LTC3559/LTC3559-1 Linear USB Battery Charger with Dual Buck Regulators DESCRIPTION FEATURES Battery Charger n Standalone USB Charger n Up to 950mA Charge Current Programmable via Single Resistor n HPWR Input Selects 20% or 100% of Programmed Charge Current n NTC Input for Temperature Qualified Charging n Internal Timer Termination n Bad Battery Detection n CHRG Indicates C/10 or Timeout Buck Regulators n 400mA Output Current n 2.25MHz Constant Frequency Operation n Zero Current in Shutdown n Low Noise Pulse Skip Operation or Power Saving Burst Mode Operation n Low No-Load Quiescent Current: 35μA n Available in a Low Profile Thermally Enhanced 16-Lead 3mm × 3mm QFN Package n Battery charge current is programmed via the PROG pin and the HPWR pin, with capability up to 950mA at the BAT pin. The battery charger has an NTC input for temperature qualified charging. The CHRG pin allows battery status to be monitored continuously during the charging process. An internal timer controls charger termination. Each monolithic synchronous buck regulator provides up to 400mA of output current while operating at efficiencies greater than 90% over the entire Li-Ion/Polymer range. A MODE pin provides the flexibility to place both buck regulators in a power saving Burst Mode® operation or a low noise pulse skip mode. The LTC3559/LTC3559-1 are offered in a low profile thermally enhanced 16-lead (3mm × 3mm) QFN package. L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. APPLICATIONS n The LTC®3559/LTC3559-1 are USB battery chargers with dual high efficiency buck regulators. The parts are ideally suited to power single-cell Li-Ion/Polymer based handheld applications needing multiple supply rails. SD/Flash-Based MP3 Players Low Power Handheld Applications TYPICAL APPLICATION USB Charger Plus Dual Buck Regulators UP TO 500mA USB (4.3V TO 5.5V) OR AC ADAPTOR VCC BAT 1μF + PVIN 2.2μF NTC LTC3559 1.74k PROG 4.7μH CHRG 4.7μH 1.2V 400mA SW2 22pF EN2 GND 10μF 309k HPWR MODE 655k FB1 SUSP EN1 2.5V 400mA SW1 22pF DIGITAL CONTROL SINGLE Li-lon CELL (2.7V TO 4.2V) 324k 10μF FB2 EXPOSED PAD 649k 3559 TA01 3559fb 1 LTC3559/LTC3559-1 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) NTC PROG CHRG VCC TOP VIEW 16 15 14 13 GND 1 12 HPWR BAT 2 11 SUSP 17 MODE 3 10 FB2 FB1 4 6 7 8 EN1 PVIN SW2 9 5 SW1 VCC (Transient); t < 1ms and Duty Cycle < 1%....................... –0.3V to 7V VCC (Static) .................................................. –0.3V to 6V BAT, CHRG, SUSP ........................................ –0.3V to 6V HPWR, NTC, PROG ....... –0.3V to Max (VCC, BAT) + 0.3V PROG Pin Current ...............................................1.25mA BAT Pin Current ..........................................................1A PVIN ................................................ –0.3V to BAT + 0.3V EN1, EN2, MODE.......................................... –0.3V to 6V FB1, FB2, SW1, SW2 ............–0.3V to PVIN + 0.3V or 6V ISW1, ISW2 ......................................................600mA DC Junction Temperature (Note 2) ............................. 125°C Operating Temperature Range (Note 3).... –40°C to 85°C Storage Temperature.............................. –65°C to 125°C EN2 UD PACKAGE 16-LEAD (3mm s 3mm) PLASTIC QFN TJMAX = 125°C, θJA = 68°C/W EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3559EUD#PBF LTC3559EUD#TRPBF LCMB 16-Lead (3mm × 3mm) Plastic QFN –40°C to 85°C LTC3559EUD-1#PBF LTC3559EUD-1#TRPBF LDQD 16-Lead (3mm × 3mm) Plastic QFN –40°C to 85°C Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ ELECTRICAL CHARACTERISTICS The l denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. SYMBOL PARAMETER CONDITIONS Battery Charger. VCC = 5V, BAT = PVIN = 3.6V, RPROG = 1.74k, HPWR = 5V, SUSP = NTC = EN1 = EN2 = 0V Input Supply Voltage VCC Battery Charger Quiescent Current (Note 4) Standby Mode, Charge Terminated IVCC Suspend Mode, VSUSP = 5V BAT Regulated Output Voltage LTC3559 VFLOAT 0°C ≤ TA ≤ 85°C, LTC3559 LTC3559-1 0°C ≤ TA ≤ 85°C, LTC3559-1 Constant-Current Mode Charge Current HPWR = 5V ICHG HPWR = 0V Battery Drain Current Standby Mode, Charger Terminated IBAT Shutdown, VCC < VUVLO, BAT = VFLOAT Suspend Mode, SUSP = 5V, BAT = VFLOAT VUVLO Undervoltage Lockout Threshold BAT = 3.5V, VCC Rising Undervoltage Lockout Hysteresis BAT = 3.5V ΔVUVLO VDUVLO Differential Undervoltage Lockout Threshold BAT = 4.05V, (VCC – BAT) Falling (LTC3559) BAT = 3.95V, (VCC – BAT) Falling (LTC3559-1) MIN l l TYP 4.3 4.179 4.165 4.079 4.065 440 84 3.85 30 30 200 8.5 4.200 4.200 4.100 4.100 460 92 –3.5 –2.5 –1.5 4.0 200 50 50 MAX UNITS 5.5 400 17 4.221 4.235 4.121 4.135 500 100 –7 –4 –3 4.125 V μA μA V V V V mA mA μA μA μA V mV 70 70 mV mV 3559fb 2 LTC3559/LTC3559-1 ELECTRICAL CHARACTERISTICS The l denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. SYMBOL ΔVDUVLO VPROG hPROG ITRKL VTRKL ΔVTRKL ΔVRECHRG tRECHRG tTERM tBADBAT hC/10 tC/10 RON(CHG) TLIM PARAMETER Differential Undervoltage Lockout Hysteresis PROG Pin Servo Voltage CONDITIONS BAT = 4.05V (LTC3559) BAT = 3.95V (LTC3559-1) HPWR = 5V HPWR = 0V BAT < VTRKL MIN Ratio of IBAT to PROG Pin Current Trickle Charge Current Trickle Charge Threshold Voltage Trickle Charge Hysteresis Voltage BAT < VTRKL BAT Rising 36 2.8 Recharge Battery Threshold Voltage Threshold Voltage Relative to VFLOAT –85 Recharge Comparator Filter Time Safety Timer Termination Period Bad Battery Termination Time End-of-Charge Indication Current Ratio End-of-Charge Comparator Filter Time Battery Charger Power FET On-Resistance (Between VCC and BAT) Junction Temperature in Constant Temperature Mode BAT Falling BAT = VFLOAT BAT < VTRKL (Note 5) IBAT Falling IBAT = 190mA 3.5 0.4 0.085 CHRG Pin Output Low Voltage ICHRG = 5mA VCHRG CHRG Pin Input Current BAT = 4.5V, VCHRG = 5V ICHRG Buck Switching Regulators, BAT = PVIN = 3.8V, EN1 = EN2 = 3.8V Input Supply Voltage LTC3559 PVIN LTC3559-1 IPVIN Pulse Skip Supply Current MODE = 0 (One Buck Enabled) (Note 6) Burst Mode Supply Current MODE = 1 (One Buck Enabled) (Note 6) Shutdown Supply Current EN1 = EN2 = 0V Supply Current in UVLO PVIN = 2.0V PVIN UVLO PVIN Falling PVIN Rising Switching Frequency MODE = 0V fOSC Input Low Voltage MODE, EN1, EN2 VIL Input High Voltage MODE, EN1, EN2 VIH Peak PMOS Current Limit MODE = 0V or 3.8V ILIMSW MAX –100 –130 mV 4.5 0.6 0.11 ms Hour Hour mA/mA ms 1.7 4 0.5 0.1 2.2 500 56 3.0 75 33.4 l 0.7 76.5 1.6 34.9 1.6 1.7 50 –1 l l l 1.2 1.9 °C 78 36.4 2.7 1 %VCC %VCC %VCC %VCC %VCC mV μA 0.4 V V 4 6.3 100 0 250 1 MΩ mV μA 3 3 1.91 220 35 0 4 2.45 2.55 2.25 1.2 550 800 l UNITS mV mV V V V mA/mA mA V mV mΩ 105 NTC VCOLD Cold Temperature Fault Threshold Voltage Rising NTC Voltage Hysteresis VHOT Hot Temperature Fault Threshold Voltage Falling NTC Voltage Hysteresis VDIS NTC Disable Threshold Voltage Falling NTC Voltage Hysteresis NTC Leakage Current VNTC = VCC = 5V INTC Logic (HPWR, SUSP, CHRG) Input Low Voltage HPWR, SUSP Pins VIL Input High Voltage HPWR, SUSP Pins VIH Logic Pin Pull-Down Resistance HPWR, SUSP Pins RDN TYP 130 130 1.000 0.200 0.100 800 46 2.9 100 4.2 4.1 400 50 2 8 2.59 0.4 1050 V V μA μA μA μA V V MHz V V mA 3559fb 3 LTC3559/LTC3559-1 ELECTRICAL CHARACTERISTICS The l denotes specifications that apply over the full operating temperature range, otherwise specifications are at TA = 25°C. SYMBOL VFB IFB DMAX RPMOS PARAMETER Feedback Voltage FB Input