Final Electrical Specifications LTC4002-4.2 Standalone Li-Ion Switch Mode Battery Charger June 2003 U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO The LTC®4002-4.2 is a complete battery charger controller for single cell 4.2V lithium-ion batteries. With a 500kHz switching frequency, the LTC4002-4.2 provides a small, simple and efficient solution to fast charge Li-Ion batteries from a wide range of supply voltages. An external sense resistor sets the charge current with ±5% accuracy. An internal resistor divider and precision reference set the final float voltage to 4.2V with ±1% accuracy. Wide Input Supply Range: 4.7V to 24V High Efficiency Current Mode PWM Controller with 500kHz Switching Frequency ±1% Charge Voltage Accuracy End-of-Charge Current Detection Output 3 Hour Charge Termination Timer Constant Switching Frequency for Minimum Noise ±5% Charge Current Accuracy Low 10µA Reverse Battery Drain Current Automatic Battery Recharge Automatic Shutdown When Input Supply is Removed Automatic Trickle Charging of Low Voltage Batteries Battery Temperature Sensing and Charge Qualification Stable with Ceramic Output Capacitor 8-Lead SO and 10-Lead DFN Packages When the input supply is removed, the LTC4002-4.2 automatically enters a low current sleep mode, dropping the battery drain current to 10µA. An internal comparator detects the near end-of-charge condition while an internal timer sets the total charge time and terminates the charge cycle. After the charge cycle ends, if the battery voltage drops below 4.05V, a new charge cycle will automatically begin. U APPLICATIO S ■ ■ Portable Computers Charging Docks Handheld Instruments , LTC and LT are registered trademarks of Linear Technology Corporation. U ■ The LTC4002-4.2 is available in the 8-lead SO and 10-lead DFN packages. TYPICAL APPLICATIO VIN 5V TO 24V B330B-13 BAT Efficiency vs Input Voltage 2 0.1µF CER VCC GATE 3 10µF CER 100 ICHRG = 1.5A RSENSE = 68mΩ (CURVES INCLUDE INPUT DIODE) Si6435ADQ 2k 5 CHRG SENSE 7 68mΩ 1 0.47µF COMP NTC BAT GND 8 2.2k T 4 6 22µF CER 90 B330B-13 L1 6.8µH EFFICIENCY (%) LTC4002ES8-4.2 CHARGE STATUS + 10k NTC Li-Ion BATTERY VBAT = 4V VBAT = 3.8V 80 70 400242 F01 NTC: DALE NTHS-1206N02 60 5 15 10 20 25 INPUT VOLTAGE (V) Figure 1. 1.5A Single Cell Li-Ion Battery Charger 400242 TA02 400242i 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. 1 LTC4002-4.2 W W U W ABSOLUTE AXI U RATI GS (Note 1) Supply Voltage (VCC) .............................................. 24V GATE .................................................. (VCC – 8V) to VCC BAT, SENSE .............................................. – 0.3V to 14V CHRG, COMP, NTC ..................................... – 0.3V to 8V Operating Temperature Range (Note 2) .. – 40°C to 85°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C U W U PACKAGE/ORDER I FOR ATIO TOP VIEW ORDER PART NUMBER 10 NC COMP 1 VCC 2 GATE 3 PGND 4 7 BAT SGND 5 6 CHRG 9 NTC 11 8 SENSE DD PACKAGE 10-LEAD (3mm × 3mm) PLASTIC DFN TJMAX = 125°C, θJA = 43°C/W EXPOSED PAD IS GND (PIN 11) MUST BE SOLDERED TO PCB LTC4002EDD-4.2 DD PART MARKING LAGG ORDER PART NUMBER TOP VIEW COMP 1 8 NTC VCC 2 7 SENSE GATE 3 6 BAT GND 4 5 CHRG LTC4002ES8-4.2 S8 PART MARKING S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 125°C, θJA = 110°C/W 400242 Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 10V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS DC Characteristics