LT3651-8.2/LT3651-8.4 Monolithic 4A High Voltage 2-Cell Li-Ion Battery Charger FEATURES DESCRIPTION Wide Input Voltage Range: 9V to 32V (40V Absolute Maximum) n Programmable Charge Current Up to 4A n Selectable C/10 or Onboard Timer Termination n Dynamic Charge Rate Programming/Soft-Start n Programmable Input Current Limit n±0.5% Float Voltage Accuracy n±7.5% Charge Current Accuracy n±4% C/10 Detection Accuracy n NTC Resistor Temperature Monitor n Auto-Recharge at 97.5% Float Voltage n Auto-Precondition at <70% Float Voltage n Bad Battery Detection with Auto-Reset n Average Current Mode, Synchronous Switcher n User Programmable Frequency n Low Profile (0.75mm) 5mm × 6mm 36-Lead QFN Package The LT®3651-8.2/LT3651-8.4 are 2-cell, 4A Li-Ion/Polymer battery chargers that operate over a 9V to 32V input voltage range. An efficient monolithic average current mode synchronous switching regulator provides constant current, constant voltage charging with programmable maximum charge current. A charging cycle starts with battery insertion or when the battery voltage drops 2.5% below the float voltage. Charger termination is selectable as either charge current or internal safety timer timeout. Charge current termination occurs when the charge current falls to one-tenth the programmed maximum current (C/10). Timer based termination is typically set to three hours and is user programmable (charging continues below C/10 until timeout). Once charging is terminated, the LT3651-8.2/LT3651-8.4 supply current drops to 85µA into a standby mode. n The LT3651-8.2/LT3651-8.4 offer several safety features. A discharged battery is preconditioned with a small trickle charge and generates a signal if unresponsive. A thermistor monitors battery temperature, halting charging if out of range. Excessive die temperature reduces charge current. Charge current is also reduced to maintain constant input current to prevent excessive input loading. APPLICATIONS Industrial Handheld Instruments 12V to 24V Automotive and Heavy Equipment n Desktop Cradle Chargers n Notebook Computers n n L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. The LT3651-8.2/LT3651-8.4 are available in a 5mm × 6mm 36-lead QFN package. TYPICAL APPLICATION 9V to 32V 2-Cell 4A Charger Si7611DN 100k 10V CLN LT3651-8.2/LT3651-8.4 ACPR BOOST FAULT CHRG SENSE BAT NTC TIMER ILIM RNG/SS GND 89 1µF CMPSH1-4 RT 301k 22µF VIN SW VBAT = 7.8V IBAT = 4A 10µH TDK SLP12575T-100M5R4 100µF 365188284 TA01a 5.5 5.0 87 4.5 POWER LOSS 86 2-CELL Li-Ion BATTERY EFFICIENCY 88 24mΩ + 6.0 85 10 15 20 VIN (V) 25 POWER LOSS (W) 10k CLP SHDN TO SYSTEM LOAD EFFICIENCY (%) VIN 9V TO 32V Efficiency, Power Loss vs VIN 90 4.0 3.5 30 1635 G07 36518284f 1 LT3651-8.2/LT3651-8.4 CLP CLN GND VIN VIN VIN RNG/SS TOP VIEW 36 35 34 33 32 31 30 29 NTC 1 28 ILIM 27 SHDN ACPR 2 BAT 3 26 CHRG 37 GND SENSE 4 25 FAULT 24 TIMER BOOST 5 23 GND GND 6 22 SW SW 7 38 SW NC 8 NC 9 21 NC 20 NC 19 NC NC 10 SW SW SW SW SW SW 11 12 13 14 15 16 17 18 SW VIN ........................................................................... 40V CLN, CLP, SHDN, CHRG, FAULT, ACPR ................................ VIN + 0.5V Up to 40V CLP – CLN..............................................................±0.5V SW ............................................................................40V SW – VIN...................................................................4.5V BOOST ........................................... SW + 10V Up to 50V SENSE, BAT ............................................................. 10V SENSE-BAT .............................................. –0.5V to 0.5V TIMER, RNG/SS, ILIM, NTC, RT ............................... 2.5V Operating Junction Temperature Range (Notes 2, 3)................................................. –40 to 125°C Storage Temperature Range.......................–65 to 150°C PIN CONFIGURATION RT (Note 1) SW ABSOLUTE MAXIMUM RATINGS UHE PACKAGE 36-LEAD (5mm × 6mm) PLASTIC QFN TJMAX = 125°C, θJA = 43°C/W EXPOSED PAD (PIN 37) IS GND, MUST BE SOLDERED TO PCB EXPOSED PAD (PIN 38) IS SW, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3651EUHE-8.2#PBF LT3651EUHE-8.2#TRPBF 365182 36-Lead (5mm × 6mm) Plastic QFN –40°C to 125°C LT3651IUHE-8.2#PBF LT3651IUHE-8.2#TRPBF 365182 36-Lead (5mm × 6mm) Plastic QFN –40°C to 125°C LT3651EUHE-8.4#PBF LT3651EUHE-8.4#TRPBF 365184 36-Lead (5mm × 6mm) Plastic QFN –40°C to 125°C LT3651IUHE-8.4#PBF LT3651IUHE-8.4#TRPBF 365184 36-Lead (5mm × 6mm) Plastic QFN –40°C to 125°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.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/ 36518284f 2 LT3651-8.2/LT3651-8.4 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = 20V, SHDN = 2V, SENSE = BAT = VBAT(FLT), CTIMER = 0.68µF, RT = 50k, CLP = CLN = VIN, BOOST – SW = 4V. PARAMETER CONDITIONS VIN Operating Range VIN OVLO Threshold MIN l VIN Rising 9.0 32 VIN OVLO Hysteresis VIN UVLO Threshold 35 MAX VIN Rising 8.7 l V 40 V V 9.0 0.2 LT3651-8.2 UNITS 32 1.1 VIN UVLO Hysteresis Battery Float Voltage, VBAT(FLT) TYP V V 8.16 8.12 8.2 l 8.24 8.28 V V 8.36 8.32 8.4 l 8.44 8.48 V V LT3651-8.4 Battery Recharge Voltage Hysteresis Threshold Voltage Relative to VBAT(FLT) –200 mV Battery Precondition Threshold Voltage, VBAT(PRE) LT3651-8.2, VBAT Rising LT3651-8.4, VBAT Rising 5.65 5.80 V V Battery Precondition Threshold Hysteresis Threshold Voltage Relative to VBAT(PRE) 90 mV Operating VIN Supply Current CC/CV Mode, Top Switch On, ISW = 0 Standby Mode Shutdown (SHDN = 0) 8.6 80 17 mA µA µA Top Switch On Voltage VIN – VSW , ISW = 4A 480 mV Bottom Switch On Voltage VSW , ISW = 4A –140 mV BOOST Supply Current Switch High, ISW = 0, 2.5V < (VBOOST – VSW) < 8.5V 40 mA BOOST Switch Drive IBOOST/ISW , ISW = 4A 25 mA/A Precondition Current Sense Voltage VSENSE – VBAT , VBAT = 5.0V Input Current Limit Voltage VCLP – VCLN, ILIM Open 14 l 70 CLP Input Bias Current 95 mV 115 120 CLN Input Bias Current nA 36 ILIM Bias Current l 43 50 mV µA 57 11.5 µA System Current Limit Programming Gain VILIM/(VCLP – VCLN), VILIM = 0.5V Maximum Charge Current Sense Voltage VSENSE – VBAT , VBAT = 7.5V, VRNG/SS > 1.1V l 88 95 103 V/V mV C/10 Trigger Sense Voltage VSENSE – VBAT l 4.5 8.6 12.3 mV BAT Input Bias Current Charging Terminated 0.1 1 µA SENSE Input Bias Current Charging Terminated 0.1 1 µA l 44 50 56 µA Charge Current Limit Programming Gain VRNG/SS/(VSENSE – VBAT), VRNG/SS = 0.5V l 8.5 10.8 12.5 V/V NTC Range Limit (High) VNTC Rising l 1.25 1.36 1.45 V NTC Range Limit (Low) VNTC Falling l 0.27 0.29 0.31 NTC Threshold Hysteresis % of Threshold NTC Disable Impedance Minimum External Impedance to GND l 150 NTC Bias Current VNTC = 0.75V l 46.5 50 53.5 µA Shutdown Threshold VSHDN Rising l 1.15 1.20 1.23 V RNG/SS Bias Current V 10 % 470 kΩ Shutdown Hysteresis 95 mV SHDN Input Bias Current –10 nA Status Low Voltage VCHRG, VFAULT , VACPR, Load = 10mA l 0.45 V 36518284f 3 LT3651-8.2/LT3651-8.4 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = 20V, SHDN = 2V, SENSE = BAT = VBAT(FLT), CTIMER = 0.68µF, RT = 50k, CLP = CLN = VIN, BOOST – SW = 4V. PARAMETER CONDITIONS MIN TYP 25 µA 0.1 0.25 V TIMER Charge/Discharge Current TIMER Disable Threshold l Full Charge Cycle Time-Out 3 Precondition Timeout l RT = 50kΩ RT = 250kΩ Minimum SW On-Time, tON(MIN) Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LT3651-8.2/LT3651-8.4 are tested under pulse loaded conditions such that TJ = TA. The LT3651-8.2E/LT3651-8.4E are guaranteed to meet performance specifications from 0°C to 85°C junction temperature. Specifications over the –40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The LT3651-8.2I/LT3651-8.4I are guaranteed over the full –40°C to 125°C operating junction temperature range. The junction temperature (TJ in °C) is calculated from the ambient temperature (TA in °C) and power dissipation (PD in Watts) according to the formula: TJ = TA + PD • θJA where θJA (in °C/W) is the package thermal impedance. –13 UNITS Hour 22.5 Timer Accuracy Switcher Operating Frequency, fO MAX Minute 13 % 1.1 250 MHz kHz 150 ns Note 3: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. The maximum rated junction temperature will be exceeded when this protection is active. Continuous operation above the specified absolute maximum operating junction temperature may impair device reliability or permanently damage the device. 