LTC4054L-4.2 150mA Standalone Linear Li-Ion Battery Charger in ThinSOT DESCRIPTIO U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Programmable Charge Current Range: 10mA to 150mA No External MOSFET, Sense Resistor or Blocking Diode Required Complete Linear Charger in ThinSOTTM Package for Single Cell/Coin 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 Max Supply Current in Shutdown Mode 2.9V Trickle Charge Threshold Soft-Start Limits Inrush Current Available in a 6-Lead Low Profile (1mm) SOT-23 Package U APPLICATIO S ■ ■ ■ Charger for Li-Ion Coin Cell Batteries Portable MP3 Players, Wireless Headsets Bluetooth Applications Multifunction Wristwatches U ■ TYPICAL APPLICATIO The LTC®4054L is a complete, constant-current/constantvoltage linear charger for single cell lithium-ion batteries. Its small size and ability to regulate low charge currents make the LTC4054L especially well-suited for portable applications using low capacity rechargeable lithium-ion coin cells. Furthermore, the LTC4054L 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 eliminate thermal overdesign. The charge voltage is fixed at 4.2V, and the charge current can be programmed externally with a single resistor. The LTC4054L automatically terminates a 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 LTC4054L automatically enters a low current state, dropping the battery drain current to less than 2µA. The LTC4054L 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 Complete Charge Cycle (130mAh Battery) 100 90mA Li-Ion Single Coin Cell Charger 90 80 1µF 4 VCC BAT LTC4054L-4.2 PROG GND 2 3 90mA 5 1.69k 4.2V COIN CELL Li-Ion BATTERY CONSTANT CURRENT 70 4.3 CONSTANT VOLTAGE 4.2 4.1 60 4.0 50 3.9 40 3.8 30 20 10 0 4054l42 TA01 4.4 3.7 VCC = 5V θJA = 130°C/W RPROG = 1.69k TA = 25°C BATTERY VOLTAGE (V) VIN 4.5V TO 6.5V CHARGE CURRENT (mA) ■ 3.6 3.5 3.4 0 0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0 2.25 TIME (HOURS) 4054l42 TA01b 4054l42f 1 LTC4054L-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 ............................................. – 0.3V to VCC + 0.3V CHRG ........................................................ –0.3V to 10V BAT ............................................................. – 0.3V to 7V BAT Short-Circuit Duration .......................... Continuous BAT Pin Current ................................................. 200mA PROG Pin Current ................................................ 1.5mA Maximum Junction Temperature .......................... 125°C Operating 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 TOP VIEW CHRG 1 LTC4054LES5-4.2 5 PROG GND 2 BAT 3 4 VCC S5 PART MARKING S5 PACKAGE 5-LEAD PLASTIC TSOT-23 LTAFA TJMAX = 125°C, θJA = 80°C/ W TO 150°C/W DEPENDING ON PC BOARD LAYOUT (NOTE 3) 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 Supply Voltage CONDITIONS MIN ICC Supply Current Charge Mode (Note 4), RPROG = 1k Standby Mode (Charge Terminated) Shutdown Mode (RPROG Not Connected, VCC < VBAT, or VCC < VUV) VFLOAT Regulated Output (Float) Voltage 0°C ≤ TA ≤ 85°C, IBAT = 40mA IBAT BAT Pin Current RPROG = 15k, Current Mode RPROG = 1k, Current Mode Standby Mode, VBAT = 4.2V Shutdown Mode (RPROG Not Connected) Sleep Mode, VCC = 0V ITRIKL Trickle Charge Current VBAT < VTRIKL, RPROG = 1k (IBAT = 150mA) ● VTRIKL Trickle Charge Threshold Voltage RPROG = 15k, VBAT Rising VTRHYS Trickle Charge Hysteresis Voltage RPROG = 15k VUV VCC Undervoltage Lockout Threshold Voltage From VCC Low to High VUVHYS VCC Undervoltage Lockout Hysteresis Voltage VMSD Manual Shutdown Threshold Voltage PROG Pin Rising PROG Pin Falling VASD VCC – VBAT Lockout Threshold Voltage VCC from Low to High VCC from High to Low ITERM C/10 