LT1510/LT1510-5 Constant-Voltage/ Constant-Current Battery Charger FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ Charges NiCd, NiMH and Lithium-Ion Batteries –– Only One 1/10W Resistor Is Needed to Program Charging Current High Efficiency Current Mode PWM with 1.5A Internal Switch and Sense Resistor 3% Typical Charging Current Accuracy Precision 0.5% Voltage Reference for Voltage Mode Charging or Overvoltage Protection Current Sensing Can Be at Either Terminal of the Battery Low Reverse Battery Drain Current: 3µA Charging Current Soft Start Shutdown Control 500kHz Version Uses Small Inductor U APPLICATIONS ■ ■ Chargers for NiCd, NiMH and Lithium Batteries Step-Down Switching Regulator with Precision Adjustable Current Limit U DESCRIPTION With switching frequency as high as 500kHz, The LT ®1510 current mode PWM battery charger is the smallest, sim- plest, most efficient solution to fast-charge modern rechargeable batteries including lithium-ion (Li-Ion), nickelmetal-hydride (NiMH)* and nickel-cadmium (NiCd)* that require constant-current and/or constant-voltage charging. The internal switch is capable of delivering 1.5A DC current (2A peak current). The 0.1Ω onboard current sense resistor makes the charging current programming very simple. One resistor (or a programming current from a DAC) is required to set the full charging current (1.5A) to within 5% accuracy. The LT1510 with 0.5% reference voltage accuracy meets the critical constant-voltage charging requirement for lithium cells. The LT1510 can charge batteries ranging from 2V to 20V. Ground sensing of current is not required and the battery’s negative terminal can be tied directly to ground. A saturating switch running at 200kHz (500kHz for LT1510-5) gives high charging efficiency and small inductor size. A blocking diode is not required between the chip and the battery because the chip goes into sleep mode and drains only 3µA when the wall adaptor is unplugged. Soft start and shutdown features are also provided. The LT1510 is available in a 16-pin fused lead power SO package with a thermal resistance of 50°C/W, an 8-pin SO and a 16-pin PDIP. , LTC and LT are registered trademarks of Linear Technology Corporation. * NiCd and NiMH batteries require charge termination circuitry (not shown in Figure 1). U TYPICAL APPLICATIONS C1 0.22µF SW VCC BOOST L1** 10µH D2 MMBD914L + PROG LT1510-5 GND VC 0.1µF SW 8.2V TO 20V VCC + –+ CIN* 10µF 1µF D3 1N5819 C1 D1 0.22µF 1N5819 D3 MBRM120T3 D1 MBRM120T3 BOOST 300Ω L1** 33µH 6.19k 1k D2 1N914 PROG 1µF VC –+ CIN* 10µF LT1510 GND 11V TO 28V 0.1µF 300Ω 3.83k 1k OVP OVP SENSE SENSE BAT + COUT*** 22µF BAT + + 4.2V Q3† 2N7002 NOTE: COMPLETE LITHIUM-ION CHARGER, NO TERMINATION REQUIRED * TOKIN OR MARCON CERAMIC SURFACE MOUNT ** COILTRONICS TP3-100, 10µH, 2.2mm HEIGHT (0.8A CHARGING CURRENT) COILTRONICS TP1 SERIES, 10µH, 1.8mm HEIGHT (<0.5A CHARGING CURRENT) *** PANASONIC EEFCD1B220 † OPTIONAL, SEE APPLICATIONS INFORMATION COUT 22µF TANT + 4.2V Q3† VN2222 + 4.2V R3 70.6k 0.25% R4 100k 0.25% 1510 F01 Figure 1. 500kHz Smallest Li-Ion Cell Phone Charger (0.8A) NOTE: COMPLETE LITHIUM-ION CHARGER, NO TERMINATION REQUIRED * TOKIN OR MARCON CERAMIC SURFACE MOUNT ** COILTRONICS CTX33-2 † OPTIONAL, SEE APPLICATIONS INFORMATION R3 240k 0.25% R4 100k 0.25% 1510 F02 Figure 2. Charging Lithium Batteries (Efficiency at 1.3A > 87%) 1 LT1510/LT1510-5 W W U W ABSOLUTE MAXIMUM RATINGS Operating Ambient Temperature Range Commercial ............................................. 0°C to 70°C Extended Commercial (Note 7) ........... – 40°C to 85°C Industrial (Note 8) .............................. – 40°C to 85°C Operating Junction Temperature Range LT1510C (Note 7) ............................. – 40°C to 125°C LT1510I ............................................ – 40°C to 125°C Lead Temperature (Soldering, 10 sec).................. 300°C Supply Voltage (VMAX) ............................................ 30V Switch Voltage with Respect to GND ...................... – 3V Boost Pin Voltage with Respect to VCC ................... 30V Boost Pin Voltage with Respect to GND ................. – 5V VC, PROG, OVP Pin Voltage ...................................... 8V IBAT (Average) ........................................................ 1.5A Switch Current (Peak)............................................... 