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| LTC4001 2A Synchronous Buck Li-Ion Charger FEATURES DESCRIPTIO Low Power Dissipation 2A Maximum Charge Current No External MOSFETs, Sense Resistor or Blocking Diode Required Remote Sensing at Battery Terminals Programmable Charge Termination Timer Preset 4.2V Float Voltage with 0.5% Accuracy Programmable Charge Current Detection/Termination Automatic Recharge Thermistor Input for Temperature Qualified Charging Compatible with Current Limited Wall Adapters Low Profile 16-Lead (4mm x 4mm) QFN Package The LTC(R)4001 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 includes complete charge termination circuitry, automatic recharge and a 1% 4.2V float voltage. Input short-circuit protection is included so no blocking diode is required. Battery charge current, charge timeout and end-of-charge indication parameters are set with external components. Additional features include shorted cell detection, temperature qualified charging and overvoltage protection. The LTC4001 is available in a low profile (0.75mm) 16-lead (4mm x 4mm) QFN package. , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. APPLICATIO S Handheld Battery-Powered Devices Handheld Computers Charging Docks and Cradles Digital Cameras Smart Phones TYPICAL APPLICATIO 2A Single Cell Li-Ion Battery Charger 1.5H SW VIN 4.5V TO 5.5V 10F PGND CHRG NTC FAULT EN PROG IDET TIMER 0.22F 274 0.1F 4001 TA01a SENSE 10F + 4.2V Li-Ion TOTAL APPLICATION CIRCUIT POWER DISSIPATION (W) VINSENSE PVIN BATSENS BAT LTC4001 SS GNDSENS U Power Loss vs VBAT Charging (PWM Mode) 1.25 1.00 0.75 0.50 0.25 VIN = 5V 2A CHARGER 0 3 3.25 3.75 3.5 VBAT (V) 4 4.25 4001 TA01b U U 4001f 1 LTC4001 ABSOLUTE (Note 1) AXI U RATI GS PACKAGE/ORDER I FOR ATIO TOP VIEW SW CHRG UF PACKAGE 16-LEAD (4mm x 4mm) PLASTIC QFN TJMAX = 125C, JA = 37C/W EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB ORDER PART NUMBER LTC4001EUF Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25C. VIN = 5V, VEN = 0V, RPROG = 549, RIDET = 549, unless otherwise specified. SYMBOL PARAMETER VIN IIN Supply Voltage CONDITIONS (Note 2) PVIN Connected to VINSENSE, PROG and IDET Pins Open, Charger On Shutdown, EN = VIN VFLOAT IBAT VBAT Regulated Float Voltage Current Mode Charge Current Measured from BATSENS to GNDSENS RPROG = 549, VBAT = 3.5V RPROG = 1.10k, VBAT = 3.5V Shutdown, EN = VIN VBAT = 2V VBAT Rising VBAT Falling VIN Rising, Measured from VINSENSE to GNDSENS VINSENSE - VBATSENS Rising (Turn-On), VBATSENSE = 4V VINSENSE - VBATSENS Falling (Turn-Off), VBATSENSE = 4V MIN 4 PVIN PVIN, 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 6V Operating Temperature Range (Note 3) .. - 40C to 85C Operating Junction Temperature (Note 5) ............................................... - 40C to 125C Storage Temperature Range ................ - 65C to 125C BATSENS TIMER 16 15 14 13 BAT 1 SENSE 2 PGND 3 GNDSENS 4 5 6 7 8 17 12 PROG 11 NTC 10 FAULT 9 VINSENSE EN IDET SS UF PART MARKING 4001 TYP MAX 5.5 2 50 UNITS V mA A V V A A A mA V V V mV mV mV MHz % m m 4001f 4.158 4.179 1.8 0.9 35 3.05 2.85 2.7 4.2 4.2 2 1 50 3.1 3.0 100 4.242 4.221 2.2 1.1 5 65 3.20 3.05 2.82 ITRIKL VTRIKL VUVL VUVL VASD fOSC D RPFET RNFET Trickle Charge Current Trickle Charge Threshold VIN Undervoltage Lockout Voltage Automatic Shutdown Threshold Voltage Oscillator Frequency Maximum Duty Factor RDS(ON) of P-Channel MOSFET RDS(ON) of N-Channel MOSFET VIN Undervoltage Lockout Hysteresis Measured from VINSENSE to GNDSENS 200 15 1.3 Measured from PVIN to SW Measured from SW to PGND 250 30 1.5 127 121 300 60 1.7 100 2 U W U U WW W LTC4001 ELECTRICAL CHARACTERISTICS The denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25C. VIN = 5V, VEN = 0V, RPROG = 