LTC4095 Standalone USB Li-Ion/Polymer Battery Charger in 2mm × 2mm DFN FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTION Full-Featured Standalone USB Li-Ion/Polymer Battery Charger 100mA to 950mA Programmable Charge Current C/10 Charge Current Detection Output Internal Safety Timer Termination NTC Thermistor Input for Temperature Qualified Charging Preset 4.2V Float Voltage with 0.5% Accuracy Constant-Current/Constant-Voltage Operation with Thermal Feedback Charge Current Monitor Output for Gas Gauging Automatic Recharge Bad-Battery Detection 8.5µA Input Supply Current in Suspend Mode Tiny 8-Lead (2mm × 2mm) DFN Package APPLICATIONS ■ ■ ■ ■ PDAs Media Players Cellular Phones Other Portable Electronics The LTC®4095 is a complete constant-current/constantvoltage linear charger for single-cell lithium-ion/polymer batteries. Its small 2mm × 2mm DFN package and low external component count make the LTC4095 especially well-suited for portable USB power applications. Up to 950mA of charge current may be programmed via a single resistor from the PROG pin to ground. The HPWR pin allows the charge current to be set at 20% or 100% of its full-scale programmed value. An internal safety timer terminates charge current. The final float voltage is preset to 4.2V and held to a tight 0.5% tolerance. Also featured is an NTC thermistor input to monitor battery temperature while charging, a C/10 current detection output, automatic recharge, bad-battery detection and low-battery trickle charge. A thermal feedback loop regulates the charge current to limit the die temperature during high power operation or high ambient thermal conditions. The LTC4095 is available in a tiny, low profile (0.75mm) 8-lead 2mm × 2mm DFN package. , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 6522118, 6570372, 6700364. TYPICAL APPLICATION 500mA Single-Cell Li-Ion Charger IN 4.3V TO 5.5V UP TO 7V TRANSIENTS CIN 1µF BAT IN LTC4095 + HPWR CHRG NTC SUSP PROG GND Li-Ion BATTERY RPROG 1.74k 4095 TA01a 4095fa 1 LTC4095 ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION (Notes 1, 2, 3) Input Supply Voltage (IN) t < 1ms and Duty Cycle < 1% .................. –0.3V to 7V Steady State............................................. –0.3V to 6V BAT, SUSP, ⎯C⎯H⎯R⎯G Voltage ............................ –0.3V to 6V PROG, NTC, HPWR Voltage ............................ –0.3V to Max (IN, BAT) + 0.3V IBAT .............................................................................1A IPROG ...................................................................1.25mA I⎯C⎯H⎯R⎯G ......................................................................50mA Junction Temperature ........................................... 125°C Operating Temperature Range ................. –40°C to 85°C Storage Temperature Range................... –65°C to 125°C TOP VIEW 8 IN BAT 1 GND 2 9 7 PROG CHRG 3 6 NTC SUSP 4 5 HPWR DC PACKAGE 8-LEAD (2mm × 2mm) PLASTIC DFN TJMAX = 125°C, θJA = 60°C/W EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB ORDER PART NUMBER DC PART MARKING LTC4095EDC LCLG Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. IN = HPWR = 5V, BAT = 3.8V, NTC = SUSP = 0V, RPROG = 1.74k unless otherwise specified. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Battery Charger IN Input Supply Voltage IIN Battery Charger Quiescent Current (Note 4) VFLOAT BAT Regulated Output Voltage ● 4.3 5.5 V 200 8.5 400 17 µA µA 4.179 4.165 4.200 4.200 4.221 4.235 V V 440 84 460 92 500 100 mA mA –3.5 –2.0 –1.3 –7 –4 –3 µA µA µA 4.0 4.125 Standby Mode; Charger Terminated Suspend Mode; SUSP = 5V 0°C ≤ TA ≤ 85°C ICHG Constant-Current Mode Charge Current HPWR = 5V HPWR = 0V IBAT Battery Drain Current Standby Mode; Charger Terminated Shutdown Mode; IN < VUVLO, BAT = 4.2V Suspend Mode; SUSP = 5V, BAT = 4.2V ● VUVLO Undervoltage Lockout Threshold BAT = 3.5V, IN Rising ΔVUVLO Undervoltage Lockout Hystersis BAT = 3.5V 3.875 VDUVLO Differential Undervoltage Lockout Threshold BAT = 4.05V, (IN – BAT), IN Falling ΔVDUVLO Differential Undervoltage Lockout Hysteresis BAT = 4.05V 125 PROG PROG Pin Servo Voltage HPWR = 5V HPWR = 0V BAT < VTRKL 1.000 0.200 0.100 hPROG Ratio of IBAT to PROG Pin Current ITRKL Trickle Charge Current BAT < VTRKL 37 46 55 mA VTRKL Trickle Charge Threshold Voltage BAT Rising 2.8 2.9 3.0 V ΔVTRKL Trickle Charge Hysteresis Voltage ΔVRECHRG Recharge Battery Threshold Voltage Threshold Voltage Relative to VFLOAT –75 –95 200 25 40 V mV 60 mV mV V V V 800 mA/mA 100 mV –115 mV 4095fa 2 LTC4095 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. IN = HPWR = 5V, BAT = 3.8V, NTC = SUSP = 0V, RPROG = 1.74k unless otherwise specified. SYMBOL PARAMETER CONDITIONS tRECHRG Recharge Comparator Filter Time BAT Falling MIN TYP MAX tTERM Safety Timer Termination Period BAT = VFLOAT 3.5 4 4.5 0.4375 0.5 0.5625 0.09 0.1 0.11 1.7 