IJS007733060B2
`
`(12) United States Patent
`US 7,733,060 B2
`(10) Patent N0.:
`
`Kojima
`(45) Date of Patent:
`Jun. 8, 2010
`
`(54) CHARGING IC, CHARGING APPARATUS
`AND ELECTRONIC DEVICE
`
`6,373,224 B1*
`6,657,416 B2 *
`6,737,830 B2 *
`
`4/2002 Goto et a1.
`12/2003 Kern et a1.
`5/2004 Bean et a1.
`
`.................. 320/119
`322/29
`
`.................. 320/125
`
`(75)
`
`Inventor: Masakazu Kojima, Kawasaki (JP)
`
`
`................. 320/125
`6/2008 Ariga et a1.
`7,391,183 B2 *
`2001/0050547 A1* 12/2001 Takimoto et a1.
`...... 323/284
`
`(73) Assignee‘ Fujitsu Limited Kawasaki (JP)
`
`2002/0171398 A1* 11/2002 Odaohhara .................. 320/128
`FOREIGN PATENT DOCUMENTS
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 193 days.
`tprl.lJo; 11/260,258
`
`(21)
`
`i:
`JP
`JP
`
`1:233:
`2003-3331:;
`3/2005
`2005-86933
`12/2005
`2005-341769
`OTHER PUBLICATIONS
`
`(22)
`
`Filed:
`
`Oct. 28, 2005
`
`(65)
`
`(30)
`
`Prior Publication Data
`
`US 2007/0001646 A1
`
`Jan. 4, 2007
`
`Foreign Application Priority Data
`
`Communication from the Japanese Patent Office dispatched Jul. 14,
`2009 in the related Japanese patent application No. 2005-193872.
`
`* cited by examiner
`
`Primary ExamineriEdward Tso
`Assistant ExamineriArun Williams
`
`Jul. 1, 2005
`
`(JP)
`
`............................. 2005-193872
`
`(74) Attorney, Agent, or Firmistaas & Halsey LLP
`
`(51)
`
`Int. Cl.
`(2006.01)
`H02] 7/00
`(52) US. Cl.
`....................... 320/125; 320/114; 320/134;
`324/427
`
`(58) Field of Classification Search ................. 320/125,
`320/128, 134, 138, 114; 324/427, 4327434;
`307/43, 52
`See application file for complete search history.
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`3,767,889 A * 10/1973 Sano et a1.
`.............. 219/137 R
`5,734,254 A *
`3/1998 Stephens ............. 320/106
`
`9/1998 Saeki et al. ........... 320/117
`5,808,444 A *
`6,127,804 A * 10/2000 Oglesbee et a1.
`.
`..... 320/125
`
`..... 320/112
`6,191,552 B1*
`2/2001 Kates et a1.
`..
`3/2001 Kitagawa .......... 320/128
`6,204,633 B1*
`
`4/2001 Matsuda ..................... 320/115
`6,211,649 B1 *
`
`(57)
`
`ABSTRACT
`
`The present invention relates to charging of rechargeable
`batteries built into electronic devices and is configured to
`constrain heat generation during the charging. A charging 1C
`used for charging a rechargeable battery built into an elec-
`tronic device is disclosed that comprises a power source unit
`which can be fed with power from an external power source
`with a drooping characteristic to pick up a constant current;
`and a control unit which applies a first constant current from
`the external power source to the rechargeable battery through
`a circuit element installed on a charging path ofthe recharge-
`able battery, the control unit applying a second constant cur-
`rent smaller than the first constant current from the power
`source unit to the rechargeable battery after the rechargeable
`battery is charged with the first constant current to a prede-
`termined voltage.
