LT3652EDDPBF [Linear]
Power Tracking 2A Battery Charger for Solar Power; 功率跟踪2A电池充电器太阳能电源
| 型号： | LT3652EDDPBF |
| 厂家： | 
Linear |
| 描述： | Power Tracking 2A Battery Charger for Solar Power |
| 文件： | 总26页 (文件大小：255K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT3652
Power Tracking 2A Battery
Charger for Solar Power
FEATURES
DESCRIPTION
The LT®3652 is a complete monolithic step-down bat-
tery 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.
n
Input Supply Voltage Regulation Loop for Peak
Power Tracking in (MPPT) Solar Applications
n
Wide Input Voltage Range: 4.95V to 32V (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 14.4V
Accommodates Li-Ion/Polymer, LiFePO , SLA,
4
NiMH/NiCd Chemistries
TheLT3652employsaninputvoltageregulationloop,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.
n
No V Blocking Diode Required for Battery
IN
Voltages ≤ 4.2V
1MHz Fixed Frequency
n
n
n
n
n
n
0.5% Float Voltage Reference Accuracy
5% Charge Current Accuracy
2.5% C/10 Detection Accuracy
Binary-Coded Open-Collector Status Pins
3mm × 3mm DFN12 or MSOP-12 Packages
The LT3652 can be configured to terminate charging
when charge current falls below 1/10 of the programmed
maximum(C/10).Oncechargingisterminated,theLT3652
enters a low-current (85μA) standby mode. An auto-re-
charge 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.
APPLICATIONS
n
Solar Powered Applications
n
Remote Monitoring Stations
n
LiFePO (Lithium Phosphate) Applications
4
n
n
Portable Handheld Instruments
12V to 24V Automotive Systems
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.
Solar Panel Input Voltage
Regulation, Tracks Max Power
Point to Greater Than 98%
TYPICAL APPLICATION
2A Solar Panel Power Manager With 7.2V LiFePO4 Battery
and 17V Peak Power Tracking
22
CMSH1-40MA
T
= 25°C
A
SOLAR PANEL INPUT
(<40V OC VOLTAGE)
SYSTEM LOAD
CMSH3-40MA
20
18
16
14
12
10
CMSH3-40MA
10μF
530k
100% TO 98% PEAK POWER
98% TO 95% PEAK POWER
SW
V
IN
LT3652
IN_REG
1μF
10μH
0.05
V
BOOST
SENSE
BAT
SHDN
CHRG
FAULT
TIMER
100k
10μF
542k
NTC
V
FB
459k
+
10k
B = 3380
0.2
0.6 0.8
1
1.2 1.4 1.6 1.8
2
0.4
CHARGER OUTPUT CURRENT (A)
3652 TA01b
2-CELL LiFePO (2 × 3.6V) BATTERY PACK
4
3652 TA01a
3652fb
1
LT3652
ABSOLUTE MAXIMUM RATINGS
(Note 1)
BAT-SENSE ......................................... –0.5V to +0.5V
NTC, TIMER,........................................................2.5V
FB
Voltages:
V ........................................................................40V
IN
IN_REG
V ..........................................................................5V
V
, SHDN, CHRG, FAULT ............ V + 0.5V, 40V
IN
Operating Junction Temperature Range
(Note 2) ............................................. –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
SW........................................................................40V
SW-V .................................................................4.5V
IN
BOOST...................................................SW+10V, 50V
BAT, SENSE...........................................................15V
PIN CONFIGURATION
TOP VIEW
TOP VIEW
1
2
3
4
5
6
12 SW
V
IN
1
2
3
4
5
6
V
12 SW
11 BOOST
10 SENSE
IN
11 BOOST
10 SENSE
V
IN_REG
V
IN_REG
SHDN
CHRG
FAULT
TIMER
SHDN
13
13
9
8
7
BAT
NTC
CHRG
FAULT
TIMER
9
8
7
BAT
NTC
V
FB
V
FB
MSE PACKAGE
12-LEAD PLASTIC MSOP
DD PACKAGE
12-LEAD (3mm × 3mm) PLASTIC DFN
T
= 125°C, θ = 43°C/W, θ = 3°C/W
T
= 125°C, θ = 43°C/W, θ = 3°C/W
JMAX
JA
JC
JMAX JA JC
EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB
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
PART MARKING*
PACKAGE DESCRIPTION
12-Lead Plastic DFN 3mm × 3mm
TEMPERATURE RANGE
–40°C to 125°C
LT3652EDD#TRPBF
LT3652IDD#TRPBF
LT3652EMSE#TRPBF
LT3652IMSE#TRPBF