Current Maximum Duty Cycle RDS(ON) of PMOS CONDITIONS RNMOS RDS(ON) of NMOS ISW = –150mA RSW(PD) SW Pull-Down in Shutdown l FB1, FB2 = 0.82V FB1, FB2 = 0V ISW = 150mA 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: TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formula: TJ = TA + (PD • θJA°C/W) Note 3: The LTC3559/LTC3559-1 are guaranteed to meet specifications from 0°C to 85°C. Specifications over the –40°C to 85°C operating MIN 780 –0.05 100 TYP 800 MAX 820 0.05 UNITS mV μA % 0.65 Ω 0.75 Ω 13 kΩ temperature range are assured by design, characterization and correlation with statistical process controls. Note 4: VCC supply current does not include current through the PROG pin or any current delivered to the BAT pin. Total input current is equal to this specification plus 1.00125 • IBAT where IBAT is the charge current. Note 5: IC/10 is expressed as a fraction of measured full charge current with indicated PROG resistor. Note 6: FB high, regulator not switching. TYPICAL PERFORMANCE CHARACTERISTICS Suspend State Supply and BAT Currents vs Temperature 10 4.250 9 4.205 VCC = 5V 4.200 4.225 IVCC 8 Battery Regulation (Float) Voltage vs Battery Charge Current, Constant-Voltage Charging Battery Regulation (Float) Voltage vs Temperature 4.195 LTC3559 4.200 4.190 5 4 VCC = 5V BAT = 4.2V SUSP = 5V EN1 = EN2 = 0V 4.185 4.175 VBAT (V) 6 VFLOAT (V) CURRENT (μA) 7 4.180 4.150 4.175 4.125 4.170 3 2 IBAT 1 4.075 0 –55 4.050 –55 –35 –35 25 5 –15 45 TEMPERATURE (°C) LTC3559-1 4.100 65 85 3559 G01 4.165 4.160 4.155 45 25 5 TEMPERATURE (°C) –15 65 85 3559 G02 4.150 VCC = 5V HPWR = 5V RPROG = 845Ω EN1 = EN2 = 0V 0 100 200 300 400 500 600 700 800 900 1000 IBAT (mA) 3559 G03 3559fb 4 LTC3559/LTC3559-1 TYPICAL PERFORMANCE CHARACTERISTICS Battery Charge Current vs Supply Voltage 500 500 VCC = 5V 495 HPWR = 5V 490 RPROG = 1.74k 485 EN1 = EN2 = 0V 470 465 460 450 400 400 350 350 300 300 IBAT (mA) IBAT (mA) 475 500 HPWR = 5V VCC = 5V RPROG = 1.74k 450 480 IBAT (mA) Battery Charge Current vs Ambient Temperature in Thermal Regulation Battery Charge Current vs Battery Voltage (LTC3559) 250 200 HPWR = 0V 100 450 445 50 440 0 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5.0 5.1 5.2 5.3 5.4 5.5 VCC (V) 50 2.5 2 3.5 3 VBAT (V) 4 3.0 BAT = 3.5V FALLING 3.7 3.6 3.5 –55 –35 25 5 45 –15 TEMPERATURE (°C) 65 0.8 BAT = 3.6 1.5 0.4 0.5 0.2 25 5 45 –15 TEMPERATURE (°C) Recharge Threshold vs Temperature 0 85 0 700 VCC = 5V 650 SUSP/HPWR Pin Rising Thresholds vs Temperature 1.2 VCC = 4V IBAT = 200mA EN1 = EN2 = 0V 1.0 91 THRESHOLD (V) RON (mΩ) 95 550 500 450 87 83 79 –35 25 5 –15 45 TEMPERATURE (°C) 65 85 0.8 0.7 0.6 350 0.5 –35 –15 5 25 45 65 85 TEMPERATURE (°C) 3559 G10 0.9 400 300 –55 VCC = 5V 1.1 600 103 99 50 100 150 200 250 300 350 400 450 500 IBAT (mA) 3559 G09 Battery Charger FET On-Resistance vs Temperature 107 VRECHARGE (mV) 65 3559 G08 3559 G07 75 –55 0.6 1.0 0 –55 –35 85 VCC = 5V HPWR = 5V RPROG = 1.74k EN1 = EN2 = 0V 1.0 BAT = 4.2 (LTC3559) VPROG (V) IBAT (μA) VCC (V) 1.2 2.0 3.8 111 PROG Voltage vs Battery Charge Current EN1 = EN2 = 0V 2.5 RISING 3.9 5 25 45 65 85 105 125 TEMPERATURE (°C) 3559 G06 Battery Drain Current in Undervoltage Lockout vs Temperature 4.0 115 0 –55 –35 –15 4.5 3559 G05 Battery Charger Undervoltage Lockout Threshold vs Temperature 4.1 VCC = 5V HPWR = 5V RPROG = 1.74k EN1 = EN2 = 0 100 3559 G04 4.2 200 150 150 455 250 3559 G11 0.4 –55 –35 45 25 5 TEMPERATURE (°C) –15 65 85 3559 G12 3559fb 5 LTC3559/LTC3559-1 TYPICAL PERFORMANCE CHARACTERISTICS CHRG Pin Output Low Voltage vs Temperature 120 CHRG Pin I-V Curve 70 VCC = 5V ICHRG = 5mA VCC = 5V BAT = 3.8V 60 1.5 50 ICHRG (mA) 100 VCHRG (mV) Timer Accuracy vs Supply Voltage 2.0 PERCENT ERROR (%) 140 80 60 40 30 40 20 20 10 0 –55 –35 25 5 45 –15 TEMPERATURE (°C) 65 1 2 4 3 CHRG (V) BAT (V) 4 3 2 CHRG (V) 1 0 –1 65 4.9 VCC (V) 5.3 5.1 VCC = 5V RPROG = 0.845k HPWR = 5V VFB = 0.82V 45 40 PVIN = 4.2V 35 PVIN = 2.7V 30 25 0 85 1 2 3 4 TIME (HOUR) 5 20 –55 –35 –15 6 3559 G17 5 25 45 65 85 105 125 TEMPERATURE (°C) 3559 G18 3559 G16 Buck Regulator Input Current vs Temperature, Pulse Skip Mode (LTC3559) Buck Regulator PVIN Undervoltage Thresholds vs Temperature Frequency vs Temperature 2.5 2.85 VFB = 0.82V 2.4 2.75 300 2.65 PVIN = 4.2V 250 PVIN = 2.7V 2.2 RISING 2.55 FALLING 2.45 200 2.1 2.0 1.9 1.8 1.7 2.35 150 PVIN = 3.8V 2.3 fOSC (MHz) 350 PVIN (V) INPUT CURRENT (μA) 400 5.5 Buck Regulator Input Current vs Temperature, Burst Mode Operation INPUT CURRENT (μA) PERCENT ERROR (%) 5 4.7 4.5 3559 G15 50 1000 800 600 400 200 0 5.0 4.5 4.0 3.5 3.0 5.0 4.0 3.0 2.0 1.0 0 IBAT (mA) VCC = 5V –15 5 25 45 TEMPERATURE (°C) 4.3 Complete Charge Cycle 2400mAh Battery (LTC3559) 6 –35 6 5 3559 G14 Timer Accuracy vs Temperature –2 –55 0 –1.0 0 3559 G13 7 0.5 –0.5 0 85 1.0 1.6 100 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 3559 G19 2.25 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 3559 G20 1.5 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 3559 G21 3559fb 6 LTC3559/LTC3559-1 TYPICAL PERFORMANCE CHARACTERISTICS Buck Regulator PMOS RDS(0N) vs Temperature (LTC3559) Buck Regulator Enable Thresholds vs Temperature PVIN = 3.8V 1100 1300 1200 1200 1100 1100 1000 1000 RDS(ON) (mΩ) VEN (mV) 1000 1300 900 800 RISING 700 900 PVIN = 2.7V 800 PVIN = 4.2V 700 FALLING 600 500 500 400 –55 –35 –15 400 –55 –35 –15 100 400 –55 –35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 3559 G24 Buck Regulator Load Regulation 2.60 Buck Regulator Line Regulation 2.60 PVIN = 3.8V VOUT = 2.5V 2.58 80 2.58 2.56 60 VOUT (V) PULSE SKIP MODE 50 40 2.54 2.52 0 0.1 1 10 ILOAD (mA) 100 2.48 2.46 VOUT = 2.5V PVIN = 4.2V 10 2.46 2.44 1 1000 10 100 1000 2.44 2.7 PVIN = 3.8V 1.24 VOUT = 1.2V Burst Mode OPERATION 80 1.24 1.21 Burst Mode OPERATION 1.20 PULSE SKIP MODE 1.19 1.21 1.20 1.19 30 1.18 1.18 20 1.17 1.17 1.16 1.16 VOUT = 1.2V PVIN = 2.7V PVIN = 4.2V 0 0.1 1 10 ILOAD (mA) 100 1000 1.15 1 10 100 1000 ILOAD (mA) 3559 G28 VOUT = 1.2V ILOAD = 200mA 1.22 VOUT (V) 1.22 60 VOUT (V) 70 4.2 1.23 1.23 10 3.9 Buck Regulator Line Regulation 1.25 1.25 40 3.6 PVIN (V) 3559 G27 Buck Regulator Load Regulation 100 PULSE SKIP MODE 3.3 3559 G26 Buck Regulator Efficiency vs ILOAD (LTC3559) 50 3.0 ILOAD (mA) 3559 G25 90 2.52 2.50 PULSE SKIP MODE 2.48 20 2.54 Burst Mode OPERATION 2.50 30 VOUT = 2.5V ILOAD = 200mA 2.56 VOUT (V) 70 5 25 45 65 85 105 125 TEMPERATURE (°C) 3559 G23 Burst Mode OPERATION 90 PVIN = 4.2V 700 600 Buck Regulator Efficiency vs ILOAD (LTC3559) EFFICIENCY (%) 800 500 5 25 45 65 85 105 125 TEMPERATURE (°C) PVIN = 2.7V 900 600 3559 G22 EFFICIENCY (%) RDS(ON) (mΩ) 1200 Buck Regulator NMOS RDS(0N) vs Temperature (LTC3559) 3559 G29 1.15 2.7 3.0 3.6 3.3 PVIN (V) 3.9 4.2 3559 G30 3559fb 7 LTC3559/LTC3559-1 TYPICAL PERFORMANCE CHARACTERISTICS Buck Regulator Pulse Skip Mode Operation Buck Regulator Start-Up Transient VOUT 500mV/DIV VOUT 20mV/DIV (AC) INDUCTOR CURRENT IL = 200mA/DIV SW 2V/DIV INDUCTOR CURRENT IL = 50mA/DIV EN 2V/DIV 3559 G33 PVIN = 3.8V 50μs/DIV PULSE SKIP MODE LOAD = 6Ω PVIN = 3.8V LOAD = 10mA Buck Regulator Burst Mode Operation 200ns/DIV 3559 G34 Buck Regulator Transient Response, Pulse Skip Mode INDUCTOR CURRENT IL = 200mA/DIV VOUT 20mV/DIV (AC) SW 2V/DIV VOUT 50mV/DIV (AC) INDUCTOR CURRENT IL = 60mA/DIV LOAD STEP 5mA TO 290mA PVIN = 3.8V LOAD = 60mA 2μs/DIV 3559 G35 PVIN = 3.8V 50μs/DIV 3559 