JP2009071534A - Voltage comparison circuit, power source management circuit using the same, and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a voltage comparison circuit stably comparing voltages. <P>SOLUTION: The voltage comparison circuit compares a first voltage V1 with a second voltage V2. A resistor R1 and a constant current source 12 are provided in series between the first voltage V1 and a ground voltage. A comparator 14 receives the second voltage V2 via one input terminal (non-inverting input terminal), and the voltage V3 at a connection node between the resistor R1 and the constant current source 12 via the other input terminal (inverting input terminal). The first voltage V1 is preferably used as the power supply voltage for the comparator 14. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a voltage comparison circuit that compares two voltages.

  Various electronic devices such as mobile phones, PDAs (Personal Digital Assistants), and notebook personal computers in recent years include digital signal processing CPUs (Central Processing Units), DSPs (Digital Signal Processors), liquid crystal panels, 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.

  Some electronic devices receive power from an external power source such as an AC adapter or USB (Universal Serial Bus) port, and can operate even when the remaining battery level is low or no battery is installed. . In this case, a power management circuit (power management IC) is provided for controlling whether the electronic device is operated by a voltage from an external power source or a voltage from the battery. When the battery is a secondary battery such as a lithium ion battery, the power management circuit is provided with a function of charging the battery with a voltage from an external power source. The power management circuit compares the voltage from the external power supply with the battery voltage, and controls which voltage is supplied to the load according to the comparison result.

Japanese Patent Laid-Open No. 9-219935 JP-A-3-49418 Japanese Patent Laid-Open No. 61-8679

  Consider a voltage comparison circuit that compares the voltage from an external power supply with the battery voltage. A general comparator has a headroom (invalid voltage region) in the vicinity of a power supply voltage and cannot perform accurate voltage comparison. Therefore, when the power supply of the voltage comparison circuit itself is supplied from either an external power supply or a battery voltage, it is difficult to directly compare the voltage of the external power supply and the battery voltage with a comparator. If resistance voltage division is used to reduce the voltage level of the external power supply voltage and the battery voltage, there is a problem that the determination condition and accuracy of voltage comparison deteriorate due to variations in resistance values. Such a problem occurs not only in the power management circuit but also in a general voltage comparison circuit.

  The present invention has been made in view of these problems, and an object thereof is to provide a voltage comparison circuit capable of performing stable voltage comparison.

  One embodiment of the present invention relates to a voltage comparison circuit that compares a first voltage and a second voltage. This voltage comparison circuit includes a resistor and a constant current source provided in series between a first voltage and a fixed voltage, a second voltage at one input terminal, and a connection point between the resistor and the constant current source at the other input terminal. A comparator for receiving a voltage of

  A voltage drop ΔV proportional to the current generated by the constant current source is generated in the resistor. Therefore, the voltage V1−ΔV (or V1 + ΔV) obtained by shifting the first voltage V1 by the voltage drop ΔV is input to the other input terminal of the comparator. Therefore, the comparator can realize a stable voltage comparison by comparing the voltage (ΔV1−ΔV) with the second voltage V2.

  The power supply voltage of the comparator may be the first voltage.

  The comparator may receive the voltage at the connection point between the resistor and the constant current source at the inverting input terminal and the second voltage at the non-inverting input terminal.

  Another aspect of the present invention is a power management circuit. The power management circuit has a first terminal to which an external power source is connected, a second terminal to which a battery is connected, a voltage from the external power source applied to the first terminal and a battery voltage from the battery. Based on the output signal of the voltage comparison circuit, one of the above-described voltage comparison circuit that compares the voltages with the other as the second voltage, the voltage from the external power supply, and the battery voltage from the battery is selected. A selection circuit; and an output terminal that outputs a voltage selected by the selection circuit to an external load circuit.

  The voltage comparison circuit receives the voltage from the external power supply as the first voltage, the battery voltage from the battery as the second voltage, the comparator receives the voltage from the external power supply as the power supply, and the inverting input terminal receives the battery voltage from the battery. The voltage at the connection point between the resistor and the constant current source may be received at the non-inverting input terminal.

  The power management circuit may further include a charge control unit that charges the battery using a voltage from an external power source.

  Yet 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, the above-described power management circuit, and a load circuit connected to an output terminal of the power management 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, two voltages can be compared with high accuracy.

  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, a reference numeral attached to a voltage signal, a current signal, or a resistor represents a voltage value, a current value, or a resistance value 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 the external power supply 210 can be attached and detached, and receives a voltage (hereinafter referred to as an external voltage) Vext from the external power supply 210. The power management circuit 100 receives the external voltage Vext and the battery voltage Vbat, selects either of them and supplies it to the load 112, and charges the battery 110 using the external voltage Vext. The load 112 includes a power supply circuit (not shown), a DSP, a liquid crystal panel, other analog circuits, and digital circuits.