LFHT
LFHT
3652
3652
12-Lead Plastic DFN 3mm × 3mm
12-Lead Plastic MSOP
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
12-Lead Plastic MSOP
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/
3652fb
2
LT3652
The l denotes the specifications which apply over the full operating
ELECTRICAL CHARACTERISTICS
temperature range, otherwise specifications are at TA = 25°C. VIN = 20V, Boost – SW = 4V, SHDN = 2V, VFB = 3.3V, CTIMER = 0.68μF.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
l
l
V
V
V
V
V
V
Operating Range
Start Voltage
V
V
= 4.2 (Notes 3, 4)
= 4.2 (Note 4)
4.95
7.5
32
V
V
IN
IN
IN
BAT
BAT
l
OVLO Threshold
OVLO Hysteresis
V
Rising
32
35
1
40
V
V
IN(OVLO)
IN(UVLO)
FB(FLT)
IN
UVLO Threshold
UVLO Hysteresis
V
Rising
4.6
0.2
4.95
V
V
IN
Float Voltage Reference
(Note 6)
3.282
3.26
3.3
3.318
3.34
V
V
l
ΔV
Recharge Reference Threshold
Voltage Relative to V
(Note 6)
(Note 6)
82.5
2.3
70
mV
V
RECHARGE
FB(FLT)
V
V
Reference Precondition Threshold
V
FB
Rising (Note 6)
FB(PRE)
Reference Precondition Threshold
Hysteresis
Voltage Relative to V
mV
FB(PREHYST)
FB(PRE)
l
l
l
V
Input Regulation Reference
V
V
= 3V; V
– V = 50mV
2.65
2.7
35
2.75
100
3.5
V
IN_REG(TH)
IN_REG
VIN
FB
SENSE
BAT
I
I
Input Regulation Reference Bias Current
Operating Input Supply Current
= V
nA
IN_REG
IN_REG(TH)
CC/CV Mode, I = 0
2.5
85
15
mA
μA
μA
SW
Standby Mode
Shutdown (SHDN = 0)
I
I
BOOST Supply Current
Switch On, I = 0,
20
mA
BOOST
SW
(BOOST – SW)
2.5 < V
< 8.5
I
BOOST Switch Drive
I
SW
= 2A
30
350
3
mA/A
mV
A
BOOST/ SW
V
Switch-On Voltage Drop
Switch Current Limit
V
IN
– V , I = 2A
SW SW
SW(ON)
l
I
2.5
SW(MAX)
V
V
V
Precondition Sense Voltage
Maximum Sense Voltage
C/10 Trigger Sense Voltage
BAT Input Bias Current
SENSE Input Bias Current
Charger Reverse Current
V
V
V
– V ; V = 2V
15
100
10
0.1
0.1
1
mV
mV
mV
μA
SENSE(PRE)
SENSE(DC)
SENSE(C/10)
BAT
SENSE
SENSE
SENSE
BAT FB
l
l
– V ; V = 3V (Note 7)
95
105
12.5
1
BAT FB
– V , Falling
7.5
BAT
I
I
I
Charging Terminated
Charging Terminated
1
μA
SENSE
V
IN
= 0; V = V
= V = 4.2V
μA
REVERSE
BAT
SENSE
SW
I
+ I
+ I
SENSE SW
BAT
I
I
V
V
Input Bias Current
Input Bias Current
Charging Terminated
CV Operation (Note 5)
65
110
1.36
0.29
20
nA
nA
V
VFB
FB
FB
VFB
l
l
V
V
V
NTC Range Limit (High)
NTC Range Limit (Low)
NTC Threshold Hysteresis
NTC Disable Impedance
NTC Bias Current
V
NTC
V
NTC
Rising
Falling
1.25
0.27
1.45
NTC(H)
0.315
V
NTC(L)
% of threshold
%
kΩ
μA
V
NTC(HYST)
l
l
l
R
Impedance to ground
250
47.5
1.15
500
50
NTC(DIS)
NTC
I
V
NTC
= 0.8V
52.5
1.25
V
V
Shutdown Threshold
Shutdown Hysteresis
SHDN Input Bias Current
Status Low Voltage
Rising
1.2
SHDN
120
–10
mV
nA
V
SHDN(HYST)
SHDN
I
l
l
V
, V
10mA Load
0.4
CHRG FAULT
I
Charge/Discharge Current
Timer Disable Threshold
25
μA
V
TIMER
V
0.1
0.25
TIMER(DIS)
3652fb
3
LT3652
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 20V, Boost – SW = 4V, SHDN = 2V, VFB = 3.3V, CTIMER = 0.68μF.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
3
MAX
UNITS
hr
t
Full Charge Cycle Timeout
Precondition Timeout
Timer Accuracy
TIMER
22.5
min
%
l
l
–10
15
10
90
f
Operating Frequency
Duty Cycle Range
1
MHz
%
O
DC
Continuous Operation
Note 4: This parameter is valid for programmed output battery float
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 0°C to 125°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
LT3652IDD specifications are guaranteed over the full –40°C to 125°C
operating junction temperature range. High junction temperatures degrade
operating lifetimes.
voltages ≤ 4.2V. V operating range minimum is 0.75V above the
IN
programmed output battery float voltage (V
+ 0.75V). V Start
BAT(FLT)
IN
Voltage is 3.3V above the programmed output battery float voltage
(V + 3.3V).