G36 Buck Regulator Transient Response, Burst Mode Operation INDUCTOR CURRENT IL = 200mA/DIV VOUT 50mV/DIV (AC) LOAD STEP 5mA TO 290mA PVIN = 3.8V 50μs/DIV 3559 G37 3559fb 8 LTC3559/LTC3559-1 PIN FUNCTIONS GND (Pin 1): Ground, Connect to Exposed Pad (Pin 17). BAT (Pin 2): Charge Current Output. Provides charge current to the battery and regulates final float voltage to 4.2V (LTC3559) or 4.1V (LTC3559-1). MODE (Pin 3): MODE Pin for Buck Regulators. When held high, both regulators are in Burst Mode operation. When held low both regulators operate in pulse skip mode. This pin is a high impedance input; do not float. FB1 (Pin 4): Buck 1 Feedback Voltage Pin. Receives feedback by a resistor divider connected across the output. EN1 (Pin 5): Enable Input Pin for Buck 1. This pin is a high impedance input; do not float. Active high. SW1 (Pin 6): Buck 1 Switching Node. External inductor connects to this node. PVIN (Pin 7): Input Supply Pin for Buck Regulators. Connect to BAT. A 2.2μF decoupling capacitor to GND is recommended. SW2 (Pin 8): Buck 2 Switching Node. External inductor connects to this node. EN2 (Pin 9): Enable Input Pin for Buck 2. This pin is a high impedance input; do not float. Active high. FB2 (Pin 10): Buck 2 Feedback Voltage Pin. Receives feedback by a resistor divider connected across the output. SUSP (Pin 11): Suspend Battery Charging Operation. A voltage greater than 1.2V on this pin puts the battery charger into suspend mode, disables the charger and resets the termination timer. A weak pull-down current is internally applied to this pin to ensure it is low at power up when the input is not being driven externally. HPWR (Pin 12): High Current Battery Charging Enabled. A voltage greater than 1.2V at this pin programs the BAT pin current at 100% of the maximum programmed charge current. A voltage less than 0.4V sets the BAT pin current to 20% of the maximum programmed charge current. When used with a 1.74k PROG resistor, this pin can toggle between low power and high power modes per USB specification. A weak pull-down current is internally applied to this pin to ensure it is low at power up when the input is not being driven externally. NTC (Pin 13): Input to the NTC Thermistor Monitoring Circuit. The NTC pin connects to a negative temperature coefficient thermistor which is typically co-packaged with the battery pack to determine if the battery is too hot or too cold to charge. If the battery temperature is out of range, charging is paused until the battery temperature re-enters the valid range. A low drift bias resistor is required from VCC to NTC and a thermistor is required from NTC to ground. To disable the NTC function, the NTC pin should be grounded. PROG (Pin 14): Charge Current Program and Charge Current Monitor Pin. Charge current is programmed by connecting a resistor from PROG to ground. When charging in constant-current mode, the PROG pin servos to 1V if the HPWR pin is pulled high, or 200mV if the HPWR pin is pulled low. The voltage on this pin always represents the battery current through the following formula: IBAT = PROG • 800 RPROG CHRG (Pin 15): Open-Drain Charge Status Output. The CHRG pin indicates the status of the battery charger. Four possible states are represented by CHRG: charging, not charging (i.e., the charge current is less than 1/10th of the full-scale charge current), unresponsive battery (i.e., the battery voltage remains below 2.9V after 1/2 hour of charging) and battery temperature out of range. CHRG requires a pull-up resistor and/or LED to provide indication. VCC (Pin 16): Battery Charger Input. A 1μF decoupling capacitor to GND is recommended. Exposed Pad (Pin 17): Ground. The Exposed Pad must be soldered to PCB ground to provide electrical contact and rated thermal performance. 3559fb 9 LTC3559/LTC3559-1 BLOCK DIAGRAM 16 VCC BAT BODY MAXER VIN 1x 800x BAT – 12 11 + 15 CHRG HPWR CA LOGIC TA SUSP TDIE PROG NTCA 13 BATTERY CHARGER PVIN 5 9 4 14 NTC NTC REF 3 2 7 MODE EN1 UNDERVOLTAGE LOCKOUT EN2 EN VFB FB1 OT DIE TEMPERATURE TDIE 0.8V – + MODE CLK VC Gm CONTROL LOGIC SW1 6 BUCK REGULATOR 1 10 FB2 BANDGAP VREF OSCILLATOR 2.25MHz CLK EN VFB 0.8V – + MODE CLK VC Gm CONTROL LOGIC SW2 8 BUCK REGULATOR 2 GND EXPOSED PAD 1 17 3559 BD 3559fb 10 LTC3559/LTC3559-1 OPERATION The LTC3559/LTC3559-1 are linear battery chargers with dual monolithic synchronous buck regulators. The buck regulators are internally compensated and need no external compensation components. The battery charger employs a constant- current/constantvoltage charging algorithm and is capable of charging a single Li-Ion battery at charging currents up to 950mA. The user can program the maximum charging current available at the BAT pin via a single PROG resistor. The actual BAT pin current is set by the status of the HPWR pin. For proper operation, the BAT and PVIN pins must be tied together. If a buck regulator is also enabled during the battery charging operation, the net current charging the battery may be lower than the actual programmed value. Refer to Figure 1 for an explanation. 500mA USB (5V) BAT VCC PVIN PROG RPROG 1.62k 300mA + SINGLE Li-lon CELL 3.6V 200mA + LTC3559/ LTC3559-1 2.2μF SUSP HIGH HIGH HIGH LOW (PULSE SKIP MODE) HPWR SW1 VOUT1 EN1 SW2 VOUT2 EN2 MODE 3559 F01 Figure 1. Current Being Delivered at the BAT Pin Is 500mA. Both Buck Regulators Are Enabled. The Sum of the Average Input Currents Drawn by Both Buck Regulators Is 200mA. This Makes the Effective Battery Charging Current Only 300mA. If the HPWR Pin Were Tied LO, the BAT Pin Current Would Be 100mA. With the Buck Regulator Conditions Unchanged, This Would Cause the Battery to Discharge at 100mA APPLICATIONS INFORMATION Battery Charger Introduction Input Current vs Charge Current The LTC3559/LTC3559-1 have a linear battery charger designed to charge single-cell lithium-ion batteries. The charger uses a constant-current/constant-voltage charge algorithm with a charge current programmable up to 950mA. Additional features include automatic recharge, an internal termination timer, low-battery trickle charge conditioning, bad-battery detection, and a thermistor sensor input for out of temperature charge pausing. The battery charger regulates the total current delivered to the BAT pin; this is the charge current. To calculate the total input current (i.e., the total current drawn from the VCC pin), it is necessary to sum the battery charge current, charger quiescent current and PROG pin current. Furthermore, the battery charger is capable of operating from a USB power source. In this application, charge current can be programmed to a maximum of 100mA or 500mA per USB power specifications. Undervoltage Lockout (UVLO) The undervoltage lockout circuit monitors the input voltage (VCC) and disables the battery charger until VCC rises above VUVLO (typically 4V). 200mV of hysteresis prevents oscillations around the trip point. In addition, a differential undervoltage lockout circuit disables the battery charger when VCC falls to within VDUVLO (typically 50mV) of the BAT voltage. 