LTC3552EDHC-1

FEATURES ■ ■ LTC3552-1 Standalone Linear Li-Ion Battery Charger and Dual Synchronous Buck Converter DESCRIPTIO The LTC®3552-1 is a complete constant-current/constantvoltage linear charger and dual fixed output DC/DC converter for single cell lithium-ion batteries. Its DFN package and low external component count make the LTC3552-1 ideally suited for portable applications. Furthermore, the LTC3552-1 is designed to work within USB power specifications. No external sense resistor or external blocking diode are required due to the internal MOSFET architecture. The charge voltage is fixed at 4.2V and the charge current is programmed with a resistor. The charge cycle terminates when the charge current drops below the programmed termination threshold after the final float voltage is reached. When the input supply (wall adapter or USB supply) is removed, the LTC3552-1 enters a low current state dropping the battery drain current to less than 2µA. Thermal regulation maximizes charge rate without risk of overheating. The synchronous step-down switching regulators generate fixed output voltages of 1.8V and 1.575V. The switching frequency is set at 2.25MHz, allowing the use of small surface mount inductors and capacitors. , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Burst Mode is a registered trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected by U.S. Patents including 6522118, 6700364, 5481178, 6580258, 6304066, 6127815, 6498466, 6611131. ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Programmable Charge Current Up to 950mA Complete Linear Charger and Dual DC/DC Regulator Dual Fixed Outputs: 1.8V at 800mA 1.575V at 400mA No MOSFET, Sense Resistor or Blocking Diode Required Thermal Regulation Maximizes Charge Rate Without Risk of Overheating* Charges Directly from a USB Port Programmable Charge Current Termination Preset 4.2V Charge Voltage with ±1% Accuracy Charge Current Monitor Output for Gas Gauging* Automatic Recharge Charge Status Output “Power Present” Output Soft-Start Limits Inrush Current Low Quiescent Current Buck Converter (40µA) Current Mode Operation, Constant Frequency (2.25MHz) Low Profile (5mm × 3mm × 0.75mm) DFN Package APPLICATIO S ■ ■ Cellular Telephones, PDAs, MP3 Players Bluetooth Applications TYPICAL APPLICATIO Single Cell Li-Ion Battery Charger with C/5 Termination and Dual DC/DC Converter VIN 4.5V TO 6.5V VIN 1µF 619Ω 1.24k ITERM PROG CHRG PWR VOUT2 1.575V/ 400mA COUT2 10µF CER 4.7µH EN SW2 CFF2 330pF VOUT2 VFB2 GND LTC3552-1 RUN1 RUN2 BAT VCC 2.2µH SW1 VOUT1 VFB1 CFF1 330pF EFFICIENCY (%) Efficiency Curve/ Power Loss of Regulators 100 95 90 VOUT1 = 1.8V VOUT2 = 1.575V 100 POWER LOSS (mW) 1000 800mA 10µF + 4.2V 1-CELL Li-Ion BATTERY VOUT1 1.8V/ 800mA COUT1 10µF CER 35521 TA01 85 80 CHANNEL 1 75 70 65 60 1 CHANNEL 2 VIN = 3.6V Burst Mode OPERATION 10 100 LOAD CURRENT (mA) 1 10 U U U 0.1 1000 35521 TAO1b 35521fa 1 LTC3552-1 ABSOLUTE (Note 1) AXI U RATI GS PACKAGE/ORDER I FOR ATIO TOP VIEW ITERM BAT CHRG RUN2 SW2 RUN1 VOUT2 VFB2 1 2 3 4 5 6 7 8 17 16 EN 15 PWR 14 VIN 13 PROG 12 SW1 11 VCC 10 VOUT1 9 VFB1 Input Supply Voltage (VIN) ......................... –0.3V to 10V PROG, ITERM .................................. –0.3V to VIN + 0.3V BAT .............................................................. –0.3V to 7V CHRG, PWR, EN ....................................... –0.3V to 10V BAT Short-Circuit Duration............................Continuous BAT Pin Current ..........................................................1A PROG Pin Current ....................................................1mA VCC Supply Voltage ...................................... –0.3V to 6V VOUT1, VOUT2, RUN1, RUN2 Voltages .............................