`
`12 Claims, 40 Drawing Sheets
`
`GHARG IMO APPARATUS
`
`
`
`
`AC ADAPTOR
`
`10
`
`
`
`cum; ING IC
`
`
`
`
`APPARATUS LOAD
`
`
`
`1
`
`APPLE1030
`
`APPLE 1030
`
`1
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 1 of 40
`
`US 7,733,060 B2
`
`FIG.1
`
` CHARGING APPARATUS
`
`AC ADAPTOR
`
`
`
`APPARATUS LOAD
`
`
`
`2
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 2 of 40
`
`US 7,733,060 B2
`
`FIG.2
`
`START CHARGING
`
`S1
`
`BATTERY STATUS CHECK
`
`82
`
`33
`
`84
`
`FIRST CONSTANT-CURRENT CHARGING
`
`Icc1
`
`RAISE BATTERY VOLTAGE T0
`
`CONSTANT-VOLTAGE CHARG | N6
`
`SECOND CONSTANT—CURRENT CHARGING
`|cc2< Icc1
`
`S5
`
`CONSTANT—VOLTAGE CHARGING
`
`COMPLETE CHARGING
`
`3
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 3 of 40
`
`US 7,733,060 B2
`
`FIG.3
`
`
`
`—>BATTERYVOLTAGE/VOLTAGE[V]
`
`
`
`
`
`5v
`
`4v
`
`Voa
`
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`
` A V MAXIMUM HEAT GENERATION
`
` CONSTANT—VOLTAGE V0
`I cc2
`CHARGING (CV)
`
`
`SECOND CONSTANT—CURRENT
`COMPLETION OF
`
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`(ccz)
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`
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`
`
`FIRST CONSTANT-CURRENT
`CHARG I NC
`
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`
`3 V
`
`
`DROOP I NC CHARACTER | ST | C
`OF AC ADAPTOR
`
`
`PRELIMINARY CHARGING (PR)
`
`
`
`—> CHARGING CURRENT E A J
`
`4
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 4 of 40
`
`US 7,733,060 B2
`
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`US. Patent
`
`Jun. 8, 2010
`
`Sheet 5 of 40
`
`US 7,733,060 B2
`
`FIG.5
`
`10
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`6
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`

`

`US. Patent
`
`Jun.8,2010
`
`Sheet 6 of 40
`
`US 7,733,060 B2
`
`FIG.6
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`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 7 of 40
`
`US 7,733,060 B2
`
`FIG.7
`
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`
`CHARGING APPARATUS
`
`
`
`AC ADAPTOR
`
`
`
`SWITCHING
`
`POWER SOURCE
`
`APPARATUS LOAD
`
`
`
`8
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 8 of 40
`
`US 7,733,060 B2
`
`FIG.
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`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 9 of 40
`
`US 7,733,060 B2
`
`FIG.9
`
`40
`
`AC ADAPTOR
`
`
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`
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`
`
`
`USB HOST
`
`42
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`
`
`
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`POWER SOURCE
`
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`
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`
`CHARGING APPARATUS
`
`36
`
`2/34
`
`32
`
`
`
`10
`
`10
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 10 of 40
`
`US 7,733,060 B2
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`US. Patent
`
`Jun. 8, 2010
`
`Sheet 11 of 40
`
`US 7,733,060 B2
`
`FIG.11
`
`AC ADAPTOR 401/
`
`SWITCHING POWER SOURCE
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`12
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`

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`US. Patent
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`Jun.8,2010
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`Sheet120f40
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`US. Patent
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`Jun.8,2010
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`Jun.8,2010
`
`Sheet 17 of 40
`
`US 7,733,060 B2
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`US. Patent
`
`Jun. 8, 2010
`
`Sheet 18 of 40
`
`US 7,733,060 B2
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`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 19 of 40
`
`US 7,733,060 B2
`
`FIG.19
`
`5V
`
`4:. <
`
`00 <
`
`
`
`
`
`—’BATTERYVOLTAGE/VOLTAGEEVJ
`
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`(V6)
`OUTPUT VOLTAGE 0F AC ADAPTOR V03
`MAXIMUM HEAT GENERATION
`
`COMPLET'ON 0F
`(DEPENDENT 0N EFFICIENCY)
`CHARGING
`V
`Hmax
`10”)
`I cc2
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`(V2)
`c
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`
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`(V3)
`CHARGING (CV)
`SECOND CONSTANT-CURRENT
`CHARGING
`(CCZ)
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`
`(CCI )
`
`os
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`CF AC ADAPTOR
`
`
`
`—> CHARGING CURRENT [A]
`
`20
`
`20
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 20 of 40
`
`US 7,733,060 B2
`
`FIG.20
`
`CV
`002
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`21
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`
`21
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 21 of 40
`
`US 7,733,060 B2
`
`FIG.21
`
`
`
`OUTPUT VOLTAGE 0F Ac ADAPTOR
`
`Voa
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`CHARG'NG
`
`l
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`V03
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`MAXIMUM HEAT GENERATION
`(DEPENDENT ON EFFICIENCY)
`Hmax
`
`SECOND CONSTANT—CURRENT CHARGING
`
`(C02)
`
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`%/_____J