  The power management circuit 100 includes a voltage comparison circuit 10, a selection circuit 20, and a charge control unit 30, and is integrated as a functional IC on a semiconductor substrate. The power management circuit 100 receives the external voltage Vext at the adapter terminal 102 and the battery voltage Vbat at the battery terminal 104. The voltage comparison circuit 10 compares the external voltage Vext and the battery voltage Vbat, and outputs a control signal S1 indicating the comparison result to the selection circuit 20. The selection circuit 20 selects either the external voltage Vext or the battery voltage Vbat based on the comparison result by the voltage comparison circuit 10, that is, the control signal S1, and outputs it to the load 112 via the output terminal 106. Charging control unit 30 charges battery 110 using external voltage Vext.

  The selection circuit 20 includes a first switch SW1, a second switch SW2, and a NOT gate 22. The first switch SW1 is provided between the output terminal 106 and the adapter terminal 102, and the second switch SW2 is provided between the output terminal 106 and the battery terminal 104. The control signal S1 is input to the first switch SW1, and the control signal S1 inverted by the NOT gate 22 is input to the second switch SW2. The first switch SW1 and the second switch SW2 are turned on when a high level is input. That is, the selection circuit 20 turns on the first switch SW1 to select the external voltage Vext when the control signal S1 is at a high level, and turns on the second switch SW2 to turn on the battery voltage Vbat when the control signal S1 is at a low level. Select. The configuration of the selection circuit 20 is not particularly limited, and a general multiplexer may be used.

  The voltage comparison circuit 10 includes a first terminal P1, a second terminal P2, an output terminal P3, a constant current source 12, a comparator 14, a resistor R1, and a pull-down resistor R2, and a first voltage V1 input to the first terminal P1. The second voltage V2 input to the second terminal P2 is compared. The external voltage Vext is input to the first terminal P1, and the battery voltage Vbat is input to the second terminal P2. That is, in FIG. 1, V1 = Vext and V2 = Vbat.

  The resistor R1 and the constant current source 12 are provided in series between the first terminal P1 to which the first voltage V1 is applied and the ground terminal to which a fixed voltage (ground voltage) is applied. The constant current source 12 generates a predetermined constant current Ic1 and passes it through the resistor R1. As a result, a voltage drop ΔV (= Ic1 × R1) occurs in the resistor R1. The resistance value of the resistor R1 and the value of the constant current Ic1 are set so that the voltage drop ΔV is about 0.1V.

The comparator 14 receives the second voltage V2 at one input terminal (inverting input terminal). The other input terminal (non-inverting input terminal) receives the voltage V3 at the connection point between the resistor R1 and the constant current source 12. The voltage V3 at the connection point is
V3 = V1-ΔV = V1-R1 × Ic1
Given in.

  In the embodiment, the power supply of the comparator 14 is the first voltage V1. The output of the comparator 14 is pulled down by a pull-down resistor R2.

The operation of the power management circuit 100 configured as described above will be described. Hereinafter, the operation of the power management circuit 100 will be described.
(1) A state in which the external power supply 210 is connected to the adapter terminal 114 and the external voltage Vext is supplied (2) A description will be given separately in two states in which the external power supply 210 is not connected to the adapter terminal 114.

(1) A state in which the external power supply 210 is connected to the adapter terminal 114 The power supply voltage is supplied to the comparator 14 of the voltage comparison circuit 10, and a voltage comparison is possible. The control signal S1 output from the comparator 14 is at a high level when V1−ΔV> V2, and is at a low level when V1−ΔV <V2. In other words, it is determined whether the difference voltage (V1−V2) between the first voltage V1 and the second voltage V2 is larger or smaller than ΔV.

  For example, when the external voltage Vext is rated 5V and the battery voltage Vbat fluctuates in the range of about 3.2V to 4.2V, the control signal S1 becomes high level and the external voltage Vext is supplied to the load 112. On the other hand, when the external voltage Vext supplied from the external power supply 210 is reduced to about 4V, the control signal S1 becomes low level, and the battery voltage Vbat is supplied to the load 112.

(2) A state in which the external power supply 210 is not connected to the adapter terminal 114 In this case, since the power supply voltage is not supplied to the comparator 14, voltage comparison is not performed, and the output of the comparator 14 is at a low level. Even if the output of the comparator 14 is open, the control signal S1 is pulled down to a low level by the pull-down resistor R2, the second switch SW2 is turned on, and the battery voltage Vbat is supplied to the load 112.

The effect of the voltage comparison circuit 10 is further clarified by the following consideration.
Consider a case where the voltage comparison is performed by resistance-dividing the first voltage V1 and the second voltage V2 without using the voltage comparison circuit 10 of FIG. When comparing by multiplying the first voltage V1 by α and the second voltage V2 by β, V1 × α and V2 × β are compared. That is, the output of the comparator is high when V1 × α> V2 × β, and low when V1 × α <V2 × β. If the values of α and β change due to variations in voltage dividing resistance, the determination conditions change.

