LTC4001 4.1V

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LTC4001-12A Synchronous Buck Li-Ion ChargerFEATURES

Low Power Dissipationn 2A Maximum Charge Current

n No External MOSFETs, Sense Resistor or Blocking Diode Required

n Remote Sensing at Battery Terminalsn Programmable Charge Termination Timern Preset 4.1V Float Voltage with ±0.5% Accuracyn 4.1V Float Voltage Improves Battery Life and High Temperature Safety Margin

n Programmable Charge Current Detection/ Terminationn Automatic Recharge

n Thermistor Input for Temperature Qualiﬁ ed Charging

n Compatible with Current Limited Wall Adaptersn Low Proﬁ le 16-Lead (4mm × 4mm) QFN PackagenDESCRIPTION

The LTC®4001-1 is a 2A Li-Ion battery charger intended for 5V wall adapters. It utilizes a 1.5MHz synchronous buck converter topology to reduce power dissipation during charging. Low power dissipation, an internal MOSFET and sense resistor allow a physically small charger that can be embedded in a wide range of handheld applications. The LTC4001-1 includes complete charge termination circuitry, automatic recharge and a ±1% 4.1V ﬂ oat voltage. Input short-circuit protection is included so no blocking diode is required.This 4.1V version of the standard LTC4001 is intended for applications which will be operated or stored above approximately 60°C. Under these conditions, the reduced ﬂ oat voltage will trade-off initial cell capacity for the beneﬁ t of increased capacity retention over the life of the battery. A reduced ﬂ oat voltage also minimizes swelling in prismatic and polymer cells, and avoids open CID (pressure fuse) in cylindrical cells.Battery charge current, charge timeout and end-of-charge indication parameters are set with external components. Additional features include shorted cell detection, tempera-ture qualiﬁ ed charging and overvoltage protection. The LTC4001-1 is available in a low proﬁ le (0.75mm) 16-lead (4mm × 4mm) QFN package.APPLICATIONS

Handheld Battery-Powered Devicesn Handheld Computers

n Charging Docks and Cradlesn Digital Camerasn Smart PhonesnL, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.TYPICAL APPLICATION

2A Single Cell Li-Ion Battery Charger1.5μHSWSENSETOTAL APPLICATION CIRCUIT POWER DISSIPATION (W)1.25

Power Loss vs VBAT Charging (PWM Mode)VIN4.5V TO 5.5V10μFVINSENSEPVINPGNDCHRGNTCFAULTENBATSENSBAT10μF1.00

+4.1VLi-Ion

0.75

LTC4001-10.50

0.25

VIN = 5V2A CHARGER3

3.25

3.753.5

VBAT (V)

4.25

40011 TA01b

PROGIDETTIMER0.22μF274Ω0.1μFSSGNDSENS0

40011 TA01a40011fa1LTC4001-1ABSOLUTE MAXIMUM RATINGS

(Note 1)PIN CONFIGURATION

TOP VIEWBATSENSTIMERIDET12PROG

11NTC10FAULT9

5SW6EN7CHRG8PVINVINSENSE

SSPVIN, VINSENSE t < 1ms, DC < 1% ....................................–0.3V to 7V Steady State .............................................–0.3V to 6V SW, SENSE, BAT, BATSENS, SS, FAULT, CHRG, EN, NTC, PROG, IDET, TIMER Voltage ........................ –0.3V to 6VOperating Temperature Range (Note 3) ..–40°C to 85°C Operating Junction Temperature (Note 5) ................................................ –40°C to 125°C Storage Temperature Range .................. –65°C to 125°C16151413

BAT1SENSE2PGND3GNDSENS4

UF PACKAGE

16-LEAD (4mm × 4mm) PLASTIC QFN

TJMAX = 125°C, θJA = 37°C/WEXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCBORDER INFORMATION

LEAD FREE FINISHLTC4001EUF-1#PBFTAPE AND REELLTC4001EUF-1#TRPBFPART MARKING40011PACKAGE DESCRIPTION16-Lead (4mm × 4mm) Plastic QFNTEMPERATURE RANGE–40°C to 85°CConsult LTC Marketing for parts speciﬁ ed with wider operating temperature ranges.Consult LTC Marketing for information on non-standard lead based ﬁ nish parts.For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel speciﬁ cations, go to: http://www.linear.com/tapeandreel/ The l denotes the speciﬁ cations which apply over the full operating temperature range, otherwise speciﬁ cations are at TA = 25°C. VIN = 5V, VEN = 0V, RPROG = 549Ω, RIDET = 549Ω, unless otherwise speciﬁ ed.SYMBOLPARAMETERVINIINSupply VoltageCONDITIONS(Note 2)PVIN Connected to VINSENSE, PROG and IDETPins Open, Charger OnShutdown, EN = VINVFLOATIBATVBAT Regulated Float VoltageCurrent Mode Charge CurrentMeasured from BATSENS to GNDSENSRPROG = 549Ω, VBAT = 3.5VRPROG = 1.10k, VBAT = 3.5VShutdown, EN = VINVBAT = 2VVBAT RisingVBAT FallingVIN Rising, Measured from VINSENSE to GNDSENSMeasured from VINSENSE to GNDSENSVINSENSE – VBATSENS Rising (Turn-On), VBATSENSE = 4VVINSENSE – VBATSENS Falling (Turn-Off), VBATSENSE = 4V20015●ELECTRICAL CHARACTERISTICS