Termination Current Threshold RPROG = 15k (IBAT = 10mA) (Note 5) RPROG = 1k (IBAT = 150mA) (Note 5) VPROG PROG Pin Voltage RPROG = 1k, Current Mode ICHRG CHRG Pin Weak Pull-Down Current VCHRG = 5V VCHRG CHRG Pin Output Low Voltage ICHRG = 5mA ∆VRECHRG Recharge Battery Hysteresis Voltage VFLOAT – VRECHRG ● MAX UNITS 6.5 V 1200 200 25 2000 500 50 µA µA µA 4.158 4.2 4.242 V 9.3 142.5 0 10 150 –2.5 ±1 ±1 10.7 157.5 –6 ±2 ±2 mA mA µA µA µA 5 15 25 mA 2.8 2.9 3 V ● ● ● ● ● ● TYP 4.25 60 80 110 mV ● 3.7 3.8 3.92 V ● 150 200 300 mV ● ● 1.15 0.9 1.21 1.0 1.30 1.1 V V 70 5 100 30 140 50 mV mV ● ● 0.085 0.088 0.10 0.10 0.115 0.112 ● 0.93 1 1.07 V 8 20 35 µA 0.35 0.6 V 150 200 mV 100 mA/mA mA/mA 4054l42f 2 LTC4054L-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) 1.5 Ω tSS Soft-Start Time IBAT = 0 to IBAT =150V/RPROG tRECHARGE Recharge Comparator Filter Time VBAT High to Low 0.75 2 4.5 ms tTERM Termination Comparator Filter Time IBAT Drops Below ICHG/10 400 1000 2500 µs IPROG PROG Pin Pull-Up Current 1.5 3 5 µA µs 100 Note 3: See Thermal Considerations. Note 4: Supply current includes PROG pin current (≈1mA) but does not include any current delivered to the battery through the BAT pin. Note 5: ITERM is expressed as a fraction of measured full charge current with indicated PROG resistor. Note 1: Absolute Maximum Ratings are those values beyond which the life of the device may be impaired. Note 2: The LTC4054LE-4.2 is 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 PROG Pin Voltage vs Temperature (Constant Current Mode) 1.0100 VCC = 5V VBAT = 4V TA = 25°C 1.0075 1.0075 1.0050 180 VCC = 5V VBAT = 4V RPROG = 1k VCC = 5V RPROG = 1k TA = 25°C 150 1.0050 RPROG = 1k IBAT (mA) 1.0000 120 1.0025 VPROG (V) VPROG (V) 1.0025 1.0000 RPROG = 15k 0.9975 0.9975 0.9950 0.9950 0.9925 0.9925 0.9900 Charge Current vs PROG Pin Voltage 4 4.5 5 5.5 VCC (V) 6 6.5 7 4054L G01 0.9900 –50 90 60 30 0 –25 0 50 25 TEMPERATURE (°C) 75 100 4054L G02 0 0.25 0.5 0.75 VPROG (V) 1 1.25 4054L G03 4054l42f 3 LTC4054L-4.2 U W TYPICAL PERFOR A CE CHARACTERISTICS PROG Pin Pull-Up Current vs Temperature and Supply Voltage 3.7 PROG Pin Current vs PROG Pin Voltage (Pull-Up Current) VCC = 5V VBAT = 4.3V TA = 25°C 3.0 3.5 –100 VCC = 6.5V VCC = 4.2V 2.9 2.0 1.5 1.0 2.7 –200 –250 –300 0.5 2.5 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 –350 0 2.0 125 –400 2.1 2.2 2.3 2.4 2 2.6 2.5 4.215 VCC = 5V RPROG = 600Ω 4.24 TA = 25°C 4.210 4.215 VCC = 5V RPROG = 1k VFLOAT (V) 4.205 4.200 4.200 4.195 4.195 4.16 4.190 4.190 60 90 120 IBAT (mA) 150 180 4.185 –50 –25 0 25 50 TEMPERATURE (°C) 4054L G07 4.185 12 10 2 4 3 VCHRG (V) 5 6 7 4054L G10 4 – 50 – 25 16 14 12 VCC = 5V VBAT = 4.3V TA = 25°C 10 6 1 7 18 14 8 0 6.5 6 20 5 0 5.5 VCC (V) 22 ICHRG (µA) 10 5 4.5 CHRG Pin I-V Curve (Weak Pull-Down State) VCC = 5V 18 VBAT = 4V VCHRG = 1V 16 15 4 4054L G09 20 VCC = 5V VBAT = 4V TA = 25°C ICHRG (mA) ICHRG (mA) 100 CHRG Pin Current vs Temperature (Strong Pull-Down State) 25 20 75 4054L G08 CHRG Pin I-V Curve (Strong Pull-Down State) 5.5 RPROG = 1k TA = 25°C 4.210 4.18 30 5 Regulated Output (Float) Voltage vs Supply Voltage 4.205 VFLOAT (V) 4.22 4.20 4.5 4 3.5 VPROG (V) 4054L G06 Regulated Output (Float) Voltage vs Temperature 4.26 0 3 4054L G05 Regulated Output (Float) Voltage vs Charge Current 4.14 2.5 VPROG (V) 4054L G04 VFLOAT (V) –150 IPROG (µA) IPROG (µA) 3.1 VCC = 5V VBAT = 4.3V TA = 25°C –50 2.5 3.3 IPROG (µA) 0 3.5 VBAT = 4.3V VPROG = 0V PROG Pin Current vs PROG Pin Voltage (Clamp Current) 8 75 50 25 TEMPERATURE (°C) 0 100 125 4054L G11 0 1 2 4 3 VCHRG (V) 5 6 7 4054L G12 4054l42f 4 LTC4054L-4.2 U W TYPICAL PERFOR A CE CHARACTERISTICS CHRG Pin Current vs Temperature (Weak Pull-Down State) Trickle