LTC1730-4/LTC1730-4.2 Lithium-Ion Battery Pulse Charger with Overcurrent Protection U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ The LTC®1730 is a complete pulse charger for 1-cell lithium-ion batteries. When charging a depleted cell, the internal MOSFET is fully on allowing the current limited input power source to provide charge current to the battery, virtually eliminating heat generation in the charger. Complete Pulse Charger for 1-Cell Lithium-Ion Batteries Sense Resistor Limits Maximum Current for Safety 1% Float Voltage Accuracy End-of-Charge (C/10) Detection Output Programmable Charge Termination Timer Internal 0.35Ω NMOS Switch No Blocking Diode Required SEL Pin to Set Either 4.1V or 4.2V/Cell (LTC1730-4) Low-Battery Drain (1µA Max) when Input Supply Is Removed Battery Temperature Sensing and Charge Qualification Automatic Trickle Charge for Low-Battery Automatic Battery Refresh As the battery accepts charge and approaches the programmed voltage, the internal MOSFET begins switching off and on with the duty cycle gradually decreasing as the battery approaches a fully charged condition. A programmable timer ends the charge cycle. The end-of-charge condition is indicated at the CHRG pin when the average charge current falls to C/10. Removing the input voltage puts the LTC1730 into a sleep mode, dropping the battery current drain to less than 1µA (maximum). An external sense resistor limits the maximum charge current as a safety precaution against a user connecting a wall adapter with the incorrect or no current limit. The internal MOSFET prevents reverse battery current from flowing if the input voltage is shorted to ground, eliminating the need for a blocking diode. U APPLICATIO S ■ ■ ■ Standalone Lithium-Ion Battery Charger Handheld Computers Cellular Telephones The LTC1730-4 is available in the 16-pin SSOP package and the LTC1730-4.2 is available in the 8-pin SO package. , LTC and LT are registered trademarks of Linear Technology Corporation. U TYPICAL APPLICATIO 1A, Single Cell 4.2V Li-Ion Battery Charger (8-Pin Package) VIN = 4.5V TO 12V WITH 1A CURRENT LIMIT 2 R3 4.1k R2 10k R1 1k VIN D3 LTC1730ES8-4.2 CHARGE STATUS GATE 3 T NTC/SHDN R4 10k NTC* TIMER 5 C1 1µF 7 0.022µF CHRG SENSE 6 C3 0.047µF 4.7Ω RSENSE 0.05Ω BAT GND 1 8 1-CELL Li-Ion BATTERY 4 CTIMER 0.1µF *NTC: DALE NTHS-1206N02 1730 TA01 1730f 1 LTC1730-4/LTC1730-4.2 W W U W ABSOLUTE AXI U RATI GS (Note 1) Supply Voltage (VCC) ............................................ 13.2V SENSE, GATE, BAT, TIMER, NTC/SHDN, SEL ............................ – 0.3V to VCC CHRG, ACPR, FAULT ..............................– 0.3V to 13.2V TOP VIEW GND* 1 16 GND* SENSE 2 15 BAT VCC 3 14 NC** ACPR 4 13 GATE FAULT 5 12 SEL CHRG 6 11 NTC/SHDN NC** 7 10 TIMER GND* 8 9 GND* ORDER PART NUMBER LTC1730EGN-4 Operating Junction Temperature Range (Note 2) .................. – 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 SENSE 1 8 BAT ACPRB 2 7 GATE VIN 3 6 CHRG GND 4 5 TIMER LTC1730ES8-4.2 S8 PACKAGE 8-LEAD PLASTIC SO GN PART MARKING GN PACKAGE 16-LEAD PLASTIC SSOP S8 PART MARKING TJMAX = 125°C, θJA = 110°C/W 17304 173042 * FOUR CORNER PINS ARE FUSED TO INTERNAL DIE ATTACH PADDLE FOR HEAT SINKING. CONNECT THESE FOUR PINS TO EXPANDED PC LANDS FOR PROPER HEAT SINKING. ** NO INTERNAL CONNECTION TJMAX = 125°C, θJA = 90°C/W Consult LTC Marketing for parts specified with wider operating temperature ranges. DC ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 6V unless otherwise noted. SYMBOL PARAMETER VCC Supply Voltage CONDITIONS MIN ICC Supply Current Charger On; Fast Charge Mode Shutdown: VNTC/SHDN = 0V Sleep Mode; VBAT = 4V ● ● ● VBAT Regulated Output Voltage LTC1730ES8-4.2 (5V ≤ VCC ≤ 12V) LTC1730EGN-4 (5V ≤ VCC ≤ 12V), SEL = GND LTC1730EGN-4 (5V ≤ VCC ≤ 12V), SEL = VCC ● ● ● IMAX Maximum Charge Overcurrent RSENSE = 0.1Ω ● ITRICKL Trickle Charge Current VBAT = 2V VTRICKL Trickle Charge Trip Threshold VASD Automatic Shutdown Threshold Voltage (Sleep Mode) (VCC – VBAT) Low to High (VCC – VBAT) High to Low RDS(ON) Internal Switch On-Resistance VBAT = 4V VSHDN Shutdown Threshold Voltage NTC/SHDN Pin High to Low ● TYP 4.5 MAX UNITS 12 V 2 2 5 5 1 mA mA µA 4.158 4.059 4.158 4.2 4.1 4.2 4.242 4.141 4.242 V V V 0.7 1 1.3 A 15 35 60 mA 2.45 2.55 V 150 mV mV 50 mV 0 Ω 0.35 1730f 2 LTC1730-4/LTC1730-4.2 DC ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 6V unless otherwise noted. SYMBOL PARAMETER CONDITIONS ICHRG CHRG Pin Pull-Down Current VCHRG = 1V, C/10 Mode TTIMER TIMER Accuracy CTIMER = 0.1µF VGATE GATE Pin Voltage VBAT = 3V VBAT = 4V TSHDN Thermal Shutdown Temperature ∆TSHDN Thermal Shutdown Hysteresis ∆VRECHRG Recharge Battery Voltage Offset from Full Charged Battery Voltage VBAT(Full Charged) – VRECHRG (Note 3) VNTC_HOT NTC/SHDN Pin Threshold Voltage (Hot) High to Low; VCC = 4V Hysteresis ● 1.95 2 50 2.05 V mV VNTC_COLD NTC/SHDN Pin Threshold Voltage (Cold) Low to High; VCC = 4V Hysteresis ● 3.4 3.5 45 3.6 V mV VSEL SEL Pin Threshold LTC173ECGN-4 VACPR ACPR Pin Output Low Voltage LTC1730EGN-4, IACPR = 5mA 0.6 V VFAULT FAULT Pin Output Low Voltage LTC1730EGN-4, IFAULT = 3mA 1.2 V VCHRG CHRG Pin Output Low Voltage ICHRG = 5mA, Charging Mode 0.9 V Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LTC1730-4/LTC1730-4.2 are guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the – 40°C to 85°C MIN TYP MAX UNITS 10 40 70 µA 10 % 7.5 10 V V 140 °C 5 °C 150 mV 0.7 V operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: For the LTC1730-4 version, the full charged VBAT value is typically 4.1V. 1730f 3 LTC1730-4/LTC1730-4.2 U W TYPICAL PERFOR A CE CHARACTERISTICS Trickle Charge Threshold Voltage vs Temperature Trickle Charge Current vs Input Supply Voltage 50 2.50 TA = 25°C 45 Trickle Charge Current vs Temperature 50 VCC = 6V VCC = 6V 45 2.48 40 35 2.46 I (mA) VTRIKL (V) I (mA) 40 30 30 2.42 25 20 5 6 9 8 VCC (V) 7 11 10 12 25 2.40 –50 –25 50 25 75 0 TEMPERATURE (°C) 1730 G01 100 20 –50 125 50 25 75 0 TEMPERATURE (°C) 100 Timer Accuracy vs Temperature VBAT = 4V 110 0.45 Overcurrent vs Temperature 1.3 VCC = 6V CTIMER = 0.1µF 1.2 tTIMER (%) VCC = 6V RSEN = 0.1Ω 1.1 IMAX (A) 105 0.40 125 1730 G03 115 0.50 0.35 –25 1730 G02 Internal Switch On-Resistance vs Temperature RDS(ON) (Ω) 35 2.44 100 95 1.0 0.9 0.30 0.25 0.20 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 125 90 0.8 85 0.7 80 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 125 0.6 –50 –25 50 25 75 0 TEMPERATURE (°C) 1730 G06 1730 G05 Battery Recharge Threshold Offset from VBAT vs Temperature 100 125 1730 G07 CHRG Pin Output Low Voltage vs Temperature 1.0 300 VCC = 6V 0.9 250 VCHRG (V) ∆VRECHRG (mV) 0.8 200 150 100 0.6 0.5 50 0 –50 –25 0.7 0.4 0 25 50 75 100 125 150 TEMPERATURE (°C) 1730 G09 0.3 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 125 1730 G08 1730f 4 LTC1730-4/LTC1730-4.2 U U U PI FU CTIO S LTC1730ES8-4.2 SENSE (Pin 1): Maximum Overcurrent Sense Input. A sense resistor (RSENSE) should be connected from VCC to the SENSE pin. When the voltage drop across RSENSE exceeds 100mV, the pass transistor immediately turns off and turns back on after a 400ms time-out period (CTIMER = 0.1µF). The on-off cycle will continue, as long as the overcurrent condition persists or until the timer runs out. If overcurrent protection is not needed, short SENSE to VCC. VCC (Pin 2): Positive Input Supply Voltage (4.5V ≤ VCC ≤ 13.2V). Bypass this pin with a 1µF capacitor in series with a 4.7Ω resistor. An RC network from the VCC pin to the GATE pin is also required. The capacitor controls