549, RIDET = 549, unless otherwise specified. SYMBOL PARAMETER tTIMER VEN VEN VPROG VIDET IIDET ICHRG VCHRG VOL VOH VRECHRG tRB tRECHRG tTRIKL ISS VCOLD Timer Accuracy Enable Input Threshold Voltage Enable Input Hysteresis PROG Pin Voltage IDET Pin Voltage IDET Threshold CHRG Pin Weak Pull-Down Current CHRG Pin Output Low Voltage FAULT Pin Output Low Voltage FAULT Pin Output High Voltage Recharge Battery Threshold Voltage Recharge Filter Time Constant Recharge Time Low-Battery Trickle Charge Time Soft-Start Ramp Current NTC Pin Cold Temperature Fault Threshold NTC Pin Hot Temperature Fault Threshold NTC Disable Threshold (Falling) NTC Disable Hysteresis Percent of Total Charge Time Percent of Total Charge Time, VBAT < 2.8V, Measured Using BATSENS and GNDSENS Pins VBAT < VFLOAT - 100mV, VBAT Across BATSENS and GNDSENS Pins From NTC to GNDSENS Pin Rising Threshold Falling Threshold From NTC to GNDSENS Pin Falling Threshold Rising Threshold From NTC to GNDSENS Pin From NTC to GNDSENS Pin 6 RPROG = 549 RIDET = 549 RIDET = 549 VCHRG = 1V ICHRG = 5mA 1mA Load 1mA Load VFLOAT - VRECHRG VBAT Falling 4.6 50 4 50 25 12.8 16 100 135 150 15 CONDITIONS CTIMER = 0.22F VEN Rising 0.6 MIN TYP 10 0.8 100 1.213 1.213 200 30 0.2 250 50 0.4 0.4 1 MAX UNITS % V mV V V mA A V V V mV ms % % A 0.74 VINSENSE 0.72 VINSENSE 0.29 VINSENSE 0.30 VINSENSE 0.015 * 0.02 * 0.025 * VINSENSE VINSENSE VINSENSE 0.01 * VINSENSE V V V V V V VHOT VDIS VDIS Note 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 is guaranteed to meet performance specifications from 0C to 85C. Specifications over the - 40C to 85C 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 dissipation PD according to the following formula: TJ = TA + (PD * 37C/W) Note 5: This IC includes overtemperature protection that is intended to protect the device during momentary overload. Junction temperature will exceed 125C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature my impair device reliability. 4001f 3 LTC4001 TYPICAL PERFOR A CE CHARACTERISTICS (TA = 25C unless otherwise noted) Oscillator Frequency vs VIN 1.00 0.75 FREQUENCY VARIATION FROM 25C (%) PERCENT VARIATION (%) 0.50 0.25 0 -0.25 -0.50 -0.75 -1.00 3 3.5 4 4.5 VIN (V) 5 5.5 6 4001 G01 0.6 TOTAL APPLICATION CIRCUIT POWER DISSIPATION (W) VBAT = 3.2V VSS = 1V Dissipation of Figure 8 Circuit vs VIN 1.4 VBAT = 4V TOTAL APPLICATION CIRCUIT POWER DISSIPATION (W) IBAT = 2A 1.2 1.0 0.8 0.6 0.4 0.2 0 4.25 IBAT = 1A IBAT = 500mA IBAT = 1.5A VPROG (V) IBAT (A) 4.5 4.75 VIN (V) 5 Trickle Charge Current vs VBAT 55 FLOAT AND RECHARGE VOLTAGES (V) 50 IBAT (mA) 45 40 0 0.5 1 1.5 VBAT (V) 2 2.5 3 4001 G07 4 UW 5.25 Oscillator Frequency vs Temperature 0.8 VIN = 5V VBAT = 3.2V VSS = 1V 1.25 Dissipation of Figure 8 Circuit vs IBAT VIN = 5V VBAT = 4V 1.00 0.4 0.75 0.2 0.50 0 0.25 -0.2 -50 -30 -10 10 30 50 70 90 110 130 150 TEMPERATURE (C) 4001 G02 0 500 1000 IBAT (mA) 1500 2000 4001 G03 PROG Pin Characteristic (VPROG vs IPROG) 1.2 1.0 0.8 0.6 0.4 0.5 Output Charging Characteristic Showing Constant Current and Constant Voltage Operation VIN = 5V 2.0 VBAT = 3.2V VBAT = 3.5V VBAT = 3.7V VBAT = 4V 1.5 1.0 0.2 0 0 5 10 IPROG (mA) 4001 G04 5.5 15 20 4001 G05 0 0 0.5 1 1.5 2 2.5 VBAT (V) 3 3.5 4 4001 G06 VFLOAT and Recharge Battery Threshold Voltage vs Temperature 4.3 VIN = 5.5V VIN = 5V VFLOAT 4.2 VIN = 4V VIN = 4.5V VRECHARGE (VBAT FALLING) 4.1 4.0 -50 -30 -10 10 30 50 70 90 110 130 150 TEMPERATURE (C) 4001 G08 4001f LTC4001 TYPICAL PERFOR A CE CHARACTERISTICS Soft-Start (PWM Mode) 400 INPUT CURRENT (IIN) 0.5A/DIV 0 INDUCTOR CURRENT (IL) 0.5A/DIV 0 SOFT-START VOLTAGE (VSS) 1V/DIV 0 EN PIN (VEN) 5V/DIV 0 VBAT = 3.5V VIN = 5V 2ms/DIV IDET (mA) PI FU CTIO S BAT (Pin 1): Battery Charger Output Terminal. Connect