2A Storage Temperature Range ................. – 65°C to 150°C W U U PACKAGE/ORDER INFORMATION TOP VIEW ORDER PART NUMBER TOP VIEW SW 1 8 VCC BOOST 2 7 PROG GND 3 6 VC SENSE 4 5 BAT S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 125°C, θJA = 125°C/ W **GND 1 16 GND** SW 2 15 VCC2 BOOST 3 14 VCC1 GND 4 13 PROG OVP 5 12 VC NC 6 11 NC SENSE 7 10 BAT **GND 8 9 ORDER PART NUMBER LT1510CS8 LT1510IS8 S8 PART MARKING LT1510CGN LT1510IGN LT1510-5CGN LT1510-5IGN GND** GN PACKAGE (0.015 IN) 16-LEAD PLASTIC SSOP TJMAX = 125°C, θJA = 75°C/ W ** FOUR CORNER PINS ARE FUSED TO INTERNAL DIE ATTACH PADDLE FOR HEAT SINKING. CONNECT THESE FOUR PINS TO EXPANDED PC LANDS FOR PROPER HEAT SINKING. 1510 1510I GN PART MARKING 1510 1510I 15105 15105I ORDER PART NUMBER TOP VIEW **GND 1 16 GND** SW 2 15 VCC2 BOOST 3 14 VCC1 GND 4 13 PROG OVP 5 12 VC SENSE 6 11 BAT GND 7 10 GND **GND 8 9 N PACKAGE 16-LEAD PDIP LT1510CN LT1510CS LT1510IN LT1510IS GND** S PACKAGE* 16-LEAD PLASTIC SO TJMAX = 125°C, θJA = 75°C/ W (N) TJMAX = 125°C, θJA = 50°C/ W (S)* * VCC1 AND VCC2 SHOULD BE CONNECTED TOGETHER CLOSE TO THE PINS. ** FOUR CORNER PINS ARE FUSED TO INTERNAL DIE ATTACH PADDLE FOR HEAT SINKING. CONNECT THESE FOUR PINS TO EXPANDED PC LANDS FOR PROPER HEAT SINKING. Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS VCC = 16V, VBAT = 8V, VMAX (maximum operating VCC) = 28V, no load on any outputs, unless otherwise noted. (Notes 7, 8) PARAMETER CONDITIONS MIN TYP MAX UNITS 2.90 2.91 4.3 4.5 mA mA Overall Supply Current VPROG = 2.7V, VCC ≤ 20V VPROG = 2.7V, 20V < VCC ≤ VMAX ● ● DC Battery Current, IBAT (Note 1) 8V ≤ VCC ≤ 25V, 0V ≤ VBAT ≤ 20V, TJ < 0°C RPROG = 4.93k RPROG = 3.28k (Note 4) RPROG = 49.3k TJ < 0°C ● ● ● ● ● 0.91 0.93 1.35 75 70 1.0 1.5 100 1.09 1.07 1.65 125 130 A A A mA mA VCC = 28V, VBAT = 20V RPROG = 4.93k RPROG = 49.3k ● ● 0.93 75 1.0 100 1.07 125 A mA 2 LT1510/LT1510-5 ELECTRICAL CHARACTERISTICS VCC = 16V, VBAT = 8V, VMAX (maximum operating VCC) = 28V, no load on any outputs, unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Overall Minimum Input Operating Voltage Undervoltage Lockout ● 7 7.8 V Reverse Current from Battery (When VCC Is Not Connected, VSW Is Floating) VBAT ≤ 20V, 0°C ≤ TJ ≤ 70°C ● 6.2 3 15 µA Boost Pin Current VCC – VBOOST ≤ 20V 20V < VCC – VBOOST ≤ 28V 2V ≤ VBOOST – VCC ≤ 8V (Switch ON) 8V < VBOOST – VCC ≤ 25V (Switch ON) ● ● ● ● 0.10 0.25 6 8 20 30 11 14 µA µA mA mA VCC = 10V ISW = 1.5A, VBOOST – VSW ≥ 2V (Note 4) ISW = 1A, VBOOST – VSW < 2V (Unboosted) ● ● 0.3 0.5 2.0 Ω Ω 20 35 mA/A 2 4 100 200 µA µA Switch Switch ON Resistance ∆IBOOST/∆ISW During Switch ON VBOOST = 24V, ISW ≤ 1A Switch OFF Leakage Current VSW = 0V, VCC ≤ 20V 20V < VCC ≤ 28V Maximum VBAT with Switch ON ● ● ● Minimum IPROG for Switch ON Minimum IPROG for Switch OFF at VPROG ≤ 1V ● 2 4 1 2.4 VCC – 2 V 20 µA mA Current Sense Amplifier Inputs (SENSE, BAT) Sense Resistance (RS1) 0.08 0.12 Ω Total Resistance from SENSE to BAT (Note 3) 0.2 0.25 Ω – 200 700 – 375 1300 µA µA VCC – 2 V BAT Bias Current (Note 5) VC < 0.3V VC > 0.6V Input Common Mode Limit (Low) ● Input Common Mode Limit (High) ● – 0.25 V Reference Reference Voltage (Note 1) S8 Package RPROG = 4.93k, Measured at PROG Pin Reference Voltage (Note 2) 16-Pin RPROG = 3.28k, Measured at OVP with VA Supplying IPROG and Switch OFF Reference Voltage Tolerance, 16-Pin Only 8V ≤ VCC ≤ 28V, 0°C ≤ TJ ≤ 70°C 8V ≤ VCC ≤ 28V, 0°C ≤ TJ ≤ 125°C 8V ≤ VCC ≤ 28V, TJ < 0°C ● ● ● ● 2.415 2.465 2.515 V 2.453 2.465 2.477 V 2.446 2.441 2.430 2.465 2.480 2.489 2.489 V V V 180 440 200 500 220 550 kHz kHz 200 230 230 575 575 kHz kHz kHz kHz Oscillator Switching Frequency LT1510 LT1510-5 Switching Frequency Tolerance All Conditions of VCC, Temperature, LT1510 LT1510, TJ < 0°C LT1510-5 LT1510-5, TJ < 0°C ● ● ● ● 170 160 425 400 LT1510 LT1510, TA = 25°C (Note 8) LT1510-5 (Note 9) ● 87 90 77 Maximum Duty Cycle ● 500 93 81 % % % 3 LT1510/LT1510-5 ELECTRICAL CHARACTERISTICS VCC = 16V, VBAT = 8V, VMAX (maximum operating VCC) = 28V, no load on any outputs, unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS VC = 1V, IVC = ±1µA 150 250 550 µmho Current Amplifier (CA2) Transconductance Maximum VC for Switch OFF ● VC ≥ 0.6V VC < 0.45V IVC Current (Out of Pin) 0.6 V 100 3 µA mA 2.5 mho Voltage Amplifier (VA), 16-Pin Only Transconductance (Note 2) Output Current from 100µA to 500µA 0.5 Output Source Current, VCC = 10V VPROG = VOVP = VREF + 10mV 1.3 OVP Input Bias Current At 0.75mA VA Output Current The ● denotes specifications which apply over the specified temperature range. Note 1: Tested with Test Circuit 1. Note 2: Tested with Test Circuit 2. Note 3: Sense resistor RS1 and package bond wires. Note 4: Applies to 16-pin only. 8-pin packages are guaranteed but not tested at – 40°C. Note 5: Current (≈ 700µA) flows into the pins during normal