36518284f 4 LT3651-8.2/LT3651-8.4 TYPICAL PERFORMANCE CHARACTERISTICS Battery Float Voltage vs Temperature IVIN (µA) ∆VBAT(FLT) (%) 0.5 0 –0.5 –25 25 50 75 0 TEMPERATURE (°C) 100 100 150 95 100 90 50 85 0 CURRENT (µA) 1.0 –1.0 –50 SENSE and BAT Pin Currents vs BAT Voltage (VSENSE = VBAT) VIN Standby Mode Current vs Temperature 80 75 70 –150 60 –250 55 –300 25 50 0 TEMPERATURE (°C) 75 36518284 G01 –350 100 IBAT –50 –200 –25 ISENSE –100 65 50 –50 125 LT3651-8.4 0 1 2 3 5 4 VBAT (V) 6 Maximum Charge Current vs VRNG/SS as a Percentage of Programmed IIN(MAX) 9 ICHG Current Limit (VSENSE – VBAT) vs Temperature 120 11 8 36518284 G03 36518284 G02 C/10 Threshold (VSENSE – VBAT) vs Temperature 7 101.0 100 9 VSENSE – VBAT (mV) ICHG(MAX) (%) 100.5 80 100.0 60 40 8 99.5 20 –25 75 0 25 50 TEMPERATURE (°C) 100 0 125 0 0.2 0.4 0.6 0.8 1.0 Charge Current vs VBAT as a Percentage of Programmed ICHG(MAX) 100 80 80 60 125 36518284 G06 60 40 40 20 20 6 100 120 LT3651-8.4 5 75 0 25 50 TEMPERATURE (°C) Maximum Input Current vs VILIM as a Percentage of Programmed IIN(MAX) 100 0 –25 36518284 G05 36518284 G04 120 99.0 –50 1.2 VRNG/SS (V) IIN(MAX) (%) 7 –50 ICHG (%) VSENSE – VBAT (mV) 10 7 8 9 VBAT (V) 36518284 G07 0 0 0.2 0.4 0.6 0.8 VILIM (V) 1.0 1.2 36518284 G08 36518284f 5 LT3651-8.2/LT3651-8.4 TYPICAL PERFORMANCE CHARACTERISTICS Topside Switch VON vs Temperature Input Current Limit Voltage Threshold vs Temperature 2.0 700 –50 ISW = 4A –100 RILIM OPEN RILIM = 10k 0 –0.5 600 VSW (mV) 0.5 550 –200 450 –1.5 –2.0 –50 –25 75 50 25 TEMPERATURE (°C) 0 100 400 –50 –25 125 50 25 75 0 TEMPERATURE (˚C) 100 36518284 G09 –250 –50 60 100 125 40 30 50 40 30 20 10 2.5 3.5 5.5 6.5 4.5 VBST – VIN (V) 10 7.5 0 1 2 3 4 5 ISW (A) 36518284 G14 36518284 G13 26518284 G12 Oscillator Frequency vs Temperature 1.0 125 60 20 75 0 25 50 TEMPERATURE (°C) 100 70 ISW = 4A IBST/ISW (mA/A) IBST/ISW (mA/A) 20 –25 75 0 25 50 TEMPERATURE (°C) Boost Switch Drive vs Switch Current 50 30 25 –25 26518284 G11 Boost Drive vs Boost Voltage ISW = 4A VBST – VIN = 4V 15 –50 125 36518284 G10 Switch Drive (IBST/ISW) vs Temperature IBST/ISW (mA/A) –150 500 –1.0 35 ISW = 4A 650 1.0 VIN – VSW (mV) ∆(VCLP – VCLN) (mV) 1.5 Bottom Side Switch VON vs Temperature Timer Resistor (RT) vs Period and Frequency 400 RT = 54.9k 300 RT (kΩ) FREQUENCY DEVIATION (%) 350 0.5 0 250 200 150 –0.5 100 –1.0 –50 –25 75 0 25 50 TEMPERATURE (°C) 100 125 26518284 G15 50 1 1000 2 500 3 4 333 250 PERIOD (µs) FREQUENCY (kHz) 5 200 6 167 36518284 G16 36518284f 6 LT3651-8.2/LT3651-8.4 PIN FUNCTIONS NTC (Pin 1): Battery Temperature Monitor Pin. This pin is used to monitor battery temperature. Typically a 10kΩ NTC (negative temperature coefficient) thermistor (B = 3380) is embedded with the battery and connected from the NTC pin to ground. The pin sources 50µA into the resistor and monitors the voltage across the thermistor, regulating charging based on the voltage. If this function is not desired, leave the NTC pin unconnected. ACPR (Pin 2): Open-Collector AC Present Status Pin. This pin sinks current to indicate that VIN is valid and the charger is on. Typically a resistor pull-up is used on this pin. This pin can be pulled up to voltages as high as VIN when disabled, and can sink currents up to 10mA when enabled. BAT (Pin 3): Battery Voltage Monitor Pin. This pin monitors battery voltage. A Kelvin connection is made to the battery from this pin and a decoupling capacitor (CBAT) is placed from this pin to ground. The charge function operates to achieve the final float voltage at this pin. The auto-restart feature initiates a new charging cycle when the voltage at the BAT pin falls 2.5% below this float voltage. Once the charge cycle is terminated, the input bias current of the BAT pin is reduced to <0.1µA to minimize battery discharge while the charger remains connected. SENSE (Pin 4): Charge Current Sense Pin. The charge current is monitored with a sense resistor (RSENSE) connected between this pin and the BAT pin. The inductor current flows through RSENSE to the battery. The voltage across this resistor sets the average charge current. The maximum average charge current (IMAX) corresponds to 95mV across the sense resistor. BOOST (Pin 5): Bootstrapped Supply Rail for Switch Drive. This pin facilitates saturation of the high side switch transistor. Connect a 1µF or greater capacitor from the BOOST pin to the SW pin. The operating range of this pin is 0V to 8.5V, referenced to the SW pin when the switch is high. The voltage on the decoupling capacitor is refreshed through a rectifying diode, with the anode connected to either the battery output voltage or an external source, and the cathode connected to the BOOST pin. GND (Pins 6, 23, 31, 37): Ground. These pins are the ground pins for the part. Pins 31, 34 and 37 must be connected together. Pins 6 and 23 are connected via the leadframe to the exposed backside Pin 37. Solder the exposed backside to the PCB for good thermal and electrical connection. SW (Pins 7, 11-18, 22, 38): Switch Output Pin. These pins are the output of the charger switches. An inductor is connected between these pins and the SENSE pin. When the switcher is active, the inductor is charged by the high side switch from VIN and discharged by the bottom side switch to GND. Solder the exposed backside, Pin 38, to the PCB for good thermal connection. NC (Pins 8-10,19-21): No Connect. These pins can be left floating (not connected). TIMER (Pin 24): End-Of-Cycle Timer Programming Pin. A capacitor on this pin to ground determines the full charge end-of-cycle time. Full charge end-of-cycle time is programmed with this capacitor. A 3 hour charge cycle is obtained with a 0.68µF capacitor. This timer also controls the bad battery fault that is generated if the battery does not reach the precondition threshold voltage within one-eighth of a full cycle (22.5 minutes for a 3 hour charge cycle). The timer based termination is disabled by connecting the TIMER pin to ground. With the timer function disabled, charging terminates when the charge current drops below a C/10 rate, or approximately 10% of maximum charge rate. FAULT (Pin 25): Open-Collector Fault Status Output. This pin indicates charge cycle fault conditions during a battery charging cycle. Typically a resistor pull-up is used on this pin. This status pin can be pulled up to voltages as high as VIN when disabled, and can sink currents up to 10mA when enabled. A temperature fault causes this pin to be pulled low. If the internal timer is used for termination, a bad battery fault also causes this pin to be pulled low. If no fault conditions exist, the FAULT pin remains high impedance. CHRG (Pin 26): Open-Collector Charger Status Output. 