DC1688A - Linear Technology

LT3652HV

3652hvfb

For more information www.linear.com/LT3652HV

TYPICAL APPLICATION

DESCRIPTION

Power Tracking 2A Battery

Charger

The LT

3652HV is a complete monolithic step-down bat-

tery charger that operates over a 4.95V to 34V input range.

The LT3652HV 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 18V can be programmed with a

resistor divider.

The LT3652HV 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

LT3652HV is powered by a solar panel, the input regulation

loop is used to maintain the panel at peak output power.

The LT3652HV can be conﬁgured to terminate charging when

charge current falls below 1/10 of the programmed maximum

(C/10). Once charging is terminated, the LT3652HV enters a

low-current (85µA) standby mode. An auto-recharge feature

starts a new charging cycle if the battery voltage falls 2.5%

below the programmed ﬂoat voltage. The LT3652HV 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.

FEATURES

APPLICATIONS

n Input Supply Voltage Regulation Loop for Peak

Power Tracking in (MPPT) Solar Applications

n Wide Input Voltage Range: 4.95V to 34V (40V Abs Max)

n Programmable Charge Rate Up to 2A

n User Selectable Termination: C/10 or On-Board

Termination Timer

n Resistor Programmable Float Voltage Up to 18V

Accommodates 4-Cell Li-Ion/Polymer, 5-Cell

LiFePO4, Lead-Acid Chemistries

n Parallelable for Higher Output Current

n 1MHz Fixed Frequency

n 0.5% Float Voltage Reference Accuracy

n 5% Charge Current Accuracy

n 2.5% C/10 Detection Accuracy

n Binary-Coded Open-Collector Status Pins

n Thermally Enhanced 3mm × 3mm DFN and MSE

Packages

n Solar Powered Applications

n Remote Monitoring Stations

n Portable Handheld Instruments

n 12V to 24V Automotive Systems

n Battery Charging from Current Limited Adapter L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and

PowerPath is a trademark of Linear Technology Corporation. All other trademarks are the

property of their respective owners.

VIN_REG Loop Servos Maximum Charge Current to Prevent AC Adapter Output from

Drooping Lower Than 24V 5-Cell LiFePO4 Charger (18V at 1.5A) with C/10 Termination

VIN

AC ADAPTER

INPUT

24VDC AT 1A

VIN_REG

VFB

BOOST

SENSE

BAT

NTC

TIMER

1µF 10V 1N4148

127k

3652 TA01a

10K

B = 3380

10µF

20µH

10µF

5-CELL LiFePO4 PACK

(18V FLOAT)

SYSTEM

LOAD

LT3652HV

44.2k

750k

MBRS340

51.1k

SHDN

CHRG

FAULT

150k

665k

0.068

ADAPTER OUTPUT CURRENT (A)

0 0.2

ADAPTER OUTPUT VOLTAGE (V)

0.6 11.2

3652 TA01b

0.4 0.8 1.61.4 21.8

1A/24VDC Unregulated Adapter

I vs V Characteristic

LT3652HV

3652hvfb

For more information www.linear.com/LT3652HV

PIN CONFIGURATION

ABSOLUTE MAXIMUM RATINGS

Voltages:

VIN ........................................................................40V

VIN_REG, SHDN, CHRG, FAULT ............ VIN + 0.5V, 40V

SW ........................................................................ 40V

SW-VIN.................................................................4.5V

BOOST ...................................................SW+10V, 50V

BAT, SENSE ...........................................................20V

(Note 1)

ORDER INFORMATION

LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LT3652HVEDD#PBF LT3652HVEDD#TRPBF LFRG 12-Lead Plastic DFN 3mm × 3mm –40°C to 125°C

LT3652HVIDD#PBF LT3652HVIDD#TRPBF LFRG 12-Lead Plastic DFN 3mm × 3mm –40°C to 125°C

LT3652HVEMSE#PBF LT3652HVEMSE#TRPBF 3652HV 12-Lead Plastic MSOP –40°C to 125°C

LT3652HVIMSE#PBF LT3652HVIMSE#TRPBF 3652HV 12-Lead Plastic MSOP –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.

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/. Some packages are available in 500 unit reels through

designated sales channels with #TRMPBF sufﬁx.

