JP2008157837A - Battery residual capacity detector and portable terminal device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery residual capacity detector not increasing a reference table even when using a step-up/down type switching power supply, and a portable terminal device using it. <P>SOLUTION: A voltage of a secondary battery 101 is measured by a voltage measuring circuit 102 in order to detect a battery residual capacity of the secondary battery 101, and each current consumed in a circuit group 108, 111, 114 is measured by a current measuring circuit 103. A current measuring resistance 105 is connected selectively in parallel with a current measuring resistance 104 by a switch 106 corresponding to an operation state of the step-up/down type switching power supply (DCDC) 112. A CPU 115 converts measurement results of the voltage measuring circuit 102 and the current measuring circuit 103 into the battery residual capacity value on reference to the reference table 116b. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a battery remaining amount detection device that detects a remaining battery amount of a secondary battery, and a portable terminal device using the same.

  In mobile devices such as mobile phone terminals, secondary batteries are used as rechargeable batteries. In the cellular phone terminal, the battery voltage is sequentially measured, and the remaining battery level table is referred to based on the measured value, and the remaining battery level is estimated and displayed.

In addition, a battery remaining amount detection device has been proposed that improves the resolution when a battery voltage change is detected in a device that uses a battery as an operating power supply (see Patent Document 1).
JP 2006-153740 A

  In recent years, in order to increase the usable time of a mobile phone terminal, a model using a secondary battery having a low end voltage has appeared. In such a terminal, a switching power supply is used to efficiently draw power from the secondary battery. In particular, the switching power supply is a step-up / step-down type corresponding to the low voltage output of the secondary battery, and when the voltage of the secondary battery becomes low, it is boosted and used.

  In the conventional mobile phone terminal, the voltage and current consumption of the secondary battery are measured, and the remaining amount of the battery is displayed based on the measurement result. However, when using a buck-boost type switching power supply, the current consumption from the secondary battery increases when switching from step-down to step-up even if the same application is operating. It becomes necessary to change the reference table of the display, which is complicated. Further, when the current consumption from the secondary battery increases, the range of the voltage across the current measurement resistor is expanded. This leads to a lack of accuracy required for the AD converter for measurement and an increase in apparatus cost.

  The present invention has been made in this background. Even when a buck-boost type switching power supply is used, the remaining battery level can be detected with a relatively simple device configuration without incurring insufficient measurement accuracy or increasing device cost. It is an object of the present invention to provide a remaining battery level detection device and a portable terminal device using the same.

  A battery remaining amount detecting device according to the present invention is a battery remaining amount detecting device that detects a remaining battery amount of a secondary battery, and uses a voltage measuring circuit that measures the voltage of the secondary battery and a current measuring resistor to measure current. A current measurement circuit for performing measurement, a step-up / step-down switching power supply that receives power supply from the secondary battery via the current measurement resistor, means for confirming the operation state of the step-up operation and the step-down operation, and the operation state In response to this, it comprises switch means for switching the resistance value of the current measurement resistor, and conversion means for converting the measurement result of the voltage measurement circuit and the current measurement circuit into a remaining battery value.

  With this configuration, the resistance value of the current measurement resistor is switched depending on whether the step-up / step-down switching power supply is performing a step-up operation or a step-down operation. Thereby, expansion of the range of the both-ends voltage of the resistance for current measurement can be suppressed.

  According to the present invention, the following effects can be obtained.

  By switching the current measurement resistance value according to the operation mode of the step-up / step-down switching power supply, it is possible to suppress fluctuations in the voltage across the current measurement resistance during the step-down operation and the step-up operation. As a result, even when a secondary battery with a low end voltage is used, it is not necessary to complicate the battery remaining amount display table. When an AD converter is used for the current measuring circuit, it is not necessary to increase the accuracy or increase the number of AD converters, thereby avoiding an increase in device cost. Also, AD conversion can be performed where the linearity characteristic is good.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings. Hereinafter, a mobile phone terminal will be described as an example.

  First, the configuration of the mobile phone terminal in the present embodiment will be described. FIG. 1 shows a block diagram of main parts related to the power source of the portable terminal.