a 10F ceramic chip capacitor between BAT and PGND to keep the ripple voltage small. SENSE (Pin 2): Internal Sense Resistor. Connect to external 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 into a low power state where the BAT drain current drops to less than 3A and the supply current is reduced to less than 50A. For normal operation, 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 30A 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 connects 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 current limited wall adapters. Decouple with a 10F 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 enters sleep mode, dropping IIN to 50A. Tie this pin directly to the terminal of the PVIN decoupling capacitor. UW IDET Threshold vs RIDET for RPROG = 549 350 300 250 200 150 100 4001 G09 CHRG Pin Temperature Fault Behavior (Detail) CHRG 1V/DIV 50 0 300 400 500 600 700 800 900 1000 1100 1200 RIDET () 4001 G10 TIME (20s/DIV) 4001 G11 U U U 4001f 5 LTC4001 PI FU CTIO S 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 0C or above 50C (typical). NTC (Pin 11): Input to the NTC (Negative Temperature Coefficient) 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, 0C) or below 0.29VIN (Hot, 50C), 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 3C 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: RPROG = 1.110 k IBAT( AMPS) where IBAT is the high rate battery charging current. 6 U U U IDET (Pin 13): Charge Rate Detection Threshold. Connecting 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 Applications Information section. SS (Pin 14): Soft-Start/Compensation. Provides soft-start function and compensation for the float 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 (F) 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 final float 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. 4001f 8 3 5 2 1 9 16 VINSENSE BATSENS BAT 50mA SENSE PGND SW PVIN S DRIVER Q OSCILLATOR CLK RAMP BLOCK DIAGRA SS LOW-BATTERY COMPARATOR 14 SS IDET COMPARATOR UNDERVOLTAGE COMPARATOR PWM ON TRICKLE ON SHUTDOWN OVERCURRENT LOW BATTERY -+ + - RECHARGE COMPARATOR 7 LOGIC 1.2V CHRG CHRG PROG ERROR AMP CHARGE CURRENT ERROR AMP 10 DISCHARGE SS PROG SHORTED 1.1V SS LOW OVERVOLTAGE FAULT FAULT SOFT-START COPMPARATOR CHIP OVERTEMP COMPARATOR CONNECT CHIP OVER TEMP GND 17 IDET 13 PROG 12 4 + - 11 NTC NTC COMPARATOR TFAULT 150mV BATTERY OVERVOLTAGE COMPARATOR + - VOLTAGE REFERENCE + - 15 TIMER + - -+ FLOAT VOLTAGE ERROR AMP TIMER + - PROG SHORT COMPARATOR + - 6 EN EN LOW CURRENT VIN GOOD RECHARGE 1.2V GNDSENS 4001 BD W LTC4001 + - - +- -+ + RD - PWM COMPARATOR + + OVERCURRENT COMPARATOR SHUTDOWN COMPARATOR CURRENT REVERSAL COMPARATOR - 7 4001f LTC4001 OPERATIO The LTC4001 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 final battery float voltage is internally set to 4.2V. 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 battery 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 float voltage, the charge current will start to decrease. When the charge current drops below the charge rate detection 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 (30A typical) to ground to indicate a near end-ofcharge 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 battery voltage drops below the recharge threshold voltage (100mV below the float voltage). A recharge cycle lasts only one-half of the normal charge time. A negative temperature coefficient (NTC) thermistor located close to the battery pack can be used to monitor 8 U battery temperature and suspend charging when battery temperature is outside the 0C to 50C 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 Blanking The 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 float