LTC1733 Monolithic Linear Lithium-Ion Battery Charger with Thermal Regulation U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO Complete Linear Charger for 1-Cell Lithium-Ion Batteries Thermal Regulation Maximizes Charging Rate without Risk of Overheating* No External MOSFET, Sense Resistor or Blocking Diode Required Up to 1.5A Charge Current Preset Charge Voltage with 1% Accuracy Programmable Charge Current with 7% Accuracy Programmable Charge Termination Timer Tiny Thermally Enhanced 10-Pin MSOP Package Charge Current Monitor Useful for Gas Gauging* C/10 Charge Current Detection Output Automatic Recharge Thermistor Input for Temperature Qualified Charging AC Present Logic Output 4.1V/4.2V Pin Selectable Output Voltage U APPLICATIO S ■ ■ ■ Cellular Telephones Handheld Computers Digital Still Cameras Charging Docks and Cradles No external current sense resistor is needed and no blocking diode is required due to the internal MOSFET architecture. The charge current and charge time can be set externally with a single resistor and capacitor, respectively. When the input supply (wall adapter) is removed, the LTC1733 automatically enters a low current sleep mode, dropping the battery drain current to less than 5µA. The LTC1733 also includes NTC temperature sensing, C/10 detection circuitry, AC present logic, 4.1V/4.2V pin selectability and low battery charge conditioning (trickle charging). The LTC1733 is available in a 10-pin thermally enhanced MSOP package. , LTC and LT are registered trademarks of Linear Technology Corporation. *Patent Pending U ■ The LTC ®1733 is a standalone constant-current/ constant-voltage linear charger for lithium-ion batteries with an on-chip power MOSFET. Internal thermal feedback regulates the charge current to limit die temperature during high power operation or high ambient temperature conditions. This feature allows the user to program a high charge current without risk of damaging the LTC1733 or the handheld product. TYPICAL APPLICATIO Charge Current vs Battery Voltage Standalone Li-Ion Battery Charger 1200 TA = 0°C VIN = 5V CONSTANT CURRENT 4.7µF 8 2 SEL VCC 9 BAT LTC1733 4 7 TIMER PROG GND NTC 5 6 0.1µF IBAT = 1A 1.5k 1% 4.2V 1-CELL Li-Ion BATTERY* CHARGE CURRENT (mA) 1000 TA = 40°C 800 TA = 25°C CONSTANT POWER 600 CONSTANT VOLTAGE 400 200 TRICKLE CHARGE 1733TA01 0 *AN OUTPUT CAPACITOR MAY BE REQUIRED DEPENDING ON BATTERY LEAD LENGTH 2 2.5 VIN = 5V θJA = 40°C/W 3 4 3.5 BATTERY VOLTAGE (V) 4.5 1733 TA01b sn1733 1733fs 1 LTC1733 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) Input Supply Voltage (VCC) ........................................ 7V BAT ............................................................................ 7V NTC, SEL, TIMER, PROG ................ –0.3V to VCC + 0.3V CHRG, FAULT, ACPR ................................... –0.3V to 7V BAT Short-Circuit Duration ........................... Continuous BAT Current (Note 2) .............................................. 1.6A PROG Current (Note 2) ........................................ 1.6mA Junction Temperature ........................................... 125°C Operating Temperature Range (Note 3) ...–40°C to 85°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C ORDER PART NUMBER TOP VIEW CHRG VCC FAULT TIMER GND 1 2 3 4 5 10 9 8 7 6 ACPR BAT SEL PROG NTC LTC1733EMSE MSE EXPOSED PAD PACKAGE 10-LEAD PLASTIC MSOP TJMAX = 125°C, θJA = 40°C/W (Note 4) EXPOSED PAD IS GROUND. (MUST BE SOLDERED TO PCB FOR MAXIMUM HEAT TRANSFER). MSE PART MARKING LTLX Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V SYMBOL PARAMETER CONDITIONS MIN VCC VCC Supply Voltage ICC VCC Supply Current Charger On; Current Mode; RPROG = 30k (Note 5) Shutdown Mode; VPROG = 3V ● ● VBAT VBAT Regulated Output Voltage SEL = 0V SEL = VCC ● ● IBAT Battery Pin Current RPROG = 3k; Current Mode RPROG = 1k; Current Mode Shutdown Mode; VPROG = 3V Sleep Mode VCC < VBAT or VCC < (VUV – ∆VUV) ITRIKL Trickle Charge Current VBAT < 2V; RPROG = 3k VTRIKL Trickle Charge Trip Threshold VBAT Rising ∆VTRIKL Trickle Charge Trip Hysteresis VUV VCC Undervoltage Lockout Voltage ∆VUV VCC Undervoltage Lockout Hysteresis VMSD Manual Shutdown Threshold Voltage VMSD-HYS VASD ● VCC Rising TYP 4.5 MAX UNITS 6.5 V 1 0.9 3 2 4.059 4.158 4.1 4.2 4.141 4.242 V V ● 465 1.395 500 1.5 ±1 ±1 535 1.605 ±5 ±5 mA A µA µA ● 35 50 65 mA ● mA mA 2.48 V 100 mV 4.2 4.5 V 150 mV 2.15 V Manual Shutdown Hysteresis Voltage 100 mV Automatic Shutdown Threshold Voltage (VCC - VBAT) Voltage Falling (VCC - VBAT) Voltage Rising 30 60 mV mV PROG Pin Voltage Rising sn1733 1733fs 2 LTC1733 ELECTRICAL CHARACTERISTICS TA = 25°C. VCC = 5V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS VPROG PROG Pin Voltage RPROG = 3k, IPROG = 500µA; Current Mode ICHRG CHRG Pin Weak Pulldown Current VCHRG CHRG Pin Output Low Voltage VACPR ACPR Pin Output Low Voltage IACPR = 5mA VFAULT FAULT Pin Output Low Voltage IFAULT = 5mA IC/10 End of Charge Indication Current Level RPROG = 3k tTIMER TIMER Accuracy CTIMER = 0.1µF ±10 % VRECHRG Recharge Battery Voltage Threshold Battery Voltage Falling, SEL = 0V Battery Voltage Falling, SEL = 5V 3.9 4.0 V V VNTC-HOT NTC Pin Hot Threshold Voltage VNTC Falling 2.5 V VHOT-HYS NTC Pin Hot Hysteresis Voltage 70 mV VNTC-COLD NTC Pin Cold Threshold Voltage VNTC Rising 4.375 VCOLD-HYS NTC Pin Cold Hystersis Voltage VNTC-DIS NTC Pin Disable Threshold Voltage VDIS-HYS NTC Pin Disable Hystersis Voltage VSEL-IL SEL Pin Threshold Input Low VSEL-IH SEL Pin Threshold Input High TLIM Junction Temperature in Constant-Temperature Mode 105 °C RON Power MOSFET “ON” Resistance 375 mΩ 1.5 V VCHRG = 1V 25 µA ICHRG = 5mA 0.35 V 0.35 V 0.35 35 50 V 65 V 70 VNTC Rising Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The Absolute Maximum BAT Current Rating of 1.6A is guaranteed by design and current density calculations. The Absolute Maximum PROG Current Rating is guaranteed to be 1/1000 of BAT current rating by design. Note 3: The LTC1733E is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the –40°C to 85°C operating mA mV 100 mV 10 mV 0.3 V 1 V temperature range are assured by design, characterization and correlation with statistical process controls. Note 4: Failure to solder the exposed backside of the package to the PC board will result in a thermal resistance much higher than 40°C/W. Note 5: Supply current includes PROG pin current but does not include any current delivered to the battery through the BAT pin. sn1733 1733fs 3 LTC1733 U W TYPICAL PERFOR A CE CHARACTERISTICS Battery Regulation Voltage vs Battery Charge Current 4.24 Battery Regulation Voltage vs Temperature VCC = 5V TA = 25°C RPROG = 1.5k 4.22 V SEL = 5V 4.20 VCC = 5V 4.22 IBAT = 10mA RPROG = 1.5k 4.20 TA = 25°C 4.22 IBAT = 10mA RPROG = 1.5k 4.20 VSEL = 5V 4.14 VBAT (V) 4.16 4.16 4.14 4.12 VSEL = 0V 4.12 4.14 4.12 VSEL = 0V 4.10 4.10 4.08 4.08 4.08 4.06 –50 0 100 200 300 400 500 600 700 800 900 1000 IBAT (mA) –25 25 0 50 75 TEMPERATURE(°C) 100 4.06 4.0 125 Charge Current vs Battery Voltage 800 IBAT (mA) IBAT (mA) 700 600 500 600 500 400 0.4 300 300 200 200 100 100 0.2 0 0 100 200 300 400 500 600 700 800 900 1000 CHARGE CURRENT (mA) 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 VBAT (V) 1733 G04 RPROG = 1.5k 900 1000 800 900 700 THERMAL CONTROL LOOP IN OPERATION 500 400 300 600 RPROG = 3k 500 400 4.0 600 IBAT (mA) IBAT (mA) 700 4.5 5.0 5.5 VCC (V) 6.0 6.5 7.0 1733 G07 4.5 5.0 5.5 VCC (V) 6.0 6.5 V = 5V 200 VCC = 3.5V BAT 100 RPROG = 1.5k VSEL = 5V 0 –25 25 0 –50 50 TEMPERATURE (°C) 75 7.0 Charge Current vs Temperature 1000 800 4.0 1733 G06 Charge Current vs Temperature with Thermal Regulation VBAT = 3.5V TA = 25°C VSEL = VCC VBAT = 4.1V TA = 25°C RPROG = 1.5k VSEL = 5V 1733 G05 Charge Current vs VCC 7.0 900 400 1100 6.5 1000 0.6 0 6.0 Charge Current vs Input Voltage 700 0.8 5.5 1100 VCC = 5V 1000 TA = 25°C 900 RPROG = 1.5k VSEL = 5V 800 1.0 5.0 1733 G03 1100 VCC = 5V 1.4 TA = 25°C RPROG = 1.5k 1.2 VSEL = 5V 4.5 1733 G02 PROG Pin Voltage vs Charge Current 1.6 VSEL = 0V VCC (V) 1733 G01 IBAT (mA) 4.16 4.10 4.06 VSEL = VCC 4.18 4.18 VBAT (V) VBAT (V) 4.18 VPROG (V) Battery Regulation Voltage vs VCC 4.24 4.24 100 1733 G08 535 530 525 520 515 510 505 500 495 490 485 480 475 470 465 –50 VCC = 5V VBAT = 4V RPROG = 3k VSEL = 5V –25 50 25 0 TEMPERATURE (°C) 75 100 1733 G09 sn1733 1733fs 4 LTC1733 U W TYPICAL PERFOR A CE CHARACTERISTICS PROG Pin Voltage vs VCC Constant Current Mode PROG Pin Voltage vs Temperature Constant Current Mode 1.515 VCC = 5V VBAT = 4V RPROG = 3k VSEL = 5V 1.510 1.505 110 IBAT (mA) 1.500 1.500 1.495 90 1.490 1.490 80 4.5 5.0 5.5 VCC (V) 6.0 6.5 7.0 1.485 –50 –25 50 25 0 TEMPERATURE (°C) 1733 G10 Trickle Charge Current vs VCC 105 103 8 7 4.0 4.5 5.0 5.5 VCC (V) 6.0 6.5 7.0 1733 G13 105 103 102 102 101 101 100 99 99 98 97 97 96 96 –25 25 0 50 75 TEMPERATURE(°C) 100 100 100 98 95 –50 75 125 1733 G14 TA = 25°C IBAT = 0mA VSEL = 5V CTIMER = 0.1µF 104 tTIMER (%) tTIMER (%) 9 50 