UNITS ms Hour tBADBAT Bad-Battery Termination Time BAT < VTRKL hC/10 End of Charge Indication Current Level (Note 5) Hour tC/10 End of Charge Comparator Filter Time IBAT Falling 2.2 ms RON_CHG Battery Charger Power FET OnResistance (Between IN and BAT) IBAT = 200mA 500 mΩ TLIM Junction Temperature in Constant Temperature 115 °C mA/mA NTC VCOLD Cold Temperature Fault Threshold Voltage Rising NTC Voltage Hysteresis 0.750 • IN 0.765 • IN 0.780 • IN 0.016 • IN V V VHOT Hot Temperature Fault Threshold Voltage Falling NTC Voltage Hysteresis 0.334 • IN 0.349 • IN 0.364 • IN 0.016 • IN V V VDIS NTC Disable Threshold Voltage Falling NTC Voltage Hysteresis 0.007 • IN 0.017 • IN 0.027 • IN 0.010 • IN mV mV INTC NTC Leakage Current NTC = IN = 5V ● –1 0 1 µA 0.4 V 3.6 6.3 MΩ 100 250 mV 0 1 µA Logic (HPWR, SUSP, ⎯C⎯H⎯R⎯G) VIL Input Low Voltage HPWR, SUSP Pins VIH Input High Voltage HPWR, SUSP Pins RDN ⎯ H ⎯ ⎯R⎯G C Logic Pin Pull-Down Resistance ⎯CH ⎯ R ⎯ G ⎯ Pin Output Low Voltage HPWR, SUSP Pins I⎯C⎯H⎯R⎯G ⎯C⎯H⎯R⎯G Pin Input Current I⎯C⎯H⎯R⎯G = 5mA BAT = 4.5V, ⎯C⎯H⎯R⎯G = 5V Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LTC4095 is guaranteed to meet performance specifications from 0°C to 85°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: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125°C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may impair device reliability. 1.2 ● 1.9 V Note 4: IN supply current does not include current through the PROG pin or any current delivered to the battery through the BAT pin. Total input current is equal to this specification plus 1.00125 • IBAT where IBAT is the charge current. Note 5: hC/10 is expressed as a fraction of measured full charge current with indicated PROG resistor. 4095fa 3 LTC4095 TYPICAL PERFORMANCE CHARACTERISTICS Battery Regulation (Float) Voltage vs Battery Charge Current Battery Regulation (Float) Voltage vs Temperature IN = 5V 4.24 RPROG = 0.845k HPWR = 5V 4.23 VBAT (V) VBAT (V) 4.22 4.20 4.19 4.18 4.17 Charge Current vs Supply Voltage (Constant Current Mode) 4.215 500 4.210 490 4.205 480 IBAT (mA) 4.25 4.21 TA = 25°C, unless otherwise noted. 4.200 IN = 5V RPROG = 1.74k HPWR = 5V 470 4.195 460 4.190 450 4.16 200 0 600 400 IBAT (mA) 800 4.185 –55 1000 –35 –15 25 45 5 TEMPERATURE (°C) 65 4095 G01 Charge Current vs Ambient Temperature with Thermal Regulation 400 HPWR = 5V IBAT (mA) IBAT (mA) 350 200 300 250 200 150 IN = 5V BAT = 3.8V 50 RPROG = 1.74k HPWR = 5V 0 –50 –25 0 25 50 75 100 125 150 TEMPERATURE (°C) HPWR = 0V 100 100 0 2 2.5 3 3.5 BAT (V) 4 4.5 2400 G31 2.0 700 IN = 5V BAT = 3.8V HPWR = 5V 0 1.0 0 100 300 200 IBAT (mA) 400 500 4095 G06 1 2 4 3 TIME (HOUR) 6 5 4095 G18 0 IN = 4V IBAT = 200mA 500 400 0.5 0.2 5.5 600 RON (mΩ) PROG (V) PROG (V) 0.4 5.3 Power FET On-Resistance vs Temperature 1.5 0.6 5.1 IN = 5V RPROG = 0.845k HPWR = 5V 0 PROG Pin Voltage vs PROG Pin Resistance (Constant Current Mode) IN = 5V RPROG = 1.74k HPWR = 5V 0.8 4.9 IN (V) 4095 G05 PROG Pin Voltage vs Charge Current 1.0 1000 800 600 400 200 0 5.0 4.5 4.0 3.5 3.0 5.0 4.0 3.0 2.0 1.0 0 IBAT (mA) 450 300 4.7 Complete Charge Cycle (2400mAh Battery) 500 IN = 5V RPROG = 1.74k 400 4.5 4095 G03 BAT (V) 500 4.3 4095 G02 Charge Current vs Battery Voltage 600 440 85 CHRG (V) 4.15 1 2 3 4 5 6 7 RPROG (kΩ) 8 9 10 4095 G07 300 –55 –35 25 5 45 –15 TEMPERATURE (°C) 65 85 "'# /& 4095fa 4 LTC4095 TYPICAL PERFORMANCE CHARACTERISTICS Recharge Threshold vs Temperature TA = 25°C, unless otherwise noted. Undervoltage Lockout Threshold vs Temperature 115 4.2 SUSP/HPWR Pins Rising Threshold Voltage vs Temperature 1.2 BAT = 3.5V 1.1 4.1 UVLO THRESHOLD (V) ∆VRECHARGE (mV) 95 85 THRESHOLD VOLTAGE (V) RISING 105 4.0 3.9 FALLING 3.8 3.7 3.6 75 –55 –35 25 5 –15 45 TEMPERATURE (°C) 65 25 5 45 –15 TEMPERATURE (°C) 4095 G09 IN = 5V BAT = 4.2V –15 25 45 5 TEMPERATURE (°C) 65 8 85 ⎯C⎯H⎯R⎯G Pin I-V Curve 70 IN = 0V 60 IN = 5V BAT = 3.8V 50 ICHRG (mA) 2.0 6 –35 4095 G11 BAT = 4.2V BAT = 3.6V 40 30 1.5 4 20 IBAT 2 0 –55 –35 25 45 5 –15 TEMPERATURE (°C) 10 65 1.0 –55 85 0 –35 45 –15 5 25 TEMPERATURE (°C) 4095 G12 65 85 0 IN = 5V ICHRG = 5mA 7 1.2 6 1.0 40 20 0 –55 –35 25 5 45 –15 TEMPERATURE (°C) 65 85 4095 G15 4 6 5 0.8 PERCENT ERROR (%) PERCENT ERROR (%) 60 3 CHRG (V) Timer Period Accuracy vs Supply Voltage 5 80 2 4095 G14 Timer Period Accuracy vs Temperature 100 1 4095 G13 ⎯C⎯H⎯R⎯G Pin Output Low Voltage vs Temperature CHRG (mV) 0.6 0.4 –55 85 2.5 IBAT (µA) SUPPLY CURRENT (µA) 65 IIN 120 0.7 Battery Drain Current in UVLO vs Temperature 10 140 0.8 4095 G10 Supply Currents in Suspend vs Temperature 12 0.9 0.5 3.5 –55 –35 85 1.0 4 3 2 1 0.6 0.4 0.2 0 0 –0.2 –1 –0.4 –2 –55 –35 –15 5 25 45 TEMPERATURE (°C) 65 85 4095 G16 –0.6 4.3 4.5 4.7 4.9 IN (V) 5.1 5.3 5.5 4095 G17 4095fa 5 LTC4095 PIN FUNCTIONS BAT (Pin 1): Single Cell Li-Ion Battery Pin. Provides charge