LT1511 LINER | Alldatasheet
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constant-voltage charging requirement for Li-Ion cells. keep the adapter current within specified levels. The LT1511 can charge batteries ranging from 1V to 20V. Figure 1. 3A Lithium-Ion Battery Charger
2 Li-Ion
, LTC and LT are registered trademarks of Linear Technology Corporation.
ABSOLUTE MAXIMUM RATINGSW WW U PACKAGE/ORDER INFORMATIONW UU ORDER PART NUMBER LT1511CSW LT1511ISW TJMAX = 125°C, θJA = 30°C/ W TOP VIEW SW PACKAGE 24-LEAD PLASTIC SO WIDE GND SW BOOST GND GND UV GND OVP CLP CLN COMP1 SENSE GND GND** V CC1* VCC2* VCC3* PROG V C UVOUT GND** COMP2 BAT SPIN Consult factory for Military grade parts. *ALL VCC PINS SHOULD BE CONNECTED TOGETHER CLOSE TO THE PINS ** ALL GND PINS ARE FUSED TO INTERNAL DIE ATTACH PADDLE FOR HEAT SINKING. CONNECT THESE PINS TO EXPANDED PC LANDS FOR PROPER HEAT SINKING. 30°C/W THERMAL RESISTANCE ASSUMES AN INTERNAL GROUND PLANE DOUBLING AS A HEAT SPREADER (Note 1) Supply Voltage V Operating Junction Temperature Range Operating Ambient Temperature ELECTRICAL CHARACTERISTICSThe l denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 16V, VBAT = 8V, VMAX (maximum operating VCC) = 28V, RS2 = RS3 = 200Ω (see Block Diagram), VCLN = VCC. No load on any outputs unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Overall Supply Current V PROG = 2.7V, VCC ≤ 20V l 4.5 6.8 mA VPROG = 2.7V, 20V < VCC ≤ 25V l 4.6 7.0 mA Sense Amplifier CA1 Gain and Input Offset Voltage 8V ≤ VCC ≤ 25V , 0V ≤ VBAT ≤ 20V (With RS2 = 200Ω , RS3 = 200Ω )R PROG = 4.93k l 95 100 105 mV (Measured across RS1)(Note 2) R PROG = 49.3k l 81 0 1 2 m V TJ < 0°C 7 13 mV VCC = 28V, VBAT = 20V RPROG = 4.93k l 90 110 mV RPROG = 49.3k l 71 3 m V TJ < 0°C 6 14 mV VCC Undervoltage Lockout (Switch OFF) Threshold Measured at UV Pin l 678 V UV Pin Input Current 0.2V ≤ VUV ≤ 8V l 0.1 5 µA UV Output Voltage at UVOUT Pin In Undervoltage State, I UVOUT = 70µA l 0.1 0.5 V UV Output Leakage Current at UVOUT Pin 8V ≤ VUV, VUVOUT = 5V l 0.1 3 µA Reverse Current from Battery (When VCC Is V BAT ≤ 20V, VUV ≤ 0.4V 3 15 µA Not Connected, VSW Is Floating)
ELECTRICAL CHARACTERISTICSThe l denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 16V, VBAT = 8V, VMAX (maximum operating VCC) = 28V, RS2 = RS3 = 200Ω (see Block Diagram), VCLN = VCC. No load on any outputs unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Overall Boost Pin Current V CC = 20V, VBOOST = 0V 0.1 10 µA VCC = 28V, VBOOST = 0V 0.25 20 µA 2V ≤ VBOOST – VCC < 8V (Switch ON) 6 9 mA 8V ≤ VBOOST – VCC ≤ 25V (Switch ON) 8 12 mA Switch Switch ON Resistance 8V ≤ VCC ≤ VMAX, ISW = 3A, VBOOST – VSW ≥ 2V l 0.15 0.25 Ω ΔIBOOST/ΔISW During Switch ON V BOOST = 24V, ISW ≤ 3A 25 35 mA/A Switch OFF Leakage Current V SW = 0V, VCC ≤ 20V l 2 100 µA 20V < VCC ≤ 28V l 4 200 µA Minimum IPROG for Switch ON l 24 2 0 µA Minimum IPROG for Switch OFF at VPROG ≤ 1V l 1 2.4 mA Maximum VBAT for Switch ON l VCC – 2 V Current Sense Amplifier CA1 Inputs (Sense, BAT) Input Bias Current l – 50 – 125 µA Input Common Mode Low l – 0.25 V Input Common Mode High l VCC – 2 V SPIN Input Current – 100 – 200 µA Reference Reference Voltage (Note 3) R PROG = 4.93k, Measured at OVP with VA Supplying IPROG and Switch OFF 2.453 2.465 2.477 V Reference Voltage All Conditions of V CC,T J > 0°C l 2.441 2.489 V TJ < 0°C (Note 4) l 2.43 2.489 V Oscillator Switching Frequency 180 200 220 kHz Switching Frequency All Conditions of V CC,T J > 0°C l 170 200 230 kHz TJ < 0°C l 160 230 kHz Maximum Duty Cycle l 85 % TA = 25°C9 0 9 3 % Current Amplifier CA2 Transconductance V C = 1V, IVC = ±1µA 150 250 550 µmho Maximum VC for Switch OFF l 0.6 V IVC Current (Out of Pin) V C ≥ 0.6V 100 µA VC < 0.45V 3 mA