25 0 TEMPERATURE (°C) Timer Accuracy vs VCC VCC = 5V IBAT = 0mA VSEL = 5V CTIMER = 0.1µF 104 11 10 –25 1733 G12 Timer Accuracy vs Temperature TA = 25°C VBAT = 2V RPROG = 1.5k VSEL = 5V 12 70 –50 100 75 1733 G11 13 IBAT (% OF PROGRAMMED CURRENT) 100 1.495 1.485 4.0 VCC = 5V VBAT = 2V RPROG = 1.5k VSEL = 5V 120 1.505 VPROG (V) VPROG (V) 130 1.515 TA = 25°C VBAT = 3.5V RPROG = 3k VSEL = 5V 1.510 Trickle Charge Current vs Temperature 95 4.0 4.5 5.0 5.5 VCC (V) 6.0 6.5 7.0 1733 G15 sn1733 1733fs 5 LTC1733 U U U PI FU CTIO S CHRG: Open-Drain Charge Status Output. When the battery is being charged, the CHRG pin is pulled low by an internal N-channel MOSFET. When the charge current drops to 10% of the full-scale current, the N-channel MOSFET latches off and a 25µA current source is connected from the CHRG pin to ground. The C/10 latch can be cleared by momentarily pulling the PROG pin above the 2.15V shutdown threshold, or by toggling VCC. When the timer runs out or the input supply is removed, the current source is disconnected and the CHRG pin is forced to a high impedance state. VCC: Positive Input Supply Voltage. When VCC is within 30mV of VBAT or less than the undervoltage lockout threshold, the LTC1733 enters sleep mode, dropping IBAT to less than 5µA. VCC can range from 4.5V to 6.5V. Bypass this pin with at least a 4.7µF ceramic capacitor to ground. FAULT: Open-Drain Fault Status Output. The FAULT opendrain logic signal indicates that the charger has timed out under trickle charge conditions (1/4 of total time period) or the NTC comparator is indicating an out-of-range battery temperature condition. When VBAT is less that 2.48V, trickle charging activates whereby the charge current drops to one tenth of its programmed value and the timer period is reduced by a factor of four. When one fourth of the timing period has elapsed, if VBAT is still less than 2.48V, trickle charging stops and the FAULT pin latches to ground. The fault can be cleared by toggling VCC, momentarily pulling the PROG pin above the 2.15V shutdown threshold, or pulling the BAT pin above 2.48V. If the NTC comparator is indicating an out-of-range battery temperature condition, then the FAULT pin will pull to ground until the temperature returns to the acceptable range. TIMER: Timer Capacitor. The timer period is set by placing a capacitor, CTIMER, to ground. The timer period is: Time (Hours) = (CTIMER • 3 hr)/(0.1µF) Short the TIMER pin to ground to disable the internal timer function. GND: Ground. Connect exposed back package to ground. NTC: Input to the NTC (Negative Temperature Coefficient) Thermistor Temperature Monitoring Circuit. With an external 10kΩ NTC thermistor to ground and a 1% resistor to VCC, this pin can sense the temperature of the battery pack and stop charging when it is out of range. When the voltage at this pin drops below (0.5)•(VCC) at hot temperatures or rises above (0.875)•(VCC) at cold, charging is suspended and the internal timer is frozen. The CHRG pin output status is not affected in this hold state. The FAULT pin is pulled to ground, but not latched. When the temperature returns to an acceptable range, charging will resume and the FAULT pin is released. The NTC feature can be disabled by grounding the NTC pin. PROG: Charge Current Program, Shutdown Input and Charge Current Monitor Pin. The charge current is programmed by connecting a resistor, RPROG to ground. When in constant-current mode, the LTC1733 servos the PROG pin voltage to 1.5V. In all modes the voltage on the PROG pin can be used to measure the charge current as follows: ICHG = (VPROG/RPROG) • 1000. The IC can be forced into shutdown by pulling the PROG pin above the 2.15V shutdown threshold voltage (note: it will not be pulled up when allowed to float). SEL: 4.1V/4.2V Battery Selection Input. Grounding this pin sets the battery float voltage to 4.1V, while connecting to VCC sets the voltage to 4.2V. BAT: Charge Current Output. A bypass capacitor of at least 1µF with a 1Ω series resistor is required to minimize ripple voltage when the battery is not present. A precision internal resistor divider sets the final float potential on this pin. The internal resistor divider is disconnected in sleep and shutdown modes. ACPR: Open-Drain Power Supply Status Output. When VCC is greater than the undervoltage lockout threshold and at least 30mV above VBAT, the ACPR pin will pull to ground. Otherwise, the pin is forced to a high impedance state. sn1733 