36518284f 7 LT3651-8.2/LT3651-8.4 PIN FUNCTIONS This pin indicates the battery charging status. Typically a resistor pull-up is used on this pin. This status pin can be pulled up to voltages as high as VIN when disabled, and can sink currents up to 10mA when enabled. CHRG is pulled low during a battery charging cycle. When the charge cycle is terminated, the CHRG pin becomes high impedance. If the internal timer is used for termination, the pin stays low during the charging cycle until the charge current drops below a C/10 rate, or approximately 10% of the maximum charge current. A temperature fault also causes this pin to be pulled low. SHDN (Pin 27): Shutdown Pin. This pin can be used for precision UVLO functions. When this pin rises above the 1.20V threshold, the part is enabled. The pin has 95mV of voltage hysteresis. When in shutdown mode, all charging functions are disabled. When the SHDN pin is pulled below 0.4V, the IC enters a low current shutdown mode where the VIN pin current is reduced to 17µA. Typical SHDN pin input bias current is 10nA. Connect the pin to VIN if the shutdown function is not desired. ILIM (Pin 28): Input Current Limit Programming. This pin allows for setting and dynamic adjustment of the system input current limit, and can be used to employ a soft-start function. The voltage on this pin sets the maximum input current by setting the maximum voltage across the input current sense resistor, placed between CLP and CLN. The effective range on the pin is 0V to 1V. 50µA is sourced from this pin usually to a resistor (RILIM) to ground. VIILIM represents approximately 11 times the maximum voltage across the input current sense resistor. If no RILIM is used the part will default to maximum input current. Soft-start functionality for input current can be implemented with a capacitor (CILIM) from ILIM to ground. The soft-start capacitor and the programming resistor can be implemented in parallel. CLP/CLN (Pin 29/Pin 30): System Current Limit Positive and Negative Input. System current levels are monitored by connecting a sense resistor from the input power supply to the CLP pin, connecting a sense resistor from the CLP pin to the CLN pin and then connecting CLN to VIN. The system load is then delivered from the CLN pin. The LT3651-8.2/LT3651-8.4 servo the maximum charge current required to maintain programmed maximum system current. The system current limit is set as a function of the voltage on the ILIM pin and the input current sense resistor. This function is disabled by shorting CLP, CLN and VIN together. VIN (Pins 32, 33, 34): Charger Input Supply. These pins provide power for the LT3651-8.2/LT3651-8.4. Charge current for the battery flows into these pins. IVIN is less than 100µA after charge termination. Connect the pins together. RNG/SS (Pin 35): Charge Current Range and Soft-Start Pin. This pin allows for setting and dynamic adjustment of the maximum charge current, and can be used to employ a soft-start function. The voltage on this pin sets the maximum charge current by setting the maximum voltage across the charge current sense resistor, RSENSE , placed between SENSE and BAT. The effective range on the pin is 0V to 1V. 50µA is sourced from this pin usually to a resistor (RRNG/SS) to ground. VRNG/SS represents approximately 10 times the maximum voltage across the charge current sense resistor. If no RRNG/ SS is used the part will default to maximum charge current. Soft-start functionality for charge current can be implemented by connecting a capacitor (CRNG/SS) from RNG/SS to ground. The soft-start capacitor and the programming resistor can be implemented in parallel. The RNG/SS pin is pulled low during fault conditions, allowing graceful recovery from faults if CRNG/SS is used. RT (Pin 36): Switcher Oscillator Timer Set Pin. A resistor from this pin to ground sets the switcher oscillator frequency. Typically this is 54.9k for fOSC = 1MHz. 36518284f 8 LT3651-8.2/LT3651-8.4 BLOCK DIAGRAM A12 RT TIMER OSC + – A11 + – COUNT RESET COUNT VC TJ A9 0.3V REV CUR INHIBIT C-EA SENSE RS – + + BAT ITH RNG/SS 10RS A8 0.1V + + 0.15V A7 PRECONDITION NTC VINT 2.7V A6 ×2.25 0.29V A1 STANDBY A4 A2 1.3V + – + + + 1.2V 8.2V* 8.0V** 5.65V† SHDN 27 TERMINATE ACPR A3 – + 1 NTC – + 35 50µA 1V 50µA 1.36V 3 SS/RESET C/10 + – 4 V-EA TERMINATE SS/RESET STATUS FAULT RS + – CHRG VIN 125°C STANDBY COUNT RESET MODE ENABLE (TIMER OR C/10) CONTROL LOGIC SW 7, 11-18, 22, 38 A14 + – 25 + A10 RIPPLE COUNTER 26 A13 35V OSC 0.2V TIMER + – 24 R LATCH S Q 5 VIN 32, 33, 34 + – 36 + – CLP + – + – 29 + CLN 8.7V OVLO + – 30 ILIM BOOST – + 28 UVLO + – STANDBY 50µA 2.4V + – A5 2 0.7V 46µA GND *VBAT(FLT): 8.2V FOR LT3651-8.2, 8.4V FOR LT3651-8.4 **VBAT(FLT) – ∆VRECHRG: 8V FOR LT3651-8.2, 8.2V FOR LT3651-8.4 †V BAT(PRE): 5.65V FOR LT3651-8.2, 5.8V FOR LT3651-8.4 6, 23, 31, 37 365148284 BD 36518284f 9 LT3651-8.2/LT3651-8.4 OPERATION Overview The LT3651-8.2/LT3651-8.4 are complete Li-Ion battery chargers, addressing wide input voltage and high currents (up to 4A). High charging efficiency is produced with a constant frequency, average current mode synchronous step-down switcher architecture. The charger includes the necessary circuitry to allow for programming and control of constant current, constant voltage (CC/CV) charging with both current only and timer termination. High charging efficiency is achieved by the switcher by using a bootstrapped supply for low switch drop for the high side driver and a MOSFET for the low side (synchronous) switch. Maximum charge current is set with an external sense resistor in series with the inductor and is adjustable through the RNG/SS pin. Total system input current is monitored with an input sense resistor and is used to maintain constant input current by regulating battery charge current. It is adjustable through the ILIM pin. If the battery voltage is low, charge current is automatically reduced to 15% of the programmed current to provide safe battery preconditioning. Once the battery voltage climbs above the battery precondition threshold, the IC automatically increases the maximum charge current to the full programmed value. Charge termination can occur when charge current decreases to one-tenth the programmed maximum charge current (C/10 termination). Alternately, termination can be time based through the use of an internal programmable charge cycle control timer. When using the timer termination, charging continues beyond the C/10 level to “top-off” a battery. Charging typically terminates three hours after initiation. When the timer-based scheme is used, bad battery detection is also supported. A system fault is triggered if a battery stays in precondition mode for more than one-eighth of the total charge cycle time. Once charging is terminated and the LT3651-8.2/ LT3651‑8.4 are not actively charging, the IC automatically enters a low