JP5014933B2 - CHARGE CONTROL CIRCUIT AND ELECTRONIC DEVICE USING THE SAME - Google Patents

Description

  The present invention relates to a charge control circuit for charging a secondary battery.

  Various electronic devices such as recent cellular phones, PDAs (Personal Digital Assistants), and notebook personal computers include a CPU (Central Processing Unit) that performs digital signal processing, a DSP (Digital Signal Processor), a liquid crystal panel, Many other electronic circuits such as analog and digital circuits are installed. In a battery-driven electronic device in which a battery is mounted as a power source, each electronic circuit inside the device operates with a battery voltage from the battery.

  In recent years, secondary batteries such as rechargeable lithium ion batteries and nickel metal hydride batteries are used. The charging operation of the secondary battery generally goes through the following process. In other words, preliminary charging is performed when the battery voltage is low, the charging current is fed back when the battery voltage increases to some extent, charging is performed so that the charging current becomes constant (constant current charging), and the battery voltage approaches the fully charged state. The battery voltage is fed back, and charging is performed so that the battery voltage matches a predetermined reference voltage (full charge voltage) (constant voltage charging). When the battery voltage matches the reference voltage, full charging is detected and the charging operation is stopped. After the completion of charging, when the battery voltage decreases to a predetermined threshold voltage (recharge detection voltage) as the battery is consumed, recharge is started (recharge detection).

JP 2004-7853 A Japanese Patent Laid-Open No. 2004-187452 JP 2005-168102 A

  In order to perform the above-described charging process, a charging control circuit is connected to the battery. FIG. 3 is a circuit diagram illustrating a configuration example of the charging control unit 30. The circuit diagram of FIG. 3 shows only blocks that perform constant voltage charging and recharge detection. Charging control unit 30 receives external voltage Vext from an external power source at adapter terminal 102. A battery 110 is connected to the battery terminal 104. The detection terminal 105 is a terminal for monitoring the battery voltage Vbat of the battery 110. The battery voltage Vbat is divided by the resistors R10 and R11 at the voltage dividing ratio α, and the first detection voltage Vdet1 is generated. The battery terminal 104 and the detection terminal 105 may be formed as a single terminal.

  The error amplifier 2 amplifies an error between the first detection voltage Vdet1 and the reference voltage Vref, and generates an error voltage Verr. Based on the error voltage Verr, the charge driver 50 charges the battery 110 by feedback so that the first detection voltage Vdet1 matches the reference voltage Vref. That is, the full charge voltage Vfull is given by Vref / α.

  Further, the battery voltage Vbat is divided by the resistors R12 and R13 at the voltage dividing ratio β, and the second detection voltage Vdet2 is generated. The comparator CMP1 compares the second detection voltage Vdet2 with the threshold voltage Vth, and outputs a detection signal S10 having a predetermined level when the second detection voltage Vdet2 decreases to the threshold voltage Vth. When the detection signal S10 becomes high level, rapid charging is started. That is, the recharge detection voltage Vrch is given by Vth / β.

  In the case of the circuit of FIG. 3, when the voltage dividing ratios α and β vary due to variations in resistance values of the resistors R10 to R13, or the input offset voltage of the error amplifier 2 or the comparator CMP1 varies, the full charge voltage Vfull and the recharge detection are detected. The voltage Vrch changes without correlation. For example, if the full charge voltage Vfull is 4.2 V and the recharge detection voltage Vrch is 4 V, the magnitude relationship may be reversed if the voltage division ratio or the input offset voltage fluctuates, and full charge detection or recharge detection may not be performed accurately. is there.

  The present invention has been made in view of these problems, and an object thereof is to provide a technique for accurately setting the full charge voltage and the recharge detection voltage.

