LTC4054ES5-4.2

LTC4054-4.2/LTC4054X-4.2 Standalone Linear Li-Ion Battery Charger with Thermal Regulation in ThinSOT FEATURES s s DESCRIPTIO s s s s s s s s s s s s s Programmable Charge Current Up to 800mA No MOSFET, Sense Resistor or Blocking Diode Required Complete Linear Charger in ThinSOTTM Package for Single Cell Lithium-Ion Batteries Constant-Current/Constant-Voltage Operation with Thermal Regulation* to Maximize Charge Rate Without Risk of Overheating Charges Single Cell Li-Ion Batteries Directly from USB Port Preset 4.2V Charge Voltage with ±1% Accuracy Charge Current Monitor Output for Gas Gauging* Automatic Recharge Charge Status Output Pin C/10 Charge Termination 25µA Supply Current in Shutdown 2.9V Trickle Charge Threshold (LTC4054) Available Without Trickle Charge (LTC4054X) Soft-Start Limits Inrush Current Available in 5-Lead SOT-23 Package The LTC®4054 is a complete constant-current/constantvoltage linear charger for single cell lithium-ion batteries. Its ThinSOT package and low external component count make the LTC4054 ideally suited for portable applications. Furthermore, the LTC4054 is specifically designed to work within USB power specifications. No external sense resistor is needed, and no blocking diode is 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. The charge voltage is fixed at 4.2V, and the charge current can be programmed externally with a single resistor. The LTC4054 automatically terminates the charge cycle when the charge current drops to 1/10th the programmed value after the final float voltage is reached. When the input supply (wall adapter or USB supply) is removed, the LTC4054 automatically enters a low current state, dropping the battery drain current to less than 2µA. The LTC4054 can be put into shutdown mode, reducing the supply current to 25µA. Other features include charge current monitor, undervoltage lockout, automatic recharge and a status pin to indicate charge termination and the presence of an input voltage. , LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation. *U.S.Patent No. 6,522,118 APPLICATIO S s s s Cellular Telephones, PDAs, MP3 Players Charging Docks and Cradles Bluetooth Applications TYPICAL APPLICATIO VIN 4.5V TO 6.5V Complete Charge Cycle (750mAh Battery) 700 600 CONSTANT CURRENT CONSTANT POWER CONSTANT VOLTAGE 4.75 4.50 600mA Single Cell Li-Ion Charger CHARGE CURRENT (mA) 500 400 300 200 100 0 1µF BAT LTC4054-4.2 PROG GND 2 4 VCC 3 600mA 5 1.65k 4.2V Li-Ion BATTERY 405442 TA01a VCC = 5V θJA = 130°C/W RPROG = 1.65k TA = 25°C 0 3.00 0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0 TIME (HOURS) 405442 TAO1b 405442xf U BATTERY VOLTAGE (V) 4.25 4.00 3.75 3.50 CHARGE TERMINATED 3.25 U U 1 LTC4054-4.2/LTC4054X-4.2 ABSOLUTE (Note 1) AXI U RATI GS PACKAGE/ORDER I FOR ATIO TOP VIEW CHRG 1 GND 2 BAT 3 4 VCC 5 PROG Input Supply Voltage (VCC) ....................... –0.3V to 10V PROG ............................................. – 0.3V to VCC + 0.3V BAT .............................................................. –0.3V to 7V CHRG ........................................................ –0.3V to 10V BAT Short-Circuit Duration .......................... Continuous BAT Pin Current ................................................. 800mA PROG Pin Current ................................................ 800µA Maximum Junction Temperature .......................... 125°C Operating Ambient Temperature Range (Note 2) .............................................. – 40°C to 85°C Storage Temperature Range ................. – 65°C to 125°C Lead Temperature (Soldering, 10 sec).................. 