JP2023034189A - Charge control circuit, and electronic apparatus - Google Patents

Abstract

To provide a charge control circuit capable of generating an appropriate system voltage in a combination with batteries having various number of cells.SOLUTION: A target voltage generation circuit 396 generates a target voltage of a system voltage VSYS in a non-charge mode. A constant current circuit CS51 sinks a constant current Ic. A first resistor R51 is connected between a first transistor M51 and the constant current circuit CS51. A first operational amplifier OA51 receives a voltage Vn1 and a battery voltage detection signal VBAT_DET and an output node is connected with a control terminal of the first transistor M51. A voltage Vn2 of a node n2 specifies the target voltage of the system voltage VSYS.SELECTED DRAWING: Figure 4

Description

The present disclosure relates to a secondary battery charging circuit.

Battery-driven electronic devices such as smart phones, tablet terminals, notebook computers, portable audio players, and digital cameras are equipped with rechargeable secondary batteries (hereinafter simply referred to as batteries). Many electronic devices incorporate a charging circuit, and can charge a battery using a USB (Universal Serial Bus) bus voltage.

Japanese Patent No. 6838879

After the charging circuit completes charging the battery, it is necessary to keep the output voltage of the charging circuit (the output voltage of the DC/DC converter) supplied to the internal circuit slightly higher than the battery voltage in order to avoid battery consumption. be.

The present inventors have studied generating a reference voltage that is a constant K times the battery voltage (K>1) and matching the output voltage of the DC/DC converter (also referred to as system voltage _VSYS ) to this reference voltage. Assuming a 2-cell battery, the battery voltage is about 8.86V. With K=1.15, the system voltage _VSYS supplied to the internal circuitry will exceed 10V. In this case, the withstand voltage of the internal circuit needs to be higher than 10V, making it impossible to use ICs and elements with a withstand voltage of 10V. This problem can be solved by making the value of K closer to 1, but in that case, when a one-cell battery is assumed, the difference between the battery voltage and the system voltage becomes small and the circuit operation becomes unstable.

It is in this context that certain aspects of the present disclosure have been made, and one exemplary objective thereof is to provide a charging control circuit capable of generating appropriate system voltages in combination with batteries of varying cell counts. .

One aspect of the present disclosure relates to a charge control circuit that controls charging of a battery using an external voltage. The charge control circuit includes a converter controller that controls the DC/DC converter that constitutes the charge circuit. The converter controller includes a target voltage generation circuit that generates a target voltage, an error amplifier that amplifies an error between a system voltage detection signal corresponding to the output voltage of the DC/DC converter and the target voltage, and a pulse signal corresponding to the output of the error amplifier. and a pulse modulator that generates The target voltage generation circuit includes a first transistor, a constant current circuit that sinks a constant current, a first resistor connected between the first transistor and the constant current circuit, a first input node, a second input node, and an output. A first input node receives the voltage of the connection node of the first resistor and the constant current circuit, a second input node receives a battery voltage detection signal corresponding to the voltage of the battery, and an output node is the first transistor. and a first operational amplifier connected to the control terminal, the target voltage depending on the voltage at the connection node of the first transistor and the first resistor.

Arbitrary combinations of the above constituent elements, and mutually replacing constituent elements and expressions in methods, apparatuses, systems, and the like are also effective as embodiments of the present invention.

According to certain aspects of the present disclosure, suitable system voltages can be generated in combination with batteries of various cell counts.

FIG. 1 is a block diagram of an electronic device including a charging circuit according to an embodiment. FIG. 2 is a circuit diagram of the charge control IC according to the embodiment. FIG. 3 is a circuit diagram showing a configuration example of a pulse modulator. FIG. 4 is a circuit diagram showing the configuration of part of the pulse modulator related to the non-charging mode. FIG. 5 is a circuit diagram showing a configuration example of a constant current circuit. FIG. 6 is a diagram for explaining the operation of an electronic device that includes the charging control IC. FIG. 7 is a perspective view of an electronic device including a charge control IC.