operation and also when an external shutdown signal on the VC pin is greater than 0.3V. Current decreases to ≈ 200µA and flows out of the pins when external shutdown holds the VC pin below 0.3V. Current drops to near zero when input voltage collapses. See external Shutdown in Applications Information section. Note 6: A linear interpolation can be used for reference voltage specification between 0°C and – 40°C. 1.2 mA 50 ● 150 nA Note 7: Commercial grade device specifications are guaranteed over the 0°C to 70°C temperature range. In addition, commercial grade device specifications are assured over the –40°C to 85°C temperature range by design or correlation, but are not production tested. Maximum allowable ambient temperature may be limited by power dissipation. Parts may not necessarily be operated simultaneously at maximum power dissipation and maximum ambient temperature. Temperature rise calculations must be done as shown in the Applications Information section to ensure that maximum junction temperature does not exceed the 125°C limit. With high power dissipation, maximum ambient temperature may be less than 70°C. Note 8: Industrial grade device specifications are guaranteed over the – 40°C to 85°C temperature range. Note 9: 91% maximum duty cycle is guaranteed by design if VBAT or VX (see Figure 8 in Application Information) is kept between 3V and 5V. Note 10: VBAT = 4.2V. U W TYPICAL PERFORMANCE CHARACTERISTICS Thermally Limited Maximum Charging Current, 8-Pin SO Thermally Limited Maximum Charging Current, 16-Pin SO 1.5 1.1 4V BATTERY 0.9 8V BATTERY 0.7 12V BATTERY 0.5 16V BATTERY 1.5 4V BATTERY 8V BATTERY 1.3 MAXIMUM CHARGING CURRENT (A) (θJA =125°C/W) TAMAX = 60°C TJMAX =125°C MAXIMUM CHARGING CURRENT (A) MAXIMUM CHARGING CURRENT (A) 1.3 12V BATTERY 1.1 16V BATTERY 0.9 (θJA =50°C/W) TAMAX =60°C TJMAX =125°C 0.7 0.5 0.3 0 5 15 10 INPUT VOLTAGE (V) 20 25 1510 G12 4 Thermally Limited Maximum Charging Current, 16-Pin GN 0 5 15 10 INPUT VOLTAGE (V) 20 25 1510 G13 1.3 4V BATTERY 1.1 8V BATTERY 0.9 θJA = 80°C/W TAMAX = 60°C TJMAX = 125°C 0.7 12V BATTERY 16V BATTERY 0.5 0 5 15 10 INPUT VOLTAGE (V) 20 25 LT1510 • TPC14 LT1510/LT1510-5 U W TYPICAL PERFORMANCE CHARACTERISTICS Efficiency of Figure 2 Circuit 100 8 7 205 6 94 ICC (mA) 92 90 88 FREQUENCY (kHz) 96 210 VCC = 16V VCC = 15V (EXCLUDING DISSIPATION ON INPUT DIODE D3) VBAT = 8.4V 98 EFFICIENCY (%) Switching Frequency vs Temperature ICC vs Duty Cycle 5 0°C 125°C 4 25°C 3 86 200 195 190 2 84 185 1 82 80 0 0.1 0.3 0.5 0.7 0.9 IBAT (A) 1.1 1.3 1.5 0 10 20 30 40 50 60 DUTY CYCLE (%) 70 180 –20 80 0 20 40 60 80 100 120 140 TEMPERATURE (°C) 1510 G04 1510 G01 ICC vs VCC 1510 G05 IVA vs ∆VOVP (Voltage Amplifier) VREF Line Regulation 7.0 4 0.003 MAXIMUM DUTY CYCLE 0.002 0°C 6.5 3 0.001 125°C 5.5 ALL TEMPERATURES ∆VOVP (mV) 6.0 ∆VREF (V) ICC (mA) 25°C 0 2 125°C –0.001 1 5.0 –0.002 4.5 0 5 10 15 VCC (V) 20 25 30 –0.003 25°C 0 5 10 15 VCC (V) 1510 G03 20 25 0 30 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 IVA (mA) 1510 G02 Maximum Duty Cycle 1510 G08 VC Pin Characteristic PROG Pin Characteristic –1.20 98 6 –1.08 97 –0.72 94 125°C IPROG (mA) –0.84 95 IVC (mA) DUTY CYCLE (%) –0.96 96 –0.60 –0.48 93 –0.36 92 –0.24 25°C 0 –0.12 91 0 90 0 20 40 60 80 100 120 140 TEMPERATURE (°C) 1510 G09 0.12 –6 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 VC (V) 1510 G10 0 1 2 3 VPROG (V) 4 5 1510 G11 5 LT1510/LT1510-5 U W TYPICAL PERFORMANCE CHARACTERISTICS Switch Current vs Boost Current vs Boost Voltage Reference Voltage vs Temperature 2.470 50 95 35 30 25 20 15 10 MAXIMUM DUTY CYCLE (%) 2.468 VBOOST = 38V 28V 18V 40 BOOST CURRENT (mA) 96 VCC = 16V REFERENCE VOLTAGE (V) 45 VBOOST vs Maximum Duty Cycle 2.466 2.464 2.462 2.460 5 0 94 93 92 91 90 89 88 87 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 SWITCH CURRENT (A) 2.458 0 25 1510 G07 50 75 100 TEMPERATURE (°C) 125 150 86 2 4 6 1510 G14 8 10 12 14 16 18 20 22 VBOOST (V) LT1510 • TPC15 U U U PIN FUNCTIONS GND: Ground Pin. BAT: Current Amplifier CA1 Input. SW: Switch Output. The Schottky catch diode must be placed with very short lead length in close proximity to SW pin and GND. PROG: 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. VCC: Supply for the Chip. For good bypass, a low ESR capacitor of 10µF or higher is required, with the lead length kept to a minimum. VCC should be between 8V and 28V and at least 2V higher than VBAT for VBAT less than 10V, and 2.5V higher than VBAT for VBAT greater than 10V. Undervoltage lockout starts and switching stops when VCC goes below 7V. Note that there is a