LP3947 USB/AC Adaptor, Single Cell Li-Ion Battery Charger IC General Description The LP3947 is a complete charge management system that safely charges and maintains a Li-Ion battery from either USB power source or AC adaptor. In USB mode, the LP3947 supports charging in low power or high power mode. Alternatively, the LP3947 can take charge from AC adaptor. In both USB and AC adaptor modes, charge current, battery regulation voltage, and End of Charge (EOC) point can be selected via I2C interface. The LP3947 can also operate on default values that are pre-programmed in the factory. The battery temperature is monitored continuously at the Ts pin to safeguard against hazardous charging conditions. The charger also has under-voltage and over-voltage protection as well as an internal 5.6 hr timer to protect the battery. The pass transistor and charge current sensing resistor are all integrated inside the LP3947. The LP3947 operates in four modes: pre-qualification, constant current, constant voltage and maintenance modes. There are two open drain outputs for status indication. An internal amplifier readily converts the charge current into a voltage. Also, the charger can operate in an LDO mode providing a maximum of 1.2 Amp to the load. Features n Supports USB Charging Scheme n Integrated Pass Transistor n n n n n n n n Near-Depleted Battery Preconditioning Monitors Battery Temperature Built-In 5.6 hour timer Under Voltage and Over Voltage Lockout Charge Status Indicators Charge Current Monitor Analog Output LDO Mode Operation can source 1 Amp Continuous Over Current/Temperature Protection Key Specifications n 1% Charger Voltage Accuracy Over 0˚C ≤ TJ ≤ 85˚C n 4.3V to 6.0V Input Voltage Range n 100 mA to 750 mA charge current range, in charger mode n 100mA to 500mA charge current range, in USB mode n LLP Package Power Dissipation: 2.7W at TA = 25˚C Applications n n n n n Cellular Phones PDAs Digital Cameras USB Powered Devices Programmable Current Sources Typical Application Circuit 20111001 More Application Circuit can be found in the Application Note section. © 2004 National Semiconductor Corporation DS201110 www.national.com LP3947 USB/AC Adaptor, Single Cell Li-Ion Battery Charger IC November 2004 LP3947 Connection Diagrams and Package Mark Information 20111002 (Top View) See NS Package Number SDA14B Pin Description Pin # Name Description 1 EN Charger Enable Input. Internally pulled high to CHG-IN pin. A HIGH enables the charger and a LOW disables the charger. 2 SCL I2C serial Interface Clock input. 3 SDA I2C serial Interface Data input/out. 4 BATT Battery supply input terminal. Must have 10 µF ceramic capacitor to GND 5 VT Regulated 2.78V output used for biasing the battery temperature monitoring thermistor. 6 VBSENSE Battery Voltage Sense connected to the positive terminal of the battery. 7 MODE Select pin between AC adaptor and USB port. A LOW sets the LP3947 in USB port and a HIGH sets it in the AC adaptor. 8 Diff-Amp Charge current monitoring differential amplifier output. Voltage output representation of the charge current. 9 Ts Multi function pin. Battery temperature monitoring input and LDO/Charger mode. Pulling this pin to VT, or removing the thermistor by physically disconnecting the battery, sets the device in LDO mode. 10 EOC Active Low Open Drain Output. Active when USB port or AC adaptor is connected and battery is fully charged. For more information, refer to “LED Charge Status Indicators” section. 11 GND Ground 12 CHG Active Low Open Drain Output. Active when USB port or AC adaptor is connected and battery is being charged. For more information, refer to “LED Charge Status Indicators” section. 