JP2009095076A - Charge controller and electronic equipment using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charge controller, which can control the charge of a secondary battery safely and optimally, and electronic equipment using it. <P>SOLUTION: This charge controller 1 is so structured as to monitor the charge current I3 of the secondary battery 3 and to control the charge of the secondary battery 3 so that its current value may be a smaller value between the target value preset within the equipment and the target value optimally set from outside the equipment. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a charge control device that performs charge control of a secondary battery (for example, a lithium ion battery), and an electronic device using the same.

  Many electronic devices equipped with a secondary battery (for example, a lithium ion battery) as a power source, such as a portable navigation system (PND [Portable Navigation Device]) and a mobile phone terminal, are host devices connected to a USB [Universal Serial Bus] port. (USB host) and a charge control device (power management IC) that performs charge control of the secondary battery upon receiving power supply from the power adapter.

  In particular, when a lithium ion battery is used as a secondary battery, the charging current must be severely controlled. Therefore, in the conventional charging control device, the ambient temperature and the current consumption of the system (consumed for operations other than charging) Current) and a target value setting (internal control) of the charging current according to the result. Further, when charging a secondary battery in response to supply from a power adapter, a target value setting (external control) of a charging current using an external resistor has been performed.

  Note that Patent Document 1 can be cited as an example of the related art related to the above-described charging control device.

Moreover, as a prior art relevant to a temperature detection circuit, patent document 2 by the applicant of this application, patent document 3, etc. can be mentioned.
JP 2003-032910 A JP 2005-016992 A JP-A-9-189614

  Certainly, with the above conventional charge control device, it is possible to perform charge control of the secondary battery by receiving power supply from a USB host or a power adapter.

  However, in the conventional charging control device, the power supply path from the USB host and the power supply path from the power adapter are separate systems, and the target value setting of the charging current is also used as the charging current supply source. Depending on whether the USB host or the power adapter is connected, the settings are different from each other.

  Specifically, in accordance with the above-mentioned example, when a USB host is connected as a charging current supply source, the target value setting (external control) of the charging current using an external resistor is not reflected at all. The user cannot arbitrarily set the target value of the charging current.

  Conversely, when a power adapter is connected as a charging current supply source, the user must set the target value of charging current to include a sufficient safety margin, taking into account changes in ambient temperature and system current consumption. This has been one of the factors that unnecessarily prolongs the charging time.

  An object of this invention is to provide the charge control apparatus which can perform charge control of a secondary battery safely and optimally, and an electronic device using the same in view of said problem.

  In order to achieve the above object, the charging control device according to the present invention monitors the charging current of the secondary battery, and the current value is arbitrarily set from a target value preset in the device and from the outside of the device. The secondary battery charging control is performed (first configuration) so as to be smaller than the target value.

  Note that the charge control device having the first configuration has at least a target value according to the ambient temperature, a target value according to the current consumption of the system, and a standard of an externally connected power supply source. The target value is set in advance, and the current value of the charging current is the smallest value among the target value set in advance inside the device and the target value arbitrarily set from outside the device. The second battery may be configured to perform charging control of the secondary battery (second configuration).

  In the charge control device having the second configuration, the target value corresponding to the ambient temperature may be set to a smaller value (third configuration) as the ambient temperature is higher.

  In the charge control device having the third configuration, the temperature sensor that detects the ambient temperature includes a pair of PNP-type bipolar transistors that operate at different emitter current densities, and the base-emitter voltage of both transistors. It is preferable to adopt a configuration (fourth configuration) that generates a temperature detection signal having a negative characteristic by utilizing the fact that the difference between the two varies depending on the ambient temperature.

  In addition, an electronic apparatus according to the present invention includes a charge control device having any one of the first to fourth configurations and a secondary battery whose charge is controlled by the charge control device (fifth). It is said that.

  According to the present invention, it is possible to perform charging control of a secondary battery safely and optimally.

  FIG. 1 is a block diagram showing an embodiment of an electronic device (for example, a portable navigation system) equipped with a charging control device according to the present invention.