parasitic diode inside from SW pin to VCC pin. Do not force VCC below SW by more than 0.7V with battery present. All VCC pins should be shorted together close to the pins. BOOST: 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, VBOOST = VCC + VBAT when switch is on. Maximum allowable VBOOST is 55V. SENSE: Current Amplifier CA1 Input. Sensing can be at either terminal of the battery. Note that current sense resistor RS1 (0.08Ω) is between Sense and BAT pins. 6 VC: This is the control signal of the inner loop of the current mode PWM. Switching starts at 0.7V and higher VC corresponds to higher charging current in normal operation. A capacitor of at least 0.1µF 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. OVP: This is the input to the amplifier VA with a threshold of 2.465V. Typical input current is about 50nA into pin. For charging lithium-ion batteries, VA monitors the battery voltage and reduces charging current when battery voltage reaches the preset value. If it is not used, the OVP pin should be grounded. LT1510/LT1510-5 W BLOCK DIAGRAM 200kHz OSCILLATOR + VCC SHUTDOWN 0.7V + – VSW BOOST S – VCC QSW R R + SW + – 1.5V SLOPE COMPENSATION PWM VBAT C1 B1 R2 + – + IPROG + GND R1 IPROG = 500µA/A 1k IBAT R3 RS1 – BAT + – VC SENSE IBAT CA1 CA2 + 60k 0VP VA gm = 0.64 VREF PROG RPROG CPROG IPROG Ω – VREF 2.465V CHARGING CURRENT IBAT = (IPROG)(2000) 1510 BD ( ) = 2.465V (2000) RPROG TEST CIRCUITS Test Circuit 1 LT1510 SENSE + – VC 60k RS1 – 1k + 0.047µF CA1 CA2 IBAT BAT + + 56µF VBAT VREF PROG 0.22µF 3.3k RPROG + LT1006 1k + LT1010 – 2N3055 1k ≈ 0.65V 20k 1510 TC01 7 LT1510/LT1510-5 TEST CIRCUITS Test Circuit 2 LT1510 OVP + VA – VREF PROG 10k IPROG 10k 0.47µF RPROG – + + LT1013 2.465V 1510 TC02 U OPERATIO The LT1510 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 RS1 to a much lower current IPROG (500µA/A) 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 charging, 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 (3µA typically) sleep mode as input drops down to 0.7V below battery voltage. To shut down the charger, simply pull the VC pin low with a transistor. U W U U APPLICATIONS INFORMATION Application Note 68, the LT1510 design manual, contains more in depth appications examples. Input and Output Capacitors In the chargers in Figures 1 and 2 on the first page of this data sheet, 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 8 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 capacitors 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 manufacturer before use. Alternatives include new high LT1510/LT1510-5 U W U U APPLICATIONS INFORMATION capacity ceramic capacitor (5µF to 10µF) 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. OS-CON can also be used. The output capacitor COUT is also assumed to absorb output switching current ripple. The general formula for capacitor current is: IRMS = V 0.29 VBAT 1 − BAT VCC ( ) (L1)(f) For example, with VCC = 16V, VBAT = 8.4V, L1 = 30µH and f = 200kHz, IRMS = 0.2A. 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 between the battery and the output capacitor depending on the ESR of the output capacitor and the battery impedance. If the ESR of COUT is 0.2Ω and the battery impedance is raised to 4Ω with a bead of inductor, only 5% of the current ripple will flow in the battery. 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 20W, a 24V adapter might be current limited at 1A. If adapter voltage is less than (20W/1A = 20V) when full power is drawn, the adapter voltage will be sucked down by the constant 20W load until it reaches a lower stable state where the switching regulators can no longer supply full load. This situation can be prevented by utilizing undevoltage 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. Internal lockout is performed by clamping the VC pin low. The VC pin is released from its clamped state when the VCC pin rises above 7V. The charger will start delivering current about 2ms after VC is released, as set by the 0.1µF at VC pin. Higher lockout voltage can be implemented with a Zener diode (see Figure 3 circuit). VIN VZ Soft Start The LT1510 is soft started by the 0.1µF capacitor on 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 0.1µF capacitor, time to reach full charge current is about 3ms and it is assumed that input voltage to the charger will reach full value in less than 3ms. Capacitance can be increased up to 0.47µF 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 computer 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 D1 1N4001 VCC VC 2k LT1510 GND 1510 F03 