voltage. Automatic Battery Recharge After the charge cycle is completed and if both the battery and the input power supply (wall adapter) are still connected, a new charge cycle will begin if the battery voltage drops below 4.1V 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 comparator is digitally qualified. Only if the battery voltage stays below the recharge threshold for at least 4ms will battery recharging occur. (GPRS qualification is available even if timeout is disabled.) Undervoltage Lockout and Automatic Shutdown Internal 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. 4001f LTC4001 OPERATIO Overvoltage, Chip Overtemperature and Short-Circuit Current Protection The LTC4001 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 float voltage by approximately 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 U exceeds approximately 160C. Battery charging will be enabled again when temperature drops to approximately 150C. 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. 4001f 9 LTC4001 APPLICATIO S I FOR ATIO Soft-Start and Compensation Capacitor Selection The LTC4001 has a low current trickle charger and a PWM-based high current charger. Soft-start is used whenever the high rate charger is initially turned on, preventing high start-up current. Soft-start ramp rate is set by the internal 12.8A pull-up current and an external capacitor. The control range on the SS pin is approximately 0.3V to 1.6V. With a 0.1F capacitor, the time to ramp up to maximum duty cycle is approximately 10ms. The external capacitor on the SS pin also sets the compensation for the current control loop and the float voltage control loop. A minimum capacitance of 10nF is required. Charge Current and IDET Programming The LTC4001 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 approximately 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 voltage on the PROG pin is nominally 1.213V. For 2A charge current: RPROG = 915 * 1.213V 554.9 2A Figure 1. Programming Charge Current and IDET Threshold with a Single Resistor 10 U 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 W UU 1.10k programs approximately 100mA and 274 approximately 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= 457.5 * 1.213 ICHARGE and IDET = ICHARGE 10 LTC4001 PROG IDET R1 274 FOR 2A GNDSENS 4001 F01 4001f LTC4001 APPLICATIO S I FOR ATIO The equations for calculating R1 (used in single resistor programming) differ from the equations for calculating RPROG and RIDET (2-resistor programming) and reflect the fact that the current from both the IDET and PROG pins must flow through a single resistor R1 when a single programming resistor is used. CHRG Status Output Pin When 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 float voltage, the N-channel MOSFET turns off and a weak 30A current source to ground is connected to the CHRG pin. This weak pulldown 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 pullup resistor. Once the charge current drops below the endof-charge threshold, the N-channel MOSFET is turned off and a 30A 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 VIN VDD LTC4001 CHRG R1 390k R2 2k PROCESSOR OUT IN 4001 F02 Figure 2. Microprocessor Interface U 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 charging has stopped. Charge Termination Battery 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) 0.0733F). 