Constant current control circuit and method applied to buck charging

Abstract

A constant current control circuit and method for BUCK charging are disclosed. The constant current control circuit includes a constant current charging unit. The constant current charging unit controls the pulse width modulation (PWM) driver based on the input current of the reverse blocking field-effect transistor (RBFET) in the BUCK charging chip to achieve constant current charging of the BUCK charging chip. The constant current control method of this invention does not introduce additional power consumption, reduces charging efficiency, and decreases chip area.

Description

Technical Field

[0001] This invention relates to the field of integrated circuits, and more specifically, to a constant current control circuit and method for BUCK charging. Background Technology

[0002] Currently, for charging chips operating in BUCK dropout mode, constant current operation is required for both the charging current and the output current of the BUCK voltage converter when the chip is in constant current mode. In existing technology, for charging chips with a battery path transistor (BATFET), the BATFET is typically connected to the system power supply pin (SYS), and the charging current is controlled by sampling the current of the BATFET to achieve constant charging current.

[0003] However, some existing charging chips do not have a battery path transistor. In these types of charging chips, a constant current state is typically achieved by connecting a sampling resistor in series at the output terminal and controlling the charging current based on the current information flowing through the sampling resistor.

[0004] For these charging chips that do not have a battery path transistor, the addition of a series resistor introduces extra power consumption into the charging path, reducing charging efficiency and increasing chip area and cost.

[0005] Therefore, there is an urgent need for a new constant current control circuit and method for BUCK charging. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a constant current control circuit and method for BUCK charging, which can ensure the constant charging current of the BUCK charging chip based on the constant current charging unit between the reverse blocking field-effect transistor and the pulse width control driver in the constant current control circuit.

[0007] The present invention adopts the following technical solution.

[0008] The first aspect of the present invention relates to a constant current control circuit for BUCK charging, wherein the constant current control circuit includes a constant current charging unit; wherein the constant current charging unit is used to control the pulse width control driver based on the input current of the reverse blocking field-effect transistor RBFET in the BUCK charging chip, so as to realize constant current charging of the BUCK charging chip.

[0009] Preferably, the constant current charging unit includes an input current sampling circuit, a comparator EA, and a reference voltage conversion circuit; wherein, the input current sampling circuit is connected at one end to a reverse blocking field-effect transistor (RBFET) and at the other end to the comparator, for sampling the input current of the RBFET at a fixed ratio and inputting the sampled voltage into the comparator EA; the reference voltage conversion circuit is connected to the comparator EA, for modulating the reference voltage and outputting the generated modulated voltage into the comparator EA; the comparator EA is connected to both the input current sampling circuit and the reference voltage conversion circuit, for comparing the sampled voltage and the modulated voltage and outputting a control signal.

[0010] Preferably, the input current sampling circuit includes a sampling current conversion resistor for converting the proportionally sampled input current of the reverse blocking field-effect transistor RBFET into a sampling voltage.

[0011] Preferably, the sampling voltage is Among them, V BAT The output voltage of the BUCK charging chip, I out R is the output current of the BUCK charging chip. s The resistance value of the sampling current conversion resistor is V. PMID K represents the output voltage of the reverse blocking field-effect transistor RBFET in the BUCK charging chip, and K is the current sampling ratio of the input current sampling circuit.

[0012] Preferably, the reference voltage converter is an RC integrator circuit, used to convert the reference voltage based on RC integration, thereby generating a modulated voltage.

[0013] Preferably, the RC integrator circuit includes an RC control circuit, a resistor R, a capacitor C, a first converter S1, and a second converter S2; wherein, one end of the first converter S1 is connected to a reference voltage, and the other end is connected to the RC control circuit when in the open state, and connected to one end of the resistor R when closed; one end of the second converter S2 is grounded, and the other end is connected to the RC control circuit when in the open state, and connected to one end of the resistor R when closed; one end of the capacitor C is connected to the other end of the resistor R and serves as the output terminal of the modulated voltage, and the other end is grounded.