  As shown in FIG. 1, the electronic device of this embodiment includes a power management IC 1, a microcomputer, a lithium ion battery 3, sense resistors 4 and 5, a port 6, a power supply line 7, a signal line 8, It has.

  The power management IC 1 is a charge control device that performs charge control of the lithium ion battery 3. The internal configuration and operation of the power management IC 1 will be described in detail later.

  The microcomputer 2 is information processing means that is driven by receiving power supply from the power management IC 1. As a power supply source externally connected to the electronic device, a USB host is connected to the port 6 or a power adapter is connected. (The connection with the USB host is established through the signal line 8), and the result is transmitted to the charge control unit 11 of the power management IC1. When the USB host is connected to the port 6, the microcomputer 2 exchanges signals with the USB host via the signal line 8.

  With regard to the above, a more specific sequence will be described. First, in response to the voltage V1 being applied to the power supply line 7, the power management IC 1 is activated. At this time, the power management IC 1 is connected to a USB host of a low power standard (upper limit value 100 [mA] of the supply current I1) considering that the type of power supply source externally connected to the electronic device is unknown. The charging control of the lithium ion battery 3 is started on the safest side.

  After that, power supply from the power management IC 1 to the microcomputer 2 is started, and when the microcomputer 2 is activated, USB host confirmation processing (USB host connection confirmation and high power / low power standard confirmation) is performed by the microcomputer 2. Is called.

  Here, when it is confirmed that the USB host of the high power standard (the upper limit value 500 [mA] of the supply current I1) is connected, the microcomputer 2 transmits the fact to the power management IC1. Receiving this, the power management IC 1 switches the charge control mode of the lithium ion battery 3 according to the monitoring result in the microcomputer 2.

  On the other hand, when it is confirmed that a low power standard USB host is connected, the microcomputer 2 transmits the fact to the power management IC 1. Receiving this, the power management IC 1 maintains the current charge control mode of the lithium ion battery 3.

  If the connection of the USB host cannot be confirmed, the microcomputer 2 recognizes that the power adapter is connected and transmits the fact to the power management IC 1. Receiving this, the power management IC 1 switches the charge control mode of the lithium ion battery 3 according to the monitoring result in the microcomputer 2.

  The lithium ion battery 3 is a secondary battery whose charge is controlled by the power management IC 1, and serves as a driving power source for the electronic device when a USB host or a power adapter is not connected to the port 6.

  The sense resistor 4 is externally connected between the terminal T1 and the terminal T2 of the power management IC 1 and is a means for converting the supply current I1 from the USB host or the power adapter into a voltage signal.

  The sense resistor 5 is externally connected between the terminal T3 and the terminal T4 of the power management IC 1, and the charging current I3 of the lithium ion battery 3 (from the supply current I1 from the USB host or the power adapter, other than the charging of the lithium ion battery 3) The surplus current obtained by subtracting the current consumption I2 of the system used in the above is converted into a voltage signal.

  The port 6 is an interface unit for externally connecting a USB host or a power adapter to the electronic device.

  The power line 7 is a line for receiving power supply from a USB host or power adapter connected to the port 6.

  The signal line 8 is a line for exchanging signals between the USB host connected to the port 6 and the microcomputer 2.

  Next, the internal configuration of the power management IC 1 will be described in detail.

  As shown in FIG. 1, the power management IC 1 includes a charge control unit 11, amplifiers 12 and 13, P-channel field effect transistors 14 and 15, a temperature sensor 16, an internal setting unit 17, and an external setting unit 18. And a DC / DC converter 19.

  The charge control unit 11 operates as a supply current control function unit and a charge current control function unit as shown in FIG. 2 by controlling the continuity (on resistance) of the transistors 14 and 15. . The operation of the charging control unit 11 will be described in detail later.

  The amplifier 12 is a means for amplifying the voltage across the sense resistor 4 and sending a supply current detection signal corresponding to the supply current I1 from the USB host or power adapter to the charge controller 11.

