Drive circuit, drive method and integrated circuit thereof

A drive circuit for a switch capacitor converter having first, second, third, and fourth power switches connected in series, can include: first, second, third, and fourth drivers configured to respectively drive the first, second, third power, and fourth power switches according to control signals; a bootstrap power supply circuit comprising a bootstrap capacitor configured to supply power to the first, second, and third drivers in a time-sharing manner; and a power supply configured to supply power to the fourth driver and charge the bootstrap capacitor, where the fourth power switch is grounded.

RELATED APPLICATIONS

This application claims the benefit of Chinese Patent Application No. 201910754639.1, filed on Aug. 15, 2019, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to the field of power electronics, and more particularly to drive circuits and methods.

BACKGROUND

Switch capacitor converters have advantages of relatively low input current, no large-scale power inductors, relatively low switching transistor voltage stress, and relatively high efficiency. Thus, switch capacitor converters are widely used today in fast charging technology for mobile devices, such as mobile phones.

DETAILED DESCRIPTION

Referring now toFIG. 1, shown is a schematic block diagram of an example switch capacitor converter with a drive circuit. In this example, the single-phase switch capacitor converter can include four switches, and each switch has an independent driver since the potential of each switch is different. Drive circuit11of the switches may provide a relatively large drive current, so the traditional integrated circuit (IC) of the switch capacitor converter would utilize three external bootstrap capacitors (e.g., CBST1, CBST2, and CBST3). The higher-power two-phase switch capacitor converter may need more external bootstrap capacitors due to the increase of the switches. In addition, the IC of the switch capacitor converter may need to provide more pins along with the increase of external bootstrap capacitors, which makes miniaturization of the IC difficult, and thus applications of the IC in small devices, such as mobile phones, may be limited.

In one embodiment, a drive circuit for a switch capacitor converter having first, second, third, and fourth power switches connected in series, can include: (i) first, second, third, and fourth drivers configured to respectively drive the first, second, third power, and fourth power switches according to control signals; (ii) a bootstrap power supply circuit comprising a bootstrap capacitor configured to supply power to the first, second, and third drivers in a time-sharing manner; and (iii) a power supply configured to supply power to the fourth driver and charge the bootstrap capacitor, where the fourth power switch is grounded.

Referring now toFIG. 2, shown is a schematic block diagram of an example switch capacitor converter with a drive circuit, in accordance with embodiments of the present invention. In this particular example, the switch capacitor converter can include drive circuit21, power switches Q1-Q4, flying capacitor Cf, and output capacitor Co. Power switches Q1-Q4may sequentially be connected in series between the first terminal and the second terminal (e.g., the ground terminal) of the input port. One end of flying capacitor Cf can connect to the common node of power switches Q1and Q2, and the other end of flying capacitor Cf can connect to the common node of power switches Q3and Q4. One end of output capacitor Co can connect to the common node of power switches Q2and Q3, and the other end of output capacitor Co can connect to the ground terminal. In particular embodiments, power switches Q1-Q4can use any suitable electrically controllable switch (e.g., a metal-oxide-semiconductor field-effect transistor (MOSFET), a bipolar-junction transistor (BJT), insulated gate bipolar transistor (IGBT), etc.).

In this example, power switches Q1and Q3can be controlled to be turned on simultaneously, power switches Q2and Q4can be controlled to be turned on simultaneously, and the on time intervals of power switches Q1and Q2may not be overlapped. The duty cycles of control signal VG1of power switch Q1and control signal VG3of power switch Q3can be equal, and the duty cycles of control signal VG2of power switch Q2and control signal VG4of power switch Q4can be equal. The on time intervals of power switches Q1and Q2may be controlled by duty cycles of the switch capacitor converter. Drive circuit21can include drivers U1, U2, U3, U4, bootstrap power supply circuit211, and power supply212. For example, drivers U1, U2, U3, and U4can generate drive signals according to control signals VG1-VG4of power switches Q1-Q4, in order to respectively drive power switch Q1-Q4.

Bootstrap power supply circuit211can include bootstrap capacitor CBST, which can supply power to drivers U1, U2, and U3in a time-sharing manner. Furthermore, bootstrap power supply circuit211can supply power to drivers U1and U3at the same time during a first part of time interval T1in an operation cycle, and may power to driver U2during a first part of time interval T2in the operation cycle. In addition, bootstrap capacitor CBST of bootstrap power supply circuit211can be charged by power supply212during a second part of time interval T1and/or during a second part of time interval T2in the operation cycle. That is, bootstrap capacitor CBST can be charged during a second part of time interval T1in the operation cycle, during a second part of time interval T2in the operation cycle, and/or charged during a second part of time interval T1and a second part of time interval T2, in the operation cycle.