(Overview of embodiment)
SUMMARY OF THE INVENTION Several exemplary embodiments of the disclosure are summarized. This summary presents, in simplified form, some concepts of one or more embodiments, as a prelude to the more detailed description that is presented later, and for the purpose of a basic understanding of the embodiments. The size is not limited. This summary is not a comprehensive overview of all possible embodiments, and it is intended to neither identify key elements of all embodiments nor delineate the scope of some or all aspects. For convenience, "one embodiment" may be used to refer to one embodiment (example or variation) or multiple embodiments (examples or variations) disclosed herein.

A charging control circuit according to one embodiment controls charging of a battery using an external voltage. The charge control circuit includes a converter controller that controls the DC/DC converter that constitutes the charge circuit. The converter controller includes a target voltage generation circuit that generates a target voltage, an error amplifier that amplifies an error between a system voltage detection signal corresponding to the output voltage of the DC/DC converter and the target voltage, and a pulse signal corresponding to the output of the error amplifier. and a pulse modulator that generates The target voltage generation circuit includes a first transistor, a constant current circuit that sinks a constant current, a first resistor connected between the first transistor and the constant current circuit, a first input node, a second input node, and an output. A first input node receives the voltage of the connection node of the first resistor and the constant current circuit, a second input node receives a battery voltage detection signal corresponding to the voltage of the battery, and an output node is the first transistor. and a first operational amplifier connected to the control terminal, the target voltage depending on the voltage at the connection node of the first transistor and the first resistor.

The first operational amplifier stabilizes the first voltage Vn1 at the connection node between the first resistor and the constant current circuit to the battery voltage detection signal V _{BAT_DET} . The second voltage Vn2 at the connection node between the first transistor and the first resistor is higher than the first voltage Vn1 by Ic×R1.
Vn2=Vn1+Ic×R1=V _{BAT_DET} +Ic×R1
Ic is the amount of constant current, and R1 is the resistance value of the first resistor.
By stabilizing the system voltage detection signal V _{SYS_DET} with the second voltage Vn2 as the target voltage, the system voltage V _SYS can be stabilized at a voltage level higher than the battery voltage V _BAT by a predetermined voltage width ΔV. This voltage width ΔV is determined by Ic and R1 and does not depend on the battery voltage _VBAT , so the voltage width is constant even if the number of cells changes. Therefore, an appropriate system voltage can be generated in combination with batteries having various numbers of cells.

In one embodiment, the constant current circuit may include a reference current source that generates a reference current and a current mirror circuit that folds the reference current.

In one embodiment, the current mirror circuit may consist of field effect transistors with a threshold voltage lower than 0.2V.

When the charge control circuit is used in combination with a single cell battery, the battery voltage V _BAT can drop as low as 2.4V. At this time, the voltage at the connection node between the first resistor and the constant current circuit becomes very low. In this case, by forming a current mirror circuit using a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) with a threshold voltage of 0.2 V or less, it is possible to accurately fold back the current.

In one embodiment, the target voltage generation circuit may further include a clamp circuit that clamps the connection node between the first transistor and the first resistor so that it does not drop below a predetermined minimum voltage. This prevents the system voltage from falling below the minimum operating voltage of the internal circuit when the battery is over-discharged.

In one embodiment, the clamp circuit includes a second transistor having a first end receiving a power supply voltage and a second end connected to a connection node between the first transistor and the first resistor, a first input node, and a second input node. and an output node, the first input node receives a set voltage that defines the minimum voltage, the second input node receives the voltage of the connection node between the first transistor and the first resistor, and the output node is the second transistor a second operational amplifier connected to the control terminal of the .

In one embodiment, the charging control circuit may be monolithically integrated on one semiconductor substrate. "Integrated integration" includes the case where all circuit components are formed on a semiconductor substrate, and the case where the main components of a circuit are integrated. A resistor, capacitor, or the like may be provided outside the semiconductor substrate. By integrating the circuits on one chip, the circuit area can be reduced and the characteristics of the circuit elements can be kept uniform.