1733fs 6 LTC1733 W W SI PLIFIED BLOCK DIAGRA VCC 2 – 105°C D1 TA D2 + TDIE M2 ×1 D3 M1 ×1000 + – MA 9 30µA NTC 6 NTC MP + VA R2 – CA + – 2.485V – HOT COLD DISABLE CHRG 1 BAT R1 R4 C1 SHDN STOP REF R3 2.15V + C/10 8 SEL R5 25µA 2.5µA 1.5V LOGIC ACPR 10 R6 ACPR 0.15V + C2 FAULT 3 R7 – FAULT CHARGE COUNTER C3 OSCILLATOR – 2.485V 4 + TO BAT 7 TIMER PROG 5 GND 1733 F01 RPROG CTIMER Figure 1. sn1733 1733fs 7 LTC1733 U OPERATIO The LTC1733 is a linear battery charger designed primarily for charging single cell lithium-ion batteries. Featuring an internal P-channel power MOSFET, the charger uses a constant-current/constant-voltage charge algorithm with programmable current and a programmable timer for charge termination. Charge current can be programmed up to 1.5A with a final float voltage accuracy of ±1%. No blocking diode or sense resistor is required thus dropping the external component count to three for the basic charger circuit. The CHRG, ACPR, and FAULT open-drain status outputs provide information regarding the status of the LTC1733 at all times. An NTC thermistor input provides the option of charge qualification using battery temperature. An internal thermal limit reduces the programmed charge current if the die temperature attempts to rise above a preset value of approximately 105°C. This feature protects the LTC1733 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 LTC1733 or the external components. Another benefit of the LTC1733 thermal limit is that charge current can be set according to typical, not worst-case, ambient temperatures for a given application with the assurance that the charger will automatically reduce the current in worst-case conditions. The charge cycle begins when the voltage at the VCC pin rises above the UVLO level and a program resistor is connected from the PROG pin to ground. At the beginning of the charge cycle, if the battery voltage is below 2.48V, the charger goes into trickle charge mode to bring the cell voltage up to a safe level for charging. The charger goes into the fast charge constant-current mode once the voltage on the BAT pin rises above 2.48V. In constantcurrent mode, the charge current is set by RPROG. When the battery approaches the final float voltage, the charge current begins to decrease as the LTC1733 switches to constant-voltage mode. When the current drops to 10% of the full-scale charge current, an internal comparator latches off the MOSFET at the CHRG pin and connects a weak current source to ground to indicate a near end-ofcharge (C/10) condition. The C/10 latch can be cleared by momentarily pulling the PROG pin above the 2.15V shutdown threshold, or momentarily removing and reapplying VCC. An external capacitor on the TIMER pin sets the total charge time. When this time elapses the charge cycle terminates and the CHRG pin assumes a high impedance state. To restart the charge cycle, simply remove the input voltage and reapply it, or force the PROG pin above the 2.15V shutdown threshold (note: simply floating the PROG pin will not restart the charging cycle. For lithium-ion and similar batteries that require accurate final float potential, the internal reference, voltage amplifier and the resistor divider provide regulation with ±1% (max) accuracy. When the input voltage is not present, the charger goes into a sleep mode, dropping battery drain current, IBAT, to less than 5µA. This greatly reduces the current drain on the battery and increases the standby time. The charger can be shut down (ICC = 0.9mA) by forcing the PROG pin above 2.15V. sn1733 1733fs 8 LTC1733 U W U U APPLICATIO S I FOR ATIO 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 150mV. 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 until VCC rises 60mV above the battery voltage. Trickle Charge and Defective Battery Detection At the beginning of a charge cycle, if the battery voltage is low (below 2.48V) the charger goes into trickle charge reducing the charge current to 10% of the full-scale current. If the low battery voltage persists for one quarter of the total charge time, the battery is assumed to be defective, the charge cycle is terminated, the CHRG pin output assumes a high impedance state, and the FAULT pin latches low. The fault can be cleared by toggling VCC, temporarily forcing the PROG pin above 2.15V, or temporarily forcing the BAT pin voltage above 2.48V. Shutdown The LTC1733 can be shutdown (ICC = 0.9mA) by pulling the PROG pin above the 2.15V