Charge Current vs Temperature Trickle Charge Current vs Supply Voltage 15 28 VCC = 5V VBAT = 4.3V 25 VCHRG = 5V 15 RPROG = 1k RPROG = 1k 12 12 19 ITRKL (mA) ITRKL (mA) ICHRG (µA) 22 9 VCC = 5V VBAT = 2.5V 6 9 VBAT = 2.5V TA = 25°C 6 16 3 13 3 RPROG = 15k 10 –50 0 25 50 TEMPERATURE (°C) –25 75 0 –50 100 –25 0 25 50 TEMPERATURE (°C) RPROG = 15k 75 4054L G13 0 100 4 4.5 5 5.5 VCC (V) 6 6.5 4054L G14 Trickle Charge Threshold vs Temperature 4054L G15 Charge Current vs Battery Voltage 3.000 160 2.950 120 7 Charge Current vs Supply Voltage 200 VCC = 5V 2.975 RPROG = 1k VBAT = 4V TA = 25°C θJA = 125°C/W 160 2.900 VCC = 5V RPROG = 1k TA = 25°C θJA = 125°C/W 80 2.875 IBAT (mA) IBAT (mA) VTRKL (V) RPROG = 1k 2.925 120 80 40 2.850 40 2.825 2.800 –50 RPROG = 15k 0 –25 0 50 25 TEMPERATURE (°C) 75 2.7 100 3.0 3.3 4.2 3.6 3.9 VBAT (V) Charge Current vs Ambient Temperature 180 4.11 RPROG = 1k 4.09 150 1.8 VCC = 5V RPROG = 1k 1.6 RDS(ON) (mΩ) VRECHRG (V) IBAT (mA) 5 5.5 VCC (V) 6 6.5 4.05 60 4.03 30 4.01 7 Power FET “ON” Resistance vs Temperature 4.07 VBAT = 4V 90 VCC = 5V θJA = 125°C/W 4.5 4054L G18 Recharge Voltage Threshold vs Temperature ONSET OF THERMAL REGULATION 4 4054L G17 4054L G16 120 0 4.5 VCC = 4.1V VBAT = 4V RPROG = 1k 1.4 1.2 1.0 RPROG = 15k 0 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 125 4054L G19 3.99 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 4054L G20 0.8 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 125 4054L G21 4054l42f 5 LTC4054L-4.2 U U U 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 LTC4054L detects an undervoltage lockout condition, CHRG is forced high impedance. 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: GND (Pin 2): Ground. The PROG pin is also 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. 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 this float voltage and 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 LTC4054L enters shutdown mode, dropping IBAT to less than 2µA. IBAT = (VPROG/RPROG) • 150 4054l42f 6 LTC4054L-4.2 W BLOCK DIAGRA 4 VCC 120°C TA TDIE 1× 150× – + BAT 5µA MA 3 R1 + VA R2 – CA + – REF 1.21V – SHDN C1 + R3 1V R4 + 0.1V C2 CHRG 1 R5 – STANDBY VCC 3µA C3 – + 2.9V TO BAT PROG 5 GND 2 RPROG 4054L42 BD 4054l42f 7 LTC4054L-4.2 U OPERATIO The LTC4054L is a single cell lithium-ion battery charger using a constant-current/constant-voltage algorithm. Its ability to control charge currents as low as 10mA make it well-suited for charging low capacity lithium-ion coin cell batteries. The LTC4054L includes an internal P-channel power MOSFET and thermal regulation circuitry. No blocking diode or external sense resistor is required; thus, the basic charger circuit requires only three external components. Furthermore, the LTC4054L is capable of operating from a USB power source. Normal Charge Cycle The charge cycle begins when the voltage at the VCC pin rises above the UVLO 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 LTC4054L supplies approximately 1/10 the programmed charge current in order to bring the battery voltage up to a safe level for full current charging. 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 LTC4054L 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 150 times the current out of the PROG pin. The program resistor and the charge current are calculated using the following equations: RPROG = 150 V 150 V , I CHG = 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: IBAT = VPROG • 150 RPROG Charge Termination The 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 LTC4054L enters standby mode, where the input supply current drops to 200µA. (Note: C/10 termination is disabled in trickle charging and thermal limiting modes.) While 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 for longer than tTERM , the LTC4054L 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 LTC4054L 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. 