

[0002] DC-DC converters are the core of modern electronic systems for voltage conversion and energy management, and are widely used in various scenarios such as consumer electronics, computing and servers, and communication and network equipment. Traditional single-topology DC-DC converters, such as Boost and Buck converters, have limited applications due to issues such as limited voltage conversion range and significant efficiency bottlenecks at extreme conversion ratios. Multimode DC-DC converters based on topology switching switch modes according to the real-time relationship between input and output voltages, overcoming the limitations of traditional single-topologies. During normal operation, the flying capacitors in a multimode DC-DC converter perform charge transport; however, during power-up, the flying capacitors have no charging path, store almost no charge, and have a zero voltage. If the circuit starts operating directly at this time, the large difference between the zero voltage on the flying capacitors and their normal operating voltage, coupled with the very low resistance in the loop, can generate a huge pulse charging current, potentially damaging circuit components. Summary of the Invention

[0003] The present invention aims to solve the above-mentioned problems by proposing a flying capacitor pre-charge circuit for a multi-mode DC-DC converter.

[0004] The technical solution of this invention is:

[0005] A pre-charge circuit for a flying capacitor in a multi-mode DC-DC converter is provided. The flying capacitor branch of the multi-mode DC-DC converter includes a power switch S1 and a flying capacitor. The input terminal of the power switch S1 is connected to the positive terminal of the input power supply, and the output terminal of the power switch S1 is connected to the positive plate of the flying capacitor, with the connection point defined as SW1. The pre-charge circuit includes a switch and a current source I connected in series. charge The switch is connected to the negative plate of the flying capacitor, and the connection point is defined as SW2. Current source I charge The outflow terminal is connected to the negative terminal of the power supply; it also includes a drive and logic control module, which is used to control the power switch S1 to turn on and control the switch of the pre-charge circuit to close when the pre-charge enable signal EN is received, so as to form a charging circuit for the flying capacitor and pre-charge the flying capacitor.

[0006] It also includes a detection module that monitors the voltage of the flying capacitor in real time. When the voltage reaches a set detection threshold, it outputs a control signal to shut off the charging circuit through the drive and logic control module.

[0007] Specifically, the current source I chargeFrom the bandgap current I BG The current is generated by a current mirror, and the switch of the pre-charge circuit is set to NMOS transistor NM3. The gate of NM3 and the gate of power switch S1 are controlled by the same control signal C_EN.

[0008] Specifically, the detection module includes a first sampling branch, a second sampling branch, a comparator, and a NAND gate. Both the first and second sampling branches consist of two resistors connected in series. The negative terminal of the comparator is connected to SW1 through the first sampling branch, and the positive terminal of the comparator is connected to SW2 and the bias current I through the second sampling branch. bias Bias current I bias Used to set detection thresholds The voltage across the comparator is:

[0009] ,

[0010] ,

[0011] in, This is the voltage at the negative terminal of the comparator. The positive voltage of the comparator and The resistance values ​​are the two series resistors in the first sampling branch. and The resistance values ​​are the two series resistors in the second sampling branch; take the resistance values. = , = Set the flying capacitor voltage detection threshold to V. F The following relationship exists:

[0012] ,

[0013] By comparison and The size of the flying capacitor voltage difference is used to detect the voltage difference. Has the set threshold been reached? ;

[0014] One input of the NAND gate is connected to the output of the comparator, the other input is connected to the enable signal EN, and the output is the control signal C_EN.

[0015] Specifically, the detection module includes a first sampling branch, a second sampling branch, a comparator, and a NAND gate. The first sampling branch consists of two resistors connected in series, and the second sampling branch consists of resistors connected in series followed by a reference voltage source. The reference voltage source is used to set the detection threshold. The negative terminal of the comparator is connected to SW1 through the first sampling branch, and the positive terminal of the comparator is connected to SW2 through the second sampling branch. The voltage across the comparator is:

[0016] ,

[0017] ,

[0018] in, This is the voltage at the negative terminal of the comparator. The positive voltage of the comparator and The resistance values ​​are the two series resistors in the first sampling branch. and The resistance values ​​are the two series resistors in the second sampling branch. Use the reference voltage source voltage; select the resistance value. = , = Set the flying capacitor voltage detection threshold to V. F The following relationship exists:

[0019] .