300°C ORDER PART NUMBER LTC4054ES5-4.2 LTC4054XES5-4.2 S5 PART MARKING LTH7 LTADY S5 PACKAGE 5-LEAD PLASTIC TSOT-23 TJMAX = 125°C, (θJA = 80°C/ W TO 150°C/W DEPENDING ON PC BOARD LAYOUT) (N0TE 3) Consult LTC Marketing for parts specified with wider operating temperature ranges. The q denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, unless otherwise noted. SYMBOL VCC ICC PARAMETER Input Supply Voltage Input Supply Current Charge Mode (Note 4), RPROG = 10k Standby Mode (Charge Terminated) Shutdown Mode (RPROG Not Connected, VCC < VBAT, or VCC < VUV) 0°C ≤ TA ≤ 85°C, IBAT = 40mA RPROG = 10k, Current Mode RPROG = 2k, Current Mode Standby Mode, VBAT = 4.2V Shutdown Mode (RPROG Not Connected) Sleep Mode, VCC = 0V VBAT < VTRIKL, RPROG = 2k (Note 5) RPROG = 10k, VBAT Rising (Note 5) RPROG = 10k (Note 5) From VCC Low to High PROG Pin Rising PROG Pin Falling VCC from Low to High VCC from High to Low RPROG = 10k (Note 6) RPROG = 2k RPROG = 10k, Current Mode VCHRG = 5V ICHRG = 5mA VFLOAT - VRECHRG 100 q q q q q q q q q q ELECTRICAL CHARACTERISTICS CONDITIONS q q q q MIN 4.25 TYP 300 200 25 MAX 6.5 2000 500 50 4.242 107 535 –6 ±2 ±2 70 3.0 110 3.92 300 1.30 1.1 140 50 0.115 0.115 1.07 35 0.6 200 UNITS V µA µA µA V mA mA µA µA µA mA V mV V mV V V mV mV mA/mA mA/mA V µA V mV VFLOAT IBAT Regulated Output (Float) Voltage BAT Pin Current 4.158 93 465 0 4.2 100 500 –2.5 ±1 ±1 45 2.9 80 3.8 200 1.21 1.0 100 30 0.10 0.10 1.0 20 0.35 150 ITRIKL VTRIKL VTRHYS VUV VUVHYS VMSD VASD ITERM VPROG ICHRG VCHRG ∆VRECHRG Trickle Charge Current Trickle Charge Threshold Voltage Trickle Charge Hysteresis Voltage VCC Undervoltage Lockout Threshold VCC Undervoltage Lockout Hysteresis Manual Shutdown Threshold Voltage VCC – VBAT Lockout Threshold Voltage C/10 Termination Current Threshold PROG Pin Voltage CHRG Pin Weak Pull-Down Current CHRG Pin Output Low Voltage Recharge Battery Threshold Voltage q 20 2.8 60 3.7 150 1.15 0.9 70 5 0.085 0.085 0.93 8 405442xf 2 U W U U WW W LTC4054-4.2/LTC4054X-4.2 The q denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, unless otherwise noted. SYMBOL TLIM RON tSS tRECHARGE tTERM IPROG PARAMETER Junction Temperature in Constant Temperature Mode Power FET “ON” Resistance (Between VCC and BAT) Soft-Start Time Recharge Comparator Filter Time Termination Comparator Filter Time PROG Pin Pull-Up Current IBAT = 0 to IBAT =1000V/RPROG VBAT High to Low IBAT Falling Below ICHG/10 0.75 400 CONDITIONS MIN TYP 120 600 100 2 1000 3 4.5 2500 MAX UNITS °C mΩ µs ms µs µA ELECTRICAL CHARACTERISTICS Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. Note 2: The LTC4054E-4.2 and the LTC4054XE-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. Note 3: See Thermal Considerations. Note 4: Supply current includes PROG pin current (approximately 100µA) 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 LTC4054X. Note 6: ITERM is expressed as a fraction of measured full charge current with indicated PROG resistor. TYPICAL PERFOR A CE CHARACTERISTICS PROG Pin Voltage vs Supply Voltage(Constant Current Mode) 1.015 1.010 1.005 VCC = 5V VBAT = 4V TA = 25°C RPROG = 10k 1.0100 1.0075 1.0050 VPROG (V) VPROG (V) 1.000 0.995 0.990 0.985 IBAT (mA) –25 0 25 50 TEMPERATURE (°C) 75 100 4054 G02 4.0 4.5 5.0 5.5 VCC (V) 6.0 UW 6.5 4054 G01 PROG Pin Voltage vs Temperature 600 VCC = 5V VBAT = 4V RPROG = 10k Charge Current vs PROG Pin Voltage VCC = 5V TA = 25°C 500 RPROG = 2k 400 300 200 100 0 1.0025 1.0000 0.9975 0.9950 0.9925 7.0 0.9900 –50 0 0.25 0.50 0.75 VPROG (V) 1.00 1.25 4054 G03 405442xf 3 LTC4054-4.2/LTC4054X-4.2 TYPICAL PERFOR A CE CHARACTERISTICS PROG Pin Pull-Up Current vs Temperature and Supply Voltage 3.7 3.5 VCC = 4.2V 3.3 IPROG (µA) IPROG (µA) VBAT = 4.3V VPROG = 0V 2.0 1.5 1.0 0.5 VCC = 5V VBAT = 4.3V TA = 25°C 2.1 2.2 2.3 VPROG (V) 2.4 2.5 2.6 IPROG (µA) 3.1 VCC = 6.5V 2.9 2.7 2.5 –50 –25 50 25 75 0 TEMPERATURE (°C) Regulated Output (Float) Voltage vs Charge Current 4.26 4.24 4.22 VFLOAT (V) VCC = 5V TA = 25°C RPROG = 1.25k VFLOAT (V) 4.18 4.16 4.14 4.12 4.10 0 100 200 300 400 IBAT (mA) 500 600 700 VFLOAT (V) 4.20 CHRG Pin I-V Curve (Strong Pull-Down State) 25 20 18 20 16 ICHRG (mA) ICHRG (µA) 15 ICHRG (mA) 10 5 VCC = 5V VBAT = 4V TA = 25°C 0 1 2 4 3 VCHRG (V) 5 6 7 0 4 UW 100 4054 G04 4054 G07 4054 G10 PROG Pin Current vs PROG Pin Voltage (Pull-Up Current) 3.5 3.0 2.5 0 –50 –100 –150 –200 –250 –300 –350 PROG Pin Current vs PROG Pin Voltage (Clamp Current) 125 0 2.0 –400 2.0 VCC = 5V VBAT = 4.3V TA = 25°C 2.5 3.0 3.5 4.0 4.5 5.0 5.5 VPROG (V) 4054 G05 4054 G06 Regulated Output (Float) Voltage vs Temperature 4.215 4.210 4.205 4.200 4.195 4.190 4.185 –50 VCC = 5V RPROG = 10k 4.215 4.210 4.205 4.200 4.195 4.190 4.185 Regulated Output (Float) Voltage vs Supply Voltage TA = 25°C RPROG = 10k –25 0 25 50 75 100 4054 G08 4.0 4.5 5.0 TEMPERATURE (°C) 5.5 VCC (V) 6.0 6.5 7.0 4054 G09 CHRG Pin Current vs Temperature (Strong Pull-Down State) 22 VCC = 5V VBAT = 4V VCHRG = 1V 20 18 16 14 12 10 8 0 25 50 75 100 125 CHRG Pin I-V Curve (Weak Pull-Down State) 14 12 10 8 6 4 –50 –25 VCC = 5V VBAT = 4.3V TA = 25°C 0 1 2 4 3 VCHRG (V) 5 6 7 TEMPERATURE (°C) 4054 G11 4054 G12 405442xf LTC4054-4.2/LTC4054X-4.2 TYPICAL PERFOR A CE CHARACTERISTICS CHRG Pin Current vs Temperature (Weak Pull-Down State) 28 25 23 ITRIKL (mA) ICHRG (µA) 30 VCC = 5V VBAT = 2.5V 20 ITRIKL (mA) 30 VBAT = 2.5V TA = 25°C 19 16 13 10 –50 10 RPROG = 10k 10 RPROG = 10k VCC = 5V VBAT = 4.3V VCHRG = 5V 50 RPROG = 2k 40 40 –25 0 25 50 TEMPERATURE (°C) Trickle Charge Threshold vs Temperature 3.000 2.975 2.950 VTRIKL (V) IBAT (mA) VCC = 5V RPROG = 10k 600 TA = 25°C 300 200 100 0 2.7 VCC = 5V θJA = 125°C/W RPROG = 2k 3.0 3.3 3.6 3.9 VBAT (V) 4.2 4.5 4054 G17 IBAT (mA) 2.925 2.900 2.875 2.850 2.825 2.800 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 4054 G16 Charge Current vs Ambient Temperature 600 RPROG = 2k 500 400 IBAT (mA) 300 200 RPROG = 10k 100 0 –50 –25 VCC = 5V VBAT = 4V θJA = 80°C/W ONSET OF THERMAL REGULATION 4.11 4.09 4.07 VRECHRG (V) 4.05 4.03 4.01 RDS(ON) (mΩ) 50 25 75 0 TEMPERATURE (°C) UW 75 4054 G13 Trickle Charge Current vs Temperature 50 Trickle Charge Current vs Supply Voltage RPROG = 2k 20 100 0 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 4054 G14 0 4.0 4.5 5.0 5.5 VCC (V) 6.0 6.5 7.0 4054 G15 Charge Current vs Battery Voltage 600 TA = 0°C 500 400 TA = 40°C 500 400 300 200 100 0 Charge Current vs Supply Voltage RPROG = 2k VBAT = 4V TA = 25°C θJA = 80°C/W ONSET OF THERMAL REGULATION RPROG = 10k 4.0 4.5 5.0 5.5 VCC (V) 6.0 6.5 7.0 4054 G18 Recharge Voltage Threshold vs Temperature 700 VCC = 5V RPROG = 10k 650 600 550 500 450 400 Power FET “ON” Resistance vs Temperature VCC = 4.2V IBAT = 100mA RPROG = 2k 100 125 3.99 –50 –25 50 25 0 TEMPERATURE (°C) 75 100 4054 G20 350 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 125 4054 G19 4054 G21 405442xf 5 LTC4054-4.2/LTC4054X-4.2 PI FU CTIO S CHRG (Pin 1): Open-Drain Charge Status Output. When the battery is charging, the CHRG pin is pulled low by an internal N-channel MOSFET. When the charge cycle is completed, a weak pull-down of approximately 20µA is connected to the CHRG pin, indicating an “AC present” condition. When the LTC4054 detects an undervoltage lockout condition, CHRG is forced high impedance. GND (Pin 2): Ground. BAT (Pin 3): Charge Current Output. Provides charge current to the