ELECTRICAL CHARACTERISTICSThe l denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 16V, VBAT = 8V, VMAX (maximum operating VCC) = 28V. No load on any outputs unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Voltage Amplifier VA Transconductance (Note 3) Output Current from 50 µA to 500µA 0.25 0.6 1.3 mho Output Source Current V OVP = VREF + 10mV, VPROG = VREF + 10mV 1.1 mA OVP Input Bias Current At 0.75mA VA Output Current ±3 ±10 nA At 0.75mA VA Output Current, TJ > 90°C –15 25 nA Current Limit Amplifier CL1, 8V ≤ Input Common Mode Turn-On Threshold 0.75mA Output Current 93 100 107 mV Transconductance Output Current from 50 µA to 500µA 0.5 1 2 mho CLP Input Current 0.75mA Output Current, V UV ≥ 0.4V 0.3 1 µA CLN Input Current 0.75mA Output Current V UV ≥ 0.4V 0.8 2 mA Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: Tested with Test Circuit 1. Note 3: Tested with Test Circuit 2. Note 4: A linear interpolation can be used for reference voltage specification between 0°C and –40 °C. TYPICAL PERFORMANCE CHARACTERISTICS UW Thermally Limited Maximum Charging Current Efficiency of Figure 1 Circuit DUTY CYCLE (%) 0 1 03 05 07 0 ICC (mA) 1511 • TPC03 20 40 60 125°C 0°C 25°C VCC = 16V ICC vs Duty Cycle INPUT VOLTAGE (V) MAXIMUM CHARGING CURRENT (A) 3.0 2.8 2.6 2.4 2.2 2.0 1511 • TPC01 10 15 20 30 (θJA=30°C/W) TAMAX=60°C TJMAX=125°C 4.2V BATTERY VIN ‡ 8V 8.4V BATTERY VIN ‡ 11V 12.6V BATTERY 16.8V BATTERY NOTE: FOR 4.2V AND 8.4V BATTERIES MAXIMUM CHARGING CURRENT IS 3A FOR VIN – VBAT ‡ 3V IBAT (A) 0.2 EFFICIENCY (%) 100 1511 • TPC02 0.6 1.4 VIN = 16.5 VBAT = 8.4V CHARGER EFFICIENCY INCLUDES LOSS IN DIODE D3
TYPICAL PERFORMANCE CHARACTERISTICS UW Switching Frequency vs Temperature VREF Line Regulation TEMPERATURE (°C) –20 FREQUENCY (kHz) 200 40 80 120 60 100 140 1511 • TPC04 210 205 200 195 190 185 180 VCC (V) ICC (mA) 7.0 6.5 6.0 5.5 5.0 4.5 5 10 15 20 1511 • TPC05 25 30 125°C 25°C 0°C MAXIMUM DUTY CYCLE ICC vs VCC VCC (V) ∆VREF (V) 0.003 0.002 0.001 –0.001 –0.002 –0.003 5 10 15 20 1511 • TPC06 25 30 ALL TEMPERATURES VC Pin CharacteristicsMaximum Duty CycleIVA vs ΔVOVP (Voltage Amplifier) IVA (mA) ∆VOVP (mV) 0.8 1511• TPC07 125°C 25°C TEMPERATURE (°C) DUTY CYCLE (%) 120 1511 • TPC08 40 80 20 60 100 140 VC (V) IVC (mA) –1.20 –1.08 –0.96 –0.84 –0.72 –0.60 –0.48 –0.36 –0.24 –0.12 0.12 1.6 1511 • TPC09 0.4 0.8 1.2 2.0 Switch Current vs Boost Current vs Boost Voltage SWITCH CURRENT (A) BOOST CURRENT (mA) 1511 • TPC11 VCC = 16V VBOOST = 38V 28V 18V TEMPERATURE REFERENCE VOLTAGE (V) 2.470 2.468 2.466 2.464 2.462 2.460 2.458 25 50 75 100 LT1511 • TPC12 125 150 Reference Voltage vs TemperaturePROG Pin Characteristics VPROG (V) 0123 54 IPROG (mA) 1511 • TPC10 125°C 25°C