current standby mode in which supply bias currents are reduced to <85µA. If the battery voltage drops 2.5% from the full charge float voltage, the LT3651-8.2/ LT3651-8.4 engage an automatic charge cycle restart. The IC also automatically restarts a new charge cycle after a bad battery fault once the failed battery is removed and replaced with another battery. After charging is completed the input bias currents on the pins connecting to the battery are reduced to minimize battery discharge. The LT3651-8.2/LT3651-8.4 contain provisions for a battery temperature monitoring circuit. Battery temperature is monitored by using a NTC thermistor located with the battery. If the battery temperature moves outside a safe charging range of 0°C to 40°C the charging cycle suspends and signals a fault condition. The LT3651-8.2/LT3651-8.4 contain two digital opencollector outputs, which provide charger status and signal fault conditions. These binary coded pins signal battery charging, standby or shutdown modes, battery temperature faults and bad battery faults. A precision undervoltage lockout is possible by using a resistor divider on the shutdown pin (SHDN). The input supply current is 17µA when the IC is in shutdown. General Operation (See Block Diagram) The LT3651-8.2/LT3651-8.4 use an average current mode control loop architecture to control average charge current. The LT3651-8.2/LT3651-8.4 sense charger output voltage via the BAT pin. The difference between this voltage and the internal float voltage reference is integrated by the voltage error amplifier (V‑EA). The amplifier output voltage (ITH) corresponds to the desired average voltage across the inductor sense resistor, RSENSE, connected between the SENSE and BAT pins. The ITH voltage is divided down by a factor of 10, and provides a voltage offset on the input of the current error amplifier (C‑EA). The difference between this imposed voltage and the current sense resistor voltage is integrated by C-EA. The resulting voltage (VC) provides a voltage that is compared against an internally generated ramp and generates the switch duty cycle that controls the charger’s switches. 36518284f 10 LT3651-8.2/LT3651-8.4 OPERATION The ITH error voltage corresponds linearly to average current sensed across the inductor current sense resistor. Maximum charge current is controlled by clamping the maximum voltage of ITH to 1V. This limits the maximum current sense voltage (voltage across RSENSE) to 95mV setting the maximum charge current. Manipulation of maximum charge current is possible through the RNG/SS and ILIM pins (see the RNG/SS: Dynamic Charge Current Adjust, RNG/SS: Soft-Start and ILIM Control sections). If the voltage on the BAT pin (VBAT) is below VBAT(PRE), A7 initiates the precondition mode. During the precondition interval, the charger continues to operate in constant current mode, but the ITH clamp is reduced to 0.15V reducing charge current to 15% of the maximum programmed value. As VBAT approaches the float voltage (VFLOAT) the voltage error amp V-EA takes control of ITH and the charger transitions into constant voltage (CV) mode. As this occurs, the ITH voltage falls from the limit clamp and charge current is reduced from the maximum value. When the ITH voltage falls below 0.1V, A8 signals C/10. If the charger is configured for C/10 termination the charge cycle is terminated. Once the charge cycle is terminated, the CHRG status pin becomes high impedance and the charger enters low current standby mode. The LT3651-8.2/LT3651-8.4 contain an internal charge cycle timer that terminates a successful charge cycle after a programmed amount of time. This timer is typically programmed to achieve end-of-cycle in three hours, but can be configured for any amount of time by setting an appropriate timing capacitor value (CTIMER). When timer termination is used, the charge cycle does not terminate after C/10 is achieved. Because the CHRG status pin responds to the C/10 current level, the IC will indicate a fully charged battery status, but the charger will continue to source low currents. At the programmed end of the cycle time the charge cycle stops and the part enters standby mode. If the battery did not achieve at least 97.5% of the full float voltage at the end-of-cycle, charging is deemed unsuccessful and another full-timer cycle is initiated. Use of the timer function also enables bad battery detection. This fault condition is achieved if the battery does not respond to preconditioning and the charger remains in (or enters) precondition mode after one-eighth of the programmed charge cycle time. A bad battery fault halts the charging cycle, the CHRG status pin goes high impedance and the FAULT pin is pulled low. When the LT3651-8.2/LT3651-8.4 terminate a charging cycle, whether through C/10 detection or by reaching timer end-of-cycle, the average current mode analog loop remains active but the internal float voltage reference is reduced by 2.5%. Because the voltage on a successfully charged battery is at the full float voltage, the voltage error amp detects an overvoltage condition and rails low. When the voltage error amp output drops below 0.3V, the IC enters standby mode, where most of the internal circuitry is disabled and the VIN bias current is reduced to <100µA. When the voltage on the BAT pin drops below the reduced float reference level, the output of the voltage error amp will climb, at which point the IC comes out of standby mode and a new charging cycle is initiated. The system current limit allows charge current to be reduced in order to maintain a constant input current. Input current is measured via a resistor (RCL) that is placed between the CLP and CLN pins. Power is applied through this resistor and is used to supply both VIN of the chip and other system loads. An offset produced on the inputs of A12 sets the threshold. When that threshold is achieved, ITH is reduced, lowering the charge current thus maintaining the maximum input current. 50µA of current is sourced from ILIM to a resistor (RILIM) that is placed from that pin to ground. The voltage on ILIM determines the regulating voltage across RCL. 1V on ILIM corresponds to 95mV across RCL. The ILIM pin clamps internally to 1V maximum. If the junction temperature of the die becomes excessive, A10 activates decreasing ITH and reduces charge current. This reduces on-chip power dissipation to safe levels but continues charging. 