`CONSTANT—VOLTAGE CHARGING (CV)
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`
`
` I pre
`
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`22
`
`22
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 22 of 40
`
`US 7,733,060 B2
`
`FIG.22
`
`
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`"//////.- LINEAR VOLTAGE REGULATOR 68
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`:SWI TCH | NG POWER SOURCE 66
`
`
`MW : SENSE RESISTOR 58
`
`23
`
`23
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 23 of 40
`
`US 7,733,060 B2
`
`5V
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`OUTPUT VOLTAGE OF AC ADAPTOR
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`CHARGING
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`24
`
`24
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`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 24 of 40
`
`US 7,733,060 B2
`
`FIG.24
`
`AMOUNT ///,
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`25
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`25
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`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 25 of 40
`
`US 7,733,060 B2
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`

`US. Patent
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`n.HJ
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`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 28 of 40
`
`US 7,733,060 B2
`
`FIG.28
`
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`36
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`30
`
`29
`
`29
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 29 of 40
`
`US 7,733,060 B2
`
`FIG.29
`
`144
`
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`
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`
`30
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 30 of 40
`
`US 7,733,060 B2
`
`FIG.30
`
`
`
`31
`
`31
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 31 of 40
`
`US 7,733,060 B2
`
`FIG.31
`
`40
`
`
`
`104
`
`32
`
`32
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 32 of 40
`
`US 7,733,060 B2
`
`FIG.32
`
`
`
`33
`
`33
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 33 of 40
`
`US 7,733,060 B2
`
`FIG.33
`
`34
`
`34
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 34 of 40
`
`US 7,733,060 B2
`
`FIG.34
`
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`164
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`35
`
`35
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 35 of 40
`
`US 7,733,060 B2
`
`
`
` 08m6432mES83525%25hzmmmzoosz<zoA|
`
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`
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`
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`
`FIG.35
`
`—>CHARGING TIME (MIN)
`
`36
`
`36
`
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 36 of 40
`
`US 7,733,060 B2
`
`FIG
`
`.36
`
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`
`37
`
`37
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 37 of 40
`
`US 7,733,060 B2
`
`
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`FIG.37
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`
`38
`
`38
`
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 38 of 40
`
`US 7,733,060 B2
`
`FIG.38
`
`mmzomAlll
`
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`
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`
`39
`
`39
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 39 of 40
`
`US 7,733,060 B2
`
`
`
`ESmwogEgofi2.5pzmmmzooz_oz<_._oA|I|
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`
`FIG.39
`
`—>CHARG|NG TIME (MIN)
`
`40
`
`40
`
`
`

`

`US. Patent
`
`Jun. 8, 2010
`
`Sheet 40 of 40
`
`US 7,733,060 B2
`
`FIG
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`.40
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`41
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`41
`
`

`

`US 7,733,060 B2
`
`1
`CHARGING IC, CHARGING APPARATUS
`AND ELECTRONIC DEVICE
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application is based upon and claims the benefit of
`priority from the prior Japanese Patent Application No. 2005 -
`193872, filed on Jul. 1, 2005, the entire contents of which are
`incorporated herein by reference.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention relates generally to a charging appa-
`ratus of rechargeable batteries built into electronic devices
`such as mobile terminals, and, more particularly, to a charg-
`ing IC (Integrated Circuit), charging apparatus and an elec-
`tronic device using as a charging source of the rechargeable
`batteries an external power source such as an AC (Alternating
`Current) adaptor or a USB (Universal Serial Bus) host such as
`a personal computer connected with a USB cable.
`2. Description of the Related Art
`In charging of a rechargeable battery built into an elec-
`tronic device such as a mobile terminal, which uses an AC
`adaptor or a personal computer as a charging source, prelimi-
`nary charging, constant-current charging or constant-voltage
`charging is selected depending on a voltage level of the
`rechargeable battery, and even in the constant-current charg-
`ing, a current value may be gradually switched.
