LTC4068-4.2/LTC4068X-4.2 Standalone Linear Li-Ion Battery Charger with Programmable Termination U FEATURES DESCRIPTIO ■ The LTC®4068 is a complete constant-current/constantvoltage linear charger for single cell lithium-ion batteries. Its DFN package and low external component count make the LTC4068 ideally suited for portable applications. Furthermore, the LTC4068 is designed to work within USB power specifications. ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Programmable Charge Current Up to 950mA Complete Linear Charger in DFN Package No MOSFET, Sense Resistor or Blocking Diode Required Thermal Regulation Maximizes Charge Rate Without Risk of Overheating* Charges Directly from a USB Port Programmable Charge Current Termination Preset 4.2V Charge Voltage with ±1% Accuracy Charge Current Monitor Output for Gas Gauging* Automatic Recharge Charge Status Output “AC Present” Output 2.9V Trickle Charge Threshold (LTC4068) Available Without Trickle Charge (LTC4068X) Soft-Start Limits Inrush Current Low Profile (3mm × 3mm × 0.75mm) DFN Package U APPLICATIO S ■ ■ Cellular Telephones, PDAs, MP3 Players Bluetooth Applications No external sense resistor or external blocking diode are required due to the internal MOSFET architecture. Thermal feedback regulates the charge current to limit the die temperature during high power operation or high ambient temperature conditions. The charge voltage is fixed at 4.2V and the charge current is programmed with a resistor. The LTC4068 terminates the charge cycle when the charge current drops below the programmed termination threshold after the final float voltage is reached. When the input supply (wall adapter or USB supply) is removed, the LTC4068 enters a low current state dropping the battery drain current to less than 2µA. Other features include charge current monitor, undervoltage lockout, automatic recharge and status pins to indicate charge termination and the presence of adequate input voltage. , LTC and LT are registered trademarks of Linear Technology Corporation. Protected by U.S. Patents, including 6522118. U TYPICAL APPLICATIO Complete Charge Cycle (750mAh Battery) 700 Single Cell Li-Ion Battery Charger with C/5 Termination VCC BAT LTC4068-4.2 1µF CHRG ACPR ITERM EN PROG GND + 1-CELL Li-Ion BATTERY 825Ω 1.65k CHARGE CURRENT (mA) VIN 4.5V TO 6.5V 600 4.50 CONSTANT VOLTAGE 500 4.25 400 4.00 300 3.75 200 100 406842 TA01 0 VCC = 5V θJA = 40°C/W RPROG = 1.65k RTERM = 825Ω TA = 25°C 3.50 BATTERY VOLTAGE (V) 600mA 4.75 CONSTANT CURRENT 3.25 3.00 0 0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0 2.25 406842 TA02 TIME (HOURS) 406842fa 1 LTC4068-4.2/LTC4068X-4.2 W W W AXI U U ABSOLUTE RATI GS U U W PACKAGE/ORDER I FOR ATIO (Note 1) Input Supply Voltage (VCC) ....................... –0.3V to 10V PROG, ITERM ................................ – 0.3V to VCC + 0.3V BAT ............................................................. –0.3V to 7V CHRG, ACPR, EN ...................................... –0.3V to 10V BAT Short-Circuit Duration .......................... Continuous BAT Pin Current ........................................................ 1A PROG Pin Current ................................................... 1mA Maximum Junction Temperature .......................... 