Power supply212can supply power to driver U4and charge bootstrap capacitor CBST, where power switch Q4is grounded. Since one end of power switch Q4is grounded, it is more convenient to drive power switch Q4. The low voltage end of driver U4may be grounded, and a drive voltage of power switch Q4can be provided by power supply212at the high voltage end of driver U4, so driver U4can output the drive voltage to drive power switch Q4when control signal VG4is active. For example, power supply212can be implemented by a liner regulator (e.g., a low-dropout regulator [LDO]). For example, bootstrap capacitor CBST can be coupled between the high voltage end and the low voltage end of driver U1, and also to the high voltage ends of drivers U2and U3.

Bootstrap power supply circuit211can include switch circuit2111for switching the connection point of one end of bootstrap capacitor CBST. Switch circuit2111can include switches K1and K2. For example, switch K1can connect between one end of bootstrap capacitor CBST and the common node of power switches Q1and Q2, and switch K2can connect between one end of bootstrap capacitor CBST and the ground. When bootstrap power supply circuit211supplies power to drivers U1and U3, or supplies power to driver U2, one end of bootstrap capacitor CBST can couple to the common node of power switches Q1and Q2. That is, bootstrap capacitor CBST can couple in parallel with driver U1, and when power supply212charges bootstrap capacitor CBST, one end of bootstrap capacitor CBST can couple to the ground.

Bootstrap power supply circuit211can also include clamp circuits2112-0and2112-1. For example, bootstrap capacitor CBST can couple to the high voltage ends of drivers U2and U3respectively through clamp circuits2112-0and2112-1. Bootstrap capacitor CBST can couple to the high voltage end of driver U2through one clamp circuit2112-0, and bootstrap capacitor CBST can connect to the high voltage end of driver U3through clamp circuit2112-1. Since the potentials across power switches Q2and Q3are different, the potentials of the low voltage ends of drivers U2and U3may also be different. Therefore, it may be necessary to clamp the output voltages of drivers U2and U3to the predetermined value through clamp circuits2112-0and2112-1, and the predetermined value can be the drive voltage that meets the driving requirements of power switches Q2and Q3. Further, the predetermined value can be equal to the output voltage of power supply212.

Referring now toFIG. 3, shown is a schematic block diagram of an example clamp circuit, in accordance with embodiments of the present invention. In this particular example, each clamp circuit2112(e.g.,2112-0) can include diode D1, transistor M1, Zener diode DZ, and resistor R. For example, the anode of diode D1can connect to bootstrap capacitor CBST, the cathode of diode D1can connect to one power end of transistor M1, and the other power end of transistor M1can connect to the high voltage end of the corresponding driver. One end of resistor R can connect to the anode of diode D1, and the other end of resistor R can connect to the control end of transistor M1. The cathode of Zener diode DZ can connect to the control end of transistor M1, and the anode of Zener diode DZ can connect to the low voltage end of the corresponding driver. Driver U1may not need to adjust the drive voltage of power switch Q1through clamp circuit2112, since bootstrap capacitor CBST can be coupled between the high voltage and low voltage ends of driver U1. When control signal VG1is active, driver U1can output the voltage between the two ends of bootstrap capacitor CBST, in order to drive power switch Q1.

In this example, drive circuit21can supply power to drivers U1and U3at the same time during a first part of time interval T1in an operation cycle, and may supply power to driver U2during a first part of time interval T2in the operation cycle. In addition, bootstrap capacitor CBST can be charged by power supply212during a second part of time interval T1, and/or a second part of time interval T2, in the operation cycle. In addition, driver U4may be powered by power supply212. In this way, the drive voltages of drivers U1-U4can be the same voltage. Therefore, drive circuit21may utilize a time-sharing control method, in order to supply power to drivers U1-U4of power switches Q1-Q4, such that only one bootstrap capacitor is required to drive power switches Q1-Q4. Also, the drive voltage of each driver may be the same when power switches do not share a common ground, which can simplify the drive circuit of the switch capacitor converter, reduce the number of drive components, and save circuit costs.

Referring now toFIG. 4, shown is a waveform diagram of example operation of the switch capacitor converter, in accordance with embodiments of the present invention. For example, VG1-VG4may represent the control signals of power switches Q1-Q4, respectively, V1may represent the control signal of switch K1, and V2may represent the control signal of switch K2. An example operation process of the switch capacitor converter of particular embodiments will be described in detail below in conjunction with the waveform diagram.