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 Detection When 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 charging 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 (20useconds typical) to a microprocessor by tying the CHRG pin to an interrupt line. Serrations within this pulse are typically 500ns wide. 20s 667ms 4001 F03 W UU Figure 3. CHRG Temperature Fault Waveform 4001f 11 LTC4001 APPLICATIO S I FOR ATIO The battery temperature is measured by placing a negative temperature coefficient (NTC) thermistor close to the battery 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 25C. The LTC4001 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 25C) hold occurs at approximately 4.1k, which occurs at 50C. 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 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 0C. The hot and cold comparators each have approximately 3C of hysteresis to prevent oscillation about the trip point. Grounding the NTC pin disables the NTC function. Thermistors The LTC4001 NTC trip points were designed to work with thermistors whose resistance temperature characteristics follow Vishay Dale's "R-T Curve 2." However, any thermistor 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 3C and 47C, a delta of 44C. This delta in temperature can be moved in either direction by changing the value of RNOM with respect to RNTC. 12 U 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: RNOM = RCOLD * RNTC at 25C 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 * RNTC at 25C 0.4086 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 44C, from before, and we want the cold trip point to be 0C, which would put the hot trip point at 44C. The RNOM needed is calculated as follows: RNOM = RCOLD * RNTC at 25C 2.815 3.266 * 100k = 116k = 2.815 W UU 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 0C and 44C 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: RNOM = R1 = RCOLD - RHOT 2.815 - 0.4086 0.4086 * (RCOLD - RHOT ) - RHOT 2.815 - 0.4086 4001f LTC4001 APPLICATIO S I FOR ATIO VINSENSE 9 RNOM 121k NTC 11 0.02 * VINSENSE GNDSENS 4 - Figure 4. Extending the Delta Temperature where 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 50C: RNOM = RCOLD - RHOT 100k * (3.2636 - 0.3602) = 2.815 - 0.4086 2.815 - 0.4086 = 120.8k, 121k is nearest 1% 0.4086 R1 = 100k * * (3.266 - 0.3602) - 0.3602 2.815 - 0.4086 = 13.3k, 13.3k is nearest 1% The final solution is as shown if Figure 4 where RNOM = 121k, R1 = 13.3k and RNTC = 100k at 25C. Input and Output Capacitors The LTC4001 uses a synchronous buck regulator to provide high battery charging current. A 10F chip ceramic + RNTC 100k 0.29 * VINSENSE - R1 13.3k + - 0.74 * VINSENSE U LTC4001 NTC BLOCK TOO COLD TOO HOT W UU + NTC ENABLE 4001 F04 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 selfresonance 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 between 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 0.1 and the battery impedance is raised to 2 with a bead or inductor, only 5% of the ripple current will flow in the battery. Similar techniques may also be applied to minimize EMI from the input leads. 4001f 13 LTC4001 APPLICATIO S I FOR ATIO Inductor Selection A 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: V2 VBAT - BAT 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 occurs at maximum VIN and VBAT = VIN/2. Peak inductor current will be: IPK = IBAT + 0.5 * IL where 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, IL should never exceed 0.4(IBAT) as this may interfere with proper operation of the output short-circuit protection comparator. 