125°C Operating Temperature Range (Note 2) .. – 40°C to 85°C Storage Temperature Range ................. – 65°C to 125°C ORDER PART NUMBER TOP VIEW ITERM 1 8 EN BAT 2 7 ACPR 6 VCC 5 PROG CHRG 3 9 GND 4 LTC4068EDD-4.2 LTC4068XEDD-4.2 DD PART MARKING DD PACKAGE 8-LEAD (3mm × 3mm) PLASTIC DFN LBHZ LBQB TJMAX = 125°C, θJA = 40°C/W (NOTE 3) EXPOSED PAD IS GROUND (PIN 9) MUST BE SOLDERED TO PCB 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 at TA = 25°C. VCC = 5V, unless otherwise noted. SYMBOL PARAMETER VCC Input Supply Voltage CONDITIONS MIN ICC Input Supply Current Charge Mode (Note 4), RPROG = 10k Standby Mode (Charge Terminated) Shutdown Mode (EN = 5V, VCC < VBAT or VCC < VUV) VFLOAT Regulated Output (Float) Voltage 0°C ≤ TA ≤ 85°C, 4.3V < VCC < 6.5V IBAT BAT Pin Current RPROG = 10k, Current Mode RPROG = 2k, Current Mode Standby Mode, VBAT = 4.2V Shutdown Mode (EN = 5V, VCC < VBAT or VCC < VUV) Sleep Mode, VCC = 0V ● ● ● ● ● ITRIKL Trickle Charge Current VBAT < VTRIKL, RPROG = 2k (Note 5) VTRIKL Trickle Charge Threshold Voltage RPROG = 10k, VBAT Rising (Note 5) VTRHYS Trickle Charge Hysteresis Voltage RPROG = 10k (Note 5) VUV VCC Undervoltage Lockout Voltage From VCC Low to High VUVHYS VEN(IL) TYP MAX UNITS 6.5 V 0.4 200 25 1 500 50 mA µA µA 4.158 4.2 4.242 92 465 100 500 –2.5 ±1 105 535 –6 ±2 mA mA µA µA ±1 ±2 µA 30 45 60 mA 2.8 2.9 3 4.25 ● ● ● 80 V V mV ● 3.7 3.8 3.92 V VCC Undervoltage Lockout Hysteresis ● 150 200 300 mV EN Pin Input Low Voltage ● 0.4 0.7 VEN(IH) EN Pin Input High Voltage ● REN EN Pin Pull-Down Resistor VASD VCC – VBAT Lockout Threshold VCC from Low to High VCC from High to Low ITERM Charge Termination Current Threshold RTERM = 1k RTERM = 5k VPROG PROG Pin Voltage RPROG = 10k, Current Mode VCHRG CHRG Pin Output Low Voltage VACPR ACPR Pin Output Low Voltage ∆VRECHRG Recharge Battery Threshold Voltage VFLOAT – VRECHRG, 0°C ≤ TA ≤ 85°C ● 0.7 V 1 V 1.2 2 5 MΩ 70 5 100 30 140 50 mV mV 90 17.5 100 20 110 22.5 mA mA 0.93 1 1.07 V ICHRG = 5mA 0.35 0.6 V IACPR = 5mA 0.35 0.6 V 100 140 mV ● ● 60 406842fa 2 LTC4068-4.2/LTC4068X-4.2 ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS TLIM Junction Temperature in Constant Temperature Mode 120 °C RON Power FET “ON” Resistance (Between VCC and BAT) 600 mΩ tSS Soft-Start Time IBAT = 0 to IBAT =1000V/RPROG tRECHARGE Recharge Comparator Filter Time VBAT High to Low 0.75 2 4.5 ms tTERM Termination Comparator Filter Time IBAT Drops Below Charge Termination Threshold 400 1000 2500 µs 100 µs Note 3: Failure to solder the exposed backside of the package to the PC board will result in a thermal resistance much higher than 40°C/W. Note 4: Supply current includes PROG pin current and ITERM pin current (approximately 100µA each) but does not include any current delivered to the battery through the BAT pin (approximately 100mA). Note 5: This parameter is not applicable to the LTC4068X. Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. Note 2: The LTC4068E-4.2/LTC4068XE-4.2 are guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. U W TYPICAL PERFOR A CE CHARACTERISTICS PROG Pin Voltage vs Supply Voltage (Constant Current Mode) 1.0100 VCC = 5V VBAT = 4V TA = 25°C RPROG = 10k 1.010 1.0075 Charge Current vs PROG Pin Voltage 600 VCC = 5V VBAT = 4V RPROG = 10k VCC = 5V TA = 25°C RPROG = 2k RTERM = 2k 500 1.0050 VPROG (V) VPROG (V) 1.005 1.000 0.995 400 1.0025 IBAT (mA) 1.015 PROG Pin Voltage vs Temperature 1.0000 0.9975 300 200 0.9950 0.990 0.985 100 0.9925 4 4.5 5 5.5 VCC (V) 6 6.5 7 405842 G01 0.9900 –50 –25 0 50 25 TEMPERATURE (°C) 0 75 100 405842 G02 0 0.2 0.4 0.6 0.8 VPROG (V) 1 1.2 405842 G03 406842fa 3 LTC4068-4.2/LTC4068X-4.2 U W TYPICAL PERFOR A CE CHARACTERISTICS Regulated Output (Float) Voltage vs Charge Current Regulated Output (Float) Voltage vs Temperature 4.26 4.215 4.215 VCC = 5V RPROG = 10k 4.210 4.16 4.205 VFLOAT (V) 4.18 TA = 25°C RPROG = 10k 4.210 4.205 4.20 VFLOAT (V) VFLOAT (V) VCC = 5V 4.24 TA = 25°C RPROG = 1.25k 4.22 Regulated Output (Float) Voltage vs Supply Voltage 4.200 4.200 4.195 4.195 4.190 4.190 4.14 4.12 4.10 0 100 200 300 400 IBAT (mA) 500 600 4.185 –50 700 –25 0 25 50 TEMPERATURE (°C) 75 CHRG Pin I-V Curve (Pull-Down State) 60 TA = 90°C 15 10 25 TA = 25°C 5 