`In regard to such charging of a rechargeable battery, known
`propositions are a charging circuit having a drooping charac-
`teristic depending on a output current (For example, Japanese
`Patent Application Laid-Open Publication No. 1999-327671
`(paragraph number 0020, FIG. 1, FIG. 2 and the like)), a
`method and apparatus used for constant-voltage charging
`after constant-current charging for charging a battery of a
`cellular phone (For example, Japanese Patent Application
`Laid-Open Publication No. 2003-274570 (paragraph number
`0016, FIG. 4, FIG. 5 and the like))
`By the way, a description is made for the charging which
`switches to constant-voltage charging after constant-current
`charging with an external power source having a drooping
`characteristic. FIG. 1 is a circuit diagram of a charging appa-
`ratus using a PMOS G’-channel Metal Oxide Semiconductor)
`transistor for charging control; FIG. 2 is a flowchart of the
`charging control; and FIG. 3 is a diagram showing a charging
`operation.
`This charging apparatus 2 is configured to use an AC adap-
`tor 8 as a charging source to charge a rechargeable battery 6
`built into an electronic device 3 along with an apparatus load
`4. The charging apparatus 2 is provided with a charging IC 10,
`and the charging IC 10 integrates circuit units such as a
`charging control unit which can be integrated into an IC. As
`an external circuit of the charging IC 10, a charging path 11 is
`formed for passing a charging current between the AC adap-
`tor 8 and the rechargeable battery 6; the charging path 11 is
`equipped with a PMOS transistor (Tr) 12 as a charging control
`element; and the PMOSTr 12 is connected serially with a
`backflow prevention diode 14 and a sense resistor 16. The
`sense resistor 16 converts the charging current flowing
`through the charging path 11 to a voltage to be detected and
`the detected current is applied to the charging IC 10 as control
`information. Control output obtained in the charging IC 10 is
`applied to a gate of the PMOSTr 12 to execute charging-
`current control or constant-voltage control.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`
`In the charging of the rechargeable battery 6 with the
`charging apparatus 2, as shown in FIG. 2, when the AC
`adaptor 8 is detected as the charging source, the output volt-
`age of the AC adaptor 8 is detected, and then, a battery status
`check is performed for a battery temperature and a battery
`voltage which indicate a battery status (step 81). If the result
`of the battery status check is normal, a charging operation is
`started. At the start of the charging operation, first constant-
`current charging CC1 is performed as fast charging (step S2),
`except the case that a battery voltage is too low (an over-
`discharge state), and the battery voltage is raised by the first
`constant-current charging CC1 to a start voltage of constant-
`voltage charging (step S3). After the battery voltage is raised,
`second constant-current charging CC2 is performed (step
`S4), and when full charging is achieved through constant-
`voltage charging (step SS), the charging is completed. To a
`constant current Icc1 of CC1, a constant current Icc2 of CC2
`is in a relationship of Icc2<Icc1.
`In this charging process, as shown in FIG. 3, after the
`rechargeable battery 6 is raised to a predetermined voltage
`(e.g., 3 [V]) through preliminary charging (PR) with a pre-
`liminary current Ipre, a charging current Ic is increased to a
`constant current Icc1 to utilize the drooping characteristic of
`the AC adaptor 8 to perform the first constant-current charg-
`ing CC1 and second constant-current charging CC2, and after
`constant charging CV, the charging of the rechargeable bat-
`tery 6 is reaches to, for example, 4.2 [V] and completed. FIG.
`3 is a diagram showing transitions of charging forms, charg-
`ing currents and charging voltages. In this case, the output
`voltage of the AC adaptor 8 is set higher than the charging
`completion voltage, and maximum heat generation happens
`at the point of time when the second constant-current charg-
`ing is switched to the constant-voltage charging.
`The heat generation amount due to the charging operation
`is described with reference to FIG. 4. FIG. 4 is a diagram
`showing transitions of the heat generation amount in each
`portion during the charging operation.