1.5H provides reasonable inductor ripple current in a typical application. With 1.5H and 2A charge current: 2.85V 2 5.5V = 0.61A IL = P-P 1.5H * 1.5MHz 2.85V - and IPK = 2.31A 14 U Remote Sensing For highest float voltage accuracy, tie GNDSENS and BATSENS directly to the battery terminals. In a similar fashion, tie BAT and PGND directly to the battery terminals. This eliminates IR drops in the GNDSENS and BATSENS lines by preventing charge current from flowing in them. Operation with a Current Limited Wall Adapter Wall adapters with or without current limiting may be used with the LTC4001, 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. For example, if the LTC4001 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 (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 softstart 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 PWM charger duty cycle ramps up to 100% (the topside PMOS switch in the LTC4001 buck regulator stays on continuously). As the battery voltage approaches VFLOAT, the float voltage error amplifier commands the PWM charger to deliver less than ILIMIT. The wall adapter exits current limit and the VIN jumps back up to VADAPTER. 4001f W UU LTC4001 APPLICATIO S I FOR ATIO LINEAR CHARGING VADAPTER VIN IBAT ITRICKLE 4001 F05 Figure 5. Charging Characteristic Battery charging current continues to drop as the VBAT rises, dropping to zero at VFLOAT. Because the voltage drop in the LTC4001 is very low when charge current is highest, power dissipation is also very low. Thermal Calculations (PWM and Trickle Charging) The LTC4001 operates as a linear charger when conditioning (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 * IIN where 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 = 368.5mW LTC4001 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 charger is: VDROP = ILIMIT * RPFET where ILIMIT is the wall adapter current limit and RPFET is the on resistance of the topside PMOS switch. U WALL ADAPTER IN CURRENT LIMIT PWM CHARGING VBAT + VDROP ILIMIT VTRIKL VBAT VFLOAT W UU The total LTC4001 power dissipation during current limited charging is: PD = (VBAT + VDROP) * (IIN + IP) + VDROP * ILIMIT where IIN is the chip quiescent current and IP is total current flowing 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 is programmed for 2A charging and 200mA IDET and that a 1.5A wall adapter is being used: ILIMIT = 1500mA, RPFET = 127m, IIN = 2mA, IP = 4mA and VBAT VFLOAT = 4.242V then: VDROP = 1500mA * 127m = 190.5mV and: PD = (4.242V + 0.1905V) * (2mA + 4mA) + 0.1905V * 1500mA = 312mW Power 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. 4001f 15 LTC4001 APPLICATIO S I FOR ATIO TJ = TA + (PD * 37C/W) Insert the highest power dissipation figure into the following equation to determine maximum junction temperature: The LTC4001 includes chip overtemperature protection. If junction temperature exceeds 160C (typical), the chip will stop battery charging until chip temperature drops below 150C. Using the LTC4001 in Applications Without a Battery The LTC4001 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 indefinite operation with a powered wall adapter there are only two requirements--that the average 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 removed (Figure 7). Since the battery is absent, VBAT begins at zero when a powered wall adapter is first connected to the battery charger. With a maximum load less than the LTC4001 trickle charge current, battery voltage will ramp WALL ADAPTER 16 U up until VBAT crosses the trickle charge threshold. When this occurs, the LTC4001 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 voltage 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 system load demands, and VBAT rapidly rises until the float voltage 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 filtering 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. LTC4001 BATTERY CHARGER SYSTEM LOAD W UU + 4001 F06 Li-Ion BATTERY Figure 6. Typical Application 4001f LTC4001 APPLICATIO S I FOR ATIO 4 VBAT (V) 3 2 1 0 0 500 2 4 6 8 10 12 14 TIME (ms) 16 18 20 22 24 VSS (mV) 250 0 0 2 4 6 8 10 12 14 TIME (ms) 16 18 20 22 24 PWM CHARGE TRICKLE CHARGE 0 2 4 6 Figure 7. Battery-Less Start-Up U 8 10 12 14 TIME (ms) 16 18 20 22 24 4001 F07 W UU 4001f 17 LTC4001 APPLICATIO S I FOR ATIO Layout Considerations Switch rise and fall times are kept under 5ns for maximum efficiency. 