current to the battery and regulates final float voltage to 4.2V. GND (Pin 2): Ground ⎯C⎯H⎯R⎯G (Pin 3): Open-Drain Charge Status Output. The ⎯C⎯H⎯R⎯G pin indicates the status of the battery charger. Four possible states are represented by ⎯C⎯H⎯R⎯G: charging, not charging (i.e., the charge current is less than 1/10th of the full-scale charge current), unresponsive battery (i.e., the battery voltage remains below 2.9V after 1/2 hour of charging) and battery temperature out of range. ⎯C⎯H⎯R⎯G requires a pull-up resistor and/or LED to provide indication. SUSP (Pin 4): Suspend Mode Input. A voltage greater than 1.2V on the SUSP pin puts the LTC4095 into suspend mode, disables the charger and resets the termination timer. A weak pull-down current is internally applied to this pin to ensure it is low when the input is not being driven externally. HPWR (Pin 5): High Power Select Input. A voltage greater than 1.2V on the HPWR pin will set the charge current to 100% of its programmed value. A voltage less than 0.4V on the pin will set the charge current to 20% of its programmed value. When used with a 1.74k PROG resistor this pin can toggle between low power and high power modes per USB specification. A weak pull-down current is internally applied to this pin to ensure it is low when the input is not being driven externally. NTC (Pin 6): Input to the NTC Thermistor Monitoring Circuit. The NTC pin connects to a negative temperature coefficient thermistor which is typically co-packaged with the battery pack to determine if the battery is too hot or too cold to charge. If the battery temperature is out of range, charging is paused until the battery temperature re-enters the valid range. A low drift bias resistor is required from IN to NTC and a thermistor is required from NTC to ground. To disable the NTC function, the NTC pin should be grounded. PROG (Pin 7): Charge Current Program and Charge Current Monitor Pin. Charge current is programmed by connecting a resistor from PROG to ground. When charging in constant-current mode, the PROG pin servos to 1V if the HPWR pin is pulled high, or 200mV if the HPWR pin is pulled low. The voltage on this pin always represents the battery current through the following formula: IBAT = PROG • 800 RPROG IN (Pin 8): Input Supply Voltage. This pin provides power to the battery charger and should be bypassed with at least a 1µF capacitor. IN can range from 4.3V to 5.5V. Exposed Pad (Pin 9): Ground. The exposed package pad is ground and must be soldered to the PCB ground for proper functionality and for maximum heat transfer. 4095fa 6 LTC4095 SIMPLIFIED BLOCK DIAGRAM 5 2.25MHz CLOCK 8 HPWR IN TREF TDIE COUNTER + – + RECHARGE BAT – + 2.9V 3 TRICKLE IBAT CHARGE CURRENT CONTROL CONTROL LOGIC BAT CONSTANT CURRENT/ CONSTANT VOLTAGE ENABLE TRICKLE CHARGE NTC TEMP FAULT CHRGR ON CHRG M1 BAT DUVLO IN NTC 1 + RECHRG – – 4.105V 6 THERMAL AMP BAD BAT TERMINATE CHARGE TEMP FAULT + 100mV IN IBAT 800 C/10 + – UVLO – BLINK LOGIC 4V SUSP PROG 7 4 GND 2 4095 F01 Figure 1. LTC4095 Block Diagram OPERATION Introduction The LTC4095 is a linear battery charger designed to charge single-cell lithium-ion batteries. The charger uses a constant-current/constant-voltage charge algorithm with a charge current programmable up to 950mA. Additional features include automatic recharge, an internal termination timer, low-battery trickle charge conditioning, bad-battery detection, and a thermistor sensor input for out of temperature charge pausing. Futhermore, the LTC4095 is capable of operating from a USB power source. In this application, charge current can be programmed to a maximum of 100mA or 500mA per USB power specifications. Input Current vs Charge Current The LTC4095 regulates the total current delivered to the BAT pin; this is the charge current. To calculate the total input current (i.e., the total current drawn from the IN pin), it is necessary to sum the battery charge current, charger quiescent current and PROG pin current. Undervoltage Lockout (UVLO) The undervoltage lockout circuit monitors the input voltage (IN) and disables the battery charger until IN rises above VUVLO (typically 4V). 