GND (Pins 1, 4, 5, 7, 16, 23, 24): Ground Pin. SW (Pin 2): Switch Output. The Schottky catch diode must be placed with very short lead length in close proximity to SW pin and GND. BOOST (Pin 3): This pin is used to bootstrap and drive the switch power NPN transistor to a low on-voltage for low power dissipation. In normal operation, V BOOST = VCC + VBAT when switch is on. Maximum allowable V BOOST is 55V. UV (Pin 6): Undervoltage Lockout Input. The rising thresh- old is at 6.7V with a hysteresis of 0.5V. Switching stops in undervoltage lockout. When the supply (normally the wall adapter output) to the chip is removed, the UV pin has to be pulled down to below 0.7V (a 5k resistor from adapter output to GND is required) otherwise the reverse battery current drained by the chip will be approximately 200µA instead of 3 µA. Do not leave UV pin floating. If it is connected to V IN with no resistor divider, the built-in 6.7V undervoltage lockout will be effective. OVP (Pin 8): This is the input to the amplifier VA with a threshold of 2.465V. Typical input current is about 3nA out of pin. For charging lithium-ion batteries, VA monitors the battery voltage and reduces charging when battery voltage reaches the preset value. If it is not used, the OVP pin should be grounded. CLP (Pin 9): This is the positive input to the supply current limit amplifier CL1. The threshold is set at 100mV. When used to limit supply current, a filter is needed to filter out the 200kHz switching noise. CLN (Pin 10): This is the negative input to the amplifier CL1. COMP1 (Pin 11): This is the compensation node for the amplifier CL1. A 200pF capacitor is required from this pin to GND if input current amplifier CL1 is used. At input adapter current limit, this node rises to 1V. By forcing COMP1 low with an external transistor, amplifier CL1 will be defeated (no adapter current limit). COMP1 can source 200µA. PIN FUNCTIONSUU U SENSE (Pin 12): Current Amplifier CA1 Input. Sensing can be at either terminal of the battery. SPIN (Pin 13): This pin is for the internal amplifier CA1 bias. It has to be connected to R S1 as shown in the 3A Lithium Battery Charger (Figure 1). BAT (Pin 14): Current Amplifier CA1 Input. COMP2 (Pin 15): This is also a compensation node for the amplifier CL1. It gets up to 2.8V at input adapter current limit and/or at constant-voltage charging. UV OUT (Pin 17): This is an open collector output for undervoltage lockout status. It stays low in undervoltage state. With an external pull-up resistor , it goes high at valid V CC. Note that the base drive of the open collector NPN comes from CLN pin. UVOUT stays low only when CLN is higher than 2V. Pull-up current should be kept under 100µA. VC (Pin 18): This is the control signal of the inner loop of the current mode PWM. Switching starts at 0.7V. Higher VC corresponds to higher charging current in normal operation. A capacitor of at least 0.33µF to GND filters out noise and controls the rate of soft-start. To shut down switching, pull this pin low. Typical output current is 30µA. PROG (Pin 19): This pin is for programming the charging current and for system loop compensation. During normal operation, VPROG stays close to 2.465V. If it is shorted to GND the switching will stop. When a microprocessor controlled DAC is used to program charging current, it must be capable of sinking current at a compliance up to 2.465V. V CC (Pins 20, 21, 22): This is the supply of the chip. For good bypass, a low ESR capacitor of 20 µF or higher is required, with the lead length kept to a minimum. V CC should be between 8V and 28V and at least 3V higher than VBAT. Undervoltage lockout starts and switching stops when VCC goes below 7V. Note that there is a parasitic diode inside from SW pin to V CC pin. Do not force V CC below SW by more than 0.7V with battery present. All three V CC pins should be shorted together close to the pins.
