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LT3652 Power Tracking 2A Battery Charger for Solar Power FEATURES
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DESCRIPTION
The LT(R)3652 is a complete monolithic step-down battery charger that operates over a 4.95V to 32V input voltage range. The LT3652 provides a constant-current/ constant-voltage charge characteristic, with maximum charge current externally programmable up to 2A. The charger employs a 3.3V float voltage feedback reference, so any desired battery float voltage up to 14.4V can be programmed with a resistor divider. The LT3652 employs an input voltage regulation loop, which reduces charge current if the input voltage falls below a programmed level, set with a resistor divider. When the LT3652 is powered by a solar panel, the input regulation loop is used to maintain the panel at peak output power. The LT3652 can be configured to terminate charging when charge current falls below 1/10 of the programmed maximum (C/10). Once charging is terminated, the LT3652 enters a low-current (85A) standby mode. An auto-recharge feature starts a new charging cycle if the battery voltage falls 2.5% below the programmed float voltage. The LT3652 also contains a programmable safety timer, used to terminate charging after a desired time is reached. This allows top-off charging at currents less than C/10.
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.
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Input Supply Voltage Regulation Loop for Peak Power Tracking in (MPPT) Solar Applications Wide Input Voltage Range: 4.95V to 32V (40V Abs Max) Programmable Charge Rate Up to 2A User Selectable Termination: C/10 or On-Board Termination Timer Resistor Programmable Float Voltage Up to 14.4V Accommodates Li-Ion/Polymer, LiFePO4, SLA, NiMH/NiCd Chemistries No VIN Blocking Diode Required for Battery Voltages 4.2V 1MHz Fixed Frequency 0.5% Float Voltage Reference Accuracy 5% Charge Current Accuracy 2.5% C/10 Detection Accuracy Binary-Coded Open-Collector Status Pins 3mm x 3mm DFN12 or MSOP-12 Packages
APPLICATIONS
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Solar Powered Applications Remote Monitoring Stations LiFePO4 (Lithium Phosphate) Applications Portable Handheld Instruments 12V to 24V Automotive Systems
TYPICAL APPLICATION
2A Solar Panel Power Manager With 7.2V LiFePO4 Battery and 17V Peak Power Tracking
CMSH1-40MA
Solar Panel Input Voltage Regulation, Tracks Max Power Point to Greater Than 98%
22 TA = 25C INPUT REGULATION VOLTAGE (V)
SYSTEM LOAD
SOLAR PANEL INPUT (<40V OC VOLTAGE) 10F 530k VIN SW LT3652 BOOST
CMSH3-40MA CMSH3-40MA 1F 10H 0.05 SENSE BAT NTC VFB 542k 459k 10k B = 3380 + 10F
20 18 16 98% TO 95% PEAK POWER 14 12 10 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 CHARGER OUTPUT CURRENT (A) 100% TO 98% PEAK POWER
VIN_REG SHDN 100k CHRG FAULT TIMER
2
2-CELL LiFePO4 (2 x 3.6V) BATTERY PACK
3652 TA01b
3652 TA01a
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LT3652 ABSOLUTE MAXIMUM RATINGS
(Note 1)
Voltages: VIN ........................................................................40V VIN_REG, SHDN, CHRG, FAULT ............ VIN + 0.5V, 40V SW ........................................................................40V SW-VIN.................................................................4.5V BOOST ...................................................SW+10V, 50V BAT, SENSE ...........................................................15V
BAT-SENSE ......................................... -0.5V to +0.5V NTC, TIMER, ........................................................2.5V VFB ..........................................................................5V Operating Junction Temperature Range (Note 2) ............................................. -40C to 125C Storage Temperature Range................... -65C to 150C
PIN CONFIGURATION
TOP VIEW TOP VIEW VIN VIN_REG SHDN CHRG FAULT TIMER 1 2 3 4 5 6 13 12 SW 11 BOOST 10 SENSE 9 BAT 8 NTC 7 VFB VIN VIN_REG SHDN CHRG FAULT TIMER 1 2 3 4 5 6 12 11 10 9 8 7 SW BOOST SENSE BAT NTC VFB
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DD PACKAGE 12-LEAD (3mm x 3mm) PLASTIC DFN TJMAX = 125C, JA = 43C/W, JC = 3C/W EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB
MSE PACKAGE 12-LEAD PLASTIC MSOP TJMAX = 125C, JA = 43C/W, JC = 3C/W EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH LT3652EDD#PBF LT3652IDD#PBF LT3652EMSE#PBF LT3652IMSE#PBF TAPE AND REEL LT3652EDD#TRPBF LT3652IDD#TRPBF LT3652EMSE#TRPBF LT3652IMSE#TRPBF PART MARKING* LFHT LFHT 3652 3652 PACKAGE DESCRIPTION 12-Lead Plastic DFN 3mm x 3mm 12-Lead Plastic DFN 3mm x 3mm 12-Lead Plastic MSOP 12-Lead Plastic MSOP TEMPERATURE RANGE -40C to 125C -40C to 125C -40C to 125C -40C to 125C
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/
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LT3652 ELECTRICAL CHARACTERISTICS
SYMBOL VIN VIN(OVLO) VIN(UVLO) VFB(FLT) VRECHARGE VFB(PRE) VFB(PREHYST) VIN_REG(TH) IIN_REG IVIN PARAMETER VIN Operating Range VIN Start Voltage OVLO Threshold OVLO Hysteresis UVLO Threshold UVLO Hysteresis Float Voltage Reference Recharge Reference Threshold Reference Precondition Threshold Reference Precondition Threshold Hysteresis Input Regulation Reference Operating Input Supply Current
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 20V, Boost - SW = 4V, SHDN = 2V, VFB = 3.3V, CTIMER = 0.68F.