200mV of hysteresis prevents oscillations around the trip point. In addition, a differential undervoltage lockout circuit disables the battery charger when IN falls to within VDUVLO (typically 40mV) of the BAT voltage. Suspend Mode The LTC4095 can also be disabled by pulling the SUSP pin above 1.2V. In suspend mode, the battery drain current is reduced to 1.3µA and the input current is reduced to 8.5µA. 4095fa 7 LTC4095 OPERATION Charge Cycle Overview Automatic Recharge When a battery charge cycle begins, the battery charger first determines if the battery is deeply discharged. If the battery voltage is below VTRKL, typically 2.9V, an automatic trickle charge feature sets the battery charge current to 10% of the full-scale value. After the battery charger terminates, it will remain off, drawing only microamperes of current from the battery. If the portable product remains in this state long enough, the battery will eventually self discharge. To ensure that the battery is always topped off, a charge cycle will automatically begin when the battery voltage falls below VRECHRG (typically 4.105V). In the event that the safety timer is running when the battery voltage falls below VRECHRG, it will reset back to zero. To prevent brief excursions below VRECHRG from resetting the safety timer, the battery voltage must be below VRECHRG for more than 1.7ms. The charge cycle and safety timer will also restart if the IN UVLO or DUVLO cycles low and then high (e.g., IN is removed and then replaced) or the charger enters and then exits suspend mode. Once the battery voltage is above 2.9V, the battery charger begins charging in constant-current mode. When the battery voltage approaches the 4.2V required to maintain a full charge, otherwise known as the float voltage, the charge current begins to decrease as the LTC4095 switches into constant-voltage mode. Trickle Charge and Defective Battery Detection Any time the battery voltage is below VTRKL, the charger goes into trickle charge mode and reduces the charge current to 10% of the full-scale current. If the battery voltage remains below VTRKL for more than 1/2 hour, the charger latches the bad-battery state, automatically terminates, and indicates via the ⎯C⎯H⎯R⎯G pin that the battery was unresponsive. If for any reason the battery voltage rises above VTRKL, the charger will resume charging. Since the charger has latched the bad-battery state, if the battery voltage then falls below VTRKL again but without rising past VRECHRG first, the charger will immediately assume that the battery is defective. To reset the charger (i.e., when the dead battery is replaced with a new battery), simply remove the input voltage and reapply it or put the part in and out of suspend mode. Charge Termination The battery charger has a built-in safety timer that sets the total charge time for 4 hours. Once the battery voltage rises above VRECHRG (typically 4.105V) and the charger enters constant-voltage mode, the 4-hour timer is started. After the safety timer expires, charging of the battery will discontinue and no more current will be delivered. Programming Charge Current The PROG pin serves both as a charge current program pin, and as a charge current monitor pin. By design, the PROG pin current is 1/800th of the battery charge current. Therefore, connecting a resistor from PROG to ground programs the charge current while measuring the PROG pin voltage allows the user to calculate the charge current. Full-scale charge current is defined as 100% of the constant-current mode charge current programmed by the PROG resistor. In constant-current mode, the PROG pin servos to 1V if HPWR is high, which corresponds to charging at the full-scale charge current, or 200mV if HPWR is low, which corresponds to charging at 20% of the fullscale charge current. Thus, the full-scale charge current and desired program resistor for a given full-scale charge current are calculated using the following equations: ICHG = 800 V RPROG RPROG = 800 V ICHG 4095fa 8 LTC4095 OPERATION In any mode, the actual battery current can be determined by monitoring the PROG pin voltage and using the following equation: IBAT = PROG • 800 RPROG Thermal Regulation To prevent thermal damage to the IC or surrounding components, an internal thermal feedback loop will automatically decrease the programmed charge current if the die temperature rises to approximately 115°C. Thermal regulation protects the LTC4095 from excessive temperature due to high power operation or high ambient thermal conditions and allows the user to push the limits of the power handling capability with a given circuit board design without risk of damaging the LTC4095 or external components. The benefit of the LTC4095 thermal regulation loop is that charge current can be set according to actual conditions rather than worst-case conditions with the assurance that the battery charger will automatically reduce the current in worst-case conditions. Charge Status Indication The ⎯C⎯H⎯R⎯G pin indicates the status of the battery charger. Four possible states are represented by ⎯C⎯H⎯R⎯G: charging, not charging, unresponsive battery and battery temperature out of range. The signal at the ⎯C⎯H⎯R⎯G pin can be easily recognized as one of the above four states by either a human or a microprocessor. The ⎯C⎯H⎯R⎯G pin, which is an open-drain output, can drive an indicator LED through a current limiting resistor for human interfacing, or simply a pull-up resistor for microprocessor interfacing. To make the ⎯C⎯H⎯R⎯G pin easily recognized by both humans and microprocessors, the pin is either a DC signal of ON for charging, OFF for not charging, or it is switched at high frequency (35kHz) to indicate the two possible faults: unresponsive battery and battery temperature out of range. When charging begins, ⎯C⎯H⎯R⎯G is pulled low and remains low for the duration of a normal charge cycle. When the charge current has dropped to below 10% of the full-scale current, the ⎯C⎯H⎯R⎯G pin is released (high impedance). If a fault occurs after the ⎯C⎯H⎯R⎯G pin is released, the pin remains high impedance. However, if a fault occurs before the ⎯C⎯H⎯R⎯G pin is released, the pin is switched at 35kHz. While switching, its duty cycle is modulated between a high and low value at a very low frequency. The low and high duty cycles are disparate enough to make an LED appear to be on or off thus giving the appearance of “blinking”. Each of the two faults has its own unique “blink” rate for human recognition as well as two unique duty cycles for microprocessor recognition. Table 1 illustrates the four possible states of the ⎯C⎯H⎯R⎯G pin when the battery charger is active. Table 1. ⎯C⎯H⎯R⎯G Output Pin FREQUENCY MODULATION (BLINK) FREQUENCY DUTY CYCLE Charging 0Hz 0 Hz (Lo-Z) 100% IBAT < C/10 0Hz 0 Hz (Hi-Z) 0% NTC Fault 35kHz 1.5Hz at 50% 6.25% to 93.75% Bad Battery 35kHz 6.1Hz at 50% 12.5% to 87.5% STATUS An NTC fault is represented by a 35kHz pulse train whose duty cycle varies between 6.25% and 93.75% at a 1.5Hz rate. A human will easily recognize the 1.5Hz rate as a “slow” blinking which indicates the out of range battery temperature while a microprocessor will be able to decode either the 6.25% or 93.75% duty cycles as an NTC fault. If a battery is found to be unresponsive to charging (i.e., its voltage remains below VTRKL for over 1/2 hour), the ⎯C⎯H⎯R⎯G pin gives the battery fault indication. For this fault, a human would easily recognize the frantic 6.1Hz “fast” blinking of the LED while a microprocessor would be able to decode either the 12.5% or 87.5% duty cycles as a bad battery fault. Although very improbable, it is possible that a duty cycle reading could be taken at the bright-dim transition (low duty cycle to high duty cycle). When this happens the duty cycle reading will be precisely 50%. If the duty cycle reading is 50%, system software should disqualify it and take a new duty cycle reading. 4095fa 9 LTC4095 OPERATION NTC Thermistor The battery temperature is measured by placing a negative temperature coefficient (NTC) thermistor close to the battery pack. The NTC circuitry is shown in Figure 3. To use this feature, connect the NTC thermistor, RNTC, between the NTC pin and ground, and a bias resistor, RNOM, from IN to NTC. RNOM should be a 1% resistor with a value equal to the value of the chosen NTC thermistor at 25°C (R25). A 100k thermistor is recommended since thermistor current is not measured by the LTC4095 and its current will have to be considered for compliance with USB specifications. The LTC4095 will pause charging when the resistance of the NTC thermistor drops to 0.54 times the value of R25 or approximately 54k (for a Vishay “Curve 1” thermistor, this corresponds to approximately 40°C). If the battery charger is in constant voltage mode, the safety timer will pause until the thermistor indicates a return to a valid temperature. As the temperature drops, the resistance of the NTC thermistor rises. The LTC4095 is also designed to pause charging when the value of the NTC thermistor increases to 3.25 times the value of R25. For a Vishay “Curve 1” thermistor, this resistance, 325k, corresponds to approximately 0°C. The hot and cold comparators each have approximately 3°C of hysteresis to prevent oscillation about the trip point. Grounding the NTC pin disables all NTC functionality. DUVLO, UVLO AND SUSPEND POWER ON FALSE IF SUSP < 0.4V AND IN > 4V AND IN > BAT + 165mV FAULT SUSPEND/SHUTDOWN MODE CHRG HIGH IMPEDANCE TRUE NTC FAULT BATTERY CHARGING SUSPENDED CHRG PULSES STANDBY MODE NO CHARGE CURRENT CHRG HIGH IMPEDANCE NO FAULT NO FAULT, BAT ≤ 2.9V TRICKLE CHARGE MODE 1/10 FULL CHARGE CURRENT CHRG STRONG PULL-DOWN 30 MINUTE TIMER BEGINS 30 MINUTE TIMEOUT 2.9V < BAT < 4.105V BAT > 2.9V CONSTANT CURRENT MODE FULL CHARGE CURRENT CHRG STRONG PULL-DOWN 4 HOUR TIMEOUT 4 HOUR CHARGE CYCLE BEGINS DEFECTIVE BATTERY NO CHARGE CURRENT CHRG PULSES CONSTANT VOLTAGE MODE 4 HOUR TERMINATION TIMER BEGINS BAT DROPS BELOW 0.105V 4 HOUR TERMINATION TIMER RESETS 4095 F02 Figure 2. State Diagram of LTC4095 Operation 4095fa 10 LTC4095 APPLICATIONS INFORMATION Alternate NTC Thermistors and Biasing In the explanation below, the following notation is used. The LTC4095 provides temperature qualified charging if a grounded thermistor and a bias resistor are connected to the NTC pin. By using a bias