–0.3V to VCC +0.3V VFB1, VFB2 ........................................–0.3V to VCC + 0.3V SW1, SW2 Voltage ...........................–0.3V to VCC + 0.3V Ambient Operating Temperature Range (Note 2) .................................... –40°C to 85°C Maximum Junction Temperature (Note 8) ............ 125°C Storage Temperature Range................... –65°C to 125°C DHC PACKAGE 16-LEAD (5mm × 3mm) PLASTIC DFN TJMAX = 125°C, θJA = 40°C/W (Note 3) EXPOSED PAD IS GROUND (PIN 17) MUST BE SOLDERED TO PCB ORDER PART NUMBER LTC3552EDHC-1 DHC PART MARKING 35521 Order Options Tape and Reel: Add #TR Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS SYMBOL Battery Charger VIN IIN Input Supply Voltage Input Supply Current Charge Mode (Note 4) Standby Mode Shutdown Mode Regulated Output (Float) Voltage BAT Pin Current PARAMETER The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 5V, VCC = 3.6V unless otherwise noted. CONDITIONS ● MIN 4.25 TYP MAX 8 UNITS V mA µA µA µA mA mA µA µA µA V mV V V ΜΩ mV mV mA mA 35521fa RPROG = 10k Charge Terminated EN = 5V, VIN < VBAT or VIN < VUV 0°C ≤ TA ≤ 85°C, 4.3V < VIN < 8V RPROG = 10k, Current Mode RPROG = 2k, Current Mode Standby Mode, VBAT = 4.2V Shutdown Mode (EN = 5V, VIN < VBAT or VIN < VUV) Sleep Mode, VIN = 0V From VIN Low to High ● ● ● 0.4 200 25 4.158 4.2 100 500 –2.5 ±1 ±1 1 500 50 4.242 105 535 –6 ±2 ±2 3.92 300 1 5 140 50 110 22.5 VFLOAT IBAT ● ● ● 92 465 VUV VUVHYS VEN(IL) VEN(IH) REN VASD ITERM VIN Undervoltage Lockout Voltage VIN Undervoltage Lockout Hysteresis EN Pin Input Low Voltage EN Pin Input High Voltage EN Pin Pull-Down Resistor VIN – VBAT Lockout Threshold Voltage Charge Termination Current Threshold ● ● ● ● ● 3.7 150 0.4 1.2 70 5 3.8 200 0.7 0.7 2 100 30 100 20 VIN from Low to High VIN from High to Low RTERM = 1k RTERM = 5k ● ● 90 17.5 2 U W U U WW W LTC3552-1 ELECTRICAL CHARACTERISTICS SYMBOL VPROG VCHRG VPWR ΔVRECHRG TLIM RON-CHRG tSS-CHRG tRECHRG tTERM Switching Regulator VCC VOUT1 VOUT2 ΔVLINE_REG ΔVLOAD_REG IS Operating Voltage Range for Converter Output Voltage Feedback of Regulator 1 Output Voltage Feedback of Regulator 2 Reference Voltage Line Regulation Output Voltage Load Regulation Input DC Supply Current (Note 6) Active Mode Sleep Mode Shutdown Oscillator Frequency Peak Switch Current Limit Regulator 1 Peak Switch Current Limit Regulator 2 0°C ≤ TA ≤ 85°C (Note 5) –40°C ≤ TA ≤ 85°C (Note 5) 0°C ≤ TA ≤ 85°C (Note 5) –40°C ≤ TA ≤ 85°C (Note 5) VCC = 2.5V to 5.5V (Note 5) (Note 5) VOUT1 = 1.5V, VOUT2 = 1.3V VOUT1 = 1.89V, VOUT2 = 1.65V RUN = 0V, VCC = 5.5V VOUT1 = 1.8V, VOUT2 = 1.575V VCC = 3V, Duty Cycle < 35% VCC = 3V, Duty Cycle < 35% ● ● ● ● The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 5V, VCC = 3.6V unless otherwise noted. PARAMETER PROG Pin Voltage CHRG Pin Output Low Voltage PWR Pin Output Low Voltage Recharge Battery Threshold Voltage Junction Temperature in ConstantTemperature Mode Charger’s Power FET “ON” Resistance (Between VIN and BAT) Charger Soft-Start Time Recharge Comparator Filter Time Termination Comparator Filter