VCC VCC Supply Voltage ICC VCC Supply Current Current Mode Shutdown Mode Sleep Mode VBAT Battery Regulated Float Voltage 5V ≤ VCC ≤ 24V (Note 2) ● 0°C ≤ TA ≤ 85°C –40°C ≤ TA ≤ 85°C 4.7 24 V 3 3 10 5 5 20 mA mA µA 4.168 4.158 4.2 ● 4.232 4.242 V V ● ● 93 90 100 107 110 mV mV 5 10 15 mV 2.9 3.05 4.2 4.5 VSNS(CHG) Constant Current Sense Voltage 3V ≤ VBAT ≤ 4V (Note 3) VSNS(TRKL) Trickle Current Sense Voltage VBAT = 0V (Note 3) VTRKL Trickle Charge Threshold Voltage VBAT Rising 2.75 VUV VCC Undervoltage Lockout Threshold Voltage VCC Rising 3.9 ∆VUV VCC Undervoltage Lockout Hysteresis Voltage VMSD Manual Shutdown Threshold Voltage VASD Automatic Shutdown Threshold Voltage VCC – VBAT 250 mV ICOMP COMP Pin Output Current VCOMP = 1.2V 100 µA ICHRG CHRG Pin Weak Pull-Down Current VCHRG = 1V VCHRG CHRG Pin Output Low Voltage ICHRG = 1mA REOC End-of-Charge Ratio VSNS(EOC)/VSNS(CHG) tTIMER Charge Time Accuracy 200 COMP Pin Falling 200 15 10 360 V V mV 500 mV µA 25 35 0.15 0.3 V 25 32 % 10 % 400242i 2 LTC4002-4.2 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 10V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX INTC NTC Pin Output Current VNTC = 0.85V ● 75 85 95 µA VNTC-HOT NTC Pin Threshold Voltage (Hot) VNTC Falling Hysteresis ● 340 355 25 370 mV mV VNTC-COLD NTC Pin Threshold Voltage (Cold) VNTC Rising Hysteresis ● 2.428 2.465 170 2.502 V mV ∆VRECHRG Recharge Battery Voltage Offset from Full Charged Battery Voltage VBAT(FULLCHARGED) – VRECHRG, VBAT Falling 100 150 200 mV ILEAK VCHRG = 8V, Charging Stops 1 µA 550 kHz 100 % CHRG Pin Leakage Current UNITS Oscillator fOSC Switching Frequency DC Maximum Duty Cycle 450 500 Gate Drive tr Rise Time CGATE = 2000pF, 10% to 90% 20 ns tf Fall Time CGATE = 2000pF, 90% to 10% 50 ns ∆VGATE Output Clamp Voltage VCC – VGATE, VCC ≥ 9V ● 8 V ∆VGATEHI Output High Voltage ∆VGATEHI = VCC – VGATE, VCC ≥ 7V ● 0.3 V ∆VGATELO Output Low Voltage ∆VGATELO = VCC – VGATE, VCC ≥ 7V ● Note 1: Absolute Maximum Rating are those values beyond which the life of a device may be impaired. TA = 25°C, VCC = 10V unless otherwise noted. U W Oscillator Frequency vs Temperature Supply Current vs VCC 4.0 4 V Note 2: The LTC4002-4.2 is tested with Test Circuit 1. Note 3: The LTC4002-4.2 is tested with Test Circuit 2. TYPICAL PERFOR A CE CHARACTERISTICS Supply Current vs Temperature 4.5 550 CURRENT MODE fOSC (kHz) ICC (mA) ICC (mA) 3.5 3 500 3.0 2.5 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 125 2 5 10 15 20 25 VCC (V) 400242 G01 400242 G02 450 – 50 – 25 75 50 25 TEMPERATURE (°C) 0 100 125 400242 G03 400242i 3 LTC4002-4.2 U W TYPICAL PERFOR A CE CHARACTERISTICS Current Mode Sense Voltage vs Temperature Oscillator Frequency vs VCC 104 500 5 15 10 20 102 VBAT = 4V 100 96 – 50 – 25 25 75 50 25 TEMPERATURE (°C) 0 VCC (V) Trickle Charge Voltage vs Temperature 3.0 125 150 VBAT = 4V 5 15 10 20 75 50 25 TEMPERATURE (°C) 25 130 5 10 100 125 400242 G10 15 20 400242 G09 CHRG Output Pin Weak Pull-Down Current vs VCC 28 VCHRG = 8V VCHRG = 8V 25 21 – 50 – 25 25 VCC (V) ICHRG (µA) ICHRG (µA) VCHG (mV) 29 25 ILOAD = 1mA 400242 G08 ILOAD = 1mA 0 20 140 CHRG Pin Weak Pull-Down Current vs Temperature 140 15 400242 G04 VCC (V) CHRG Pin Output Low Voltage vs Temperature 100 – 50 – 25 10 VCC (V) 2.9 2.8 100 5 CHRG Pin Output Low Voltage vs VCC 400242 G07 180 98 125 VCHRG (mV) VTRKL (V) VTRKL (V) 2.9 75 50 25 TEMPERATURE (°C) 100 Trickle Charge Voltage vs VCC 3.0 0 100 VBAT = 4V 400242 G05 400242 G04 2.8 – 50 – 25 Current Mode Sense Voltage vs VCC VSNS (mV) VSNS (mV) fOSC (kHz) 510 490 TA = 25°C, VCC = 10V unless otherwise noted. 