  This mobile phone terminal uses a secondary battery 101 that can be used up to a place where the end voltage is lower than before. The voltage measurement circuit 102 measures the voltage of the secondary battery 101. The current measurement circuit 103 measures the voltage across the current measurement resistor A104. This measured value is converted into a current value based on the resistance value. As described above, the voltage measurement circuit 102 and the current measurement circuit 103 essentially measure a voltage value using an AD (analog-digital) converter, and the same AD converter is switched and used. It is also possible.

  The CPU 115 is a processor (central processing unit) for controlling the voltage measurement circuit 102 and the current measurement circuit 103 and performing data calculation (including conversion of the measurement voltage of the current measurement circuit 103 into a current value). is there. The memory 116 stores various data including a processing program 116a to be processed by the CPU 115 and a reference table 116b to be described later, and provides a work area and a temporary storage area for the CPU 115. The display unit 117 is controlled by the CPU 115 and displays various types of information of the mobile phone terminal including the battery remaining amount display on the display screen.

  This terminal includes a plurality of circuit groups that operate at different voltage values. The present embodiment includes a circuit group 108 that operates with a 2.8V power supply, a circuit group 111 that operates with a 1.5V power supply, and a circuit group 114 that operates with a 3.3V power supply. The circuit group 108 is supplied with power from the LDO group 107 having a 2.8V system voltage output. LDO is an abbreviation for Low Drop Out, and is a series regulator (or linear voltage regulator) that stabilizes and outputs a DC input voltage. The circuit group 111 is supplied with power from the LDO group 110 having a 1.5 V system voltage output. In order to increase the consumption efficiency of the secondary battery 101, a step-down DCDC 109 is disposed in front of the LDO group 110.

  The circuit group 114 is supplied with power from the LDO group 113 having 3.3V system voltage output. In order to increase the efficiency of consumption from the secondary battery 101 and operate until the output of the secondary battery becomes a low voltage, a step-up / step-down DCDC 112 is arranged in front of the LDO group 113.

  In the present embodiment, a current measuring resistor B105 connected in parallel to the current measuring resistor A104 is provided. A switch (SW) 106 is connected in series to the current measuring resistor B105. The switch 106 is controlled to be turned on / off in accordance with a DCDC-MODE signal 118 representing the operating state of the step-up / step-down DCDC 112. That is, the switch 106 is turned off if the step-up / step-down DCDC 112 is a step-down operation, and is turned on if the step-up / step-down DCDC 112 is a step-up operation. When the switch 106 is turned on, the current measuring resistor B105 is connected in parallel to the current measuring resistor A104. That is, the resistance of the current measurement resistor measured by the current measurement circuit 103 becomes a parallel combined resistance of two resistors, and functions so that the resistance value decreases when the switch 106 is turned on.

  Next, the operation of the mobile phone terminal of FIG. First, the operation of the battery remaining amount display will be described.

  When the circuit group 108, the circuit group 111, and the circuit group 114 operate, current is consumed from the secondary battery 101 through the current measurement resistor A104. Although the CPU 115, the memory 116, and the display unit 117 are shown separately from these circuit groups in the figure, they are actually a part of these circuit groups.

  The CPU 115 measures the voltage of the secondary battery 101 as a digital value by AD conversion of the voltage measurement circuit 102 and stores the result in the memory 116. Further, the CPU 115 measures the current consumed from the secondary battery 101 by the AD conversion of the current measuring circuit 103 from the potential difference generated at both ends of the current measuring resistor A104, and stores the measurement result (digital value) in the memory 116. To do. At this time, the resistance value used for converting the voltage value into the current value regardless of the presence or absence of boosting is the resistance value of the current measuring resistor A104. The CPU 115 predicts the remaining battery level by comparing the obtained voltage and current consumption data of the secondary battery 101 with a reference table (data table) prepared by storing in the memory 116 in advance, and displays the display unit. The remaining battery power is displayed to 117.

  Note that a charging circuit for charging the secondary battery 101 is not shown.

  Here, in order to better understand the present invention, the operation without the resistor B 105 and the switch 106 will be briefly described.