(embodiment)
Preferred embodiments will be described below with reference to the drawings. The same or equivalent constituent elements, members, and processes shown in each drawing are denoted by the same reference numerals, and duplication of description will be omitted as appropriate. Moreover, the embodiments are illustrative rather than limiting the invention, and not all features and combinations thereof described in the embodiments are necessarily essential to the invention.

In this specification, "a state in which member A is connected to member B" refers to a case in which member A and member B are physically directly connected, or a case in which member A and member B are electrically connected to each other. It also includes the case of being indirectly connected through other members that do not substantially affect the connected state or impair the functions and effects achieved by their combination.

Similarly, "the state in which member C is provided between member A and member B" and "the state in which member C is connected between member A and member B" refer to member A and member C, Or, in addition to the case where the member B and the member C are directly connected, it does not substantially affect their electrical connection state, or impair the functions and effects achieved by their connection, etc. Including the case where it is indirectly connected via a member of

FIG. 1 is a block diagram of an electronic device 100 including a charging circuit 200 according to an embodiment. The electronic device 100 mainly includes a battery 102 , a USB (Universal Serial Bus) receptacle 104 , an internal circuit 110 and a charging circuit 200 . The battery 102 is a secondary battery that can be repeatedly charged, and examples thereof include a lithium ion battery, a lithium ion polymer battery, a nickel hydrogen battery, a nickel cadmium battery, and the like. In this embodiment, the battery 102 is assumed to be a 1- to 4-cell lithium ion battery.

The USB receptacle 104 is connected to an external power source such as an external device or a charger via a USB cable, and supplied with an external voltage V _BUS .

The internal circuit 110 is the main circuit of the electronic device 100 and includes a CPU (Central Processing Unit), a microcontroller, a display, a power supply circuit, an audio circuit, and the like. The configuration of the internal circuit 110 varies depending on the type of the electronic device 100 and is not particularly limited.

The charging circuit 200 charges the battery 102 using the external voltage V _BUS when the external power supply is connected to the electronic device 100 and the external voltage V _BUS is supplied. When the external voltage V _BUS is supplied, the internal circuitry 110 is supplied with power from the external power supply in addition to or instead of power from the battery 102 .

The charging circuit 200 includes a charging control IC 300 and its peripheral circuit 210 . The peripheral circuit 210 includes a DC/DC converter main circuit (simply referred to as a DC/DC converter) 212, a first switch SW1, and a second switch SW2.

A first switch SW1 is provided between the VBUS terminal of the USB receptacle 104 and the input terminal of the DC/DC converter 212 . The charge control IC 300 turns on the first switch SW1 when the external voltage _VBUS is supplied. This supplies the external voltage V _BUS to the DC/DC converter 212 .

The output of DC/DC converter 212 is connected to internal circuit 110 . Also, the output of the DC/DC converter 212 is connected to the battery 102 via the second switch SW2. In this embodiment, DC/DC converter 212 is a buck-boost converter and includes transistors M11-M14, inductor L1, and capacitors C1 and C2. The charge control IC 300 controls the transistors M11 to M14 to step up or step down the external voltage V _BUS to charge the battery 102 .

A battery voltage V _BAT is input to the VBAT terminal of the charge control IC 300 . A current detection signal VSR indicating a charging current _ICHG to the battery 102 is input to the current detection terminal _SR . For example, a sense resistor may be inserted in the charging path and the voltage drop of this sense resistor may be used as the current detection signal _VSR .

Specifically, when the voltage V _BAT of battery 102 is low, charge control IC 300 controls DC/DC converter 212 in a CC (Constant Current) mode in which the charging current is constant. In the CC mode, switching of the DC/DC converter 212 is controlled so that the current detection signal _VSR approaches the target value VSR _(REF) .

When the battery 102 approaches a fully charged state, the charge control IC 300 controls the DC/DC converter 212 in a CV (Constant Voltage) mode that stabilizes the voltage V _BAT of the battery 102 to a target voltage corresponding to the fully charged voltage. . In CV mode, switching of DC/DC converter 212 is controlled such that battery voltage V _BAT approaches target value V _BAT(REF) .