MIN4TYPMAX5.5250UNITSVmAμAVVAAμAmAVVVmV4.0594.0791.80.9353.052.852.74.14.121503.13.0100250304.1414.1212.21.1±5653.203.052.82ITRIKLVTRIKLVUVLΔVUVLVASDTrickle Charge CurrentTrickle Charge ThresholdVIN Undervoltage Lockout VoltageVIN Undervoltage Lockout HysteresisAutomatic Shutdown Threshold Voltage30060mVmV40011fa2LTC4001-1E LECTRICAL CHARACTERISTICS The l denotes the speciﬁ cations which apply over the full operating SYMBOLPARAMETERfOSCDRPFETRNFETtTIMERVENΔVENVPROGVIDETIIDETICHRGVCHRGVOLVOHOscillator FrequencyMaximum Duty FactorRDS(ON) of P-Channel MOSFETRDS(ON) of N-Channel MOSFETTimer AccuracyEnable Input Threshold VoltageEnable Input HysteresisPROG Pin VoltageIDET Pin VoltageIDET ThresholdCHRG Pin Weak Pull-Down CurrentCHRG Pin Output Low VoltageFAULT Pin Output Low VoltageFAULT Pin Output High VoltageRPROG = 549ΩRIDET = 549ΩRIDET = 549ΩVCHRG = 1VICHRG = 5mA1mA Load1mA LoadVFLOAT – VRECHRG VBAT Falling4.6504Percent of Total Charge TimePercent of Total Charge Time, VBAT < 2.8V, Measured Using BATSENS and GNDSENS PinsVBAT < VFLOAT – 100mV, VBAT Across BATSENSand GNDSENS PinsFrom NTC to GNDSENS Pin Rising Threshold Falling ThresholdFrom NTC to GNDSENS Pin Falling Threshold Rising ThresholdFrom NTC to GNDSENS PinFrom NTC to GNDSENS Pin0.015 • VINSENSE6502512.81610013515015Measured from PVIN to SWMeasured from SW to PGNDCTIMER = 0.22μFVEN Rising0.6127121±100.81001.2131.213200300.2250500.40.41CONDITIONSMIN1.3TYP1.5MAX1.7100temperature range, otherwise speciﬁ cations are at TA = 25°C. VIN = 5V, VEN = 0V, RPROG = 549Ω, RIDET = 549Ω, unless otherwise speciﬁ ed.UNITSMHz%mΩmΩ%VmVVVmAμAVVVmVms%%μAVRECHRGRecharge Battery Threshold VoltagetRBtRECHRGtTRIKLISSVCOLDRecharge Filter Time ConstantRecharge TimeLow-Battery Trickle Charge TimeSoft-Start Ramp CurrentNTC Pin Cold Temperature Fault ThresholdNTC Pin Hot Temperature Fault ThresholdNTC Disable Threshold (Falling)NTC Disable Hysteresis0.74 VINSENSE0.72 VINSENSE0.29 VINSENSE0.30 VINSENSE0.02 • VINSENSE0.01 • VINSENSE0.025 • VINSENSEVVVVVVVHOTVDISΔVDISNote 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime.Note 2: Operation with current limited wall adapters is allowed down to the undervoltage lockout threshold.Note 3: The LTC4001E-1 is guaranteed to meet performance speciﬁ ca-tions from 0°C to 85°C. Speciﬁ cations over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls.Note 4: TJ is calculated from the ambient temperature TA and power dis-sipation PD according to the following formula: TJ = TA + (PD • 37°C/W)Note 5: This IC includes overtemperature protection that is intended to protect the device during momentary overload. Junction temperature will exceed 125°C when overtemperature protection is active. Continuous operation above the speciﬁ ed maximum operating junction temperature my impair device reliability.40011fa3LTC4001-1TYPICAL PERFORMANCE CHARACTERISTICS

Oscillator Frequency vs VIN1.000.75PERCENT VARIATION (%)0.500.250–0.25–0.50–0.75–1.00

3.5

4.5

VIN (V)

5.5

FREQUENCY VARIATION FROM 25°C (%)VBAT = 3.2VVSS = 1V0.8

(TA = 25°C unless otherwise noted)Dissipation of Figure 8 Circuit vs IBAT1.25TOTAL APPLICATION CIRCUIT POWERDISSIPATION (W)VIN = 5VVBAT = 4V

Oscillator Frequency vs TemperatureVIN = 5VVBAT = 3.2VVSS = 1V0.61.00

0.4

0.75

0.20.50

00.25

–0.2

–50–30–101030507090110130150

TEMPERATURE (°C)

40011 G02

0500

1000

IBAT (mA)

15002000

40011 G03

40011 G01

Dissipation of Figure 8 Circuit vs VIN1.4TOTAL APPLICATION CIRCUIT POWERDISSIPATION (W)1.2

1.0

1.00.80.60.40.204.25

IBAT = 1AIBAT = 500mAIBAT = 1.5AVPROG (V)0.80.60.40.20

VBAT = 4VIBAT = 2A1.2

PROG Pin Characteristic (VPROG vs IPROG)VIN = 5V2.0

Output Charging Characteristic Showing Constant Current and Constant Voltage OperationIBAT (A)15

40011 G05

VBAT = 3.2VVBAT = 3.5VVBAT = 3.7VVBAT = 4V1.5

1.0

0.5

4.54.75VIN (V)

55.255.5

40011 G04

0510IPROG (mA)

00.511.5

22.5VBAT (V)

33.54

40011 G06

Trickle Charge Current vs VBAT55

FLOAT AND RECHARGE VOLTAGES (V)4.2

VFLOAT and Recharge Battery Threshold Voltage vs TemperatureVIN = 5.5V50IBAT (mA)VIN = 5V4.1

VFLOAT45

VIN = 4VVIN = 4.5VVRECHARGE(VBAT FALLING)4.0

00.51

1.5VBAT (V)

22.53

40011 G07

3.9

–50–30–101030507090110130150

TEMPERATURE (°C)

40011 G08

40011fa4LTC4001-1TYPICAL PERFORMANCE CHARACTERISTICS

Soft-Start (PWM Mode)400

INPUT

CURRENT (IIN)