the slew rate at the VCC pin, while the resistor limits the inrush current when the input voltage is first applied. When the pass transistor turns on, VCC ramps down in a controlled manner, with a slope equal to 10µA/C. When the pass transistor turns off, VCC ramps up with a slope of 40µA/C. CHRG (Pin 3): Open-Drain Charge Status Output. When a depleted battery is being charged, the CHRG pin is pulled to ground by an N-MOSFET capable of driving an LED. Once the duty cycle at the GATE pin drops below 10%, the N-MOSFET turns off and a weak 40µA current source to ground turns on to indicate a near end-of-charge (C/10) condition. When a time-out occurs or the input supply is removed, the CHRG pin goes high impedance. GND (Pin 4): Electrical Ground Connection and provides a thermal path from the IC to the PC board copper. Use large copper pads and traces for maximum heat transfer. TIMER (Pin 5): Timer Set Pin. The timer period is set by a capacitor (CTIMER) to ground. The timer period is: tTIMER = (CTIMER • 3Hr)/(0.1µF). The minimum ON time, OFF time and the overcurrent time-out period are all set by the same timer period. NTC/SHDN (Pin 6): Input to the NTC (Negative Temperature Coefficient) Thermistor Monitoring and Shutdown Circuitry. 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 the temperature is out of range. When the voltage at this pin drops below 0.5 • VCC, or 2V at hot temperature or rises above 0.875 • VCC, or 3.5V at cold (with VCC = 4V), the charge cycle is suspended and the internal timer is frozen. The CHRG pin output status is not affected in this hold state. When this pin is pulled below 50mV, the IC goes into the shutdown mode. The charging stops (the GATE pin is pulled to ground) the timer is reset and the CHRG pin goes into a high impedance state. GATE (Pin 7): Gate Drive Output Pin for Internal and External Pass Transistors. An external N-MOSFET transistor can be connected in parallel with the internal transistor to reduce the on-resistance for higher charge current. In this case, an external blocking diode is required to prevent damage to the battery if VCC is shorted to ground. A 10µA current source pulls this pin up to the charge pump potential when turned on and a 40µA current source pulls it down to ground to turn it off. If an overcurrent condition is detected, the GATE pin is immediately pulled to ground. A series RC network from the GATE to the VCC pin is required to control the slew rate at the VCC pin when the switch is turned on or off. The slew rate control prevents excessive current from the capacitor located in the wall adapter from flowing into the battery when the pass transistor is turned on. The voltage at this pin is internally clamped to 12V above the BAT pin. BAT (Pin 8): Battery Sense Input Pin. This pin is clamped to 4.7V if the battery is disconnected while charging. An internal resistor divider presets the final float voltage to 4.2V. If the voltage at the BAT pin drops 150mV below final float voltage after the charge cycle has ended, the timer resets and a new charge cycle begins. LTC1730EGN-4 GND (Pins 1, 8, 9, 16): Refer to LTC1730ES8-4.2 SENSE (Pin 2): Refer to LTC1730ES8-4.2 VCC (Pin 3): Refer to LTC1730ES8-4.2 ACPR (Pin 4): Wall Adapter Present Open-Drain Output. When the input voltage (wall adapter) is applied to the LTC1730, this pin is pulled to ground by an internal 1730f 5 LTC1730-4/LTC1730-4.2 U U U PI FU CTIO S N-channel MOSFET. This output can sink up to 5mA suitable for driving an LED. condition is detected, the FAULT pin is pulled low and latched. FAULT (Pin 5): Fault Condition Detection Open-Drain Output. This output can sink up to 3mA suitable for driving an external LED. The internal N-channel MOSFET pulls this pin to ground when either one