  On the other hand, since the voltage comparison circuit 10 according to the embodiment compares the voltage obtained by shifting the first voltage V1 by ΔV with the second voltage V2, the resistance value of the resistor R1 and the constant current Ic1 vary. However, since ΔV always takes a value of 0 or more, the comparison condition (magnitude relationship) between the first voltage V1 and the second voltage V2 is maintained, so the determination condition does not change.

Further, using the first voltage V1 level-shifted as the power supply voltage of the comparator 14, and paying attention to the output of the comparator 14, the logical value when V1−ΔV> V2 is not supplied with the power supply voltage and the comparator The voltage V3 obtained by level-shifting the first voltage V1 is input to the inverting input terminal and the second voltage V2 is input to the non-inverting input terminal so as to match the logical value when 14 is inoperable.
As a result, when the external power supply 210 is not connected, the selection circuit 20 can be controlled without operating the comparator 14, so that the power consumption of the circuit can be reduced.

  From a certain point of view, the external voltage Vext that is the first voltage V1 in the embodiment is a voltage that is normally assumed to be higher than the battery voltage Vbat that is the second voltage V2. That is, the first voltage V1 that is assumed to have a high voltage level is used as the power supply voltage for the comparator 14, and the first voltage V1 is level-shifted and compared with the second voltage V2, thereby being close to the power supply voltage for the comparator 14 Since the use of headroom can be avoided, accurate voltage comparison is possible.

  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 only the first voltage V1 is shifted has been described in the embodiment, the second voltage V2 may be level-shifted similarly to the first voltage V1.

  In the embodiment, the case where the voltage comparison circuit 10 is used for the power management circuit 100 has been described. However, the voltage comparison circuit 10 may be used for other voltage comparison processing. Depending on the voltage comparison processing, the voltage V3 obtained by shifting the first voltage V1 may be input to the non-inverting input terminal, and the second voltage V2 may be input to the inverting input terminal. 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 circuit based on the ground voltage (0 V) has been described in the embodiment, the present invention may be applied to a circuit based on a negative power supply.

It is a circuit diagram which shows the structure of an electronic device provided with the power supply management circuit which concerns on embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Power management circuit, 102 ... Adapter terminal, 104 ... Battery terminal, 106 ... Output terminal, 10 ... Voltage comparison circuit, 12 ... Constant current source, 14 ... Comparator, R1 ... Resistance, R2 ... Pull-down resistance, P1 ... 1st Terminal, P2 ... second terminal, P3 ... output terminal, 20 ... select circuit, SW1 ... first switch, SW2 ... second switch, 22 ... NOT gate, 30 ... charge control unit, 110 ... battery, 112 ... load, 114 DESCRIPTION OF SYMBOLS ... Adapter terminal, 200 ... Electronic device, 210 ... External power supply, V1 ... 1st voltage, V2 ... 2nd voltage, Vext ... External voltage, Vbat ... Battery voltage.

Claims (7)

A voltage comparison circuit for comparing a first voltage and a second voltage,
A resistor and a constant current source provided in series between the first voltage and a fixed voltage;
A comparator that receives the second voltage at one input terminal and a voltage at a connection point between the resistor and the constant current source at the other input terminal;
A voltage comparison circuit comprising:   The voltage comparison circuit according to claim 1, wherein a power supply voltage of the comparator is the first voltage.   3. The voltage comparison circuit according to claim 2, wherein the comparator receives a voltage at a connection point between the resistor and the constant current source at an inverting input terminal, and receives the second voltage at a non-inverting input terminal. A first terminal to which an external power supply is connected;
A second terminal to which a battery is connected;
2. The voltage comparison according to claim 1, wherein one of a voltage from the external power source applied to the first terminal and a battery voltage from the battery is used as the first voltage and the other is used as the second voltage. Circuit,
A selection circuit that selects either the voltage from the external power supply or the battery voltage from the battery based on the output signal of the voltage comparison circuit;
An output terminal for outputting the voltage selected by the selection circuit to an external load circuit;
A power management circuit comprising:   The voltage comparison circuit receives a voltage from the external power supply as the first voltage, a battery voltage from the battery as the second voltage, the comparator receives a voltage from the external power supply as a power supply, and an inverting input thereof. 5. The power management circuit according to claim 4, wherein a battery voltage from the battery is received at a terminal, and a voltage at a connection point between the resistor and the constant current source is received at a non-inverting input terminal.   The power management circuit according to claim 4, further comprising a charge control unit that charges the battery using a voltage from the external power source. Battery,
An adapter terminal to which an external power supply can be attached and detached;
A power management circuit according to any one of claims 4 to 6,
A load circuit connected to an output terminal of the power management circuit;
An electronic device comprising:

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