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. VIN 4.5V TO 5.5V R1 10k C1 R2 10F 1k D1 LED TO P FROM P R3 10k AT 25C L1: VISHAY DALE IHLP-2525AH-01 R3: NTC VISHAY DALE NTHS0603N02N1002J Figure 8. 2A Li-Ion Battery Charger with 3Hr Timer, Temperature Qualification, Soft-Start, Remote Sensing and C/10 Indication 18 U With the exception of the input and output filter capacitors (which should be connected to PGND) all other components that return to ground should be connected to GNDSENS. Recommended Components Manufacturers For a list of recommend component manufacturers, contact the Linear Technology application department. L1 1.5H SW VINSENSE PVIN PGND CHRG NTC FAULT EN PROG IDET C2 0.22F R4 549 R5 549 C3 0.1F 4001 F08 W UU SENSE BATSENS BAT C4 10F + 2AHr 4.2V Li-Ion LTC4001 TIMER SS GNDSENS 4001f LTC4001 PACKAGE DESCRIPTIO 4.35 0.05 2.15 0.05 2.90 0.05 (4 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS BOTTOM VIEW--EXPOSED PAD 4.00 0.10 (4 SIDES) PIN 1 TOP MARK (NOTE 6) 2.15 0.10 (4-SIDES) 0.75 0.05 R = 0.115 TYP PIN 1 NOTCH R = 0.20 TYP OR 0.35 x 45 CHAMFER NOTE: 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 SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE Information 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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. U UF Package 16-Lead Plastic QFN (4mm x 4mm) (Reference LTC DWG # 05-08-1692) 0.72 0.05 PACKAGE OUTLINE 0.30 0.05 0.65 BSC 15 16 0.55 0.20 1 2 (UF16) QFN 10-04 0.200 REF 0.00 - 0.05 0.30 0.05 0.65 BSC 4001f 19 LTC4001 RELATED PARTS PART NUMBER LT 1511 LT1513 LT1571 LTC1729 (R) DESCRIPTION COMMENTS 3A Constant Current/Constant Voltage Battery Charger High Efficiency, Minimum External Components to Fast Charge Lithium, NIMH and NiCd Batteries, 24-Lead SO Package SEPIC Constant or Programmable Current/Constant Voltage Battery Charger 1.5A Switching Charger Li-Ion Battery Charger Termination Controller Charger Input Voltage May Be Higher, Equal to or Lower Than Battery Voltage, 500kHz Switching Frequency, DD Pak and TO-220 Packages 1- or 2-Cell Li-Ion, 500kHz or 200kHz Switching Frequency, Termination Flag, 16- and 28-Lead SSOP Packages Trickle Charge Preconditioning, Temperature Charge Qualification, Time or Charge Current Termination, Automatic Charger and Battery Detection, and Status Output, MS8 and SO-8 Packages Constant Current/Constant Voltage Switching Regulator, Input Current Limiting Maximizes Charge Current, 20-Lead TSSOP and 28-Lead SSOP Packages Complete Charger for 1- or 2-Cell Li-Ion Batteries, Onboard Timer Termination, Up to 4A Charge Current, 10-Lead DFN and SO-8 Packages Complete Charger for 2-, 3- or 4-Cell Li-Ion Batteries, AC Adapter Current Limit and Thermistor Sensor, 16-Lead Narrow SSOP Package Complete Charger for 3- or 4-Cell Li-Ion Batteries, AC Adapter Current Limit, Thermistor Sensor and Indicator Outputs, 24-Lead SSOP Package Complete Charger for 2- to 6-Cell Li-Ion Batteries or 4- to 18-Cell Nickel Batteries, Up to 96% Efficiency, 20-Lead SSOP Package LT1769 2A Switching Charger LTC4002 LTC4006 LTC4007 LTC4008 Standalone Li-Ion Switch Mode Battery Charger Small, High Efficiency, Fixed Voltage Li-Ion Battery Charger with Termination High Efficiency, Programmable Voltage Battery Charger with Termination 4A, High Efficiency, Multi-Chemistry Battery Charger 4001f 20 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 LT 0406 * PRINTED IN THE USA www.linear.com (c) LINEAR TECHNOLOGY CORPORATION 2006 |
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