13 ISEL Control pin to switch between low power (100 mA) mode and high power (500 mA) mode in USB mode. This pin is pulled high internally as default to set the USB in 100 mA mode. This pin has to be externally pulled low to go into 500 mA mode. 14 CHG-IN Charger input from a regulated, current limited power source. Must have a 1 µF ceramic capacitor to GND Ordering Information LP3947 Supplied as 1000 Units, Tape and Reel LP3947 Supplied as 4500 Units Tape and Reel Default Options* Package Marking LP3947ISD-09 LP3947ISDX-09 ICHG = 500 mA VBATT = 4.1V EOC = 0.1C L00055B LP3947ISD-51 LP3947ISDX-51 ICHG = 500 mA VBATT = 4.2V EOC = 0.1C L00056B *Other default options are available. Please contact National Semiconductor sales office/distributors for availability and specifications. www.national.com 2 LP3947 LP3947 Functional Block Diagram 20111003 3 www.national.com LP3947 Absolute Maximum Ratings Operating Ratings (Notes 1, 2) (Notes 1, 2) CHG-IN If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. EN, ISEL, MODE, SCL, SDA, VT (Note 3) CHG-IN Operating Temperature −40˚C to +85˚C Thermal Resistance θJA 37˚C/W −0.3V to +6V Junction Temperature 150˚C Storage Temperature −40˚C to +150˚C Power Dissipation (Note 4) ESD (Note 5) Human Body Model Machine Model 0V to 6V Junction Temperature −0.3V to +6.5V All pins except GND and CHG-IN (Note 3) 0.3V to 6.5V −40˚C to +125˚C Maximum Power Dissipation (Note 6) 1.21W 1.89W 2 kV 200V Electrical Characteristics Unless otherwise noted, VCHG-IN = 5V, VBATT = 4V, CCHG-IN = 1 µF, CBATT = 10 µF. Typical values and limits appearing in normal type apply for TJ = 25˚C. Limits appearing in boldface type apply over the entire junction temperature range for operation, TJ = −40˚C to +85˚C. (Notes 7, 8, 9) Symbol Parameter Conditions Typ Limit Min Max 4.5 6 4.3 6 Units VCC SUPPLY VCHG-IN Input Voltage Range VUSB ICC VOK-TSHD VUVLO-TSHD VOVLO-TSHD Quiescent Current Adaptor OK Trip Point (CHG-IN) Under Voltage Lock-Out Trip Point Over Voltage Lock-Out Trip Point Thermal Shutdown Temperature VCHG-IN ≤ 4V 2 20 EOC = Low, adaptor connected, VBATT = 4.1V 50 150 V µA VCHG-IN –VBATT (Rising) 60 mV VCHG-IN –VBATT (Falling) 50 mV VCHG-IN (Rising) 3.95 3.6 4.3 V VCHG-IN (Falling) 3.75 3.4 4.1 V VCHG-IN (Rising) 5.9 VCHG-IN (Falling) 5.7 (Note 8) 160 Thermal Shutdown Hysteresis V ˚C 20 BATTERY CHARGER ICHG Fast Charge Current Range Fast Charge Current Accuracy ISEL = High, In USB Mode 100 ISEL = Low, In USB Mode 500 mA In AC Adaptor Mode 100 750 ICHARGE = 100 mA or 150 mA −20 +20 mA ICHARGE ≥ 200 mA −10 +10 % IPRE-CHG Pre-Charge Current VBATT = 2V 45 70 mA IEOC End of Charge Current Accuracy 100 mA to 450 mA, 0.1C EOC Only (Note 10) −10 +10 mA 500 mA to 750 mA, All EOC Points −20 +20 % VBATT Battery Regulation Voltage (For 4.1V TJ = 0˚C to +85˚C Cell) TJ = −40˚C to +85˚C Battery Regulation Voltage (For 4.2V TJ = 0˚C to +85˚C Cell) TJ = −40˚C to +85˚C VCHG-Q www.national.com Full Charge Qualification Threshold VBATT Rising, Transition from Pre-Charge to Full Current 4 4.1 4.059 4.141 4.1 4.038 4.162 4.1 4.158 4.242 4.2 4.137 4.263 3.0 V V (Continued) Unless otherwise noted, VCHG-IN = 5V, VBATT = 4V, CCHG-IN = 1 µF, CBATT = 10 µF. Typical values and limits appearing in normal type apply for TJ = 25˚C. Limits appearing in boldface type apply over the entire junction temperature range for operation, TJ = −40˚C to +85˚C. (Notes 7, 8, 9) Symbol Parameter Conditions Typ Restart Threshold Voltage (For 4.1V Cell) VBATT Falling, Transition from EOC, to Pre-Qualification State Restart Threshold Voltage (For 4.2V Cell) Internal Current Sense Resistance Limit Min Max 3.9 3.77 4.02 VBATT Falling, Transition from EOC, to Pre-Qualification State 4.00 3.86 4.12 (Note 8) 120 Units BATTERY CHARGER VBAT-RST RSENSE V mΩ Internal Current Sense Resistor Load Current ICHGMON tOUT VOL Diff-Amp Output Charger Time