20 TA = 90°C 1 4 3 VCHRG (V) 2 5 6 1 4 3 VACPR (V) 2 5 405842 G07 3.000 2.975 RPROG = 2k VTRKL (V) 30 VCC = 5V RPROG = 10k 6 0 25 50 TEMPERATURE (°C) 75 100 405842 G09 Charge Current vs Battery Voltage 600 LTC4068 ONLY LTC4068 ONLY 500 400 2.925 2.900 300 200 6.5 7 405842 G10 2.800 –50 VCC = 5V θJA = 40°C/W RPROG = 2k 100 2.825 5.5 VCC (V) –25 2.850 RPROG = 10k 5 0 –50 7 2.875 20 4.5 RPROG = 10k 2.950 40 4 30 Trickle Charge Threshold Voltage vs Temperature 50 10 LTC4068 ONLY 405842 G08 LTC4068 ONLY VBAT = 2.5V TA = 25°C 6 IBAT (mA) 60 VCC = 5V VBAT = 2.5V 10 VCC = 5V VBAT = 4V 0 Trickle Charge Current vs Supply Voltage 7 20 0 7 6.5 40 15 5 VCC = 5V VBAT = 4V 0 6 RPROG = 2k 10 0 5.5 VCC (V) 50 ITRKL (mA) 20 TA = –40°C IACPR (mA) ICHRG (mA) 25 TA = 25°C 5 4.5 Trickle Charge Current vs Temperature 30 TA = –40°C 4 405842 G06 ACPR Pin I-V Curve (Pull-Down State) 30 ITRKL (mA) 4.185 405842 G05 405842 G04 0 100 –25 0 50 25 TEMPERATURE (°C) 75 100 405842 G11 0 2.4 2.7 3 3.3 3.6 VBAT (V) 3.9 4.2 4.5 405842 G12 406842fa 4 LTC4068-4.2/LTC4068X-4.2 U W TYPICAL PERFOR A CE CHARACTERISTICS Charge Current vs Ambient Temperature Charge Current vs Supply Voltage 600 600 ONSET OF THERMAL REGULATION RPROG = 2k 500 500 RPROG = 2k 400 IBAT (mA) IBAT (mA) 400 VBAT = 4V 300 TA = 25°C θJA = 40°C/W 200 200 RPROG = 10k 100 0 VCC = 5V VBAT = 4V θJA = 40°C/W 300 4 5 4.5 5.5 VCC (V) RPROG = 10k 100 6 6.5 0 –50 7 –25 50 25 75 0 TEMPERATURE (°C) 100 405842 G13 405842 G14 Power FET “ON” Resistance vs Temperature 700 650 125 Recharge Threshold Voltage vs Temperature 4.16 VCC = 4.2V IBAT = 100mA RPROG = 2k 4.14 VCC = 5V RPROG = 10k 4.12 VRECHRG (V) RDS(ON) (mΩ) 600 550 500 4.10 4.08 450 4.06 400 350 –50 –25 0 25 50 75 TEMPERATURE (°C) 100 125 405842 G17 4.04 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 405842 G15 U U U PI FU CTIO S ITERM (Pin 1): Charge Termination Program. The charge termination current threshold current is programmed by connecting a 1% resistor, RTERM, to ground. The current threshold ITERM, is set by the following formula: ITERM = 100V 100V , RTERM = RTERM ITERM BAT (Pin 2): Charge Current Output. Provides charge current to the battery from the internal P-channel MOSFET, and regulates the final float voltage to 4.2V. An internal precision resistor divider from this pin sets the float voltage. This divider is disconnected in shutdown mode to minimize current drain from the battery. CHRG (Pin 3): Charge Status Open-Drain Output. When the battery is charging, the CHRG pin is pulled low by an internal N-channel MOSFET. When the charge cycle is completed, CHRG becomes high impedance. GND (Pins 4, 9): Ground/Exposed Pad. The exposed backside package pad (Pin 9) is electrical ground and must be soldered to the PC board for maximum heat transfer. 406842fa 5 LTC4068-4.2/LTC4068X-4.2 U U U PI FU CTIO S PROG (Pin 5): Charge Current Program and Charge Current Monitor. Charge current is programmed by connecting a 1% resistor, RPROG, to ground. When charging in constant-current mode, this pin servos to 1V. In all modes, the voltage on this pin can be used to measure the charge current using the following formula: When VCC is within 100mV of the BAT pin voltage, the LTC4068 enters shutdown mode dropping the battery drain current to less than 2µA. ACPR (Pin 7): Power Supply Status Open-Drain Output. When VCC is greater than the undervoltage lockout threshold and at least 100mV above VBAT, the ACPR pin is pulled to ground; otherwise, the pin is high impedance. IBAT = (VPROG/RPROG) • 1000 This pin is clamped to approximately 2.4V. Driving this pin to voltages beyond the clamp voltage can draw large currents and should be avoided. EN (Pin 8): Enable Input . A logic high on the EN pin will put the LTC4068 