3559fb 11 LTC3559/LTC3559-1 APPLICATIONS INFORMATION Suspend Mode The battery charger can also be disabled by pulling the SUSP pin above 1.2V. In suspend mode, the battery drain current is reduced to 1.5μA and the input current is reduced to 8.5μA. Charge Cycle Overview When a battery charge cycle begins, the battery charger first determines if the battery is deeply discharged. If the battery voltage is below VTRKL, typically 2.9V, an automatic trickle charge feature sets the battery charge current to 10% of the full-scale value. Once the battery voltage is above 2.9V, the battery charger begins charging in constant-current mode. When the battery voltage approaches the 4.2V (LTC3559) or 4.1V (LTC3559-1) required to maintain a full charge, otherwise known as the float voltage, the charge current begins to decrease as the battery charger switches into constantvoltage mode. Trickle Charge and Defective Battery Detection Any time the battery voltage is below VTRKL, the charger goes into trickle charge mode and reduces the charge current to 10% of the full-scale current. If the battery voltage remains below VTRKL for more than 1/2 hour, the charger latches the bad-battery state, automatically terminates, and indicates via the CHRG pin that the battery was unresponsive. If for any reason the battery voltage rises above VTRKL, the charger will resume charging. Since the charger has latched the bad-battery state, if the battery voltage then falls below VTRKL again but without rising past VRECHRG first, the charger will immediately assume that the battery is defective. To reset the charger (i.e., when the dead battery is replaced with a new battery), simply remove the input voltage and reapply it or put the part in and out of suspend mode. Charge Termination The battery charger has a built-in safety timer that sets the total charge time for 4 hours. Once the battery voltage rises above VRECHRG and the charger enters constant-voltage mode, the 4-hour timer is started. After the safety timer expires, charging of the battery will discontinue and no more current will be delivered. Automatic Recharge After the battery charger terminates, it will remain off, drawing only microamperes of current from the battery. If the portable product remains in this state long enough, the battery will eventually self discharge. To ensure that the battery is always topped off, a charge cycle will automatically begin when the battery voltage falls below VRECHRG. In the event that the safety timer is running when the battery voltage falls below VRECHRG, it will reset back to zero. To prevent brief excursions below VRECHRG from resetting the safety timer, the battery voltage must be below VRECHRG for more than 1.7ms. The charge cycle and safety timer will also restart if the VCC UVLO or DUVLO cycles low and then high (e.g., VCC is removed and then replaced) or the charger enters and then exits suspend mode. Programming Charge Current The PROG pin serves both as a charge current program pin, and as a charge current monitor pin. By design, the PROG pin current is 1/800th of the battery charge current. Therefore, connecting a resistor from PROG to ground programs the charge current while measuring the PROG pin voltage allows the user to calculate the charge current. Full-scale charge current is defined as 100% of the constant-current mode charge current programmed by the PROG resistor. In constant-current mode, the PROG pin servos to 1V if HPWR is high, which corresponds to charging at the full-scale charge current, or 200mV if HPWR is low, which corresponds to charging at 20% of the fullscale charge current. Thus, the full-scale charge current and desired program resistor for a given full-scale charge current are calculated using the following equations: ICHG = 800 V RPROG RPROG = 800 V ICHG 3559fb 12 LTC3559/LTC3559-1 APPLICATIONS INFORMATION In any mode, the actual battery current can be determined by monitoring the PROG pin voltage and using the following equation: IBAT = PROG • 800 RPROG Thermal Regulation To prevent thermal damage to the IC or surrounding components, an internal thermal feedback loop will automatically decrease the programmed charge current if the die temperature rises to approximately 115°C. Thermal regulation protects the battery charger from excessive temperature due to high power operation or high ambient thermal conditions and allows the user to push the limits of the power handling capability with a given circuit board design without risk of damaging the LTC3559/LTC3559-1 or external components. The benefit of the LTC3559/ LTC3559-1 battery charger thermal regulation loop is that charge current can be set according to actual conditions rather than worst-case conditions with the assurance that the battery charger will automatically reduce the current in worst-case conditions. Charge Status Indication The CHRG pin indicates the status of the battery charger. Four possible states are represented by CHRG: charging, not charging, unresponsive battery and battery temperature out of range. The signal at the CHRG pin can be easily recognized as one of the above four states by either a human or a microprocessor. The CHRG pin, which is an open-drain output, can drive an indicator LED through a current limiting resistor for human interfacing, or simply a pull-up resistor for microprocessor interfacing. To make the CHRG pin easily recognized by both humans and microprocessors, the pin is either low for charging, high for not charging, or it is switched at high frequency (35kHz) to indicate the two possible faults: unresponsive battery and battery temperature out of range. When charging begins, CHRG is pulled low and remains low for the duration of a normal charge cycle. When the charge current has dropped to below 10% of the full-scale current, the CHRG pin is released (high impedance). If a fault occurs after the CHRG pin is released, the pin remains high impedance. However, if a fault occurs before the CHRG pin is released, the pin is switched at 35kHz. While switching, its duty cycle is modulated between a high and low value at a very low frequency. The low and high duty cycles are disparate enough to make an LED appear to be on or off thus giving the appearance of “blinking”. Each of the two faults has its own unique “blink” rate for human recognition as well as two unique duty cycles for microprocessor recognition. Table 1 illustrates the four possible states of the CHRG pin when the battery charger is active. Table 1. CHRG Output Pin FREQUENCY MODULATION (BLINK) FREQUENCY DUTY CYCLE Charging 0Hz 0 Hz (Lo-Z) 100% IBAT < C/10 0Hz 0 Hz (Hi-Z) 0% NTC Fault 35kHz 1.5Hz at 50% 6.25% to 93.75% Bad Battery 35kHz 6.1Hz at 50% 12.5% to 87.5% STATUS An NTC fault is represented by a 35kHz pulse train whose duty cycle varies between 6.25% and 93.75% at a 1.5Hz rate. A human will easily recognize the 1.5Hz rate as a “slow” blinking which indicates the out of range battery temperature while a microprocessor will be able to decode either the 6.25% or 93.75% duty cycles as an NTC fault. If a battery is found to be unresponsive to charging (i.e., its voltage remains below VTRKL for over 1/2 hour), the CHRG pin gives the battery fault indication. For this fault, a human would easily recognize the frantic 6.1Hz “fast” blinking of the LED while a microprocessor would be able to decode either the 12.5% or 87.5% duty cycles as a bad battery fault. Although very improbable, it is possible that a duty cycle reading could be taken at the bright-dim transition (low duty cycle to high duty cycle). When this happens the duty cycle reading will be precisely 50%. If the duty cycle reading is 50%, system software should disqualify it and take a new duty cycle reading. 