[0020] By comparison and The size of the flying capacitor voltage difference is used to detect the voltage difference. Has the set threshold been reached? ;

[0021] One input of the NAND gate is connected to the output of the comparator, the other input is connected to the enable signal EN, and the output is the control signal C_EN.

[0022] Specifically, the multi-mode DC-DC converter is a hybrid architecture DC-DC converter that supports switching between at least mode 1 and mode 2. The flying capacitor is fixedly connected to the input power supply in mode 1 and performs charge transfer in mode 2.

[0023] A method for pre-charging the flying capacitor of a multimode DC-DC converter includes:

[0024] Pre-charge start-up steps: Before power-on soft start, in response to the effective level of the enable signal EN, control the power switch S1 to turn on and close the pre-charge circuit switch between the SW2 node and the negative terminal of the power supply.

[0025] Constant current charging steps: The flying capacitor is charged with a constant current through the controllable current source in the pre-charging circuit, so that the voltage of the flying capacitor gradually increases.

[0026] Threshold detection steps: Real-time detection of the voltage difference across the flying capacitor to determine whether it reaches the set detection threshold;

[0027] Pre-charge termination procedure: When the set detection threshold is reached, the pre-charge circuit switch and power switch S1 are turned off, ending the pre-charge process and entering normal operation mode.

[0028] The beneficial effects of this invention are as follows: The flying capacitor pre-charging method of this invention makes the flying capacitor charging current controllable, avoiding damage to the device caused by large pulse currents. At the same time, the control method of this invention is relatively simple and does not generate significant additional losses during normal operation of the DC-DC converter. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a hybrid architecture DC-DC converter.

[0030] Figure 2 This is one of the circuit diagrams for the flying capacitor pre-charge technology.

[0031] Figure 3 This is the second schematic diagram of the flying capacitor pre-charge technology circuit.

[0032] Figure 4 This is a schematic diagram of the specific circuit for the flying capacitor pre-charging technology.

[0033] Figure 5 This is a schematic diagram of a control circuit for a flying capacitor pre-charging technology.

[0034] Figure 6 This is a schematic diagram of another flying capacitor pre-charge technology control circuit. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings.

[0036] This invention uses a hybrid architecture DC-DC converter as an example for illustration, and its structure is as follows: Figure 1 As shown. The hybrid architecture DC-DC converter includes power switching devices S1-S5, power inductor L, and flying capacitor C. F Output capacitor C O and load resistance R L .

[0037] When S1 and S3 are normally on, S2 is normally off, and S4 and S5 are alternately on in different configurations, the converter operates in mode 1; in this mode, the voltage conversion ratio is... for:

[0038] ,

[0039] Theoretically, the voltage conversion ratio under this mode is The range is (1, ∞).

[0040] When S1, S3, and S4 are turned on in the same switch configuration, and S2 and S5 are turned on in another switch configuration, the converter operates in mode 2; in this mode, the voltage conversion ratio is... for:

[0041] ,

[0042] Theoretically, the voltage conversion ratio M1 in this mode is in the range of (2, ∞).

[0043] When the conversion ratio is low, the circuit operates in mode 1, which is a typical Boost circuit structure. When the conversion ratio is high, the circuit operates in mode 2, which is a hybrid Boost circuit structure, and can reduce the inductor current in steady state. In mode 1, the flying capacitor is fixedly connected to the input voltage VIN. In mode 2, the voltage across the flying capacitor is VIN and it performs charge transfer. The SW1 node switches between VIN and 2VIN.

[0044] Before the circuit soft-starts, all switches are off, and the flying capacitor has no charging path, so its voltage is zero. After the soft-start begins, the circuit initially operates in mode 1, and subsequently operates in the corresponding mode based on the output voltage level. If the flying capacitor is not pre-charged before the soft-start begins, the circuit VIN-S1-C will be interrupted the moment S1 and S3 are turned on. F -S3 will generate a huge pulse charging current, which may even damage the switching device. This invention proposes a flying capacitor pre-charging technology for a multi-mode DC-DC converter. At the SW2 node of the flying capacitor negative plate, pre-charging is achieved by adding an additional branch and current source. The aim is to complete the charging of the flying capacitor with a controllable current before the circuit starts working, so as to avoid damage to the device.

