1、1LTC4054-4.2/LTC4054X-4.2405442xfFEATURESDESCRIPTIOUAPPLICATIO SUTYPICAL APPLICATIOUStandalone LinearLi-Ion Battery Charger withThermal Regulation in ThinSOT, LTC and LT are registered trademarks of Linear Technology Corporation.nProgrammable Charge Current Up to 800mAnNo MOSFET, Sense Resistor or B
2、lockingDiode RequirednComplete Linear Charger in ThinSOTTMPackage forSingle Cell Lithium-Ion BatteriesnConstant-Current/Constant-Voltage Operation withThermal Regulation* to Maximize Charge RateWithout Risk of OverheatingnCharges Single Cell Li-Ion Batteries Directlyfrom USB PortnPreset 4.2V Charge
3、Voltage with 1% AccuracynCharge Current Monitor Output for GasGauging*nAutomatic RechargenCharge Status Output PinnC/10 Charge Terminationn25A Supply Current in Shutdownn2.9V Trickle Charge Threshold (LTC4054)nAvailable Without Trickle Charge (LTC4054X)nSoft-Start Limits Inrush CurrentnAvailable in
4、5-Lead SOT-23 PackagenCellular Telephones, PDAs, MP3 PlayersnCharging Docks and CradlesnBluetooth ApplicationsThinSOT is a trademark of Linear Technology Corporation.*U.S.Patent No. 6,522,118The LTC4054 is a complete constant-current/constant-voltage linear charger for single cell lithium-ion batter
5、ies.Its ThinSOT package and low external component countmake the LTC4054 ideally suited for portable applications.Furthermore, the LTC4054 is specifically designed to workwithin USB power specifications.No external sense resistor is needed, and no blockingdiode is required due to the internal MOSFET
6、 architecture.Thermal feedback regulates the charge current to limit thedie temperature during high power operation or highambient temperature. The charge voltage is fixed at 4.2V,and the charge current can be programmed externally witha single resistor. The LTC4054 automatically terminatesthe charg
7、e cycle when the charge current drops to 1/10ththe programmed value after the final float voltage isreached.When the input supply (wall adapter or USB supply) isremoved, the LTC4054 automatically enters a low currentstate, dropping the battery drain current to less than 2A.The LTC4054 can be put int
8、o shutdown mode, reducingthe supply current to 25A.Other features include charge current monitor, undervoltagelockout, automatic recharge and a status pin to indicatecharge termination and the presence of an input voltage.600mA Single Cell Li-Ion ChargerVCC1.65k4.2VLi-IonBATTERY405442 TA01aLTC4054-4
9、.21FVIN4.5V TO 6.5VBAT4352PROGGND600mAComplete Charge Cycle (750mAh Battery)TIME (HOURS)0CHARGE CURRENT (mA)1.5405442 TAO1b0.5 1.0 2.070060050040030020010004.754.504.254.003.753.503.253.000.25 0.75 1.25 1.75CONSTANTPOWERCONSTANTVOLTAGECONSTANTCURRENTCHARGETERMINATEDBATTERY VOLTAGE (V)VCC= 5VJA= 130C
10、/WRPROG= 1.65kTA= 25C2LTC4054-4.2/LTC4054X-4.2405442xf(Note 1)Input Supply Voltage (VCC) . 0.3V to 10VPROG. 0.3V to VCC+ 0.3VBAT 0.3V to 7VCHRG 0.3V to 10VBAT Short-Circuit Duration ContinuousBAT Pin Current . 800mAPROG Pin Current 800AMaximum Junction Temperature 125COperating Ambient Temperature R
11、ange(Note 2) 40C to 85CStorage Temperature Range . 65C to 125CLead Temperature (Soldering, 10 sec) 300CTJMAX= 125C, (JA= 80C/ W TO150C/W DEPENDING ON PC BOARD LAYOUT)(N0TE 3)ORDER PARTNUMBERS5 PART MARKINGLTH7LTADYSYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITSVCCInput Supply Voltage l 4.25 6.5 VICCIn
12、put Supply Current Charge Mode (Note 4), RPROG= 10k l 300 2000 AStandby Mode (Charge Terminated) l 200 500 AShutdown Mode (RPROGNot Connected, l 25 50 AVCC2.9VBAT 2.9VCHRG: STRONGPULL-DOWNCHARGE MODEFULL CURRENTCHRG: STRONGPULL-DOWNSHUTDOWN MODECHRG: Hi-Z IN UVLOWEAK PULL-DOWNOTHERWISEPROGRECONNECTE