  As shown in FIG. 2, when the battery voltage is high, the step-up / step-down DCDC 112 operates as a step-down DCDC and supplies power to the 3.3 V LDO group 113. At this time, the step-up / step-down DCDC 112 has Vin × Iin = η (Vout × Iout) and is stepped down, that is, Vin> Vout, and therefore, Iin <Iout.

  Here, η is the efficiency of DCDC, and η ≦ 1. When Iin is small, it means that the battery consumption is low, so the voltage decrease of the secondary battery 101 is gradual. The CPU 115 displays the remaining amount of the battery on the display unit 117 by comparing the data obtained from the voltage measurement circuit 102 and the current measurement circuit 103 with a reference table according to a gradual decrease in the battery voltage.

  Next, when the battery voltage drops and the boundary where the 3.3 V LDO group 113 can output a stable output voltage, the step-up / step-down DCDC 112 performs an operation of stepping up and down.

  When the battery voltage further decreases, the step-up / step-down DCDC 112 performs only the boosting operation. In the step-up operation, in the step-up / step-down DCDC 112, since Vin <Vout, Iin> Iout. Even if the same circuit is operating (that is, even if the power consumption of the load of the step-up / step-down DCDC 112 is not changed), whether the step-up / step-down type DCDC 112 is operating in a step-down type or a step-up type, The current consumption from the secondary battery 101 is different. When operating in the step-up type, the current consumption of the battery increases, so the voltage of the secondary battery 101 decreases more rapidly than in the step-down type. The CPU 115 needs to display the remaining amount of the battery on the display unit 117 by comparing the data obtained from the voltage measurement circuit 102 and the current measurement circuit 103 with a reference table according to a rapid decrease in the battery voltage.

  Therefore, in the conventional operation, in order to refer to the reference table corresponding to the operation mode of the step-up / step-down DCDC 112, the CPU 115 needs to know which mode the step-up / step-down DCDC 112 is operating, and the circuit group 108, When the operation patterns 111 and 114 increase, the number of reference tables for displaying the remaining battery level referred to by the CPU 115 increases, so that the case division becomes complicated. Further, when the step-up / step-down DCDC 112 is operating in a step-up type, the current consumption from the secondary battery 101 increases, so the voltage drop across the current measurement resistor A104 also increases, and the current conversion circuit 103 has a necessary AD conversion range. It is necessary to devise measures such as increasing the accuracy of AD conversion corresponding to the increase, leading to an increase in the cost of the apparatus.

  In the present embodiment, the current measurement resistor B105 is added, and the SW 106 is turned on when the step-up / step-down DCDC 112 is operating in the step-up type, whereby the current measurement circuit 103 measures whether or not the step-up operation is performed. In order to prevent the voltage value from changing, the current measurement resistor A105 is connected in parallel to the current measurement resistor A104 during the boosting operation to reduce the resistance value, and the current measurement circuit 103 measures the potential difference between both ends of the parallel resistor. I made it. Since the parallel resistance value is decreased as the current increases, the data of the current measurement circuit 103 does not depend on the operation mode of the step-up / step-down DCDC 112, and it is not necessary to increase the reference table for displaying the remaining battery level for the boost operation. . In addition, since the potential difference of the parallel resistance does not change, it is not necessary to expand the AD measurement measurable range of the current measurement circuit 103 or increase its accuracy.

  FIG. 3 is a view showing the internal configuration of the step-up / step-down DCDC 112 shown in FIG. 1 together with its peripheral portion. The voltage measuring circuit 102, the current measuring circuit 103, etc. are not shown.

  The step-up / step-down DCDC 112 is constituted by an integrated circuit, and has a mode signal output terminal DCDC-MODE, a power input terminal, a connection terminal of the coil 35, and an output voltage terminal.

  The output voltage Vout at the output voltage terminal is obtained when the driver control unit 10 controls an output circuit including FETs (voltage effect transistors) 31 to 34 (Tr1 to Tr4) and a coil 35. The drain of Tr1 is connected to the power input terminal of the secondary battery 101 via current measuring resistors A and B, and the source thereof is connected to one end of the coil 35. The drain of Tr2 is connected to the source of Tr1, and the source is grounded. The drain of Tr4 is connected to the other end of the coil 35, and the source is connected to the output voltage terminal. The drain of Tr3 is connected to the drain of Tr3, and the source is grounded. The gates of Tr1 to Tr4 are controlled by the driver control unit 10 in the manner described later.