Time IBAT = 0 to IBAT = 1000V/RPROG VBAT High to Low IBAT Drops Below Charge Termination Threshold 0.75 0.4 CONDITIONS RPROG = 10k, Current Mode ICHRG = 5mA IPWR = 5mA VFLOAT – VRECHRG, 0°C < TA < 85°C 60 MIN 0.93 TYP 1 0.35 0.35 100 120 600 100 2 1 4.5 2.5 MAX 1.07 0.6 0.6 140 UNITS V V V mV °C mΩ µs ms ms 2.5 1.764 1.755 1.544 1.536 1.8 1.8 1.575 1.575 0.3 0.5 700 40 0.1 1.8 0.95 0.6 2.25 1.2 0.7 0.35 0.3 0.01 5.5 1.836 1.836 1.607 1.607 0.5 V V V V V %/V % 950 60 1 2.7 1.6 0.9 0.45 0.45 1 1.5 1 µA µA µA MHz A A Ω Ω µA V µA fOSC ILIM RDS(ON) ISW(LKG) VRUN IRUN Converter Top Switch On-Resistance (Note 7) Converter Bottom Switch On-Resistance (Note 7) Switch Leakage Current RUN Threshold Voltage RUN Leakage Current VCC = 5V, VRUN = 0V, VFB = 0V ● ● 0.3 1 0.01 Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LTC3552E-1 is guaranteed to meet performance specifications from 0°C to 85°C Specifications over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: 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. See Thermal Considerations. Note 4: Supply current includes PROG pin current and ITERM pin current (approximately 100µA each) but does not include any current delivered to the battery through the BAT pin (approximately 100mA). Note 5: The converter is tested in a proprietary test mode that connects the output of the error amplifier to the SW pin, which is connected to an external servo loop. Note 6: Dynamic supply current is higher due to the internal gate charge being delivered at the switching frequency. Note 7: The regulator power switch on-resistances are guaranteed by correlation to wafer level measurements. Note 8: TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formula: TJ = TA + (PD • θJA) 35521fa 3 LTC3552-1 TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C Unless Otherwise Specified. Battery Charger PROG Pin Voltage vs Supply Voltage (Constant-Current Mode) 1.015 1.010 1.005 VPROG (V) VPROG (V) 1.000 0.995 0.990 0.985 VBAT = 4V RPROG = 10k 1.0100 1.0075 1.0050 IBAT (mA) 1.0025 1.0000 0.9975 0.9950 0.9925 4 4.5 5 5.5 6.5 6 VIN (V) 7 7.5 8 0.9900 –50 –25 50 25 TEMPERATURE (°C) 0 75 100 35521 G02 Regulated Output (Float) Voltage vs Charge Current 4.26 VIN = 5V 4.24 RPROG = 1.25k 4.22 VFLOAT (V) VFLOAT (V) 4.215 4.210 4.205 4.200 4.195 4.190 4.18 4.16 4.14 4.12 4.10 0 100 200 300 400 IBAT (mA) 500 600 700 35521 G04 VFLOAT (V) 4.20 CHRG Pin I-V Curve (Pull-Down State) 30 TA = –40°C 25 20 ICHRG (mA) 15 10 5 0 0 1 2 4 3 VCHRG (V) 5 6 7 35521 G07 TA = 25°C IPWR (mA) TA = 90°C IBAT (mA) 4 UW VIN = 5V VBAT = 4V PROG Pin Voltage vs Temperature 600 VIN = 5V VBAT = VBSENSE = 4V RPROG = 10k 500 400 300 200 100 0 Charge Current vs PROG Pin Voltage VIN = 5V RPROG = 2k RTERM = 2k 0 0.2 0.4 0.6 0.8 VPROG (V) 1 1.2 35521 G03 35521 G01 Regulated Output (Float) Voltage vs Temperature VIN = 5V RPROG = 10k 4.215 Regulated Output (Float) Voltage vs Supply Voltage RPROG = 10k 4.210 4.205 4.200 4.195 4.190 4.185 4.185 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 35521 G05 4 4.5 5 5.5 6.5 6 VIN (V) 7 7.5 8 35521 G06 PWR Pin I-V Curve (Pull-Down State) 30 TA = –40°C 25 20 15 10 5 0 0 1 2 4 3 VPWR (V) 5 6 7 35521 G08 Charge Current vs Battery Voltage 600 TA = 25°C 500 400 300 200 100 0 2.4 VIN = 5V θJA = 40°C/W RPROG = 2k 2.7 3 3.3 3.6 VBAT (V) 3.9 4.2 4.5 35521 G09 TA = 90°C VIN = 5V VBAT = 4V 35521fa LTC3552-1 TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C Unless Otherwise Specified. Battery Charger Charge Current vs Supply Voltage 600 500 400 IBAT (mA) 300 200 100 0 RPROG = 10k VBAT = 4V θJA = 40°C/W IBAT (mA) RPROG = 2k 500 RPROG = 2k 400 300 200 100 0 –50 RPROG = 10k VIN = 5V VBAT = 4V θJA = 40°C/W 600 ONSET OF THERMAL REGULATION 4 4.5 5 Power FET “On” Resistance vs Temperature 700 VIN = 4.2V = 100mA I 650 BAT RPROG = 2k 600 RDS(ON) (mΩ) 4.12 550 500 450 400 350 –50 VRECHRG (V) 4.10 4.08 4.06 4.16 4.14 –25 UW 5.5 Charge Current vs Ambient Temperature 6 6.5 VIN (V) 7 7.5 8 –25 35521 G10 50 25 75 0 TEMPERATURE (°C) 100 125 35521 G11 Recharge Threshold Voltage vs Temperature VIN = 5V RPROG = 10k 0 25 50 75 TEMPERATURE (°C) 100 125 35521 G12 4.04 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 35521 G13 35521fa 5 LTC3552-1 TYPICAL PERFOR A CE CHARACTERISTICS Switching Regulator Burst Mode Operation SW 5V/DIV IL 200mA/DIV VOUT1 RIPPLE 20mV/DIV VCC = 3.6V 2µs/DIV VOUT1 = 1.8V ILOAD = 60mA REGULATOR 1; CIRCUIT OF FIGURE 2 35521 G14 Efficiency vs Supply Voltage 100 95 90 EFFICIENCY (%) 85 80 75 70 65 60 2 VOUT1 = 1.8V, REGULATOR 1 Burst Mode OPERATION CIRCUIT OF FIGURE 2 2.5 3 3.5 4 VCC (V) 4.5 5 5.5 6 IOUT = 1mA IOUT = 10mA IOUT = 100mA IOUT = 800mA FREQUENCY (MHz) 2.5 FREQUENCY DEVIATION (%) Output Voltage Error vs Temperature 1.0 0.8 OUTPUT VOLTAGE ERROR (%) 0.6 0.4 0.2 0 –0.2 –0.4 –0.6 –0.8 –1.0 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 125 35521 G20 VCC = 3.6V RDS(ON) (mΩ) RDS(ON) (mΩ) 6 UW TA = 25°C Unless Otherwise Specified. Load Step VOUT1 200mV/DIV VOUT2 200mV/DIV Load Step IL 500mA/DIV ILOAD: 80mA800mA 500mA/DIV IL 200mA/DIV ILOAD 40mA400mA 200mA/DIV 20µs/DIV VCC = 3.6V VOUT1 = 1.8V ILOAD = 80mA TO 800mA REGULATOR 1; CIRCUIT OF FIGURE 2 35521 G15 VCC = 3.6V 20µs/DIV VOUT2 = 1.575V ILOAD = 40mA TO 400mA REGULATOR 2; CIRCUIT OF FIGURE 2 35521 G16 Oscillator Frequency vs Temperature VCC = 3.6V 10 8 6 4 2 0 –2 –4 –6 –8 2.0 –50 –25 –10 50 25 75 0 TEMPERATURE (°C) 100 125 35521 G18 Oscillator Frequency Error vs Supply Voltage 2.4 2.3 2.2 2.1 2 3 4 VCC (V) 5 6 35521 G19 35521 G17 RDS(ON) vs Supply Voltage 500 450 400 350 300 250 200 1 2 SYNCHRONOUS SWITCH 550 500 450 MAIN SWITCH 400 350 300 250 200 150 3 4 VCC (V) 5 6 7 35521 G21 RDS(ON) vs Junction Temperature VCC = 2.7V VCC = 4.2V VCC = 3.6V 100 –50 –25 MAIN SWITCH SYNCHRONOUS SWITCH 25 50 75 100 125 150 0 JUNCTION TEMPERATURE (°C) 35521 G22 35521fa LTC3552-1 TYPICAL PERFOR A CE CHARACTERISTICS Switching Regulator Efficiency vs Load Current 100 95 90 EFFICIENCY (%) 85 80 75 70 65 60 1 VCC = 3.6V Burst Mode OPERATION CIRCUIT OF FIGURE 2 10 100 LOAD CURRENT (mA) 1000 35521 G23 VOUT1 = 1.8V VOUT ERROR (%) VOUT2 = 1.575V VOUT ERROR (%) Efficiency vs Load Current 100 95 90 EFFICIENCY (%) 85 80 75 70 65 60 1 10 100 LOAD CURRENT (mA) 1000 35521 G26 VOUT1 = 1.8V REGULATOR 1; CIRCUIT OF FIGURE 2 VCC = 2.7V EFFICIENCY (%) VCC = 3.6V VCC = 4.2V UW TA = 25°C Unless Otherwise Specified. Load Regulation 2.0 1.5 1.0 0.5 0 –0.5 –1.0 –1.5 –2.0 1 VCC = 3.6V Burst Mode OPERATION CIRCUIT OF FIGURE 2 10 100 LOAD CURRENT (mA) 1000 35521 G24 Line Regulation 0.5 0.4 0.3 0.2 0.1 0 –0.1 –0.2 –0.3 –0.4 –0.5 2.5 3 3.5 4 VCC (V) 4.5 5 5.5 35521 G25 IOUT = 200mA VOUT1 = 1.8V VOUT1 = 1.8V VOUT2 = 1.575V VOUT2 = 1.575V Load Regulation 100 95 90 85 80 75 70 65 60 1 10 100 LOAD CURRENT (mA) 1000 35521 G27 VOUT2 = 