battery and regulates the final float voltage to 4.2V. An internal precision resistor divider from this pin sets the float voltage which is disconnected in shutdown mode. VCC (Pin 4): Positive Input Supply Voltage. Provides power to the charger. VCC can range from 4.25V to 6.5V and should be bypassed with at least a 1µF capacitor. When VCC drops to within 30mV of the BAT pin voltage, the LTC4054 enters shutdown mode, dropping IBAT to less than 2µA. PROG (Pin 5): Charge Current Program, Charge Current Monitor and Shutdown Pin. The 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: IBAT = (VPROG/RPROG) • 1000 The PROG pin can also be used to shut down the charger. Disconnecting the program resistor from ground allows a 3µA current to pull the PROG pin high. When it reaches the 1.21V shutdown threshold voltage, the charger enters shutdown mode, charging stops and the input supply current drops to 25µA. This pin is also clamped to approximately 2.4V. Driving this pin to voltages beyond the clamp voltage will draw currents as high as 1.5mA. Reconnecting RPROG to ground will return the charger to normal operation. 6 U U U 405442xf LTC4054-4.2/LTC4054X-4.2 BLOCK DIAGRA 120°C TDIE MA R1 CA – + – SHDN C1 R3 1V R4 + CHRG 1 STANDBY TRICKLE CHARGE DISABLED ON LTC4054X C3 3µA C2 0.1V R5 – + – TO BAT 2.9V PROG 5 VCC + – + W 4 VCC TA 1× 1000× 5µA BAT 3 + VA R2 – REF 1.21V GND RPROG 2 405442 BD 405442xf 7 LTC4054-4.2/LTC4054X-4.2 OPERATIO The LTC4054 is a single cell lithium-ion battery charger using a constant-current/constant-voltage algorithm. It can deliver up to 800mA of charge current (using a good thermal PCB layout) with a final float voltage accuracy of ± 1%. The LTC4054 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 LTC4054 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 or when a battery is connected to the charger output. If the BAT pin is less than 2.9V, the charger enters trickle charge mode. In this mode, the LTC4054 supplies approximately 1/10 the programmed charge current to bring the battery voltage up to a safe level for full current charging. (Note: The LTC4054X 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 LTC4054 enters constant-voltage mode and the charge current begins to decrease. When the charge current drops to 1/10 of the programmed value, the charge cycle ends. Programming Charge Current The charge current is programmed using a single resistor from the PROG pin to ground. The battery charge current is 1000 times the current out of the PROG pin. The program resistor and the charge current are calculated using the following equations: 1000V 1000V RPROG = , ICHG = ICHG RPROG The charge current out of the BAT pin can be determined at any time by monitoring the PROG pin voltage using the following equation: 8 U IBAT = VPROG •1000 RPROG Charge Termination A charge cycle is terminated when the charge current falls to 1/10th the programmed value after the final float voltage is reached. This condition is detected by using an internal, filtered comparator to monitor the PROG pin. When the PROG pin voltage falls below 100mV1 for longer than tTERM (typically 1ms), charging is terminated. The charge current is latched off and the LTC4054 enters standby mode, where the input supply current drops to 200µA. (Note: C/10 termination is disabled in trickle charging and thermal limiting modes). When charging, transient loads on the BAT pin can cause the PROG pin to fall below 100mV for short periods of time before the DC charge current has dropped to 1/10th 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 1/10th the programmed value, the LTC4054 terminates the charge