3559fb 13 LTC3559/LTC3559-1 APPLICATIONS INFORMATION NTC Thermistor The battery temperature is measured by placing a negative temperature coefficient (NTC) thermistor close to the battery pack. The NTC circuitry is shown in Figure 3. To use this feature, connect the NTC thermistor, RNTC, between the NTC pin and ground, and a bias resistor, RNOM, from VCC to NTC. RNOM should be a 1% resistor with a value equal to the value of the chosen NTC thermistor at 25°C (R25). A 100k thermistor is recommended since thermistor current is not measured by the battery charger and its current will have to be considered for compliance with USB specifications. The battery charger will pause charging when the resistance of the NTC thermistor drops to 0.54 times the value of R25 or approximately 54k (for a Vishay “Curve 1” thermistor, this corresponds to approximately 40°C). If the battery charger is in constant-voltage mode, the safety timer will pause until the thermistor indicates a return to a valid temperature. As the temperature drops, the resistance of the NTC thermistor rises. The battery charger is also designed to pause charging when the value of the NTC thermistor increases to 3.25 times the value of R25. For a Vishay “Curve 1” thermistor, this resistance, 325k, corresponds to approximately 0°C. The hot and cold comparators each have approximately 3°C of hysteresis to prevent oscillation about the trip point. Grounding the NTC pin disables all NTC functionality. DUVLO, UVLO AND SUSPEND DISABLE MODE NO POWER ON IF SUSP < 0.4V AND VCC > 4V AND VCC > BAT + 130mV CHRG HIGH IMPEDANCE YES FAULT NTC FAULT STANDBY MODE BATTERY CHARGING SUSPENDED CHRG PULSES NO CHARGE CURRENT CHRG HIGH IMPEDANCE NO FAULT BAT b 2.9V TRICKLE CHARGE MODE 1/10 FULL CHARGE CURRENT CHRG STRONG PULL-DOWN 30 MINUTE TIMER BEGINS 2.9V < BAT < VRECHRG BAT > 2.9V CONSTANT CURRENT MODE FULL CHARGE CURRENT CHRG STRONG PULL-DOWN 4-HOUR TIMEOUT 30 MINUTE TIMEOUT DEFECTIVE BATTERY NO CHARGE CURRENT CHRG PULSES CONSTANT VOLTAGE MODE 4-HOUR TERMINATION TIMER BEGINS BAT DROPS BELOW VRECHRG 4-HOUR TERMINATION TIMER RESETS 3559 F02 Figure 2. State Diagram of the Battery Charger Operation 3559fb 14 LTC3559/LTC3559-1 APPLICATIONS INFORMATION Alternate NTC Thermistors and Biasing In the explanation below, the following notation is used. The battery charger provides temperature qualified charging if a grounded thermistor and a bias resistor are connected to the NTC pin. By using a bias resistor whose value is equal to the room temperature resistance of the thermistor (R25) the upper and lower temperatures are pre-programmed to approximately 40°C and 0°C, respectively (assuming a Vishay “Curve 1” thermistor). R25 = Value of the thermistor at 25°C The upper and lower temperature thresholds can be adjusted by either a modification of the bias resistor value or by adding a second adjustment resistor to the circuit. If only the bias resistor is adjusted, then either the upper or the lower threshold can be modified but not both. The other trip point will be determined by the characteristics of the thermistor. Using the bias resistor in addition to an adjustment resistor, both the upper and the lower temperature trip points can be independently programmed with the constraint that the difference between the upper and lower temperature thresholds cannot decrease. Examples of each technique are given below. NTC thermistors have temperature characteristics which are indicated on resistance-temperature conversion tables. The Vishay-Dale thermistor NTHS0603N011-N1003F, used in the following examples, has a nominal value of 100k and follows the Vishay “Curve 1” resistance-temperature characteristic. 16 VCC 13 RNTC|HOT = Value of the thermistor at the hot trip point rCOLD = Ratio of RNTC|COLD to R25 rHOT = Ratio of RNTC|HOT to R25 RNOM = Primary thermistor bias resistor (see Figure 3) R1 = Optional temperature range adjustment resistor (see Figure 4) The trip points for the battery charger’s temperature qualification are internally programmed at 0.349 • VCC for the hot threshold and 0.765 • VCC for the cold threshold. Therefore, the hot trip point is set when: RNTCHOT | RNOM + RNTCHOT | RNTC|COLD RNOM + RNTC|COLD + NTC 16 – • VCC = 0.349 • VCC and the cold trip point is set when: NTC BLOCK 0.765 • VCC (NTC RISING) RNOM 100k RNTC|COLD = Value of thermistor at the cold trip point • VCC = 0.765 • VCC VCC 0.765 • VCC (NTC RISING) RNOM 105k TOO_COLD 13 – + NTC TOO_COLD R1 12.7k RNTC 100k – 0.349 • VCC (NTC FALLING) + – RNTC 100k TOO_HOT 0.349 • VCC (NTC FALLING) + + + NTC_ENABLE 0.017 • VCC (NTC FALLING) TOO_HOT – 0.017 • VCC (NTC FALLING) 3559 F03 Figure 3. Typical NTC Thermistor Circuit NTC_ENABLE – 3559 F04 Figure 4. NTC Thermistor Circuit with Additional Bias Resistor 3559fb 15 LTC3559/LTC3559-1 APPLICATIONS INFORMATION Solving these equations for RNTC|COLD and RNTC|HOT results in the following: RNTC|HOT = 0.536 • RNOM and RNTC|COLD = 3.25 • RNOM By setting RNOM equal to R25, the above equations result in rHOT = 0.536 and rCOLD = 3.25. Referencing these ratios to the Vishay Resistance-Temperature Curve 1 chart gives a hot trip point of about 40°C and a cold trip point of about 0°C. The difference between the hot and cold trip points is approximately 40°C. By using a bias resistor, RNOM, different in value from R25, the hot and cold trip points can be moved in either direction. The temperature span will change somewhat due to the nonlinear behavior of the thermistor. The following equations can be used to easily calculate a new value for the bias resistor: RNOM = rHOT • R25 0.536 RNOM = rCOLD • R25 3.25 where rHOT and rCOLD are the resistance ratios at the desired hot and cold trip points. Note that these equations are linked. Therefore, only one of the two trip points can be chosen, the other is determined by the default ratios designed in the IC. Consider an example where a 60°C hot trip point is desired. From the Vishay Curve 1 R-T characteristics, rHOT is 0.2488 at 60°C. Using the above equation, RNOM should be set to 46.4k. With this value of RNOM, the cold trip point is about 16°C. Notice that the span is now 44°C rather than the previous 40°C. The upper and lower temperature trip points can be independently programmed by using an additional bias resistor as shown in Figure 4. The following formulas can be used to compute the values of RNOM and R1: RNOM = RNOM = 3.266 – 0.4368 • 100k = 104.2k 2.714 the nearest 1% value is 105k. R1 = 0.536 • 105k – 0.4368 • 100k = 12.6k the nearest 1% value is 12.7k. The final solution is shown in Figure 4 and results in an upper trip point of 45°C and a lower trip point of 0°C. USB and Wall Adapter Power Although the battery charger is designed to draw power from a USB port to charge Li-Ion batteries, a wall adapter can also be used. Figure 5 shows an example of how to combine wall adapter and USB power inputs. A P-channel MOSFET, MP1, is used to prevent back conduction into the USB port when a wall adapter is present and Schottky diode, D1, is used to prevent USB power loss through the 1k pull-down resistor. Typically, a wall adapter can supply significantly more current than the 500mA-limited USB port. Therefore, an N-channel MOSFET, MN1, and an extra program resistor are used to increase the maximum charge current to 950mA when the wall adapter is present. 