Out Low Level Output Voltage 1.2 ICHG = 50 mA 0.583 ICHG = 100 mA 0.663 ICHG = 750 mA 1.790 V TJ = 0˚C to 85˚C 5.625 4.78 6.42 TJ = −40˚C to +85˚C 5.625 4.5 6.75 EOC, CHG Pins each at 9 mA A 100 Hrs mV TEMPERATURE SENSE COMPARATORS VUTLO VOTLO Low Voltage Threshold High Voltage Threshold VLDO LDO Mode Voltage Threshold VT Voltage Output Voltage at Ts Pin, Rising 2.427 Voltage at Ts Pin, Falling 2.369 Voltage at Ts Pin, Rising 1.470 Voltage at Ts Pin, Falling 1.390 Voltage at Ts Pin, % of VT V V 97 % 2.787 V LDO MODE (Ts = HIGH) VOUT Output Voltage Regulation ILOAD = 50 mA 4.10 ILOAD = 750 mA 4.06 V LOGIC LEVELS VIL Low Level Input Voltage EN, ISEL, MODE VIH High Level Input Voltage EN, ISEL, MODE 2.0 IIL Input Current EN, ISEL = LOW IIH Input Current 0.4 V −10 +10 µA MODE = LOW −5 +5 µA EN, ISEL, MODE = HIGH −5 +5 µA V Electrical Characteristics, I2C Interface Unless otherwise noted, VCHG-IN = VDD = 5V, VBATT = 4V. Typical values and limits appearing in normal type apply for TJ = 25˚C. Limits appearing in boldface type apply over the entire junction temperature range for operation, TJ = −40˚C to +125˚C. (Notes 7, 8, 9) Symbol Parameter Conditions Typ Limit Min Max Units VIL Low Level Input Voltage SDA & SCL (Note 8) 0.4 0.3 VDD VIH High Level Input Voltage SDA & SCL (Note 8) 0.7 VDD VDD +0.5 V VOL Low Level Output Voltage SDA & SCL (Note 8) 0 0.2 VDD V VHYS Schmitt Trigger Input Hysteresis SDA & SCL (Note 8) 0.1 VDD FCLK Clock Frequency (Note 8) tHOLD Hold Time Repeated START Condition (Note 8) tCLK-LP CLK Low Period tCLK-HP CLK High Period V V 400 kHz 0.6 µs (Note 8) 1.3 µs (Note 8) 0.6 µs 5 www.national.com LP3947 Electrical Characteristics LP3947 Electrical Characteristics, I2C Interface (Continued) Unless otherwise noted, VCHG-IN = VDD = 5V, VBATT = 4V. Typical values and limits appearing in normal type apply for TJ = 25˚C. Limits appearing in boldface type apply over the entire junction temperature range for operation, TJ = −40˚C to +125˚C. (Notes 7, 8, 9) Symbol tSU Parameter Set-Up Time Repeated START Condition Conditions Typ (Note 8) Limit Min Max Units 0.6 µs ns tDATA-HOLD Data Hold Time (Note 8) 300 tDATA-SU Data Set-Up Time (Note 8) 100 ns tSU Set-Up Time for STOP Condition (Note 8) 0.6 µs tTRANS Maximum Pulse Width of Spikes that (Note 8) must be Suppressed by the Input Filter of both DATA & CLK Signals. 50 ns Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the Electrical Characteristics tables. Note 2: All voltages are with respect to the potential at the GND pin. Note 3: Caution must be taken to avoid raising pins EN and VT 0.3V higher than VCHG-IN and raising pins ISEL, MODE, SCL and SDA 0.3V higher than VBATT. Note 4: The Absolute Maximum power dissipation depends on the ambient temperature and can be calculated using the formula P = (TJ – TA)θJA, (1) where TJ is the junction temperature, TA is the ambient temperature, and θJA is the junction-to-ambient thermal resistance. The 1.89W rating appearing under Absolute Maximum Ratings results from substituting the Absolute Maximum junction temperature, 150˚C, for TJ, 80˚C for TA, and 37˚C/W for θJA. More power can be dissipated safely at ambient temperatures below 80˚C. Less power can be dissipated safely at ambient temperatures above 80˚C. The Absolute Maximum power dissipation can be increased by 27 mW for each degree below 80˚C, and it must be de-rated by 27 mW for each degree above 80˚C. Note 5: The human-body model is used. The human-body model is 100 pF discharged through 1.5 kΩ. Note 6: Like the Absolute Maximum power dissipation, the maximum power dissipation for operation depends on the ambient temperature. The 1.21W rating appearing under Operating Ratings results from substituting the maximum junction temperature for operation, 