  The amplifier 13 is means for amplifying the voltage across the sense resistor 5 and sending a charge current detection signal corresponding to the charge current I3 of the lithium ion battery 3 to the charge control unit 11.

  The transistor 14 is internally connected between the terminal T2 and the terminal T3, and is means for increasing or decreasing the current value of the supply current I1 in accordance with the conductivity control.

  The transistor 15 is internally connected between the terminal T4 and the terminal T5, and is means for increasing or decreasing the current value of the charging current I3 in accordance with the conductivity control.

  The temperature sensor 16 is means for generating a temperature detection signal Sout corresponding to the ambient temperature T and sending it to the charge control unit 11. The internal configuration and operation of the temperature sensor 16 will be described in detail later.

  The internal setting unit 17 is a unit that presets a target value of the charging current I3 according to the USB host standard (high power / low power) and sends the set value to the charging control unit 11.

  The external setting unit 18 is a unit that arbitrarily sets a target value of the charging current I3 using an external resistor or the like, and sends the set value to the charging control unit 11.

  The DC / DC converter 19 operates by receiving the voltage V2 obtained at the terminal T3, and supplies a predetermined drive voltage to each circuit unit (microcomputer 2 in the example of FIG. 1) constituting the electronic device. Series regulators and switching regulators can be used.

  Next, charge control of the lithium ion battery 3 by the power management IC 1 (particularly the charge control unit 11) will be described in detail.

  FIGS. 3A to 3D respectively show charge control according to the ambient temperature T, charge control according to the system current I2, charge control according to the internal set value, and charge control according to the external set value. It is a figure for demonstrating individually.

  As indicated by the solid line L1 in FIG. 3A, the charge control unit 11 sets the target value of the charging current I3 to a smaller value as the ambient temperature T is higher based on the temperature detection signal Sout obtained by the temperature sensor 16. Thus, the charging control of the lithium ion battery 3 is performed.

  Further, as indicated by a solid line L2 in FIG. 3B, the charging control unit 11 detects the current consumption I2 of the system from the potential difference between the terminal voltage V1 obtained at the terminal T1 and the terminal voltage V2 obtained at the terminal T3. Then, the charging control of the lithium ion battery 3 is performed so that the target value of the charging current I3 becomes smaller as the current value increases.

  Further, as indicated by solid lines L3a and L3b in FIG. 3C, the charging control unit 11 determines the USB host standard based on the target value (fixed value) of the charging current I3 preset by the internal setting unit 17. Charge control of the lithium ion battery 3 according to (high power / low power) is performed.

  Further, as indicated by a solid line L4 in FIG. 3D, the charge control unit 11 determines the lithium ion battery 3 based on the target value (variable value) of the charging current I4 arbitrarily set by the external setting unit 18. Perform charging control.

  Here, the feature of the present invention is that the charging control shown in FIGS. 3A to 3D is not performed separately, but as shown in FIG. Charging is performed by selecting the smallest value among the set target values (see the solid lines L1, L2, and L3 in FIG. 3) and the target values arbitrarily set from outside the apparatus (see the solid line L4 in FIG. 3). The lithium ion battery 3 is not overloaded by controlling the current I3 within the allowable power consumption.

  By adopting such a configuration, even when the external setting value (L4) is set to a high value, for example, the current value of the charging current I3 is increased by increasing the ambient temperature T or increasing the system current I2. When the situation has to be squeezed, the set values (L1, L2) are preferentially applied, so that the charging can be continued safely. On the other hand, when such a situation is not reached, a large charging current I3 is set by the external set value (L4), so that the charging time can be shortened.

  In addition, when the USB is used, conventionally, the upper limit values (L3a, L3b) of the charging current I3 are fixedly set, and it is determined that it is dangerous for the user to charge at the upper limit value. Even this could not be changed. On the other hand, according to the present invention, if the external setting value (L4) is set lower than the internal setting values (L3a, L3b), the upper limit current value when using the USB can be arbitrarily reduced.

  Next, the configuration and operation of the temperature sensor 16 will be described in detail with reference to FIG.