13、DORUVLO CONDITIONSTOPSPROG FLOATEDORUVLO CONDITIONICCDROPS TO 25APOWER ONPROG 100mVSTANDBY MODENO CHARGE CURRENTCHRG: WEAKPULL-DOWN2.9V BAT 4.05V405442 F01Figure 1. State Diagram of a Typical Charge Cycle10LTC4054-4.2/LTC4054X-4.2405442xfAPPLICATIO S I FOR ATIOWU UUStability ConsiderationsThe consta
14、nt-voltage mode feedback loop is stable with-out an output capacitor provided a battery is connected tothe charger output. With no battery present, an outputcapacitor is recommended to reduce ripple voltage. Whenusing high value, low ESR ceramic capacitors, it is recom-mended to add a 1 resistor in
15、series with the capacitor.No series resistor is needed if tantalum capacitors areused.In constant-current mode, the PROG pin is in the feedbackloop, not the battery. The constant-current mode stabilityis affected by the impedance at the PROG pin. With noadditional capacitance on the PROG pin, the ch
16、arger isstable with program resistor values as high as 20k. How-ever, additional capacitance on this node reduces themaximum allowed program resistor. The pole frequencyat the PROG pin should be kept above 100kHz. Therefore,if the PROG pin is loaded with a capacitance, CPROG, thefollowing equation c
17、an be used to calculate the maximumresistance value for RPROG:RCPROGPROGpi12105Average, rather than instantaneous, charge current maybe of interest to the user. For example, if a switching powersupply operating in low current mode is connected inparallel with the battery, the average current being p
18、ulledout of the BAT pin is typically of more interest than theinstantaneous current pulses. In such a case, a simple RCfilter can be used on the PROG pin to measure the averagebattery current as shown in Figure 2. A 10k resistor hasbeen added between the PROG pin and the filter capacitorto ensure st
19、ability.Power DissipationThe conditions that cause the LTC4054 to reduce chargecurrent through thermal feedback can be approximated byconsidering the power dissipated in the IC. Nearly all ofthis power dissipation is generated by the internalMOSFETthis is calculated to be approximately:PD= (VCC VBAT
20、) IBATwhere PDis the power dissipated, VCCis the input supplyvoltage, VBATis the battery voltage and IBATis the chargecurrent. The approximate ambient temperature at whichthe thermal feedback begins to protect the IC is:TA= 120C PDJATA= 120C (VCC VBAT) IBAT JAExample: An LTC4054 operating from a 5V
21、USB supply isprogrammed to supply 400mA full-scale current to adischarged Li-Ion battery with a voltage of 3.75V. Assum-ing JAis 150C/W (see Board Layout Considerations), theambient temperature at which the LTC4054 will begin toreduce the charge current is approximately:TA= 120C (5V 3.75V) (400mA) 1
22、50C/WTA= 120C 0.5W 150C/W = 120C 75CTA= 45CPROG10kRPROGCFILTER405442 F02CHARGECURRENTMONITORCIRCUITRYLTC4054GNDFigure 2. Isolating Capacitive Load on PROG Pin and Filtering11LTC4054-4.2/LTC4054X-4.2405442xfThe following table lists thermal resistance for severaldifferent board sizes and copper areas
23、. All measurementswere taken in still air on 3/32“ FR-4 board with the devicemounted on topside.Table 1. Measured Thermal Resistance (2-Layer Board*)COPPER AREA BOARD THERMAL RESISTANCETOPSIDE BACKSIDE AREA JUNCTION-TO-AMBIENT2500mm22500mm22500mm2125C/W1000mm22500mm22500mm2125C/W225mm22500mm22500mm2
24、130C/W100mm22500mm22500mm2135C/W50mm22500mm22500mm2150C/WTable 2. Measured Thermal Resistance (4-Layer Board*)COPPER AREA BOARD THERMAL RESISTANCE(EACH SIDE) AREA JUNCTION-TO-AMBIENT2500mm2*2500mm280C/WIncreasing Thermal Regulation CurrentReducing the voltage drop across the internal MOSFETcan signi
25、ficantly decrease the power dissipation in the IC.This has the effect of increasing the current delivered tothe battery during thermal regulation. One method is bydissipating some of the power through an external compo-nent, such as a resistor or diode.Example: An LTC4054 operating from a 5V wall ad