125˚C, for TJ, 80˚C for TA, and 37˚C/W for θJA into (1) above. More power can be dissipated at ambient temperatures below 80˚C. Less power can be dissipated at ambient temperatures above 80˚C. The maximum power dissipation for operation can be increased by 27 mW for each degree below 80˚C, and it must be de-rated by 27 mW for each degree above 80˚C. Note 7: All limits are guaranteed. All electrical characteristics having room-temperature limits are tested during production with TJ = 25˚C. All hot and cold limits are guaranteed by correlating the electrical characteristics to process and temperature variations and applying statistical process control. Note 8: Guaranteed by design. Note 9: LP3947 is not intended as a Li-Ion battery protection device, any battery used in this application should have an adequate internal protection. Note 10: The ± 10 mA limits apply to all charge currents from 100 mA to 450 mA, to 0.1C End Of Charge (EOC). The limits increase proportionally with higher EOC points. For example, at 0.2C, the End Of Charge current accuracy becomes ± 20 mA. 20111004 FIGURE 1. Li-Ion Charging Profile www.national.com 6 LP3947 CHARGER OPERATION The LP3947 charge cycle is initiated with AC adaptor or USB power source insertion. If the voltage on the CHG-IN pin meets under-voltage (VUVLO-TSHD), over-voltage (VOVLOTSHD) requirements, and the Adaptor OK signal is detected, then pre-qualification cycle begins (see Figure 1). In this cycle, a safe current level, less than 70mA, is pumped into the battery while the voltage across the battery terminals is measured. Once this voltage exceeds 3.0V, the controller will initiate constant current fast charge cycle. If the CHG-IN pin is connected to an AC adaptor, the default charge current is 500 mA and I2C interface can be used to program this parameter. If the CHG-IN pin is connected to the USB port, constant current cycle will start with a default of 100 mA. During this cycle, the 5.6 hr safety timer starts counting. If the 5.6 hr safety timers times out during constant current cycle, charging is terminated. As the battery is charged during constant current mode, the voltage across pack terminal increases until it reaches 4.2V (or 4.1V). As soon as pack terminal reaches 4.2V (or 4.1V), the controller starts operating in constant voltage mode by applying regulated When charging source comes from the USB port, charging starts with 100 mA (low power mode, ISEL = high). The USB controller can set the ISEL pin low to charge the battery at 500 mA. A simple external circuit selects between an AC adaptor or the USB port. The circuit is designed with priority given to the AC adaptor. 20111006 FIGURE 2. LP3947 with External Switch 7 www.national.com LP3947 VBATT voltage across the battery terminals. During this cycle, the charge current, ICHG, continues to decrease with time and when it drops below 0.1C (default value), the EOC signal is activated indicating successful completion of the charge cycle. The EOC current can be programmed to 0.1C, 0.15C, or 0.2C. The default value is 0.1C. After completing the full charge cycle, the controller will start the maintenance cycle where battery pack voltage is monitored continuously. During the maintenance cycle, if the pack voltage drops 200 mV below the termination voltage, charge cycle will be initiated providing that the wall adaptor is plugged in and is alive. Charging terminates when the battery temperature is out of range. For more explanation, please refer to “Ts Pin” section. The LP3947 with I2C interface allows maximum flexibility in selecting the charge current, battery regulation voltage and EOC current. The LP3947 operates in default mode during power up. See the “I2C Interface” section for more detail. Application