1Any external sources that hold the PROG pin above 100mV will prevent the LTC4054L from terminating a charge cycle. 4054l42f 8 LTC4054L-4.2 U OPERATIO POWER ON BAT < 2.9V PROG RECONNECTED OR UVLO CONDITION STOPS TRICKLE CHARGE MODE 1/10TH FULL CURRENT CHRG: STRONG PULL-DOWN BAT > 2.9V SHUTDOWN MODE CHARGE MODE ICC DROPS TO <25µA FULL CURRENT CHRG: Hi-Z IN UVLO WEAK PULL-DOWN OTHERWISE CHRG: STRONG PULL-DOWN BAT > 2.9V PROG < 100mV STANDBY MODE NO CHARGE CURRENT PROG FLOATED OR UVLO CONDITION CHRG: WEAK PULL-DOWN 2.9V < BAT < 4.05V 4054L42 F01 Figure 1. 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 (~20uA), and high impedance. The strong pull-down state indicates that the LTC4054L is in a charge cycle. Once the charge cycle has terminated, the pin state is determined by undervoltage lockout conditions. A weak pull-down indicates that VCC meets the UVLO conditions and the LTC4054L is ready to charge. High impedance indicates that LTC4054L is in undervoltage lock-out mode: either VCC is within 100mV of 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 LTC4054L 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 LTC4054L. 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. 4054l42f 9 LTC4054L-4.2 U OPERATIO Manual Shutdown Automatic Recharge At any point in the charge cycle, the LTC4054L can be put into shutdown mode by removing RPROG thus floating the PROG pin. This reduces the battery drain current to less than 2µA and the supply current to less than 50µA. A new charge cycle can be initiated by reconnecting the program resistor. Once the charge cycle is terminated, the LTC4054L 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 pull-down state during recharge cycles. 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 LTC4054L is in undervoltage lockout mode: either VCC is within 100mV of the BAT pin voltage or insufficient voltage is applied to the VCC pin. 4054l42f 10 LTC4054L-4.2 U W U U APPLICATIO S I FOR ATIO Stability Considerations 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. 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: RPROG ≤ Power Dissipation The conditions that cause the LTC4054L 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 from 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: 1 • CPROG 2π • 105 TA = 120°C – PDθJA TA = 120°C – (VCC – VBAT) • IBAT • θJA CHARGE CURRENT MONITOR CIRCUITRY 10k PROG LTC4054L RPROG CFILTER GND 4054L42 F02 Figure 2. Isolating Capacitive Load on PROG Pin and Filtering 4054l42f 11 LTC4054L-4.2 U W U U APPLICATIO S I FOR ATIO Example: An LTC4054L operating from a 6V wall adapter is programmed to supply 150mA full-scale current to a discharged Li-Ion battery with a voltage of 3.75V. Assuming θJA is 200°C/W, the ambient temperature at which the LTC4054L will begin to reduce the charge current is approximately: TA = 120°C – (6V – 3.75V) • (150mA) • 200°C/W TA = 120°C – 0.3375W • 200°C/W = 120°C – 67.5°C TA = 52.5°C The LTC4054L can be used above 52.5°C, but the charge current will be reduced from 150mA. 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 60°C = (6V – 3.75V) • 200°C/W 450°C/A IBAT = 133mA 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 LTC4054L 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. 