TOP VIEW

DD PACKAGE

12-LEAD (3mm × 3mm) PLASTIC DFN

1SW

BOOST

SENSE

BAT

NTC

VFB

VIN

VIN_REG

SHDN

CHRG

FAULT

TIMER 67

GND

VIN

VIN_REG

SHDN

CHRG

FAULT

TIMER

BOOST

SENSE

BAT

NTC

VFB

TOP VIEW

GND

MSE PACKAGE

12-LEAD PLASTIC MSOP

TJMAX = 125°C, θJA = 43°C/W, θJC = 3°C/W

EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB

TJMAX = 125°C, θJA = 43°C/W, θJC = 3°C/W

EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB

BAT-SENSE ......................................... –0.5V to +0.5V

NTC, TIMER, ........................................................2.5V

VFB ..........................................................................5V

Operating Junction Temperature Range

(Note 2) ............................................. –40°C to 125°C

Storage Temperature Range ................... –65°C to 150°C

LT3652HV

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SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

VIN VIN Operating Range

VIN Start Voltage

VBAT = 4.2 (Notes 3, 4)

VBAT = 4.2 (Note 4)

4.95

7.5

34 V

VIN(OVLO) OVLO Threshold

OVLO Hysteresis

VIN Rising l34 35

40 V

VIN(UVLO) UVLO Threshold

UVLO Hysteresis

VIN Rising 4.6

0.2

4.95 V

VFB(FLT) Float Voltage Reference (Note 6)

3.282

3.26

3.3 3.318

3.34

ΔVRECHARGE Recharge Reference Threshold Voltage Relative to VFB(FLT) (Note 6) 82.5 mV

VFB(PRE) Reference Precondition Threshold VFB Rising (Note 6) 2.3 V

VFB(PREHYST) Reference Precondition Threshold

Hysteresis

Voltage Relative to VFB(PRE) (Note 6) 70 mV

VIN_REG(TH) Input Regulation Reference VFB = 3V; VSENSE – VBAT = 50mV l2.65 2.7 2.75 V

IIN_REG Input Regulation Reference Bias Current VIN_REG = VIN_REG(TH) l35 100 nA

IVIN Operating Input Supply Current CC/CV Mode, ISW = 0

Standby Mode

Shutdown (SHDN = 0)

l2.5

3.5 mA

µA

IBOOST BOOST Supply Current Switch On, ISW = 0,

2.5 < V(BOOST – SW) < 8.5

20 mA

IBOOST/ISW BOOST Switch Drive ISW = 2A 30 mA/A

VSW(ON) Switch-On Voltage Drop VIN – VSW, ISW = 2A 350 mV

ISW(MAX) Switch Current Limit l2.5 3 A

VSENSE(PRE) Precondition Sense Voltage VSENSE – VBAT; VFB = 2V 15 mV

VSENSE(DC) Maximum Sense Voltage VSENSE – VBAT; VFB = 3V (Note 7) l95 100 105 mV

VSENSE(C/10) C/10 Trigger Sense Voltage VSENSE – VBAT, Falling l7.5 10 12.5 mV

IBAT BAT Input Bias Current Charging Terminated 0.1 1 µA

ISENSE SENSE Input Bias Current Charging Terminated 0.1 1 µA

IVFB VFB Input Bias Current Charging Terminated 65 nA

IVFB VFB Input Bias Current CV Operation (Note 5) 110 nA

VNTC(H) NTC Range Limit (High) VNTC Rising l1.25 1.36 1.45 V

VNTC(L) NTC Range Limit (Low) VNTC Falling l0.27 0.29 0.315 V

VNTC(HYST) NTC Threshold Hysteresis % of threshold 20 %

RNTC(DIS) NTC Disable Impedance Impedance to ground l250 500 kΩ

INTC NTC Bias Current VNTC = 0.8V l47.5 50 52.5 µA

VSHDN Shutdown Threshold Rising l1.15 1.2 1.25 V

VSHDN(HYST) Shutdown Hysteresis 120 mV

ISHDN SHDN Input Bias Current –10 nA

VCHRG, VFAULT Status Low Voltage 10mA Load l0.4 V

ITIMER Charge/Discharge Current 25 µA

VTIMER(DIS) Timer Disable Threshold l0.1 0.25 V

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, Boost – SW = 4V, SHDN = 2V, VFB = 3.3V, CTIMER = 0.6 8µF.

ELECTRICAL CHARACTERISTICS

LT3652HV

3652hvfb

For more information www.linear.com/LT3652HV

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

tTIMER Full Charge Cycle Timeout 3 hr

Precondition Timeout 22.5 min

Timer Accuracy l–10 10 %

fOOperating Frequency 1 MHz

DC Duty Cycle Range Continuous Operation l15 90 %

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, Boost – SW = 4V, SHDN = 2V, VFB = 3.3V, CTIMER = 0.6 8µF.

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 LT3652HV is tested under pulsed load conditions such that

TJ ≅ TA. The LT3652HVE is 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

LT3652HVI speciﬁcations are guaranteed over the full –40°C to 125°C

operating junction temperature range. Note that the maximum ambient

temperature consistent with these speciﬁcations is determined by speciﬁc

operating conditions in conjunction with board layout, the rated package

thermal impedance and other environmental factors.

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 125°C.