36518284f 11 LT3651-8.2/LT3651-8.4 APPLICATIONS INFORMATION OSC Frequency A precision resistor to ground sets the LT3651-8.2/ LT3651‑8.4 switcher oscillator frequency, fOSC, permitting user adjustability of the frequency value. Typically this frequency is in the 200kHz to 1MHz range. Power consideration may necessitate lower frequency operation especially if the charger is operated with very high voltages. Adjustability also allows the user to position switching harmonics if their system requires. The timing resistor, RT , value is set by the following: RT = 54.9 (kΩ) fOSC (MHz ) Set RT to 54.9k for 1MHz operation. VIN Input Supply The LT3651-8.2/LT3651-8.4 are biased directly from the charger input supply through the VIN pin. This supply provides large switched currents, so a high quality, low ESR decoupling capacitor is required to minimize voltage glitches on VIN. The VIN decoupling capacitor (CVIN) absorbs all input switching ripple current in the charger. Size is determined by input ripple voltage with the following equation: CIN(BULK) ICHG(MAX) • VBAT fOSC (MHz ) • ∆VIN • VIN (µF ) where ∆VIN is the input ripple, ICHG(MAX) is the maximum charge current and f is the oscillator frequency. A good starting point for ∆VIN is 0.1V. Worst-case conditions are with VBAT high and VIN at minimum. So for a 15V VIN(MIN), IMAX = 4A and a 1MHz oscillator frequency: CIN(BULK) = The capacitor must have an adequate ripple current rating. RMS ripple current, ICVIN(RMS) is approximated by: V ICVIN(RMS) ≈ICHG(MAX) • BAT • VIN VIN –1 VBAT which has a maximum at VIN = 2 • VBAT , where ICVIN(RMS) = ICHG(MAX)/2. In the example above that requires a capacitor RMS rating of 2A. Boost Supply The BOOST bootstrapped supply rail drives the internal switch and facilitates saturation of the high side switch transistor. The BOOST voltage is normally created by connecting a 1µF capacitor from the BOOST pin to the SW pin. Operating range of the BOOST pin is 2V to 8.5V, as referenced to the SW pin. The boost capacitor is normally charged via a diode connected from the battery or an external source through the low side switch. Rate the diode average current greater than 0.1A and its reverse voltages greater than VIN(MAX). If an external supply that is greater than the input is available (VBOOST – VIN > 2V), it may be used in place of the bootstrap capacitor and diode. VIN ,VBOOST Start-Up Requirement The LT3651-8.2/LT3651-8.4 operate with a VIN range of 9V to 32V. The charger begins a charging cycle when the detected battery voltage is below the auto-restart float voltage and the part is enabled. 4 • 8.2 = 22µF 1• 0.1• 15 36518284f 12 LT3651-8.2/LT3651-8.4 APPLICATIONS INFORMATION When VIN is below 10.5V and the BOOST capacitor is uncharged, the high side switch would normally not have sufficient head room to start switching. During normal operation the low side switch is deactivated when charge current is very low to prevent reverse current in the inductor. However in order to facilitate start-up, the LT36518.2/LT3651-8.4 enable the switch if VBOOST voltage is low. This allows initial charging of the BOOST capacitor which then permits the high side switch to saturate and efficiently operate. The boost capacitor charges to full potential after a few cycles. The design should consider that as the switcher turns on and input current increases, input voltage drops due to source input impedance and input capacitance. This potentially allows the input voltage to drop below the internal VIN UVLO turn-on and thus disrupt normal behavior and potentially stall start-up. If an input current sense resistor is used, its drop must be considered as well. These problems are worsened because input current is largest at low input voltage. Pay careful attention to drops in the power path. Adding a soft-start capacitor to the RNG/SS pin and setting UVLO to 9V with the SHDN pin is required at low VIN. BAT Output Decoupling It is recommended that the LT3651-8.2/LT3651-8.4 charger output have a decoupling capacitor. If the battery can be disconnected from the charger output this capacitor is required. The value of this capacitor (CBAT) is related to the minimum operational VIN voltage such that: 350µF CBAT ≈ 20µF + VIN(MIN) The voltage rating on CBAT must meet or exceed the battery float voltage. RSENSE: Charge Current Programming The LT3651-8.2/LT3651-8.4 charger is configurable to charge at average currents as high as 4A (see Figure 1). If RNG/SS maximum voltage is not limited, the inductor sense resistor, RSENSE, has 95mV across it at maximum charge current so: RSENSE = 0.095V ICHG(MAX) where ICHG(MAX) is the maximum average charge current. RSENSE is 24mΩ for a 4A charger. SW BOOST LT3651-8.2 LT3651-8.4 SENSE RSENSE BAT + 365142 F01 Figure 1. Programming Maximum Charge Current Using RSENSE 36518284f 13 LT3651-8.2/LT3651-8.4 APPLICATIONS INFORMATION Inductor Selection The primary criteria for inductor value selection in the LT3651-8.2/LT3651-8.4 charger is the ripple current created during switching. Ripple current, ∆IMAX, is typically set within a range of 25% to 35% of the maximum charge current, IMAX. This percentage typically gives a good compromise between losses due to ripple and inductor size. An approximate formula for inductance is: V +V VBAT + VF L= • 1– BAT F (µH) ∆IMAX • fOSC (MHz ) VIN + VF Worse-case ripple is at high VIN and high VBAT . VF is the forward voltage of the synchronous switch (approximately 0.14V at 4A). Figure 2 shows inductance for the case of a 4A charger. The inductor must have a saturation current equal to or exceeding the maximum peak current in the inductor. Peak current is ICHG(MAX) + ∆ICHG(MAX)/2. Magnetics vendors typically specify inductors with maximum RMS and saturation current ratings. Select an inductor that has a saturation current rating at or above peak current, and an RMS rating above ICHG(MAX). Inductors must also meet a maximum volt-second product requirement. If this specification is not in the data sheet of an inductor, consult the vendor to make sure the maximum volt-second product is not being exceeded by your design. The minimum required volt-second product is approximately: VBAT fOSC(MHz) V • 1– BAT ( V • µs ) VIN(MAX) Acceptable power inductors are available from several manufacturers such a Würth Elektronik, Vishay, Coilcraft and TDK. System Input Current Limit The LT3651-8.2/LT3651-8.4 contain a PowerPath control feature to help manage supply load currents. The charger adjusts charger output current in response to a system load so as to maintain a constant input supply load. If overall input supply current exceeds the programmed maximum value the charge current is diminished in an attempt to keep supply current constant. One application where this is helpful is if you have a current limited input supply. Setting the maximum input current limit below the supply limit prevents supply collapse. A resistor, RCL, is placed between the input supply and the system and charger loads as shown in Figure 3. 4 L (µH) 3 INPUT SUPPLY CLP LT3651-8.2 LT3651-8.4 CLN 2 1 0 IMAX = 4A fOSC = 1MHz 25% TO 35% RIPPLE 9 10 15 20 25 30 VIN(MAX) (V) RCL SYSTEM LOAD VIN ILIM RLIM 365142 F03 36512 F02 Figure 2. Inductance (L) vs Maximum VIN Figure 3. Input Current Limit Configuration 36518284f 14 LT3651-8.2/LT3651-8.4 APPLICATIONS INFORMATION The LT3651-8.2/LT3651-8.4 source 50µA from the ILIM pin, so a voltage is developed by simply connecting a resistor to ground. The voltage on the ILIM pin corresponds to 11.5 times the maximum voltage across the input sense resistor (RCL). Input current limit is defined by: IINPUT(MAX) = VILIM 50µA •RILIM = 11.5 •RCL 11.5 •RCL The programming range for ILIM is 0V to 1V. Voltages higher than 1V have no effect on the maximum input current. The default maximum sense voltage is 95mV and is obtained if RILIM is greater than 20k or if the pin is left open. For example, say you want a maximum input current of 2A and the charger is designed for 4A maximum average charge current, which is 1A VIN referred (4A times duty cycle). Using the full ILIM range, the maximum voltage across RCL is 95mV. So RCL is set at 95mV/2A = 