of the following conditions is detected: CHRG (Pin 6): Refer to LTC1730ES8-4.2 1. The voltage at the NTC pin is out of the normal operation range. This usually means the battery pack temperature is too high or too low. Once the temperature is back to normal, the FAULT pin becomes high impedance. NTC/SHDN (Pin 11): Refer to LTC1730ES8-4.2 2. The BAT pin potential stays below 2.45V for more than 1/4 of the programmed charge time. When this GATE (Pin 13): Refer to LTC1730ES8-4.2 NC (Pins 7, 14): No Internal Connection. Connecting these pins to ground will help transfer heat from the package. TIMER (Pin 10): Refer to LTC1730ES8-4.2 SEL (Pin 12): 4.1V/4.2V Battery Selection Input. Grounding this pin will set the output float voltage to 4.1V, while connecting to VCC will set the voltage to 4.2V. BAT (Pin 15): Refer to LTC1730ES8-4.2 W BLOCK DIAGRA VCC CHRG 100mV C5 + – + 35mA N1 SENSE – 40µA GATE Q-PUMP (3X) 40mV 0.125R – C6 C/10 STOP IMAX COLD 0.375R NTC/SHDN C4 NSW + ACPR BAT – + – + – C7 C3 LOGIC HOT R1 – VMAX + + 0.5R + C8 C2 SHDN 121mV R2 – VBAT – + OSCILLATOR C1 CLK FAULT R3 – VMIN R5 + FAULT ON RECHRG C9 + R4 SEL 4.1V/4.2V ACPR – –+ 1.21V 150mV 1703 BD TIMER GND 1730f 6 LTC1730-4/LTC1730-4.2 U OPERATIO The LTC1730 is a complete lithium-ion battery pulse charger with an internal 0.35Ω N-MOSFET switch driven by an internal charge pump. The charge current is set by the current limit of the input supply (wall adapter). An external RSENSE sets the maximum allowable charge over current (IMAX = 0.1V/RSENSE) and prevents a wall adapter with the wrong current limit from damaging the battery. If the current limit of the input supply is above IMAX, the charging will be immediately terminated and will retry after 400ms (CTIMER = 0.1µF). If the battery is disconnected while in fast charge mode, the N-channel MOSFET turns off when the voltage at the BAT pin rises above 4.7V, and turns back on when the voltage drops below the float voltage. A charge cycle begins when the voltage at the VCC pin rises above the BAT pin by 40mV and the voltage at the NTC/ SHDN pin is in between 0.5 • VCC and 0.875 • VCC. The charger will go into trickle charge mode if the battery voltage is below 2.45V. The trickle charge current is preset to 35mA and is provided by an internal current source. In trickle mode, the charge pump and pass transistor are off. When the battery voltage exceeds 2.45V, the charger goes into the fast charge mode. In this mode, the charge pump turns on and ramps up the gate voltage of the pass transistor turning it on. The voltage at the VCC pin then ramps down to VBAT plus the voltage drop across the pass transistor and RSENSE, thus reducing the power dissipation in the pass transistor. The charge current is determined by the current limit of the input supply. When the battery voltage reaches the final float voltage, the pass transistor turns off for 100ms (minimum offtime). It remains off as long as the battery voltage stays above the float voltage after the 100ms off-time. After the minimum off-time, if the battery voltage drops below the float voltage, the pass transistor turns back on for at least 380ms (minimum on-time). As the battery approaches full charge, the off-time will get longer and the on-time will stay at 380ms. The voltage at the BAT pin will be slightly higher than the final float voltage due to the ESR associated with the battery pack. This voltage level should not turn on the overvoltage protection circuitry often located in the battery pack. When the duty cycle at the GATE pin drops below 10%, a comparator turns off the N-FET at the CHRG pin and connects a weak current source (40µA) to ground to indicate a near end-of-charge (C/10) condition. The pulse charging will continue until the timer stops. An