ELECTRICAL CHARACTERISTICS

LT3652HV

3652hvfb

For more information www.linear.com/LT3652HV

TYPICAL PERFORMANCE CHARACTERISTICS

Switch Forward Drop (VIN – VSW)

vs Temperature

CC/CV Charging; SENSE Pin Bias

Current vs VSENSE

C/10 Threshold (VSENSE–VBAT)

vs Temperature

VFB Reference Voltage

vs Temperature

VIN Standby Mode Current

vs Temperature

Switch Drive (ISW/IBOOST)

vs Switch Current

TJ = 25°C, unless otherwise noted.

TEMPERATURE (°C)

–50

VFB (FLT)

3.296

3.298

3.300

3.302

050 75

3652 G01a

3.304

–25 25 100 125

TEMPERATURE (°C)

–50

IVIN CURRENT (µA)

100

050 75

3652 G02

–25 25 100

SWITCH CURRENT (A)

ISW/IBOOST

1.6

0.4 0.8 1.2

0.2 1.8

0.6 1.0 1.4 2.0

3652 G03

TEMPERATURE (°C)

–50

320

SW(ON)

(mV)

340

360

380

480

420

050 75

3652 G04

440

460

400

–25 25 100 125

ISW = 2A

VSENSE (V)

–350

SENSE

(µA)

–250

–150

–50

100

122.5

–300

–200

–100

0.5 1.5

3652 G05

VBAT = VBAT(PRE)

VBAT = VBAT(FLT)

TEMPERATURE (°C)

–50

SENSE(C/10)

(mV)

050 75

3652 G06

–25 25 100 125

TEMPERATURE (°C)

–50

VIN_REG(TH) (V)

2.680

2.685

2.690

2.715

2.710

2.705

2.700

2.695

050 75

3652 G01

2.720

–25 25 100 125

VIN_REG Threshold

vs Temperature: ICHG at 50%

LT3652HV

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TYPICAL PERFORMANCE CHARACTERISTICS

Maximum Charge Current

(VSENSE–VBAT) vs Temperature

Thermal Foldback – Maximum

Charge Current (VSENSE–VBAT)

vs Temperature

CC/CV Charging; BAT Pin Bias

Current vs VBAT

TA = 25°C, unless otherwise noted.

TEMPERATURE (°C)

–50

99.0

VSENSE(DC) (mV)

99.2

99.6

99.8

100.0

101.0

100.4

050 75

3652 G07

99.4

100.6

100.8

100.2

–25 25 100 125

VFB = 3V

TEMPERATURE (°C)

SENSE(DC)

(mV)

100

120

45 65 85 105 12535 13525 55 75 95 115

3652 G08

VBAT (V)

–0.4

IBAT (mA)

0.0

0.4

0.8

2.2

1.6

122.5

2.0

1.2

–0.2

0.2

0.6

1.0

1.8

1.4

0.5 1.5 3

3652 G09

VBAT(FLT)

VIN_REG (V)

2.65

VSENSE(DC) (mV)

2.67 2.69 2.7

3652 G10

100

2.66 2.68 2.722.71 2.73 2.74 2.75

VBAT(FLT) (V)

0 2

IRFB (µA)

3652 G11

64 8 10 12 1614

TIME (MINUTES)

EFFICIENCY (%)

CHARGE CURRENT (A); POWER LOSS (W)

0.5

2.0

2.5

1.5

1.0

40 80 100

3652 G12

3.0

20 60 140120 160 180 200

CHARGE

CURRENT

EFFICIENCY

POWER

LOSS

VIN = 20V

Maximum Charge Current

(VSENSE–VBAT) vs VIN_REG Voltage

VFLOAT Programming Resistor

Current vs VFLOAT for 2-Resistor

Network

Charge Current, Efﬁciency, and

Power Loss vs Time

(ICHG(MAX) = 2A; VFLOAT = 8.2V)

Charger Efﬁciency vs Battery

Voltage (ICHG = 2A)

VBAT (V)

EFFICIENCY

(%)

5 7 9 11 134 14 153 6 8 10 12

3652 G13

VIN = 20V WITH INPUT BLOCKING DIODE

Battery Bias Current with

Charger Disabled (IBAT + ISENSE +

IBOOST + ISW)

VBAT (V)

BATTERY CURRENT (µA)

3652 F14

214

416

10 18

VIN FLOATING

VIN = 20V

VSHDN = 0V

LT3652HV

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PIN FUNCTIONS

VIN (Pin 1): Charger Input Supply. VIN operating range

is 4.95V to 34V. VIN must be 3.3V greater than the pro-

grammed output battery ﬂoat voltage (VBAT(FLT)) for reli-

able start-up. (VIN – VBAT(FLT)) ≥ 0.75V is the minimum

operating voltage, provided (VBOOST – VSW) ≥ 2V. IVIN ~

85µA after charge termination. This pin is typically con-

nected to the cathode of a blocking diode.