[0045] Figure 2 This is one of the circuit diagrams for the flying capacitor pre-charge technology proposed in this invention. Since the power stages are not yet operational at this time... Figure 1 The relevant power stage circuitry has been omitted, and the corresponding important nodes have been labeled. This scheme only adds a branch for a switch and current source between the SW2 node and ground, and the power transistor S1 uses an NMOS. During pre-charging, the power transistor S1 is turned on, and at the same time, the lower branch switch is closed, VIN-S1-I charge A current source forms a loop to charge the flying capacitor with a constant current. When no pre-charge command is received, the switch is turned off, and simultaneously, the drive and logic module controls the power transistor S1 to turn off, cutting off the charging loop. The lower branch current source I... charge This refers to the charging current of the flying capacitor, which is determined by designing a current source I. charge The size of the flying capacitor can control its charging rate.

[0046] Figure 3This is the second schematic diagram of the flying capacitor pre-charge technology circuit proposed in this invention. Since the power stages are not yet operational at this point... Figure 1 The relevant power stage circuitry has been omitted, but important nodes have been labeled. This circuit diagram only shows power transistor S1 implemented using a PMOS; its operating principle is the same as... Figure 2 same.

[0047] Figure 4 This is a specific circuit diagram of the flying capacitor pre-charging technology proposed in this invention. The specific circuit implementation is not unique; only one example is used here to illustrate the principle. Current source I charge With bandgap current I BG The current is generated via a current mirror; NM3 is a switch, and S1 is a power transistor, both controlled by signal C_EN during the pre-charge phase. At the start of pre-charge, switch NM3 is turned on, and power transistor S1 is simultaneously turned on via the driver and logic module. The flying capacitor charges with the current set by NM2, eventually reaching a voltage of VIN. When the flying capacitor voltage reaches the set threshold, switch NM3 and power transistor S1 are turned off via C_EN, ending the pre-charge process.

[0048] Figure 5 This is one of the control circuits for the flying capacitor pre-charging technology proposed in this invention. The specific circuit implementation is not unique; only two examples are used here to illustrate the principle. The control circuit mainly consists of a comparator, which detects the current flying capacitor charging voltage level by comparing the voltages at the junctions of SW1 and SW2 during the pre-charging phase. The comparator's positive terminal voltage V... + Negative terminal voltage V-, bias current I bias Node voltage V SW1 V SW2 Set the flying capacitor voltage detection threshold to V. F The following relationship exists:

[0049] ,

[0050] ,

[0051] Ignoring the effect of hysteresis, at the inflection point of the comparator output voltage, we have:

[0052] ,

[0053] Take the resistance value = , = Then the following relationship exists:

[0054] ,

[0055] The enable signal EN is active high. When the enable signal EN is low or the comparator output C_finish is low, the control signal C_EN is high, and the switch NM3 and power transistor S1 in the pre-charge branch are off, stopping pre-charging. When the enable signal EN is high and the comparator output C_finish is high, C_EN is low, turning on the switch NM3 and power transistor S1 in the pre-charge branch to begin pre-charging.

[0056] Figure 6 This is the second control circuit for the flying capacitor pre-charging technology proposed in this invention. The control principle is... Figure 6 They are the same, differing only in the setting of the comparison thresholds for node voltages SW1 and SW2. The comparator positive terminal voltage V... + Negative terminal voltage V-, reference voltage V ref Node voltage V SW1 V SW2 Set the flying capacitor voltage detection threshold to V. F The following relationship exists:

[0057] ,

[0058] ,

[0059] Ignoring the effect of hysteresis, at the inflection point of the comparator output voltage, we have:

[0060] ,

[0061] Take the resistance value = , = Then the following relationship exists:

[0062] .