25 22 75 50 25 TEMPERATURE (°C) 0 100 125 400242 G23 5 10 15 VCC (V) 20 25 400242 G11 400242i 4 LTC4002-4.2 U W TYPICAL PERFOR A CE CHARACTERISTICS Trickle Charge Sense Voltage vs Temperature 11 10 9 75 50 25 TEMPERATURE (°C) 0 100 ICOMP (µA) 10.0 102 VBAT = 2.5V VBAT = 2.5V 9.6 – 50 – 25 125 5 10 15 20 100 100 10 15 20 400242 G16 Recharge Voltage Offset from Full Charged Voltage vs Temperature Recharge Voltage Offset from Full Charged Voltage vs VCC 125 5 10 15 20 25 VCC (V) 400242 G18 125 End-of-Charge Ratio vs Temperature REOC (%) ∆VRECHRG (mV) 100 100 29 150 140 75 50 25 TEMPERATURE (°C) 75 50 25 TEMPERATURE (°C) 0 400242 G17 160 0 85 81 – 50 – 25 25 400242 G15 110 – 50 – 25 VNTC = 0V VCC (V) 190 ∆VRECHRG (mV) 89 VNTC = 0V 5 25 NTC Pin Output Current vs Temperature 85 84 125 150 20 400242 G14 INTC (µA) INTC (µA) ICOMP (µA) 86 75 50 25 TEMPERATURE (°C) 15 10 VCC (V) NTC Pin Output Current vs VCC VCOMP = 0V 0 5 400242 G13 COMP Pin Output Current vs Temperature 96 – 50 – 25 100 98 25 VCOMP = 0V VCC (V) 400242 G12 104 COMP Pin Output Current vs VCC Trickle Charge Sense Voltage vs VCC VSNS (mV) VSNS (mV) 10.4 TA = 25°C, VCC = 10V unless otherwise noted. 400242 G19 25 21 – 50 – 25 75 50 25 TEMPERATURE (°C) 0 100 125 400242 G20 400242i 5 LTC4002-4.2 U W TYPICAL PERFOR A CE CHARACTERISTICS End-of-Charge Ratio vs VCC Undervoltage Lockout Threshold vs Temperature 4.4 VUV (V) REOC (%) 29 25 21 5 10 15 VCC (V) 20 25 400242 G21 U U U PI FU CTIO S TA = 25°C, VCC = 10V unless otherwise noted. VCC RISING 4.2 4.0 – 50 – 25 75 50 25 TEMPERATURE (°C) 0 100 125 400242 G22 (DFN/SO-8) COMP (Pin 1/Pin 1): Compensation, Soft-Start and Shutdown Control Pin. The COMP pin is the control signal of the inner loop of the current mode PWM. Charging begins when the COMP pin reaches 800mV. The recommended compensation components are a 0.47µF (or larger) capacitor and a 2.2k series resistor. A 100µA current into the compensation capacitor also sets the soft-start slew rate. Pulling the COMP pin below 350mV will shut down the charger. VCC (Pin 2/Pin 2): Positive Supply Voltage Input. VCC can range from 4.7V to 24V. A 0.1µF or higher capacitor is required at the VCC pin with the lead length kept to a minimum. A 10µF low ESR capacitor is also required at the source pins of the power P-channel MOSFET. GATE (Pin 3/Pin 3): Gate Drive Output. Driver Output for the P-Channel MOSFET. The voltage at this pin is internally clamped to 8V below VCC, allowing a low voltage MOSFET with gate-to-source breakdown voltage of 8V or less to be used. PGND, SGND, Exposed Pad, GND (Pins 4, 5, 11/4): IC Ground. CHRG (Pin 6/Pin 5): Open-Drain Charge Status Output. When the battery is being charged, the CHRG pin is pulled low by an internal N-channel MOSFET. When the charge current drops to 25% of the full-scale current for more than 120µs, the N-channel MOSFET turns off and a 25µA current source is connected from the CHRG pin to GND. When the timer runs out or the input supply is removed, the 25µA current source is turned off and the CHRG pin becomes high impedance. BAT (Pin 7/Pin 6): Battery Sense Input. A bypass capacitor of 22µF is required to minimize ripple voltage. An internal resistor divider, which is disconnected in sleep mode, sets the final