0.5A/DIV

350

300IDET (mA)250200150100

VBAT = 3.5VVIN = 5V

2ms/DIV

40011 G09

IDET Threshold vs RIDET for RPROG = 549ΩCHRG Pin Temperature Fault Behavior (Detail)INDUCTORCURRENT (IL)

0.5A/DIV

SOFT-STARTVOLTAGE (VSS)

1V/DIV0ENPIN (VEN)

5V/DIV0

CHRG1V/DIV

300400500600700800900100011001200

RIDET (Ω)

40011 G10

TIME (20μs/DIV)

40011 G11

PIN FUNCTIONS

BAT (Pin 1): Battery Charger Output Terminal. Connect a 10μF ceramic chip capacitor between BAT and PGND to keep the ripple voltage small.SENSE (Pin 2): Internal Sense Resistor. Connect to ex-ternal inductor.PGND (Pin 3): Power Ground.GNDSENS (Pin 4): Ground Sense. Connect this pin to the negative battery terminal. GNDSENS provides a Kelvin connection for PGND and must be connected to PGND schematically.SW (Pin 5): Switch Node Connection. This pin connects to the drains of the internal main and synchronous power MOSFET switches. Connect to external inductor.EN (Pin 6): Enable Input Pin. Pulling the EN pin high places the LTC4001-1 into a low power state where the BAT drain current drops to less than 3μA and the supply current is reduced to less than 50μA. For normal opera-tion, pull the pin low.CHRG (Pin 7): Open-Drain Charge Status Output. When the battery is being charged, CHRG is pulled low by an internal N-channel MOSFET. When the charge current drops below the IDET threshold (set by the RIDET programming resistor) for more than 5milliseconds, the N-channel MOSFET turns off and a 30μA current source is connected from CHRG to ground. (This signal is latched and is reset by initiating a new charge cycle.) When the timer runs out or the input supply is removed, the current source will be disconnected and the CHRG pin is forced to a high impedance state. A temperature fault causes this pin to blink.PVIN (Pin 8): Positive Supply Voltage Input. This pin con-nects to the power devices inside the chip. VIN ranges from 4V to 5.5V for normal operation. Operation down to the undervoltage lockout threshold is allowed with cur-rent limited wall adapters. Decouple with a 10μF or larger surface mounted ceramic capacitor.VINSENSE (Pin 9): Positive Supply Sense Input. This pin connects to the inputs of all input comparators (UVL, VIN to VBAT). It also supplies power to the controller portion of this chip. When the BATSENS pin rises to within 30mV of VINSENSE, the LTC4001-1 enters sleep mode, dropping IIN to 50μA. Tie this pin directly to the terminal of the PVIN decoupling capacitor.FAULT (Pin 10): Battery Fault. This pin is a logic high if a shorted battery is detected or if a temperature fault is detected. A temperature fault occurs with the temperature monitor circuit enabled and the thermistor temperature is either below 0°C or above 50°C (typical).40011fa5LTC4001-1PIN FUNCTIONS

NTC (Pin 11): Input to the NTC (Negative Temperature Coefﬁ cient) Thermistor Temperature Monitoring Circuit. Under normal operation, tie a thermistor from the NTC pin to the GNDSENS pin and a resistor of equal value from NTC to VIN. When the voltage on this pin is above 0.74VIN (Cold, 0°C) or below 0.29VIN (Hot, 50°C), charging is disabled and the CHRG pin blinks. When the voltage on NTC comes back between 0.74VIN and 0.29VIN, the timer continues where it left off and charging resumes. There is approximately 3°C of temperature hysteresis associated with each of the input comparators. If the NTC function is not used connect the NTC pin to GNDSENS. This will disable all of the NTC functions. NTC should never be pulled above VIN.PROG (Pin 12): Charge Current Program. The RPROG resistor connects from this pin to GNDSENS, setting the current:1.110k

RPROG=

IBAT(AMPS)

where IBAT is the high rate battery charging current.IDET (Pin 13): Charge Rate Detection Threshold. Connect-ing a resistor, RIDET to GNDSENS programs the charge rate detection threshold. If RIDET = RPROG, CHRG provides an IBAT/10 indication. For other thresholds see the Applica-tions Information section.SS (Pin 14): Soft-Start/Compensation. Provides soft-start function and compensation for the ﬂ oat voltage control loop and compensation for the charge current control loop. Tie a soft-start/compensation capacitor between this pin and GNDSENS.TIMER (Pin 15): Timer Capacitor. The timer period is set by placing a capacitor, CTIMER, to GNDSENS. Set CTIMER to: CTIMER = Time (Hrs) • 0.0733 (μF)where time is the desired charging time.Connect this pin to IDET to disable the timer. Connect this pin to GNDSENS to end battery charging when IBAT drops below the IDET charge rate threshold.BATSENS (Pin 16): Battery Sense Input. An internal resistor divider sets the ﬁ nal ﬂ oat voltage at this pin. The resistor divider is disconnected in sleep mode or when EN = H to reduce the battery drain current. Connect this pin to the positive battery terminal.Exposed Pad (Pin 17): Ground. This pin must be soldered to the PCB ground (PGND) for electrical contact and rated thermal performance. 40011fa6+PVINBATSDRIVERQCURRENTREVERSALCOMPARATOROVERCURRENTCOMPARATORSHUTDOWNCOMPARATORPGNDSWSENSE50mAVINSENSEBATSENS+835+21916OSCILLATORCLKBLOCK DIAGRAM