48mΩ. When the system load exceeds 1A (= 2A – 1A) charge current is reduced such that the total input current stays at 2A. When the system load is 2A the charge current is 0. This feature only controls charge current so if the system load exceeds the maximum limit and no other limitation is designed, the input current exceeds the maximum desired, though the charge current reduces to 0A. When the input limiter reduces charge current it does not impact the internal system timer if used. See Figure 4. If reduced voltage overhead or better efficiency is required then reduce the maximum voltage across RCL. So for instance, a 10k RILIM sets the maximum RCL voltage to 43mV. This reduction comes at the expense of slightly increased limit variation. Note the LT3651-8.2/LT3651-8.4 internally integrate the input limit signals. This should normally provide sufficient filtering and reduce the sensitivity to current spikes. For the best accuracy take care to provide good Kelvin connections from RCL to CLP, CLN. Further flexibility is possible by dynamically altering the ILIM pin. Different resistor values could be switched in to create unique input limit conditions. The ILIM pin can also be tied to a servo amplifier for other options. See the information in the following section concerning IRNG/SS programming for examples. CURRENT (A) 3 INPUT CURRENT 2 CHARGE CURRENT (VIN REFERRED) 1 0 0 2 1 SYSTEM LOAD CURRENT (A) 365142 F04 Figure 4. Input Current Limit for 4A Maximum Charger and 6A System Current Limit 36518284f 15 LT3651-8.2/LT3651-8.4 APPLICATIONS INFORMATION RNG/SS: Dynamic Current Adjust The RNG/SS pin gives the user the capability to adjust maximum charge current dynamically. The part sources 50µA from the pin, so connecting a resistor to ground develops a voltage. The voltage on the RNG/SS pin corresponds to ten times the maximum voltage across the charge current sense resistor, RSENSE. The defining equations for charge current are: IMAX(RNG/SS) = VRNG/SS 50µA •RRNG/SS = 10.8 •RSENSE 10.8 •RSENSE IMAX(RNG/SS) is the maximum charge current. The programming range for RNG/SS is 0V to 1V. Voltages higher than 1V have no effect on the maximum charge current. The default maximum sense voltage is 95mV and is obtained if RRNG/SS is greater than 20k or if the pin is left open. For example, say you want to reduce the maximum charge current to 50% of the maximum value. Set RNG/SS to 0.5V (50% of 1V), imposing a 46mV maximum sense voltage. Per the above equation, 0.5V on RNG/SS requires a 10k resistor. If the charge current needs to be dynamically adjustable then Figure 5 shows one method. Active servos can also be used to impose voltages on the RNG/SS pin, provided they can only sink current. Active circuits that source current cannot be used to drive the RNG/SS pin. An example is shown in Figure 6. RNG/SS: Soft-Start Soft-start functionality is also supported by the RNG/SS pin. The 50µA sourced from the RNG/SS pin can linearly charge a capacitor, CRNG/SS, connected from the RNG/ SS pin to ground (see Figure 7). The maximum charge current follows this voltage. Thus, the charge current increases from zero to the fully programmed value as the capacitor charges from 0V to 1V. The value of CRNG/SS is calculated based on the desired time to full current (tSS) following the relation: CRNG/SS = 50µA • tSS The RNG/SS pin is pulled to ground internally when charging is terminated so each new charging cycle begins with a soft-start cycle. RNG/SS is also pulled to ground during bad battery and NTC fault conditions, so a graceful recovery from these faults is possible. LT3651-8.2 LT3651-8.4 LT3651-8.2 LT3651-8.4 RNG/SS RNG/SS 10k + – LOGIC HIGH = HALF CURRENT SERVO REFERENCE 365142 F06 365142 F05 Figure 5. Using the RNG/SS Pin for Digital Control of Maximum Charge Current Figure 6. Driving the RNG/SS Pin with a Current-Sink Active Servo Amplifier LT3651-8.2 LT3651-8.4 RNG/SS CRNG/SS 365142 F07 Figure 7. Using the RNG/SS Pin for Soft-Start 36518284f 16 LT3651-8.2/LT3651-8.4 APPLICATIONS INFORMATION Status Pins The LT3651-8.2/LT3651-8.4 report charger status through two open-collector outputs, the CHRG and FAULT pins. These pins can accept voltages as high as VIN, and can sink up to 10mA when enabled. The CHRG pin indicates that the charger is delivering current at greater than a C/10 rate, or one-tenth of the programmed maximum charge current. The FAULT pin signals bad battery and NTC faults. These pins are binary coded, and signal state following the table below. On indicates the pin pulled low, and Off indicates pin high impedance. Table 1. Status Pins State Table STATUS PINS STATE CHARGER STATUS CHRG FAULT Off Off Not Charging—Standby or Shutdown Mode Off On Bad Battery Fault (Precondition Timeout/EOC Failure) On Off Normal Charging at C/10 or Greater On On NTC Fault (Pause) the charger terminates and the LT3651-8.2/LT3651‑8.4 enter standby mode. The CHRG status pin follows the charge cycle and is high impedance when the charger is not actively charging. When VBAT drops below 97.5% of the full-charged float voltage, whether by battery loading or replacement of the battery, the charger automatically re-engages and starts charging. There is no provision for bad battery detection if C/10 termination is used. Timer Termination The LT3651-8.2/LT3651-8.4 support a timer-based termination scheme, in which a battery charge cycle is terminated after a specific amount of time elapses. Timer termination is engaged when a capacitor (CTIMER) is connected from the TIMER pin to ground. The timer cycle end-of-cycle (tEOC) occurs based on CTIMER following the relation: CTIMER = tEOC (Hrs) • 0.68 (µF ) 3 C/10 Termination The LT3651-8.2/LT3651-8.4 support a low current based termination scheme, where a battery charge cycle terminates when the current output from the charger falls to below one-tenth the maximum current, as programmed with RSENSE. The C/10 threshold current corresponds to 9mV across RSENSE. This termination mode is engaged by shorting the TIMER pin to ground. so a typical 3 hour timer end-of-cycle would use a 0.68µF capacitor. When C/10 termination is used, a LT3651-8.2/LT3651-8.4 charger sources battery charge current as long as the average current level remains above the C/10 threshold. As the full-charge float voltage is achieved, the charge current falls until the C/10 threshold is reached, at which time The CHRG status pin continues to signal charging at a C/10 rate, regardless of which termination scheme is used. When timer termination is used, the CHRG status pin is pulled low during a charge cycle until the charger output current falls below the C/10 threshold. The charger continues to “top off” the battery until timer end-of-cycle, when the LT3651-8.2/LT3651-8.4 terminate the charge cycle and enters standby mode. Termination at the end of the timer cycle only occurs if the 36518284f 17 LT3651-8.2/LT3651-8.4 APPLICATIONS INFORMATION charge cycle was successful. A successful charge cycle occurs when the battery is charged to within 2.5% of the full-charge float voltage. If a charge cycle is not successful at end-of-cycle, the timer cycle resets and charging continues for another full-timer cycle. triggered when the voltage on BAT remains below the precondition threshold for greater than one-eighth of a full