VIN_REG (Pin 2): Input Voltage Regulation Reference. Maxi-

mum 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 LT3652HV 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 15µA. 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 volt-

age. 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 tem-

perature 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 volt-

age. 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 termina-

tion, a bad battery fault also causes this pin to be pulled

low. If no fault conditions exist, the FA U LT 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-of-

cycle 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 one-

eighth of tEOC, or:

tPRE = CTIMER • 5.5 • 105

A 0.68µF 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 18V.

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 (Ω)

R2 = (R1 • 2.5 • 105)/(R1 - (2.5 • 105)) (Ω)

R1 is connected from BAT to VFB, and R2 is connected

from VFB to ground.

LT3652HV

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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 10kΩ, B = 3380 NTC thermistor

from the NTC pin to ground. The pin sources 50µA, and

monitors the voltage across the 10kΩ thermistor. When

the voltage on this pin is above 1.36 (T < 0°C) or below

0.29V (T > 40°C), charging is disabled and the CHRG and

FA U LT pins are both pulled low. If internal timer termina-

tion 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 5°C 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

10µF decoupling capacitance (CBAT) to ground. Depend-

ing 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 termi-

nated, the input bias current of the BAT pin is reduced to

< 0.1µA, 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 cur-

rent as high as 2A. The sense resistor value follows the

relation:

RSENSE = 0.1/ICHG(MAX) (Ω)

Once a charge cycle is terminated, the input bias current of

the SENSE pin is reduced to < 0.1µA, 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 1µF 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 0.175Ω.

GND (Pin 13): Ground Reference and Backside Exposed

Lead Frame Thermal Connection. Solder the exposed lead

frame to the PCB ground plane.

PIN FUNCTIONS

LT3652HV

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BLOCK DIAGRAM

3652 BD

–

+–

–

TIMER

10mΩ

35V

0.1V

OFFSET

2.3V

4.6V

RESET

ENABLE

COUNT

RESET

C/10

PRECONDITION

1.36V

0.29V

46µA

VIN_REG

BOOST

VIN

SENSE

BAT

VFB

NTC

VINT

2.7V

1.3V

1V 0.15V

1.2V 3.3V 3.218V

TERMINATE

50µA

0.7V

CONTROL LOGIC

RIPPLE

COUNTER

STATUS

TIMER

OSC.

NTC

0.2V

125°C

COUNT

OSC

1MHz

LATCH

C-EA

30mV

x2.25

10 × RS

0.3V

TDIE

ITH

MODE

(TIMER OR C/10)

TERMINATE

2.7V

UVLO

OVLO

–

FAULT

CHRG

STANDBY

SHDN

V-EA

–

+–

STANDBY

–

LT3652HV

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For more information www.linear.com/LT3652HV

APPLICATIONS INFORMATION

Overview

LT3652HV 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 fre-

quency, average-current mode step-down architecture.

The LT3652HV 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 34V. 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 15µA.

The LT3652HV employs an input voltage regulation loop,

which reduces charge current if a monitored input voltage

falls below a programmed level. When the LT3652HV is

to maintain the panel at peak output power.

The LT3652HV 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 LT3652HV 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 pro-

grammed maximum charge current. The LT3652HV 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 LT3652HV automati-

cally enters a low-current standby mode where supply

bias currents are reduced to 85µA. 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

LT3652HV 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 LT3652HV contains provisions for a battery tem-

perature monitoring circuit. This feature monitors battery

temperature using a thermistor during the charging cycle.

If the battery temperature moves outside a safe charg-

ing range of 0°C to 40°C, the IC suspends charging and

signals a fault condition until the temperature returns to

the safe charging range.

The LT3652HV 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 LT3652HV uses average current mode control loop

architecture, such that the IC servos directly to average

charge current. The LT3652HV 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 volt-

age 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.

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 con-

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stant-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 tem-

perature approaches 125°C.

If the voltage on the VFB pin is below 2.3V (VFB(PRE)),

the LT3652HV 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 volt-

age, 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 volt-

age 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 LT3652HV 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 con-

figured 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 LT3652HV re-initiates, and

charging continues for another full timer cycle.

Use of the timer function also enables bad-battery detec-

tion. 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 high-

impedance, and the FAULT pin is pulled low.

When the LT3652HV 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 dis-

abled, and the VIN bias current is reduced to 85µA. 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 LT3652HV is biased through a reverse-current block-

ing element from the charger input supply to 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 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.

The simple worst-case of ½ • ICHG(MAX) is commonly

used for design.

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Bulk capacitance is a function of desired input ripple volt-

age (ΔVIN), and follows the relation:

CIN(BULK) = ICHG(MAX) • (VBAT/VIN)/ΔVIN (µF)

Input ripple voltages above 0.1V are not recommended.

10µF is typically adequate for most charger applica-

tions.