into shutdown mode where the battery drain current is reduced to less than 2µA and the supply current is reduced to less than 50µA. A logic low or floating the EN pin (allowing an internal 2MΩ pull-down resistor to pull this pin low) enables charging. VCC (Pin 6): Positive Input Supply Voltage. Provides power to the charger. VCC can range from 4.25V to 6.5V. This pin should be bypassed with at least a 1µF capacitor. W BLOCK DIAGRA 6 VCC 120°C TA 1× 1× TDIE 1000× – + BAT 5µA MA 2 R1 + ACPR 7 VA R2 – CHRG CA 3 + – REF 1.211V R3 * 1V CHARGE ACPR R4 LOGIC + TERM 0.1V C1 R5 – EN SHDN EN 8 C2* – + 2.9V TO BAT *TRICKLE CHARGE DISABLED ON THE LTC4068X PROG ITERM 1 5 RTERM GND 4, 9 RPROG 406842 BD 406842fa 6 LTC4068-4.2/LTC4068X-4.2 U OPERATIO The LTC4068 is a single cell lithium-ion battery charger using a constant-current/constant-voltage algorithm. It can deliver up to 950mA of charge current (using a good thermal PCB layout) with a final float voltage accuracy of ±1%. The LTC4068 includes an internal P-channel power MOSFET and thermal regulation circuitry. No blocking diode or external current sense resistor is required; thus, the basic charger circuit requires only two external components. Furthermore, the LTC4068 is capable of operating from a USB power source. Normal Charge Cycle A charge cycle begins when the voltage at the VCC pin rises above the UVLO threshold level and a 1% program resistor is connected from the PROG pin to ground. If the BAT pin is less than 2.9V, the charger enters trickle charge mode. In this mode, the LTC4068 supplies approximately 1/10th the programmed charge current to bring the battery voltage up to a safe level for full current charging. (Note: The LTC4068X does not include this trickle charge feature.) When the BAT pin voltage rises above 2.9V, the charger enters constant-current mode where the programmed charge current is supplied to the battery. When the BAT pin approaches the final float voltage (4.2V), the LTC4068 enters constant-voltage mode and the charge current begins to decrease. When the charge current drops to the programmed termination threshold (set by the external resistor RTERM), the charge cycle ends. Programming Charge Current The charge current is programmed using a single resistor from the PROG pin to ground. The charge current out of the BAT pin is 1000 times the current out of the PROG pin. The program resistor and the charge current are calculated using the following equations: RPROG = 1000 V 1000 V , I CHG = ICHG RPROG Charge current out of the BAT pin can be determined at any time by monitoring the PROG pin voltage and using the following equation: IBAT = VPROG • 1000 RPROG Programming Charge Termination The charge cycle terminates when the charge current falls below the programmed termination threshold. This threshold is set by connecting an external resistor, RTERM, from the ITERM pin to ground. The charge termination current threshold (ITERM) is set by the following equation: ITERM = 100V ICHG RPROG 100V = • , RTERM = RTERM 10 RTERM ITERM The termination condition is detected by using an internal filtered comparator to monitor the ITERM pin. When the ITERM pin voltage drops below 100mV* for longer than tTERM (typically 1ms), charging is terminated. The charge current is latched off and the LTC4068 enters standby mode where the input supply current drops to 200µA. (Note: Termination is disabled in trickle charging and thermal limiting modes.) ITERM can be set to be 1/10th of ICHG by shorting the ITERM pin to the PROG pin, thus eliminating the need for external resistor RTERM. When configured in this way, ITERM is always set to ICHG/10, and the programmed charge current is set by the equation: 500V 500V ICHG = ,RPROG = RPROG ICHG ** When charging, transient loads on the BAT pin can cause the ITERM pin to fall below 100mV for short periods of time before the DC charge current has dropped to 10% of the programmed value. The 1ms filter time (tTERM) on the termination comparator ensures that transient loads of this nature do not result in premature charge cycle termination. Once the average charge current drops below the programmed termination threshold, the LTC4068 terminates the charge cycle and ceases to provide any current out of the BAT pin. In this state, any load on the BAT pin must be supplied by the battery. The LTC4068 constantly monitors the BAT pin voltage in standby mode. If this voltage drops below the 4.1V recharge * Any external sources that hold the ITERM pin above 100mV will prevent the LTC4068 from terminating a charge cycle. ** These equations apply only when the ITERM pin is shorted to the PROG pin. 406842fa 7 LTC4068-4.2/LTC4068X-4.2 U OPERATIO threshold (VRECHRG), another charge cycle begins and charge current is once again supplied to the battery. To manually restart a charge cycle when in standby mode, the input voltage must be removed and reapplied or the charger must be shut down and restarted using the EN pin. Figure 1 shows the state diagram of a typical charge cycle. POWER ON BAT < 2.9V TRICKLE CHARGE MODE EN DRIVEN LOW OR UVLO CONDITION STOPS 1/10TH FULL CURRENT LTC4068 ONLY CHRG: STRONG PULL-DOWN BAT > 2.9V SHUTDOWN MODE CHARGE MODE ICC DROPS TO <25µA FULL CURRENT CHRG: Hi-Z Undervoltage Lockout (UVLO) CHRG: STRONG PULL-DOWN STANDBY MODE NO CHARGE CURRENT CHRG: Hi-Z 406842 F01 An internal thermal feedback loop reduces the programmed charge current if the die temperature attempts to rise above a preset value of approximately 120°C. This feature protects the LTC4068 from excessive temperature and allows the user to push the limits of the power handling capability of a given circuit board without risk of damaging the LTC4068. The charge current can be set according to typical (not worst case) ambient temperature with the assurance that the charger will automatically reduce the current in worst-case conditions. DFN power considerations are discussed further in the Applications Information section. BAT > 2.9V ITERM < 100mV EN DRIVEN HIGH OR UVLO CONDITION Thermal Limiting 2.9V < BAT < 4.1V Figure 1. State Diagram of a Typical Charge Cycle Charge Status Indicator (CHRG) The charge status output has two states: pull-down and high impedance. The pull-down state indicates that the LTC4068 is in a charge cycle. Once the charge cycle has terminated or the LTC4068 is disabled, the pin state becomes high impedance. Power Supply Status Indicator (ACPR) The power supply status output has two states: pull-down and high impedance. The pull-down state indicates that VCC is above the UVLO threshold (3.8V) and is also 100mV above the battery voltage. If these conditions are not met, the ACPR pin is high impedance indicating that the LTC4068 is unable to charge the battery. An internal undervoltage lockout circuit monitors the input voltage and keeps the charger in shutdown mode until VCC rises above the undervoltage lockout threshold. The UVLO circuit has a built-in hysteresis of 200mV. Furthermore, to protect against reverse current in the power MOSFET, the UVLO circuit keeps the charger in shutdown mode if VCC falls to within 30mV of the BAT voltage. If the UVLO comparator is tripped, the charger will not come out of shutdown mode until VCC rises 100mV above the BAT voltage. Manual Shutdown At any point in the charge cycle, the LTC4068 can be put into shutdown mode by driving the EN pin high. This reduces the battery drain current to less than 2µA and the supply current to less than 50µA. When