external capacitor at the TIMER pin sets the total charge time, the minimum on- and off-time and the overcurrent retry period. After a time-out has occurred, the charge cycle is terminated and the CHRG pin is forced high impedance. To restart the charge cycle, momentarily pull the NTC/SHDN pin below 50mV or remove and reapply the input voltage. After the charging stops, if the battery voltage drops 150mV below the final float voltage, due to external loading or internal leakage, a new charge cycle will automatically begins. The charger can be shut down by pulling the NTC/SHDN pin to ground. When the input voltage is not present, the charger goes into a sleep mode, dropping battery drain current to less than 1µA. 1730f 7 LTC1730-4/LTC1730-4.2 U W U U APPLICATIO S I FOR ATIO Stop Charging The charger is off when any of the following conditions exist. The voltage at the VCC pin is less than 40mV above VBAT (sleep mode), or the potential at the NTC/SHDN pin is less than 50mV (shutdown mode). The trickle charge current source and the internal pass transistor are turned off. The internal resistor divider is disconnected to reduce the current drain on the battery when in sleep mode. an external capacitor from the TIMER pin to ground. The total charge time is: Time (Hours)= (3 Hour)(CTIMER/0.1µF) The timer starts when the input voltage (at least 40mV greater than VBAT) is applied and the potential at the NTC/ SHDN pin is between 0.5 • VCC and 0.875 • VCC. After a time-out has occurred, the charging stops and the CHRG pin becomes high impedance. Input Voltage (Wall Adapter) CHRG Status Output Pin The input voltage to the LTC1730 must have some method of current limit capability. The current limit level of the input power source must be lower than the overcurrent limit (IMAX) set by the sense resistor (IMAX = 100mV/RSENSE). If a wall adapter without current limit is used, or the current limit level is above IMAX, the charger will turn on briefly and then immediately turn off after the overcurrent condition is detected. This cycle will be resumed every 400ms (CTIMER = 0.1µF) until the total charge time has run out. If overcurrent protection is not needed, short the SENSE pin to VCC. This open-drain output requires a pull-up resistor and can be used to indicate three charging conditions. When fast charging begins, an N-FET (capable of driving an LED) turns on, pulling this pin to ground. Once the duty cycle at the GATE pin drops below 10%, the N-FET turns off and a 40µA current source to ground turns on. When a time-out occurs or the input supply is removed, the CHRG pin goes high impedance indicating that the charge cycle has ended. By using two different value resistors, a microprocessor can detect three states from this pin: charging, C/10 and stop charging (see Figure 1). Trickle Charge and Defective Battery Detection At the begining of the charge cycle, if the cell voltage is low (less than 2.45V) the charger goes into a 35mA trickle charge mode. If the low cell voltage persists for one quarter of the total charge time, the battery is considered defective and the charge cycle is terminated. The CHRG pin output is then forced to a high impedance state. V+ VDD 2 VCC LTC1730 CHRG 3 620k 2k MICROPROCESSOR OUT IN 1730 F01 Figure 1. Interfacing with Microprocessor Battery Charge Current The battery charge current is determined by the current limit of the input supply (wall adapter). However, this current must not exceed the maximum charge overcurrent, IMAX. If an overcurrent condition is detected, the charging is immediately terminated, the GATE pin is pulled to ground and the charge pump turns off. The charging will resume after a 400ms time off (CTIMER = 0.1µF). Programming the Timer The programmable timer is used