[0014] Preferably, the modulation voltage is V ref_ichg_o =D×V ref_ichg Among them, V ref_ichg As a reference voltage, and has D is the duty cycle of the modulation voltage, and has Where T is the target period of the constant current control circuit for BUCK charging, T on T represents the on-time of the high-side switching HSFET within one cycle. offThe off-time of the high-side HSFET within one cycle.

[0015] Preferably, the control signals of the first switch S1 and the second switch S2 are determined based on the control signals of the high-side switch HSFET and the low-side switch LSFET in the BUCK charging chip; and the duty cycle of the control signal of the high-side switch HSFET is less than or equal to the duty cycle D of the modulation voltage.

[0016] Preferably, the negative input terminal of comparator EA is connected to the input current of the reverse blocking field-effect transistor RBFET, the positive input terminal receives the output from the reference voltage conversion circuit, and the output terminal is connected to the pulse width control driver.

[0017] A second aspect of the present invention relates to a constant current control method for BUCK charging, characterized in that it is implemented using a constant current control circuit for BUCK charging as described in the first aspect of the present invention.

[0018] The beneficial effects of this invention are that, compared with the prior art, the constant current control circuit and method for BUCK charging in this invention can ensure the constant charging current of the BUCK charging chip based on the constant current charging unit between the reverse blocking field-effect transistor and the pulse width control driver in the constant current control circuit. Since no additional series resistor is required, the constant current control method in this invention does not introduce additional power consumption, reduce charging efficiency, or decrease chip area. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the circuit structure of a BUCK charging chip with a battery path transistor (BATFET) in the prior art of this invention.

[0020] Figure 2 This is a schematic diagram of the circuit structure of a BUCK charging chip that does not have a battery path transistor (BATFET) in the prior art of this invention.

[0021] Figure 3 This is a schematic diagram of the circuit structure of a constant current control circuit applied to BUCK charging according to the present invention.

[0022] Figure 4 This is a schematic diagram of the RC integrator circuit in a constant current control circuit applied to BUCK charging according to the present invention.

[0023] Figure 5 This is a schematic diagram of voltage and current signals in one embodiment of a constant current control circuit applied to BUCK charging according to the present invention;

[0024] Figure 6This is a schematic diagram of voltage and current signals in another embodiment of a constant current control circuit applied to BUCK charging according to the present invention. Detailed Implementation

[0025] The present application will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and should not be construed as limiting the scope of protection of the present application.

[0026] Figure 1 This is a schematic diagram of the circuit structure of a BUCK charging chip with a battery path transistor (BATFET) in the prior art of this invention. Figure 1 As shown, a BUCK charging chip with a battery path transistor (BATFET) includes common BUCK charging chip structures such as a reverse blocking field-effect transistor (RBFET), a PWM (Pulse Width Modulation) controller and driver, a high-side switch (HSFET), a low-side switch (LSFET), an inductor, and a capacitor. In addition, to achieve constant current output, a comparator EA is added to the chip. The negative input of comparator EA is connected to the voltage sampled from the battery path transistor (BATFET), and the positive input is connected to a reference voltage. The control signal output from the comparator is connected to the PWM controller and driver, controlling the high-side and low-side switches of the PWM controller and driver to synchronously turn on or off. Therefore, the charging chip achieves a constant charging current.

[0027] Figure 2 This is a schematic diagram of the circuit structure of a BUCK charging chip that does not have a battery path transistor (BATFET) in the prior art of this invention. Figure 2 As shown, a BUCK charging chip without a battery path transistor (BATFET) is also included, representing a general structure in charging chips. However, since this charging chip lacks a battery path transistor, a sampling resistor is needed at its output terminal to sample the output current and achieve constant current based on the sampled output current. However, this approach introduces additional power consumption due to the added sampling resistor, resulting in lower charging efficiency, larger chip area, and higher chip cost.