BAT(FLT)
Note 5: Output battery float voltage (V ) programming resistor
BAT(FLT)
divider equivalent resistance = 250k compensates for input bias current.
Note 6: All V voltages measured through 250k series resistance.
FB
SENSE(DC)
Note 7: V
approaches 125°C.
is reduced by thermal foldback as junction temperature
Note 3: V minimum voltages below the start threshold are only
IN
supported if (V -V ) > 2V.
BOOST SW
3652fb
4
LT3652
TJ = 25°C, unless otherwise noted.
TYPICAL PERFORMANCE CHARACTERISTICS
VIN Standby Mode Current
vs Temperature
VIN_REG Threshold
VFB Reference Voltage
vs Temperature
vs Temperature: ICHG at 50%
2.720
2.715
2.710
2.705
2.700
2.695
2.690
2.685
2.680
100
95
90
85
80
75
70
65
3.304
3.302
3.300
3.298
3.296
–50
0
25
50
75 100 125
–50
–25
0
25
50
75 100 125
–25
50
–50
0
25
75
100
–25
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
3652 G01
3652 G01a
3652 G02
Switch Forward Drop (VIN – VSW
vs Temperature
)
Switch Drive (ISW/IBOOST
vs Switch Current
)
480
36
33
30
27
24
21
18
15
12
9
I
= 2A
SW
460
440
420
400
380
360
340
320
6
3
0
–50
0
25
50
75 100 125
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
–25
TEMPERATURE (°C)
SWITCH CURRENT (A)
3652 G03
3652 G04
C/10 Threshold (VSENSE–VBAT
vs Temperature
)
CC/CV Charging; SENSE Pin Bias
Current vs VSENSE
12
11
10
9
100
50
V
= V
BAT(PRE)
BAT
0
V
= V
BAT(FLT)
–50
BAT
–100
–150
–200
–250
–300
–350
8
–50
0
25
50
75 100 125
–25
0
0.5
1
1.5
2
2.5
(V)
TEMPERATURE (°C)
V
SENSE
3652 G05
3652 G06
3652fb
5
LT3652
TA = 25°C, unless otherwise noted.
TYPICAL PERFORMANCE CHARACTERISTICS
Thermal Foldback – Maximum
Maximum Charge Current
(VSENSE–VBAT) vs Temperature
CC/CV Charging; BAT Pin Bias
Current vs VBAT
Charge Current (VSENSE–VBAT
vs Temperature
)
120
100
80
60
40
20
0
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
101.0
100.8
100.6
100.4
100.2
100.0
99.8
V
= 3V
FB
99.6
99.4
99.2
V
BAT(FLT)
3
99.0
25 35 45 55 65 75 85 95 105 115 125 135
0
0.5
1
1.5
2
2.5
(V)
–50
0
25
50
75 100 125
–25
TEMPERATURE (°C)
V
TEMPERATURE (°C)
BAT
3652 G08
3652 G09
3652 G07
VFLOAT Programming Resistor
Current vs VFLOAT for 2-Resistor
Network
Maximum Charge Current
(VSENSE–VBAT) vs VIN_REG Voltage
12
10
8
100
80
60
40
20
0
6
4
2
0
2.65 2.66 2.67 2.68 2.69 2.7 2.71 2.72 2.73 2.74 2.75
(V)
0
2
4
6
V
8
10 12 14 16
(V)
V
IN_REG
BAT(FLT)
3652 G10
3652 G11
Charge Current, Efficiency, and
Power Loss vs Time
(ICHG(MAX) = 2A; VFLOAT = 8.2V)
Charger Efficiency vs Battery
Voltage (ICHG = 2A)
95
85
75
65
55
3.0
2.5
2.0
1.5
1.0
0.5
0
90
88
86
84
82
80
78
76
74
72
70
V
= 20V
IN
EFFICIENCY
POWER
LOSS
CHARGE
CURRENT
45
35
V
= 20V WITH INPUT BLOCKING DIODE
IN
0
20 40 60 80 100 120 140 160 180 200
TIME (MINUTES)
3
4
5
6
7
8
V
9
10 11 12 13 14 15
(V)
BAT
3652 G13
3652 G12
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6
LT3652
PIN FUNCTIONS
V
(Pin 1): Charger Input Supply. V operating range
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 FAULT pin remains
high-impedance.
IN
IN
is 4.95V to 32V. V must be 3.3V greater than the pro-
IN
grammed output battery float voltage (V
able start-up. (V – V
) for reli-
BAT(FLT)
) ≥ 0.75V is the minimum
IN
BAT(FLT)
operating voltage, provided (V
85μA after charge termination.
– V ) ≥ 2V. I
~
VIN
BOOST
SW
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:
V
(Pin 2): Input Voltage Regulation Reference.