shutdown threshold voltage. In shutdown the internal linear regulator is turned off, and the internal timer is reset. Recharge The LTC1733 has the ability to recharge a battery assuming that the battery voltage has been charged above 4.05V (SEL = 5V) or 3.95V (SEL = 0V). Once above these thresholds, a new charge cycle will begin if the battery voltage drops below 4V (SEL = 5V) or 3.9V (SEL = 0V) due to either a load on the battery or self-discharge. The recharge circuit integrates the BAT pin voltage for a few milliseconds to prevent a transient from restarting the charge cycle. If the battery voltage remains below 2.48V during trickle charge for 1/4 of the programmed time, the battery may be defective and the charge cycle will end. In addition, the recharge comparator is disabled and a new charge cycle will not begin unless the input voltage is toggled, the PROG pin is pulled above the 2.15V shutdown threshold, or the BAT pin is pulled above the 2.48V trickle charge threshold. Programming Charge Current The formula for the battery charge current (see Figure 1) is: ICHG = (IPROG) • 1000 = (1.5V / RPROG) • 1000 or RPROG = 1500/ICHG where RPROG is the total resistance from the PROG pin to ground. Under trickle charge conditions, this current is reduced to 10% of the full-scale value. For example, if 500mA charge current is required, calculate: RPROG = 1500/0.5A = 3kΩ For best stability over temperature and time, 1% metalfilm resistors are recommended. If the charger is in constant-temperature or constantvoltage mode, the battery current can be monitored by measuring the PROG pin voltage as follows: ICHG = (VPROG / RPROG) • 1000 Programming the Timer The programmable timer is used to terminate the charge cycle. The timer duration is programmed by an external capacitor at the TIMER pin. The total charge time is: Time (Hours) = (3 Hours) • (CTIMER / 0.1µF) or CTIMER = 0.1µF • Time (Hours)/3 (Hours) The timer starts when an input voltage greater than the undervoltage lockout threshold level is applied and the program resistor is connected to ground. After a time-out occurs, the charge current stops, and the CHRG output assumes a high impedance state to indicate that the charging has stopped. Connecting the TIMER pin to ground disables the timer function. sn1733 1733fs 9 LTC1733 U W U U APPLICATIO S I FOR ATIO Open-Drain Status Outputs The LTC1733 has three open-drain status outputs: ACPR, CHRG and FAULT. The ACPR pin pulls low when an input voltage greater than the undervoltage lockout threshold is applied and goes high impedance when power (VIN < VUV) is removed. CHRG and FAULT work together to indicate the status of the charge cycle. Table 1 describes the status of the charge cycle based on the CHRG and FAULT outputs. V+ VDD 8 VCC 400k LTC1733 CHRG 3 µPROCESSOR 2k OUT IN 1733 F02 Figure 2. Microprocessor Interface Table 1. FAULT CHRG Description High Low Charge cycle has started, C/10 has not been reached and charging is proceeding normally. Low Low Charge cycle has started, C/10 has not been reached, but the charge current and timer have been paused due to an NTC out-oftemperature condition. High 25µA pulldown C/10 has been reached and charging is proceeding normally. Low 25µA pulldown C/10 has been reached but the charge current and timer have paused due to an NTC out-of-temperature condition. High High Normal timeout (charging has terminated). Low High If FAULT goes low and CHRG goes high impedance simultaneously, then the LTC1733 has timed out due to a bad cell (VBAT <2.48V after one-quarter the programmed charge time). If CHRG goes high impedance first, then the LTC1733 has timed out normally (charging has terminated), but NTC is indicating an outof-temperature condition. CHRG Status Output Pin When the charge cycle starts, the CHRG pin is pulled to ground by an internal N-channel MOSFET capable of driving an LED. When the charge current drops to 10% of the full-scale current (C/10), the N-channel MOSFET is latched off and a weak 25µA current source to ground is connected to the CHRG pin. After a time-out occurs, the pin assumes a high impedance state. By using two different value pull-up resistors a microprocessor can detect three states from this pin (charging, C/10, and time-out). See Figure 2. When the LTC1733 is in charge mode, the CHRG pin is pulled low by the internal N-channel MOSFET. To detect this mode, force the digital output pin, OUT, high and measure the voltage at the CHRG pin. The N-channel MOSFET will pull the pin low even with the 2k pull-up resistor. Once the charge current drops to 10% of the fullscale current (C/10), the N-channel MOSFET is turned off and a 25µA current source is connected to the CHRG pin. The IN pin will then be pulled high by the 2k pull-up. By forcing the OUT pin to a high impedance state, the current source will pull the pin low through the 400k resistor. When the internal timer has expired, the CHRG pin will assume a high impedance state and the 400k resistor will then pull the pin high to indicate that charging has terminated. 