Notes LP3947 Application Notes (Continued) 20111007 FIGURE 3. LP3947 Charger Flow Chart www.national.com 8 LP3947 Application Notes (Continued) CHARGE CURRENT SELECTION IN CONSTANT CURRENT MODE to set the charge current in the LP3947. In the USB mode, the LP3947 will initially charge with 100 mA (ISEL = high). By setting the ISEL pin low, charge current can be programmed to 500 mA. In addition, with ISEL = low, the charge current can be programmed to different values via the I2C interface. In the AC adaptor mode, the LP3947 is designed to provide a charge current ranging from 100 mA to 750 mA, in steps of 50 mA, to support batteries with different capacity ratings. The default value is 500 mA. No external resistor is required TABLE 1. Charge Current Selection in AC Adaptor/USB Mode MODE Pin AC Adaptor Mode USB Mode ISEL Pin Functions HIGH HIGH HIGH LOW ISEL polarity is irrelevant. Default 500 mA charge current. Can be reprogrammed via I2C. LOW HIGH 100 mA charge current LOW LOW Default 500 mA charge current. Can be reprogrammed via I2C. BATTERY VOLTAGE SELECTION CHARGE CURRENT SENSE DIFFERENTIAL AMPLIFIER The battery voltage regulation can be set to 4.1V or 4.2V by default. Please refer to the Ordering Information table for more detail. The charge current is monitored across the internal 120 mΩ current sense resistor. The differential amplifier provides the analog representation of the charge current. Charge current can be calculated using the following equation: END OF CHARGE (EOC) CURRENT SELECTION The EOC thresholds can be programmed to 0.1C, 0.15C or 0.2C in the LP3947. The default value is 0.1C, which provides the highest energy storage, but at the expense of longer charging time. On the other hand, 0.2C takes the least amount of charging time, but yields the least energy storage. Where voltage at Diff Amp output (VDIFF) is in volt, and charge current (ICHG) is in amps. 20111009 FIGURE 4. Charge Current Monitoring Circuit (Diff-Amp) Monitoring the Diff Amp output during constant voltage cycle can provide an accurate indication of the battery charge status and time remaining to EOC. This feature is particularly useful during constant voltage mode. The current sense circuit is operational in the LDO mode as well. It can be used to monitor the system current consumption during testing. LED CHARGE STATUS INDICATORS The LP3947 is equipped with two open drain outputs to drive a green LED and a red LED. These two LEDs work together in combinations to indicate charge status or fault conditions. Table 2 shows all the conditions. 9 www.national.com LP3947 Application Notes (Continued) TABLE 2. LED Indicator Summary RED LED (CHG) GREEN LED (EOC) Charger Off OFF OFF Charging Li Ion Battery* ON OFF Maintenance Mode OFF ON Charging Li Ion Battery after Passing Maintenance Mode OFF ON EN Pin = LOW OFF ON LDO Mode OFF OFF 5.6 Hr Safety Timer Flag/Battery Temperature Violation ON ON * Charging Li Ion battery for the first time after VCHG-IN insertion. Ts PIN The LP3947 continuously monitors the battery temperature by measuring the voltage between the Ts pin and ground. Charging stops if the battery temperature is outside the permitted temperature range set by the battery’s internal thermistor RT and the external bias resistor RS. A 1% precision resistor should be used for RS. A curve 2 type thermistor is recommended for RT. The voltage across RT is proportional to the battery temperature. If the battery temperature is outside of the range during the charge cycle, the LP3947 will suspend charging. As an example, for a temperature range of 0˚C to 50˚C, a 10kΩ for the thermistor and a 4.1kΩ for Rs should be used. When battery temperature returns to the permitted range, charging resumes from the beginning of the flow