SSLOW-BATTERYCOMPARATOR14PWM ONIDETCOMPARATORUNDERVOLTAGECOMPARATORSSTRICKLE ONSHUTDOWNLOW BATTERYOVERCURRENT–+RECHARGE–COMPARATOR7LOGIC1.2VCHRGCHRG10DISCHARGE SSPROG SHORTED1.1VSS LOWOVERVOLTAGEPROG SHORTCOMPARATORFAULTPROGERRORAMPCHARGE CURRENTERROR AMPFAULTSOFT-STARTCOPMPARATOR150mVCHIPOVERTEMPCOMPARATORCONNECTCHIP OVER TEMPGND17IDET13PROG124+–11NTCNTCCOMPARATORTFAULTBATTERYOVERVOLTAGECOMPARATORVOLTAGEREFERENCE+–15TIMER+––+FLOAT VOLTAGEERROR AMPTIMER+–6ENENLOW CURRENTVIN GOODRECHARGE+––+–+––+++–1.2VRAMPRD–PWMCOMPARATOR–GNDSENS40011 BDLTC4001-140011fa7LTC4001-1OPERATION

The LTC4001-1 is a constant current, constant voltage Li-Ion battery charger based on a synchronous buck architecture. Low power dissipation makes continuous high rate (2A) battery charging practical. The battery DC charge current is programmed by a resistor RPROG (or a DAC output current) at the PROG pin. The ﬁ nal battery ﬂ oat voltage is internally set to 4.1V.Charging begins when the VIN voltage rises above the UVLO level (approximately 2.75V), VIN is 250mV greater than the battery voltage and EN is low. At the beginning of the charge cycle, if the battery voltage is less than the trickle charge threshold, 3V, the charger goes into trickle charge mode and delivers approximately 50mA to the bat-tery using a linear charger. If the battery voltage stays low for more than one quarter of the charge time, the battery is considered faulty, the charge cycle is terminated and the FAULT pin produces a logic high output.When the battery voltage exceeds the trickle charge threshold, the low rate linear charger is turned off and the high rate PWM charger ramps up (based on the SS pin capacitance) reaching its full-scale constant current (set via the PROG pin). When the battery approaches the ﬂ oat voltage, the charge current will start to decrease. When the charge current drops below the charge rate detec-tion threshold (set via the IDET pin) for more than 5ms, an internal comparator turns off the internal pull-down N-channel MOSFET at the CHRG pin, and connects a weak current source (30μA typical) to ground to indicate a near end-of-charge condition.Total charge time is set by an external capacitor connected to the timer pin. After timeout occurs, the charge cycle is terminated and the CHRG pin is forced to a high impedance state. To restart the charge cycle, remove and reapply the input voltage, or momentarily shut the charger down via the EN pin. Also, a new charge cycle will begin if the bat-tery voltage drops below the recharge threshold voltage (100mV below the ﬂ oat voltage). A recharge cycle lasts only one-half of the normal charge time. A negative temperature coefﬁ cient (NTC) thermistor located close to the battery pack can be used to monitor battery temperature and suspend charging when battery tempera-ture is outside the 0°C to 50°C window. A temperature fault drives the FAULT pin high and makes the CHRG pin blink. When the input voltage (VIN) is present, the charger can be shut down by pulling the EN pin up.IDET BlankingThe IDET comparator provides an end-of-charge indication by sensing when battery charge current is less than the IDET threshold. To prevent a false end-of-charge indication from occurring during soft-start, this comparator is blanked until the battery voltage approaches the ﬂ oat voltage.Automatic Battery RechargeAfter the charge cycle is completed and if both the battery and the input power supply (wall adapter) are still con-nected, a new charge cycle will begin if the battery voltage drops below 4V due to self-discharge or external loading. This will keep the battery near maximum capacity at all times without manually restarting the charge cycle. In some applications such as battery charging in GPRS cellphones, large load current transients may cause battery voltage to momentarily drop below the recharge threshold. To prevent these transients from initiating a recharge cycle when it is not needed, the output of the recharge compara-tor is digitally qualiﬁ ed. Only if the battery voltage stays below the recharge threshold for at least 4ms will battery recharging occur. (GPRS qualiﬁ cation is available even if timeout is disabled.)Undervoltage Lockout and Automatic ShutdownInternal undervoltage lockout circuits monitor VIN and keep the charger circuits shut down until VIN rises above the undervoltage lockout threshold (3V). The UVLO has a built-in hysteresis of 100mV. Furthermore, to protect against reverse current, the charger also shuts down if VIN is less than VBAT. If automatic shutdown is tripped, VIN must increase to more than 250mV above VBAT to allow charging.40011fa8LTC4001-1OPERATION

Overvoltage, Chip Overtemperature and Short-Circuit Current ProtectionThe LTC4001-1 includes overvoltage, chip overtemperature and several varieties of short-circuit protection. A comparator turns off both chargers (high rate and trickle) if battery voltage exceeds the ﬂ oat voltage by ap-proximately 5%. This may occur in situations where the battery is accidentally disconnected while battery charging is underway.A comparator continuously monitors on-chip temperature and will shut off the battery charger when chip temperature exceeds approximately 160°C. Battery charging will be enabled again when temperature drops to approximately 150°C.Short-circuit protection is provided in several different ways. First, a hard short on the battery terminals will cause the charge to enter trickle charge mode, limiting charge current to the trickle charge current (typically 50mA). Second, PWM charging is prevented if the high rate charge current is programmed far above the 2A maximum recommended charge current (via the PROG pin). Third, an overcurrent comparator monitors the peak inductor current.40011fa9LTC4001-1APPLICATIONS INFORMATION

Soft-Start and Compensation Capacitor SelectionThe LTC4001-1 has a low current trickle charger and a PWM-based high current charger. Soft-start is used when-ever the high rate charger is initially turned on, preventing high start-up current. Soft-start ramp rate is set by the internal 12.8μA pull-up current and an external capacitor. The control range on the SS pin is approximately 0.3V to 1.6V. With a 0.1μF capacitor, the time to ramp up to maximum duty cycle is approximately 10ms.The external capacitor on the SS pin also sets the compensa-tion for the current control loop and the ﬂ oat voltage control loop. A minimum capacitance of 10nF is required.Charge Current and IDET ProgrammingThe LTC4001-1 has two different charge modes. If the battery is severely depleted (battery voltage less than 2.9V) a 50mA trickle current is initially used. If the battery voltage is greater than the trickle charge threshold, high rate charging is used.This higher charge current is programmable and is ap-proximately 915 times the current delivered by the PROG pin. This current is usually set with an external resistor from PROG to GNDSENS, but it may also be set with a current output DAC connected to the PROG pin. The volt-age on the PROG pin is nominally 1.213V.For 2A charge current: RPROG=