to terminate the charge and sets the minimum ON/OFF time and the overcurrent time-off period. The length of the timer is programmed by When the LTC1730 is in charge mode, the CHRG pin is pulled to ground by an internal N-MOSFET. To detect this mode, force the digital output pin, OUT, high and measure the voltage at the CHRG pin. The N-MOSFET will pull the pin low even with a 2k pull-up resistor. Once the charge current drops below 10% of the full scale current (C/10), the N-MOSFET is turned off and a 40µA current source is connected to the CHRG pin. By forcing the OUT pin to a high impedance state, the current source will pull the pin low through the 620k resistor. When the internal timer has expired, the CHRG pin becomes high impedance and the 620k resistor will pull the pin high to indicate that charging has stopped. 1730f 8 LTC1730-4/LTC1730-4.2 U W U U APPLICATIO S I FOR ATIO End-of-Charge (C/10) The LTC1730 includes a comparator to monitor the duty cycle at the GATE pin to detect a near end-of-charge condition. When the duty cycle falls below 10%, the comparator trips and turns off the N-MOSFET at the CHRG pin and switches in a weak (40µA) current source to ground. The end-of-charge comparator is disabled in trickle charge mode. Internal Pass Transistor An N-channel MOSFET (0.35Ω) is included in the LTC1730 as the pass transistor. The gate of the MOSFET is controlled by an internal charge pump. The body is connected to ground instead of source terminal. There is no body diode from the BAT pin back to the VCC pin; therefore, no blocking diode is required in series with the battery or the input supply. This will not only reduce the cost but also the heat generated when in fast charge mode. An internal thermal shutdown circuit turns off the pass transistor if the die temperature exceeds approximately 140°C with 5°C of thermal hysteresis. Gate Drive The pass transistor gate drive consists of a regulated 10µA current source charge pump. A series RC network is required from the GATE pin to the VCC pin. When the pass transistor is turned on, the voltage at the VCC pin starts slewing down to a voltage equal to VBAT plus the voltage drop across the pass transistor and RSENSE. The slew rate is equal to 10µA/C. By ramping the VCC pin down slowly, the inrush current is reduced. The resistor in series with the capacitor is required to limit the transient current when the input supply is first applied. When the charge pump is turned off, a 40µA current source to ground starts pulling the GATE voltage down. Once the pass transistor is off, the voltage at the VCC pin begins slewing up with the rate equal to 40µA/C. With this external capacitor, the voltage at the VCC pin is ramping at a controlled manner (Figure 2). For higher current applications an external power N-MOSFET can be connected in parallel with the internal pass transistor. Because the charge pump output is clamped to 12V 10µA/C 40µA/C VCC 40µA/C GATE VOLTAGE 10µA/C 10µA/C 40µA/C 1730 TA02 Figure 2. Slew Rate at GATE and VCC Pins with the RC Network from GATE to VCC above VBAT, the external N-MOSFET gate to source breakdown voltage should be rated at 20V or more. Battery Temperature Detection A negative temperature coefficient (NTC) thermistor located close to the battery pack can be used to monitor battery temperature and will not allow charging unless the battery temperature is within an acceptable range. Connect a 10kΩ thermistor between ground and the NTC/SHDN pin and a 4.1k resistor from the NTC/SHDN pin to VCC. If the temperature rises to 50°C, the resistance of the thermister will be approximately 4.1kΩ (Dale NTHS-1206N02) and the LTC1730 will go into a hold mode. For cold temperatures, the threshold of the hold mode is at 0°C (RNTC ≈ 28kΩ). The