  FIG. 5 is a circuit diagram showing a configuration example of the temperature sensor 16.

  The temperature sensor 16 of this configuration example includes a pair of PNP-type bipolar transistors Pa and Pb (in this configuration example, an emitter area ratio of 1: N) operating at different emitter current densities JEa and JEb. This is a configuration that generates a temperature detection signal Sout having a negative characteristic by utilizing the fact that the difference voltage ΔVF (= VBE1−VBE2) between the base-emitter voltages VBE1 and VBE2 of Pb varies according to the ambient temperature T. As the remaining components, PNP type bipolar transistors Pc to Pg, NPN type bipolar transistors Na and Nb, constant current sources Ia and Ib, and resistors Ra to Rd are provided.

  The collectors of the transistors Pa and Pb are connected to the ground terminal via the constant current sources Ia and Ib, respectively. The emitters of the transistors Pa and Pb are both connected to the collector of the transistor Pe. The emitters of the transistors Pc to Pe are all connected to the application terminal of the power supply voltage Vcc. The bases of the transistors Pc to Pe are all connected to the collector of the transistor Pd. The collector of the transistor Pc is connected to the collector of the transistor Na. The collector of the transistor Pd is connected to the collector of the transistor Nb. The bases of the transistors Na and Nb are both connected to the collector of the transistor Na. The emitter of the transistor Na is connected to the output terminal of the temperature detection signal Sout. The emitter of the transistor Nb is connected to the base of the transistor Pa. The emitter of the transistor Pf is connected to the base of the transistor Pa, and is also connected to the application terminal of the power supply voltage Vcc via the resistors Rc and Ra. The collector of the transistor Pf is connected to the ground terminal. The base of the transistor Pf is connected to the collector of the transistor Pa. The emitter of the transistor Pg is connected to the application terminal of the power supply voltage Vcc via resistors Rd and Rb. A connection node between the resistor Rb and the resistor Rd is connected to the base of the transistor Pb. The collector of the transistor Pg is connected to the ground terminal. The base of the transistor Pg is connected to the collector of the transistor Pb.

  In the temperature sensor 16 having the above-described configuration, the collector voltage and the emitter current of the transistors Pa and Pb are feedback-controlled (so-called common mode feedback control) so that the emitter currents of the transistors Na and Nb coincide with each other. As a result, the voltage level of the temperature detection signal Sout generated by the temperature sensor 16 becomes a value represented by the following equation (1).

  Further, the difference voltage ΔVF included in the above equation (1) is developed into a form represented by the following equation (2) based on the diode equation.

  In the above equation (2), k represents the Boltzmann constant, T represents the ambient temperature (absolute temperature), q represents the charge amount of electrons, and JEa and JEb represent the emitter current densities of the transistors Pa and Pb, respectively.

  As can be seen from the above equation (2), the difference voltage ΔVF between the base-emitter voltages VBEa and VBEb of the pair of transistors Pa and Pb operating at different emitter current densities JEa and JEb is a fluctuation value according to the ambient temperature T. Become.

  Therefore, from the above equations (1) and (2), the voltage level of the temperature detection signal Sout becomes a fluctuation value of a negative characteristic corresponding to the ambient temperature T as shown by the following equation (3).

  As described above, the temperature sensor 16 of this configuration example generates the temperature detection signal Sout having a negative characteristic corresponding to the ambient temperature T by using the PNP bipolar transistors Pa and Pb instead of the NPN bipolar transistor. It is said that.

  By adopting such a configuration, unlike a conventional configuration in which a negative temperature characteristic is realized by generating a positive temperature detection signal using an NPN bipolar transistor and logically inverting this, an offset of an inverting amplifier or Since the temperature detection signal Sout can be directly used for the charge control of the lithium ion battery 3 without considering the temperature characteristics, the charge control according to the ambient temperature T can be performed with high accuracy. Further, since there is no need to provide an inverting amplifier, it is possible to reduce the area of the temperature sensor 16 and reduce power consumption.