Referring now toFIG. 5, shown is a schematic block diagram of example operation of the switch capacitor converter in the first time interval, in accordance with embodiments of the present invention. In this example, the switch capacitor converter may operate during a first part of time interval T1. Control signals VG1and VG3respectively corresponding to power switches Q1and Q3can both be active (e.g., VG1=1, VG3=1), and control signals VG2and VG4respectively corresponding to power switches Q2and Q4may both be inactive (e.g., VG2=0, VG4=0), during a first part of time interval T1. In this example, control signal with logic ‘1’ represents an active high level, and control signal with ‘0’ represents an inactive low level. Here, the dashed line is the power supply path for the drive circuit to supply power to the drivers, and the dotted line is the power path of the switch capacitor converter.

Switch K1in switch circuit2111can be controlled by control signal V1. During a first part of time interval T1, control signal V1can be at a high level, and switch K1may be turned on, so one end of bootstrap capacitor CBST can effectively connect to the low voltage end of driver U1. Bootstrap capacitor CBST can supply power to driver U1of power switch Q1, and control signal VG1of power switch Q1may be equal to 1, so driver U1can activate a drive signal to drive power switch Q1to turn on. In general, the voltage across flying capacitor Cf is ½*Vin. At this stage, power switch Q1can be turned on, and the voltage at the first end of flying capacitor Cf may be Vin, such the voltage at the second end of flying capacitor Cf is ½*Vin. During a first part of time interval T1, control signal VG3of power switch Q3can be equal to 1, and bootstrap capacitor CBST may supply power to driver U3of the power switch Q3through clamp circuit2112-1corresponding to driver U3, so driver U3may activate the drive signal to drive power switch Q3to turn on.

At this stage, the low voltage end of driver U3is ½ *Vin, and the voltage at the first end of bootstrap capacitor CBST can be the sum of the voltage across bootstrap capacitor CBST and Vin. Thus, the input voltage of clamp circuit2112-1corresponding to driver U3with respect to the low voltage end of driver U3(not with respect to the ground) at this stage can be the sum of the voltage across bootstrap capacitor CBST and the voltage across flying capacitor Cf. In addition, clamp circuit2112-1corresponding to driver U3may reduce its output voltage to the acceptable operating voltage of driver U3or to be equal to the voltage across bootstrap capacitor CBST, such as by linear voltage regulation. During time interval T1, power switches Q1and Q3can be turned on, and input voltage Vin may supply power to the load via Q1-Cf-Q3-load. In addition, power switches Q1and Q3can respectively correspond to an internal capacitor, and bootstrap capacitor CBST may further supply power to internal capacitors C1and C3corresponding to power switches Q1and Q3during the first part of time interval T1in the operation cycle.

Referring now toFIG. 6, shown is another schematic block diagram of example operation of the switch capacitor converter in the first time interval, in accordance with embodiments of the present invention. In this example, the switch capacitor converter can operate during a second part of time interval T1. Control signals VG1and VG3respectively corresponding to power switches Q1and Q3may both be active (e.g., VG1=1, VG3=1), and control signals VG2and VG4respectively corresponding to power switches Q2and Q4may both be inactive (e.g., VG2=0, VG4=0), during a second part of time interval T1. Here, the dashed line is the power supply path for the drive circuit to supply power to the drivers, and the dotted line is the power path of the switch capacitor converter.

Switch K2in switch circuit2111can be controlled by control signal V2. During a second part of time interval T1, control signal V2can be at a high level, and switch K2may be turned on. Thus, one end of bootstrap capacitor CBST can be grounded, and the other end of bootstrap capacitor CBST may be coupled to power supply212. In this way, bootstrap capacitor CBST can be charged by power supply212. In addition, the drive voltages of drivers U1and U3can be maintained by the internal capacitors C1and C3, respectively, during the second part of time interval T1in the operation cycle.

Referring now toFIG. 7, shown is a schematic block diagram of example operation of the switch capacitor converter in the second time interval, in accordance with embodiments of the present invention. In this example, the switch capacitor converter may operate during a first part of time interval T2. Control signals VG1and VG3respectively corresponding to power switches Q1and Q3can both be inactive (e.g., VG1=0, VG3=0), and control signals VG2and VG4respectively corresponding to power switches Q2and Q4may both be active (e.g., VG2=1, VG4=1) during a first part of time interval T2. In this example, active high signals are utilize, the dashed line is the power supply path for the drive circuit to supply power to the drivers, and the dotted line is the power path of the switch capacitor converter.