  One embodiment of the present invention relates to a charge control circuit that receives an external voltage and charges a battery. The charge control circuit includes an input terminal for receiving an external voltage from an external power source, a battery, a battery terminal for detecting the battery voltage, and an error voltage corresponding to an error between the battery voltage and a predetermined full charge voltage. An amplifier to be generated; and a charge driver that receives an error voltage from the amplifier and supplies a charging current to the battery so that the battery voltage matches the full charge voltage by feedback. The amplifier functions as a comparator that compares the battery voltage with a predetermined recharge detection voltage in order to detect the recharge timing after the battery voltage matches the full charge voltage.

  According to this aspect, the full charge voltage and the recharge detection voltage can be set relatively accurately by sharing a single amplifier during constant voltage charging and during recharge detection.

  The amplifier receives a voltage dividing circuit that divides the battery voltage by a switchable first and second voltage dividing ratio to generate a detection voltage, a detection voltage from the voltage dividing circuit, and a predetermined reference voltage. And a differential amplifier. When the battery is charged, the output signal of the differential amplifier is output to the charge driver for feedback, and when the recharge timing is detected, it may be used as a comparison result between the battery voltage and the recharge detection voltage. Good.

  Another embodiment of the present invention is an electronic device. This electronic device includes a battery, an adapter terminal to which an external power source can be attached and detached, and the above-described charging control circuit.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, etc. are also effective as an aspect of the present invention.

  According to the present invention, the full charge voltage and the recharge detection voltage can be set relatively accurately.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. The embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

In this specification, “the state in which the member A is connected to the member B” means that the member A and the member B are physically directly connected, or the member A and the member B are in an electrically connected state. Including the case of being indirectly connected through other members that do not affect the above.
Similarly, “the state in which the member C is provided between the member A and the member B” refers to the case where the member A and the member C or the member B and the member C are directly connected, as well as an electrical condition. It includes the case of being indirectly connected through another member that does not affect the connection state.

  Further, in this specification, reference numerals attached to voltage signals or resistors represent respective voltage values or resistance values as necessary.

  FIG. 1 is a circuit diagram illustrating a configuration of an electronic device 200 including a power management circuit 100 according to an embodiment. The electronic device 200 is, for example, a battery-driven information terminal device such as a mobile phone terminal, a PDA, or a notebook PC. The electronic device 200 includes a power management circuit 100, a battery 110, an adapter terminal 114, and a load 112.

  The battery 110 is a secondary battery such as a lithium ion battery or a nickel metal hydride battery, and outputs a battery voltage Vbat. The adapter terminal 114 is a terminal to which an external power source 210 such as an AC adapter or USB (Universal Serial Bus) can be attached and detached, and receives a voltage (hereinafter referred to as an external voltage) Vext from the external power source 210. The power management circuit 100 charges the battery 110 using the external voltage Vext. Further, the power management circuit 100 stabilizes the battery voltage Vbat by stepping up or down to a predetermined voltage and supplies the voltage to the load 112. The load 112 includes a DSP, a liquid crystal panel (not shown), other analog circuits, and digital circuits.

  The power management circuit 100 includes a charge control unit 30, a state machine 60, and a power circuit 62. An external voltage Vext is applied to the adapter terminal 102, and a battery 110 is connected to the battery terminal 104. The detection terminal 105 is provided for monitoring the battery voltage Vbat. The battery terminal 104 and the detection terminal 105 may be a common terminal. The state machine 60 manages and controls the operation mode of the power management circuit 100. The power supply circuit 62 includes a switching regulator and a linear regulator, selects and stabilizes either the battery voltage Vbat or the external voltage Vext, and outputs the selected voltage to the load 112.

  Charging control unit 30 receives external voltage Vext and charges battery 110. The charge control unit 30 is a mode for rapidly charging the battery 110 (rapid charge mode), a mode for constant current charge (constant current charge mode), a mode for constant voltage charge (constant voltage charge mode), and the battery voltage Vbat is a recharge detection voltage. It operates in one of the modes (recharge detection mode) for detecting that the voltage has dropped to Vrch (= 4.0 V). Each mode is controlled by the state machine 60.