in shutdown mode, the CHRG pin is in the high impedance state. A new charge cycle can be initiated by driving the EN pin low. An internal resistor pull-down on this pin forces the LTC4068 to be enabled if the pin is allowed to float. Automatic Recharge Once the charge cycle is terminated, the LTC4068 continuously monitors the voltage on the BAT pin using a comparator with a 2ms filter time (tRECHARGE). A charge cycle restarts when the battery voltage falls below 4.10V (which corresponds to approximately 80% to 90% battery capacity). This ensures that the battery is kept at, or near, a fully 406842fa 8 LTC4068-4.2/LTC4068X-4.2 U W U U APPLICATIO S I FOR ATIO charged condition and eliminates the need for periodic charge cycle initiations. The CHRG output enters a pulldown state during recharge cycles. If the battery is removed from the charger, a sawtooth waveform of approximately 100mV appears at the charger output. This is caused by the repeated cycling between termination and recharge events. This cycling results in pulsing at the CHRG output; an LED connected to this pin will exhibit a blinking pattern, indicating to the user that a battery is not present. The frequency of the sawtooth is dependent on the amount of output capacitance. Stability Considerations The constant-voltage mode feedback loop is stable without an output capacitor, provided a battery is connected to the charger output. With no battery present, an output capacitor on the BAT pin is recommended to reduce ripple voltage. When using high value, low ESR ceramic capacitors, it is recommended to add a 1Ω resistor in series with the capacitor. No series resistor is needed if tantalum capacitors are used. In constant-current mode, the PROG pin is in the feedback loop, not the battery. The constant-current mode stability is affected by the impedance at the PROG pin. With no additional capacitance on the PROG pin, the charger is stable with program resistor values as high as 20k; however, additional capacitance on this node reduces the maximum allowed program resistor. The pole frequency at the PROG pin should be kept above 100kHz. Therefore, if the PROG pin is loaded with a capacitance, CPROG, the following equation can be used to calculate the maximum resistance value for RPROG: RPROG ≤ 1 2π • 105 • CPROG Average, rather than instantaneous charge current may be of interest to the user. For example, if a switching power supply operating in low current mode is connected in parallel with the battery, the average current being pulled out of the BAT pin is typically of more interest than the instantaneous current pulses. In such a case, a simple RC filter can be used on the PROG pin to measure the average battery current, as shown in Figure 2. A 10k resistor has been added between the PROG pin and the filter capacitor to ensure stability. LTC4068-4.2 10k PROG GND RPROG CFILTER CHARGE CURRENT MONITOR CIRCUITRY 406842 F02 Figure 2. Isolating Capacitive Load on PROG Pin and Filtering Power Dissipation It is not necessary to design for worst-case power dissipation scenarios because the LTC4068 automatically reduces the charge current during high power conditions. The conditions that cause the LTC4068 to reduce charge current through thermal feedback can be approximated by considering the power dissipated in the IC. Nearly all of this power dissipation is generated by the internal MOSFET—this is calculated to be approximately: PD = (VCC – VBAT) • IBAT where PD is the power dissipated, VCC is the input supply voltage, VBAT is the battery voltage and IBAT is the charge current. The approximate ambient temperature at which the thermal feedback begins to protect the IC is: TA = 120°C – PDθJA TA = 120°C – (VCC – VBAT) • IBAT • θJA