IN_REG
Maximumchargecurrentisreducedwhenthispinisbelow
2.7V. Connecting a resistor divider from V to this pin
enablesprogrammingofminimumoperationalV voltage.
IN
6
IN
t
= C
• 4.4 • 10
TIMER
EOC
This is typically used to program the peak power voltage
forasolarpanel. TheLT3652servosthemaximumcharge
current required to maintain the programmed operational
V voltage, through maintaining the voltage on V
A bad battery fault is generated if the battery does not
achieve the precondition threshold voltage within one-
eighth of t , or:
EOC
IN
IN_REG
5
at or above 2.7V. If the voltage regulation feature is not
used, connect the pin to V .
t
= C
• 5.5 • 10
TIMER
PRE
IN
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
SHDN (Pin 3): Precision Threshold Shutdown Pin. The
enable threshold is 1.2V (rising), with 120mV of input
hysteresis.Wheninshutdownmode,allchargingfunctions
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
threshold, or I
/10
CHG(MAX)
mode where V currentisreducedto15μA. Typical SHDN
IN
V (Pin7):BatteryFloatVoltageFeedbackReference. The
FB
pin input bias current is 10nA. If the shutdown function
charge function operates to achieve a final float voltage of
is not desired, connect the pin to V .
IN
3.3V on this pin. Output battery float voltage (V
)
BAT(FLT)
can be
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
is programmed using a resistor divider. V
programmed up to 14.4V.
BAT(FLT)
The auto-restart feature initiates a new charging cycle
as V when disabled, and can sink currents up to 10mA
IN
when the voltage at the V pin falls 2.5% below the float
FB
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.
voltage reference.
The V pin input bias current is 110nA. Using a resistor
FB
divider with an equivalent input resistance at the V pin
FB
of 250k compensates for input bias current error.
Required resistor values to program desired V
follow the equations:
BAT(FLT)
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
5
R1 = (V
• 2.5 • 10 )/3.3
(Ω)
(Ω)
BAT(FLT)
5
5
R2 = (R1 • 2.5 • 10 )/(R1 - (2.5 • 10 ))
as V when disabled, and can sink currents up to 10mA
IN
R1 is connected from BAT to V , and R2 is connected
FB
when enabled. This pin indicates fault conditions during a
from V to ground.
FB
batterychargingcycle. Atemperaturefaultcausesthispin
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7
LT3652
PIN FUNCTIONS
NTC (Pin 8): Battery Temperature Monitor Pin. This pin is
the input to the NTC (Negative Temperature Coefficient)
thermistortemperaturemonitoringcircuit.Thisfunctionis
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
FAULT pins are both pulled low. If internal timer termina-
tion is being used, the timer is paused, suspending the
chargingcycle.ChargingresumeswhenthevoltageonNTC
returns to within the 0.29V to 1.36V active region. There
isapproximately5°Coftemperaturehysteresisassociated
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.
charge current. The maximum charge current (I
)
CHG(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:
R
SENSE
= 0.1/I
(Ω)
CHG(MAX)
Onceachargecycleisterminated, theinputbiascurrentof
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.Thispinfacilitatessaturationoftheswitchtransistor.
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.
BAT (Pin 9): Charger Output Monitor Pin. Connect a
10μF decoupling capacitance (C ) to ground. Depend-
BAT
ing on application requirements, larger value decoupling
capacitors may be required. The charge function operates
to achieve the programmed output battery float voltage
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
(V
) at this pin. This pin is also the reference for
BAT(FLT)
the SW pin to the V supply. The drive circuitry for this
IN
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.
switch is bootstrapped above the V supply using the
IN
BOOST supply pin, allowing saturation of the switch for
maximum efficiency. The effective on-resistance of the
boosted switch is 0.175Ω.
SENSE (Pin 10): Charge Current Sense Pin. Connect the
SGND (Pin 13): Ground Reference and Backside Exposed
Lead Frame Thermal Connection. Solder the exposed lead
frame to the PCB ground plane.
inductorsenseresistor(R
)fromtheSENSEpintothe
SENSE
BAT pin. The voltage across this resistor sets the average
3652fb
8
LT3652
BLOCK DIAGRAM
V
+
–
IN_REG
125°C
+
–
STANDBY
UVLO
+
–
T
2.7V
DIE
4.6V
BOOST
+
–
OVLO
V
IN
35V
10mΩ
+
–
R
0.2V
TIMER
LATCH
S
Q
30mV
–
+
OSC
1MHz
+
–
TIMER
OSC.