  In particular, in the power management IC 1 that controls the charging of the lithium ion battery 3, high absolute accuracy is required for the detection of the ambient temperature T. Therefore, the temperature sensor 16 is preferably configured as described above.

  In the temperature sensor 16 configured as described above, it is desirable that the transistor Pc and the transistor Pd, the transistor Na and the transistor Nb, and the transistor Pf and the transistor Pg are sufficiently paired. With such a configuration, the collector voltages of the transistors Pa and Pb are not easily affected by fluctuations in the power supply, so that stable temperature detection can be performed.

  Further, the temperature sensor 16 having the above-described configuration is connected to the power supply voltage via the resistors Ra and Rc having the same resistance as the resistors Rb and Rd in addition to the path for drawing current from the emitter of the transistor Nb as the emitter current of the transistor Pf. It has a path for drawing current from the application end of Vcc. With the configuration having such a current path, it is possible to eliminate the error factor of the current flowing into the emitters of the transistors Pf and Pg, so that the ambient temperature T can be detected with higher accuracy and higher linearity. . Of course, when importance is attached to chip size reduction, the above-described current path may be eliminated.

  Further, in the temperature sensor 16 having the above-described configuration, the resistors Ra to Rd are configured such that their resistance values can be adjusted by laser trimming or the like. By adopting such a configuration, it is possible to arbitrarily adjust the dependence characteristic of the temperature detection signal Sout with respect to the ambient temperature T even after the circuit is formed.

  In the above embodiment, the configuration using a lithium ion battery as a secondary battery has been described as an example. However, the configuration of the present invention is not limited to this, and other types of secondary batteries are used. It does not matter as a configuration using

  The configuration of the present invention can be variously modified within the scope of the present invention in addition to the above embodiment.

  INDUSTRIAL APPLICABILITY The present invention is a technique useful for improving both safety and charging performance of a charge control device that performs charge control of a secondary battery.

These are block diagrams which show one Embodiment of the electronic device carrying the charge control apparatus which concerns on this invention. These are the block diagrams for demonstrating typically the charge control operation by power management IC1. These are the figures for demonstrating separately the charging control according to ambient temperature, the charging control according to a system current, the charging control according to an internal setting value, and the charging control according to an external setting value. These are figures which show an example of the charge control operation | movement by power management IC1. FIG. 3 is a circuit diagram showing a configuration example of a temperature sensor 16.

Explanation of symbols

1 Power management IC (charge control device)
DESCRIPTION OF SYMBOLS 11 Charge control part 12, 13 Amplifier 14, 15 P channel type field effect transistor 16 Temperature sensor 17 Internal setting part 18 External setting part 19 DC / DC converter 2 Microcomputer 3 Lithium ion battery (secondary battery)
4, 5 Sense resistance 6 Port 7 Power line 8 Signal line Pa to Pg PNP type bipolar transistor Na, Nb NPN type bipolar transistor Ia, Ib Constant current source Ra to Rd Resistance

Claims (5)

  The charging current of the secondary battery is monitored, and the secondary battery has a current value that is smaller than a target value preset in the apparatus and a target value arbitrarily set from the outside of the apparatus. A charge control device that performs charge control of a battery.   Inside the device, at least a target value according to the ambient temperature, a target value according to the current consumption of the system, and a target value according to the standard of the externally connected power supply source are preset, and the charging current The charging control of the secondary battery is performed so that the current value becomes the smallest value among the target value preset in the device and the target value arbitrarily set from the outside of the device. The charge control device according to claim 1.   The charge control device according to claim 2, wherein the target value corresponding to the ambient temperature is set to be smaller as the ambient temperature is higher.   A temperature sensor that detects the ambient temperature has a pair of PNP-type bipolar transistors that operate at different emitter current densities, and utilizes the fact that the difference between the base-emitter voltages of both transistors varies with the ambient temperature. The charge control device according to claim 3, wherein a temperature detection signal having a negative characteristic is generated.   An electronic apparatus comprising: the charge control device according to claim 1; and a secondary battery whose charge is controlled by the charge control device.

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