chart and the 5.6 hr safety timer is reset. Refer to Figure 3. LP3947 Charger Flow Chart for more information. Ts ≥ 2.7V LDO Mode www.national.com 2.427v ≤ Ts < 2.7V 0V ≤ Ts ≤ 1.39V Charger Off 1.39V < Ts < 2.427V Charger On EN PIN The Enable pin is used to enable/disable the charger, in both the charger mode and the LDO mode, see Figures 5, 6. The enable pin is internally pulled HIGH to the CHG-IN pin. When the charger is disabled, it draws less than 4 µA of current. Charger Status in Relation to Ts Voltage Charger Status Charger Status LDO MODE The charger is in the LDO mode when the Ts pin is left floating. This mode of operation is used primarily during system level testing of the handset to eliminate the need for battery insertion. CAUTION: battery may be damaged if device is operating in LDO mode with battery connected. The internal power FET provides up to 1.2 amp of current at BATT pin in this mode. The LDO output is set to 4.1V. When operating at higher output currents, care must be taken not to exceed the package power dissipation rating. See “Thermal Performance of LLP Package” section for more detail. In absence of the thermistor, Ts pin will be pulled high to VT and the LP3947 goes into LDO mode. In this mode, the internal power FET provides up to 1.2 amp of current at the BATT pin. The LDO output is set to 4.1V or 4.2V, depending on the programmed battery regulation voltage. When operating at higher output currents, care must be taken not to exceed the package power dissipation rating. See “Thermal Performance of LLP Package” section for more detail. Voltage on the Ts Pin Voltage on the Ts Pin 10 LP3947 Application Notes (Continued) 20111010 FIGURE 5. Power Up Timing Diagram in Charger Mode (1.39V < Ts < 2.427V) 20111011 FIGURE 6. Power Up Timing Diagram in LDO Mode (Ts ≥ 2.7V) MODE PIN The mode pin toggles the LP3947 between the AC adaptor mode and the USB mode. When CHG-IN is connected to a USB port, this pin must be set low. When CHG-IN is connected to an AC adaptor, this pin must be tied high to either the BATT pin or to the wall adaptor input. Caution: MODE pin should never be tied to CHG-IN pin directly, as it will turn on an internal diode. mode. It will turn the charger off when the 5.6 hr timer is up while the charger is still in constant current mode. In this case, both LEDs will turn on, indicating a fault condition. When the battery temperature is outside the specified temperature range, the 5.6 hr safety timer will reset upon recovery of the battery temperature. I2C INTERFACE I2C interface is used in the LP3947 to program various parameters as shown in Table 3. The LP3947 operates on default settings following power up. Once programmed, the LP3947 retains the register data as long as the battery voltage is above 2.85V. 5.6 HR SAFETY TIMER IN CHARGER MODE The LP3947 has a built-in 5.6 hr back up safety timer to prevent over-charging a Li Ion battery. The 5.6 hr timer starts counting when the charger enters the constant current 11 www.national.com LP3947 Application Notes (Continued) TABLE 3. LP3947 Serial Port Communication address code 7h’47 LP3947 Control and Data Codes Addrs Register 7 6 5 4 3 2 1 0 8'h00 Charger Register -1 Batt Voltage (0) = 4.1V 1 = 4.2V AC Adaptor Charge Current Code 3 (1) AC Adaptor Charge Current Code 2 (0) AC Adaptor Charge Current Code 1 (0) AC Adaptor Charge Current Code 0 (0) 8'h01 Charger Register -2 EOC (Green LED) R/O Charging (Red LED) R/O EOC SEL-1 (0) EOC SEL-0 (1) 8'h02 Charger Register -3 USB Charge Current Code 3 (1) USB Charge Current Code 2 (0) USB Charge Current Code 1 (0) USB Charge Current Code 0 (0) Numbers in parentheses indicate default setting. “0” bit is set to low state, and “1” bit is set to high state. R/O –Read Only, All other