  Charging control unit 30 receives external voltage Vext at input terminal 32. The battery terminal 34 is provided for detecting the battery voltage Vbat while being connected to the battery 110. The charge control unit 30 includes an amplifier 40 and a charge driver 50. In the constant current charging mode, the amplifier 40 generates an error voltage Verr corresponding to an error between the battery voltage Vbat and the full charge voltage Vfull (= 4.2 V).

  The charging driver 50 receives the error voltage Verr from the amplifier 40 and supplies the charging current Ichg to the battery 110 so that the battery voltage Vbat matches the full charge voltage Vull by feedback. The charge driver 50 may include an output transistor (not shown) having one end connected to the battery 110 side and the other end connected to the external power source 210 side. In this case, the state of charge is adjusted by applying a voltage corresponding to the error voltage Verr to the gate (base) of the output transistor and controlling the on-resistance of the output transistor.

  However, the charge driver 50 is not limited to such a linear regulator type, and may be a switching regulator type. In the case of a switching regulator, the error voltage Verr is sliced with a triangular wave or sawtooth wave periodic voltage to generate a pulse-width modulated signal, and on / off of the switching element is controlled based on this signal. In addition, the charging driver 50 can use various known circuits.

  In the present embodiment, the amplifier 40 functions as an error amplifier in the constant voltage charging mode, and in the recharge detection mode for detecting the recharge start timing after the battery voltage Vbat matches the full charge voltage Vfull, It functions as a comparator that compares the battery voltage Vbat with a predetermined recharge detection voltage Vrch.

  The state machine 60 outputs to the amplifier 40 and the charge driver 50 an enable signal EN that is at a high level in the constant voltage charge mode and at a low level in the recharge detection mode. The charge driver 50 is turned off when the enable signal EN is at a low level, that is, during the recharge detection mode in which the amplifier 40 functions as a comparator. At this time, the feedback path is interrupted, and the output of the amplifier 40 is used as the recharge detection signal S10.

  FIG. 2 is a circuit diagram showing a configuration of the amplifier 40 of FIG. The amplifier 40 includes a voltage dividing circuit 42, a first differential amplifier AMP1, and a second differential amplifier AMP2. The voltage dividing circuit 42 divides the battery voltage Vbat to generate a detection voltage Vdet. The voltage dividing ratio of the voltage dividing circuit 42 is switched between two values according to the mode of the charging control unit 30. Specifically, the first voltage division ratio α is set in the constant voltage charge mode, and the second voltage division ratio β is set in the recharge detection mode. That is, the detection voltage Vdet is Vdet = α × Vbat in the constant voltage charge mode, and Vdet = β × Vbat in the recharge detection mode.

  The voltage dividing circuit 42 includes a first resistor R1 and a second resistor R2 provided in series between a terminal 44 to which the battery voltage Vbat is applied and a ground terminal. The voltage at the connection point of the first resistor R1 and the second resistor R2 is output as the detection voltage Vdet to the first differential amplifier AMP1 at the subsequent stage. At least one of the first resistor R1 and the second resistor R2 is configured as a variable resistor. In FIG. 2, the second resistor R2 is a variable resistor and includes resistors R21 and R22 and a switch SW20. The switch SW20 is provided in parallel with the resistor R22. When the switch SW20 is turned on, the resistor R22 is bypassed, the effective resistance value of the second resistor R2 is R21, and when the switch SW20 is turned off, the effective resistance is set. The value is R21 + R22. That is, the resistance value of the second resistor R2 changes corresponding to the on / off of the switch SW20, and the voltage dividing ratio of the voltage dividing circuit 42 is switched. The switch SW20 is turned on when the enable signal EN is at a high level in the constant voltage charging mode, and the switch SW20 is turned off when the enable signal EN is at a low level in the recharge detection mode.

  When the voltage dividing circuit 42 of FIG. 2 is used, the first voltage dividing ratio α is given by α = R21 / (R1 + R21), and the second voltage dividing ratio β is given by β = (R21 + R22) / (R1 + R21 + R22).