SW
SENSE
BAT
V
C
R
R
S
S
–
C-EA
STANDBY
+
RIPPLE
COUNTER
OFFSET
COUNT
V
+
–
FB
RESET
–
COUNT
0.3V
V-EA
+
COUNT
MODE
RESET
ENABLE
I
TH
10 × R
S
(TIMER OR C/10)
CHRG
FAULT
CONTROL LOGIC
TERMINATE
STATUS
–
+
C/10
0.1V
–
+
1V
0.15V
PRECONDITION
2.3V
NTC
–
+
SHDN
V
INT
2.7V
x2.25
+
–
–
+
STANDBY
1.2V 3.3V
3.218V
1.36V
TERMINATE
50μA
–
+
0.29V
NTC
3652 BD
+
–
1.3V
0.7V
46μA
3652fb
9
LT3652
APPLICATIONS INFORMATION
Overview
Once charging is terminated, the LT3652 automatically
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 LT3652
engages an automatic charge cycle restart. The IC also
automatically restarts a new charge cycle after a bad bat-
tery fault once the failed battery is removed and replaced
with another battery.
LT3652isacompletemonolithic, mid-power, multi-chem-
istry buck battery charger, addressing high input voltage
applicationswithsolutionsthatrequireaminimumofexter-
nal 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
chargefromvoltagesashighas32V. Aprecisionthreshold
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 LT3652 contains provisions for a battery temperature
monitoringcircuit. Thisfeaturemonitorsbatterytempera-
ture using a thermistor during the charging cycle. If the
battery temperature moves outside a safe charging 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 LT3652 employs an input voltage regulation loop,
which reduces charge current if a monitored input volt-
age 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 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.
The LT3652 automatically enters a battery precondition
modeifthesensedbatteryvoltageisverylow.Inthismode,
the charge current is reduced to 15% of the programmed
General Operation (See Block Diagram)
maximum, as set by the inductor sense resistor, R
.
SENSE
The LT3652 uses average current mode control loop
architecture, such that the IC servos directly to average
chargecurrent.TheLT3652senseschargeroutputvoltage
Once the battery voltage reaches 70% of the fully charged
float voltage, the IC automatically increases maximum
charge current to the full programmed value.
through a resistor divider via the V pin. The difference
FB
between the voltage on this pin and an internal 3.3V volt-
age reference is integrated by the voltage error amplifier
(V-EA). This amplifier generates an error voltage on its
The LT3652 can use a charge-current based C/10 termina-
tion 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
internalchargecyclecontroltimer,fortimer-basedtermina-
tion. 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.
output (I ), which corresponds to the average current
TH
sensedacrosstheinductorcurrentsenseresistor, R
,
SENSE
which is connected between the SENSE and BAT pins.
The I voltage is then divided down by a factor of 10,
TH
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
resultingvoltage(V )usedasathresholdthatiscompared
C
against an internally generated ramp. The output of this
comparison controls the charger’s switch.
3652fb
10
LT3652
APPLICATIONS INFORMATION
The I error voltage corresponds linearly to average
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.
TH
current sensed across the inductor current sense resistor,
allowing maximum charge current control by limiting the
effective voltage range of I . A clamp limits this voltage
TH
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-
stant-current (CC) mode, which corresponds to 100mV
across R
. The I voltage is pulled down to reduce
SENSE
TH
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.
this maximum charge current should the voltage on the
V
pin falls below 2.7V (V ) or the die tem-
IN_REG
IN_REG(TH)
perature approaches 125°C.
If the voltage on the V pin is below 2.3V (V
),
FB(PRE)
FB
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
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
as set by R
.
SENSE
Whenthechargeroutputvoltageapproachesthefloatvolt-
age,orthevoltageontheV pinapproaches3.3V(V ),
FB
FB(FLT)
the charger transitions into constant-voltage (CV) mode
and charge current is reduced from the maximum value.
over-voltage condition and I is pulled low. When the
TH
As this occurs, the I voltage falls from the limit clamp
voltage error amp output drops below 0.3V, the IC enters
TH
and servos to lower voltages. The IC monitors the I volt-
standby mode, where most of the internal circuitry is dis-
TH
age as it is reduced, and detection of C/10 charge current
abled, and the V bias current is reduced to 85μA. When
IN
is achieved when I = 0.1V. If the charger is configured
the voltage on the V pin drops below the reduced float
TH
FB
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.
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.
V Input Supply
IN
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 con-
figured for any amount of time by setting an appropriate
TheLT3652isbiaseddirectlyfromthechargerinputsupply
through the V pin. This supply provides large switched
IN
currents, so a high-quality, low ESR decoupling capacitor
is recommended to minimize voltage glitches on V . The
IN
V decouplingcapacitor(C )absorbsallinputswitching
timing capacitor value (C
). When timer termination
IN
VIN
TIMER
is used, the charge cycle does not terminate when C/10
is achieved. Because the CHRG status pin responds to
3652fb
11
LT3652
APPLICATIONS INFORMATION
ripple current in the charger, so it must have an adequate
BOOST Supply
ripple current rating. RMS ripple current (I
) is:
CVIN(RMS)
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-
1/2
I
≅I
• (V / V )•([V / V ] – 1) ,
CVIN(RMS) CHG(MAX) BAT IN IN BAT
where I
is the maximum average charge current
). The above relation has a maximum at
CHG(MAX)
SW
(100mV/R
SENSE
LT3652
V = 2 • V , where:
IN
BAT
BOOST
SENSE
R
I
= I /2.