Charge Current Programming

The LT3652HV charger is configurable to charge at aver-

age 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 cur-

rent. A 2A charger, for example, would use a 0.05Ω sense

resistor.

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-

enced to the SW pin. Connect a 1µF 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.

APPLICATIONS INFORMATION

Figure 1. Programming Maximum Charge

Current Using RSENSE

BOOST

SENSE

BAT

RSENSE

LT3652HV

3652 F01

Figure 2. Zener Diode Reduces Refresh

Voltage for BOOST Pin

BOOST

SENSE

BAT

LT3652HV

3652 F02

VIN / BOOST Start-Up Requirement

The LT3652HV operates with a VIN range of 4.95V to 34V,

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 LT3652HV 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 switch-

ing begins and the BOOST supply capacitor gets charged

such that (VBOOST – VSW) > 2V, the VIN requirement no

longer applies.

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APPLICATIONS INFORMATION

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 LT3652HV charger output requires bypass capacitance

connected from the BAT pin to ground (CBAT). A 10µF

ceramic capacitor is required for all applications. In systems

where the battery can be disconnected from the charger

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 LT3652HV

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 oc-

cur without additional output bulk capacitance. For these

applications, place a 100µF 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 10µF 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

LT3652HV 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 peak-to-

peak inductor ripple current (ΔIL) can be approximated

using the relation:

L=10 •RSENSE

ΔIL

ICHG(MAX)

• VBAT(FLT) • 1– VBAT(FLT)

VIN(MAX)

⎡

⎣

⎢

⎤

⎦

⎥

⎥ µH

( )

In the above relation, VIN(MAX) is the maximum operational

voltage. 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 < ΔIL/ICHG(MAX) < 0.35.

Figure 3. 14.4V at 1.5A Switched Inductor Values

MAXIMUM OPERATIONAL VIN VOLTAGE (V)

18 20 22

SWITCHED INDUCTOR VALUE (µH)

3652 F03

26 2824 30 32

Magnetics vendors typically specify inductors with maxi-

mum RMS and saturation current ratings. Select an inductor

that has a saturation current rating at or above ICHG(MAX)

+ ∆IL/ICHG(MAX), and an RMS rating above ICHG(MAX). In-

ductors 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 •µS

( )

Rectifier Selection

The rectifier diode from SW to GND, in a LT3652HV 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

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.

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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) •

IN(MAX)

– V

BAT(PRE)

VIN(MAX)

(A)

For example, a rectifier diode for a 7.2V, 2A charger with

a 25V maximum input voltage would require:

IDIODE(MAX) >2A •

25V

−

0.7(7.2V)

25V ,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 18V.

Figure 4. Feedback Resistors from BAT to VFB

Program Float Voltage

BAT +

VFB

RFB2

RFB1

LT3652HV

3652 F04

Because the battery voltage is across the VBAT(FLT) pro-

gramming 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 ob-

tain, 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.

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) = 10µA yields:

RFB2 = 3.3/10µA

RFB2 = 330k

Solving for RFB1:

RFB1 = 330k/11

RFB1 = 30k

The divider equivalent resistance is:

RFB1||RFB2 = 27.5k

BAT +

VFB

RFB2

RFB3

RFB1

LT3652HV

3652 F05

Figure 5. A Three-Resistor Feedback Network Can

Ease Component Selection

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 (Ω)

RFB2 = (RFB1 • (2.5 • 105))/(RFB1- (2.5 • 105)) (Ω)

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.

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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. Spe-

cial 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

cleaning measures should be implemented to prevent

board contamination, and low-leakage solder flux is

recommended.

Input Supply Voltage Regulation

The LT3652HV contains a voltage monitor pin that enables

programming a minimum operational voltage. Connect-

ing 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 LT3652HV charger, the supply volt-

age 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 LT3652HV

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 ac-

complished by connecting a resistor divider as shown in

Figure 6. The ratio of RIN1/RIN2 for a desired minimum

voltage (VIN(MIN)) is:

RIN1/RIN2 = (VIN(MIN)/2.7) – 1

APPLICATIONS INFORMATION

If the voltage regulation feature is not used, connect the

VIN_REG pin to VIN.

MPPT Temperature Compensation

A typical solar panel is comprised of a number of series-con-

nected 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 25°C 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 LT3652HV 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

Figure 6. Resistor Divider Sets Minimum VIN

VIN

VIN_REG

RIN2

RIN1 LT3652HV

INPUT

SUPPLY

3652 F06

Figure 7. Temperature Characteristics for Solar Panel

Output Voltage

TEMPERATURE (°C)

PANEL VOLTAGE (V)

25 45 55

15 35

3652 F07

VOC(25°C)

VMP(25°C)

VMP

VOC

VOC TEMP CO.