CONDITIONS VBAT = 4.2 (Notes 3, 4) VBAT = 4.2 (Note 4) VIN Rising VIN Rising (Note 6) Voltage Relative to VFB(FLT) (Note 6) VFB Rising (Note 6) Voltage Relative to VFB(PRE) (Note 6) VFB = 3V; VSENSE - VBAT = 50mV CC/CV Mode, ISW = 0 Standby Mode Shutdown (SHDN = 0) Switch On, ISW = 0, 2.5 < V(BOOST - SW) < 8.5 ISW = 2A VIN - VSW, ISW = 2A
l l l l l l l l
MIN 4.95 7.5 32
TYP
MAX 32
UNITS V V V V V V V V mV V mV
35 1 4.6 0.2
40 4.95 3.318 3.34
3.282 3.26
3.3 82.5 2.3 70
2.65
2.7 35 2.5 85 15 20 30 350
2.75 100 3.5
V nA mA A A mA mA/A mV A mV
Input Regulation Reference Bias Current VIN_REG = VIN_REG(TH)
IBOOST IBOOST/ISW VSW(ON) ISW(MAX) VSENSE(PRE) VSENSE(DC) VSENSE(C/10) IBAT ISENSE IREVERSE IVFB IVFB VNTC(H) VNTC(L) VNTC(HYST) RNTC(DIS) INTC VSHDN VSHDN(HYST) ISHDN VCHRG, VFAULT ITIMER VTIMER(DIS)
BOOST Supply Current BOOST Switch Drive Switch-On Voltage Drop Switch Current Limit Precondition Sense Voltage Maximum Sense Voltage C/10 Trigger Sense Voltage BAT Input Bias Current SENSE Input Bias Current Charger Reverse Current IBAT + ISENSE + ISW VFB Input Bias Current VFB Input Bias Current NTC Range Limit (High) NTC Range Limit (Low) NTC Threshold Hysteresis NTC Disable Impedance NTC Bias Current Shutdown Threshold Shutdown Hysteresis SHDN Input Bias Current Status Low Voltage Charge/Discharge Current Timer Disable Threshold
2.5 95 7.5
3 15 100 10 0.1 0.1 1 65 110 105 12.5 1 1
VSENSE - VBAT; VFB = 2V VSENSE - VBAT; VFB = 3V (Note 7) VSENSE - VBAT, Falling Charging Terminated Charging Terminated VIN = 0; VBAT = VSENSE = VSW = 4.2V Charging Terminated CV Operation (Note 5) VNTC Rising VNTC Falling % of threshold Impedance to ground VNTC = 0.8V Rising
l l l l l l l
mV mV A A A nA nA
1.25 0.27 250 47.5 1.15
1.36 0.29 20 500 50 1.2 120 -10
1.45 0.315
V V % k
52.5 1.25
A V mV nA
10mA Load
l
0.4 25 0.1 0.25
V A V
l
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LT3652 ELECTRICAL CHARACTERISTICS
SYMBOL tTIMER PARAMETER Full Charge Cycle Timeout Precondition Timeout Timer Accuracy fO DC Operating Frequency Duty Cycle Range Continuous Operation
l l
The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = 20V, Boost - SW = 4V, SHDN = 2V, VFB = 3.3V, CTIMER = 0.68F.
CONDITIONS MIN TYP 3 22.5 -10 1 15 90 10 MAX UNITS hr min % MHz %
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 LT3652EDD is guaranteed to meet performance specifications from 0C to 125C junction temperature. Specifications over the -40C to 125C operating junction temperature range are assured by design, characterization, and correlation with statistical process controls. The LT3652IDD specifications are guaranteed over the full -40C to 125C operating junction temperature range. High junction temperatures degrade operating lifetimes. Note 3: VIN minimum voltages below the start threshold are only supported if (VBOOST-VSW) > 2V.
Note 4: This parameter is valid for programmed output battery float voltages 4.2V. VIN operating range minimum is 0.75V above the programmed output battery float voltage (VBAT(FLT) + 0.75V). VIN Start Voltage is 3.3V above the programmed output battery float voltage (VBAT(FLT) + 3.3V). Note 5: Output battery float voltage (VBAT(FLT)) programming resistor divider equivalent resistance = 250k compensates for input bias current. Note 6: All VFB voltages measured through 250k series resistance. Note 7: VSENSE(DC) is reduced by thermal foldback as junction temperature approaches 125C.
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LT3652 TYPICAL PERFORMANCE CHARACTERISTICS
VIN_REG Threshold vs Temperature: ICHG at 50%
2.720 2.715 2.710 VFB (FLT) 2.705 2.700 2.695 3.298 2.690 2.685 2.680 -50 -25 50 25 0 75 TEMPERATURE (C) 100 125 3.296 -50 -25 50 25 0 75 TEMPERATURE (C) 100 125 IVIN CURRENT (A) 3.302 VIN_REG(TH) (V) 3.304
TJ = 25C, unless otherwise noted. VIN Standby Mode Current vs Temperature
100 95 90 85 80 75 70 65 -50
VFB Reference Voltage vs Temperature
3.300
-25
50 25 0 TEMPERATURE (C)
75
100
3652 G02
3652 G01
3652 G01a
Switch Drive (ISW/IBOOST) vs Switch Current
36 33 30 27 VSW(ON) (mV) 24 ISW/IBOOST 21 18 15 12 9 6 3 0 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 SWITCH CURRENT (A)
3652 G03
Switch Forward Drop (VIN - VSW) vs Temperature
480 460 440 420 400 380 360 340 320 -50 -25 50 25 0 75 TEMPERATURE (C) 100 125 ISW = 2A
3652 G04
CC/CV Charging; SENSE Pin Bias Current vs VSENSE
100 50 0 -50 ISENSE (A) -100 -150 -200 -250 -300 -350 0 0.5 1 1.5 2.5 VSENSE (V) 2
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C/10 Threshold (VSENSE -VBAT ) vs Temperature
12
VBAT = VBAT(PRE)
11 VBAT = VBAT(FLT) VSENSE(C/10) (mV)
10
9
8 -50
-25
50 25 0 75 TEMPERATURE (C)
100
125
3652 G06
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LT3652 TYPICAL PERFORMANCE CHARACTERISTICS
Maximum Charge Current (VSENSE -VBAT ) vs Temperature
101.0 100.8 100.6 VSENSE(DC) (mV) VSENSE(DC) (mV) 100.4 100.2 100.0 99.8 99.6 99.4 99.2 99.0 -50 0 -25 50 25 0 75 TEMPERATURE (C) 100 125 25 35 45 55 65 75 85 95 105 115 125 135 TEMPERATURE (C)
3652 G08
TA = 25C, unless otherwise noted. CC/CV Charging; BAT Pin Bias Current vs VBAT
2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 -0.4 0 0.5 1 1.5
Thermal Foldback - Maximum Charge Current (VSENSE -VBAT ) vs Temperature
120 100 80 60 40 20
VFB = 3V
IBAT (mA)
VBAT(FLT) 2 2.5 VBAT (V) 3
3652 G09
3652 G07
Maximum Charge Current (VSENSE -VBAT ) vs VIN_REG Voltage
100 12 10 8 IRFB (A) 60 6 4 20 2 0
VFLOAT Programming Resistor Current vs VFLOAT for 2-Resistor Network
80 VSENSE(DC) (mV)
40
0 2.65 2.66 2.67 2.68 2.69 2.7 2.71 2.72 2.73 2.74 2.75 VIN_REG (V)
3652 G10
0
2
4
6 8 10 VBAT(FLT) (V)
12
14
16
3652 G11
Charge Current, Efficiency, and Power Loss vs Time (ICHG(MAX) = 2A; VFLOAT = 8.2V)
3.0 CHARGE CURRENT (A); POWER LOSS (W) VIN = 20V 2.5 2.0 1.5 1.0 0.5 0 0 CHARGE CURRENT POWER LOSS EFFICIENCY 85 EFFICIENCY (%) 75 65 55 45 35 20 40 60 80 100 120 140 160 180 200 TIME (MINUTES)
3652 G12
Charger Efficiency vs Battery Voltage (ICHG = 2A)
95 90 88 86 84 82 80 78 76 74 72 70 3 4 5 6 7 8 9 10 11 12 13 14 15 VBAT (V)
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EFFICIENCY (%)
VIN = 20V WITH INPUT BLOCKING DIODE
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LT3652 PIN FUNCTIONS