float voltage at this pin. If the battery connection is opened when charging, an overvoltage circuit will limit the charger output voltage to 10% above the programmed float voltage. When VBAT is within 250mV of VCC, the LTC4002-4.2 is forced into sleep mode, dropping ICC to 10µA. SENSE (Pin 8/Pin 7): Current Amplifier Sense Input. A sense resistor, RSENSE, must be connected between the SENSE and BAT pins. The maximum charge current is equal to 100mV/RSENSE. NTC (Pin 9/Pin 8): NTC (Negative Temperature Coefficient) Thermistor Input. With an external 10kΩ NTC thermistor to ground, this pin senses the temperature of the battery pack and stops the charger when the temperature is out of range. When the voltage at this pin drops below 350mV at 400242i 6 LTC4002-4.2 U U U PI FU CTIO S (DFN/SO-8) hot temperature or rises above 2.465V at cold temperature, charging is suspended and the internal timer stops. The CHRG pin output is not affected during this hold state. To disable the temperature qualification function, ground the NTC pin. NC (Pin 10/NA): No Connect. W BLOCK DIAGRA VCC CLK: 100µA COMP ISLOP IL DRIVER – GATE S Q + CPWM R R 20mV RSLOP + +– CEOC RIL – 100mV + M1 SENSE –+ CA – BAT + M2 VA – 4.2V + M3 CLB – 90µA 2.9V + COV – UVLO 4.2V + UV CSD 350mV CHRG – + EOC SD RQ CRQ LOGIC Q4 – 4.05V + 2.465V C/10 STOP Q5 4.62V TEMP VCC CCOLD NTC_DISABLE – 25µA 85µA NTC – GND CHOT + 350mV + – 400242 BD 50mV 400242i 7 LTC4002-4.2 TEST CIRCUITS Test Circuit 1 15V – 1.5V LT1006 + 0V LTC4002-4.2 SENSE – 100µA COMP CA BAT RSENSE 10Ω + VBAT 400242 TC01 Test Circuit 2 15V – 1.5V LT1006 + 0V SENSE – COMP 100µA CA BAT RSENSE 10Ω + 1mA – VA 4.2V + LTC4002-4.2 400242 TC02 400242i 8 LTC4002-4.2 U OPERATIO The LTC4002 is a constant current, constant voltage Li-Ion battery charger controller that uses a current mode PWM step-down (buck) switching architecture. The charge current is set by an external sense resistor (RSENSE) across the SENSE and BAT pins. The final battery float voltage is internally set to 4.2V. For batteries like lithiumion that require accurate final float voltage, the internal 2.465V reference, voltage amplifier and the resistor divider provide regulation with ±1% accuracy. A charge cycle begins when the voltage at the VCC pin rises above the UVLO level (4.2V) and is 250mV or more greater than the battery voltage. At the beginning of the charge cycle, if the battery voltage is less than 2.9V, the charger goes into trickle charge mode. The trickle charge current is internally set to 10% of the full-scale current. If the battery voltage stays low for 30 minutes, the battery is considered faulty and the charge cycle is terminated. When the battery voltage exceeds 2.9V, the charger goes into the full-scale constant current charge mode. In constant current mode, the charge current is set by the external sense resistor RSENSE and an internal 100mV reference; IBAT = 100mV/RSENSE. When the current drops to 25% of the full-scale charge current, an internal comparator turns off the internal pulldown N-channel MOSFET at the CHRG pin, and connects a weak current source to ground to indicate a near end-ofcharge condition. An internal 3 hour timer determines the total charge time. After a time out occurs, the charge cycle is terminated and the CHRG pin is forced high impedance. To restart the charge cycle, remove and reapply the input voltage or momentarily shut the charger down. Also, a