VOC – VMP

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power tracking (MPPT) application. As the temperature

characteristic for a typical solar panel VMP voltage is highly

linear, a simple solution for tracking that characteristic can

be implemented using an LM234 3-terminal temperature

sensor. This creates an easily programmable, linear tem-

perature dependent characteristic.

In the circuit shown in figure 8,

APPLICATIONS INFORMATION

Battery Voltage Temperature Compensation

Some battery chemistries have charge voltage require-

ments that vary with temperature. Lead-acid batteries in

particular experience a significant change in charge volt-

age requirements as temperature changes. For example,

manufacturers of large lead-acid batteries recommend a

float charge of 2.25V/cell at 25°C. 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 ac-

complished 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 25°C,

or 13.5V, and a –3.3mV/°C per cell temperature coefficient,

or –19.8mV/°C. Using the feedback network shown in

Figure 9, with the desired temperature coefficient (TC)

Figure 8. MPPT Temperature Compensation Network

VIN_REG

LT3652HV

VIN

IN LM234

3658 F08

V+

V–

RSET

RIN1

RIN2

RIN1 = –RSET • (TC • 4405), and

RIN2 = RIN1/({[VMP(25°C) + RIN1 • (0.0674/RSET)]/VIN_REG} – 1)

Where: TC = temperature coefficient (in V/°C), and

VMP(25°C) = maximum power voltage at 25°C

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

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(25°C)) of 17.6V can be inserted into the equations to

calculate the appropriate resistor values for the tempera-

ture compensation network in Figure 8. With RSET equal

to 1000Ω, then:

RSET = 1k

RIN1 = –1k • (–0.078 • 4405 ) = 344k

RIN2 = 344k/({[17.6 + 344k • (0.0674/1k)]/2.7} – 1)

= 24.4k

LT3652HV

RFB3

215k RFB2

43k

RSET

2.4k

RFB1

210k

6-CELL

LEAD-ACID

BATTERY

LM234

3652 F09a

V+

V–

BAT

VFB

Figure 9. Lead-Acid 6-Cell Float Charge Voltage vs

Temperature Has –19.8mV/°C Characteristic Using LM234 with

Feedback Network

TEMPERATURE (°C)

–10

FLOAT

(V)

10 5040 60

0 20 30

3652 F09b

12.6

12.8

13.0

13.2

13.4

13.6

13.8

14.0

14.2

14.3

–19.8mV/°C

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APPLICATIONS INFORMATION

and 25°C float voltage (VFLOAT(25°C)) 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(25°C) + 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)

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 charac-

teristic follows the relation VFLOAT(1-CELL) = 4 × 10–5 (T2)

– 6 × 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.

Status Pins

The LT3652HV 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 pro-

grammed 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:

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)

If the battery is removed from an LT3652HV charger that

is configured for C/10 termination, a sawtooth waveform

LT3652HV

196k

198k

6-CELL

LEAD-ACID

BATTERY

22k

B = 3380

3652 F10a

BAT

69k

VFB

TEMPERATURE (°C)

–10

FLOAT

(V)

10 5040 60

0 20 30

3652 F10b

12.8

13.0

13.2

13.4

13.6

13.8

14.0

14.6

14.4

14.2

14.8

THEORETICAL VFLOAT

PROGRAMMED VBAT(FLOAT)

Figure 10. Thermistor-Based Temperature Compensation Network Programs VFLOAT to Closely Match Ideal

Lead-Acid Float Charge Voltage for 6-Cell Charger

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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 LT3652HV 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.

When C/10 termination is used, a LT3652HV 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 LT3652HV 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.

Timer Termination

The LT3652HV 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 × 10–7 (Hours)

Timer EOC is typically set to 3 hours, which requires a

0.68µF 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 LT3652HV

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

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 LT3652HV has a precondition mode, where charge cur-

rent 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 LT3652HV incorporates 70mV of threshold

hysteresis to prevent mode glitching.

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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 high-

impedance. 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 LT3652HV 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 initi-

ate a charge cycle reset. As such, removing a bad battery

resets the LT3652HV, so a new charge cycle is started by

connecting another battery to the charger output.

Battery Temperature Monitor and Fault

The LT3652HV can accommodate battery temperature

monitoring by using an NTC (negative temperature co-effi-

cient) 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 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 LT3652HV

triggers 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 correspond to 5°C.

APPLICATIONS INFORMATION

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 45°C.

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 condi-

tion is relieved.

Thermal Foldback

The LT3652HV contains a thermal foldback protection

feature that reduces maximum charger output current if

the IC junction temperature approaches 125°C. In most

cases, on-chip temperatures servo such that any exces-

sive temperature conditions are relieved with only slight

reductions in maximum charger current.

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 LT3652HV will suspend charging and enter standby

mode until the excessive temperature condition is relieved.

Layout Considerations

The LT3652HV 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 pos-

sible. Shielding these signals from switching noise with

a ground plane is recommended.