The charge control IC 300 turns on (fully turns on) the second switch SW2 during charging of the battery 102 in CC mode or CV mode. Charging control IC 300 stops switching DC/DC converter 212 to complete charging of battery 102 when charging current I _CHG drops to termination current I _TERM in CV mode. When charging is completed, the charge control IC 300 turns off the second switch SW2.

After the charging is completed and the second switch SW2 is turned off, while the external voltage V _BUS is being supplied, the charging control IC 300 sets the system voltage V _SYS supplied to the internal circuit 110 higher than the voltage V _BAT of the battery 102. Stabilize to slightly higher target level V _SYS(REF) . Thereby, the internal circuit can be operated by the external power source without consuming the battery 102 .

When the battery 102 is deeply discharged and trickle charging is performed with a minute current, the charging control IC 300 controls the control terminal of the second switch SW2 so that the current detection signal _VSR approaches the target value for trickle charging. may be feedback-controlled.

When the external voltage V _BUS is not supplied to the electronic device 100 , that is, in the non-charging state, the charge control IC 300 turns on the switch SW 2 and supplies the voltage V _BAT of the battery 102 to the internal circuit 110 .

The above is the configuration of the electronic device 100 . Next, the configuration of the charging control IC 300 will be described. FIG. 2 is a circuit diagram of the charging control IC 300 according to the embodiment. The charging control IC 300 is a functional IC integrated on one semiconductor substrate.

The charging control IC 300 includes a power path control section 310, a gate driver 312, a voltage selection circuit 320, a first regulator 322, a second regulator 324, a converter controller 330, a USB charger detector 340, an interface circuit 342, a logic circuit 350, and a latch circuit. 360 and a switch control unit 370 .

The power path control unit 310 monitors the voltage _VBUS of the VBUS terminal and detects whether or not the external voltage _VBUS is supplied. The ACGATE terminal is connected to the gate of the MOSFET that is the first switch SW1. The gate driver 312 turns on the first switch SW1 connected to the ACGATE terminal when the external voltage V _BUS is detected.

The VIN terminal of the charging control IC 300 is connected to the output side of the first switch SW1. The voltage selection circuit 320 selects the effective (in other words, the highest) one of the voltage V _IN of the VIN terminal, the voltage V _BUS of the VBUS terminal, and the voltage V _BAT of the battery terminal BATT. The voltage selection circuit 320 can be composed of a diode OR circuit.

The output voltage V _OR of the voltage selection circuit 320 is input to the first regulator 322 . A first regulator 322 receives voltage V _OR and produces a first power supply voltage V _REG regulated to a predetermined target level (eg, 5V).

A second regulator 324 receives the first power supply voltage V _REG and produces a second power supply voltage V _REF regulated to a lower target level (eg, 1.5V). The second power supply voltage V _REF is used as the power supply voltage for the logic circuit 350 .

The second regulator 324 and the first regulator 322 can be composed of linear regulators (also called LDO: Low Drop Output).

Converter controller 330 drives and controls DC/DC converter 212 . A pulse modulator 331 generates a pulse signal Sp for controlling the DC/DC converter 212 . In CC mode, pulse modulator 331 feedback-controls the duty cycle of pulse signal Sp so that current detection signal _VSR approaches its target voltage. The current sense signal _VSR may be an amplified voltage drop across the sense resistor. In the CV mode, the pulse modulator 331 feedback-controls the duty cycle of the pulse signal Sp so that the battery voltage V _BAT approaches its target voltage.

After the charging is completed, the pulse modulator 331 turns off the second switch SW2, and while the external voltage V _BUS is being supplied, the system voltage V _SYS supplied to the internal circuit 110 is higher than the voltage V _BAT of the battery 102. The duty cycle of the pulse signal Sp is feedback controlled so that it approaches the slightly higher target level V _SYS(REF) .

The PWM logic section 334 receives the pulse signal Sp generated by the pulse modulator 331 and controls the step-down driver 336 and the step-up driver 338 . Specifically, the PWM logic unit 334 is in the step-down mode when V _IN >V _BAT , and in the step-up mode when V _IN <V _BAT . In buck mode, the boost driver 338 locks the LG2 terminal low and the HG2 terminal high. As a result, the transistor M13 in FIG. 1 is turned off and the transistor M14 is turned on. The step-down driver 336 outputs complementary gate signals based on the pulse signal Sp from the LG1 terminal and the HG1 terminal to complementarily switch the transistors M13 and M14.