Figure 3. Undervoltage Lockout The lockout voltage will be VIN = VZ + 1V. For example, for a 24V adapter to start charging at 22VIN, choose VZ = 21V. When VIN is less than 22V, D1 keeps VC low and charger off. Charging Current Programming The basic formula for charging current is (see Block Diagram): 2.465V IBAT = IPROG 2000 = 2000 RPROG ( )( ) ( ) 9 LT1510/LT1510-5 U U W U APPLICATIONS INFORMATION where RPROG is the total resistance from PROG pin to ground. For example, 1A charging current is needed. RPROG = even this low current drain. A 47k resistor from adapter output to ground should be added if Q3 is used to ensure that the gate is pulled to ground. With divider current set at 25µA, R4 = 2.465/25µA = 100k and, (2.465V)(2000) = 4.93k 1A Charging current can also be programmed by pulse width modulating IPROG with a switch Q1 to RPROG at a frequency higher than a few kHz (Figure 4). Charging current will be proportional to the duty cycle of the switch with full current at 100% duty cycle. When a microprocessor DAC output is used to control charging current, it must be capable of sinking current at a compliance up to 2.5V if connected directly to the PROG pin. LT1510 PROG R3 = (R4)(V ) = 100k (8.4 − 2.465) 2.465 + R4(0.05µA) 2.465 + 100k (0.05µA) BAT − 2.465 = 240k Lithium-ion batteries typically require float voltage accuracy of 1% to 2%. Accuracy of the LT1510 OVP voltage is ±0.5% at 25°C and ±1% over full temperature. This leads to the possibility that very accurate (0.1%) resistors might be needed for R3 and R4. Actually, the temperature of the LT1510 will rarely exceed 50°C in float mode because charging currents have tapered off to a low level, so 0.25% resistors will normally provide the required level of overall accuracy. 300Ω External Shutdown RPROG 4.64k CPROG 1µF Lithium-Ion Charging The LT1510 can be externally shut down by pulling the VC pin low with an open drain MOSFET, such as VN2222. The VC pin should be pulled below 0.8V at room temperature to ensure shutdown. This threshold decreases at about 2mV/°C. A diode connected between the MOSFET drain and the VC pin will still ensure the shutdown state over all temperatures, but it results in slightly different conditions as outlined below. The circuit in Figure 2 uses the 16-pin LT1510 to charge lithium-ion batteries at a constant 1.3A until battery voltage reaches a limit set by R3 and R4. The charger will then automatically go into a constant-voltage mode with current decreasing to zero over time as the battery reaches full charge. This is the normal regimen for lithium-ion charging, with the charger holding the battery at “float” voltage indefinitely. In this case no external sensing of full charge is needed. If the VC pin is held below threshold, but above ≈ 0.4V, the current flowing into the BAT pin will remain at about 700µA. Pulling the VC pin below 0.4V will cause the current to drop to ≈ 200µA and reverse, flowing out of the BAT pin. Although these currents are low, the long term effect may need to be considered if the charger is held in a shutdown state for very long periods of time, with the charger input voltage remaining. Removing the charger input voltage causes all currents to drop to near zero. Current through the R3/R4 divider is set at a compromise value of 25µA to minimize battery drain when the charger is off and to avoid large errors due to the 50nA bias current of the OVP pin. Q3 can be added if it is desired to eliminate If it is acceptable to have 200µA flowing into the battery while the charger is in shutdown, simply pull the VC pin directly to ground with the external MOSFET. The resistor divider used to sense battery voltage will pull current out 5V 0V Q1 VN2222 PWM IBAT = (DC)(1A) 1510 F04 Figure 4. PWM Current Programming 10 LT1510/LT1510-5 U U W U APPLICATIONS INFORMATION of the battery, canceling part or all of the 200µA. Note that if net current is into the battery and the battery is removed, the charger output voltage will float high, to near input voltage. This could be a problem when reinserting the battery, if the resulting output capacitor/battery surge current is high enough to damage either the battery or the capacitor. If net current into the battery must be less than zero in shutdown, there are several options. Increasing divider current to 300µA - 400µA will ensure that net battery current is less than zero. For long term storage conditions however, the divider may need to be disconnected with a MOSFET switch as shown in Figures 2 and 5. A second option is to connect a 1N914 diode in series with the