LT3652HV

3652hvfb

For more information www.linear.com/LT3652HV

APPLICATIONS INFORMATION

High current paths and transients should be kept iso-

lated 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 posi-

VIN

RSENSE

SENSE

BAT

VFB

GND

LT3652HV

BAT

3652 F11

Figure 11. Component Orientation Isolates High Current Paths

from Sensitive Nodes

tive 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 LT3652HV 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.

LT3652HV

3652hvfb

For more information www.linear.com/LT3652HV

TYPICAL APPLICATIONS

2A Solar Panel Power Manager With 7.2V LiFePO4 Battery

and 17V Peak Power Tracking

Solar Panel Input Voltage Regulation,

Tracks Max Power Point to

Greater Than 98%

VIN

6V TO 34V (40V MAX)

VIN_REG

VFB

BOOST

SENSE

BAT

NTC

TIMER

CMDSH2-4L

SYSTEM

LOAD

1µF

30k

223k

3652 TA05

10µF

0.05

5.6µH

LT3652HV

SHDN

CHRG

FAULT

CMSH3-40MACMSH3-40MA

330k

LiFePO4 CELL

Basic 2A 1-Cell LiFePO4 Charger (3.6V Float) with C/10 Termination

VIN

SOLAR

PANEL INPUT

(<40V OC

VOLTAGE)

VIN_REG

VFB

BOOST

SENSE

BAT

NTC

TIMER

CMSH3-40MA

SYSTEM LOAD

1µF

542k

459k

3652 TA02

10k

B = 3380

2-CELL LiFePO4 (2 × 3.6V) BATTERY PACK

10µF

CMSH1-40MA

10µF

10µH

0.05

LT3652HV

530k

100k

SHDN

CHRG

FAULT

CMSH3-40MA

CHARGER OUTPUT CURRENT (A)

0.2

INPUT REGULATION VOLTAGE (V)

0.6 11.2

3652 TA03

0.4 0.8 1.61.4 21.8

100% TO 98% PEAK POWER

98% TO 95% PEAK POWER

TA = 25°C

LT3652HV

3652hvfb

For more information www.linear.com/LT3652HV

3.00 ±0.10

(4 SIDES)

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

0.40 ±0.10

BOTTOM VIEW—EXPOSED PAD

1.65 ±0.10

0.75 ±0.05

R = 0.115

TYP

127

PIN 1

TOP MARK

(SEE NOTE 6)

0.200 REF

0.00 – 0.05

(DD12) DFN 0106 REV A

0.23 ±0.05

PIN 1 NOTCH

R = 0.20 OR

0.25 × 45°

CHAMFER

2.38 ±0.10

2.25 REF

0.45 BSC

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED

0.25 ±0.05

2.25 REF

2.38 ±0.05

1.65 ±0.05

2.10 ±0.05

0.70 ±0.05

3.50 ±0.05

PACKAGE

OUTLINE

0.45 BSC

DD Package

12-Lead Plastic DFN (3mm × 3mm)

(Reference LTC DWG # 05-08-1725 Rev A)

Please refer to http://www.linear.com/product/LT3652HV#packaging for the most recent package drawings.

MSOP (MSE12) 0213 REV G

0.53 ±0.152

(.021 ±.006)

SEATING

PLANE

0.18

(.007)

1.10

(.043)

MAX

0.22 –0.38

(.009 – .015)

TYP

0.86

(.034)

REF

0.650

(.0256)

BSC

12 11 10 9 8 7

DETAIL “B”

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

6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL

NOT EXCEED 0.254mm (.010") PER SIDE.

0.254

(.010) 0° – 6° TYP

DETAIL “A”

GAUGE PLANE

RECOMMENDED SOLDER PAD LAYOUT

BOTTOM VIEW OF

EXPOSED PAD OPTION

2.845 ±0.102

(.112 ±.004)

2.845 ±0.102

(.112 ±.004)

4.039 ±0.102

(.159 ±.004)

(NOTE 3)

1.651 ±0.102

(.065 ±.004)

1.651 ±0.102

(.065 ±.004)

0.1016 ±0.0508

(.004 ±.002)

1 2 3 4 5 6

3.00 ±0.102

(.118 ±.004)

(NOTE 4)

0.406 ±0.076

(.016 ±.003)

REF

4.90 ±0.152

(.193 ±.006)

DETAIL “B”

CORNER TAIL IS PART OF

THE LEADFRAME FEATURE.