915•1.213V

󰀁554.9󰀂

The IDET threshold (a charge current threshold used to determine when the battery is nearly fully charged) is programmed in much the same way as the PROG pin, except that the IDET threshold is 91.5 times the current delivered by the IDET pin. This current is usually set with an external resistor from IDET to ground, but it may also be set with a current output DAC. The voltage on the PROG pin is nominally 1.213V. For 200mA IDET current (corresponding to C/10 for a 2AHr battery): RIDET=

91.5•1.213V

󰀁554.9󰀂

0.2A

1.10kΩ programs approximately 100mA and 274Ω ap-proximately 400mA.For applications where IDET is set to one tenth of the high rate charge current, and slightly poorer charger current and IDET threshold accuracy is acceptable, the PROG and IDET pins may be tied together and a single resistor, R1, can program both (Figure 1).R1= and IDET=

ICHARGE10457.5•1.213ICHARGE

LTC4001-1PROGIDETR1274Ω FOR 2AGNDSENS40011 F01

Figure 1. Programming Charge Current and IDET Threshold with a Single Resistor40011fa10LTC4001-1APPLICATIONS INFORMATION

The equations for calculating R1 (used in single resistor programming) differ from the equations for calculating ect RPROG and RIDET (2-resistor programming) and reﬂthe fact that the current from both the IDET and PROG pins must ﬂ ow through a single resistor R1 when a single programming resistor is used.CHRG Status Output PinWhen a charge cycle starts, the CHRG pin is pulled to ground by an internal N-channel MOSFET which is capable of driving an LED. When the charge current drops below the end-of-charge (IDET) threshold for at least 4ms, and the battery voltage is close to the ﬂ oat voltage, the N-channel MOSFET turns off and a weak 30μA current source to ground is connected to the CHRG pin. This weak pull-down remains until the charge cycle ends. After charging ends, the pin will become high impedance. By using two different value resistors, a microprocessor can detect three states from this pin (charging, end-of-charge and charging stopped). See Figure 2.To detect the charge mode, force the digital output pin, OUT, high and measure the voltage on the CHRG pin. The N-channel MOSFET will pull the pin low even with a 2k pull-up resistor. Once the charge current drops below the end-of-charge threshold, the N-channel MOSFET is turned off and a 30μA current source is connected to the CHRG pin. The IN pin will then be pulled high by the 2k resistor connected to OUT. Now force the OUT pin into a high impedance state, the current source will pull the pin low through the 390k resistor. When charging stops, the CHRG pin changes to a high impedance state and the 390k resistor will then pull the pin high to indicate charg-ing has stopped.Charge TerminationBattery charging may be terminated several different ways, depending on the connections made to the TIMER pin. For time-based termination, connect a capacitor between the TIMER pin and GNDSENS (CTIMER = Time(Hrs) 0.0733μF). Charging may be terminated when charge current drops below the IDET threshold by tying TIMER to GNDSENS. Finally, charge termination may be defeated by tying TIMER to IDET. In this case, an external device can terminate charging by pulling the EN pin high.Battery Temperature DetectionWhen battery temperature is out of range (either too hot or too cold) charging is temporarily halted and the FAULT pin is driven high. In addition, if the battery is still charg-ing at a high rate (greater than the IDET current) when a temperature fault occurs, the CHRG pin NMOS turns on and off at approximately 50kHz, alternating between a high and low duty factor at an approximate rate of 1.5Hz (Figure 3). This provides a low rate visual indication (1.5Hz) when driving an LED from the CHRG pin while providing a fast temperature fault indication (20μs typical) to a mi-croprocessor by tying the CHRG pin to an interrupt line. Serrations within this pulse are typically 500ns wide.VINVDDLTC4001-1CHRGR1390kR22kμPROCESSOROUTIN40011 F02

20μs667ms40011 F03Figure 2. Microprocessor InterfaceFigure 3. CHRG Temperature Fault Waveform40011fa11LTC4001-1APPLICATIONS INFORMATION

The battery temperature is measured by placing a negative temperature coefﬁ cient (NTC) thermistor close to the bat-tery pack. To use this feature, connect the NTC thermistor, RNTC, between the NTC pin and GNDSENS and the resistor, RNOM, from the NTC pin to VINSENSE. RNOM should be a 1% resistor with a value equal to the value of the chosen NTC thermistor at 25°C. The LTC4001-1 goes into hold mode when the resistance, RHOT, of the NTC thermistor drops to 0.41 times the value of RNOM. For instance for RNTC = 10k. (The value for a Vishay NTHS0603N02N1002J thermistor at 25°C) hold occurs at approximately 4.1k, which occurs at 50°C. The hold mode freezes the timer and stops the charge cycle until the thermistor indicates a return to a valid temperature. As the temperature drops, the resistance of the NTC thermistor rises. The LTC4001-1 is designed to go into hold mode when the value of the NTC thermistor increases to 2.82 times the value of RNOM. This resistance is RCOLD. For the Vishay 10k thermistor, this value is 28.2k, which corresponds to approximately 0°C. The hot and cold comparators each have approximately 3°C of hysteresis to prevent oscillation about the trip point. Grounding the NTC pin disables the NTC function.ThermistorsThe LTC4001-1 NTC trip points were designed to work with thermistors whose resistance temperature characteristics follow Vishay Dale’s “R-T Curve 2.” However, any thermis-tor whose ratio of RCOLD to RHOT is about 7 will also work (Vishay Dale R-T Curve 2 shows a ratio of RCOLD to RHOT of 2.815/0.4086 = 6.89). Power conscious designs may want to use thermistors whose room temperature value is greater than 10k. Vishay Dale has a number of values of thermistor from 10k to 100k that follow the “R-T Curve 1.” Using these as indicated in the NTC Thermistor section will give temperature trip points of approximately 3°C and 47°C, a delta of 44°C. This delta in temperature can be moved in either direction by changing the value of RNOM with respect to RNTC. Increasing RNOM will move the trip points to higher temperatures. To calculate RNOM for a shift to lower temperature for example, use the following equation:R