1.575V REGULATOR 2; CIRCUIT OF FIGURE 2 VCC = 2.7V VCC = 3.6V VCC = 4.2V 35521fa 7 LTC3552-1 PI FU CTIO S ITERM (Pin 1): Charge Termination Program. The charge termination current threshold is programmed by connecting a 1% resistor, RTERM, to ground. The current threshold ITERM, is set by the following formula: 100 V 100 V ITERM = , R TERM = R TERM ITERM BAT (Pin 2): Charge Current Output. Provides charge current to the battery from the internal P-channel MOSFET, and regulates the final float voltage to 4.2V. An internal precision resistor divider from this pin sets the float voltage. This divider is disconnected in shutdown mode to minimize current drain from the battery. CHRG (Pin 3): Charge Status Open-Drain Output. When the battery is charging, the CHRG pin is pulled low by an internal N-channel MOSFET. When the charge cycle is completed, CHRG becomes high impedance. RUN2 (Pin 4): Regulator 2 Enable. Forcing this pin to VCC enables regulator 2, while forcing it to GND causes regulator 2 to shut down. This pin must be driven; do not float. SW2 (Pin 5): Regulator 2 Switch Node Connection to the Inductor. This pin swings from VCC to GND. RUN1 (Pin 6): Regulator 1 Enable. Forcing this pin to VCC enables regulator 1, while forcing it to GND causes regulator 1 to shut down. This pin must be driven; do not float. VOUT2 (Pin 7): Output Voltage Feedback Pin for Regulator 2. Internal resistors divide the output voltage down for comparison to the internal reference voltage. VFB2 (Pin 8): Output Feedback for Regulator 2. Receives the feedback voltage from internal resistive divider across the output. Normal voltage for this pin is 0.6V. VFB1 (Pin 9): Output Feedback for Regulator 1. Receives the feedback voltage from internal resistive divider across the output. Normal voltage for this pin is 0.6V. VOUT1 (Pin 10): Output Voltage Feedback Pin for Regulator 1. Internal resistors divide the output voltage down for comparison to the internal reference voltage. VCC (Pin 11): Buck Regulators Input Supply. Provides power to the switchers. Must be closely decoupled to GND. SW1 (Pin 12): Regulator 1 Switch Node Connection to the Inductor. This pin swings from VCC to GND. PROG (Pin 13): Charge Current Program and Charge Current Monitor. Charge current is programmed by connecting a 1% resistor, RPROG, to ground. When charging in constant-current mode, this pin servos to 1V. In all modes, the voltage on this pin can be used to measure the charge current using the following formula: V IBAT = PROG • 1000 RPROG This pin is clamped to approximately 2.4V. Driving this pin to voltages beyond the clamp voltage should be avoided. VIN (Pin 14): Charger Input Supply. Provides power to the charger. VIN can range from 4.25V to 8V. This pin should be bypassed with at least a 1µF capacitor. When VIN is within 100mV of the BAT pin voltage, the charger enters shutdown mode dropping the battery drain current to less than 2µA. PWR (Pin 15): Power Supply Status Open-Drain Output. When VIN is greater than the undervoltage lockout threshold and at least 100mV above VBAT, the PWR pin is pulled to ground; otherwise, the pin is high impedance. EN (Pin 16): Enable Input. A logic high on the EN pin will put the charger into shutdown mode where the battery drain current is reduced to less than 2µA and the supply current is reduced to less than 50µA. A logic low or floating the EN pin (allowing an internal 2MΩ pull-down resistor to pull this pin low) enables charging. Exposed Pad (GND) (Pin 17): Ground. The exposed backside of the package (Pin 17) is ground and must be soldered to the PCB for maximum heat transfer. 