cycle and ceases to provide any current through the BAT pin. In this state, all loads on the BAT pin must be supplied by the battery. The LTC4054 constantly monitors the BAT pin voltage in standby mode. If this voltage drops below the 4.05V recharge threshold (VRECHRG), another charge cycle begins and 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 PROG pin. Figure 1 shows the state diagram of a typical charge cycle. Charge Status Indicator (CHRG) The charge status output has three different states: strong pull-down (~10mA), weak pull-down (~20µA) and high impedance. The strong pull-down state indicates that the LTC4054 is in a charge cycle. Once the charge cycle has terminated, the pin state is determined by undervoltage Note 1: Any external sources that hold the PROG pin above 100mV will prevent the LTC4054 from terminating a charge cycle. 405442xf LTC4054-4.2/LTC4054X-4.2 OPERATIO lockout conditions. A weak pull-down indicates that VCC meets the UVLO conditions and the LTC4054 is ready to charge. High impedance indicates that the LTC4054 is in undervoltage lockout mode: either VCC is less than 100mV above the BAT pin voltage or insufficient voltage is applied to the VCC pin. A microprocessor can be used to distinguish between these three states—this method is discussed in the Applications Information section. Thermal Limiting 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 LTC4054 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 LTC4054. 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. ThinSOT power considerations are discussed further in the Applications Information section. Undervoltage Lockout (UVLO) 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 battery voltage. If the UVLO comparator is tripped, the charger will not come out of shutdown mode until VCC rises 100mV above the battery voltage. Manual Shutdown At any point in the charge cycle, the LTC4054 can be put into shutdown mode by removing RPROG thus floating the PROG pin. This reduces the battery drain current to less U than 2µA and the supply current to less than 50µA. A new charge cycle can be initiated by reconnecting the program resistor. In manual shutdown, the CHRG pin is in a weak pull-down state as long as VCC is high enough to exceed the UVLO conditions. The CHRG pin is in a high impedance state if the LTC4054 is in undervoltage lockout mode: either VCC is within 100mV of the BAT pin voltage or insufficient voltage is applied to the VCC pin. Automatic Recharge Once the charge cycle is terminated, the LTC4054 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 4.05V (which corresponds to approximately 80% to 90% battery capacity). This ensures that the battery is kept at or near a fully charged condition and eliminates the need for periodic charge cycle initiations. CHRG output enters a strong pulldown state during recharge cycles. POWER ON BAT < 2.9V TRICKLE CHARGE MODE 1/10TH FULL CURRENT CHRG: STRONG PULL-DOWN BAT > 2.9V SHUTDOWN MODE ICC DROPS TO 2.9V Figure 1. State Diagram of a Typical Charge Cycle 405442xf 9 LTC4054-4.2/LTC4054X-4.2 APPLICATIO S I FOR ATIO 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 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: 1 RPROG ≤ 5 •C 2π • 10 PROG 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. 