resistor whose value is equal to the room temperature resistance of the thermistor (R25) the upper and lower temperatures are pre-programmed to approximately 40°C and 0°C, respectively (assuming a Vishay “Curve 1” thermistor). R25 = Value of the thermistor at 25°C The upper and lower temperature thresholds can be adjusted by either a modification of the bias resistor value or by adding a second adjustment resistor to the circuit. If only the bias resistor is adjusted, then either the upper or the lower threshold can be modified but not both. The other trip point will be determined by the characteristics of the thermistor. Using the bias resistor in addition to an adjustment resistor, both the upper and the lower temperature trip points can be independently programmed with the constraint that the difference between the upper and lower temperature thresholds cannot decrease. Examples of each technique are given below. NTC thermistors have temperature characteristics which are indicated on resistance-temperature conversion tables. The Vishay-Dale thermistor NTHS0603N011-N1003F, used in the following examples, has a nominal value of 100k and follows the Vishay “Curve 1” resistance-temperature characteristic. 8 IN 6 RNTC|HOT = Value of the thermistor at the hot trip point rCOLD = Ratio of RNTC|COLD to R25 rHOT = Ratio of RNTC|HOT to R25 RNOM = Primary thermistor bias resistor (see Figure 3) R1 = Optional temperature range adjustment resistor (see Figure 4) The trip points for the LTC4095’s temperature qualification are internally programmed at 0.349 • IN for the hot threshold and 0.765 • IN for the cold threshold. Therefore, the hot trip point is set when: RNTCHOT | RNOM + RNTCHOT | RNTC|COLD RNOM + RNTC|COLD + NTC 8 – • IN = 0.349 • IN and the cold trip point is set when: LTC4095 NTC BLOCK 0.765 • IN (NTC RISING) RNOM 100k RNTC|COLD = Value of thermistor at the cold trip point • IN = 0.765 • IN IN 0.765 • IN (NTC RISING) RNOM 105k TOO_COLD 6 – + NTC TOO_COLD R1 12.7k RNTC 100k – – 0.349 • IN (NTC FALLING) + RNTC 100k TOO_HOT 0.349 • IN (NTC FALLING) + + + NTC_ENABLE NTC_ENABLE 0.017 • IN (NTC FALLING) TOO_HOT – 0.017 • IN (NTC FALLING) 4095 F03 Figure 3. Typical NTC Thermistor Circuit – 4095 F04 Figure 4. NTC Thermistor Circuit with Additional Bias Resistor 4095fa 11 LTC4095 APPLICATIONS INFORMATION Solving these equations for RNTC|COLD and RNTC|HOT results in the following: RNTC|HOT = 0.536 • RNOM and RNTC|COLD = 3.25 • RNOM By setting RNOM equal to R25, the above equations result in rHOT = 0.536 and rCOLD = 3.25. Referencing these ratios to the Vishay Resistance-Temperature Curve 1 chart gives a hot trip point of about 40°C and a cold trip point of about 0°C. The difference between the hot and cold trip points is approximately 40°C. By using a bias resistor, RNOM, different in value from R25, the hot and cold trip points can be moved in either direction. The temperature span will change somewhat due to the nonlinear behavior of the thermistor. The following equations can be used to easily calculate a new value for the bias resistor: RNOM = rHOT • R25 0.536 RNOM = rCOLD • R25 3.25 where rHOT and rCOLD are the resistance ratios at the desired hot and cold trip points. Note that these equations are linked. Therefore, only one of the two trip points can be chosen, the other is determined by the default ratios designed in the IC. Consider an example where a 60°C hot trip point is desired. From the Vishay Curve 1 R-T characteristics, rHOT is 0.2488 at 60°C. Using the above equation, RNOM should be set to 46.4k. With this value of RNOM, the cold trip point is about 16°C. Notice that the span is now 44°C rather than the previous 40°C. The upper and lower temperature trip points can be independently programmed by using an additional bias resistor as shown in Figure 4. The following formulas can be used to compute the values of RNOM and R1: r –r RNOM = COLD HOT • R25 2.714 R1 = 0.536 • RNOM – rHOT • R25 12 For example, to set the trip points to 0°C and 45°C with a Vishay Curve 1 thermistor choose: RNOM = 3.266 – 0.4368 • 100k = 104.2k 2.714 the nearest 1% value is 105k. R1 = 0.536 • 105k – 0.4368 • 100k = 12.6k the nearest 1% value is 12.7k. The final solution is shown in Figure 4 and results in an upper trip point of 45°C and a lower trip point of 0°C. USB and Wall Adapter Power Although the LTC4095 is designed to draw power from a USB port to charge Li-Ion batteries, a wall adapter can also be used. 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 conduction into the USB port when a wall adapter is present and Schottky diode, D1, is used to prevent USB power loss through the 1k pull-down resistor. Typically, a wall adapter can supply significantly more current than the 500mA-limited USB port. Therefore, an N-channel MOSFET, MN1, and an extra program resistor are used to increase the maximum charge current to 950mA when the wall adapter is present. 