Example: An LTC4068 operating from a 5V supply is programmed to supply 800mA full-scale current to a discharged Li-Ion battery with a voltage of 3.3V. Assuming θJA is 50°C/W (see Thermal Considerations), the ambient temperature at which the LTC4068 will begin to reduce the charge current is approximately: TA = 120°C – (5V – 3.3V) • (800mA) • 50°C/W TA = 120°C – 1.36W • 50°C/W = 120°C – 68°C TA = 52°C 406842fa 9 LTC4068-4.2/LTC4068X-4.2 U W U U APPLICATIO S I FOR ATIO The LTC4068 can be used above 52°C ambient but the charge current will be reduced from the programmed 800mA. The approximate current at a given ambient temperature can be approximated by: IBAT = 120°C – TA (VCC – VBAT ) • θJA Using the previous example with an ambient temperature of 60°C, the charge current will be reduced to approximately: IBAT = 120°C – 60°C (5V – 3.3V) • 50°C/W = 60°C 85°C/A IBAT = 706mA Moreover, when thermal feedback reduces the charge current the voltage at the PROG pin is also reduced proportionally as discussed in the Operation section. It is important to remember that LTC4068 applications do not need to be designed for worst-case thermal conditions since the IC will automatically reduce power dissipation when the junction temperature reaches approximately 120°C. Thermal Considerations In order to deliver maximum charge current under all conditions, it is critical that the exposed metal pad on the backside of the LTC4068 package is soldered to the PC board ground. Correctly soldered to a 2500mm2 doublesided 1oz copper board, the LTC4068 has a thermal resistance of approximately 40°C/W. Failure to make thermal contact between the exposed pad on the backside of the package and the copper board will result in thermal resistances far greater than 40°C/W. As an example, a correctly soldered LTC4068 can deliver over 800mA to a battery from a 5V supply at room temperature. Without a good backside thermal connection, this number will drop considerably. ceramic capacitors. Because of the self-resonant and high Q characteristics of some types of ceramic capacitors, high voltage transients can be generated under some start-up conditions such as connecting the charger input to a live power source. Adding a 1.5Ω resistor in series with an X5R ceramic capacitor will minimize start-up voltage transients. For more information, see Application Note 88. Charge Current Soft-Start The LTC4068 includes a soft-start circuit to minimize the inrush current at the start of a charge cycle. When a charge cycle is initiated, the charge current ramps from zero to full-scale current over a period of approximately 100µs. This has the effect of minimizing the transient current load on the power supply during start-up. USB and Wall Adapter Power The LTC4068 allows charging from both a wall adapter and a USB port. Figure 3 shows how to combine wall adapter and USB power inputs. A P-channel MOSFET, MP1, is used to prevent back conducting into the USB port when a wall adapter is present and a Schottky diode, D1, is used to prevent USB power loss through the 1k pulldown resistor. Typically a wall adapter can supply more current than the 500mA-limited USB port. Therefore, an N-channel MOSFET, MN1, and an extra 3.3k program resistor are used to increase the charge current to 800mA when the wall adapter is present. The charge termination threshold remains fixed at 80mA. 5V WALL ADAPTER 800mA ICHG USB POWER 500mA ICHG LTC4068-4.2 2 BAT 1 6 VCC ITERM 5 4, 9 GND PROG MP1 Many types of capacitors can be used for input bypassing; however, caution must be exercised when using multilayer SYSTEM LOAD 1.25k + 3.3k 1k VCC Bypass Capacitor ICHG D1 MN1 2k Li-Ion BATTERY 406842 F03 Figure 3. Combining Wall Adapter and USB Power 406842fa 10 