8 U U U 35521fa LTC3552-1 BLOCK DIAGRA W 120°C TA TDIE 1× 1× 1000× CA VIN 14 MA PWR 15 VA CHRG 3 – + R3 1V CHARGE PWR R4 – TERM LOGIC EN EN 16 RENABLE SHDN C1 0.1V R5 + REGULATOR 1 VCC BURST CLAMP VCC VOUT1 10 SLOPE COMP 0.6V R1 VFB1 9 R2 VFB + EA – ITH 0.35V EN BURST SLEEP – ICOMP + – + S Q RS LATCH R Q SWITCHING LOGIC AND BLANKING CIRCUIT 0.55V – UVDET UV + ANTI SHOOTTHRU 12 SW1 + OVDET 0.65V OV IRCMP RUN1 6 0.6V REF RUN2 4 OSC OSC VOUT2 VFB2 7 8 REGULATOR 2 (IDENTICAL TO REGULATOR 1) R1 = 240k, R2 = 120k, FOR REGULATOR 1 R1 = 195k, R2 = 120k, FOR REGULATOR 2 5 SW2 – SHUTDOWN + – + 5µA R1 – 2 BAT + R2 – REF 1.21V 1 13 17 ITERM PROG GND RPROG RTERM 5Ω VCC 11 VCC 35521fa 9 LTC3552-1 OPERATIO The LTC3552-1 is made up of two circuit blocks: a standalone constant-current/constant-voltage linear charger for a single-cell lithium-ion battery and a high efficiency dual DC/DC switching regulator. The charger can deliver up to 950mA of charge current (using a good thermal PCB layout) with a final float voltage accuracy of ±1%. An internal P-channel power MOSFET and thermal regulation circuitry are included. No blocking diode or external current sense resistor is required; furthermore, the charger is capable of operating from a USB power source. The switching regulators use a constant frequency, current mode step-down architecture. Both main (P-channel MOSFET) and synchronous (N-channel MOSFET) switches are internal. The LTC3552-1 requires no external diodes or sense resistors. LITHIUM-ION BATTERY CHARGER Normal Charge Cycle A charge cycle begins when the voltage at the VIN pin rises above the UVLO threshold level and a 1% program resistor is connected from the PROG pin to ground. The charger enters constant-current mode where the programmed charge current is supplied to the battery. When the BAT pin approaches the final float voltage (4.2V), the charger enters constant-voltage mode and the charge current begins to decrease. When the charge current drops to the programmed termination threshold (set by the external resistor RTERM), the charge cycle ends. Figure 1 shows the state diagram of a typical charge cycle. Charge Status Indicator (CHRG) The open drain charge status output has two states: pulldown and high impedance. The pull-down state indicates that the charger is in a charge cycle. Once the charge cycle has terminated or the charger is disabled, the pin becomes high impedance. Automatic Recharge Once the charge cycle terminates, the charger continuously monitors the voltage on the BAT pin using a comparator with a 2ms filter time (tRECHARGE). A charge cycle restarts when the battery voltage falls below 4.10V (which corre- 10 U sponds to approximately 80% to 90% battery capacity). This ensures that the battery is kept at, or near, a fully charged condition and eliminates the need for periodic charge cycle initiations. The CHRG output enters a pulldown state during recharge cycles. If the battery is removed from the charger, a sawtooth waveform of approximately 100mV appears at the charger output. This is caused by the repeated cycling between termination and recharge events. This cycling results in pulsing at