– + VSW 0.7V 1.5V VBAT VREF VC GND UV SLOPE COMPENSATION PWM CA2 CA1 VA 6.7V VREF 2.465V SHUTDOWN 200kHz OSCILLATOR S R R R RPROG VCC UVOUT VCC BOOST SW SENSE SPIN BAT IPROG RS3 RS2 RS1 IBAT 0VP BAT
1511 BDPROG
IBAT = (IPROG)(RS2) RS1 CPROG 75k QSW VCC gm = 0.64Ω CL1 CLP 100mV CLN COMP1 COMP2 (RS3 = RS2) 2.465V RPROG RS2 RS1(( ))
≈ 0.65V VBAT VC CA2 CA1 300Ω 20k RS1 10ΩBAT SENSE SPIN 1511 • TC01 PROG RPROG 0.047µF LT1511 1µF 60k LT1006 RS2 200Ω RS3 200Ω VREF 2.465V VA 10k 10k OVP 1511 • TC02 IPROG RPROG LT1511 PROG LT1013 0.47µF OPERATIONU The LT1511 is a current mode PWM step-down (buck) switcher. The battery DC charging current is programmed by a resistor RPROG (or a DAC output current) at the PROG pin (see Block Diagram). Amplifier CA1 converts the charging current through R S1 to a much lower current IPROG fed into the PROG pin. Amplifier CA2 compares the output of CA1 with the programmed current and drives the PWM loop to force them to be equal. High DC accuracy is achieved with averaging capacitor CPROG. Note that IPROG has both AC and DC components. IPROG goes through R1 and generates a ramp signal that is fed to the PWM control comparator C1 through buffer B1 and level shift resistors R2 and R3, forming the current mode inner loop. The Boost pin drives the switch NPN QSW into saturation and reduces power loss. For batteries like lithium-ion that require both constant-current and constant-voltage charg- ing, the 0.5%, 2.465V reference and the amplifier VA reduce the charging current when battery voltage reaches the preset level. For NiMH and NiCd, VA can be used for overvoltage protection. When input voltage is not present, the charger goes into low current (3 µA typically) sleep mode as input drops down to 0.7V below battery voltage. To shut down the charger, simply pull the V C pin low with a transistor. Test Circuit 2
APPLICATIONS INFORMATIONWU UU Input and Output Capacitors In the 3A Lithium Battery Charger (Figure 1), the input capacitor (CIN) is assumed to absorb all input switching ripple current in the converter, so it must have adequate ripple current rating. Worst-case RMS ripple current will be equal to one half of output charging current. Actual capacitance value is not critical. Solid tantalum capacitors such as the AVX TPS and Sprague 593D series have high ripple current rating in a relatively small surface mount package, but caution must be used when tantalum capaci- tors are used for input bypass. High input surge currents can be created when the adapter is hot-plugged to the charger and solid tantalum capacitors have a known failure mechanism when subjected to very high turn-on surge currents. Highest possible voltage rating on the capacitor will minimize problems. Consult with the manu- facturer before use. Alternatives include new high capacity ceramic (5µF to 20µF) from Tokin or United Chemi-Con/ Marcon, et al., and the old standby, aluminum electrolytic, which will require more microfarads to achieve adequate ripple rating. Sanyo OS-CON can also be used. The output capacitor (C OUT) is also assumed to absorb output switching current ripple. The general formula for capacitor current is: IRMS = (L1)(f) VBAT VCC()0.29 (VBAT) 1 – For example, V CC = 16V, V BAT = 8.4V, L1 = 20 µH, and f = 200kHz, IRMS = 0.3A. EMI considerations usually make it desirable to minimize ripple current in the battery leads, and beads or inductors may be added to increase battery impedance at the 200kHz switching frequency. Switching ripple current splits be- tween the battery and the output capacitor depending on the ESR of the output capacitor and the battery imped- ance. If the ESR of C OUT is 0.2Ω and the battery impedance is rased to 4 Ω with a bead or inductor, only 5% of the current ripple will flow in the battery. Soft-Start The