new charge cycle will begin if the battery voltage drops below the recharge threshold voltage of 4.05V. When the input voltage is present, the charger can be shut down (ICC = 3mA) by pulling the COMP pin low. When the input voltage is not present, the charger goes into sleep mode, dropping ICC to 10µA. This will greatly reduce the current drain on the battery and increase the standby time. A 10kΩ NTC (negative temperature coefficient) thermistor can be connected from the NTC pin to ground for battery temperature qualification. The charge cycle is suspended when the temperature is outside of the 0°C to 50°C window (with DALE NTHS-1206N02). When the battery voltage approaches the programmed float voltage, the charge current will start to decrease. 400242i 9 LTC4002-4.2 U W U U APPLICATIO S I FOR ATIO Undervoltage Lockout (UVLO) CHRG Status Output Pin An undervoltage lockout circuit monitors the input voltage and keeps the charger off until VCC rises above 4.2V and at least 250mV above the battery voltage. To prevent oscillation around the threshold voltage, the UVLO circuit has 200mV of built-in hysteresis. 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 to 25% of the full-scale current for more than 120µs, the N-channel MOSFET turns off and a weak 25µA current source to ground is connected to the CHRG pin. This weak 25µA pull-down remains until the timer ends the charge cycle, or the charger is in manual shutdown or sleep mode. Trickle Charge and Defective Battery Detection At the beginning of a charge cycle, if the battery voltage is below 2.9V, the charger goes into trickle charge mode with the charge current reduced to 10% of the full-scale current. If the low-battery voltage persists for 30 minutes, the battery is considered defective, the charge cycle is terminated and the CHRG pin is forced to be high impedance. Shutdown The LTC4002 can be shut down by pulling the COMP pin to ground which pulls the GATE pin high and turns off the external P-channel MOSFET. When the COMP pin is released, the internal timer is reset and a new charge cycle starts. In shutdown, the output of the CHRG pin is high impedance and the quiescent current remains at 3mA. Removing the input power supply will put the charger into sleep mode. If the voltage at the VCC pin drops below (VBAT + 250mV) or below the UVLO level (4.2V), the LTC4002-4.2 goes into a low current (ICC = 10µA) sleep mode, reducing the battery drain current. After a time out occurs (charge cycle ends), the pin will go into 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 at the CHRG pin. The N-channel MOSFET will pull the pin low even with a 2k pull-up resistor. Once the charge current drops to 25% of the full-scale current, the N-channel MOSFET is turned off and a 25µA 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 400k resistor. When the internal timer has expired, the CHRG pin changes to a high impedance state and the 400k resistor will then pull the pin high to indicate the charging has stopped. VDD VCC LTC4002-4.2 400k 2k CHRG µPROCESSOR OUT IN 400242 F02 Figure 2. Microprocessor Interface 400242i 10 LTC4002-4.2 U W U U APPLICATIO S I FOR ATIO Gate Drive Automatic Battery Recharge The LTC4002-4.2 gate driver can provide high transient currents to drive the external pass transistor. The rise and fall times are typically 20ns and 50ns respectively when driving a 2000pF load, which is typical for