timer cycle (one-eighth end-of-cycle). A bad battery fault is also triggered if a normally charging battery re-enters precondition mode after one-eighth end-of-cycle. When VBAT drops below 97.5% of the full-charge float voltage, whether by battery loading or replacement of the battery, the charger automatically re-engages and starts charging. When a bad battery fault is triggered, the charge cycle is suspended, so the CHRG status pin becomes high impedance. The FAULT pin is pulled low to signal a fault detection. The RNG/SS pin is also pulled low during this fault, to accommodate a graceful restart, in the event that a soft-start function is incorporated (see the RNG/SS: Soft-Start section). Precondition and Bad Battery Fault A LT3651-8.2/LT3651-8.4 charger has a precondition mode, in which charge current is limited to 15% of the programmed IMAX, as set by RSENSE. The precondition current corresponds to 14mV across RSENSE. Precondition mode is engaged while the voltage on the BAT pin is below the precondition threshold (VBAT(PRE)). Once the BAT voltage rises above the precondition threshold, normal full-current charging can commence. The LT3651-8.2/LT3651-8.4 incorporate 2.5% of threshold for hysteresis to prevent mode glitching. When the internal timer is used for termination, bad battery detection is engaged. This fault detection feature is designed to identify failed cells. A bad battery fault is Cycling the charger’s power or SHDN function initiates a new charge cycle, but a LT3651-8.2/LT3651-8.4 charger does not require a reset. Once a bad battery fault is detected, a new timer charge cycle initiates when the BAT pin exceeds the precondition threshold voltage. During a bad battery fault, 1mA is sourced from the charger. Removing the failed battery allows the charger output voltage to rise and initiate a charge cycle reset. In that way removing a bad battery resets the LT3651-8.2/LT3651-8.4. A new charge cycle is started by connecting another battery to the charger output. 36518284f 18 LT3651-8.2/LT3651-8.4 APPLICATIONS INFORMATION Battery Temperature Fault: NTC Thermal Foldback The LT3651-8.2/LT3651-8.4 can accommodate battery temperature monitoring by using an NTC (negative temperature coefficient) thermistor close to the battery pack. The temperature monitoring function is enabled by connecting a 10kΩ, B = 3380 NTC thermistor from the NTC pin to ground. If the NTC function is not desired, leave the pin unconnected. The LT3651-8.2/LT3651-8.4 contain a thermal foldback protection feature that reduces maximum charger output current if the internal IC junction temperature approaches 125°C. In most cases, on-chip temperature servos such that any overtemperature conditions are relieved with only slight reductions in maximum charge current. The NTC pin sources 50µA and monitors the voltage dropped across the 10kΩ thermistor. When the voltage on this pin is above 1.36V (0°C) or below 0.29V (40°C), the battery temperature is out of range, and the LT3651-8.2/ LT3651-8.4 trigger an NTC fault. The NTC fault condition remains until the voltage on the NTC pin corresponds to a temperature within the 0°C to 40°C range. Both hot and cold thresholds incorporate hysteresis that corresponds to 2.5°C. In some cases, the thermal foldback protection feature can reduce charge currents below the C/10 threshold. In applications that use C/10 termination (TIMER = 0V), the LT3651-8.2/LT3651-8.4 suspend charging and enters standby mode until the overtemperature condition is relieved. During an NTC fault, charging is halted and both status pins are pulled low. If timer termination is enabled, the timer count is suspended and held until the fault condition is relieved. The RNG/SS pin is also pulled low during this fault, to accommodate a graceful restart in the event that a soft-start function is being incorporated (see the RNG/ SS: Soft-Start section). If higher operational charging temperatures are desired, the temperature range can be expanded by adding series resistance to the 10k NTC resistor. Adding a 0.91k (0TC) resistor will increase the effective temperature threshold to 45°C. Layout Considerations The LT3651-8.2/LT3651-8.4 switch node has rise and fall times that are typically less than 10ns to maximize conversion efficiency. These fast switch times require care in the board layout to minimize noise problems. The philosophy is to keep the physical area of high current loops small (the inductor charge/discharge paths) to minimize magnetic radiation. Keep traces wide and short to minimize parasitic inductance and resistance and shield fast switching voltage nodes (SW, BOOST) to reduce capacitive coupling. 36518284f 19 LT3651-8.2/LT3651-8.4 APPLICATIONS INFORMATION The switched node (SW pin) trace should be kept as short as possible to minimize high frequency noise. The VIN capacitor (CIN) should be placed close to the IC to minimize this switching noise. Short, wide traces on these nodes minimize stray inductance and resistance. Keep the BOOST decoupling capacitor in close proximity to the IC to minimize ringing from trace inductance. Route the SENSE and BAT traces together and keep the traces as short as possible. Shielding these signals from switching noise with ground is recommended. Make Kelvin connections to the battery and sense resistor. Keep high current paths and transients isolated from battery ground, to assure an accurate output voltage reference. Effective grounding is achieved by considering switched current in the ground plane, and careful component placement and orientation can effectively steer these high currents such that the battery reference does not get corrupted. Figure 8 illustrates the high current, high speed current loops. When the top switch is enabled (charge loop), current flows from the input bypass capacitor (CIN) through the switch and inductor to the battery positive terminal. When the top switch is disabled (discharge loop), current to the battery positive terminal is provided from ground through the synchronous switch. In both cases, these switched currents return to ground via the output bypass capacitor (CBAT). Power Considerations The LT3651-8.2/LT3651-8.4 packaging is designed to efficiently remove heat from the IC via the exposed pad on the backside of the package, which is soldered to a copper footprint on the PCB. This footprint should be made as large as possible to reduce the thermal resistance of the IC case to ambient air. Consideration should be given for power dissipation and overall efficiency in a LT3651-8.2/LT3651-8.4 charger. A detailed analysis is beyond the scope of the data sheet, however following are general guidelines. The major components of power loss are: conduction and transition losses of the LT3651-8.2/LT3651-8.4 switches; losses in the inductor and sense resistors; and AC losses in the decoupling capacitors. Switch conduction loss is fixed. Transition losses are adjustable by changing switcher frequency. Higher input voltages cause an increase in transition losses, decreasing overall efficiency. However transition losses are inversely proportional to switcher oscillator frequency so lowering operating frequency reduces these losses. But lower operating frequency usually requires higher inductance to maintain inductor ripple current (inversely proportional). Inductors with larger values typically have more turns, increasing ESR unless you increase wire diameter making them physically BOOST VIN CBOOST CIN LT3651-8.2 LT3651-8.4 CHARGE RSENSE SW + DISCHARGE CBAT BATTERY 365142 F08 Figure 8 36518284f 20 LT3651-8.2/LT3651-8.4 APPLICATIONS INFORMATION larger. So there is an efficiency and board size trade-off. Secondarily, inductor AC losses increase with frequency and lower ripple reduces AC capacitor losses. The following simple rules of thumb assume a charge current of 4A and battery voltage of 7.5V, with 1MHz oscillator, 24mΩ sense resistor and 3.3µH/20mΩ inductor. A 1% increase in efficiency represents a 0.35W reduction in power loss at 85% overall efficiency. One way to do this is to decrease resistance in the high current path. A reduction of 0.2W at 4A requires a 22mΩ reduction in resistance. This can be done by reducing inductor ESR. It is also possible to lower the sense resistance (with a reduction in RRNG/SS as well), with a trade-off of slightly less accurate current accuracy. All high current board traces should have the lowest resistance possible. Addition of input current limit sense resistance reduces efficiency. Charger efficiency drops approximately linearly with increasing frequency all other things constant. At 15V VIN there is a 1% improvement in efficiency for every 200kHz reduction in frequency (100kHz to 1MHz); At 28V VIN, 1% for every 100kHz. Of course all of these must be experimentally confirmed in the actual charger. TYPICAL APPLICATIONS 9V to 32V 4A Charger with High Voltage Current Foldback SBM540 CIN 22µF SMAZ24 18.2V CLP RT 54.9k CLN VIN SHDN SW ACPR FAULT BOOST CHRG LT3651-8.2/LT3651-84 SENSE NC RT TIMER ILIM RNG/SS 5 VIN MAXIMUM CHARGE CURRENT (A) RIL 1k 120k Maximum Charge Current vs VIN BAT NTC GND 1µF 3.3µH 1N5819 RSENSE 24mΩ CBAT 100µF + 2-CELL Li-Ion BATTERY 365142 TA02a 4 3 2 1 0 5 10 15 20 VIN (V) 25 30 35 3651 TA02b 36518284f 21 LT3651-8.2/LT3651-8.4 TYPICAL APPLICATIONS 12V to 32V 4A Charger with Low Voltage Current Foldback Using the RNG/SS Pin SMAZ9V1 9.1V RT 54.9k CLP SHDN SW ACPR FAULT BOOST CHRG LT3651-82/LT3651-84 NC SENSE RT TIMER ILIM 68k CIN 22µF VIN CLN 5 TO SYSTEM LOAD MAXIMUM CHARGE CURRENT (A) SBM540 VIN 1µF 3.3µH 1N5819 RSENSE 24mΩ BAT NTC RNG/SS GND CBAT 100µF Maximum Charge Current vs VIN + 2-CELL Li-Ion BATTERY 3 2 0 365142 TA03a 5.1k 4 10 15 30 CLP 180k 20k RT 54.9k CLN VIN SHDN SW ACPR FAULT BOOST CHRG LT3651-8.2/LT3651-8.4 NC SENSE RT TIMER ILIM RNG/SS CIN 22µF BAT NTC GND 25 TO SYSTEM LOAD 24 23 1µF 3.3µH 1N5819 RSENSE 24mΩ CBAT 100µF 22k 22 21 20 19 18 17 + 2-CELL Li-Ion BATTERY 365142 TA05a 0.1µF Input Power vs VIN INPUT POWER (W) RSENSE 50mΩ SBM540 8.2V 35 3651 TA03b VIN 180k 25 VIN (V) 1µF 9V to 32V 4A Charger with Approximately Constant Input Power 6.2V 20 16 15 5 10 15 20 VIN (V) 25 30 35 365142 TA05b 36518284f 22 LT3651-8.2/LT3651-8.4 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. UHE Package Variation: UHE36MA 36-Lead Plastic QFN (5mm × 6mm) (Reference LTC DWG # 05-08-1753 Rev A) 0.70 ±0.05 1.52 ±0.05 2.54 ±0.05 5.50 ±0.05 0.25 ±0.05 4.10 ±0.05 3.50 REF 3.45 ±0.05 3.45 ±0.05 PACKAGE OUTLINE 0.76 ±0.05 0.25 ±0.05 0.50 BSC 4.50 REF 5.10 ±0.05 6.50 ±0.05 RECOMMENDED SOLDER PAD LAYOUT APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 5.00 ±0.10 0.00 – 0.05 0.200 REF R = 0.10 TYP PIN 1 NOTCH R = 0.30 TYP OR 0.35 × 45° CHAMFER 3.50 REF 35 36 0.40 ±0.10 PIN 1 TOP MARK (SEE NOTE 6) 1 2 2.54 ±0.10 6.00 ±0.10 3.45 ±0.10 4.50 REF 1.52 ±0.10 3.45 ±0.10 (UHE36MA) QFN 0410 REV A 0.75 ±0.05 NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 0.25 ±0.05 R = 0.125 TYP 0.50 BSC BOTTOM VIEW—EXPOSED PAD 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.20mm 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 36518284f 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 LT3651-8.2/LT3651-8.4 TYPICAL APPLICATION 9V to 32V 4A Charger with 3-Hour Charge Timeout, 6.3A Input Current Limit, 10ms Soft-Start and Battery Temperature Monitoring RIL 16mΩ SBM540 VIN 50k 50k 50k CIN 22µF 1µF VLOGIC 50k CLP SHDN VIN SW CLN LT3651-8.2 NC LT3651-8.4 ACPR TO CONTROLLER FAULT CHRG CTIMER 0.68µF 0.47µF 3.3µH 1N5819 SENSE BAT NTC ILIM RNG/SS GND TIMER 1µF BOOST RT RT 54.9k TO SYSTEM LOAD RSENSE 24mΩ CBAT 100µF NTC B 10k + 2-CELL Li-Ion BATTERY 3651 TA04 RELATED PARTS PART NUMBER DESCRIPTION LT3651-4.1/LT3651-4.2 Monolithic 4A Switch Mode Synchronous 1-Cell Li-Ion Battery Charger LT3650 2A Monolithic Li-Ion Battery Charger LT3652/LT3652HV LTC4000 LTC4002 LTC4006 LTC4007 LTC4008 LTC4009/LTC4009-1 LTC4009-2 LTC4012/LTC4012-1/ LTC4012-2/LTC4012-3 COMMENTS Standalone, 4.75 ≤ VIN ≤ 32V (40V Abs Max), 1MHz, 4A, Programmable Charge Current Timer or V/10 Termination 5mm × 6mm QFN-36 Package High Efficiency, Wide Input Voltage Range Charger, Time or Charge Current Termination, Automatic Restart, Temperature Monitoring, Programmable Charge Current, Input Current Limit, 12-Lead DFN and MSOP Packages Power Tracking 2A Battery Charger Input Supply Voltage Regulation Loop for Peak Power Tracking in (MPPT) Solar Applications, Standalone, 4.95V ≤ VIN ≤ 32V (40V Abs Max), 1MHz, 2A Programmable Charge Current, Timer or C/10 Termination, 3mm × 3mm DFN-12 Package and MSOP-12 Packages. LT3652HV Version Up to VIN = 34V High Voltage High Current Controller for Complete High Performance Battery Charger When Paired with a DC/DC Converter Battery Charging and Power Management Wide Input and Output Voltage Range: 3V to 60V ±0.25% Accurate Programmable Float Voltage, Programmable C/X or Timer Based Charge Termination NTC Input for Temperature Qualified Charging, 28-Lead 4mm × 5mm QFN or SSOP Packages Standalone Li-Ion Switch Mode Complete Charger for 1- or 2-Cell Li-Ion Batteries, Onboard Timer Termination, Battery Charger Up to 4A Charge Current, 10-Lead DFN and SO-8 Packages Small, High Efficiency, Fixed Voltage Complete Charger for 2-, 3- or 4-Cell Li-Ion Batteries, AC Adapter Current Limit Li-Ion Battery Charger with Termination and Thermistor Sensor, 16-Lead Narrow SSOP Package High Efficiency, Programmable Voltage Complete Charger for 3- or 4-Cell Li-Ion Batteries, AC Adapter Current Limit, Battery Charger with Termination Thermistor Sensor and Indicator Outputs, 24-Lead SSOP Package 4A, High Efficiency, Multi-Chemistry Complete Charger for 2- to 6-Cell Li-Ion Batteries or 4- to 18-Cell Nickel Batteries, Battery Charger Up to 96% Efficiency, 20-Lead SSOP Package High Efficiency, Multi-Chemistry Complete Charger for 1- to 4-Cell Li-Ion Batteries or 4- to 18-Cell Nickel Batteries, Battery Charger Up to 93% Efficiency, 20-Lead (4mm × 4mm) QFN Package, LTC4009-1 for 4.1V Float Voltage, LTC4009-2 for 4.2V Float Voltage 4A, High Efficiency, Multi-Chemistry PowerPath Control, Constant-Current/Constant-Voltage Switching Regulator Battery Charger with PowerPath Control Charger, Resistor, Voltage/Current Programming, AC Adapter Current Limit and Thermistor Sensor and Indicator Outputs, 1 to 4-cell Li, Up to 18-cell Ni, SLA and SuperCap Compatible; 4mm × 4mm QFN-20 Package; LTC4012-1 Version for 4.1V Li Cells, LTC4012-2 Version for 4.2V Li Cells, LTC4012-3 Version Has Extra GND Pin 36518284f 24 Linear Technology Corporation LT 1212 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2012