RNOM=COLD•RNTCat25°C

2.815 where RCOLD is the resistance ratio of RNTC at the desired cold temperature trip point. If you want to shift the trip points to higher temperatures use the following equation: RNOM=

RHOT•Rat25°C0.4086NTC

where RHOT is the resistance ratio of RNTC at the desired hot temperature trip point.Here is an example using a 100k R-T Curve 1 thermistor from Vishay Dale. The difference between trip points is 44°C, from before, and we want the cold trip point to be 0°C, which would put the hot trip point at 44°C. The RNOM needed is calculated as follows:RNOM= RCOLD•Rat25°C2.815NTC3.266

•100k=116k=

2.815

The nearest 1% value for RNOM is 115k. This is the value used to bias the NTC thermistor to get cold and hot trip points of approximately 0°C and 44°C respectively. To extend the delta between the cold and hot trip points a resistor, R1, can be added in series with RNTC (see Figure 4). The values of the resistors are calculated as follows:R–R

RNOM=COLDHOT2.815–0.40860.4086

•(RCOLD–RHOT)–RHOTR1=

2.815–0.4086 40011fa12LTC4001-1APPLICATIONS INFORMATION

VINSENSE9RNOM121kNTC11R113.3k0.74 • VINSENSELTC4001-1 NTC BLOCK–TOO COLD+–TOO HOT0.29 • VINSENSERNTC100k++0.02 • VINSENSEGNDSENS4NTC ENABLE–40011 F04

Figure 4. Extending the Delta Temperaturewhere RNOM is the value of the bias resistor, RHOT and RCOLD are the values of RNTC at the desired temperature trip points. Continuing the example from before with a desired hot trip point of 50°C:RNOM=RCOLD–RHOT100k•(3.2636–0.3602)=2.815–0.40862.815–0.4086=120.8k,121kisnearest1%capacitor is recommended for both the input and output capacitors because it provides low ESR and ESL and can handle the high RMS ripple currents. However, some high Q capacitors may produce high transients due to self-resonance under some start-up conditions, such as connecting the charger input to a hot power source. For more information, refer to Application Note 88.EMI considerations usually make it desirable to minimize ripple current in the battery leads, and beads or inductors may be added to increase battery impedance at the 1.5MHz switching frequency. Switching ripple current splits be-tween the battery and the output capacitor depending on the ESR of the output capacitor and the battery impedance. If the ESR of the output capacitor is 0.1Ω and the battery impedance is raised to 2Ω with a bead or inductor, only 5% of the ripple current will ﬂ ow in the battery. Similar techniques may also be applied to minimize EMI from the input leads.0.4086󰀁󰀄R1=100k•󰀂•(3.266–0.3602)–0.3602󰀅󰀃2.815–0.4086󰀆=13.3k,13.3kisnearest1%The ﬁ nal solution is as shown if Figure 4 where RNOM = 121k, R1 = 13.3k and RNTC = 100k at 25°C.Input and Output CapacitorsThe LTC4001-1 uses a synchronous buck regulator to provide high battery charging current. A 10μF chip ceramic 40011fa13LTC4001-1APPLICATIONS INFORMATION

Inductor SelectionA high (1.5MHz) operating frequency was chosen for the buck switcher in order to minimize the size of the inductor. However, take care to use inductors with low core losses at this frequency. A good choice is the IHLP-2525AH-01 from Vishay Dale.To calculate the inductor ripple current:VBAT2

VBAT–

VIN󰀁IL=

L•f where VBAT is the battery voltage, VIN is the input voltage, L is the inductance and f is the PWM oscillator frequency (typically 1.5MHz). Maximum inductor ripple current oc-curs at maximum VIN and VBAT = VIN/2.Peak inductor current will be: IPK = IBAT + 0.5 • ΔILwhere IBAT is the maximum battery charging current.When sizing the inductor make sure that the peak current will not exceed the saturation current of the inductors. Also, ΔIL should never exceed 0.4(IBAT) as this may in-terfere with proper operation of the output short-circuit protection comparator. 1.5μH provides reasonable inductor ripple current in a typical application. With 1.5μH and 2A charge current:2.85V2

2.85V–

5.5V=0.61A󰀁IL=P-P

1.5μH•1.5MHz and IPK = 2.31ARemote SensingFor highest ﬂ oat voltage accuracy, tie GNDSENS and BATSENS directly to the battery terminals. In a similar fash-ion, tie BAT and PGND directly to the battery terminals. This eliminates IR drops in the GNDSENS and BATSENS lines by preventing charge current from ﬂ owing in them.Operation with a Current Limited Wall AdapterWall adapters with or without current limiting may be used with the LTC4001-1, however, lowest power dissipation battery charging occurs with a current limited wall adapter. To use this feature, the wall adapter must limit at a current smaller than the high rate charge current programmed into the LTC4001-1. For example, if the LTC4001-1 is programmed to charge at 2A, the wall adapter current limit must be less than 2A.To understand operation with a current limited wall adapter, assume battery voltage, VBAT, is initially below VTRIKL, the trickle charge threshold (Figure 5). Battery charging begins at approximately 50mA, well below the wall adapter current limit so the voltage into the LTC4001-1 (VIN) is the wall adapter’s rated output voltage (VADAPTER). Battery voltage rises eventually reaching VTRIKL. The linear charger shuts off, the PWM (high rate) charger turns on and a soft-start cycle begins. Battery charging current rises during the soft-start cycle causing a corresponding increase in wall adapter load current. When the wall adapter reaches current limit, the wall adapter output voltage collapses and the LTC4001-1 PWM charger duty cycle ramps up to 100% (the topside PMOS switch in the LTC4001-1 buck regulator stays on continuously). As the battery voltage oat voltage error ampliﬁ er com-approaches VFLOAT, the ﬂmands the PWM charger to deliver less than ILIMIT. The wall adapter exits current limit and the VIN jumps back up 40011fa14LTC4001-1APPLICATIONS INFORMATION