VIN (Pin 1): Charger Input Supply. VIN operating range is 4.95V to 32V. VIN must be 3.3V greater than the programmed output battery float voltage (VBAT(FLT)) for reliable start-up. (VIN - VBAT(FLT)) 0.75V is the minimum operating voltage, provided (VBOOST - VSW) 2V. IVIN ~ 85A after charge termination. VIN_REG (Pin 2): Input Voltage Regulation Reference. Maximum charge current is reduced when this pin is below 2.7V. Connecting a resistor divider from VIN to this pin enables programming of minimum operational VIN voltage. This is typically used to program the peak power voltage for a solar panel. The LT3652 servos the maximum charge current required to maintain the programmed operational VIN voltage, through maintaining the voltage on VIN_REG at or above 2.7V. If the voltage regulation feature is not used, connect the pin to VIN. SHDN (Pin 3): Precision Threshold Shutdown Pin. The enable threshold is 1.2V (rising), with 120mV of input hysteresis. When in shutdown mode, all charging functions are disabled. The precision threshold allows use of the SHDN pin to incorporate UVLO functions. If the SHDN pin is pulled below 0.4V, the IC enters a low current shutdown mode where VIN current is reduced to 15A. Typical SHDN pin input bias current is 10nA. If the shutdown function is not desired, connect the pin to VIN. CHRG (Pin 4): Open-Collector Charger Status Output; typically pulled up through a resistor to a reference voltage. This status pin can be pulled up to voltages as high as VIN when disabled, and can sink currents up to 10mA when enabled. During a battery charging cycle, if required charge current is greater than 1/10 of the programmed maximum current (C/10), CHRG is pulled low. A temperature fault also causes this pin to be pulled low. After C/10 charge termination or, if the internal timer is used for termination and charge current is less than C/10, the CHRG pin remains high-impedance. FAULT (Pin 5): Open-Collector Charger Status Output; typically pulled up through a resistor to a reference voltage. This status pin can be pulled up to voltages as high as VIN when disabled, and can sink currents up to 10mA when enabled. This pin indicates fault conditions during a battery charging cycle. 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. TIMER (Pin 6): End-Of-Cycle Timer Programming Pin. If a timer-based charge termination is desired, connect a capacitor from this pin to ground. Full charge end-ofcycle time (in hours) is programmed with this capacitor following the equation: tEOC = CTIMER * 4.4 * 106 A bad battery fault is generated if the battery does not achieve the precondition threshold voltage within oneeighth of tEOC, or: tPRE = CTIMER * 5.5 * 105 A 0.68F capacitor is typically used, which generates a timer EOC at three hours, and a precondition limit time of 22.5 minutes. If a timer-based termination is not desired, the timer function 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 threshold, or ICHG(MAX)/10 VFB (Pin 7): Battery Float Voltage Feedback Reference. The charge function operates to achieve a final float voltage of 3.3V on this pin. Output battery float voltage (VBAT(FLT)) is programmed using a resistor divider. VBAT(FLT) can be programmed up to 14.4V. The auto-restart feature initiates a new charging cycle when the voltage at the VFB pin falls 2.5% below the float voltage reference. The VFB pin input bias current is 110nA. Using a resistor divider with an equivalent input resistance at the VFB pin of 250k compensates for input bias current error. Required resistor values to program desired VBAT(FLT) follow the equations: R1 = (VBAT(FLT) * 2.5 * 105)/3.3 R2 = (R1 * 2.5 * 105)/(R1 - (2.5 * 105)) () ()
R1 is connected from BAT to VFB, and R2 is connected from VFB to ground.
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LT3652 PIN FUNCTIONS
NTC (Pin 8): Battery Temperature Monitor Pin. This pin is the input to the NTC (Negative Temperature Coefficient) thermistor temperature monitoring circuit. This function is enabled by connecting a 10k, B = 3380 NTC thermistor from the NTC pin to ground. The pin sources 50A, and monitors the voltage across the 10k thermistor. When the voltage on this pin is above 1.36 (T < 0C) or below 0.29V (T > 40C), charging is disabled and the CHRG and FAULT pins are both pulled low. If internal timer termination is being used, the timer is paused, suspending the charging cycle. Charging resumes when the voltage on NTC returns to within the 0.29V to 1.36V active region. There is approximately 5C of temperature hysteresis associated with each of the temperature thresholds. The temperature monitoring function remains enabled while the thermistor resistance to ground is less than 250k, so if this function is not desired, leave the NTC pin unconnected. BAT (Pin 9): Charger Output Monitor Pin. Connect a 10F decoupling capacitance (CBAT) to ground. Depending on application requirements, larger value decoupling capacitors may be required. The charge function operates to achieve the programmed output battery float voltage (VBAT(FLT)) at this pin. This pin is also the reference for the current sense voltage. Once a charge cycle is terminated, the input bias current of the BAT pin is reduced to < 0.1A, to minimize battery discharge while the charger remains connected. SENSE (Pin 10): Charge Current Sense Pin. Connect the inductor sense resistor (RSENSE) from the SENSE pin to the BAT pin. The voltage across this resistor sets the average charge current. The maximum charge current (ICHG(MAX)) corresponds to 100mV across the sense resistor. This resistor can be set to program maximum charge current as high as 2A. The sense resistor value follows the relation: RSENSE = 0.1/ICHG(MAX) () Once a charge cycle is terminated, the input bias current of the SENSE pin is reduced to < 0.1A, to minimize battery discharge while the charger remains connected. BOOST (Pin 11): Bootstrapped Supply Rail for Switch Drive. This pin facilitates saturation of the switch transistor. Connect a 1F or greater capacitor from the BOOST pin to the SW pin. Operating range of this pin is 0V to 8.5V, referenced to the SW pin. 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. SW (Pin 12): Switch Output Pin. This pin is the output of the charger switch, and corresponds to the emitter of the switch transistor. When enabled, the switch shorts the SW pin to the VIN supply. The drive circuitry for this switch is bootstrapped above the VIN supply using the BOOST supply pin, allowing saturation of the switch for maximum efficiency. The effective on-resistance of the boosted switch is 0.175. SGND (Pin 13): Ground Reference and Backside Exposed Lead Frame Thermal Connection. Solder the exposed lead frame to the PCB ground plane.