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 a 10k NTC thermistor between the NTC pin and ground and a resistor (RHOT) from the NTC pin to VCC. RHOT should be a 1% resistor with a value equal to the value of the chosen NTC thermistor at 50°C (this value is 4.1k for a Vishay NTHS0603N02N1002J thermistor). The LTC1733 goes into hold mode when the resistance of the NTC thermistor drops below 4.1k which should be at 50°C. The hold mode freezes the timer and stops the charge cycle until the thermistor indicates a return to a valid temperature. As the temperature drops, the sn1733 1733fs 10 LTC1733 U W U U APPLICATIO S I FOR ATIO resistance of the NTC thermistor rises. The LTC1733 is designed to go into hold mode when the value of the NTC thermistor increases to seven times the value of RHOT. For a Vishay NTHS0603N02N1002J thermistor, this value is 28.2k which corresponds to approximately 0°C. The hot and cold comparators each have approximately 2°C of hysteresis to prevent oscillation about the trip point. The NTC function can be disabled by grounding the NTC pin. Furthermore, it is essential that the VCC connection to RHOT is made according to standard Kelvin sense techniques. Since VCC is a high current path into the LTC1733, it is essential to minimize voltage drops between the VCC input pin and the top of RHOT. NTC Trip Point Errors VCC – 7/8 VCC RHOT 1% TOO COLD + NTC RNTC 10k package temperature rather than the battery temperature. This problem can be eliminated by thermally coupling the NTC thermistor to the battery and not to the LTC1733. + 1/2 VCC TOO HOT – + 3/160 VCC DISABLE NTC – LTC1733 1733 F03 Figure 3. Thermistors The LTC1733 NTC trip points were designed to work with thermistors whose resistance-temperature characteristics follow Vishay Dale’s “R-T Curve 2”. The Vishay NTHS0603N02N1002J is an example of such a thermistor. However, Vishay Dale has many thermistor products that follow the “R-T Curve 2” characteristic in a variety of sizes. Futhermore, any thermistor whose ratio of RCOLD to RHOT is about 7.0 will also work (Vishay Dale R-T Curve 2 shows a ratio of RCOLD to RHOT of 2.816/0.4086 = 6.9). NTC Layout Considerations It is important that the NTC thermistor not be in close thermal contact with the LTC1733. Because the LTC1733 package can reach temperatures in excess of the 50°C trip point, the NTC function can cause a hysteretic oscillation which turns the charge current on and off according to the When a 1% resistor is used for RHOT, the major error in the 50°C trip point is determined by the tolerance of the NTC thermistor. A typical 10k NTC thermistor has a ±10% tolerance. By looking up the temperature coefficient of the thermistor at 50°C, the tolerance error can be calculated in degrees centigrade. Consider the Vishay NTHS0603N02N1002J thermistor which has a temperature coefficient of –3.3%/°C at 50°C. Dividing the tolerance by the temperature coefficient, ±10%/(–3.3%/°C) = ±3°C, gives the temperature error of the hot trip point. The cold trip point is a little more complicated because its error depends on the tolerance of the NTC thermistor and the degree to which the ratio of its value at 0°C and its value at 50°C varies from 7 to 1. Therefore, the cold trip point error can be calculated using the tolerance, TOL, the temperature coefficient of the thermistor at 0°C, TC (in %/°C), the value of the thermistor at 0°C, RCOLD, and the value of the thermistor at 50°C, RHOT. The formula is: 1 + TOL RCOLD • – 1 • 100 RHOT Temperature Error (°C) = 7 TC For example, the Vishay NTHS0603N02N1002J thermistor with a tolerance of ±10%, TC of –4.5%/°C, and RCOLD/ RHOT of 6.89, has a cold trip point error of: 1 ± 0.10 • 6.89 – 1 • 100 Temperature Error (°C) = 7 – 4.5 = –1.8°C, +2.5°C sn1733 1733fs 11 LTC1733 U W U U APPLICATIO S I FOR ATIO If a thermistor with a tolerance less than ±10% is used, the trip point errors begin to depend on errors other than thermistor tolerance including the input offset voltage of the internal comparators of the LTC1733 and the effects of internal voltage drops due to high charging currents. 