[0028] To improve charging efficiency and reduce chip area, this invention proposes a constant current control circuit for BUCK charging. Figure 3 This is a schematic diagram of the circuit structure of a constant current control circuit applied to BUCK charging according to the present invention. Figure 3As shown, in a first aspect, the present invention relates to a constant current control circuit for BUCK charging. The constant current control circuit includes a constant current charging unit; wherein the constant current charging unit is used to control the pulse width control driver based on the input current of the reverse blocking field-effect transistor RBFET in the BUCK charging chip, so as to realize constant current charging of the BUCK charging chip.

[0029] Preferably, the constant current charging unit includes an input current sampling circuit, a comparator EA, and a reference voltage conversion circuit; wherein, the input current sampling circuit is connected at one end to a reverse blocking field-effect transistor (RBFET) and at the other end to the comparator, for sampling the input current of the RBFET at a fixed ratio and inputting the sampled voltage into the comparator EA; the reference voltage conversion circuit is connected to the comparator EA, for modulating the reference voltage and outputting the generated modulated voltage into the comparator EA; the comparator EA is connected to both the input current sampling circuit and the reference voltage conversion circuit, for comparing the sampled voltage and the modulated voltage and outputting a control signal.

[0030] Preferably, the input current sampling circuit includes a sampling current conversion resistor for converting the proportionally sampled input current of the reverse blocking field-effect transistor RBFET into a sampling voltage.

[0031] Preferably, the sampling voltage is Among them, V BAT The output voltage of the BUCK charging chip, I out R is the output current of the BUCK charging chip. s The resistance value of the sampling current conversion resistor is V. PMID K represents the output voltage of the reverse blocking field-effect transistor RBFET in the BUCK charging chip, and K is the current sampling ratio of the input current sampling circuit.

[0032] Specifically, the sampling voltage is obtained based on the relationship between the input and output current and voltage of the BUCK voltage converter. In this invention, the power of the BUCK voltage converter is constant; therefore, the input power of the BUCK voltage converter equals the output power, which is V. PMID ×I in =V BAT ×I out Among them, I in This is the reverse blocking current of the RBFET. Based on this formula, we can derive I. in =(V BAT / V PMID )×I outSince the sampling voltage in this invention is obtained by multiplying the input current of the reverse blocking field-effect transistor (RBFET) by the resistance value of the sampling current conversion resistor after proportional sampling, the calculation formula for the sampling voltage described above is obtained.

[0033] Figure 4 This is a schematic diagram of the RC integrator circuit in a constant current control circuit applied to BUCK charging according to the present invention. Figure 4 As shown, the reference voltage converter is an RC integrator circuit, which is used to convert the duty cycle of the reference voltage based on RC integration, thereby generating a modulated voltage.

[0034] Preferably, the RC integrator circuit includes an RC control circuit, a resistor R, a capacitor C, a first converter S1, and a second converter S2; wherein, one end of the first converter S1 is connected to a reference voltage, and the other end is connected to the RC control circuit when in the open state, and connected to one end of the resistor R when closed; one end of the second converter S2 is grounded, and the other end is connected to the RC control circuit when in the open state, and connected to one end of the resistor R when closed; one end of the capacitor C is connected to the other end of the resistor R and serves as the output terminal of the modulated voltage, and the other end is grounded.

[0035] Preferably, the modulation voltage is V sense_iac =D×V ref_ichg Among them, V ref_ichg As a reference voltage, and has D is the duty cycle of the modulation voltage, and has

[0036] Preferably, the control signals for the first switch S1 and the second switch S2 are determined based on the control signals of the high-side switch HSFET and the low-side switch LSFET in the BUCK charging chip; and the duty cycle of the high-side switch HSFET control signal is less than or equal to the duty cycle D of the modulation voltage. Specifically, when the sum of the duty cycle of the modulation voltage (i.e., the duty cycle of the high-side switch HSFET control signal) and the duty cycle of the low-side switch LSFET control signal is 1, the circuit is in continuous operation mode, and its output inductor current is continuous. When the sum of the duty cycle of the modulation voltage (i.e., the duty cycle of the high-side switch HSFET control signal) and the duty cycle of the low-side switch LSFET control signal is less than 1, the circuit is in discontinuous operation mode, and its output inductor current is discontinuous. After one cycle of rise and fall ends, the inductor current will be at 0A for a period of time.