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LT3652 BLOCK DIAGRAM
125C TDIE VIN_REG 2.7V BOOST
TIMER
0.2V
R LATCH S Q OSC 1MHz
TIMER OSC. VC
+ -
RS
-
STANDBY RIPPLE COUNTER COUNT RESET C-EA
+
OFFSET
COUNT 0.3V
-
+
RESET ENABLE CHRG FAULT
COUNT
ITH 10 x RS
MODE (TIMER OR C/10)
CONTROL LOGIC TERMINATE
STATUS C/10
0.1V 1V 0.15V
PRECONDITION NTC
VINT 2.7V
x2.25
STANDBY 1.36V 50A 0.29V 1.2V 3.3V 3.218V
TERMINATE
-+
0.7V
1.3V
46A
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+ -
+ -
- +
OVLO
- +
+ -
STANDBY
UVLO
4.6V
35V
+ -
30mV
- +
VIN 10m
+ -
+ -
+- + - - +
SW
SENSE
RS
BAT
-
V-EA
VFB
+
2.3V SHDN
NTC
3652 BD
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LT3652 APPLICATIONS INFORMATION
Overview LT3652 is a complete monolithic, mid-power, multi-chemistry buck battery charger, addressing high input voltage applications with solutions that require a minimum of external components. The IC uses a 1MHz constant frequency, average-current mode step-down architecture. The LT3652 incorporates a 2A switch that is driven by a bootstrapped supply to maximize efficiency during charging cycles. Wide input range allows operation to full charge from voltages as high as 32V. A precision threshold shutdown pin allows incorporation of UVLO functionality using a simple resistor divider. The IC can also be put into a low-current shutdown mode, in which the input supply bias is reduced to only 15A. The LT3652 employs an input voltage regulation loop, which reduces charge current if a monitored input voltage falls below a programmed level. When the LT3652 is powered by a solar panel, the input regulation loop is used to maintain the panel at peak output power. The LT3652 automatically enters a battery precondition mode if the sensed battery voltage is very low. In this mode, the charge current is reduced to 15% of the programmed maximum, as set by the inductor sense resistor, RSENSE. Once the battery voltage reaches 70% of the fully charged float voltage, the IC automatically increases maximum charge current to the full programmed value. The LT3652 can use a charge-current based C/10 termination scheme, which ends a charge cycle when the battery charge current falls to one tenth of the programmed maximum charge current. The LT3652 also contains an internal charge cycle control timer, for timer-based termination. When using the internal timer, the IC combines C/10 detection with a programmable time constraint, during which the charging cycle can continue beyond the C/10 level to top-off a battery. The charge cycle terminates when a specific time elapses, typically 3 hours. When the timer-based scheme is used, the IC also supports bad battery detection, which triggers a system fault if a battery stays in precondition mode for more than one eighth of the total charge cycle time. Once charging is terminated, the LT3652 automatically enters a low-current standby mode where supply bias currents are reduced to 85A. The IC continues to monitor the battery voltage while in standby, and if that voltage falls 2.5% from the full-charge float voltage, the LT3652 engages 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. The LT3652 contains provisions for a battery temperature monitoring circuit. This feature monitors battery temperature using a thermistor during the charging cycle. If the battery temperature moves outside a safe charging range of 0C to 40C, the IC suspends charging and signals a fault condition until the temperature returns to the safe charging range. The LT3652 contains two digital open-collector 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. General Operation (See Block Diagram) The LT3652 uses average current mode control loop architecture, such that the IC servos directly to average charge current. The LT3652 senses charger output voltage through a resistor divider via the VFB pin. The difference between the voltage on this pin and an internal 3.3V voltage reference is integrated by the voltage error amplifier (V-EA). This amplifier generates an error voltage on its output (ITH), which corresponds to the average current sensed across the inductor current sense resistor, RSENSE, which is connected between the SENSE and BAT pins. The ITH voltage is then divided down by a factor of 10, and imposed on the input of the current error amplifier (C-EA). The difference between this imposed voltage and the current sense resistor voltage is integrated, with the resulting voltage (VC) used as a threshold that is compared against an internally generated ramp. The output of this comparison controls the charger's switch.
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LT3652 APPLICATIONS INFORMATION
The ITH error voltage corresponds linearly to average current sensed across the inductor current sense resistor, allowing maximum charge current control by limiting the effective voltage range of ITH. A clamp limits this voltage to 1V which, in turn, limits the current sense voltage to 100mV. This sets the maximum charge current, or the current delivered while the charger is operating in constant-current (CC) mode, which corresponds to 100mV across RSENSE. The ITH voltage is pulled down to reduce this maximum charge current should the voltage on the VIN_REG pin falls below 2.7V (VIN_REG(TH)) or the die temperature approaches 125C. If the voltage on the VFB pin is below 2.3V (VFB(PRE)), the LT3652 engages precondition mode. During the precondition interval, the charger continues to operate in constant-current mode, but the maximum charge current is reduced to 15% of the maximum programmed value as set by RSENSE. When the charger output voltage approaches the float voltage, or the voltage on the VFB pin approaches 3.3V (VFB(FLT)), the charger transitions into constant-voltage (CV) mode and charge current is reduced from the maximum value. As this occurs, the ITH voltage falls from the limit clamp and servos to lower voltages. The IC monitors the ITH voltage as it is reduced, and detection of C/10 charge current is achieved when ITH = 0.1V. If the charger is configured for C/10 termination, this threshold is used to terminate the charge cycle. Once the charge cycle is terminated, the CHRG status pin becomes high-impedance and the charger enters low-current standby mode. The LT3652 contains 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 (EOC) in 3 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 when 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 continues to source low currents into the battery until the programmed EOC time has elapsed, at which time the charge cycle will terminate. At EOC when the charging cycle terminates, if the battery did not achieve at least 97.5% of the full float voltage, charging is deemed unsuccessful, the LT3652 re-initiates, and charging continues for another full timer cycle. Use of the timer function also enables bad-battery detection. This fault condition is achieved if the battery does not respond to preconditioning, such that the charger remains in (or enters) precondition mode after 1/8th of the programmed charge cycle time. A bad battery fault halts the charging cycle, the CHRG status pin goes highimpedance, and the FAULT pin is pulled low. When the LT3652 terminates a charging cycle, whether through C/10 detection or by reaching timer EOC, 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 over-voltage condition and ITH is pulled 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 85A. When the voltage on the VFB 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. VIN Input Supply The LT3652 is 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 recommended to minimize voltage glitches on VIN. The VIN decoupling capacitor (CVIN) absorbs all input switching
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LT3652 APPLICATIONS INFORMATION
ripple current in the charger, so it must have an adequate ripple current rating. RMS ripple current (ICVIN(RMS)) is: ICVIN(RMS) ICHG(MAX) * (VBAT / VIN)*([VIN / VBAT] - 1)1/2, where ICHG(MAX) is the maximum average charge current (100mV/RSENSE). The above relation has a maximum at VIN = 2 * VBAT, where: ICVIN(RMS) = ICHG(MAX)/2.
BAT
3652 F01
BOOST Supply The BOOST bootstrapped supply rail drives the internal switch and facilitates saturation of the switch transistor. Operating range of the BOOST pin is 0V to 8.5V, as refer-
SW LT3652 BOOST SENSE RSENSE
The simple worst-case of 1/2 * ICHG(MAX) is commonly used for design. Bulk capacitance is a function of desired input ripple voltage (VIN), and follows the relation: CIN(BULK) = ICHG(MAX) * (VBAT/VIN) / VIN (F) Input ripple voltages above 0.1V are not recommended. 10F is typically adequate for most charger applications. Charge Current Programming The LT3652 charger is configurable to charge at average currents as high as 2A. Maximum charge current is set by choosing an inductor sense resistor (RSENSE) such that the desired maximum average current through that sense resistor creates a 100mV drop, or: RSENSE = 0.1 / ICHG(MAX) where ICHG(MAX) is the maximum average charge current. A 2A charger, for example, would use a 0.05 sense resistor.
Figure 1. Programming Maximum Charge Current Using RSENSE
enced to the SW pin. Connect a 1F or greater capacitor from the BOOST pin to the SW pin. The voltage on the decoupling capacitor is refreshed through a diode, with the anode connected to either the battery output voltage or an external source, and the cathode connected to the BOOST pin. Rate the diode average current greater than 0.1A, and reverse voltage greater than VIN(MAX). To refresh the decoupling capacitor with a rectifying diode from the battery with battery float voltages higher than 8.4V, a >100mA Zener diode can be put in series with the rectifying diode to prevent exceeding the BOOST pin operating voltage range.