In the boost mode, the buck driver 336 will tie the LG1 terminal low and the HG1 terminal high. As a result, the transistor M11 in FIG. 1 is turned on and the transistor M12 is turned off. The boosting driver 338 outputs complementary gate signals based on the pulse signal Sp from the LG2 terminal and the HG2 terminal, and complementarily switches the transistors M13 and M14.

Although the step-down driver 336 and the step-up driver 338 include a bootstrap circuit or charge pump for driving the N-channel transistors M11 and M14, they are omitted in FIGS.

The DPI and DPO terminals of the charge control IC 300 are connected to the USB data signal lines D+ and D-. Since the USB charger does not perform communication using the data signal lines D+ and D-, the data signal lines D+ and D- are short-circuited on the charger side. The USB charger detector 340 monitors whether the data signal lines D+ and D- are shorted, and determines whether the USB receptacle 104 is connected to a USB charger or a general USB port. do.

The interface circuit 342 is provided for the charge control IC 300 to communicate with an external circuit (not shown in FIG. 1). For example, the interface circuit 342 is an I ² C (Inter IC) interface or SPI (Serial Peripheral Interface).

The logic circuit 350 is a control logic that controls the charging control IC 300 as a whole. The logic circuit 350 operates using the second power supply voltage V _REF generated by the second regulator 324 as a power supply.

The switch control unit 370 controls the second switch SW2 connected to the BGATE terminal according to the operation state of the charging circuit 200. FIG. Specifically, the second switch SW2 is fully turned on during charging in the CC mode and the CV mode. During trickle charging (or precharging), the gate voltage of the MOSFET, which is the second switch SW2, is adjusted so that the charging current _ICHG approaches the target value for trickle charging (or precharging). When the external voltage _VBUS is not supplied to the electronic device 100, the second switch SW2 is fully turned on.

FIG. 3 is a circuit diagram showing a configuration example of the pulse modulator 331. As shown in FIG. The pulse modulator 331 comprises a plurality of operational amplifiers OA41-OA43, transistors M41-M43, a current source 390, a PWM comparator 392 and an oscillator 394. The operational amplifier OA41 is an error amplifier for CC mode and amplifies the error between the current detection signal _VSR and its target voltage VSR _(REF) . The operational amplifier OA42 is an error amplifier for CV mode and amplifies the error between the battery voltage detection signal V _BAT and its target voltage V _{BAT (REF)} . The operational amplifier OA43 is an error amplifier for non-charging mode, and amplifies the error between the system voltage V _SYS and its target voltage V _{SYS (REF)} .

The outputs of the three operational amplifiers OA41-OA43 are combined by an open-drain circuit including transistors M41-M43. The drains of the transistors M41-M43 are connected to the current source 390, and the error voltage _VERR generated at their connection node is supplied to the PWM comparator 392. The PWM comparator 392 compares the triangular wave or sawtooth wave carrier signal generated by the oscillator 394 with the error voltage V _ERR and outputs a pulse signal Sp indicating the comparison result.

FIG. 4 is a circuit diagram showing a configuration of part of pulse modulator 331 related to the non-charging mode.

The pulse modulator 331 includes a target voltage generation circuit 396, an operational amplifier OA43, resistors R61 to R64, and a transistor M61.

The error amplifier EA51 amplifies the error between the system voltage detection signal V _{SYS_DET} corresponding to the system voltage V _SYS output from the DC/DC converter 212 and its target voltage V _{SYS_DET (REF)} . A resistor R61 and a resistor R62 are connected in series between the SYS terminal and ground. A resistor R61 and a resistor R62 are voltage dividing circuits that divide the system voltage _VSYS to generate a system voltage detection signal _{VSYS_DET} . Error amplifier EA51 and resistors R61 and R62 correspond to operational amplifier OA43 in FIG.