CHG(MAX)
SENSE
CVIN(RMS)
BAT
3652 F01
The simple worst-case of ½ • I
used for design.
is commonly
CHG(MAX)
Figure 1. Programming Maximum Charge
Current Using RSENSE
Bulk capacitance is a function of desired input ripple volt-
age (ΔV ), and follows the relation:
IN
enced to the SW pin. Connect a 1μF or greater capacitor
from the BOOST pin to the SW pin.
C
= I
• (V /V ) / ΔV (μF)
CHG(MAX) BAT IN IN
IN(BULK)
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
Input ripple voltages above 0.1V are not recommended.
10μF is typically adequate for most charger applica-
tions.
Charge Current Programming
greater than V
.
IN(MAX)
The LT3652 charger is configurable to charge at average
currents as high as 2A. Maximum charge current is set by
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.
choosing an inductor sense resistor (R
) such that
SENSE
the desired maximum average current through that sense
resistor creates a 100mV drop, or:
R
= 0.1 / I
CHG(MAX)
SENSE
where I
is the maximum average charge current.
CHG(MAX)
A 2A charger, for example, would use a 0.05Ω sense
resistor.
3652fb
12
LT3652
APPLICATIONS INFORMATION
output, additional bypass capacitance may be desired for
visual indication for a no-battery condition (see the Status
Pins section).
SW
LT3652
BOOST
SENSE
If it is desired to operate a system load from the LT3652
chargeroutputwhenthebatteryisdisconnected,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,placea100μFlowESRnon-ceramiccapacitor
(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
BAT
3652 F02
Figure 2. Zener Diode Reduces Refresh
Voltage for BOOST Pin
V / BOOST Start-Up Requirement
IN
with long wires. The voltage rating of C must meet or
BAT
The LT3652 operates with a V range of 4.95V to 32V,
exceed the battery float voltage.
IN
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
Inductor Selection
The primary criterion for inductor value selection in an
LT3652chargeristheripplecurrentcreatedinthatinductor.
Oncetheinductancevalueisdetermined,aninductormust
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 (ΔI
can be approximated using the relation:
available, the internal switch requires (V – V ) ≥ 3.3V
IN
SW
to reliably operate. This requirement does not exist if the
BOOST supply is available and (V – V ) > 2V.
BOOST
SW
When an LT3652 charger is not switching, the SW pin is
at the same potential as the battery, which can be as high
)
MAX
as V
. As such, for reliable start-up, the V supply
BAT(FLT)
IN
must be at least 3.3V above V
. Once switching
BAT(FLT)
begins and the BOOST supply capacitor gets charged
such that (V – V ) > 2V, the V requirement no
L = (10 R
[1 – (V
/ ΔI
) • V
•
SENSE
MAX
BAT(FLT)
BOOST
longer applies.
SW
IN
/ V
)] (μH)
IN(MAX)
BAT(FLT)
InlowV applications, theBOOSTsupplycanbepowered
IN
by an external source for start-up, eliminating the V
IN
In the above relation, ΔI
is the normalized ripple cur-
MAX
start-up requirement.
rent, V
is the maximum operational voltage, and
IN(MAX)
V is the forward voltage of the rectifying Schottky diode.
F
V
Output Decoupling
BAT
Ripple current is typically set within a range of 25% to
An LT3652 charger output requires bypass capacitance
35% of I
, so an inductor value can be determined
CHG(MAX)
by setting 0.25 < ΔI
connected from the BAT pin to ground (C ). A 10μF
BAT
< 0.35.
MAX
ceramiccapacitorisrequiredforallapplications.Insystems
where the battery can be disconnected from the charger
3652fb
13
LT3652
APPLICATIONS INFORMATION
forward voltage yields the lowest power loss and highest
efficiency. The rectifier diode must be rated to withstand
16
14
12
10
8
reverse voltages greater than the maximum V voltage.
IN
The minimum average diode current rating (I
)
DIODE(MAX)
is calculated with maximum output current (I
),
CHG(MAX)
maximum operational V , and output at the precondition
IN
threshold (V
, or 0.7 • V
):
BAT(PRE)
BAT(FLT)
6
I
> I
• (V
– V
) / V ) (A)
IN(MAX)
DIODE(MAX) CHG(MAX)
IN(MAX)
BAT(PRE)
4
12
16
20
24
28
32
MAXIMUM OPERATIONAL V VOLTAGE (V)
IN
For example, a rectifier diode for a 7.2V, 2A charger with
a 25V maximum input voltage would require:
3652 F03
Figure 3. 7.2V at 1.5A Switched Inductor Values
I
I
> 2 • (25 – 0.7[7.2]) / 25), or
> 1.6A
DIODE(MAX)
DIODE(MAX)
Magnetics vendors typically specify inductors with
maximum RMS and saturation current ratings. Select an
inductorthathasasaturationcurrentratingatorabove(1+
Battery Float Voltage Programming
Theoutputbatteryfloatvoltage(V
ΔI
/2) • I
, and an RMS rating above I
CHG(MAX)
.