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LT3652 APPLICATIONS INFORMATION
SW LT3652 BOOST SENSE
output, additional bypass capacitance may be desired for visual indication for a no-battery condition (see the Status Pins section). If it is desired to operate a system load from the LT3652 charger output when the battery is disconnected, additional bypass capacitance is required. In this type of application, excessive ripple and/or low amplitude oscillations can occur without additional output bulk capacitance. For these applications, place a 100F low ESR non-ceramic capacitor (chip tantalum or organic semiconductor capacitors such as Sanyo OS-CONs or POSCAPs) from BAT to ground, in parallel with the 10F ceramic bypass capacitor. This additional bypass capacitance may also be required in systems where the battery is connected to the charger with long wires. The voltage rating of CBAT must meet or exceed the battery float voltage. Inductor Selection The primary criterion for inductor value selection in an LT3652 charger is the ripple current created in that inductor. Once the inductance value is determined, an inductor must also have a saturation current equal to or exceeding the maximum peak current in the inductor. An inductor value (L), given the desired amount of ripple current (IMAX) can be approximated using the relation: L = (10 RSENSE / IMAX) * VBAT(FLT) * [1 - (VBAT(FLT) / VIN(MAX))] (H)
BAT
3652 F02
Figure 2. Zener Diode Reduces Refresh Voltage for BOOST Pin
VIN / BOOST Start-Up Requirement The LT3652 operates with a VIN range of 4.95V to 32V, however, a start-up voltage requirement exists due to the nature of the non-synchronous step-down switcher topology used for the charger. If there is no BOOST supply available, the internal switch requires (VIN - VSW) 3.3V to reliably operate. This requirement does not exist if the BOOST supply is available and (VBOOST - VSW) > 2V. When an LT3652 charger is not switching, the SW pin is at the same potential as the battery, which can be as high as VBAT(FLT). As such, for reliable start-up, the VIN supply must be at least 3.3V above VBAT(FLT). Once switching begins and the BOOST supply capacitor gets charged such that (VBOOST - VSW) > 2V, the VIN requirement no longer applies. In low VIN applications, the BOOST supply can be powered by an external source for start-up, eliminating the VIN start-up requirement. VBAT Output Decoupling An LT3652 charger output requires bypass capacitance connected from the BAT pin to ground (CBAT). A 10F ceramic capacitor is required for all applications. In systems where the battery can be disconnected from the charger
In the above relation, IMAX is the normalized ripple current, VIN(MAX) is the maximum operational voltage, and VF is the forward voltage of the rectifying Schottky diode. Ripple current is typically set within a range of 25% to 35% of ICHG(MAX), so an inductor value can be determined by setting 0.25 < IMAX < 0.35.
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LT3652 APPLICATIONS INFORMATION
16 SWITCHED INDUCTOR VALUE (H) 14 12 10 8 6 4 12
forward voltage yields the lowest power loss and highest efficiency. The rectifier diode must be rated to withstand reverse voltages greater than the maximum VIN voltage. The minimum average diode current rating (IDIODE(MAX)) is calculated with maximum output current (ICHG(MAX)), maximum operational VIN, and output at the precondition threshold (VBAT(PRE), or 0.7 * VBAT(FLT)): IDIODE(MAX) > ICHG(MAX) * (VIN(MAX) - VBAT(PRE)) / VIN(MAX)) (A)
20 24 28 16 32 MAXIMUM OPERATIONAL VIN VOLTAGE (V)
3652 F03
For example, a rectifier diode for a 7.2V, 2A charger with a 25V maximum input voltage would require: IDIODE(MAX) > 2 * (25 - 0.7[7.2]) / 25), or IDIODE(MAX) > 1.6A Battery Float Voltage Programming The output battery float voltage (VBAT(FLT)) is programmed by connecting a resistor divider from the BAT pin to VFB. VBAT(FLT) can be programmed up to 14.4V.
BAT LT3652 VFB
3652 F04
Figure 3. 7.2V at 1.5A Switched Inductor Values
Magnetics vendors typically specify inductors with maximum RMS and saturation current ratings. Select an inductor that has a saturation current rating at or above (1+ IMAX/2) * ICHG(MAX), 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: VBAT(FLT) * (1 - VBAT(FLT)/VIN(MAX)) (V * S) Rectifier Selection The rectifier diode from SW to GND, in a LT3652 battery charger provides a current path for the inductor current when the main power switch is disabled. The rectifier is selected based upon forward voltage, reverse voltage, and maximum current. A Schottky diode is required, as low
+ RFB1
RFB2
Figure 4. Feedback Resistors from BAT to VFB Program Float Voltage
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LT3652 APPLICATIONS INFORMATION
Using a resistor divider with an equivalent input resistance at the VFB pin of 250k compensates for input bias current error. Required resistor values to program desired VBAT(FLT) follow the equations: RFB1 = (VBAT(FLT) * 2.5 * 105) / 3.3 RFB2 = (R1 * (2.5 * 105)) / (R1- (2.5 * 105)) () () For a three-resistor network, RFB1 and RFB2 follow the relation: RFB2/RFB1 = 3.3/(VBAT(FLT) - 3.3) Example: For VBAT(FLT) = 3.6V: RFB2/RFB1 = 3.3/(3.6 - 3.3) = 11. Setting divider current (IRFB) = 10A yields: RFB2 = 3.3/10A RFB2 = 330k Solving for RFB1: RFB1 = 330k/11 RFB1 = 30k The divider equivalent resistance is: RFB1||RFB2 = 27.5k To satisfy the 250k equivalent resistance to the VFB pin: RFB3 = 250k - 27.5k RFB3 = 223k. Because the VFB pin is a relatively high impedance node, stray capacitances at this pin must be minimized. Special attention should be given to any stray capacitances that can couple external signals onto the pin, which can produce undesirable output transients or ripple. Effects of parasitic capacitance can typically be reduced by adding a small-value (20pF to 50pF) feedforward capacitor from the BAT pin to the VFB pin. Extra care should be taken during board assembly. Small amounts of board contamination can lead to significant shifts in output voltage. Appropriate post-assembly board
The charge function operates to achieve the final float voltage of 3.3V on the VFB pin. The auto-restart feature initiates a new charging cycle when the voltage at the VFB pin falls 2.5% below that float voltage. Because the battery voltage is across the VBAT(FLT) programming resistor divider, this divider will draw a small amount of current from the battery (IRFB) at a rate of: IRFB = 3.3 / RFB2 Precision resistors in high values may be hard to obtain, so for some lower VBAT(FLT) applications, it may be desirable to use smaller-value feedback resistors with an additional resistor (RFB3) to achieve the required 250k equivalent resistance. The resulting 3-resistor network, as shown in Figure 5, can ease component selection and/or increase output voltage precision, at the expense of additional current through the feedback divider.