5V WALL ADAPTER 950mA ICHG USB POWER 500mA ICHG BAT D1 8 MP1 1 IBAT LTC4095 IN PROG MN1 1.65k 7 + Li-Ion BATTERY 1.74k 1k 4095 F05 Figure 5. Combining Wall Adapter and USB Power Power Dissipation The conditions that cause the LTC4095 to reduce charge current through thermal feedback can be approximated by considering the power dissipated in the IC. For high 4095fa LTC4095 APPLICATIONS INFORMATION charge currents, the LTC4095 power dissipation is approximately: PD = (IN – BAT) • IBAT where PD is the power dissipated, IN is the input supply voltage, BAT is the battery voltage and IBAT is the charge current. It is not necessary to perform any worst-case power dissipation scenarios because the LTC4095 will automatically reduce the charge current to maintain the die temperature at approximately 115°C. However, the approximate ambient temperature at which the thermal feedback begins to protect the IC is: TA = 115°C – PDθJA TA = 115°C – (IN – BAT) • IBAT • θJA Example: Consider an LTC4095 operating from a USB port providing 500mA to a 3.5V Li-Ion battery. The ambient temperature above which the LTC4095 will begin to reduce the 500mA charge current is approximately: USB Inrush Limiting When a USB cable is plugged into a portable product, the inductance of the cable and the high-Q ceramic input capacitor form an L-C resonant circuit. If there is not much impedance in the cable, it is possible for the voltage at the input of the product to reach as high as twice the USB voltage (~10V) before it settles out. In fact, due to the high voltage coefficient of many ceramic capacitors (a nonlinearity), the voltage may even exceed twice the USB voltage. To prevent excessive voltage from damaging the LTC4095 during a hot insertion, the soft connect circuit in Figure 6 can be employed. In this circuit, capacitor C2 holds MN1 off when the cable is first connected. Eventually C2 begins to charge up to the USB input voltage applying increasing gate support to MN1. The long time constant of R1 and C1 prevent the current from building up in the cable too fast thus dampening out any resonant overshoot. TA = 115°C – (5V – 3.5V) • (500mA) • 60°C/W TA = 115°C – 0.75W • 60°C/W = 115°C – 45°C TA = 70°C The LTC4095 can be used above 70°C, but the charge current will be reduced from 500mA. The approximate current at a given ambient temperature can be calculated: IBAT = 115°C – TA (IN – BAT ) • θJA 8 5V USB INPUT R1 40k USB CABLE C2 100nF IN C1 10µF 2 LTC4095 GND MN1 Si2302 4095 F06 Figure 6. USB Soft Connect Circuit Battery Charger Stability Considerations Furthermore, the voltage at the PROG pin will change proportionally with the charge current as discussed in the Programming Charge Current section. The LTC4095’s battery charger contains both a constantvoltage and a constant-current control loop. The constantvoltage loop is stable without any compensation when a battery is connected with low impedance leads. Excessive lead length, however, may add enough series inductance to require a bypass capacitor of at least 1µF from BAT to GND. Furthermore, a 4.7µF capacitor in series with a 0.2Ω to 1Ω resistor from BAT to GND is required to keep ripple voltage low when the battery is disconnected. It is important to remember that LTC4095 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 115°C. High value, low ESR multilayer ceramic chip capacitors reduce the constant-voltage loop phase margin, possibly resulting in instability. Ceramic capacitors up to 22µF may be used in parallel with a battery, but larger ceramics should be decoupled with 0.2Ω to 1Ω of series resistance. Using the previous example with an ambient temperature of 88°C, the charge current will be reduced to approximately: IBAT = 115°C – 88°C 27°C = = 300mA (5V – 3.5V ) • 60°C/W 90°C/A 4095fa 13 LTC4095 APPLICATIONS INFORMATION In constant-current mode, the PROG pin is in the feedback loop rather than the battery voltage. Because of the additional pole created by any PROG pin capacitance, capacitance on this pin must be kept to a minimum. With no additional capacitance on the PROG pin, the battery charger is stable with program resistor values as high as 25k. 