Charge control circuit

• US 20070290655A1
• Filed: 05/09/2007
• Published: 12/20/2007
• Est. Priority Date: 05/09/2006
• Status: Active Grant

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: Yamamoto, Isao, Nate, Satoru
• Granted Patent: US 7,898,217 B2
• Time in Patent Office: Days
• US Class Current: 320/163
• CPC Class Codes: H02J 7/00 Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
• CPC Class Codes: H02J 7/0068 Battery or charger load switching, e.g. concurrent charging and load supply H02J7/0013 takes precedence

Abstract

In a charge control circuit that adjusts a charging current flowing through a battery to be charged from a power supply, a sense resistor is provided on a charging path to the battery from an external power supply. A charging current adjustment circuit adjusts the charging current based on an error voltage between a voltage drop across the sense resistor and a predetermined reference voltage. The charging control circuit is integrated in a package. The charging current is inputted to a current input terminal. A battery terminal outputs the charging current to the battery. The current input terminal and the battery terminal also function as terminals used to measure a resistance value of the sense resistor. A voltage monitoring terminal is provided to measure the reference voltage in an inspection process.

Claims

1. A charge control circuit for adjusting a charging current flowing through a battery to be charged from a power supply, the circuit comprising:

a sense resistor provided on a charging path leading to the battery from the power supply;

a charging current adjustment circuit which adjusts the charging current based on an error voltage between a voltage drop across said sense resistor and a predetermined reference voltage, wherein said sense resistor and said charging current adjusting circuit are integrated;

a current input terminal which receives an input of the charging current;

an battery terminal which outputs the charging current to the battery;

a terminal used to measure a resistance value of said sense resistor in an inspection process; and

a terminal used to measure the reference voltage in the inspection process.

2. A charge control circuit according to claim 1, said charging current adjustment circuit comprising:

a voltage conversion circuit which converts a voltage drop across said sense resistor into a voltage potential to ground voltage;

a variable voltage source which generates the predetermined reference voltage;

an error amplifier which generates an error voltage between the reference voltage and the voltage drop; and

a current adjusting unit which adjusts an on-state of a charging transistor provided on the charging path, according to the error voltage outputted from the error amplifier,

wherein said variable voltage source comprises an adjusting means which adjusts the reference voltage by a trimming process.

3. A charge control circuit according to claim 1, further comprising a switch pass circuit which comprises a plurality of input terminals and a single output terminal and which selectively connects any one of the input terminals to the output terminal,

wherein the output terminal of said switch pass circuit is configured such that the output terminal thereof is capable of monitoring voltage from outside and voltage is applicable thereto, and

wherein a terminal, among terminals in said charge control circuit, at which a voltage to be measured in an inspection process appears and which does not need to be connected with outside at the time of an actual charging operation is connected with one of the plurality of input terminals.

4. A charge control circuit according to claim 3, wherein the terminals at which voltage to be measured in an inspection process appears comprise a terminal of said sense resistor and a terminal at which the reference voltage appears.

5. A charge control circuit according to claim 1, further comprising a switch pass circuit which comprises a plurality of input terminals and a single output terminal and which selectively connects any one of the input terminals to the output terminal,

wherein a terminal, among terminals in said charge control circuit, to which a voltage is to be applied from outside in an inspection process and which does not need to be connected with outside at the time of an actual charging operation is connected with one of the plurality of input terminals.

6. A charge control circuit according to claim 5, wherein the terminals to which a voltage is to be applied from outside in the inspection process comprise a terminal of said sense resistor and a terminal at which the reference voltage appears.

7. A charge control circuit according to claim 1, further comprising:

an auxiliary terminal configured such that a voltage is capable of being applied thereto from outside in an inspection process; and

a subsidiary resistor provided between said auxiliary terminal and one end of said sense resistor,

wherein said charging current adjustment circuit adjusts the charging current based on voltage across said subsidiary resistor and the predetermined reference voltage.

8. A charge control circuit according to claim 7, further comprising a bypass switch, provided in parallel with said subsidiary resistor, which turns off during an inspection process and turns on during a charging operation.

9. A charging circuit for charging a battery based on supply voltage from a power supply, the circuit comprising:

a charging transistor provided on a path leading to the battery from the power supply; and

a charge control circuit, structured to adjust a charging current supplied to the battery by adjusting an on-state of said charging transistor, the charge control circuit comprising;

a sense resistor provided on a charging path leading to the battery from the power supply;

a charging current adjustment circuit which adjusts the charging current based on an error voltage between a voltage drop across said sense resistor and a predetermined reference voltage, wherein said sense resistor and said charging current adjusting circuit are integrated;

a current input terminal which receives an input of the charging current;

an battery terminal which outputs the charging current to the battery;

a terminal used to measure a resistance value of said sense resistor in an inspection process; and

a terminal used to measure the reference voltage in the inspection process.

10. An electronic apparatus, comprising:

a battery;

a charging circuit comprising;

a charging transistor provided on a path leading to the battery from the power supply; and

a charge control circuit structured to adjust a charging current supplied to the battery by adjusting an on-state of said charging transistor, the charge control circuit comprising;

a sense resistor provided on a charging path leading to the battery from the power supply;

a charging current adjustment circuit which adjusts the charging current based on an error voltage between a voltage drop across said sense resistor and a predetermined reference voltage, wherein said sense resistor and said charging current adjusting circuit are integrated;

a current input terminal which receives an input of the charging current;

an battery terminal which outputs the charging current to the battery;

a terminal used to measure a resistance value of said sense resistor in an inspection process; and

a terminal used to measure the reference voltage in the inspection process

wherein the charging circuit is structured to charge said battery based on the supply voltage from the power supply; and

a load circuit driven by said battery.

11. A method for correcting a charging current of a charge control circuit having a structure including a sense resistor provided on a charging path leading to a battery from a power supply and a charging current adjustment circuit which adjusts the charging current based on an error voltage between a voltage drop across the sense resistor and a predetermined reference voltage, the method comprising:

measuring a resistance value of the sense resistor;

measuring the reference voltage;

calculating the charging current by dividing the measured reference voltage by the measured resistance value of the sense resistor;

calculating a difference current between the calculated charging current and a target value of the charging current;

calculating an amount of adjustment for the reference voltage by dividing the calculated difference current by the resistance value of the sense resistor; and

adding or subtracting the calculated amount of adjustment for the reference voltage to or from the reference voltage.