BAT LT3652 RFB3 VFB
3652 F05
+ RFB1
RFB2
Figure 5. A Three-Resistor Feedback Network Can Ease Component Selection
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15
LT3652 APPLICATIONS INFORMATION
cleaning measures should be implemented to prevent board contamination, and low-leakage solder flux is recommended. Input Supply Voltage Regulation The LT3652 contains a voltage monitor pin that enables programming a minimum operational voltage. Connecting a resistor divider from VIN to the VIN_REG pin enables programming of minimum input supply voltage, typically used to program the peak power voltage for a solar panel. Maximum charge current is reduced when the VIN_REG pin is below the regulation threshold of 2.7V. If an input supply cannot provide enough power to satisfy the requirements of an LT3652 charger, the supply voltage will collapse. A minimum operating supply voltage can thus be programmed by monitoring the supply through a resistor divider, such that the desired minimum voltage corresponds to 2.7V at the VIN_REG pin. The LT3652 servos the maximum output charge current to maintain the voltage on VIN_REG at or above 2.7V. Programming of the desired minimum voltage is accomplished by connecting a resistor divider as shown in Figure 6. The ratio of RIN1/RIN2 for a desired minimum voltage (VIN(MIN)) is:
PANEL VOLTAGE (V) VOC(25C)
MPPT Temperature Compensation A typical solar panel is comprised of a number of series-connected cells, each cell being a forward-biased p-n junction. As such, the open-circuit voltage (VOC) of a solar cell has a temperature coefficient that is similar to a common p-n diode, or about -2mV/C. The peak power point voltage (VMP) for a crystalline solar panel can be approximated as a fixed voltage below VOC, so the temperature coefficient for the peak power point is similar to that of VOC. Panel manufacturers typically specify the 25C values for VOC, VMP, and the temperature coefficient for VOC, making determination of the temperature coefficient for VMP of a typical panel straight forward. The LT3652 employs a feedback network to program the VIN input regulation voltage. Manipulation of the network makes for efficient implementation of various temperature compensation schemes for a maximum peak power tracking (MPPT) application. As the temperature characteristic for a typical solar panel VMP voltage is highly linear, a
VOC TEMP CO. VOC
RIN1/RIN2 = (VIN(MIN)/2.7) - 1 If the voltage regulation feature is not used, connect the VIN_REG pin to VIN.
VMP(25C) VMP VOC - VMP
5 INPUT SUPPLY RIN1
15
35 25 TEMPERATURE (C)
45
55
3652 F07
VIN LT3652 VIN_REG RIN2
3652 F06
Figure 7. Temperature Characteristics for Solar Panel Output Voltage
Figure 6. Resistor Divider Sets Minimum VIN
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LT3652 APPLICATIONS INFORMATION
simple solution for tracking that characteristic can be implemented using an LM234 3-terminal temperature sensor. This creates an easily programmable, linear temperature dependent characteristic. In the circuit shown in figure 8,
VIN V+ RIN1 V- R RSET VIN VIN_REG RIN2 LT3652
As the temperature coefficient for VMP is similar to that of VOC, the specified temperature coefficient for VOC (TC) of -78mV/C and the specified peak power voltage (VMP(25C)) of 17.6V can be inserted into the equations to calculate the appropriate resistor values for the temperature compensation network in Figure 8. With RSET equal to 1000, then: RSET = 1k RIN1 = -1k * (-0.078 * 4405 ) = 344k RIN2 = 344k/({[17.6 + 344k * (0.0674/1k)]/2.7} - 1) = 24.4k Battery Voltage Temperature Compensation
LM234
3658 F08
Figure 8. MPPT Temperature Compensation Network
RIN1 = -RSET * (TC * 4405), and RIN2 = RIN1/({[VMP(25C) + RIN1 * (0.0674/RSET)]/VIN_REG} - 1) Where: TC = temperature coefficient (in V/C), and VMP(25C) = maximum power voltage at 25C For example, given a common 36-cell solar panel that has the following specified characteristics: Open Circuit Voltage (VOC) = 21.7V Maximum Power Voltage (VMP) = 17.6V Open-Circuit Voltage Temperature Coefficient (VOC) = -78mV/C
Some battery chemistries have charge voltage requirements that vary with temperature. Lead-acid batteries in particular experience a significant change in charge voltage requirements as temperature changes. For example, manufacturers of large lead-acid batteries recommend a float charge of 2.25V/cell at 25C. This battery float voltage, however, has a temperature coefficient which is typically specified at -3.3mV/C per cell. In a manner similar to the MPPT temperature correction outlined previously, implementation of linear battery charge voltage temperature compensation can be accomplished by incorporating an LM234 into the output feedback network. For example, a 6-cell lead acid battery has a float charge voltage that is commonly specified at 2.25V/cell at 25C, or 13.5V, and a -3.3mV/C per cell temperature coefficient,
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LT3652 APPLICATIONS INFORMATION
or -19.8mV/C. Using the feedback network shown in Figure 9, with the desired temperature coefficient (TC) and 25C float voltage (VFLOAT(25C)) specified, and using a convenient value of 2.4k for RSET, necessary resistor values follow the relations: RFB1 = -RSET * (TC * 4405) = -2.4k * (-0.0198 * 4405) = 210k RFB2 = RFB1 / ({[VFLOAT(25C) + RFB1 * (0.0674/ RSET)] / VFB} - 1) = 210k/({[13.5 + 210k * (0.0674/2.4k)]/3.3} - 1) = 43k RFB3 = 250k - RFB1||RFB2 = 250k - 210k||43k = 215k (see the Battery Float Voltage Programming section)
VFB LT3652 BAT RFB1 210k VFB LT3652 69k
While the circuit in Figure 9 creates a linear temperature characteristic that follows a typical -3.3mV/C per cell lead-acid specification, the theoretical float charge voltage characteristic is slightly nonlinear. This nonlinear characteristic follows the relation VFLOAT(1-CELL) = 4 x 10-5 (T2) - 6 x 10-3(T) + 2.375 (with a 2.18V minimum), where T = temperature in C. A thermistor-based network can be used to approximate the nonlinear ideal temperature characteristic across a reasonable operating range, as shown in Figure 10.
BAT 196k
6-CELL LEAD-ACID BATTERY +
69k 198k
22k B = 3380
LM234 V+ R RSET 2.4k V- 6-CELL LEAD-ACID BATTERY VFLOAT (V) + 14.8 14.6 14.4 14.2 14.0 13.8 13.6 13.4 13.2 13.0 -19.8mV/C 12.8 -10 0 20 30 10 40 TEMPERATURE (C) PROGRAMMED VBAT(FLOAT)
3652 F10a
RFB3 215k
RFB2 43k
THEORETICAL VFLOAT
3652 F09a
14.3 14.2 14.0 13.8 VFLOAT (V) 13.6 13.4 13.2 13.0 12.8 12.6 -10 0 20 30 10 40 TEMPERATURE (C) 50 60
50
60
3652 F10b
Figure 10. Thermistor-Based Temperature Compensation Network Programs VFLOAT to Closely Match Ideal Lead-Acid Float Charge Voltage for 6-Cell Charger
3652 F09b
Figure 9. Lead-Acid 6-Cell Float Charge Voltage vs Temperature Has -19.8mV/C Characteristic Using LM234 with Feedback Network
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18
LT3652 APPLICATIONS INFORMATION
Status Pins The LT3652 reports 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 that a C/10 rate, or 1/10th of the programmed maximum charge current. The FAULT pin signals bad battery and NTC faults. These pins are binary coded, and signal following the table below, where ON indicates pin pulled low, and OFF indicates pin high-impedance: When C/10 termination is used, a LT3652 charger will source 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 charger terminates and the LT3652 enters standby mode. The CHRG status pin follows the charger 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.