LINEAR CHARGING

VADAPTER

VIN

WALL ADAPTER IN CURRENT LIMIT

PWMCHARGING

VBAT + VDROP

ILIMIT

IBAT

ITRICKLE

40011 F05

VTRIKL

VBAT

VFLOAT

Figure 5. Charging Characteristicto VADAPTER. Battery charging current continues to drop as the VBAT rises, dropping to zero at VFLOAT. Because the voltage drop in the LTC4001-1 is very low when charge current is highest, power dissipation is also very low.Thermal Calculations (PWM and Trickle Charging)The LTC4001-1 operates as a linear charger when condition-ing (trickle) charging a battery and operates as a high rate buck battery charger at all other times. Power dissipation should be determined for both operating modes.For linear charger mode: PD = (VIN – VBAT) • ITRIKL + VIN • IINwhere IIN is VIN current consumed by the IC.Worst-case dissipation occurs for VBAT = 0, maximum VIN, and maximum quiescent and trickle charge current. For example with 5.5V maximum input voltage and 65mA worst case trickle charge current, and 2mA worst case chip quiescent current: PD = (5.5 – 0) • 65mA + 5.5 • 2mA = 368.5mWLTC4001-1 power dissipation is very low if a current limited wall adapter is used and allowed to enter current limit. When the wall adapter is in current limit, the voltage drop across the LTC4001-1 charger is: VDROP = ILIMIT • RPFETwhere ILIMIT is the wall adapter current limit and RPFET is the on resistance of the topside PMOS switch.The total LTC4001-1 power dissipation during current limited charging is: PD = (VBAT + VDROP) • (IIN + IP) + VDROP • ILIMITwhere IIN is the chip quiescent current and IP is total cur-rent ﬂ owing through the IDET and PROG programming pins. Maximum dissipation in this mode occurs with the highest VBAT that keeps the wall adapter in current limit (which is very close to VFLOAT), highest quiescent current IIN, highest PMOS on resistance RPFET, highest ILIMIT and highest programming current IP.Assume the LTC4001-1 is programmed for 2A charging and 200mA IDET and that a 1.5A wall adapter is being used: ILIMIT = 1500mA, RPFET = 127mΩ, IIN = 2mA, IP = 4mA and VBAT ≈ VFLOAT = 4.141Vthen: VDROP = 1500mA • 127mΩ = 190.5mVand: PD = (4.141V + 0.1905V) • (2mA + 4mA) + 0.1905V • 1500mA = 312mWPower dissipation in buck battery charger mode may be estimated from the dissipation curves given in the Typical Performance Characteristics section of the data sheet. This will slightly overestimate chip power dissipation because it assumes all loss, including loss from external components, occurs within the chip.40011fa15LTC4001-1APPLICATIONS INFORMATION

Insert the highest power dissipation ﬁ gure into the following equation to determine maximum junction temperature: TJ = TA + (PD • 37°C/W)The LTC4001-1 includes chip overtemperature protection. If junction temperature exceeds 160°C (typical), the chip will stop battery charging until chip temperature drops below 150°C.Using the LTC4001-1 in Applications Without a BatteryThe LTC4001-1 is normally used in end products that only operate with the battery attached (Figure 6). Under these conditions the battery is available to supply load transient currents. For indeﬁ nite operation with a powered wall adapter there are only two requirements—that the aver-age current drawn by the load is less than the high rate charge current, and that VBAT stays above the trickle charge threshold when the load is initially turned on and during other load transients. When making this determination take into account battery impedance. If battery voltage is less than the trickle charge threshold, the system load may be turned off until VBAT is high enough to meet these conditions.The situation changes dramatically with the battery re-moved (Figure 7). Since the battery is absent, VBAT begins at zero when a powered wall adapter is ﬁ rst connected to the battery charger. With a maximum load less than the LTC4001-1 trickle charge current, battery voltage will ramp up until VBAT crosses the trickle charge threshold. When this occurs, the LTC4001-1 switches over from trickle charge to high rate (PWM) charge mode but initially delivers zero current (because the soft-start pin is at zero). Battery volt-age drops as a result of the system load, crossing below the trickle charge threshold. The charger re-enters trickle charge mode and the battery voltage ramps up again until the battery charger re-enters high rate mode.The soft-start voltage is slightly higher this time around (than in the previous PWM cycle). Every successive time that the charger enters high rate (PWM) charge mode, the soft-start pin is at a slightly higher voltage. Eventually high rate charge mode begins with a soft-start voltage that causes the PWM charger to provide more current than the oat system load demands, and VBAT rapidly rises until the ﬂvoltage is reached.For battery-less operation, system load current should be restricted to less than the worst case trickle charge current (preferably less than 30mA) when VBAT is less than 3.15V (through an undervoltage lockout or other means). Above VBAT = 3.15V, system load current less than or equal to the high rate charge current is allowed. If operation without a battery is required, additional low-ESR output ﬁ ltering improves start-up and other load transients. Battery-less start-up is also improved if a 10k resistor is placed in series with the soft-start capacitor.WALLADAPTERLTC4001-1BATTERYCHARGERSYSTEMLOAD+40011 F06Li-IonBATTERYFigure 6. Typical Application40011fa16LTC4001-1APPLICATIONS INFORMATION