LTC4068-4.2/LTC4068X-4.2 U W U U APPLICATIO S I FOR ATIO Reverse Polarity Input Voltage Protection DRAIN-BULK DIODE OF FET In some applications, protection from reverse polarity voltage on VCC is desired. If the supply voltage is high enough, a series blocking diode can be used. In other cases, where the voltage drop must be kept low, a P-channel MOSFET can be used (as shown in Figure 4). LTC4068 VCC VIN 405842 F04 Figure 4. Low Loss Input Reverse Polarity Protection U PACKAGE DESCRIPTIO DD Package 8-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1698) 0.675 ±0.05 3.5 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.28 ± 0.05 0.50 BSC 2.38 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.115 TYP 5 3.00 ±0.10 (4 SIDES) 0.38 ± 0.10 8 1.65 ± 0.10 (2 SIDES) PIN 1 TOP MARK (DD8) DFN 0203 0.200 REF 0.75 ±0.05 0.00 – 0.05 4 0.28 ± 0.05 1 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-1) 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 406842fa 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. 11 LTC4068-4.2/LTC4068X-4.2 U TYPICAL APPLICATIO S Full Featured Single Cell Li-Ion Charger Li-Ion Battery Charger with Reverse Polarity Input Protection VIN 5V 1k 1k 5V WALL ADAPTER 6 500mA VCC 1µF 6 VCC 2 7 ACPR BAT 1 3 CHRG ITERM LTC4068-4.2 8 5 EN PROG GND BAT LTC4068-4.2 1µF 1µF 1k + 2k 1-CELL Li-Ion BATTERY 4, 9 ITERM 8 EN PROG GND 500mA 2 1 + 5 1-CELL Li-Ion BATTERY 1k 4, 9 406842 TA04 405642 TA03 USB/Wall Adapter Power Li-Ion Charger 5V WALL ADAPTER BAT IBAT 2 + LTC4068-4.2 6 USB POWER VCC 1µF 1k ITERM PROG GND 4, 9 1 5 1-CELL Li-Ion BATTERY 1.25k 5k 100mA/ 500mA µC 406842 TA05 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1732 Lithium-Ion Linear Battery Charger Controller Simple Charger uses External FET, Features Preset Voltages, C/10 Charger Detection and Programmable Timer, Input Power Good Indication LTC1733 Monolithic Lithium-Ion Linear Battery Charger Standalone Charger with Programmable Timer, Up to 1.5A Charge Current TM LTC1734 Lithium-Ion Linear Battery Charger in ThinSOT Simple ThinSOT Charger, No Blocking Diode, No Sense Resistor Needed LTC1734L Lithium-Ion Linear Battery Charger in ThinSOT Low Current Version of LTC1734; 50mA ≤ ICHRG ≤ 180mA LTC1998 Lithium-Ion Low Battery Detector 1% Accurate 2.5µA Quiescent Current, SOT-23 LTC4007 4A Multicell Li-Ion Battery Charger Standalone Charger, 6V ≤ VIN ≤ 28V, Up to 96% Efficiency, ±0.8% Charging Voltage Accuracy LTC4050 Lithium-Ion Linear Battery Charger Controller C/10 Charger Detection and Programmable Timer, Thermistor Interface LTC4052 Monolithic Lithium-Ion Battery Pulse Charger No Blocking Diode or External Power FET Required, ≤1.5A Charge Current LTC4053 USB Compatible Monolithic Li-Ion Battery Charger Standalone Charger with Programmable Timer, Up to 1.25A Charge Current LTC4054 Standalone Linear Li-Ion Battery Charger in ThinSOT Thermal Regulation Prevents Overheating, C/10 Termination, C/10 Indicator, Up to 800mA Charge Current LTC4057 Li-Ion Linear Battery Charger Up to 800mA Charge Current, Thermal Regulation, ThinSOT Package LTC4058 LTC4058X Standalone Li-Ion Linear Charger in DFN Up to 950mA Charge Current, Kelvin Sense for High Accuracy, C/10 Charge Termination LTC4410 USB Power Manager For Simultaneous Operation of USB Peripheral and Battery Charging from USB Port, Keeps Current Drawn from USB Port Constant, Keeps Battery Fresh, Use with the LTC4053, LTC1733, or LTC4054 LTC4411 LTC4412 Low Loss PowerPathTM Controller in ThinSOT Automatic Switching Between DC Sources, Load Sharing, Replaces ORing Diodes ThinSOT and PowerPath are trademarks of Linear Technology Corporation. 406842fa 12 Linear Technology Corporation LT/TP 0904 1K 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 2004