A resistor R63, a transistor M61, and a resistor R64 are connected in series between the BATT terminal and the ground. Transistor M61 is on in the non-charging mode. A resistor R63 and a resistor R64 are voltage dividing circuits that divide the battery voltage V _BAT to generate a battery voltage detection signal V _{BAT_DET} . A battery voltage detection signal V _{BAT_DET} is input to the target voltage generation circuit 396 . A target voltage generation circuit 396 generates a target voltage V _{SYS_DET (SYS)} based on the battery voltage detection signal V _{BAT_DET} .

The target voltage generation circuit 396 includes a constant current circuit CS51, a first transistor M51, a first resistor R51, a first operational amplifier OA51, and a clamp circuit 397.

The first transistor M51 is a P-channel MOSFET, and its source is connected to a 5V system (V _REG ) power supply line.

Constant current circuit CS51 sinks constant current Ic. The first resistor R51 is connected between the drain of the first transistor M51 and the constant current circuit CS51.

The first input node (-) of the first operational amplifier OA51 receives the battery voltage detection signal V _{BAT_DET} , and the second input node (+) receives the voltage of the connection node n1 between the first resistor R51 and the constant current circuit CS51. Vn1 is input. The output of the first operational amplifier OA51 is connected to the gate of the first transistor M51.

The target voltage _{VSYS_DET(REF)} corresponds to the voltage Vn2 at the connection node n2 between the first transistor M51 and the first resistor R51. A second resistor R52 is connected between the connection node n2 and the ground.

The first operational amplifier OA51 adjusts the gate voltage of the transistor M51 so that Vn1=V _{BAT_DET} . Since the constant current Ic generated by the constant current circuit CS51 flows through the first resistor R51, a voltage drop ΔV=R51×Ic occurs. That is, the voltage Vn2 of the node n2 is represented by Equation (1).
Vn2= _{VSYS_DET(REF)} =Vn1+ΔV
=V _{BAT_DET} +R51×Ic (1)

The clamp circuit 397 clamps the connection node n2 between the first transistor M51 and the first resistor R51 so as not to fall below a predetermined minimum voltage _VMIN . Clamp circuit 397 includes a second transistor M52 and a second operational amplifier OA52.

The first transistor M51 is a P-channel MOSFET, its source is connected to the 5V system (V _REG ) power supply line, and its drain is connected to the node n2. A set voltage V _DAC that defines the minimum voltage V _MIN is input to the first input node (-) of the second operational amplifier OA52. A set voltage V _DAC is generated by a D/A converter 399 and may be adjustable.

The second input node (+) of the second operational amplifier OA52 receives the voltage Vn2 of the connection node n2, and the output node of the second operational amplifier OA52 is connected to the control terminal (gate) of the second transistor M52.

The above is the configuration of the pulse modulator 331 .
Assume that the voltage dividing ratio of the resistors R61 and R62 is α, and the voltage dividing ratio of the resistors R63 and R64 is β.
V _{SYS_DET} = α V _SYS
V _{BAT_DET} =β·V _BAT
Substituting this into equation (1), we get
_{VSYS_DET(REF)} =β· _VBAT +R51×Ic (1′)

At steady state,
_{VSYS_DET} = _{VSYS_DET(REF)}
holds, we obtain equation (2).
α· _VSYS =β· _VBAT +R51×Ic (2)
Therefore, the target level V _SYS(REF) of the system voltage V _SYS in the steady state is expressed by equation (3).
_VSYS(REF) =β/ _αVBAT +R51×Ic/α (3)

If we let α=β, then we obtain equation (3′).
_VSYS(REF) = _VBAT +R51×Ic/α (3′)

R51×Ic/α can be about 100 mV to 300 mV, and may be 200 mV, for example.

According to this pulse modulator 331, the system voltage V _SYS is stabilized at a voltage level higher than the battery voltage V _BAT by the voltage width ΔV represented by R51×Ic/α, as shown in equation (3). can do. This voltage width ΔV is determined according to the resistance value of the first resistor R51, the constant current Ic generated by the constant current circuit CS51, and the voltage division ratio α, and is not affected by the battery voltage V _BAT .