5V WALL ADAPTER 950mA ICHG USB POWER 500mA ICHG IBAT D1 BAT BATTERY CHARGER VCC MP1 PROG MN1 1.65k + Li-Ion BATTERY 1.74k 1k 3559 F05 Figure 5. Combining Wall Adapter and USB Power rCOLD – rHOT • R25 2.714 R1 = 0.536 • RNOM – rHOT • R25 16 For example, to set the trip points to 0°C and 45°C with a Vishay Curve 1 thermistor choose: 3559fb LTC3559/LTC3559-1 APPLICATIONS INFORMATION Power Dissipation The conditions that cause the LTC3559/LTC3559-1 to reduce charge current through thermal feedback can be approximated by considering the power dissipated in the IC. For high charge currents, the LTC3559/LTC3559-1 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 charge current. It is not necessary to perform any worst-case power dissipation scenarios because the LTC3559/LTC3559-1 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 – PDθ JA TA = 105°C – ( VCC – VBAT ) • IBAT • θ JA Example: Consider an LTC3559/LTC3559-1 operating from a USB port providing 500mA to a 3.5V Li-Ion battery. The ambient temperature above which the LTC3559/ LTC3559-1 will begin to reduce the 500mA charge current is approximately: TA = 105°C – ( 5V – 3.5V ) • ( 500mA ) • 68°C / W TA = 105°C – 0.75W • 68°C / W = 105°C – 51° TA = 54°C The LTC3559/LTC3559-1 can be used above 70°C, but the charge current will be reduced from 500mA. The approximate current at a given ambient temperature can be calculated: IBAT = 105°C – TA ( VCC – VBAT ) • θJA Using the previous example with an ambient temperature of 88°C, the charge current will be reduced to approximately: IBAT = 105°C – 88°C 17°C = (5V – 3.5V ) • 68°C / W 102°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 LTC3559/LTC3559-1 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. Battery Charger Stability Considerations The LTC3559/LTC3559-1 battery charger contains two control loops: the constant-voltage and constant-current loops. The constant-voltage loop is stable without any compensation when a battery is connected with low impedance leads. Excessive lead length, however, may add enough series inductance to require a bypass capacitor of at least 1.5μF from BAT to GND. Furthermore, a 4.7μF capacitor with a 0.2Ω to 1Ω series resistor from BAT to GND is required to keep ripple voltage low when the battery is disconnected. High value capacitors with very low ESR (especially ceramic) reduce the constant-voltage loop phase margin, possibly resulting in instability. Ceramic capacitors up to 22μF may be used in parallel with a battery, but larger ceramics should be decoupled with 0.2Ω to 1Ω of series resistance. In constant-current mode, the PROG pin is in the feedback loop, not the battery. Because of the additional pole created by the PROG pin capacitance, capacitance on this pin must be kept to a minimum. With no additional capacitance on the PROG pin, the charger is stable with program resistor values as high as 25K. However, additional capacitance on this node reduces the maximum allowed program resistor. The pole frequency at the PROG pin should be kept above 100kHz. Therefore, if the PROG pin is loaded with a capacitance, CPROG, the following equation should be used to calculate the maximum resistance value for RPROG: RPROG ≤ 1 5 2π • 10 • CPROG IBAT = 167mA 3559fb 17 LTC3559/LTC3559-1 APPLICATIONS INFORMATION 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 6. A 10k resistor has been added between the PROG pin and the filter capacitor to ensure stability. LTC3559/ LTC3559-1 10k PROG GND CFILTER RPROG CHARGE CURRENT MONITOR CIRCUITRY 3559 F06 Figure 6. Isolated Capacitive Load on PROG Pin and Filtering USB Inrush Limiting When a USB cable is plugged into a portable product, the inductance of the cable and the high-Q ceramic input capacitor form an L-C resonant circuit. If there is not much impedance in the cable, it is possible for the voltage at the input of the product to reach as high as twice the USB voltage (~10V) before it settles out. In fact, due to the high voltage coefficient of many ceramic capacitors (a nonlinearity), the voltage may even exceed twice the USB voltage. To prevent excessive voltage from damaging the LTC3559/LTC3559-1 during a hot insertion, the soft connect circuit in Figure 7 can be employed. In the circuit of Figure 7, capacitor C1 holds MP1 off when the cable is first connected. Eventually C1 begins to charge up to the USB voltage applying increasing gate support to MP1. The long time constant of R1 and C1 prevents MP1 Si2333 C1 100nF USB CABLE R1 40k C2 10μF LTC3559/ LTC3559-1 GND 3559 F07 Figure 7. USB Soft Connect Circuit Buck Switching Regulator General Information The LTC3559/LTC3559-1 contain two 2.25MHz constantfrequency current mode switching regulators that provide up to 400mA each. Both switchers can be programmed for a minimum output voltage of 0.8V and can be used to power a microcontroller core, microcontroller I/O, memory or other logic circuitry. Both regulators support 100% duty cycle operation (dropout mode) when the input voltage drops very close to the output voltage and are also capable of operating in Burst Mode operation for highest efficiencies at light loads (Burst Mode operation is pin selectable). The switching regulators also include soft-start to limit inrush current when powering on, short circuit current protection, and switch node slew limiting circuitry to reduce radiated EMI. A single MODE pin sets both regulators in Burst Mode operation or pulse skip operating mode while each regulator is enabled individually through their respective enable pins EN1 and EN2. The buck regulators input supply (PVIN) should be connected to the battery pin (BAT). This allows the undervoltage lockout circuit on the BAT pin to disable the buck regulators when the BAT voltage drops below 2.45V. Do not drive the buck switching regulators from a voltage other than BAT. A 2.2μF decoupling capacitor from the PVIN pin to GND is recommended. Buck Switching Regulator Output Voltage Programming Both switching regulators can be programmed for output voltages greater than 0.8V. The output voltage for each buck switching regulator is programmed using a resistor divider from the switching regulator output connected to the feedback pins (FB1 and FB2) such that: VOUT = 0.8(1 + R1/R2) VCC 5V USB INPUT the current from building up in the cable too fast thus dampening out any resonant overshoot. Typical values for R1 are in the range of 40k to 1M. The capacitor CFB cancels the pole created by feedback resistors and the input capacitance of the FB pin and also helps to improve transient response for output voltages much greater than 0.8V. A variety of capacitor sizes can be used for CFB but a value of 10pF is recommended for 3559fb 18 LTC3559/LTC3559-1 APPLICATIONS INFORMATION most applications. Experimentation with capacitor sizes between 2pF and 22pF may yield improved transient response if so desired by the user. Buck Switching Regulator Operating Modes The step-down switching regulators include two possible operating modes to meet the noise/power needs of a variety of applications. In pulse skip mode, an internal latch is set at the start of every cycle, which turns on the main P-channel MOSFET switch. During each cycle, a current comparator