  The detection voltage Vdet is input to one input terminal of the first differential amplifier AMP1, and a predetermined reference voltage Vref is input to the other input terminal. The reference voltage Vref is generated by a band gap reference circuit (not shown). The error voltage Verr generated by the first differential amplifier AMP1 is a differential signal, and is output to the charge driver 50 for feedback in the constant voltage charging mode. In the recharge detection mode, the differential error voltage Verr is used as a comparison result between the battery voltage Vbat and the recharge detection voltage Vrch.

  In the circuit of FIG. 2, a second differential amplifier AMP2 is provided after the first differential amplifier AMP1. The second differential amplifier AMP2 has a single-ended output, receives the differential error voltage Verr output from the first differential amplifier AMP1, amplifies the difference between the two signals, and outputs a high level or a low level. The detection signal S10 is generated. The detection signal S10 notifies the state machine 60 that the detection voltage Vdet has decreased to the reference voltage Vref. When the detection voltage Vdet decreases to the reference voltage Vref, the state machine 60 transitions to a constant voltage charging mode or a constant current charging mode in order to start recharging.

  The second differential amplifier AMP2 has an enable terminal, and on / off is controlled based on the enable signal EN from the state machine 60. The second differential amplifier AMP2 is turned off when the enable signal EN is at a high level in the constant voltage charging mode, and is turned on when the enable signal EN is at a low level in the recharge detection mode. The second differential amplifier AMP2 is used by comparing the battery voltage Vbat and the recharge detection voltage Vrch, and is unnecessary during the constant voltage charging mode. Therefore, the current consumption can be reduced by providing an enable function and shutting down.

The operation of the charging control unit 30 configured as described above will be described.
The state machine 60 transits to the constant voltage charging mode through the rapid charging mode and the constant current charging mode. In the constant voltage charging mode, the enable signal EN becomes a high level, the charging driver 50 is set to an on state, and the second differential amplifier AMP2 of the amplifier 40 is set to an off state. The voltage dividing ratio of the voltage dividing circuit 42 is set to α, and Vdet = Vbat × α. The loop including the first differential amplifier AMP1 and the charge driver 50 provides feedback so that Vdet = Vref is satisfied, that is, Vbat = Vref / α.

  When full charge is detected by a full charge detection circuit (not shown), the state machine 60 transitions to a recharge detection mode. The state machine 60 sets the enable signal EN to a low level, turns off the charge driver 50 to cut off the feedback loop, and sets the second differential amplifier AMP2 of the amplifier 40 to an operating state. Further, the voltage dividing ratio of the voltage dividing circuit 42 is set to β. The differential error voltage Verr from the first differential amplifier AMP1 is determined according to the magnitude relationship between the detection voltage Vdet and the reference voltage Vref. The second differential amplifier AMP2 determines the magnitude relationship between the detection voltage Vdet and the reference voltage Vref based on the differential error voltage Verr, and generates a detection signal S10. When Vdet <Vref, that is, when Vbat <Vref / β, the detection signal S10 becomes high level, and the state machine 60 transitions to the constant voltage charging mode.

  The effect of the charging control unit 30 according to the present embodiment becomes clearer by comparison with FIG. In the circuit of FIG. 3, an input offset voltage is generated in each of the error amplifier 2 and the comparator CMP1, and each input offset voltage is independently generated without correlation. Therefore, the magnitude relationship between the full charge voltage Vfull and the recharge detection voltage Vrch may be reversed. In order to set the full charge voltage Vfull and the recharge detection voltage Vrch with high accuracy, a trimming mechanism is provided on both the resistors R10 and R11 and the resistors R12 and R13, or the reference voltage Vref and the threshold voltage Vth are set. Since adjustment is required independently, there is a problem that the circuit scale increases and the manufacturing cost related to trimming increases.

  On the other hand, in the charge control unit 30 according to the embodiment, the circuit area can be reduced because the single first differential amplifier AMP1 is used. Further, the error amplification at the time of constant voltage charging and the voltage comparison at the time of recharging detection are affected by a common input offset voltage, so that it is difficult to affect the magnitude relationship between the full charge voltage Vfull and the recharge detection voltage Vrch. There is.