FIG. 5 is a circuit diagram showing a configuration example of the constant current circuit CS51. Constant current circuit CS51 includes a reference current source CCS71 and a current mirror circuit CM71. A reference current source CCS71 produces a reference current _IREF . A current mirror circuit CM71 folds back the reference current _IREF to generate a constant current Ic.

Current mirror circuit CM71 includes transistors M71 and M72. When used with a one-cell battery 102, the battery voltage V _BAT can drop as low as 2.4V. Assuming that the voltage division ratio of the resistors R63 and R64 is 1/24, the voltage Vn1 at the connection node between the first resistor R51 and the constant current circuit CS51 is 0.1V. In this case, if normal MOSFETs with a threshold voltage of 0.5 V or more are used as the transistors M71 and M72, the current mirror circuit CM71 may not operate normally. Therefore, MOSFETs with a threshold voltage of 0.2 V or less are preferably used for the transistors M71 and M72. Thereby, even when the system voltage _VSYS becomes low, the current can be accurately folded back.

FIG. 6 is a diagram for explaining the operation of electronic device 100 including charging control IC 300. As shown in FIG. The horizontal axis is time. The left vertical axis represents voltage, and the right vertical axis represents current.

When the battery is deeply discharged, trickle charging is performed. During trickle charging, charge control IC 300 stabilizes the output voltage (system voltage) V _SYS of DC/DC converter 212 to a predetermined target voltage V _SYSREG . The on-resistance of the second switch SW2 is feedback-controlled, and the battery 102 is charged with the charging current _ICHG stabilized at the trickle charge target value _ITR . This causes the battery voltage V _BAT to rise.

When the battery voltage V _BAT exceeds the threshold for precharging, it switches to precharging. In precharging, the battery 102 is charged with a charging current I _CHG (=I _PRE ) that is higher than in trickle charging.

When the battery voltage V _BAT reaches the voltage V _SYSREG , the CC mode is entered and the charging current I _CHG is regulated to the constant current I _CC . As the charging of the battery 102 progresses, the charging current I _CHG can no longer maintain the constant current I _CC and decreases, shifting to the CV mode. Charging is complete when the charging current I - _{- CHG} drops to the termination current I - - _TERM .

After the power reception is completed, the second switch SW2 is turned off. Also, the charge control IC 300 enters the non-charge mode and stabilizes the system voltage V _SYS to a voltage level higher than the battery voltage V _BAT by a voltage width ΔV.

The above is the operation of the electronic device 100 . Next, its advantages will be explained.

Consider a system that uses the charge control IC 300 with a two-cell battery 102, for example. When the battery voltage V _BAT is 8.86V and ΔV=200 mV, the system voltage V _SYS will be regulated at 9.06V. In other words, the withstand voltage of the internal circuit 110 is sufficient with 10V, and the choice of parts increases.

Further, by providing the clamp circuit 397 in the pulse modulator 331, it is possible to prevent the system voltage _VSYS from falling below the minimum operating voltage of the internal circuit 110 when the battery 102 is over-discharged.

(Application)
Next, the application of the charge control IC 300 will be explained. FIG. 7 is a perspective view of electronic device 100 including charging control IC 300. As shown in FIG. In this example, electronic device 100 is a battery-powered device such as a smart phone, tablet computer, laptop computer, portable music player, or the like. The electronic device 100 is provided with a receptacle 104 for pointing a USB cable. A battery 102 , a charge control IC 300 , a peripheral circuit 210 , and an internal circuit 110 are housed inside the housing of the electronic device 100 .

(Modification)
The embodiment has been described above. It should be understood by those skilled in the art that this embodiment is merely an example, and that various modifications can be made to the combination of each component and each treatment process, and that such modifications are within the scope of the present invention. be. Such modifications will be described below.

(Modification 1)
DC/DC converter 212 may be a step-down converter or a step-up converter. The type of DC/DC converter 212 may be determined according to the magnitude relationship between the external voltage V _BUS and the voltage of battery 102 .

(Modification 2)
Transistors M11-M14 of FIG. 1 may be integrated into charge control IC 300. FIG. Also, the first switch SW1 and the second switch SW2 may be integrated into the charge control IC 300 .