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 has a parasitic capacitance, CPROG, the following equation should be used to calculate the maximum resistance value for RPROG: RPROG ≤ 1 5 2π • 10 • CPROG The stability of the constant-current loop also needs to be considered when average, rather than instantaneous, battery current is 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 an be used on the PROG pin to measure the average battery current as shown in Figure 7. A 10k resistor has been added between the PROG pin and the filter capacitor to ensure stability. LTC4095 PROG GND 2 7 Board Layout Considerations In order to deliver maximum charge current under all conditions, it is critical that the exposed metal pad on the backside of the LTC4095 package is soldered to the PC board ground. Correctly soldered to a 2500mm2 double-sided 1oz. copper board the LTC4095 has a thermal resistance of approximately 60°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 60°C/W. As an example, a correctly soldered LTC4095 can deliver over 950mA to a battery from a 5V supply at room temperature. Without a backside thermal connection, this number could drop to less than 500mA. IN Bypass Capacitor Many types of capacitors can be used for input bypassing; however, caution must be exercised when using multi-layer 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. For more information, refer to Application Note 88. 10k RPROG CFILTER CHARGE CURRENT MONITOR CIRCUITRY 4095 F04 Figure 7. Isolating Capacitive Load on PROG Pin and Filtering 4095fa 14 LTC4095 PACKAGE DESCRIPTION DC Package 8-Lead Plastic DFN (2mm × 2mm) (Reference LTC DWG # 05-08-1719 Rev Ø) 0.70 ±0.05 2.55 ±0.05 1.15 ±0.05 0.64 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.45 BSC 1.37 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED R = 0.05 TYP 2.00 ±0.10 (4 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) R = 0.115 TYP 5 8 0.40 ± 0.10 0.64 ± 0.10 (2 SIDES) PIN 1 NOTCH R = 0.20 OR 0.25 × 45° CHAMFER (DC8) DFN 0106 REVØ 4 0.200 REF 1 0.23 ± 0.05 0.45 BSC 0.75 ±0.05 1.37 ±0.10 (2 SIDES) 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 4095fa 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 LTC4095 TYPICAL APPLICATION 500mA Single-Cell Li-Ion Charger IN 4.3V TO 5.5V UP TO 7V TRANSIENTS R1 510Ω LED CIN 1µF 100k IN LTC4095 CHRG SUSPEND 100 500 460mA BAT NTC SUSP PROG HPWR GND T 100k + Li-Ion BATTERY 1.74k 4095 TA02 RELATED PARTS PART NUMBER Battery Chargers LTC1734 LTC1734L LTC4052 LTC4053 LTC4054 DESCRIPTION COMMENTS LTC4057 LTC4058 LTC4059 Lithium-Ion Linear Battery Charger in ThinSOTTM Lithium-Ion Linear Battery Charger in ThinSOT Monolithic Lithium-Ion Battery Pulse Charger USB Compatible Monolithic Li-Ion Battery Charger Standalone Linear Li-Ion Battery Charger with Integrated Pass Transistor in ThinSOT Lithium-Ion Linear Battery Charger Standalone 950mA Lithium-Ion Charger in DFN 900mA Linear Lithium-Ion Battery Charger LTC4059A 900mA Linear Lithium-Ion Battery Charger Simple ThinSOT Charger, No Blocking Diode, No Sense Resistor Needed Low Current Version of LTC1734, 50mA ≤ ICHRG ≤ 180mA No Blocking Diode or External Power FET Required, ≤1.5A Charge Current Standalone Charger with Programmable Timer, Up to 1.25A Charge Current Thermal Regulation Prevents Overheating, C/10 Termination, C/10 Indicator, Up to 800mA Charge Current Up to 800mA Charge Current, Thermal Regulation, ThinSOT Package C/10 Charge Termination, Battery Kelvin Sensing, ±7% Charge Accuracy 2mm × 2mm DFN Package, Thermal Regulation, Charge Current Monitor Output 2mm × 2mm DFN Package, Thermal Regulation, Charge Current Monitor Output, ACPR Function 4.2V, ±0.35% Float Voltage, Up to 1A Charge Current, 3mm × 3mm DFN LTC4061 Standalone Li-Ion Charger with Thermistor Interface LTC4061-4.4 Standalone Li-Ion Charger with Thermistor Interface LTC4062 Standalone Linear Li-Ion Battery Charger with Micropower Comparator LTC4063 Li-Ion Charger with Linear Regulator LTC4065/LTC4065A Standalone 750mA Li-Ion Charger in 2mm × 2mm DFN LTC4069 Standalone Li-Ion Battery Charger with NTC Thermistor Input in 2mm × 2mm DFN Power Management LTC3405/LTC3405A 300mA (IOUT), 1.5MHz, Synchronous Step-Down DC/DC Converter LTC3406/LTC3406A 600mA (IOUT), 1.5MHz, Synchronous Step-Down DC/DC Converter LTC3440 600mA (IOUT), 2MHz, Synchronous BuckBoostDC/DC Converter LTC4411/LTC4412 Low Loss PowerPathTM Controller in ThinSOT LTC4413 Dual Ideal Diode in DFN 4.4V (Max), ±0.4% Float Voltage, Up to 1A Charge Current, 3mm × 3mm DFN 4.2V, ±0.35% Float Voltage, Up to 1A Charge Current, 3mm × 3mm DFN Up to 1A Charge Current, 100mA, 125mV LDO, 3mm × 3mm DFN 4.2V, ±0.6% Float Voltage, Up to 750mA Charge Current, 2mm × 2mm 6-Pin DFN 4.2V, ±0.6% Float Voltage, Up to 750mA Charge Current, Timer Termination + C/10 Detection Output 95% Efficiency, VIN: 2.7V to 6V, VOUT = 0.8V, IQ = 20µA, ISD < 1µA, ThinSOT Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT = 0.6V, IQ = 20µA, ISD < 1µA, ThinSOT Package 95% Efficiency, VIN: 2.5V to 5.5V, VOUT = 2.5V, IQ = 25µA, ISD < 1µA, MS Package Automatic Switching Between DC Sources, Load Sharing, Replaces ORing Diodes 2-Channel Ideal Diode ORing, Low Forward ON Resistance, Low Regulated Forward Voltage, 2.5V ≤ VIN ≤ 5.5V ThinSOT and PowerPath are trademarks of Linear Technology Corporation. 4095fa 16 Linear Technology Corporation LT 0307 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 2007