[0037] Specifically, the duty cycle D can be converted using an RC integrator circuit, meaning the turn-on and turn-off times of switches S1 and S2 can be designed to be the same as the turn-on and turn-off times of HSFET and LSFET. When the charging chip operates in continuous mode, this ensures that the output of the RC integrator circuit, controlled by the control signal, matches the period and duty cycle of the PWM output signal. When the product of the capacitor and resistor in the RC integrator circuit is much greater than the period of the PWM output signal (i.e., RC >> T), the output of the RC integrator circuit is V. ref_ichg_o =D×V ref_ichg .

[0038] Preferably, the negative input terminal of comparator EA is connected to the input current of the reverse blocking field-effect transistor RBFET, the positive input terminal receives the output from the reference voltage conversion circuit, and the output terminal is connected to the pulse width control driver.

[0039] Figure 5 This is a schematic diagram of voltage and current signals in one embodiment of a constant current control circuit applied to BUCK charging according to the present invention. Figure 5 As shown, when the output of the RC integrator circuit just satisfies the duty cycle of... When the duty cycle is exactly equal to the ratio of the input and output voltages, the charging chip operates in continuous mode. In this mode, the control signals for the charging chip are as shown in the PWM diagram. The input to the HSFET control signal is the same, while the input to the LSFET control signal is exactly opposite. Simultaneously, to ensure the duty cycle, the control signals for the first and second switches in continuous operation mode are also adapted to the outputs of the HSFET and LSFET. Ultimately, in this situation, the output current of the charging chip equals the inductor current iL, which is... Figure 3 The Iout shown is an example. Because the output current rises and falls systematically, a constant current state for the charging current can be maintained for a certain period of time.

[0040] Figure 6 This is a schematic diagram of voltage and current signals in another embodiment of a constant current control circuit applied to BUCK charging according to the present invention. Figure 6 As shown, when the duty cycle cannot meet the above conditions, the control signals input to the high-side switch HSFET and the low-side switch LSFET cannot correspond well with the control signals of the first and second switches S1 and S2 in the RC integrator circuit. That is, when the two control signals of the high-side switch HSFET and the low-side switch LSFET cannot be completely inversely related, the output inductor current iL is discontinuous, that is, after each rise and fall, it will be reset to zero for a period of time before starting the next cycle.

[0041] A second aspect of the present invention relates to a constant current control method for BUCK charging, which is implemented using a constant current control circuit for BUCK charging as described in the first aspect of the present invention.

[0042] The beneficial effects of this invention are that, compared with the prior art, the constant current control circuit and method for BUCK charging in this invention can ensure the constant charging current of the BUCK charging chip based on the constant current charging unit between the reverse blocking field-effect transistor and the pulse width control driver in the constant current control circuit. Since no additional series resistor is required, the constant current control method in this invention does not introduce additional power consumption, reduce charging efficiency, or decrease chip area.

[0043] The applicant of this invention has provided a detailed description of the embodiments of the invention in conjunction with the accompanying drawings. However, those skilled in the art should understand that the above embodiments are merely preferred embodiments of the invention. The detailed description is only intended to help readers better understand the spirit of the invention and is not intended to limit the scope of protection of the invention. On the contrary, any improvements or modifications made based on the inventive spirit of the invention should fall within the scope of protection of the invention.