10 U 10k PROG LTC4054 GND 405442 F02 W UU CHARGE CURRENT MONITOR CIRCUITRY CFILTER RPROG Figure 2. Isolating Capacitive Load on PROG Pin and Filtering Power Dissipation The conditions that cause the LTC4054 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 LTC4054 operating from a 5V USB supply is programmed to supply 400mA full-scale current to a discharged Li-Ion battery with a voltage of 3.75V. Assuming θJA is 150°C/W (see Board Layout Considerations), the ambient temperature at which the LTC4054 will begin to reduce the charge current is approximately: TA = 120°C – (5V – 3.75V) • (400mA) • 150°C/W TA = 120°C – 0.5W • 150°C/W = 120°C – 75°C TA = 45°C 405442xf LTC4054-4.2/LTC4054X-4.2 APPLICATIO S I FOR ATIO The LTC4054 can be used above 45°C ambient, but the charge current will be reduced from 400mA. The approximate current at a given ambient temperature can be approximated by: IBAT = (VCC – VBAT ) • θJA 120°C – 60°C 120°C – TA Using the previous example with an ambient temperature of 60°C, the charge current will be reduced to approximately: IBAT 60°C = = 5V – 3.75V • 150°C /W 187.5°C /A IBAT = 320mA ( ) 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 LTC4054 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 Because of the small size of the ThinSOT package, it is very important to use a good thermal PC board layout to maximize the available charge current. The thermal path for the heat generated by the IC is from the die to the copper lead frame, through the package leads, (especially the ground lead) to the PC board copper. The PC board copper is the heat sink. The footprint copper pads should be as wide as possible and expand out to larger copper areas to spread and dissipate the heat to the surrounding ambient. Feedthrough vias to inner or backside copper layers are also useful in improving the overall thermal performance of the charger. Other heat sources on the board, not related to the charger, must also be considered when designing a PC board layout because they will affect overall temperature rise and the maximum charge current. U The following table lists thermal resistance for several different board sizes and copper areas. All measurements were taken in still air on 3/32" FR-4 board with the device mounted on topside. Table 1. Measured Thermal Resistance (2-Layer Board*) COPPER AREA TOPSIDE BACKSIDE 2500mm2 1000mm2 225mm2 100mm2 50mm2 2500mm2 2500mm2 2500mm2 2500mm2 2500mm2 BOARD AREA 2500mm2 2500mm2 2500mm2 2500mm2 2500mm2 THERMAL RESISTANCE JUNCTION-TO-AMBIENT 125°C/W 125°C/W 130°C/W 135°C/W 150°C/W *Each layer uses one ounce copper W UU Table 2. Measured Thermal Resistance (4-Layer Board**) COPPER AREA (EACH SIDE) 2500mm2*** BOARD AREA 2500mm2 THERMAL RESISTANCE JUNCTION-TO-AMBIENT 80°C/W *Top and bottom layers use two ounce copper, inner layers use one ounce copper. **10,000mm2 total copper area Increasing Thermal Regulation Current Reducing the voltage drop across the internal MOSFET can significantly decrease the power dissipation in the IC. This has the effect of increasing the current delivered to the battery during thermal regulation. One method is by dissipating some of the power through an external component, such as a resistor or diode. Example: An LTC4054 operating from a 5V wall adapter is programmed to supply 800mA full-scale current to a discharged Li-Ion battery with a voltage of 3.75V. Assuming θJA is 125°C/W, the approximate charge current at an ambient temperature of 25°C is: IBAT = 120°C – 25°C = 608mA (5V – 3.75V)• 125°C / W By dropping voltage across a resistor in series with a 5V wall adapter (shown in Figure 3), the on-chip power dissipation can be decreased, thus increasing the thermally regulated charge current IBAT = 120°C – 25°C (VS – IBATRCC – VBAT )• θ JA 405442xf 11 LTC4054-4.2/LTC4054X-4.2 APPLICATIO S I FOR ATIO VS RCC VCC BAT 1µF LTC4054-4.2 PROG GND RPROG Li-Ion CELL 405442 F03 Figure 3. A Circuit to Maximize Thermal Mode Charge Current Solving for IBAT using the