compares the peak inductor current to the output of an error amplifier. The output of the current comparator resets the internal latch, which causes the main P-channel MOSFET switch to turn off and the N-channel MOSFET synchronous rectifier to turn on. The N-channel MOSFET synchronous rectifier turns off at the end of the 2.25MHz cycle or if the current through the N-channel MOSFET synchronous rectifier drops to zero. Using this method of operation, the error amplifier adjusts the peak inductor current to deliver the required output power. All necessary compensation is internal to the step-down switching regulator requiring only a single ceramic output capacitor for stability. At light loads in pulse skip mode, the inductor current may reach zero on each pulse which will turn off the N-channel MOSFET synchronous rectifier. In this case, the switch node (SW1 or SW2) goes high impedance and the switch node voltage will “ring”. This is discontinuous operation, and is normal behavior for a switching regulator. At very light loads in pulse skip mode, the step-down switching PVIN EN MP PWM CONTROL MODE SW L VOUT + MN CO CFB R1 0.8V During Burst Mode operation, the step-down switching regulators automatically switch between fixed frequency PWM operation and hysteretic control as a function of the load current. At light loads the step-down switching regulators control the inductor current directly and use a hysteretic control loop to minimize both noise and switching losses. During Burst Mode operation, the output capacitor is charged to a voltage slightly higher than the regulation point. The step-down switching regulator then goes into sleep mode, during which the output capacitor provides the load current. In sleep mode, most of the switching regulator’s circuitry is powered down, helping conserve battery power. When the output voltage drops below a pre-determined value, the step-down switching regulator circuitry is powered on and another burst cycle begins. The sleep time decreases as the load current increases. Beyond a certain load current point (about 1/4 rated output load current) the step-down switching regulators will switch to a low noise constant frequency PWM mode of operation, much the same as pulse skip operation at high loads. For applications that can tolerate some output ripple at low output currents, Burst Mode operation provides better efficiency than pulse skip at light loads. The step-down switching regulators allow mode transition on-the-fly, providing seamless transition between modes even under load. This allows the user to switch back and forth between modes to reduce output ripple or increase low current efficiency as needed. Burst Mode operation is set by driving the MODE pin high, while pulse skip mode is achieved by driving the MODE pin low. Buck Switching Regulator in Shutdown FB GND regulators will automatically skip pulses as needed to maintain output regulation. At high duty cycle (VOUT > PVIN/2) in pulse skip mode, it is possible for the inductor current to reverse causing the buck converter to switch continuously. Regulation and low noise operation are maintained but the input supply current will increase to a couple mA due to the continuous gate switching. R2 3559 F08 The buck switching regulators are in shutdown when not enabled for operation. In shutdown, all circuitry in the buck switching regulator is disconnected from the regulator input supply, leaving only a few nanoamps of Figure 8. Buck Converter Application Circuit 3559fb 19 LTC3559/LTC3559-1 APPLICATIONS INFORMATION leakage pulled to ground through a 10k resistor on the switch (SW1 or SW2) pin when in shutdown. Buck Switching Regulator Dropout Operation It is possible for a step-down switching regulator’s input voltage to approach its programmed output voltage (e.g., a battery voltage of 3.4V with a programmed output voltage of 3.3V). When this happens, the PMOS switch duty cycle increases until it is turned on continuously at 100%. In this dropout condition, the respective output voltage equals the regulator’s input voltage minus the voltage drops across the internal P-channel MOSFET and the inductor. Buck Switching Regulator Soft-Start Operation Soft-start is accomplished by gradually increasing the peak inductor current for each switching regulator over a 500μs period. This allows each output to rise slowly, helping minimize the battery in-rush current required to charge up the regulator’s output capacitor. A soft-start cycle occurs whenever a switcher first turns on, or after a fault condition has occurred (thermal shutdown or UVLO). A soft-start cycle is not triggered by changing operating modes using the MODE pin. This allows seamless output operation when transitioning between operating modes. Buck Switching Regulator Switching Slew Rate Control The buck switching regulators contain circuitry to limit the slew rate of the switch node (SW1 and SW2). This circuitry is designed to transition the switch node over a period of a couple of nanoseconds, significantly reducing radiated EMI and conducted supply noise while maintaining high efficiency. Buck Switching Regulator Low Supply Operation An undervoltage lockout (UVLO) circuit on PVIN shuts down the step-down switching regulators when BAT drops below 2.45V. This UVLO prevents the step-down switching regulators from operating at low supply voltages where loss of regulation or other undesirable operation may occur. Buck Switching Regulator Inductor Selection The buck regulators are designed to work with inductors in the range of 2.2μH to 10μH, but for most applications a 4.7μH inductor is suggested. Larger value inductors reduce ripple current which improves output ripple voltage. Lower value inductors result in higher ripple current which improves transient response time. To maximize efficiency, choose an inductor with a low DC resistance. For a 1.2V output efficiency is reduced about 2% for every 100mΩ series resistance at 400mA load current, and about 2% for every 300mΩ series resistance at 100mA load current. Choose an inductor with a DC current rating at least 1.5 times larger than the maximum load current to ensure that the inductor does not saturate during normal operation. If output short circuit is a possible condition the inductor should be rated to handle the maximum peak current specified for the buck regulators. Different core materials and shapes will change the size/current and price/current relationship of an inductor. Toroid or shielded pot cores in ferrite or permalloy materials are small and don’t radiate much energy, but generally cost more than powdered iron core inductors with similar electrical characteristics. Inductors that are very thin or have a very small volume typically have much higher DCR losses, and will not give the best efficiency. The choice of which style inductor to use often depends more on the price vs size, performance, and any radiated EMI requirements than on what the buck regulator requires to operate. The inductor value also has an effect on Burst Mode operation. Lower inductor values will cause Burst Mode switching frequency to increase. Table 2 shows several inductors that work well with the LTC3559/LTC3559-1. These inductors offer a good compromise in current rating, DCR and physical size. Consult each manufacturer for detailed information on their entire selection of inductors. 