The driver control unit 10 operates by receiving the oscillation output of the oscillator (OSC) 11, the output voltage control signal 16, and the operation state signal 20. Specifically, the operation is as follows.
(1) During step-down (VBAT> Vout): Tr1 and Tr2 are switched, Tr3 is OFF, and Tr4 is ON.
(2) During boosting (VBAT <Vout): Tr1 is ON, Tr2 is OFF, and Tr3 and Tr4 are switched.
(3) During step-up / step-down (VBAT≈Vout): The step-down operation and the step-up operation are repeated so that Vout becomes constant.

  The output voltage control signal 16 is generated by the comparator 12 that compares the voltage obtained by dividing the output voltage Vout with the series resistors 14 and 15 with the reference voltage Ref. The operating state signal 20 is generated by a comparator 17 that compares a voltage obtained by dividing the series resistors 14 and 15 with a voltage obtained by dividing the input voltage VBAT by the series resistors 18 and 19. That is, the current operating state of the step-up / step-down DCDC 112 is determined substantially based on the potential difference between VBAT and Vout.

  In this example, the operating state signal 20 is at a low level during step-down and is at a high level during step-up, and changes between a low level and a high level during step-up / step-down. The filter 21 functions to remove a change in the operation state signal 20 during the step-up / step-down operation.

  An output 22 of the filter 21 is output as a DCDC-MODE signal 118 representing an operation mode of the step-up / step-down DCDC 112 by a drain output 24 via an output buffer 23 (here, FET) for level conversion. The switch 106 is ON / OFF controlled by the DCDC-MODE signal 118.

  In the configuration of FIG. 3, since the switch for switching the current measuring resistor is controlled by hardware, the burden on software can be reduced.

  FIG. 4 shows an internal configuration example of the filter 21. The filter 21 includes a plurality of D flip-flops (DFF) 41 to 44 connected in multiple stages, an AND circuit 45, a NOR circuit 46, and a JK flip-flop 47. As shown in the timing chart of FIG. 5, the filter 21 outputs the operation state signal 20 as it is at the time of step-down and low pressure, and the state before the step-up / step-down operation (in the direction in which the battery is consumed) at the time of step-up / step-down operation. If so, it operates to hold the step-down and the step-up if it is charged.

  FIG. 6A is a graph showing the current flowing through the resistor connected to the current measuring circuit 103 and the voltage at both ends when the present invention is not applied. In this graph, the vertical axis represents the voltage across the resistor, and the horizontal axis represents the current. There is a relationship of V0 / I0 = resistance value of the resistor A. FIG. 6B is graphs G1 and G2 showing the current flowing through the resistor connected to the current measuring circuit 103 and the voltage at both ends when the switch 106 is OFF and ON in the present embodiment. The graph in FIG. 6A corresponds to the graph G1 when the switch 106 in FIG. 6B is OFF. The graph G2 in FIG. 6B corresponds to the time when the switch 106 is turned on, and the combined value of the two parallel resistors is lower than the original resistance value. Therefore, the voltage at both ends is a voltage value until the current reaches I1 (> I0). Do not exceed Vo. Therefore, even if the current value exceeds I1, it is not necessary to expand the measurable range of the AD converter.

  FIG. 7 shows a configuration example of the reference table 116b (FIG. 1) used in the present embodiment. This reference table 116b is a data table in which the corresponding battery remaining value is associated with the combination of the measured voltage value and current value. This reference table 116b suffices as a single table regardless of the DCDC-MODE value (L or H).