pass transistor turns off and the timer is frozen at hold mode while the output status at the CHRG pin remains the same. The charge cycle begins or resumes once the temperature is within the acceptable range. Thermal Considerations The power handling capability is limited by the maximum rated junction temperature (125°C) and the amount of PC board copper used as a heat sink. The power dissipated by the device consists of two components: 1. Input supply current multiplied by the input voltage 2. The voltage drop across the switch (SENSE pin to BAT pin) multiplied by the charge current The LTC1730 has internal thermal shutdown designed to protect the IC from overtemperature conditions. For continuous charging in the fast charge mode, the maximum junction temperature must not be exceeded. It is important to give careful consideration to all sources of thermal resistance from junction to ambient. Additional heat sources mounted nearby must also be considered. 1730f 9 LTC1730-4/LTC1730-4.2 U W U U APPLICATIO S I FOR ATIO Surface mount packages rely primarily on the copper leads (pins) to conduct the heat from the package to the surrounding PC board copper which is acting as a heat sink. The ground pin is especially important for conducting heat as well as providing an electrical connection. Use generous amounts of copper around the ground pin and also consider feedthrough vias (plated through holes) to backside or inner copper layers to maximize power dissipation. Table 1. SO-8 Package Thermal Resistance Table 1 lists the thermal resistance for the SO-8 package. Measured values of thermal resistance for several different board sizes and copper areas are listed. All measurements were taken in still air on 0.062" FR-4 board with one ounce copper. The float voltage at the BAT pin can be selected by the SEL pin. Shorting the SEL pin to ground will set the float voltage to 4.1V, while connecting it to VCC sets it to 4.2V. This feature allows the charger to be used with different types of Li-Ion cells. Calculating Junction Temperature ACPR Output Pin (LTC1730EGN-4) Example: Find the maximum junction temperature for a battery voltage of 4V (VCC will collapse to approximately VBAT in the fast charge mode), charge current of 1A and a maximum ambient temperature of 75°C. When the input voltage is 40mV higher than the voltage at the BAT pin, the ACPR pin is pulled low to ground to indicate that the input supply (wall adapter) is applied. After the input supply is removed, this pin becomes high impedance. An internal 80ms delay prevents the LTC1730 from turning off if the voltage at the VCC pin rings and gets too close to VBAT because of the parasitic inductance. The power dissipated by the IC is: P = (IBAT • IBAT • RDS(ON)) + (VCC • ICC) COPPER AREA TOPSIDE BACKSIDE TOTAL BOARD AREA THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 2500mm2 2500mm2 2500mm2 80°C/W 1000mm2 2500mm2 2500mm2 80°C/W 250mm2 2500mm2 2500mm2 85°C/W *Device is mounted on topside. Output Voltage Selection (LTC1730EGN-4) = (1A • 1A • 0.35Ω) + (4V • 1mA) = 0.35 + 0.004 = 0.354W The SO-8 package for the LTC1730 features a special lead frame with a lower thermal resistance and higher allowable power dissipation. The junction-to-ambient thermal resistance of this package when soldered to a PC board is approximately 80°C/W depending on the copper area. So the junction temperature rise above ambient will be approximately: (0.354W)(80°C/W) = 28.3°C The maximum junction temperature is equal to the maximum junction temperature rise above ambient plus the maximum ambient temperature or: FAULT Output Pin (LTC1730EGN-4) The FAULT pin is pulled to ground when either one of the following conditions is detected: 1. The voltage at the NTC/SHDN pin is out of the operation range. With a 10k negative temperature coefficient thermistor placed near the battery pack, this pin indicates that the temperature of the pack is either too cold or too hot and the charger is suspended. Once the temperature is back to the operational range, the FAULT pin becomes high impedance and the charging resumes. 