3559fb 20 LTC3559/LTC3559-1 APPLICATIONS INFORMATION Table 2 Recommended Inductors INDUCTOR TYPE L (μH) MAX IDC(A) MAX DCR(Ω) SIZE IN MM (L × W × H) MANUFACTURER DB318C 4.7 3.3 4.7 3.3 4.7 3.3 1.07 1.20 0.79 0.90 1.15 1.37 0.1 0.07 0.24 0.20 0.13* 0.105* 3.8 × 3.8 × 1.8 3.8 × 3.8 × 1.8 3.6 × 3.6 × 1.2 3.6 × 3.6 × 1.2 3.0 × 2.8 × 1.2 3.0 × 2.8 × 1.2 Toko www.toko.com 4.7 3.3 4.7 3.3 4.7 0.9 1.1 0.5 0.6 0.75 0.11 0.085 0.17 0.123 0.19 4 × 4 × 1.8 4 × 4 × 1.8 3.2 × 3.2 × 1.2 3.2 × 3.2 × 1.2 4.9 × 4.9 × 1 Sumida www.sumida.com 4.7 3.3 4.7 3.3 4.7 3.3 4.7 3.3 1.3 1.59 0.8 0.97 1.29 1.42 1.08 1.31 0.162 0.113 0.246 0.165 0.117* 0.104* 0.153* 0.108* 3.1 × 3.1 × 1.8 3.1 × 3.1 × 1.8 3.1 × 3.1 × 1.2 3.1 × 3.1 × 1.2 5.2 × 5.2 × 1.2 5.2 × 5.2 × 1.2 5.2 × 5.2 × 1.0 5.2 × 5.2 × 1.0 Cooper www.cooperet.com 4.7 3.3 1.1 1.3 0.2 0.13 3.0 × 3.0 × 1.5 3.0 × 3.0 × 1.5 Coilcraft www.coilcraft.com D312C DE2812C CDRH3D16 CDRH2D11 CLS4D09 SD3118 SD3112 SD12 SD10 LPS3015 *Typical DCR Buck Switching Regulator Input/Output Capacitor Selection Low ESR (equivalent series resistance) ceramic capacitors should be used at both switching regulator outputs as well as the switching regulator input supply. Only X5R or X7R ceramic capacitors should be used because they retain their capacitance over wider voltage and temperature ranges than other ceramic types. A 10μF output capacitor is sufficient for most applications. For good transient response and stability the output capacitor should retain at least 4μF of capacitance over operating temperature and bias voltage. The switching regulator input supply should be bypassed with a 2.2μF capacitor. Consult manufacturer for detailed information on their selection and specifications of ceramic capacitors. Many manufacturers now offer very thin (< 1mm tall) ceramic capacitors ideal for use in height-restricted designs. Table 3 shows a list of several ceramic capacitor manufacturers. Table 3: Recommended Ceramic Capacitor Manufacturers AVX (803) 448-9411 www.avxcorp.com Murata (714) 852-2001 www.murata.com Taiyo Yuden (408) 537-4150 www.t-yuden.com TDK (888) 835-6646 www.tdk.com PCB Layout Considerations As with all DC/DC regulators, careful attention must be paid while laying out a printed circuit board (PCB) and to component placement. The inductors, input PVIN capacitor and output capacitors must all be placed as close to the LTC3559/LTC3559-1 as possible and on the same side as the LTC3559/LTC3559-1. All connections must be made on that same layer. Place a local unbroken ground plane below these components that is tied to the Exposed Pad (Pin 17) of the LTC3559/LTC3559-1. The Exposed Pad must also be soldered to system ground for proper operation. 3559fb 21 LTC3559/LTC3559-1 TYPICAL APPLICATIONS The Output Voltage of a Buck Regulator Is Programmed for 3.3V. When BAT Voltage Approaches 3.3V, the Regulator Operates in Dropout and the Output Voltage Will Be BAT – (ILOAD • 0.6). An LED at CHRG Gives a Visual Indication of the Battery Charger State. A 3-Resistor Bias Network for NTC Sets Hot and Cold Trip Points at Approximately 55°C and 0°C UP TO 950mA ADAPTER 4.5V TO 5.5V VCC 510Ω BAT 1μF 110k + PVIN 2.2μF NTC SINGLE Li-lon CELL 2.7V TO 4.2V (LTC3559) 2.7V TO 4.1V (LTC3559-1) 28.7k LTC3559/ LTC3559-1 100k NTC NTH50603N01 4.7μH CHRG 887Ω PROG 3.3V AT 400mA SW1 1.02M 22pF 10μF FB1 324k SUSP HPWR 4.7μH DIGITALLY CONTROLLED MODE EN1 1.8V AT 400mA SW2 806k 22pF 649k EN2 GND 10μF FB2 EXPOSED PAD 3559 TA03 Buck Regulator Efficiency vs ILOAD 100 100 Burst Mode OPERATION 90 80 80 70 70 EFFICIENCY (%) EFFICIENCY (%) 90 Buck Regulator Efficiency vs ILOAD 60 PULSE SKIP MODE 50 40 60 PULSE SKIP MODE 50 40 30 30 20 VOUT = 1.8V PVIN = 2.7V PVIN = 4.2V 10 0 0.1 Burst Mode OPERATION 1 10 ILOAD (mA) 100 1000 3559 TA02b 20 PVIN = 4.2V VOUT = 3.3V 10 0 0.1 1 10 ILOAD (mA) 100 1000 3559 TA02c 3559fb 22 LTC3559/LTC3559-1 TYPICAL APPLICATIONS The Battery Can be Charged with Up to 950mA of Charge Current. Buck Regulator 2 Is Enabled Only After VOUT1 Is Up to Approximately 0.7V. This Provides a Sequencing Function Which May Be Desirable in Applications Where a Microprocessor Needs to Be Powered Up Before Peripherals. CHRG Interfaces to a Microprocessor Which Decodes the Battery Charger State UP TO 950mA ADAPTER 4.5V TO 5.5V VCC BAT 1μF 100k + PVIN 2.2μF NTC 100k 100k NTC NTH50603NO1 SINGLE Li-lon CELL 2.7V TO 4.2V (LTC3559) 2.7V TO 4.1V (LTC3559-1) LTC3559/ LTC3559-1 4.7μH TO MICROPROCESSOR CHRG 2.5V AT 400mA SW1 887Ω 655k PROG 22pF 10μF 22pF 1.2V AT 400mA 10μF FB1 309k SUSP HPWR DIGITALLY CONTROLLED 4.7μH SW2 MODE 324k EN1 FB2 649k EN2 GND EXPOSED PAD 3559 TA02 PACKAGE DESCRIPTION UD Package 16-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1691) BOTTOM VIEW—EXPOSED PAD 3.00 p 0.10 (4 SIDES) 0.70 p0.05 15 PIN 1 TOP MARK (NOTE 6) 3.50 p 0.05 1.45 p 0.05 2.10 p 0.05 (4 SIDES) 16 0.40 p 0.10 1 1.45 p 0.10 (4-SIDES) PACKAGE OUTLINE 0.25 p0.05 0.50 BSC PIN 1 NOTCH R = 0.20 TYP OR 0.25 s 45o CHAMFER R = 0.115 TYP 0.75 p 0.05 2 (UD16) QFN 0904 0.200 REF 0.00 – 0.05 0.25 p 0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WEED-2) 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 3559fb 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. 23 LTC3559/LTC3559-1 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC3550 Dual Input USB/AC Adapter Li-Ion Battery Charger with Adjustable Output 600mA Buck Converter Synchronous Buck Converter, Efficiency: 93%, Adjustable Output at 600mA, Charge Current: 950mA Programmable, USB Compatible, Automatic Input Power Detection and Selection LTC3552 Standalone Linear Li-Ion Battery Charger with Adjustable Synchronous Buck Converter, Efficiency: >90%, Adjustable Outputs at Output Dual Synchronous Buck Converter 800mA and 400mA, Charge Current Programmable Up to 950mA, USB Compatible, 5mm × 3mm DFN16 Package LTC3552-1 Standalone Linear Li-Ion Battery Charger with Dual Synchronous Buck Converter Synchronous Buck Converter, Efficiency: >90%, Outputs 1.8V at 800mA and 1.575 at 400mA, Charge Current Programmable Up to 950mA, USB Compatible LTC3455 Dual DC/DC Converter with USB Power Manager and Li-Ion Battery Charger Seamless Transition Between Input Power Sources: Li-Ion Battery, USB and 5V Wall Adapter, Two High Efficiency DC/DC Converters: Up to 96%, Full-Featured Li-Ion Battery Charger with Accurate USB Current Limiting (500mA/100mA) Pin-Selectable Burst Mode Operation, Hot SwapTM Output for SDIO and Memory Cards, 4mm × 4mm QFN24 Package LTC3456 2-Cell, Multi-Output DC/DC Converter with USB Power Manager Seamless Transition Between 2-Cell Battery, USB and AC Wall Adapter Input Power Sources, Main Output: Fixed 3.3V Output, Core Output: Adjustable From 0.8V to VBATT(MIN), Hot Swap Output for Memory Cards, Power Supply Sequencing: Main and Hot Swap Accurate USB Current Limiting, High Frequency Operation: 1MHz, High Efficiency: Up to 92%, 4mm × 4mm QFN24 Package LTC4080 500mA Standalone Charger with 300mA Synchronous Buck Charges Single-Cell Li-Ion Batteries, Timer Termination +C/10, Thermal Regulation, Buck Output: 0.8V to VBAT, Buck Input VIN: 2.7V to 5.5V, 3mm × 3mm DFN10 Package Hot Swap is a trademark of Linear Technology Corporation. 3559fb 24 Linear Technology Corporation LT 0508 REV B • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2007