MOSFET drain. This will limit how far the VC pin will be pulled down, and current (≈ 700µA) will flow into the BAT pin, and therefore out of the battery. This is not usually a problem unless the charger will remain in the shutdown state with input power applied for very long periods of time. Removing input power to the charger will cause the BAT pin current to drop to near zero, with only the divider current remaining as a small drain on the battery. Even that current can be eliminated with a switch as shown in Figures 2 and 5. R3 12k LT1510 Q3 VN2222 – + R5 220k VIN OVP VBAT + – 4.2V period, after which the LT1510 can be shut down by pulling the VC pin low with an open collector or drain. Some external means must be used to detect the need for additional charging if needed, or the charger may be turned on periodically to complete a short float-voltage cycle. Current trip level is determined by the battery voltage, R1 through R3, and the internal LT1510 sense resistor (≈ 0.18Ω pin-to-pin). D2 generates hysteresis in the trip level to avoid multiple comparator transitions. Nickel-Cadmium and Nickel-Metal-Hydride Charging The circuit in Figure 6 uses the 8-pin LT1510 to charge NiCd or NiMH batteries up to 12V with charging currents of 0.5A when Q1 is on and 50mA when Q1 is off. D3 1N5819 C1 D1 0.22µF 1N5819 SW VCC + BOOST PROG L1** 33µH D2 1N914 WALL ADAPTER 1µF R1 100k 300Ω LT1510 GND CIN* 10µF 0.1µF VC R2 11k 1k Q1 VN2222 IBAT SENSE BAT * TOKIN OR MARCON CERAMIC SURFACE MOUNT ** COILTRONICS CTX33-2 + COUT 22µF TANT + 2V TO 20V ON: IBAT = 0.5A OFF: IBAT = 0.05A 1510 F05.5 Figure 6. Charging NiMH or NiCd Batteries (Efficiency at 0.5A ≈ 90%) 4.2V R4 4.99k 0.25% For a 2-level charger, R1 and R2 are found from: 1510 F05 Figure 5. Disconnecting Voltage Divider Some battery manufacturers recommend termination of constant-voltage float mode after charging current has dropped below a specified level (typically 50mA to 100mA) and a further time-out period of 30 minutes to 90 minutes has elapsed. This may extend the life of the battery, so check with manufacturers for details. The circuit in Figure 7 will detect when charging current has dropped below 75mA. This logic signal is used to initiate a time-out IBAT = R1 = (2000)(2.465) RPROG (2.465)(2000) ILOW R2 = (2.465)(2000 ) IHI − ILOW All battery chargers with fast-charge rates require some means to detect full charge state in the battery to terminate the high charging current. NiCd batteries are typically charged at high current until temperature rise or battery 11 LT1510/LT1510-5 U U W U APPLICATIONS INFORMATION BAT 0.18Ω INTERNAL SENSE RESISTOR LT1510 ADAPTER OUTPUT SENSE R1* 1.6k D1 1N4148 C1 0.1µF 3 2 R2 D2 560k 1N4148 R4 470k 8 – 7 LT1011 GND 3.3V OR 5V + NEGATIVE EDGE TO TIMER 4 1 R3 430k * TRIP CURRENT = R1(VBAT) (R2 + R3)(0.18Ω) 1510 F06 Figure 7. Current Comparator for Initiating Float Time-Out voltage decrease is detected as an indication of near full charge. The charging current is then reduced to a much lower value and maintained as a constant trickle charge. An intermediate “top off” current may be used for a fixed time period to reduce 100% charge time. NiMH batteries are similar in chemistry to NiCd but have two differences related to charging. First, the inflection characteristic in battery voltage as full charge is approached is not nearly as pronounced. This makes it more difficult to use dV/dt as an indicator of full charge, and change of temperature is more often used with a temperature sensor in the battery pack. Secondly, constant trickle charge may not be recommended. Instead, a moderate level of current is used on a pulse basis (≈ 1% to 5% duty cycle) with the time-averaged value substituting for a constant low trickle. battery and 1.1A for a 4.2V battery. This assumes a 60°C maximum ambient temperature. The 16-pin SO, with a thermal resistance of 50°C/W, can provide a full 1.5A charging current in many situations. The 16-pin PDIP falls between these extremes. Graphs are shown in the Typical Performance Characteristics section. ( )( ) ( ) (V ) 7.5mA + (0.012)(I ) + PBIAS = 3.5mA VIN + 1.5mA VBAT 2 BAT VIN [ BAT 2 ] (I )(V ) 1+ V30 = 55(V ) (I ) (R )(V ) + (t )(V )(I )(f) = V = (0.18Ω)(I ) BAT BAT BAT PDRIVER IN 2 Thermal Calculations If the LT1510 is used for charging currents above 0.4A, a thermal calculation should be done to ensure that junction temperature will not exceed 125°C. Power dissipation in the IC is caused by bias and driver current, switch resistance, switch transition losses and the current sense resistor. The following