quadratic formula2. IBAT =  4R (120°C – TA ) (VS – VBAT ) –  (VS – VBAT )2 CC    θ JA 2RCC Using RCC = 0.25Ω, VS = 5V, VBAT = 3.75V, TA = 25°C and θJA = 125°C/W we can calculate the thermally regulated charge current to be: IBAT = 708.4mA While this application delivers more energy to the battery and reduces charge time in thermal mode, it may actually lengthen charge time in voltage mode if VCC becomes low 1000 VS = 5V 800 CHARGE CURRENT (mA) 600 VS = 5.5V 400 THERMAL MODE 200 VS = 5.25V DROPOUT 0 0 0.25 0.5 0.75 1.0 RCC (Ω) Note 2: Large values of RCC will result in no solution for IBAT. This indicates that the LTC4054 will not generate enough heat to require thermal regulation. 405442xf 12 U enough to put the LTC4054 into dropout. Figure 4 shows how this circuit can result in dropout as RCC becomes large. This technique works best when RCC values are minimized to keep component size small and avoid dropout. Remember to choose a resistor with adequate power handling capability. VCC Bypass Capacitor Many types of capacitors can be used for input bypassing, however, caution must be exercised when using multilayer 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, refer to Application Note 88. Charge Current Soft-Start The LTC4054 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 the 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. CONSTANT CURRENT VBAT = 3.75V TA = 25°C θJA = 125°C/W RPROG = 1.25kΩ 1.25 1.5 1.75 405442 F04 W UU Figure 4. Charge Current vs RCC LTC4054-4.2/LTC4054X-4.2 APPLICATIO S I FOR ATIO CHRG Status Output Pin The CHRG pin can provide an indication that the input voltage is greater than the undervoltage lockout threshold level. A weak pull-down current of approximately 20µA indicates that sufficient voltage is applied to VCC to begin charging. When a discharged battery is connected to the charger, the constant current portion of the charge cycle begins and the CHRG pin pulls to ground. The CHRG pin can sink up to 10mA to drive an LED that indicates that a charge cycle is in progress. When the battery is nearing full charge, the charger enters the constant-voltage portion of the charge cycle and the charge current begins to drop. When the charge current drops below 1/10 of the programmed current, the charge cycle ends and the strong pull-down is replaced by the 20µA pull-down, indicating that the charge cycle has ended. If the input voltage is removed or drops below the undervoltage lockout threshold, the CHRG pin becomes high impedance. Figure 5 shows that by using two different value pull-up resistors, a microprocessor can detect all three states from this pin. V+ VDD VCC LTC4054 CHRG 800k 2k µPROCESSOR OUT IN 405442 F05 Figure 5. Using a Microprocessor to Determine CHRG State 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 To detect when the LTC4054 is in 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 voltage low even with the 2k pull-up resistor. Once the charge cycle terminates, the N-channel MOSFET is turned off and a 20µA current source is connected to the CHRG pin. The IN pin will then be pulled high by the 2k pull-up resistor. To determine if there is a weak pull-down current, the OUT pin should be forced to a high impedance state. The weak current source will pull the IN pin low through the 800k resistor; if CHRG is high impedance, the IN pin will be pulled high, indicating that the part is in a UVLO state. Reverse Polarity Input Voltage Protection 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 Pchannel MOSFET can be used (as shown in Figure 6). DRAIN-BULK DIODE OF FET VIN LTC4054 VCC 4054 F06 W UU Figure 6. Low Loss Input Reverse Polarity Protection 405442xf 13 LTC4054-4.2/LTC4054X-4.2 APPLICATIO S I FOR ATIO USB and Wall Adapter Power The LTC4054 allows charging from both a wall adapter and a USB port. Figure 7 shows an example of 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 pull-down resistor. Typically a wall adapter can supply more current than the 500mA-limited USB port. Therefore, an N-channel MOSFET, MN1, and an extra 10k program resistor are used to increase the charge current to 600mA when the wall adapter is present. 