2. The voltage at the BAT pin stays below 2.45V for 1/4 of the programmed charge time. If VBAT remains low even with 35mA of trickle charge current for 1/4 of the total TJMAX = 75°C + 28.3°C = 103.3°C 1730f 10 LTC1730-4/LTC1730-4.2 U U W U APPLICATIO S I FOR ATIO charge time, the battery is considered defective. The charger turns off and the FAULT pin is pulled low. This pin will stay low until the LTC1730 is reset by either removing the input power supply or momentarily shutting down the charger. After reset, the charger is back in the charge mode and the FAULT pin becomes high impedance again. U PACKAGE DESCRIPTIO GN Package 16-Lead Plastic SSOP (Narrow .150 Inch) (Reference LTC DWG # 05-08-1641) 0.189 – 0.196* (4.801 – 4.978) 0.015 ± 0.004 × 45° (0.38 ± 0.10) 0.007 – 0.0098 (0.178 – 0.249) 0.053 – 0.068 (1.351 – 1.727) 16 15 14 13 12 11 10 9 0.004 – 0.0098 (0.102 – 0.249) 0.009 (0.229) REF 0° – 8° TYP 0.016 – 0.050 (0.406 – 1.270) 0.008 – 0.012 (0.203 – 0.305) 0.229 – 0.244 (5.817 – 6.198) 0.0250 (0.635) BSC * DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE ** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 0.150 – 0.157** (3.810 – 3.988) 1 GN16 (SSOP) 1098 2 3 4 5 6 7 8 S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch) (Reference LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 0°– 8° TYP 0.016 – 0.050 (0.406 – 1.270) 0.014 – 0.019 (0.355 – 0.483) TYP *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 8 7 6 5 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) BSC 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) SO8 1298 1 2 3 4 1730f Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 11 LTC1730-4/LTC1730-4.2 U TYPICAL APPLICATIO S Single Cell 4.2V Li-Ion Battery Charger (16-Pin Package) VIN = 5V TO 12V WITH 600mA CURRENT LIMIT 4.1k 1k 1k 3 1k 4.7Ω VCC 10k 1µF LTC1730EGN-4 6 4 5 11 0.047µF CHRG ACPR SENSE FAULT GATE NTC/SHDN 0.1Ω 2 13 15 BAT 0.022µF VCC 12 10k NTC* SEL 1, 8, 9,16 GND TIMER NC 10 Li-Ion BATTERY 7, 14 0.1µF *NTC: DALE NTHS-1206N02 1730 TA04 Using External N-MOSFET for Higher Charge Current VIN = 5V TO 12V WITH 2A CURRENT LIMIT D1 MBRS120T3 2 R4 4.1k R2 10k VCC R1 1k C3 0.047µF LTC1730ES8-4.2 D3 CHARGE STATUS SENSE 3 6 CHRG NTC/SHDN GATE BAT 4.7Ω RSENSE 25mΩ C1 1µF 1 7 8 Q1 Si2302DS 0.022µF Li-Ion BATTERY R3 10k NTC* TIMER 5 GND 4 CTIMER 0.1µF *NTC: DALE NTHS-1206N02 1730 TA03 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1731 Li-Ion Linear Battery Charger Controller CC/CV Charges Li-Ion Cells, 8-Lead MSOP LTC1732 Li-Ion Linear Battery Charger Controller Stand Alone Charger, Automatic Battery Detection, 10-Lead MSOP LT1510-5 500kHz CC/CV Switching Battery Charger Most Compact, Up to 1.5A, Charges NiCd, NiMH, Li-Ion Cells LTC1729 Termination Controller for Li-Ion Time or Charge Current Termination, Automatic Charger/Battery Detection Status Output, Preconditioning, 8-Lead MSOP LTC1733 Li-Ion Battery Charger with Internal FET 1.5A CC/CV, 10-Lead Enhanced MSOP, Thermal Regulation for Constant Temperature, No Blocking Diode, No Sense Resistor Required LTC1734 ThinSOT Li-Ion Battery Charger Only Two External Components, Up to 700mA ICHARGE, No Reverse Current Diode Required, No Sense Resistor Required LTC4050 Li-Ion Linear Charger with Thermistor Interface Stand Alone Charger; 10-Lead MSOP, Up to 1A Charge Current 1730f 12 Linear Technology Corporation LT/TP 0902 1K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2001