equations show that maximum practical charging current for the 8-pin SO package (125° C/W thermal resistance) is about 0.8A for an 8.4V 12 PSW BAT SW BAT OL IN IN PSENSE 2 BAT RSW = Switch ON resistance ≈ 0.35Ω tOL = Effective switch overlap time ≈ 10ns f = 200kHz (500kHz for LT1510-5) BAT LT1510/LT1510-5 U U W U APPLICATIONS INFORMATION Example: VIN = 15V, VBAT = 8.4V, IBAT = 1.2A; ( )( ) ( ) PDRIVER 0.045W = = 14mA VX 3.3V Total board area becomes an important factor when the area of the board drops below about 20 square inches. The graph in Figure 9 shows thermal resistance vs board area for 2-layer and 4-layer boards. Note that 4-layer boards have significantly lower thermal resistance, but both types show a rapid increase for reduced board areas. Figure 10 shows actual measured lead temperature for chargers operating at full current. Battery voltage and input voltage will affect device power dissipation, so the data sheet power calculations must be used to extrapolate these readings to other situations. PBIAS = 3.5mA 15 + 1.5mA 8.4 (8.4) + 2 15 [7.5mA + (0.012)(1.2)] = 0.17W 2 (1.2)(8.4) 1+ 830.4 = = 0.13W 55(15) 2 1.2) (0.35)(8.4) ( = + PDRIVER PSW 15 ( )( )( 10 • 10 −9 15 1. 2 200kHz = 0.28 + 0.04 = 0.32W ( )( ) PSENSE = 0.18 1.2 2 The average IVX required is: ) Vias should be used to connect board layers together. Planes under the charger area can be cut away from the rest of the board and connected with vias to form both a = 0.26W Total power in the IC is: SW 0.17 + 0.13 + 0.32+ 0.26 = 0.88W D2 SENSE VX ( )( )( ) = 55(V ) IN For example, VX = 3.3V, PDRIVER 3.3V 1.2A 8.4V 3.3V 1 + 30 ( )( )( ) = 55 (15V) 10µF Figure 8 60 THERMAL RESISTANCE (°C/W) PDRIVER V VX 1 + X 30 1510 F07 + IVX The PDRIVER term can be reduced by connecting the boost diode D2 (see Figures 2 and 6 circuits) to a lower system voltage (lower than VBAT) instead of VBAT (see Figure 8). Then, BOOST L1 Temperature rise will be (0.88W)(50°C/W) = 44°C. This assumes that the LT1510 is properly heat sunk by connecting the four fused ground pins to the expanded traces and that the PC board has a backside or internal plane for heat spreading. IBAT VBAT LT1510 C1 55 50 2-LAYER BOARD 45 4-LAYER BOARD 40 35 S16, MEASURED FROM AIR AMBIENT TO DIE USING COPPER LANDS AS SHOWN ON DATA SHEET 30 25 0 = 0.045W 5 20 15 25 10 BOARD AREA (IN2) 30 35 1510 F08 Figure 9. LT1510 Thermal Resistance 13 LT1510/LT1510-5 U W U U APPLICATIONS INFORMATION 90 LEAD TEMPERATURE (°C) event of an input short. The body diode of Q2 creates the necessary pumping action to keep the gate of Q1 low during normal operation (see Figure 11). NOTE: PEAK DIE TEMPERATURE WILL BE ABOUT 10°C HIGHER THAN LEAD TEMPERATURE AT 1.3A CHARGING CURRENT 80 70 2-LAYER BOARD Q1 60 VIN + 4-LAYER BOARD 50 VCC ICHRG = 1.3A VIN = 16V VBAT = 8.4V VBOOST = VBAT TA = 25°C 40 30 20 0 5 20 15 25 10 BOARD AREA (IN2) SW Q2 D1 BOOST L1 D2 30 35 SENSE VX 3V TO 6V 1510 F09 Figure 10. LT1510 Lead temperature Q1: Si4435DY Q2: TP0610L low thermal resistance system and to act as a ground plane for reduced EMI. Maximum duty cycle for the LT1510 is typically 90% but this may be too low for some applications. For example, if an 18V ±3% adapter is used to charge ten NiMH cells, the charger must put out 15V maximum. A total of 1.6V is lost in the input diode, switch resistance, inductor resistance and parasitics so the required duty cycle is 15/16.4 = 91.4%. As it turns out, duty cycle can be extended to 93% by restricting boost voltage to 5V instead of using VBAT as is normally done. This lower boost voltage VX (see Figure 8) also reduces power dissipation in the LT1510, so it is a win-win decision. Even Lower Dropout For even lower dropout and/or reducing heat on the board, the input diode D3 (Figures 2 and 6) should be replaced with a FET. It is pretty straightforward to connect a P-channel FET across the input diode and connect its gate to the battery so that the FET commutates off when the input goes low. The problem is that the gate must be pumped low so that the FET is fully turned on even when the input is only a volt or two above the battery voltage. Also there is a turn off speed issue. The FET should turn off instantly when the input is dead shorted to avoid large current surges form the battery back through the charger into the FET. Gate capacitance slows turn off, so a small P-FET (Q2) discharges the gate capacitance quickly in the BAT CX 10µF VBAT + HIGH DUTY CYCLE CONNECTION 1510 F10 Figure 11. Replacing the Input Diode Higher Duty Cycle for the LT1510 Battery Charger 14 LT1510 C3 RX 50k Layout