105°C. As the battery voltage rises, the LTC1733 either returns to constant-current mode or it enters constantvoltage mode straight from constant-temperature mode. Regardless of mode, the voltage at the PROG pin is proportional to the current being delivered to the battery. Constant-Current/Constant-Voltage/ Constant-Temperature Power Dissipation The LTC1733 uses a unique architecture to charge a battery in a constant-current, constant-voltage, constanttemperature fashion. Figure 1 shows a simplified block diagram of the LTC1733. Three of the amplifier feedback loops shown control the constant-current, CA, constantvoltage, VA, and constant-temperature, TA modes. A fourth amplifier feedback loop, MA, is used to increase the output impedance of the current source pair, M1 and M2 (note that M1 is the internal P-channel power MOSFET). It ensures that the drain current of M1 is exactly 1000 times greater than the drain current of M2. Amplifiers CA, TA, and VA are used in three separate feedback loops to force the charger into constant-current, temperature, or voltage mode, respectively. Diodes, D1, D2, and D3 provide priority to whichever loop is trying to reduce the charging current the most. The outputs of the other two amplifiers saturate low which effectively removes their loops from the system. When in constantcurrent mode, CA servos the voltage at the PROG pin to be precisely 1.50V (or 0.15V when in trickle-charge mode). TA limits the die temperature to approximately 105°C when in constant-temperature mode and the PROG pin voltage gives an indication of the charge current as discussed in “Programming Charge Current” . VA servos its inverting input to precisely 2.485V when in constantvoltage mode and the internal resistor divider made up of R1 and R2 ensures that the battery voltage is maintained at either 4.1V or 4.2V. Again, the PROG pin voltage gives an indication of the charge current. In typical operation, the charge cycle begins in constantcurrent mode with the current delivered to the battery equal to 1500V/RPROG. If the power dissipation of the LTC1733 results in the junction temperature approaching 105°C, the amplifier (TA) will begin decreasing the charge current to limit the die temperature to approximately The conditions that cause the LTC1733 to reduce charge current due to the thermal protection feedback can be approximated by considering the power dissipated in the IC. For high charge currents, the LTC1733 power dissipation is 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 battery charge current. It is not necessary to perform any worstcase power dissipation scenarios because the LTC1733 will automatically reduce the charge current to maintain the die temperature at approximately 105°C. However, the approximate ambient temperature at which the thermal feedback begins to protect the IC is: TA = 105°C – PDθJA TA = 105°C – (VCC – VBAT) • IBAT • θJA Example: Consider an LTC1733 operating from a 5V wall adapter providing 1.2A to a 3.75V Li-Ion battery. The ambient temperature above which the LTC1733 will begin to reduce the 1.2A charge current is approximately: TA = 105°C – (5V – 3.75V) • 1.2A • 40°C/W TA = 105°C – 1.5W • 40°C/W = 105°C – 60°C = 45°C The LTC1733 can be used above 45°C, but the charge current will be reduced below 1.2A. The approximate charge current at a given ambient temperature can be approximated by: IBAT = 105°C – TA (VCC – VBAT )• θ JA Consider the above example with an ambient temperature of 55°C. The charge current will be reduced to approximately: sn1733 1733fs 12 LTC1733 U W U U APPLICATIO S I FOR ATIO IBAT = 105°C – 55°C 50°C = = 1A (5V – 3.75V)• 40°C / W 50°C / A Furthermore, the voltage at the PROG pin will change proportionally with the charge current as discussed in the Programming Charge Current section. It is important to remember that LTC1733 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 105°C. See Design Note 283 for additional information. Board Layout Considerations In order to be able to deliver maximum charge current under all conditions, it is critical that the exposed pad on the backside of the LTC1733 package is soldered to the board. Correctly soldered to a 2500mm2 double-sided 1oz. copper board the LTC1733 has a thermal resistance of approximately 40°C/W. Failure to make thermal contact between the exposed pad on the backside of the package and the copper board will result in thermal resistances far greater than 40°C/W. As an example, a correctly soldered LTC1733 can deliver over 1250mA to a battery from a 5V supply at room temperature. Without a backside thermal connection, this number could drop to less than 500mA. 