Switch K1in switch circuit2111can be controlled by control signal V1. During a first part of time interval T2, control signal V1may be at a high level, and switch K1can be turned on. Thus, one end of bootstrap capacitor CBST can effectively connect to the low voltage end of driver U1. Bootstrap capacitor CBST can supply power to driver U2of the power switch Q2through clamp circuit2112-0corresponding to driver U2, and control signal VG2of power switch Q2may be equal to 1, so driver U2can activate drive signal to drive power switch Q2to turn on. In general, the voltage across flying capacitor Cf is ½*Vin. Here, control signal VG4of power switch Q4may be equal to 1, and power supply212can supply power to driver U4of the power switch Q4, so driver U4can activate the drive signal to drive power switch Q4to turn on. At this stage, power switch Q4can be turned on, and the voltage at the second end of flying capacitor Cf may be zero, such that the voltage at the first end of flying capacitor Cf is ½*Vin. That is, the low voltage end of driver U2is ½*Vin.

The voltage at the first end of bootstrap capacitor CBST can be the sum of the voltage across bootstrap capacitor CBST and ½*Vin, so the input voltage of clamp circuit2112-0corresponding to driver U2with respect to the low voltage end of driver U2(not with respect to the ground) at this stage can be the voltage across bootstrap capacitor CBST. Here, clamp circuit2112-0corresponding to driver U2can reduce its output voltage to the acceptable operating voltage of driver U2or to be equal to the voltage across bootstrap capacitor CBST, such as by linear voltage regulation. During time interval T2, power switches Q2and Q4can be turned on, and the voltage across flying capacitor Cf can supply power to the load via Cf-Q2-load-Q4. In addition, power switch Q2may correspond to an internal capacitor, and bootstrap capacitor CBST can supply power to internal capacitor C2corresponding to power switch Q2during the first part of time interval T2in the operation cycle.

Referring now toFIG. 8, shown is another schematic block diagram of example operation of the switch capacitor converter in the second time interval, in accordance with embodiments of the present invention. In this example, the switch capacitor converter works during a second part of time interval T2. Control signals VG1and VG3respectively corresponding to power switches Q1and Q3may both be inactive (e.g., VG1=0, VG3=0), and control signals VG2and VG4respectively corresponding to power switches Q2and Q4may both be active (e.g., VG2=1, VG4=1), during a second part of time interval T2. Here, the dashed line is the power supply path for the drive circuit to supply power to the drivers, and the dotted line is the power path of the switch capacitor converter.

Switch K2in switch circuit2111can be controlled by control signal V2. During a second part of time interval T2, control signal V2can be at a high level, and switch K2may be turned on. Thus, one end of bootstrap capacitor CBST can be grounded, and the other end of bootstrap capacitor CBST can effectively connect to power supply212. In this way, bootstrap capacitor CBST may be charged by power supply212. In addition, the drive voltage of driver U2can be maintained by the internal capacitor C2, and the drive voltage of driver U4can be maintained by capacitor CVDD, during a second part of time interval T2.

Therefore, drive circuit21of certain embodiments may utilize a time-sharing control method to supply power to drivers U1-U4of power switches Q1-Q4, such that only one bootstrap capacitor is required to drive power switches Q1-Q4, and the drive voltage of each driver is insured to be the same when power switches do not share the common ground. This can simplify the drive circuit of the switch capacitor converter, reduce the number of drive components, and save circuit costs.

Particular embodiments may also provide a drive method for a switch capacitor converter having a first, second, third, and fourth power switches connected in series. The method can include driving, by first, second, third, and fourth drivers, the first, second, third, and fourth power switches respectively according to control signals. The method can also include supplying, by a bootstrap power supply circuit, power to the first, second, and third drivers in a time-sharing manner, where the bootstrap power supply circuit includes a bootstrap capacitor. The method can also include supplying the fourth driver and charging the bootstrap capacitor, by a power supply, where the fourth power switch is grounded.

The power can be supplied, by the bootstrap power supply circuit, to the first and third drivers at the same time during a first part of a first time interval in an operation cycle. Also power can be supplied, by the bootstrap power supply circuit, to the second driver during a first part of a second time interval in the operation cycle. In addition the bootstrap capacitor can be charged, by the power supply, during a second part of the first time interval, and/or a second part of the second time interval, in the operation cycle.

Particular embodiments can also provide an integrated circuit that is applied to the switch capacitor converter, and the integrated circuit can include the above drive circuit. The integrated circuit may only utilize two pins to connect the external bootstrap capacitor (e.g., capacitor CBST). In addition, the internal capacitor (e.g., capacitors C1, C2, and C3) corresponding to each power switch can have a smaller capacitance and may be integrated internally without occupying any pins, thereby saving pins of integrated circuit.