26、apter isprogrammed to supply 800mA full-scale current to adischarged Li-Ion battery with a voltage of 3.75V. Assum-ing JAis 125C/W, the approximate charge current at anambient temperature of 25C is:ICCVVCWmABAT=120 255 3 75 125608(. ) /By dropping voltage across a resistor in series with a 5Vwall ad
27、apter (shown in Figure 3), the on-chip powerdissipation can be decreased, thus increasing the ther-mally regulated charge currentICCVIR VBATS BAT CC BAT JA=120 25( )APPLICATIO S I FOR ATIOWU UUThe LTC4054 can be used above 45C ambient, but thecharge current will be reduced from 400mA. The approxi-ma
28、te current at a given ambient temperature can beapproximated by:ICTVVBATACC BAT JA=()120 Using the previous example with an ambient temperatureof 60C, the charge current will be reduced to approxi-mately:ICCVV CWCCAImABATBAT=()=120 605 3 75 15060187 5320. /./Moreover, when thermal feedback reduces t
29、he chargecurrent, the voltage at the PROG pin is also reducedproportionally as discussed in the Operation section.It is important to remember that LTC4054 applications donot need to be designed for worst-case thermal conditionssince the IC will automatically reduce power dissipationwhen the junction
30、 temperature reaches approximately120C.Thermal ConsiderationsBecause of the small size of the ThinSOT package, it is veryimportant to use a good thermal PC board layout tomaximize the available charge current. The thermal pathfor the heat generated by the IC is from the die to thecopper lead frame,
31、through the package leads, (especiallythe ground lead) to the PC board copper. The PC boardcopper is the heat sink. The footprint copper pads shouldbe as wide as possible and expand out to larger copperareas to spread and dissipate the heat to the surroundingambient. Feedthrough vias to inner or bac
32、kside copperlayers are also useful in improving the overall thermalperformance of the charger. Other heat sources on theboard, not related to the charger, must also be consideredwhen designing a PC board layout because they will affectoverall temperature rise and the maximum charge current.*Each lay
33、er uses one ounce copper*Top and bottom layers use two ounce copper, inner layers use one ounce copper.*10,000mm2total copper area12LTC4054-4.2/LTC4054X-4.2405442xfAPPLICATIO S I FOR ATIOWU UUSolving for IBATusing the quadratic formula2.IVV VVRCTRBATS BAT S BATCC AJACC=( ) ( )()24 1202Using RCC= 0.2
34、5, VS= 5V, VBAT= 3.75V, TA= 25C andJA= 125C/W we can calculate the thermally regulatedcharge current to be:IBAT= 708.4mAWhile this application delivers more energy to the batteryand reduces charge time in thermal mode, it may actuallylengthen charge time in voltage mode if VCCbecomes lowRCC()0CHARGE
35、 CURRENT (mA)100080060040020000.5 1.0 1.25405442 F040.25 0.75 1.5 1.75CONSTANTCURRENTVBAT= 3.75VTA= 25CJA= 125C/WRPROG= 1.25kTHERMALMODEDROPOUTVS= 5.25VVS= 5.5VVS= 5VFigure 4. Charge Current vs RCCenough to put the LTC4054 into dropout. Figure 4 showshow this circuit can result in dropout as RCCbeco
36、meslarge.This technique works best when RCCvalues are minimizedto keep component size small and avoid dropout. Remem-ber to choose a resistor with adequate power handlingcapability.VCCBypass CapacitorMany types of capacitors can be used for input bypassing,however, caution must be exercised when usi
37、ng multi-layer ceramic capacitors. Because of the self-resonant andhigh Q characteristics of some types of ceramic capaci-tors, high voltage transients can be generated under somestart-up conditions, such as connecting the charger inputto a live power source. Adding a 1.5 resistor in serieswith an X