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 BOARD AREA THERMAL RESISTANCE JUNCTION-TO-AMBIENT 2500mm2 2500mm2 2500mm2 125°C/W 1000mm2 2500mm2 2500mm2 125°C/W 225mm2 2500mm2 2500mm2 130°C/W 100mm2 2500mm2 2500mm2 135°C/W 50mm2 2500mm2 2500mm2 150°C/W *Each layer uses one ounce copper Table 2. Measured Thermal Resistance (4-Layer Board**) COPPER AREA (EACH SIDE) BOARD AREA THERMAL RESISTANCE JUNCTION-TO-AMBIENT 2500mm2*** 2500mm2 80°C/W **Top and bottom layers use two ounce copper, inner layers use one ounce copper. ***10,000mm2 total copper area 4054l42f 12 LTC4054L-4.2 U W U U APPLICATIO S I FOR ATIO 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 LTC4054L 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. 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 3 shows that by using two different value pull-up resistors, a microprocessor can detect all three states from this pin. To detect when the LTC4054L 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. V+ VCC LTC4054L CHRG VDD 800k 2k µPROCESSOR OUT IN 4054L42 F03 Figure 3. Using a Microprocessor to Determine CHRG State 4054l42f 13 LTC4054L-4.2 U W U U APPLICATIO S I FOR ATIO Reverse Polarity Input Voltage Protection USB and Wall Adapter Power 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). The LTC4054L allows charging from both a wall adapter and a USB port. Figure 5 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. DRAIN-BULK DIODE OF FET VIN LTC4054L VCC 4054L42 F04 5V WALL ADAPTER BAT Figure 4. Low Loss Input Reverse Polarity Protection 4 VCC PROG 5 MP1 1k 100mA SYSTEM LOAD LTC4054L-4.2 D1 USB POWER 3 + Li-Ion BATTERY 1.5k 4054l42 F05 Figure 5. Combining Wall Adapter and USB Power 4054l42f 14 LTC4054L-4.2 U PACKAGE DESCRIPTIO S5 Package 5-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1635) 0.62 MAX 0.95 REF 2.90 BSC (NOTE 4) 1.22 REF 1.4 MIN 3.85 MAX 2.62 REF 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 0.01 – 0.10 1.00 MAX DATUM ‘A’ 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 1.90 BSC S5 TSOT-23 0302 4054l42f 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. 15 LTC4054L-4.2 U TYPICAL APPLICATIO S Basic Li-Ion Battery Charger with Reverse Polarity Input Protection Full Featured Single Cell Li-Ion Charger VIN = 5V CHARGING 4 VCC 330Ω BAT 3 4 5V WALL ADAPTER 1µF 100mA CHRG GND 2 PROG 1µF 5 BAT 3 100mA LTC4054L-4.2 LTC4054L-4.2 1 VCC + GND 2 PROG 5 + 1.5k 1.5k 4054L42 TA03 SHDN 4054L42 TA02 USB/Wall Adapter Power Li-Ion Charger 5V WALL ADAPTER BAT 3 + LTC4054L-4.2 4 USB POWER 1µF 1k VCC PROG GND 2 100mA Li-Ion CELL 5 1.5k 4054L42 TA05 RELATED PARTS PART NUMBER LTC1731 DESCRIPTION Lithium-Ion Linear Battery Charger Controller LTC1732 Lithium-Ion Linear Battery Charger Controller LTC1733 LTC1734 LTC1734L LTC1998 LTC4050 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 LTC4052 LTC4053 LTC4054 Monolithic Lithium-Ion Battery Pulse Charger USB Compatible Monolithic Li-Ion Battery Charger 800mA Standalone Linear Li-Ion Battery Charger with Thermal Regulation in ThinSOT Standalone Lithium-Ion Linear Battery Charger in ThinSOT Monolithic Lithium-Ion Linear Battery Charger with Thermal Regulation in ThinSOT 950mA Standalone Li-Ion Charger in 3mm × 3mm DFN USB Power Manager LTC4056 LTC4057 LTC4058 LTC4410 COMMENTS Simple Charger uses External FET, Features Preset Voltages, C/10 Charger Detection and Programmable Timer 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, Safety Current Limit Standalone Charger with Programmable Timer, Up to 1.25A Charge Current No External MOSFET, Sense Resistor or Blocking Diode Required, Charge Current Monitor for Gas Gauging, C/10 Charge Termination 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 USB Compatible, Thermal Regulation Protects Against Overheating 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 4054l42f 16 Linear Technology Corporation LT/TP 1203 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