a P-channel MOSFET with RDS(ON) in the range of 50mΩ. After the 3 hour charge cycle is completed and 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 4.05V due to self-discharge or external loading. This will keep the battery capacity at more than 80% at all times without manually restarting the charge cycle. A voltage clamp is added to limit the gate drive to 8V below VCC. For example, if VCC is 10V then the GATE output will pull down to 2V max. This allows low voltage P-channel MOSFETs with superior RDS(ON) to be used as the pass transistor thus increasing efficiency. Stability Both the current loop and the voltage loop share a common, high impedance, compensation node (COMP pin). A series capacitor and resistor on this pin compensates both loops. The resistor is included to provide a zero in the loop response and boost the phase margin. The compensation capacitor also provides a soft-start function for the charger. Upon start-up, the COMP pin voltage will quickly rise to 0.05V, due to the 2.2k series resistor, then ramp at a rate set by the internal 100µA pullup current source and the external capacitor. Battery charge current starts ramping up when the COMP pin voltage reaches 0.8V and full current is achieved with the COMP pin at 1.3V. With a 0.47µF capacitor, time to reach full charge current is about 235ms. Capacitance can be increased up to 1µF if a longer start-up time is needed. Battery Temperature Detection A negative temperature coefficient (NTC) thermistor located close to the battery pack can be used to monitor battery temperature and will not allow charging unless the battery temperature is within an acceptable range. Connect a 10kΩ thermistor (DALE NTHS-1206N02) from the NTC pin to ground. If the temperature rises to 50°C, the resistance of the NTC will be approximately 4.1kΩ. With the 85µA pull-up current source, the Hot temperature voltage threshold is 350mV. For Cold temperature, the voltage threshold is set at 2.456V which is equal to 0°C (RNTC ≅ 28.4kΩ) with 85µA of pull-up current. If the temperature is outside the window, the GATE pin will be pulled up to VCC and the timer frozen while the output status at the CHRG pin remains the same. The charge cycle begins or resumes once the temperature is within the acceptable range. Short the NTC pin to ground to disable the temperature qualification feature. 400242i 11 LTC4002-4.2 U W U U APPLICATIO S I FOR ATIO Input and Output Capacitors Since the input capacitor is assumed to absorb all input switching ripple current in the converter, it must have an adequate ripple current rating. Worst-case RMS ripple current is approximately one-half of output charge current. Actual capacitance value is not critical. Solid tantalum capacitors have a high ripple current rating in a relatively small surface mount package, but caution must be used when tantalum capacitors are used for input bypass. High input surge currents can be created when the adapter is hot-plugged to the charger and solid tantalum capacitors have a known failure mechanism when subjected to very high turn-on surge currents. Selecting the highest possible voltage rating on the capacitor will minimize problems. Consult with the manufacturer before use. The selection of output capacitor COUT is primarily determined by the ESR required to minimize ripple voltage and load step transients. The output ripple ∆VOUT is approximately bounded by: 