Considerations Switch rise and fall times are under 10ns for maximum efficiency. To prevent radiation, the catch diode, SW pin and input bypass capacitor leads should be kept as short as possible. A ground plane should be used under the switching circuitry to prevent interplane coupling and to act as a thermal spreading path. All ground pins should be connected to expand traces for low thermal resistance. The fast-switching high current ground path including the switch, catch diode and input capacitor should be kept very short. Catch diode and input capacitor should be close to the chip and terminated to the same point. This path contains nanosecond rise and fall times with several amps of current. The other paths contain only DC and /or 200kHz triwave and are less critical. Figure 13 shows critical path layout. Figure 12 indicates the high speed, high current switching path. SWITCH NODE L1 VBAT VIN CIN HIGH FREQUENCY CIRCULATING PATH COUT BAT 1510 F12 Figure 12. High Speed Switching Path LT1510/LT1510-5 U U W U APPLICATIONS INFORMATION GND LT1510 D1 GND GND SW VCC2 BOOST VCC1 GND PROG OVP L1 CIN VC SENSE BAT GND GND GND GND 1510 F11 Figure 13. Critical Electrical and Thermal Path Layer U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. GN Package 16-Lead Plastic SSOP (Narrow 0.150) (LTC DWG # 05-08-1641) 0.015 ± 0.004 × 45° (0.38 ± 0.10) 0.0075 – 0.0098 (0.191 – 0.249) 0.053 – 0.069 (1.351 – 1.748) 0.004 – 0.009 (0.102 – 0.249) 0° – 8° TYP 0.016 – 0.050 (0.406 – 1.270) 16 15 14 13 12 11 10 9 0.229 – 0.244 (5.817 – 6.198) 0.025 (0.635) BSC 0.008 – 0.012 (0.203 – 0.305) 0.189 – 0.196* (4.801 – 4.978) 0.150 – 0.157** (3.810 – 3.988) 1 2 3 4 5 6 8 7 * DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE ** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE GN16 (SSOP) 0895 N Package 16-Lead PDIP (Narrow 0.300) (LTC DWG # 05-08-1510) 0.130 ± 0.005 (3.302 ± 0.127) 0.300 – 0.325 (7.620 – 8.255) 0.015 (0.381) MIN 0.009 – 0.015 (0.229 – 0.381) ( +0.025 0.325 –0.015 +0.635 8.255 –0.381 ) 0.770* (19.558) MAX 0.045 – 0.065 (1.143 – 1.651) 0.065 (1.651) TYP 0.125 (3.175) MIN 0.005 (0.127) MIN 0.100 ± 0.010 (2.540 ± 0.254) 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 0.255 ± 0.015* (6.477 ± 0.381) 0.018 ± 0.003 (0.457 ± 0.076) *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm) S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 0°– 8° TYP 0.016 – 0.050 0.406 – 1.270 0.014 – 0.019 (0.355 – 0.483) N16 0695 0.189 – 0.197* (4.801 – 5.004) 8 7 6 5 0.228 – 0.244 (5.791 – 6.197) 0.150 – 0.157** (3.810 – 3.988) 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) BSC *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 1 2 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. 3 4 SO8 0695 15 LT1510/LT1510-5 U TYPICAL APPLICATION Adjustable Voltage Regulator with Precision Adjustable Current Limit 0.22µF LT1510 1N5819 SW VCC2 VIN 18V TO 25V + 100µF VCC1 PROG BOOST RPROG 4.93k 1k 30µH 0.01µF VC GND 1N914 0.1µF OVP SENSE BAT POT 5k CURRENT LIMIT LEVEL = ( ) 2.465V (2000) RPROG + 500µF POT 100k VOUT 2.5V TO 15V CURRENT LIMIT LEVEL 50mA TO 1A 1µF 1k 1510 TA01 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. S Package 16-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.386 – 0.394* (9.804 – 10.008) 16 0.008 – 0.010 (0.203 – 0.254) 0.014 – 0.019 (0.355 – 0.483) 13 12 11 10 9 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 0° – 8° TYP 0.016 – 0.050 0.406 – 1.270 14 0.004 – 0.010 (0.101 – 0.254) 0.053 – 0.069 (1.346 – 1.752) 0.010 – 0.020 × 45° (0.254 – 0.508) 15 0.050 (1.270) TYP 1 2 3 4 5 6 7 8 S16 0695 *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC 1325 Microprocessor-Controlled Battery Management System Can Charge, Discharge and Gas Gauge NiCd, NiMH and Pb-Acid Batteries with Software Charging Profiles LT1372/LT1377 500kHz/1MHz Step-Up Switching Regulators High Frequency, Small Inductor, High Efficiency Switchers, 1.5A Switch LT1373 250kHz Step-Up Switching Regulator High Efficiency, Low Quiescent Current, 1.5A Switch LT1376 500kHz Step-Down Switching Regulator High Frequency, Small Inductor, High Efficiency Switcher, 1.5A Switch LT1511 3A Constant-Voltage/Constant-Current Battery Charger High Efficiency, Minimal External Components to Fast Charge Lithium, NiMH and NiCd Batteries LT1512 SEPIC Battery Charger VIN Can Be Higher or Lower Than Battery Voltage ® 16 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 ● (408) 432-1900 FAX: (408) 434-0507● TELEX: 499-3977 ● www.linear-tech.com 1510fc LT/GP 1197 REV C 4K • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 1995