the CHRG output; an LED connected to this pin will exhibit a pulsing pattern, indicating to the user that a battery is not present. The frequency of the sawtooth is dependent on the amount of output capacitance. Power Supply Status Indicator (PWR) The power supply status output has two states: pull-down and high impedance. The pull-down state indicates that VIN is above the UVLO threshold (3.8V) and is also 100mV above the battery voltage. If these conditions are not met, the PWR pin is high impedance indicating that the charger is unable to charge the battery. POWER ON EN DRIVEN LOW OR UVLO CONDITION ENDS SHUTDOWN MODE ICC DROPS TO 1µF) input capacitors. The discharged load input capacitors are effectively put in parallel with COUT, causing a rapid drop in VOUT. No regulator can deliver enough current to prevent this problem, if the switch connecting the load has low resistance and is driven quickly. The solution is to limit the turn-on speed of the load switch driver. A Hot Swap™ controller is designed specifically for this purpose and usually incorporates current limiting, short-circuit protection, and soft-start. Efficiency Considerations The efficiency of a switching regulator is equal to the output power divided by the input power times 100%. It is often useful to analyze individual losses to determine what is limiting the efficiency and which change would produce the most improvement. Percent efficiency can be expressed as: % Efficiency = 100% – (L1 + L2 + L3 + ...) U where L1, L2, etc. are the individual losses as a percentage of input power. Although all dissipative elements in the circuit produce losses, four main sources usually account for most of the losses in LTC3552-1 circuits: 1) VCC quiescent current, 2) switching losses, 3) I2R losses, 4) other losses. 1) The VCC current is the DC supply current given in the Electrical Characteristics which excludes MOSFET driver and control currents. VCC current results in a small (96%, Accurate USB Current Limiting (500mA/100mA), 4mm × 4mm QFN-24 Package High Efficiency: Up to 95%, IQ: 40μA, 2.25MHz Frequency, MSOP-10 and 3mm × 3mm DFN-10 Packages Buck Efficiency: 93%, Charger: Automatic Input Power Detection and Selection, Charge Current: 950mA, USB Compatible, 3mm × 5mm DFN-16 Package Charges Single-Cell Li-Ion Batteries, From USB, MS Package Thermal Regulation Prevents Overheating, C/10 Termination, C/10 Indicator, Up to 800mA Charge Current Charges Single-Cell Li-Ion Batteries Directly From USB Port, Thermal Regulation, 4mm × 4mm QFN-16 Package C/10 Charge Termination, Battery Kelvin Sensing, ±7% Charge Accuracy Charge Current Programmable Up to 1A Charges Single-Cell Li-Ion From USB Port, DFN Package Charge Current Up to 950mA, Thermal Regulation, 3mm × 3mm DFN-8 Package VIN: 3V to 28V, Automatic Switching Between DC Sources LTC4053-4.2 LTC4054/LTC4054X LTC4055 LTC4058/LTC4058X LTC4061 LTC4066 LTC4068/LTC4068X LTC4412 PowerPath and ThinSOT are registered trademarks of Linear Technology Corporation. 35521fa 20 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● U VIN RUN1 RUN2 VCC 4.7µF BAT LTC3552-1 4.7µH SW2 COUT2 10µF CER CFF2 330pF VOUT2 VFB2 SW1 VOUT1 CFF1 330pF 800mA 2.2µH 1k CHRG PWR EN + VFB1 GND ITERM PROG 1k 1.24k VOUT1 1.8V/800mA COUT1 10µF CER 4.2V 1-CELL Li-Ion BATTERY 35521 TA03 LT/LWI 0606 REV A • PRINTED IN USA www.linear.com © LINEAR TECHNOLOGY CORPORATION 2006