1 ∆VOUT ≤ ∆IL ESR + 8 fOSCCOUT Since ∆IL increases with input voltage, the output ripple is highest at maximum input voltage. Typically, once the ESR requirement is satisfied, the capacitance is adequate for filtering and has the necessary RMS current rating. Switching ripple current splits between the battery and the output capacitor depending on the ESR of the output capacitor and the battery impedance. EMI considerations usually make it desirable to minimize ripple current in the battery leads. Ferrite beads or an inductor may be added to increase battery impedance at the 500kHz switching frequency. If the ESR of the output capacitor is 0.2Ω and the battery impedance is raised to 4Ω with a bead or inductor, only 5% of the current ripple will flow in the battery. Design Example As a design example, take a charger with the following specifications: VIN = 5V to 24V, VBAT = 4V nominal, IBAT = 1.5A, fOSC = 500kHz, see Figure 1. First, calculate the SENSE resistor : RSENSE = 100mV/1.5A = 68mΩ Choose the inductor for about 65% ripple current at the maximum VIN: L= 4V 4V 1– = 6.838µH (500kHz)(0.65)(1.5A) 24V Selecting a standard value of 6.8µH results in a maximum ripple current of : ∆IL = 4V 4V 1– = 980.4mA (500kHz)(6.8µH) 24V 400242i 12 LTC4002-4.2 U W U U APPLICATIO S I FOR ATIO Next, choose the P-channel MOSFET. The Si6435ADQ in a TSSOP-8 package with RDS(ON) = 42mΩ (nom), 55mΩ (max) offers a small solution. The maximum power dissipation with VIN = 5V and VBAT = 4V at 50°C ambient temperature is: (1.5A) (55m Ω)(4V) = 0.099 W PD = 5V TJ = 50°C + (0.099W)(65°C/W) = 56.5°C 2 CIN is chosen for an RMS current rating of about 0.8A at 85°C. The output capacitor is chosen for an ESR similar to the battery impedance of about 100mΩ. The ripple voltage on the BAT pin is: ∆IL(MAX) (ESR) 2 (0.98A)(0.1Ω) = 49mV = 2 C1: Taiyo Yuden TMK325BJ106MM C2: Taiyo Yuden JMK325BJ226MM L1: TOKO B952AS-6R8N VOUT(RIPPLE) = The Schottky diode D2 shown in Figure 1 conducts current when the pass transistor is off. In a low duty cycle case, the current rating should be the same or higher than the charge current. Also it should withstand reverse voltage as high as VIN. Board Layout Suggestions When laying out the printed circuit board, the following considerations should be taken to ensure proper operation of the LTC4002-4.2. GATE pin rise and fall times are 20ns and 50ns respectively (with CGATE = 2000pF). To minimize radiation, the catch diode, pass transistor and the input bypass capacitor traces should be kept as short as possible. The positive side of the input capacitor should be close to the source of the P-channel MOSFET; it provides the AC current to the pass transistor. The connection between the catch diode and the pass transistor should also be kept as short as possible. The SENSE and BAT pins should be connected directly to the sense resistor (Kelvin sensing) for best charge current accuracy. The compensation capacitor connected at the COMP pin should return to the ground pin of the IC or as close to it as possible. This will prevent ground noise from disrupting the loop stability. The ground pin also works as a heat sink, therefore use a generous amount of copper around the ground pin. This is especially important for high VCC and/or high gate capacitance applications. 