14 U 5V WALL ADAPTER 600mA ICHG USB POWER 500mA ICHG D1 4 MP1 LTC4054-4.2 3 BAT VCC PROG 10k 1k MN1 2k 405442 F07 W UU ICHG SYSTEM LOAD 5 + Li-Ion BATTERY Figure 7. Combining Wall Adapter and USB Power 405442xf LTC4054-4.2/LTC4054X-4.2 PACKAGE DESCRIPTIO U S5 Package 5-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1635) 2.90 BSC (NOTE 4) 1.22 REF 1.4 MIN 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.30 – 0.45 TYP 5 PLCS (NOTE 3) 0.95 BSC 0.80 – 0.90 0.20 BSC 1.00 MAX DATUM ‘A’ 0.01 – 0.10 1.90 BSC S5 TSOT-23 0302 0.62 MAX 0.95 REF 3.85 MAX 2.62 REF 0.30 – 0.50 REF 0.09 – 0.20 (NOTE 3) NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. JEDEC PACKAGE REFERENCE IS MO-193 405442xf 15 LTC4054-4.2/LTC4054X-4.2 TYPICAL APPLICATIO S USB/Wall Adapter Power Li-Ion Charger 5V WALL ADAPTER USB POWER 1k 4 1µF BAT LTC4054-4.2 VCC 5 PROG GND 2 10k 2.5k 100mA/ 500mA µC 405442 TA05 3 800mA Li-Ion Charger with External Power Dissipation 405442 TA02 VIN = 5V 0.25Ω 4 1µF VCC BAT PROG 3 5 800mA LTC4054-4.2 GND 2 1.25k RELATED PARTS PART NUMBER LTC1732 LTC1733 LTC1734 LTC1734L LTC1998 LTC4050 DESCRIPTION Lithium-Ion Linear Battery Charger Controller Monolithic Lithium-Ion Linear Battery Charger Lithium-Ion Linear Battery Charger in ThinSOT Lithium-Ion Linear Battery Charger in ThinSOT Lithium-Ion Low Battery Detector Lithium-Ion Linear Battery Charger Controller COMMENTS Simple Charger uses External FET, Features Preset Voltages, C/10 Charger Detection and Programmable Timer, Input Power Good Indication Standalone Charger with Programmable Timer, Up to 1.5A Charge Current Simple ThinSOT Charger, No Blocking Diode, No Sense Resistor Needed Low Current Version of LTC1734 1% Accurate 2.5µA Quiescent Current, SOT-23 Simple Charger uses External FET, Features Preset Voltages, C/10 Charger Detection and Programmable Timer, Input Power Good Indication, Thermistor Interface No Blocking Diode or External Power FET Required Standalone Charger with Programmable Timer, Up to 1.25A Charge Current LTC4052 LTC4053 LTC4054L LTC4056 LTC4057 LTC4410 Monolithic Lithium-Ion Battery Pulse Charger USB Compatible Monolithic Li-Ion Battery Charger 10mA to 150mA Standalone Monolithic Lithium-Ion Low Current Version of LTC4054 Linear Battery Charger in ThinSOT Standalone Lithium-Ion Linear Battery Charger in ThinSOT Monolithic Lithium-Ion Linear Battery Charger with Thermal Regulation in ThinSOT USB Power Manager Standalone Charger with Programmable Timer, No Blocking Diode, No Sense Resistor Needed No External MOSFET, Sense Resistor or Blocking Diode Required, Charge Current Monitor for Gas Gauging 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 405442xf 16 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 q FAX: (408) 434-0507 q U Full Featured Single Cell Li-Ion Charger VIN = 5V IBAT + Li-Ion CELL 4 VCC 330Ω 1 BAT PROG 3 5 1µF 500mA LTC4054-4.2 CHRG GND 2 + 2k SHDN Basic Li-Ion Charger with Reverse Polarity Input Protection 5V WALL ADAPTER 4 3 5 500mA VCC BAT PROG + 1µF LTC4054-4.2 + GND 2 2k 405442 TA03 405442 TA04 LT/TP 0903 1K • PRINTED IN USA www.linear.com © LINEAR TECHNOLOGY CORPORATION 2003