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 hot power source. For more information refer to Application Note 88. Stability The constant-voltage mode feedback loop is stable without any compensation when a battery is connected. However, a 1µF capacitor with a 1Ω series resistor to GND is recommended at the BAT pin to keep ripple voltage low when the battery is disconnected. In the constant-current mode it is the PROG pin that is in the feedback loop and not the battery. The constantcurrent mode stability is affected by the impedance at the PROG pin. With no additional capacitance on the PROG pin, stability is acceptable with program resistor values as high as 50k. However, additional capacitance on this node reduces the maximum allowed program resistor. The pole frequency at the PROG pin should be kept above 500kHz. Therefore, if the PROG pin is loaded with a capacitance, C, the following equation should be used to calculate the maximum resistance value for RPROG: RPROG < 1/(6.283 • 500E3 • C) Average, rather than instantaneous, battery 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 4. A 10k resistor is added between the PROG pin and the filter capacitor and monitoring circuit to ensure stability. LTC1733 PROG GND 5 CHARGE CURRENT MONITOR CIRCUITRY 10k 7 RPROG CFILTER 1733 F04 Figure 4. Isolating Capacitive Load on PROG Pin and Filtering. sn1733 1733fs 13 LTC1733 U TYPICAL APPLICATIO Basic Li-Ion Battery Charger with Reverse Polarity Input Protection 2 5V WALL ADAPTER 8 LTC1733 VCC BAT IBAT = 1A 9 SEL + 4.7µF 4 0.1µF TIMER PROG GND NTC 5 6 7 4.2V Li-Ion BATTERY 1.5k 1% 1733 F06 sn1733 1733fs 14 LTC1733 U PACKAGE DESCRIPTIO MSE Package 10-Lead Plastic MSOP (Reference LTC DWG # 05-08-1663) BOTTOM VIEW OF EXPOSED PAD OPTION 2.794 ± 0.102 (.110 ± .004) 5.23 (.206) MIN 0.889 ± 0.127 (.035 ± .005) 1 2.06 ± 0.102 (.081 ± .004) 1.83 ± 0.102 (.072 ± .004) 2.083 ± 0.102 3.2 – 3.45 (.082 ± .004) (.126 – .136) 10 0.50 0.305 ± 0.038 (.0197) (.0120 ± .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT 3.00 ± 0.102 (.118 ± .004) (NOTE 3) 3.00 ± 0.102 (.118 ± .004) NOTE 4 4.88 ± 0.10 (.192 ± .004) 0.254 (.010) DETAIL “A” 0° – 6° TYP 1 2 3 4 5 GAUGE PLANE 0.53 ± 0.01 (.021 ± .006) DETAIL “A” 0.18 (.007) 0.497 ± 0.076 (.0196 ± .003) REF 10 9 8 7 6 SEATING PLANE 0.86 (.034) REF 1.10 (.043) MAX 0.17 – 0.27 (.007 – .011) 0.50 (.0197) TYP 0.13 ± 0.05 (.005 ± .002) MSOP (MSE) 1001 NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX sn1733 1733fs 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 LTC1733 U TYPICAL APPLICATIO Full Featured Single Cell Li-Ion Charger VIN = 5V 1k 8 SEL 1k 1k 2 VCC 4k 1% ACPR 10 1 4.7µF 3 CHRG FAULT LTC1733 6 9 NTC BAT 4 RNTC 10k TIMER PROG GND 0.1µF 5 7 3k 1% IBAT = 500mA 1µF + 1Ω 4.2V Li-Ion BATTERY 1733 F05 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1571 200kHz/500kHz Switching Battery Charger Up to 1.5A Charge Current; Preset and Adjustable Battery Voltages LTC1729 Lithium-Ion Battery Charger Termination Controllers Time or Charge Current Termination, Preconditioning 8-Lead MSOP LTC1730 Lithium-Ion Battery Pulse Charger No Blocking Diode Required, Current Limit for Maximum Safety LTC1731 Lithium-Ion Linear Battery Charger Controller Simple Charger uses External FET, Features Preset Voltages, C/10 Charger Detection and Programmable Timer LTC1732 Lithium-Ion Linear Battery Charger Controller Simple Charger uses External FET, Features Preset Voltages, C/10 Charger Detection and Programmable Timer, Input Power Good Indication LTC1734 Lithium-Ion Linear Battery Charger in ThinSOT Simple ThinSOT Charger, No Blocking Diode, No Sense Resistor Needed LTC1998 Lithium-Ion Low Battery Detector 1% Accurate 2.5µA Quiescent Current, SOT-23 LTC4050 Lithium-Ion Linear Battery Charger Controller Simple Charger uses External FET, Features Preset Voltages, C/10 Charger Detection and Programmable Timer, Input Power Good Indication, Thermistor Interface sn1733 1733fs 16 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LT/TP 0602 2K • PRINTED IN USA