CHARGER STATUS Not Charging -- Standby or Shutdown Mode Bad Battery Fault (Precondition Timeout / EOC Failure) Normal Charging at C/10 or Greater NTC Fault (Pause)
STATUS PINS STATE CHRG OFF OFF ON ON FAULT OFF ON OFF ON
Timer Termination The LT3652 supports 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 EOC (TEOC) occurs based on CTIMER following the relation: CTIMER = TEOC * 2.27 x 10-7 (Hours)
If the battery is removed from an LT3652 charger that is configured for C/10 termination, a sawtooth waveform of approximately 100mV appears at the charger output, due to cycling between termination and recharge events, This cycling results in pulsing at the CHRG output. An LED connected to this pin will exhibit a blinking pattern, indicating to the user that a battery is not present. The frequency of this blinking pattern is dependent on the output capacitance. C/10 Termination The LT3652 supports a low-current based termination scheme, where a battery charge cycle terminates when the current output from the charger falls to below one-tenth of the maximum current, as programmed with RSENSE. The C/10 threshold current corresponds to 10mV across RSENSE. This termination mode is engaged by shorting the TIMER pin to ground.
Timer EOC is typically set to 3 hours, which requires a 0.68F capacitor. The CHRG status pin continues to signal charging at a C/10 rate, regardless of what termination scheme is used. When timer termination is used, the CHRG status pin is pulled low during a charging cycle until the charger output current falls below the C/10 threshold. The charger continues to top-off the battery until timer EOC, when the LT3652 terminates the charging cycle and enters standby mode. Termination at the end of the timer cycle only occurs if the charging cycle was successful. A successful charge cycle is when the battery is charged to within 2.5% of the
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LT3652 APPLICATIONS INFORMATION
full-charge float voltage. If a charge cycle is not successful at EOC, the timer cycle resets and charging continues for another full timer 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 reengages and starts charging. Preconditioning and Bad Battery Fault A LT3652 has a precondition mode, where charge current is limited to 15% of the programmed ICHG(MAX), as set by RSENSE. The precondition current corresponds to 15mV across RSENSE. Precondition mode is engaged while the voltage on the VFB pin is below the precondition threshold (2.3V, or 0.7 * VBAT(FLT)). Once the VFB voltage rises above the precondition threshold, normal full-current charging can commence. The LT3652 incorporates 70mV of threshold hysteresis to prevent mode glitching. When the internal timer is used for termination, bad battery detection is engaged. There is no provision for bad battery detection if C/10 termination is used. A bad battery fault is triggered when the voltage on VFB remains below the precondition threshold for greater than 1/8 of a full timer cycle (1/8 EOC). A bad battery fault is also triggered if a normally charging battery re-enters precondition mode after 1/8 EOC. When a bad battery fault is triggered, the charging cycle is suspended, so the CHRG status pin becomes highimpedance. The FAULT pin is pulled low to signal a fault detection. Cycling the charger's power or SHDN function initiates a new charging cycle, but a LT3652 charger does not require a reset. Once a bad battery fault is detected, a new timer charging cycle initiates when the VFB pin exceeds the precondition threshold voltage. During a bad battery fault, 0.5mA is sourced from the charger, so removing the failed battery allows the charger output voltage to rise and initiate a charge cycle reset. As such, removing a bad battery resets the LT3652, so a new charge cycle is started by connecting another battery to the charger output. Battery Temperature Monitor and Fault The LT3652 can accommodate battery temperature monitoring by using an NTC (negative temperature co-efficient) thermistor close to the battery pack. The temperature monitoring function is enabled by connecting a 10k, B = 3380 NTC thermistor from the NTC pin to ground. If the NTC function is not desired, leave the pin unconnected. The NTC pin sources 50A, and monitors the voltage dropped across the 10k thermistor. When the voltage on this pin is above 1.36V (0C) or below 0.29V (40C), the battery temperature is out of range, and the LT3652 triggers an NTC fault. The NTC fault condition remains until the voltage on the NTC pin corresponds to a temperature within the 0C to 40C range. Both hot and cold thresholds incorporate hysteresis that correspond to 5C. 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 resistor will increase the effective hot temperature to 45C. 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. Thermal Foldback The LT3652 contains a thermal foldback protection feature that reduces maximum charger output current if the IC junction temperature approaches 125C. In most cases, on-chip temperatures servo such that any excessive temperature conditions are relieved with only slight reductions in maximum charger current.
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LT3652 APPLICATIONS INFORMATION
In some cases, the thermal foldback protection feature can reduce charger currents below the C/10 threshold. In applications that use C/10 termination (TIMER=0V), the LT3652 will suspend charging and enter standby mode until the excessive temperature condition is relieved. Layout Considerations The LT3652 switch node has rise and fall times that are typically less than 10nS to maximize conversion efficiency. The switch node (Pin SW) trace should be kept as short as possible to minimize high frequency noise. The input capacitor (CIN) should be placed close to the IC to minimize this switching noise. Short, wide traces on these nodes also help to avoid voltage stress from inductive ringing. The BOOST decoupling capacitor should also be in close proximity to the IC to minimize inductive ringing. The SENSE and BAT traces should be routed together, and these and the VFB trace should be kept as short as possible. Shielding these signals from switching noise with a ground plane is recommended. High current paths and transients should be kept isolated from battery ground, to assure an accurate output voltage reference. Effective grounding can be 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 11 illustrates an effective grounding scheme using component placement to control ground currents. When the switch is enabled (loop #1), current flows from the input bypass capacitor (CIN) through the switch and inductor to the battery positive terminal. When the switch is disabled (loop #2), the current to the battery positive terminal is provided from ground through the freewheeling Schottky diode (DF). In both cases, these switch currents return to ground via the output bypass capacitor (CBAT). The LT3652 packaging has been 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.