  In the charge control unit 30 of the embodiment, a common voltage dividing circuit 42 is provided to switch the voltage dividing ratio. As a result, the variation in resistance value in the voltage dividing circuit 42 affects both the full charge voltage Vfull and the recharge detection voltage Vrch, so that a correlation is maintained. In the case where the voltage dividing circuit 42 is provided with a trimming mechanism, the cost can be reduced because the trimming process is performed once. In other words, if the trimming is performed so that the full charge voltage Vfull approaches the target value, the recharge detection voltage Vrch can be automatically approximated to the target value.

  Those skilled in the art will understand that the above-described embodiment is an exemplification, and that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  Although the case where the voltage dividing ratio of the voltage dividing circuit 42 is switched has been described in the embodiment, the reference voltage Vref may be switched between two values corresponding to the full charge voltage Vfull and the recharge detection voltage Vrch with the voltage dividing ratio constant. Also in this case, the magnitude relationship between the full charge voltage Vfull and the recharge detection voltage Vrch can be maintained.

  In the embodiment, the amplifier 40 is composed of two amplifiers, the first differential amplifier AMP1 and the second differential amplifier AMP2, but the present invention is not limited to this. When the first differential amplifier AMP1 is a single-ended differential amplifier, the second differential amplifier AMP2 can be omitted.

  In the embodiment, the setting of the logic level of each signal is an example, and the circuit configuration may be changed by inverting as appropriate.

  Although the present invention has been described using specific words and phrases based on the embodiments, the embodiments are merely illustrative of the principles and applications of the present invention, and the embodiments are defined in the claims. Many modifications and arrangements can be made without departing from the spirit of the present invention.

It is a circuit diagram which shows the structure of an electronic device provided with the power supply management circuit which concerns on embodiment. FIG. 2 is a circuit diagram illustrating a configuration of an amplifier in FIG. 1. It is a circuit diagram which shows the structural example of the charge control part contrasted with embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Power management circuit, 102 ... Adapter terminal, 104 ... Battery terminal, 105 ... Detection terminal, 30 ... Charge control part, 32 ... Input terminal, 40 ... Amplifier, 42 ... Voltage divider circuit, 44 ... Terminal, 50 ... Charge driver , 60 ... state machine, 62 ... power supply circuit, 110 ... battery, 112 ... load, 114 ... adapter terminal, 200 ... electronic equipment, 210 ... external power supply, Vext ... external voltage, Vbat ... battery voltage, R1 ... first resistance, R2 ... second resistor, AMP1 ... first differential amplifier, AMP2 ... second differential amplifier.

Claims (3)

A charge control circuit for charging a battery in response to an external voltage,
An input terminal for receiving an external voltage from an external power source;
The battery is connected, and battery terminals for detecting battery voltage;
An amplifier that generates an error voltage according to an error between the battery voltage and a predetermined full charge voltage;
A charge driver that receives an error voltage from the amplifier and charges the battery by supplying a charging current so that the battery voltage matches the full charge voltage by feedback; and
With
The amplifier functions as a comparator that compares the battery voltage with a predetermined recharge detection voltage in order to detect a recharge timing after the battery voltage matches the full charge voltage. circuit. The amplifier is
A voltage dividing circuit for dividing the voltage of the battery by a switchable first and second voltage dividing ratio to generate a detection voltage;
A differential amplifier to which the detection voltage from the voltage dividing circuit and a predetermined reference voltage are input;
Including
The output signal of the differential amplifier is output to the charge driver for feedback when the battery is charged, and when the recharge timing is detected, the battery voltage and the recharge detection voltage are compared. The charge control circuit according to claim 1, wherein the charge control circuit is used as: Battery,
An adapter terminal to which an external power supply can be attached and detached;
The charge control circuit according to claim 1 or 2, wherein the battery is charged;
An electronic device comprising:

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