MAX
CHG(MAX)
)isprogrammed
BAT(FLT)
Inductorsmustalsomeetamaximumvolt-secondproduct
requirement. If this specification is not in the data sheet of
aninductor,consultthevendortomakesurethemaximum
volt-secondproductisnotbeingexceededbyyourdesign.
The minimum required volt-second product is:
by connecting a resistor divider from the BAT pin to V .
FB
V
can be programmed up to 14.4V.
BAT(FLT)
BAT
+
LT3652
R
R
FB1
FB2
V
• (1 – V
/V
) (V • μS)
V
FB
BAT(FLT)
BAT(FLT) IN(MAX)
3652 F04
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
selectedbaseduponforwardvoltage, reversevoltage, and
maximum current. A Schottky diode is required, as low
Figure 4. Feedback Resistors from BAT to VFB
Program Float Voltage
3652fb
14
LT3652
APPLICATIONS INFORMATION
For a three-resistor network, R
relation:
and R
follow the
Usingaresistordividerwithanequivalentinputresistance
FB1
FB2
at the V pin of 250k compensates for input bias current
FB
error.RequiredresistorvaluestoprogramdesiredV
BAT(FLT)
R
/R = 3.3/(V
FB2 FB1
– 3.3)
BAT(FLT)
follow the equations:
Example:
For V
= 3.6V:
BAT(FLT)
5
R
R
= (V
• 2.5 • 10 ) / 3.3
(Ω)
(Ω)
FB1
BAT(FLT)
R
/R = 3.3/(3.6 - 3.3) = 11.
FB2 FB1
5
5
= (R1 • (2.5 • 10 )) / (R1- (2.5 • 10 ))
FB2
Setting divider current (I ) = 10μA yields:
RFB
R
= 3.3/10μA
FB2
The charge function operates to achieve the final float
voltage of 3.3V on the V pin. The auto-restart feature
R
= 330k
FB2
FB
initiates a new charging cycle when the voltage at the V
pin falls 2.5% below that float voltage.
FB
Solving for R
:
FB1
R
= 330k/11
FB1
Because the battery voltage is across the V
pro-
BAT(FLT)
R
FB1
= 30k
gramming resistor divider, this divider will draw a small
amount of current from the battery (I ) at a rate of:
The divider equivalent resistance is:
||R = 27.5k
RFB
I
= 3.3 / R
FB2
R
RFB
FB1 FB2
Precision resistors in high values may be hard to ob-
tain, so for some lower V applications, it may be
To satisfy the 250k equivalent resistance to the V
pin:
FB
BAT(FLT)
desirable to use smaller-value feedback resistors with an
R
= 250k − 27.5k
FB3
additional resistor (R ) to achieve the required 250k
FB3
R
FB3
= 223k.
equivalent resistance. The resulting 3-resistor network,
as shown in Figure 5, can ease component selection
and/orincreaseoutputvoltageprecision,attheexpenseof
additional current through the feedback divider.
Because the V pin is a relatively high impedance node,
FB
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 pro-
duce undesirable output transients or ripple. Effects of
parasitic capacitance can typically be reduced by adding
a small-value (20pF to 50pF) feedforward capacitor from
BAT
+
LT3652
R
FB1
R
FB3
V
FB
3652 F05
the BAT pin to the V pin.
R
FB2
FB
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
Figure 5. A Three-Resistor Feedback Network Can
Ease Component Selection
3652fb
15
LT3652
APPLICATIONS INFORMATION
cleaning measures should be implemented to prevent
board contamination, and low-leakage solder flux is
recommended.
MPPT Temperature Compensation
Atypicalsolarpaneliscomprisedofanumberofseries-con-
nectedcells,eachcellbeingaforward-biasedp-njunction.
As such, the open-circuit voltage (V ) of a solar cell has
OC
Input Supply Voltage Regulation
a temperature coefficient that is similar to a common p-n
The LT3652 contains a voltage monitor pin that enables
programming a minimum operational voltage. Connect-
diode, or about –2mV/°C. The peak power point voltage
(V ) for a crystalline solar panel can be approximated as
MP
ing a resistor divider from V to the V
pin enables
a fixed voltage below V , so the temperature coefficient
IN
IN_REG
OC
programming of minimum input supply voltage, typically
for the peak power point is similar to that of V .
OC
used to program the peak power voltage for a solar panel.
Panel manufacturers typically specify the 25°C values for
Maximum charge current is reduced when the V
is below the regulation threshold of 2.7V.
pin
IN_REG
V , V , and the temperature coefficient for V , making
OC MP
OC
determination of the temperature coefficient for V of a
MP
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 volt-
typical panel straight forward.