CIN
CBAT
VBAT
1 2 DF
RSENSE
LT3652 VIN SW
+
SENSE BAT VFB
3652 F11
Figure 11. Component Orientation Isolates High Current Paths from Sensitive Nodes
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LT3652 TYPICAL APPLICATIONS
2-Cell Li-Ion Charger (8.3V at 2A) With 3 Hour Timer Termination Powered by Inexpensive 12V at 1A Unregulated Wall Adapter; VIN_REG Loop Servos Maximum Charge Current to Prevent AC Adapter Output from Drooping Lower than 12V
AC ADAPTER INPUT 12V AT 1A SH-DC121000 MBRS340 330k 47k 1F 51k 10k 10k LT3652 VIN_REG SHDN CHRG FAULT TIMER 0.68F R1 10k B = 3380 VIN SW 1F 1N914 BOOST SENSE BAT NTC VFB 626k 412k + 10F VISHAY 1HLP-2525CZ8R2M11 8.2H 0.05 MBRS340 SYSTEM LOAD D3
+
100F
10F
SH-DC121000 AC Adapter V vs I Characteristics
20 18 16 OUTPUT VOLTAGE (V) 14 12 10 8 6 4 2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 OUTPUT CURRENT (A)
3652 TA02b
REMOVABLE 2-CELL Li-Ion PACK (8.3V FLOAT)
3652 TA02a
Basic 2A 1-Cell LiFePO4 Charger (3.6V Float) With C/10 Termination
CMSH3-40MA VIN 5V TO 32V (40V MAX) LT3652 VIN_REG SHDN CHRG FAULT TIMER VIN SW 1F CMDSH2-4L BOOST SENSE BAT NTC VFB
3652 TA03
5.6H 0.05 SYSTEM LOAD
10F
30k 223k 330k
C3 10F
+
LiFePO4 CELL
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LT3652 PACKAGE DESCRIPTION
DD Package 12-Lead Plastic DFN (3mm x 3mm)
(Reference LTC DWG # 05-08-1725 Rev A)
0.70 0.05
3.50 0.05 2.10 0.05
2.38 0.05 1.65 0.05 PACKAGE OUTLINE
0.25 0.05 0.45 BSC 2.25 REF RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
R = 0.115 TYP 7
0.40 0.10 12
3.00 0.10 (4 SIDES) PIN 1 TOP MARK (SEE NOTE 6)
2.38 0.10 1.65 0.10 PIN 1 NOTCH R = 0.20 OR 0.25 x 45 CHAMFER
6 0.200 REF 0.75 0.05 2.25 REF 0.00 - 0.05
1
0.23 0.05 0.45 BSC
(DD12) DFN 0106 REV A
BOTTOM VIEW--EXPOSED PAD NOTE: 1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD AND TIE BARS SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
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LT3652 PACKAGE DESCRIPTION
MSE Package 12-Lead Plastic MSOP Exposed Die Pad ,
(Reference LTC DWG # 05-08-1666 Rev B)
BOTTOM VIEW OF EXPOSED PAD OPTION 2.845 (.112 0.102 .004) 2.845 (.112 1 0.102 .004) 6 0.35 REF
0.889 (.035
0.127 .005)
5.23 (.206) MIN
1.651 (.065
0.102 3.20 - 3.45 .004) (.126 - .136)
0.12 REF DETAIL "B" CORNER TAIL IS PART OF DETAIL "B" THE LEADFRAME FEATURE. FOR REFERENCE ONLY 7 NO MEASUREMENT PURPOSE
12
0.65 0.42 0.038 (.0256) (.0165 .0015) BSC TYP RECOMMENDED SOLDER PAD LAYOUT
4.039 0.102 (.159 .004) (NOTE 3)
12 11 10 9 8 7
0.406 0.076 (.016 .003) REF
0.254 (.010) GAUGE PLANE
DETAIL "A" 0 - 6 TYP 4.90 0.152 (.193 .006) 3.00 0.102 (.118 .004) (NOTE 4)
0.53 0.152 (.021 .006) DETAIL "A" 0.18 (.007) 123456 1.10 (.043) MAX 0.86 (.034) REF
SEATING PLANE
NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
0.22 -0.38 (.009 - .015) TYP
0.650 (.0256) BSC
0.1016 (.004
0.0508 .002)
MSOP (MSE12) 0608 REV B
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24
LT3652 REVISION HISTORY
REV B DATE 2/10 DESCRIPTION Add MSOP-12 Package
(Revision history begins at Rev B)
PAGE NUMBER 1, 2, 24
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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.
25
LT3652 TYPICAL APPLICATION
1A Solar Panel Powered 3-Stage 12V Lead-Acid Fast/Float Charger; 1A Charger Fast Charges with CC/CV Characteristics Up to 14.4V; When Charge Current Falls to 0.1A Charger Switches to 13.5V Float Charge Mode; Charger Re-Initiates 14.4V Fast Charge Mode if Battery Voltage Falls Below 13.2V and Trickle Charges at 0.15A if Battery Voltage is Below 10V; 0C to 45C Battery Temperature Charging Range
SOLAR PANEL INPUT <40V OC VOLTAGE 16V PEAK POWER VOLTAGE MBRS140 10F 499k VIN LT3652 VIN_REG SHDN 100k CHRG FAULT TIMER 4.7F 1M 1N4148 100k SW 1F 1N914 BOOST SENSE BAT 910 NTC 174k VFB + 12V LEAD ACID BATTERY 309k 10F BZX84C6V2L WURTH 7447779122 22H 0.1 MBRS340 SYSTEM LOAD
+
100F
10k B = 3380 muRata NCP18XH103
3652 TA04
RELATED PARTS
PART NUMBER DESCRIPTION COMMENTS Standalone, 4.75V VIN 32V (40V Absolute Maximum), 1MHz, 2A Programmable Charge Current, Timer or C/10 Termination, Small and Few External Components, 3mm x 3mm DFN12 Package, -4.1 for 4.1V Float Voltage Batteries, -4.2 for 4.2V Float Voltage Batteries Standalone, 9V VIN 32V (40V Absolute Maximum), 1MHz, 2A Programmable Charge Current, Timer or C/10 Termination, Small and Few External Components, 3mm x 3mm DFN12 Package, -8.2 for 2 x 4.1V Float Voltage Batteries, -8.4 for 2 x 4.2V Float Voltage Batteries Standalone, 4V VIN 5.5V (6V Absolute Maximum, 7V Transient), 1.5MHz, Synchronous Rectification Efficiency >90%, Adjustable Timer Termination, Small and Few External Components, 4mm x 4mm QFN-16 Package -1 for 4.1V Float Voltage Batteries Standalone, 4.7V VIN 24V, 500kHz Frequency, 3 Hour Charge Termination Complete Charger for 3- or 4-Cell Li-Ion Batteries, AC Adapter Current Limit, 16-Pin Narrow SSOP Package LT3650-4.1/LT3650-4.2 Monolithic 2A Switch Mode 1-Cell Li-Ion Battery Charger
LT3650-8.2/LT3650-8.4 Monolithic 2A Switch Mode 2-Cell Li-Ion Battery Charger
LTC4001/LTC4001-1
Monolithic 2A Switch Mode Synchronous Li-Ion Battery Charger
LTC4002 LTC4006
Switch Mode Lithium-Ion Battery Charger Small, High Efficiency, Fixed Voltage, Lithium-Ion Battery Charger with Termination and Thermistor Sensor High Efficiency, Programmable Voltage Battery Charger with Termination 4A, High Efficiency, Multi-Chemistry Battery Charger
Complete Charger for 3- or 4-Cell Li-Ion Batteries, AC Adapter Current Limit, Thermistor Sensor and Indicator Outputs LTC4008 Constant-Current/Constant-Voltage Switching Regulator Charger, Resistor Voltage/Current Programming, AC Adapter Current Limit and Thermistor Sensor and Indicator Outputs LTC4009/LTC4009-1/ 4A, High Efficiency, Multi-Chemistry Constant-Current/Constant-Voltage Switching Regulator Charger, Resistor LTC4009-2 Battery Charger 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 x 4mm QFN-20 Package -1 Version for 4.1V Li Cells, -2 Version for 4.2V Li Cells LTC40012/LTC40012-1/ 4A, High Efficiency, Multi-Chemistry PowerPath Control, Constant-Current/Constant-Voltage Switching Regulator LTC40012-2/ LTC4012-3 Battery Charger with PowerPathTM 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 x 4mm QFN-20 Package -1 Version for 4.1V Li Cells, -2 Version for 4.2V Li Cells, -3 Version has Extra GND Pin PowerPath is a trademark of Linear Technology Corporation.
3652fb
LTC4007
26 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
LT 0210 REV B * PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2010

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