(Modification 3)
In the embodiment, power supply by USB has been described, but the USB standard is not limited, and may be USB-PD or USB Type C. Also, the supply of the external voltage V _BUS is not limited to USB, and the present disclosure is applicable to other forms of power supply.

(Modification 4)
When the constant current circuit CS51 of FIG. 5 is used, the transistors M71 and M72 may be composed of normal (0.5 to 0.7 V) threshold MOSFETs. For example, if the charge control IC 300 is specified to support only batteries with 2 or more cells, no low voltage threshold MOSFETs are required. Alternatively, if the specifications are set so as to support a one-cell battery, the voltage Vn2 can be increased by increasing the voltage division ratio β, eliminating the need for a low threshold voltage.

(Modification 5)
In embodiments, the transistors shown as MOSFETs may be configured with bipolar transistors.

The embodiments described using specific terms merely show the principle and application of the present invention, and the embodiments do not deviate from the spirit of the present invention defined in the scope of claims. , many modifications and changes in arrangement are permitted.

100 Electronic Device 102 Battery 104 USB Receptacle 110 Internal Circuit 200 Charging Circuit 210 Peripheral Circuit 212 DC/DC Converter 300 Charging Control IC
SW1 first switch SW2 second switch 310 power path control section 312 gate driver 320 voltage selection circuit 322 first regulator 324 second regulator 330 converter controller 331 pulse modulator 334 PWM logic section 336 step-down driver 338 step-up driver 340 USB charger detector 342 interface circuit 350 logic circuit 370 switch controller 390 current source 392 PWM comparator 394 oscillator 396 target voltage generation circuit R51 first resistor R52 second resistor OA51 first operational amplifier OA52 second operational amplifier CS51 constant current circuit CCS71 reference current source EA51 Error amplifiers M41, M42, M43 Transistors OA41, OA42, OA43 Operational amplifiers R61, R62, R63, R64 Resistors

Claims (7)

A charging control circuit for controlling charging of a battery using an external voltage,
A converter controller that controls a DC/DC converter that constitutes a charging circuit,
The converter controller
a target voltage generation circuit that generates a target voltage;
an error amplifier that amplifies an error between a system voltage detection signal corresponding to the output voltage of the DC/DC converter and the target voltage;
a pulse modulator that generates a pulse signal corresponding to the output of the error amplifier;
with
The target voltage generation circuit is
a first transistor;
a constant current circuit that sinks constant current;
a first resistor connected between the first transistor and the constant current circuit;
It has a first input node, a second input node and an output node, the voltage of the connection node of the first resistor and the constant current circuit is received at the first input node, and the voltage of the battery is at the second input node. a first operational amplifier receiving a corresponding battery voltage detection signal, the output node of which is connected to the control terminal of the first transistor;
wherein the target voltage is according to the voltage of a connection node between the first transistor and the first resistor. The constant current circuit is
a reference current source for generating a reference current;
a current mirror circuit that folds back the reference current;
2. The charge control circuit of claim 1, comprising: 3. The charge control circuit according to claim 2, wherein said current mirror circuit is composed of field effect transistors having a threshold voltage lower than 0.2V. The target voltage generation circuit is
4. The charge control circuit according to claim 1, further comprising a clamp circuit that clamps a connection node between said first transistor and said first resistor so that it does not fall below a predetermined minimum voltage. The clamp circuit is
a second transistor having a first end receiving a power supply voltage and a second end connected to the connection node between the first transistor and the first resistor;
having a first input node, a second input node and an output node, receiving a set voltage defining the minimum voltage at the first input node, and receiving the first transistor and the first resistor at the second input node; a second operational amplifier receiving the voltage of the connection node of and having the output node connected to the control terminal of the second transistor;
5. The charge control circuit of claim 4, comprising: 6. The charging control circuit according to any one of claims 1 to 5, which is monolithically integrated on one semiconductor substrate. a battery;
a charging control circuit according to any one of claims 1 to 6, which controls charging of the battery;
An electronic device.

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