`In the charging operation, for the heat generation in the
`PMOSTr 12, diode 14 and sense resistor 16 in the first con-
`stant-current charging CC1 region (t1 to t2), the heat genera-
`tion of the diode 14 is largest and accounts for one-half ofthe
`total heat generation amount. In the second constant-current
`charging CC2 region (t2 to t3), the total heat generation
`amount is larger than the constant-current charging CC1
`region (t1 to t2), and the heat generation amounts of the diode
`14 and sense resistor 16 is smaller than the CC1 rcgion (t1 to
`t2), while the heat generation amounts of the PMOSTr 12
`accounts for two third of the total heat generation amount. In
`the constant-voltage charging CV region (t3 to t4), the heat
`generation amount is reduced dependently on reduction ofthe
`charging current. In the total heat generation amount of the
`region (t1 to t4), the heat generation amount of the PMOSTr
`12 is largest. In this heat generation, when making the shift to
`the constant-current charging CC2, PMOSTr 12 generates
`heat depending on electric power applying a voltage. Such
`heat generation leads to energy loss.
`By the way, a start voltage ofthe constant-current charging
`CC1 is set to, for example, about 3 [V], and the charging
`current Ic is dependent on the output of the AC adaptor 8
`because the drooping characteristic of the AC adaptor 8 is
`used. Therefore, in the CC1 region, the charging current Ic is
`on the order of 670 [mA]. Assuming that an output voltage of
`the AC adaptor 8 is Voa and a battery voltage is Vb, the output
`voltage Voa is as follows:
`
`Voa : Vb+(extemal part resistance [£2]><IC)
`
`(1)
`
`42
`
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`US 7,733,060 B2
`
`3
`The external part generates heat depending on this accept-
`able loss.
`
`In this case, assuming that a voltage drop ofthe diode 14 is
`0.3 [V], the heat generation amount Pd is as follows:
`Pd:0.3 [ijIC
`
`(2)
`
`When a constant current Icc2 in the CC2 region is set to, for
`example, 350 [mA], ifthe output voltage Voa is about 5 .4 [V],
`a large portion of a difference voltage AV (:Voa—Vb)
`between the battery voltage Vb and the output voltage Voa of
`the AC adaptor 8 is concentrated on the PMOStr 12, and the
`heat generation amount ofthe PMOStr 12 accounts for a large
`portion ofthe total heat generation amount. Assuming that the
`loss due to the external part is about 456 [mW], about 318
`[mW] is lost by the heat generation of the PMOSTr 12. Since
`the charging current Ic comes down below CC1 at the time of
`the shift to CC2, the battery voltage Vb comes down to on the
`order of 3.9 [V] and then, the battery voltage Vb is raised by
`the constant-current charging CC2 to make the shift to the
`constant-voltage charging CV at the battery voltage Vb:4.2
`[V].
`In the constant-voltage charging CV, constant-voltage con-
`trol is performed such that the battery voltage Vb will be 4.2
`[V], and as the rechargeable battery 6 approaches full charge,
`the charging current Ic is reduced. In the CV region, since the
`charging current is small, the heat generation is lower than the
`CC2. The charging is completed and the charging operation is
`terminated ifthe charging current Ic reduced to on the order of
`50 [mA].
`A charging apparatus 2 in FIG. 5 is a case that a PMOSTr
`18 is used as a backfiow prevention element, instead of the
`diode 14 described above. In FIG. 5, the same symbols are
`added to the same portions as FIG. 1. In the charging appa-
`ratus 2, the PMOSTr 18 is operated by a control signal applied
`from the charging IC 10 to a gate to regulate the direction of
`the charging current Ic passing through the charging path 11.
`In regard to the heat generation amount of the charging
`apparatus 2 shown in FIG. 5, as shown in FIG. 6, in the first
`constant-current charging CC1 region (t1 to t2) the heat gen-
`eration of the sense resistor 16 is largest and accounts for
`one-half of the total heat generation amount. The total heat
`generation amount in the second constant-current charging
`CC2 region (t2 to t3) is about twice larger than the constant-
`current charging CC1 region (t1 to t2), and the heat generation
`amounts of the PMOSTr 18 and the sense resistor 16 are
`
`dropped to on the order of one-fifth of the total heat genera-
`tion amount, while the heat generation amount of the
`PMOSTr 12 accounts for four-fifth of the total heat genera-
`tion amount. In the constant-voltage charging CV region (t3
`to t4), the heat generation amount is reduced dependently on
`reduction of the charging current. In this heat generation,
`when making the shift to the constant-current charging CC2,
`PMOSTr 12 generates heat depending on electric power
`applying a voltage. As described above, such heat generation
`leads to energy loss.