FOR REFERENCE ONLY

NO MEASUREMENT PURPOSE

0.12 REF

0.35

REF

5.10

(.201)

MIN

3.20 – 3.45

(.126 – .136)

0.889 ±0.127

(.035 ±.005)

0.42 ±0.038

(.0165 ±.0015)

TYP

0.65

(.0256)

BSC

MSE Package

12-Lead Plastic MSOP, Exposed Die Pad

(Reference LTC DWG # 05-08-1666 Rev G)

PACKAGE DESCRIPTION

LT3652HV

3652hvfb

For more information www.linear.com/LT3652HV

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibilit y is assumed for its use. Linear Technology Corporation makes no representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

REVISION HISTORY

REV DATE DESCRIPTION PAGE NUMBER

A01/13 Added new Battery Bias Current curve 6

B01/16 Enhanced Pin Conﬁguration

Added Note 2 to top of Electrical Characteristics

Enhanced Note 2

Changed Name of Pin 13

Modiﬁed Inductor Selection section

Modiﬁed Battery Float Voltage Programming Equations

3, 4

LT3652HV

3652hvfb

For more information www.linear.com/LT3652HV

 LINEAR TECHNOLOGY CORPORATION 2010

LT 0116 REV B • PRINTED IN USA

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LT3652HV

RELATED PARTS

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; 0°C to 45°C Battery Temperature Charging Range

VIN

SOLAR PANEL INPUT

<40V OC VOLTAGE

16V PEAK POWER VOLTAGE

VIN_REG

VFB

BOOST

SENSE

BAT

NTC

TIMER

22µH MBRS340

309k

100k

1µF 1N4148 BZX84C6V2L

910

174k

1N41481M

SYSTEM

LOAD

WURTH

7447779122

12V LEAD

ACID BATTERY

10k

B = 3380

muRata

NCP18XH103

10µF

0.1

100µF

LT3652HV

10µF

4.7µF

SHDN

CHRG

FAULT

499k

100k +

3652 TA04

MBRS140

PART NUMBER DESCRIPTION COMMENTS

LT3650-8.2/LT3650-8.4 Monolithic 2A Switch Mode 2-Cell Li-Ion

Battery Charger

Standalone, 9V ≤ VIN ≤ 32V (40V Absolute Maximum), 1MHz, 2A Programmable

Charge Current, Timer or C/10 Termination, Small and Few External

Components, 3mm × 3mm DFN12 Package, –8.2 for 2 × 4.1V Float Voltage

Batteries, –8.4 for 2 × 4.2V Float Voltage Batteries

LTC4001/LTC4001-1 Monolithic 2A Switch Mode Synchronous

Li-Ion Battery Charger

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 × 4mm QFN-16 Package –1 for 4.1V Float

Voltage Batteries

LTC4002 Switch Mode Lithium-Ion Battery Charger Standalone, 4.7V ≤ VIN ≤ 24V, 500kHz Frequency, 3 Hour Charge Termination

LTC4006 Small, High Efficiency, Fixed Voltage,

Lithium-Ion Battery Charger with

Termination and Thermistor Sensor

Complete Charger for 3- or 4-Cell Li-Ion Batteries, AC Adapter Current Limit,

16-Pin Narrow SSOP Package

LTC4007 High Efficiency, Programmable Voltage

Battery Charger with Termination

Complete Charger for 3- or 4-Cell Li-Ion Batteries, AC Adapter Current Limit,

Thermistor Sensor and Indicator Outputs

LTC4008 4A, High Efficiency, Multi-Chemistry

Battery Charger

Constant-Current/Constant-Voltage Switching Regulator Charger, Resistor

Voltage/Current Programming, AC Adapter Current Limit and Thermistor Sensor

and Indicator Outputs

LTC4012/LTC4012-1/

LTC4012-2/ LTC4012-3

4A, High Efficiency, Multi-Chemistry

Battery Charger with PowerPath™ Control

PowerPath Control, Constant-Current/Constant-Voltage Switching Regulator

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 –1 Version for 4.1V Li Cells,

–2 Version for 4.2V Li Cells, –3 Version has Extra GND Pin

LTC4015 Multichemistry Buck Battery Charger

Controller with Digital Telemetry System

Multichemistry Li-Ion/Polymer, LiFePO4, or Lead-Acid Battery Charger with

Termination, Digital Telemetry System Monitors VBAT, IBAT, RBAT, NTC Ratio

(Battery Temperature), VIN, IIN, VSYSTEM, Die Temperature, Coulomb Counter and

Integrated 14-Bit ADC, Maximum Power Point Tracking, Wide Charging Input

Voltage Range: 4.5V to 35V, Wide Battery Voltage Range: Up to 35V,

5mm × 7mm QFN-38 Package

LTC4020 55V Buck-Boost Multi-Chemistry Battery

Charger

Wide Voltage Range: 4.5V to 55V Input, Up to 55V Output (60V Absolute

Maximums), Synchronous Buck-Boost DC/DC Controller, Li-Ion and Lead-Acid

Charge Algorithms, Input Voltage Regulation for High Impedance Input Supplies

and Solar Panel Peak Power Operation, Low Proﬁle (0.75mm) 38-Pin 5mm ×

7mm QFN Package