VBAT (V)3

00500

1214

TIME (ms)

VSS (mV)250

1214TIME (ms)

PWMCHARGE

TRICKLECHARGE

0246810

1214TIME (ms)

1618202224

40011 F07

Figure 7. Battery-Less Start-Up40011fa17LTC4001-1APPLICATIONS INFORMATION

Layout Considerations Switch rise and fall times are kept under 5ns for maximum efﬁ ciency. To minimize radiation, the SW pin and input bypass capacitor leads (between PVIN and PGND) should be kept as short as possible. A ground plane should be used under the switching circuitry to prevent interplane coupling. The Exposed Pad must be connected to the ground plane for proper power dissipation. The other paths contain only DC and/or 1.5MHz tri-wave ripple current and are less critical.With the exception of the input and output ﬁ lter ca-pacitors (which should be connected to PGND) all other components that return to ground should be connected to GNDSENS. Recommended Components ManufacturersFor a list of recommend component manufacturers, contact the Linear Technology application department.L11.5μHSWSENSEVIN4.5V TO 5.5VR110kC1R210μF1kD1LEDVINSENSEPVINPGNDCHRGNTCBATSENSBATC410μF+2AHr4.1VLi-Ion

LTC4001-1TO μPFROM μPR310kAT 25°CFAULTENPROGIDETC20.22μFR5549ΩTIMERSSGNDSENSR4549ΩC30.1μF40011 F08L1: VISHAY DALE IHLP-2525AH-01

R3: NTC VISHAY DALE NTHS0603N02N1002J

Figure 8. 2A Li-Ion Battery Charger with 3Hr Timer, Temperature Qualiﬁ cation, Soft-Start, Remote Sensing and C/10 Indication40011fa18LTC4001-1PACKAGE DESCRIPTION

UF Package16-Lead Plastic QFN (4mm × 4mm)(Reference LTC DWG # 05-08-1692)0.72 ±0.054.35 ± 0.052.15 ± 0.052.90 ± 0.05(4 SIDES)PACKAGE OUTLINE0.30 ±0.050.65 BSCRECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

BOTTOM VIEW—EXPOSED PAD

4.00 ± 0.10(4 SIDES)PIN 1TOP MARK(NOTE 6)2.15 ± 0.10(4-SIDES)0.75 ± 0.05R = 0.115TYPPIN 1 NOTCH R = 0.20 TYPOR 0.35 × 45° CHAMFER

15160.55 ± 0.2012(UF16) QFN 10-040.200 REF0.00 – 0.05NOTE:

1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WGGC)2. DRAWING NOT TO SCALE

3. ALL DIMENSIONS ARE IN MILLIMETERS

4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE

MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE5. EXPOSED PAD SHALL BE SOLDER PLATED

6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE

0.30 ± 0.050.65 BSC40011faInformation furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.19LTC4001-1RELATED PARTS

PART NUMBERDESCRIPTIONLT®1511LT1513LT1571LTC17293A Constant-Current/Constant-Voltage Battery ChargerCOMMENTSHigh Efﬁ ciency, Minimum External Components to Fast Charge Lithium, NIMH and NiCd Batteries, 24-Lead SO PackageSEPIC Constant or Programmable Current/Constant- Charger Input Voltage May Be Higher, Equal to or Lower Than Battery Voltage, Voltage Battery Charger500kHz Switching Frequency, DD Pak and TO-220 Packages1.5A Switching ChargerLi-Ion Battery Charger Termination Controller1- or 2-Cell Li-Ion, 500kHz or 200kHz Switching Frequency, Termination Flag, 16- and 28-Lead SSOP PackagesTrickle Charge Preconditioning, Temperature Charge Qualiﬁ cation,Time or Charge Current Termination, Automatic Charger and Battery Detection, and Status Output, MS8 and SO-8 PackagesConstant-Current/Constant-Voltage Switching Regulator, Input Current Limiting Maximizes Charge Current, 20-Lead TSSOP and 28-Lead SSOP Packages4.2V Float Voltage, Standalone, 4V ≤ VIN ≤ 5.5V, 6VMAX, 7V Transient,1.5MHz, Efﬁ ciency > 90%, 4mm × 4mm QFN-16 PackageComplete Charger for 1- or 2-Cell Li-Ion Batteries, Onboard Timer Termination, Up to 4A Charge Current, 10-Lead DFN and SO-8 PackagesComplete Charger for 2-, 3- or 4-Cell Li-Ion Batteries, AC Adapter Current Limit and Thermistor Sensor, 16-Lead Narrow SSOP PackageComplete Charger for 3- or 4-Cell Li-Ion Batteries, AC Adapter Current Limit, Thermistor Sensor and Indicator Outputs, 24-Lead SSOP PackageLT1769LTC4001LTC4002LTC4006LTC4007LTC40082A Switching ChargerMonolithic 2A Switchmode Synchronous Li-Ion Battery ChargerStandalone Li-Ion Switch Mode Battery ChargerSmall, High Efﬁ ciency, Fixed Voltage Li-Ion Battery Charger with TerminationHigh Efﬁ ciency, Programmable Voltage Battery Charger with Termination4A, High Efﬁ ciency, Multi-Chemistry Battery ChargerComplete Charger for 2- to 6-Cell Li-Ion Batteries or 4- to 18-Cell Nickel Batteries, Up to 96% Efﬁ ciency, 20-Lead SSOP Package40011fa20Linear Technology CorporationLT 1207 REV A • PRINTED IN USA

1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com© LINEAR TECHNOLOGY CORPORATION 2007

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