Claims

1. A flying capacitor pre-charge circuit for a multimode DC-DC converter, wherein the flying capacitor branch of the multimode DC-DC converter includes a power switch S1 and a flying capacitor, wherein the input terminal of the power switch S1 is connected to the positive terminal of the input power supply, and the output terminal of the power switch S1 is connected to the positive plate of the flying capacitor, with the connection point defined as SW1, characterized in that, The pre-charge circuit includes a switch and a current source I connected in series. charge The switch is connected to the negative plate of the flying capacitor, and the connection point is defined as SW2. Current source I charge The outflow terminal is connected to the negative terminal of the power supply; it also includes a drive and logic control module, which is used to control the power switch S1 to turn on and control the switch of the pre-charge circuit to close when the pre-charge enable signal EN is received, so as to form a charging circuit for the flying capacitor and pre-charge the flying capacitor. It also includes a detection module that monitors the voltage of the flying capacitor in real time. When the voltage reaches a set detection threshold, it outputs a control signal to shut off the charging circuit through the drive and logic control module.

2. The flying capacitor pre-charge circuit of the multimode DC-DC converter according to claim 1, characterized in that, The current source I charge From the bandgap current I BG The current is generated by a current mirror, and the switch of the pre-charge circuit is set to NMOS transistor NM3. The gate of NM3 and the gate of power switch S1 are controlled by the same control signal C_EN.

3. The flying capacitor pre-charge circuit of the multimode DC-DC converter according to claim 1, characterized in that, The detection module includes a first sampling branch, a second sampling branch, a comparator, and a NAND gate. Both the first and second sampling branches consist of two resistors connected in series. The negative terminal of the comparator is connected to SW1 through the first sampling branch, and the positive terminal of the comparator is connected to SW2 and the bias current I through the second sampling branch. bias Bias current I bias Used to set detection thresholds The voltage across the comparator is: ， ， in, This is the voltage at the negative terminal of the comparator. The positive voltage of the comparator and The resistance values ​​are the two series resistors in the first sampling branch. and The resistance values ​​are the two series resistors in the second sampling branch; take the resistance values. = , = Set the flying capacitor voltage detection threshold to V. F The following relationship exists: ， By comparison and The size of the flying capacitor voltage difference is used to detect the voltage difference. Has the set threshold been reached? ; One input of the NAND gate is connected to the output of the comparator, the other input is connected to the enable signal EN, and the output is the control signal C_EN.

4. The flying capacitor pre-charge circuit of the multimode DC-DC converter according to claim 1, characterized in that, The detection module includes a first sampling branch, a second sampling branch, a comparator, and a NAND gate. The first sampling branch consists of two resistors connected in series, and the second sampling branch consists of resistors connected in series followed by a reference voltage source. The reference voltage source is used to set the detection threshold. The negative terminal of the comparator is connected to SW1 through the first sampling branch, and the positive terminal of the comparator is connected to SW2 through the second sampling branch. The voltage across the comparator is: ， ， in, This is the voltage at the negative terminal of the comparator. The positive voltage of the comparator and The resistance values ​​are the two series resistors in the first sampling branch. and The resistance values ​​are the two series resistors in the second sampling branch. Use the reference voltage source voltage; select the resistance value. = , = Set the flying capacitor voltage detection threshold to V. F The following relationship exists: 。 5. Through comparison and The size of the flying capacitor voltage difference is used to detect the voltage difference. Has the set threshold been reached? ; One input of the NAND gate is connected to the output of the comparator, the other input is connected to the enable signal EN, and the output is the control signal C_EN.

6. The flying capacitor pre-charge circuit of the multimode DC-DC converter according to claim 1, characterized in that, The multi-mode DC-DC converter is a hybrid architecture DC-DC converter that supports switching between at least mode 1 and mode 2. The flying capacitor is fixedly connected to the input power supply in mode 1 and performs charge transfer in mode 2.

7. A method for pre-charging the flying capacitor of a multimode DC-DC converter, used in the pre-charging circuit of the multimode DC-DC converter according to any one of claims 1-5, comprising: Pre-charge start-up steps: Before power-on soft start, in response to the effective level of the enable signal EN, control the power switch S1 to turn on and close the pre-charge circuit switch between the SW2 node and the negative terminal of the power supply. Constant current charging steps: The flying capacitor is charged with a constant current through the controllable current source in the pre-charging circuit, so that the voltage of the flying capacitor gradually increases. Threshold detection steps: Real-time detection of the voltage difference across the flying capacitor to determine whether it reaches the set detection threshold; Pre-charge termination steps: When the set detection threshold is reached, the pre-charge circuit switch and power switch S1 are turned off, the pre-charge ends and the system enters normal operation mode.

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