bits are Read and Write. TABLE 4. Charger Current and EOC Current Programming Code End of Charge Current Selection Code Data Code Charger Current Selection Code ISET (mA) 4h'00 100 4h'01 150 0.1C 4h'02 200 0.15C 4h'03 250 0.2C 4h'04 300 4h'05 350 4h'06 400 4h'07 450 4h'08 500 4h'09 550 4h'0A 600 4h'0B 650 4h'0C 700 4h'0D 750 20111012 w = write (sda = “0”) r = read (sda = “1”) ack = acknowledge (sda pulled low by either master or slave) Nack = No Acknowledge rs = repeated start FIGURE 7. LP3947 (Slave) Register Write www.national.com 12 LP3947 Application Notes (Continued) 20111013 w = write (sda = “0”) r = read (sda = “1”) ack = acknowledge (sda pulled low by either master or slave) Nack = No Acknowledge rs = repeated start FIGURE 8. LP3947 (Slave) Register Read charged, then 740 mA of ICHG can safely charge the battery. More power can be dissipated at ambient temperatures below 70˚C. Less power can be dissipated at ambient temperatures above 70˚C. The maximum power dissipation for operation can be increased by 27 mW for each degree below 70˚C, and it must be de-rated by 27 mW for each degree above 70˚C. THERMAL PERFORMANCE OF LLP PACKAGE The LP3947 is a monolithic device with an integrated pass transistor. To enhance the power dissipation performance, the Leadless Lead frame Package, or LLP, is used. The LLP package is designed for improved thermal performance because of the exposed die attach pad at the bottom center of the package. It brings advantage to thermal performance by creating a very direct path for thermal dissipation. Compared to the traditional leaded packages where the die attach pad is embedded inside the mold compound, the LLP reduces a layer of thermal path. The thermal advantage of the LLP package is fully realized only when the exposed die attach pad is soldered down to a thermal land on the PCB board and thermal vias are planted underneath the thermal land. Based on a LLP thermal measurement, junction to ambient thermal resistance (θJA) can be improved by as much as two times if a LLP is soldered on the board with thermal land and thermal vias than if not. An example of how to calculate for LLP thermal performance is shown below: LAYOUT CONSIDERATION The LP3947 has an exposed die attach pad located at the bottom center of the LLP package. It is imperative to create a thermal land on the PCB board when designing a PCB layout for the LLP package. The thermal land helps to conduct heat away from the die, and the land should be the same dimension as the exposed pad on the bottom of the LLP (1:1 ratio). In addition, thermal vias should be added inside the thermal land to conduct more heat away from the surface of the PCB to the ground plane. Typical pitch and outer diameter for these thermal vias are 1.27 mm and 0.33 mm respectively. Typical copper via barrel plating is 1oz although thicker copper may be used to improve thermal performance. The LP3947 bottom pad is connected to ground. Therefore, the thermal land and vias on the PCB board need to be connected to ground. For more information on board layout techniques, refer to Application Note 1187 “Leadless Leadframe Package (LLP).” The application note also discusses package handling, solder stencil, and assembly. By substituting 37˚C/W for θJA, 125˚C for TJ and 70˚C for TA, the maximum power dissipation allowed from the chip is 1.48W. If VCHG-IN is at 5.0V and a 3.0V battery is being 13 www.national.com LP3947 USB/AC Adaptor, Single Cell Li-Ion Battery Charger IC Physical Dimensions inches (millimeters) unless otherwise noted NS Package Number SDA14B National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. For the most current product information visit us at www.national.com. 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