  FIG. 8 shows a block diagram of a main part related to the power source of the mobile terminal according to a modification of the configuration of FIG. In the configuration of FIG. 3, the switch 106 is directly controlled by the DCDC-MODE signal 118, but in the configuration of FIG. 8, the switch 106 is controlled via the CPU 115. In this example, control is performed using the port 115a of the CPU 115. Since the other configuration is the same as the configuration of FIG. The LDO group 107 is supplied from the same power supply voltage as the port. The operation of the mobile terminal in FIG. 8 is substantially the same as the operation in FIG. Although FIG. 8 shows an example in which the port 115a controls only the SW 116 (one FET), a combination of a parallel resistor and SW may be added to individually control a plurality of SWs. Which SW is turned on can be determined according to the current operation mode that the CPU 115 can grasp and the value of DCDC-MODE. For example, when the parallel resistors B, C, and D are selectively connected to the resistor A by individual SWs, the resistor B is turned on at the time of boosting and talking, the resistor C is turned on at the time of boosting and TV operation, and the game is boosted It is possible to control so that the resistor D is turned ON during operation.

  The preferred embodiments of the present invention have been described above, but various modifications and changes other than those mentioned above can be made.

It is a block diagram of the principal part relevant to the power supply of the portable terminal which concerns on embodiment of this invention. It is explanatory drawing of operation | movement of the buck-boost type DCDC shown in FIG. It is the figure which showed the internal structure of buck-boost type DCDC with the periphery part. It is a figure which shows the internal structural example of the filter shown in FIG. FIG. 5 is a timing chart for explaining the operation of the filter shown in FIG. 4. It is the graph showing the electric current which flows into the resistance connected to the electric current measurement circuit in FIG. 1, and both-ends voltage. It is a figure which shows the structural example of the reference table used in embodiment of this invention. It is a block diagram of the principal part relevant to the power supply of a portable terminal based on the modification of embodiment of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Driver control part, 12 ... Comparator, 14, 15 ... Series resistance, 16 ... Output voltage control signal, 17 ... Comparator, 18, 19 ... Series resistance, 20 ... Operation state signal, 21 ... Filter, 22 ... Output , 23 ... Output buffer, 35 ... Coil, 45 AND circuit, 46 ... NOR circuit, 47 ... Flip-flop, 101 ... Secondary battery, 102 ... Voltage measurement circuit, 103 ... Current measurement circuit, 104 ... Current measurement resistor A, 105 ... Current measuring resistor B, 106 ... Switch, 107 ... LDO group, 108 ... Circuit group, 109 ... Step-down DCDC, 110 ... LDO group, 111 ... Circuit group, 112 ... Buck-boost DCDC, 113 ... LDO group, 114 ... Circuit group, 115a ... port, 116 ... memory, 116a ... processing program, 116b ... reference table, 117 ... display unit, 118 ... DCDC-MOD Signal

Claims (4)

A battery level detection device for detecting the remaining battery level of a secondary battery,
A voltage measuring circuit for measuring the voltage of the secondary battery;
A current measurement circuit that performs current measurement using a current measurement resistor;
A step-up / step-down switching power supply that receives power supply from the secondary battery via the current measurement resistor;
Means for confirming the operating state of the step-up operation and step-down operation;
Switch means for switching a resistance value of the current measuring resistor according to the operating state;
A battery remaining amount detecting device comprising: a conversion unit that converts measurement results of the voltage measuring circuit and the current measuring circuit into a battery remaining value.   2. The remaining battery level according to claim 1, wherein the conversion unit includes a data table in which the measurement results of the voltage measurement circuit and the current measurement circuit are associated with the remaining battery level value for each operation state of the step-up operation and the step-down operation. Detection device.   The battery remaining amount detection device according to claim 1, wherein the switch unit includes a switch element that selectively connects another current measurement resistor in parallel to the current measurement resistor according to the operation state. A battery remaining amount detection device, and a display unit for displaying the battery remaining amount obtained by the conversion unit,
The battery remaining amount detecting device is
A battery level detection device for detecting the remaining battery level of a secondary battery,
A voltage measuring circuit for measuring the voltage of the secondary battery;
A current measurement circuit that performs current measurement using a current measurement resistor;
A step-up / step-down switching power supply that receives power supply from the secondary battery via the current measurement resistor;
Means for confirming the operating state of the step-up operation and step-down operation;
Switch means for switching a resistance value of the current measuring resistor according to the operating state;
A portable terminal device comprising: conversion means for converting the measurement results of the voltage measurement circuit and the current measurement circuit into a battery remaining value.

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