Claims

1. A constant current control circuit applied to BUCK charging, characterized in that: the constant current control circuit comprises a constant current charging unit; wherein the constant current charging unit is configured to control a pulse width control driver based on an input current of a reverse blocking field effect transistor (RBFET) in the BUCK charging chip, so as to realize constant current charging of the BUCK charging chip; the constant current charging unit comprises an input current sampling circuit, a comparator EA and a reference voltage conversion circuit; wherein the input current sampling circuit has one end connected to the RBFET and the other end connected to the comparator, and is configured to collect an input current of the RBFET at a fixed ratio and input a collected sampling voltage into the comparator EA, wherein the sampling voltage is obtained by multiplying a resistance value of a sampling current conversion resistor by the input current of the RBFET collected at the fixed ratio; the reference voltage conversion circuit is connected to the comparator EA and is configured to modulate a reference voltage and output a generated modulation voltage to the comparator EA; and the comparator EA is connected to the input current sampling circuit and the reference voltage conversion circuit respectively and is configured to output a control signal after comparing the sampling voltage and the modulation voltage.

2. The constant current control circuit applied to BUCK charging according to claim 1, characterized in that: the input current sampling circuit comprises a sampling current conversion resistor, which is configured to convert the input current of the RBFET collected at the fixed ratio into the sampling voltage.

3. The constant current control circuit applied to BUCK charging according to claim 2, characterized in that: K is a current sampling ratio of the input current sampling circuit.

4. The constant current control circuit applied to BUCK charging according to claim 1, characterized in that: the reference voltage converter is an RC integration circuit, which is configured to realize conversion of the reference voltage based on RC integration, so as to generate the modulation voltage.

5. The constant current control circuit applied to BUCK charging according to claim 4, characterized in that: the RC integration circuit comprises an RC control circuit, a resistor R, a capacitor C, a first switch S1 and a second switch S2; wherein one end of the first switch S1 is connected to the reference voltage, and the other end is connected to the RC control circuit in an open state and is connected to one end of the resistor R in a closed state; one end of the second switch S2 is grounded, and the other end is connected to the RC control circuit in the open state and is connected to one end of the resistor R in the closed state; and one end of the capacitor C is connected to the other end of the resistor R and serves as an output end of the modulation voltage, and the other end is grounded.

6. The constant current control circuit applied to BUCK charging according to claim 5, characterized in that:

7. The constant current control circuit applied to BUCK charging according to claim 6, characterized in that: ​ ​ ​ ​ The sampling voltage is where I out is the output current of the BUCK charging chip, and has I out = V PMID x I in / V BAT , V BAT is the output voltage of the BUCK charging chip, R s is the resistance value of the sampling current conversion resistor, V PMID to charge the output voltage of the reverse blocking field effect transistor (RBFET) in the BUCK chip, ​ I in to reverse block field effect transistors RBFETs. ​ ​ ​ ​ ​ ​ ​ ​ The modulated voltage is V ref_ichg_o = D x V ref_ichg ; where V ref_ichg is a reference voltage, and there is D is the duty cycle of the modulated voltage, and has Wherein, K is the current sampling ratio of the input current sampling circuit, T is the target period of the constant current control circuit of the BUCK charging, T on is the on duration of the high-side switch HSFET in a period, off is the off duration of the high-side switch HSFET in a period, BAT is the output voltage of the BUCK charging chip, PMID is the output voltage of the reverse blocking field effect transistor RBFET in the BUCK charging chip. ​ The control signals of the first switcher S1 and the second switcher S2 are determined based on the control signals of the high-side switch HSFET and the low-side switch LSFET in the BUCK charging chip; and The duty cycle of the control signal of the high-side switch HSFET is less than or equal to the duty cycle D of the modulated voltage.

8. The constant current control circuit applied to BUCK charging according to claim 1, characterized in that: The negative phase input end of the comparator EA is connected to the input current of the reverse blocking field effect transistor RBFET, the positive phase input end receives the output from the reference voltage conversion circuit, and the output end is connected to the pulse width control driver.

9. A constant current control method applied to BUCK charging, characterized in that, The constant current control circuit applied to BUCK charging is implemented by using the constant current control circuit applied to BUCK charging according to any one of claims 1-8.

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