`In a charging apparatus 2 shown in FIG. 7, a switching
`power source 20 is disposed with in the charging IC 10, and
`the output ofthe switching power source 20 is picked up after
`passing though a filter circuit 26 consisting of an inductor 22
`and capacitor 24 and is supplied to the rechargeable battery 6
`through the charging path 11. In this case, although the
`PMOSTr 18 for backflow prevention is disposed in the charg-
`ing path 11, the PMOSTr 18 may be omitted.
`In the charging apparatus 2, the AC adaptor 8 is used as a
`charging source, and the output ofthe AC adaptor 8 is applied
`to the switching power source 20 to generate constant cur-
`rents Icc1, Icc2 and a constant voltagch which achieve a first
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`
`second constant-current
`constant-current charging CC1,
`charging CC2 and constant-voltage charging CV. Therefore,
`in regard to the heat generation amount of the charging appa-
`ratus 2 (FIG. 7), as shown in FIG. 8, in the first constant-
`current charging CC1 region (t1 to t2) the heat generation of
`the switching power source 20 is largest and accounts for
`one-half of the total heat generation amount. The total heat
`generation amount in the constant-current charging CC2
`region (t2 to t3) is reduced to on the order of one-half of the
`constant-current charging CC1 region (t1 to t2); the heat
`generation amount of the switching power source 20 also
`comes down to on the order of one-half of the total heat
`
`generation amount as compared to the region of the constant-
`current charging CC1 (t1 to t2); and in the constant-voltage
`charging CV region (t3 to t4), the heat generation amount is
`reduced dependently on reduction of the charging current.
`By using such a switching power source 20, when the
`charging current Ic of the constant-current charging CC1 is
`enlarged,
`the heat generation amount
`is increased, and
`although the capacity of the switching power source 20 may
`be increased in order to constrain the heat generation, the cost
`is increased. In other words, if a DC-DC conversion effi-
`ciency nof the switching power source 20 is 11:90 [%], the
`heat generation amount Ph is Ph:about 347 [mW] and the
`heat generation amount is increased. By increasing the output
`current of the switching power source 20 to on the order of
`700 [mA] in order to ensure the charging current Ic, the cost
`is increased.
`
`Therefore, in regard to electronic devices, such as cellular
`phones, equipped with rechargeable batteries, device chassis
`are miniaturized and thinned as well as equipped batteries are
`planned to be large capacity, and it is requested to constrain
`the heat generation when the devices are operated for phone
`calls and the like during the charging operation.
`Japanese Patent Application Laid-Open Publication Nos.
`1999-327671 and 2003-274570 do not disclose such issues
`
`and not disclose or indicate any configurations for solving the
`issues.
`
`SUMMARY OF THE INVENTION
`
`An object of the present invention relates to charging of
`rechargeable batteries built into electronic devices and is to
`constrain heat generation during the charging.
`Another object of the present invention relates to charging
`of rechargeable batteries using external devices such as Ac
`adaptors or USB hosts and is to plan to promote the efficiency
`of the charging.
`The configurations ofthe present invention for solving the
`issues are listed and described.
`
`In order to achieve the above objects, according to a first
`aspect ofthe present invention there is provided a charging IC
`used for charging a rechargeable battery built into an elec-
`tronic device, comprising a power source unit which can be
`fed with power from an external power source with a droop-
`ing characteristic to pick up a constant current; and a control
`unit which applies a first constant current from the external
`power source to the rechargeable battery through a circuit
`element disposed on a charging path of the rechargeable
`battery, the control unit applying a second constant current
`smaller than the first constant current from the power source
`unit to the rechargeable battery after the rechargeable battery
`is charged with the first constant current to a predetermined
`voltage.
`According to such a configuration, the rechargeable battery
`is charged by applying the first constant current
`to the
`rechargeable battery from the external power source, such as
`
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`US 7,733,060 B2
`
`5
`an AC adaptor, with the drooping characteristic, and after the
`rechargeable battery is charged to the predetermined voltage,
`the rechargeable battery can be charged by applying the sec-
`ond constant current from the power source unit built into the
`charging IC to the rechargeable battery. In this charging, a
`current value is large for the first constant current supplied to
`the rechargeable battery from the external power source with
`the drooping characteristic, and the second constant current
`supplied from the power source unit built into the charging IC
`is smaller than the first constant current. Therefore, although
`the cause ofthe heat generation on the charging IC side exists
`in the power source unit applying the second constant current,
`the heat genera