400242i 13 LTC4002-4.2 U PACKAGE DESCRIPTIO DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1699) 0.675 ±0.05 3.50 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.38 ±0.05 (2 SIDES) R = 0.115 TYP 6 RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 3.00 ±0.10 (4 SIDES) 0.38 ± 0.10 10 1.65 ± 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 5) (DD10) DFN 0403 5 0.200 REF 1 0.75 ±0.05 0.00 – 0.05 0.25 ± 0.05 0.50 BSC 2.38 ±0.10 (2 SIDES) BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 2. ALL DIMENSIONS ARE IN MILLIMETERS 3. 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 4. EXPOSED PAD SHALL BE SOLDER PLATED 5. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 400242i 14 LTC4002-4.2 U PACKAGE DESCRIPTIO S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610) .189 – .197 (4.801 – 5.004) NOTE 3 .045 ±.005 .050 BSC 8 .245 MIN 7 6 5 .160 ±.005 .150 – .157 (3.810 – 3.988) NOTE 3 .228 – .244 (5.791 – 6.197) .030 ±.005 TYP 1 RECOMMENDED SOLDER PAD LAYOUT .010 – .020 × 45° (0.254 – 0.508) .008 – .010 (0.203 – 0.254) 0°– 8° TYP .016 – .050 (0.406 – 1.270) NOTE: 1. DIMENSIONS IN .053 – .069 (1.346 – 1.752) .014 – .019 (0.355 – 0.483) TYP INCHES (MILLIMETERS) 2. DRAWING NOT TO SCALE 3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm) 2 3 4 .004 – .010 (0.101 – 0.254) .050 (1.270) BSC SO8 0303 400242i 15 LTC4002-4.2 U TYPICAL APPLICATIO Single Cell 4.2V, 2A Li-Ion Battery Charger VIN 5V TO 12V 100k 1/2 Si9933ADY VCC GATE 3 LTC4002ES8-4.2 5 1 0.47µF C1 10µF CER 2 0.1µF CER CHRG SENSE COMP BAT NTC GND 8 4 2.2k T 10k NTC 1/2 Si9933ADY B330-13 L1 6.8µH 7 6 RSENSE 50mΩ C2 22µF CER + Li-Ion BATTERY 400242 TA01 NTC: DALE NTHS-1206N02 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1732/LTC4050 Constant Voltage/Constant Current Li-Ion Linear Battery Chargers Standalone Battery Charger, No uC or Firmware Required, Auto Recharge of Low Battery, 10-Pin MSOP, Input Supply Detection LTC1733 Li-Ion Battery Charger with Termal Regulation Standalone Charger, Constant-Current/Constant-Voltage/ Constant-Temperature, Integrated MOSFET, No External Sense Resistor or Blocking Diodes LTC1734/LTC1734L SOT-23 Li-Ion Battery Chargers Need Only Two External Components, Monitors Charge Current, No Reverse Diode or Sense Resistor Required, 50mA to 700mA LTC1980 Combination Battery Charger and DC/DC Converter Wall Adapter May Be Above or Below Battery Voltage, Standalone, 1-, 2-Cell Li-Ion, Also for Charging NiMH and NiCd Batteries LTC4006/LTC4007 LTC4008 4A Multiple Cell Li-Ion, NiCd, NiMH, Lead Acid Battery Chargers 6V ≤ VIN ≤ 28V, High Efficiency ≥ 90%, VOUT ≤ 28V, Digital Interface I/O, Small Inductor LTC4052/LTC1730 Integrated Pulse Chargers for a 1-Cell Li-Ion Battery 0.35Ω Internal N-FET Requires No Blocking Diode, Current Limit for Safety LTC4053 USB Compatible Li-Ion Linear Battery Charger Charges from USB Input or AC/DC, 100mA/500mA Up to 1.25A, Thermal Regulation, Fully Integrated LTC4054 Standalone Linear Li-Ion Battery Charger with Integrated Pass Transistor in ThinSOTTM Thermal Regulation Prevents Overheating, C/10 Termination, C/10 Indicator LTC4056 Standalone SOT-23 Li-Ion Linear Battery Charger Charge Termination Included, ICH ≤ 700mA, 8-Lead ThinSOT Package LTC4412 TM Low Loss PowerPath Controller in ThinSOT Automatic Switching Between DC Sources, Simplified Load Sharing PowerPath and ThinSOT are trademarks of Linear Technology Corporation. 400242i 16 Linear Technology Corporation LT/TP 0603 1K PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2003