38、5R ceramic capacitor will minimize start-upvoltage transients. For more information, refer to Applica-tion Note 88.Charge Current Soft-StartThe LTC4054 includes a soft-start circuit to minimize theinrush current at the start of a charge cycle. When a chargecycle is initiated, the charge current ramp
39、s from zero to thefull-scale current over a period of approximately 100s.This has the effect of minimizing the transient current loadon the power supply during start-up.Note 2: Large values of RCCwill result in no solution for IBAT. This indicates that the LTC4054will not generate enough heat to req
40、uire thermal regulation.Figure 3. A Circuit to Maximize Thermal Mode Charge CurrentVCCRPROGRCCLi-IonCELL405442 F03LTC4054-4.21FVSBATPROGGND13LTC4054-4.2/LTC4054X-4.2405442xfFigure 5. Using a Microprocessor to Determine CHRG StateCHRG Status Output PinThe CHRG pin can provide an indication that the i
41、nputvoltage is greater than the undervoltage lockout thresholdlevel. A weak pull-down current of approximately 20Aindicates that sufficient voltage is applied to VCCto begincharging. When a discharged battery is connected to thecharger, the constant current portion of the charge cyclebegins and the
42、CHRG pin pulls to ground. The CHRG pincan sink up to 10mA to drive an LED that indicates that acharge cycle is in progress.When the battery is nearing full charge, the charger entersthe constant-voltage portion of the charge cycle and thecharge current begins to drop. When the charge currentdrops be
43、low 1/10 of the programmed current, the chargecycle ends and the strong pull-down is replaced by the20A pull-down, indicating that the charge cycle hasended. If the input voltage is removed or drops below theundervoltage lockout threshold, the CHRG pin becomeshigh impedance. Figure 5 shows that by u
44、sing twodifferent value pull-up resistors, a microprocessor candetect all three states from this pin.APPLICATIO S I FOR ATIOWU UUInformation furnished by Linear Technology Corporation is believed to be accurate and reliable.However, no responsibility is assumed for its use. Linear Technology Corpora
45、tion makes no represen-tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.Figure 6. Low Loss Input Reverse Polarity ProtectionVIN VCCLTC4054DRAIN-BULKDIODE OF FET4054 F06CHRG OUTIN2k800k405442 F05LTC4054 PROCESSORV+VDDVCCTo detect when the
46、 LTC4054 is in charge mode, force thedigital output pin (OUT) high and measure the voltage atthe CHRG pin. The N-channel MOSFET will pull the pinvoltage low even with the 2k pull-up resistor. Once thecharge cycle terminates, the N-channel MOSFET is turnedoff and a 20A current source is connected to
47、the CHRGpin. The IN pin will then be pulled high by the 2k pull-upresistor. To determine if there is a weak pull-down current,the OUT pin should be forced to a high impedance state.The weak current source will pull the IN pin low throughthe 800k resistor; if CHRG is high impedance, the IN pinwill be
48、 pulled high, indicating that the part is in a UVLOstate.Reverse Polarity Input Voltage ProtectionIn some applications, protection from reverse polarityvoltage on VCCis desired. If the supply voltage is highenough, a series blocking diode can be used. In othercases, where the voltage drop must be ke
49、pt low a P-channel MOSFET can be used (as shown in Figure 6).14LTC4054-4.2/LTC4054X-4.2405442xfUSB and Wall Adapter PowerThe LTC4054 allows charging from both a wall adapterand a USB port. Figure 7 shows an example of how tocombine wall adapter and USB power inputs. A P-channelMOSFET, MP1, is used to prevent back conducting into theUSB port when a wall adapter is present and a Schottkydiode, D1, is used to prevent USB power loss through the1k pu