LT1511 is soft started by the 0.33µF capacitor on the VC pin. On start-up, VC pin voltage will rise quickly to 0.5V, then ramp at a rate set by the internal 45µA pull-up current and the external capacitor. Battery charging current starts ramping up when VC voltage reaches 0.7V and full current is achieved with VC at 1.1V. With a 0.33µF capacitor, time to reach full charge current is about 10ms and it is assumed that input voltage to the charger will reach full value in less than 10ms. The capacitor can be increased up to 1µF if longer input start-up times are needed. In any switching regulator, conventional timer-based soft starting can be defeated if the input voltage rises much slower than the time out period. This happens because the switching regulators in the battery charger and the com- puter power supply are typically supplying a fixed amount of power to the load. If input voltage comes up slowly compared to the soft start time, the regulators will try to deliver full power to the load when the input voltage is still well below its final value. If the adapter is current limited, it cannot deliver full power at reduced output voltages and the possibility exists for a quasi “latch” state where the adapter output stays in a current limited state at reduced output voltage. For instance, if maximum charger plus computer load power is 30W, a 15V adapter might be current limited at 2.5A. If adapter voltage is less than (30W/2.5A = 12V) when full power is drawn, the adapter voltage will be sucked down by the constant 30W load until it reaches a lower stable state where the switching regu- lators can no longer supply full load. This situation can be prevented by utilizing undervoltage lockout , set higher than the minimum adapter voltage where full power can be achieved. A fixed undervoltage lockout of 7V is built into the VCC pin, but an additional adjustable lockout is also available on the UV pin. Internal lockout is performed by clamping the VC pin low. The VC pin is released from its clamped state when the UV pin rises above 6.7V and is pulled low when the UV pin drops below 6.2V (0.5V hysteresis). At the same time UV OUT goes high with an external pull-up resistor. This signal can be used to alert the system that charging is about to start. The charger will start delivering current about 4ms after V C is released, as set by the 0.33 µF
grounding technique to work. the maximum possible rate of which the adapter is capable. and CLN pins should be connected to VCC. where RPROG is the total resistance from PROG pin to ground. Figure 2. Adapter Current Limiting
Figure 7. Lower VBOOST heat sinking effectiveness of extended areas of the board. lead temperatures for chargers operating at full current. used to extrapolate these readings to other situations. Vias should be used to connect board layers together.
layer board of reasonable size. Figure 10 with a 10µF CX bypass capacitor. the input is only a volt or two above the battery voltage. Figure 9. LT1511 Lead Temperature Figure 8. LT1511 Thermal Resistance
1511 F10
1511 F11
Figure 11. Replacing the Input Diode Figure 10. High Duty Cycle
spec limit of 20V. This restricts VIN to a maximum of 20V. For low dropout operation with VIN > 20V consult factory. Figure 13. High Speed Switching Path
1511 F12a
1511 F12b
inputs are pulled to ground by a powered-down adapter. connected to expanded traces for low thermal resistance. an actual LT1511 circuit PCB layout or Gerber file. Information furnished by Linear Technology Corporation is believed to be accurate and reliable. tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
- PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS.
Figure 14. Critical Electrical and Thermal Path Layout Dimensions in inches (millimeters) unless otherwise noted.