The LT3652 employs a feedback network to program the
V input regulation voltage. Manipulation of the network
IN
makesforefficientimplementationofvarioustemperature
compensationschemesforamaximumpeakpowertrack-
ing (MPPT) application. As the temperature characteristic
age corresponds to 2.7V at the V
pin. The LT3652
IN_REG
servos the maximum output charge current to maintain
the voltage on V at or above 2.7V.
for a typical solar panel V voltage is highly linear, a
MP
IN_REG
Programming of the desired minimum voltage is ac-
complished by connecting a resistor divider as shown in
Figure 6. The ratio of R /R for a desired minimum
IN1 IN2
V
TEMP CO.
OC
voltage (V
) is:
IN(MIN)
V
OC
V
OC(25°C)
R
/R = (V
/2.7) – 1
IN1 IN2
IN(MIN)
V
MP(25°C)
V
– V
MP
V
OC
MP
If the voltage regulation feature is not used, connect the
V
pin to V .
IN_REG
IN
5
15
25
35
45
55
TEMPERATURE (°C)
3652 F07
INPUT
SUPPLY
V
IN
LT3652
Figure 7. Temperature Characteristics for Solar Panel
Output Voltage
R
R
IN1
IN2
V
IN_REG
3652 F06
Figure 6. Resistor Divider Sets Minimum VIN
3652fb
16
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.
As the temperature coefficient for V is similar to that
MP
of V , the specified temperature coefficient for V
OC
OC
(TC) of –78mV/°C and the specified peak power voltage
(V ) of 17.6V can be inserted into the equations to
MP(25°C)
calculate the appropriate resistor values for the tempera-
In the circuit shown in figure 8,
ture compensation network in Figure 8. With R
to 1000Ω, then:
equal
SET
V
IN
R
R
R
= 1k
LM234
R
SET
IN1
IN2
+
–
V
V
R
= –1k • (–0.078 • 4405 ) = 344k
IN1
IN2
V
IN
R
SET
= 344k/({[17.6 + 344k • (0.0674/1k)]/2.7} – 1)
= 24.4k
V
IN_REG
LT3652
R
Battery Voltage Temperature Compensation
3658 F08
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.
Figure 8. MPPT Temperature Compensation Network
R
= –R • (TC • 4405), and
SET
IN1
R
= R /({[V
+ R • (0.0674/R )]/V
} – 1)
IN2
IN1
MP(25°C)
IN1
SET
IN_REG
Where: TC = temperature coefficient (in V/°C), and
= maximum power voltage at 25°C
V
MP(25°C)
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, given a common 36-cell solar panel that has
the following specified characteristics:
Open Circuit Voltage (V ) = 21.7V
OC
For example, a 6-cell lead acid battery has a float charge
voltage that is commonly specified at 2.25V/cell at 25°C,
or13.5V,anda–3.3mV/°Cpercelltemperaturecoefficient,
Maximum Power Voltage (V ) = 17.6V
MP
Open-Circuit Voltage Temperature Coefficient (V ) =
OC
–78mV/°C
3652fb
17
LT3652
APPLICATIONS INFORMATION
or –19.8mV/°C. Using the feedback network shown in
Figure 9, with the desired temperature coefficient (TC)
While the circuit in Figure 9 creates a linear temperature
characteristic that follows a typical –3.3mV/°C per cell
lead-acidspecification,thetheoreticalfloatchargevoltage
characteristic is slightly nonlinear. This nonlinear charac-
and 25°C float voltage (V
) specified, and using
SET
FLOAT(25°C)
a convenient value of 2.4k for R , necessary resistor
–5
2
values follow the relations:
teristic follows the relation V
= 4 × 10 (T )
FLOAT(1-CELL)
–3
– 6 × 10 (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.
R
= –R • (TC • 4405)
FB1
SET
= –2.4k • (–0.0198 • 4405) = 210k
R
FB2
= R / ({[V
+ R • (0.0674/
FB1
FB1
FLOAT(25°C)
)] / V } – 1)
R
SET
FB
= 210k/({[13.5 + 210k • (0.0674/2.4k)]/3.3} – 1)
= 43k
BAT
6-CELL
LEAD-ACID
BATTERY
196k
69k
R
FB3
= 250k - R ||R
FB1 FB2
+
= 250k – 210k||43k = 215k (see the Battery Float
Voltage Programming section)
198k
22k
V
FB
B = 3380
LT3652
69k
BAT
LM234
3652 F10a
+
V
R
FB1
R
+
210k
14.8
14.6
14.4
14.2
–
R
SET
V
2.4k
V
FB
6-CELL
R
FB3
215k
LT3652
LEAD-ACID
BATTERY
R
FB2
43k
14.0
13.8
13.6
13.4
13.2
THEORETICAL V
BAT(FLOAT)
FLOAT
3652 F09a
14.3
14.2
14.0
13.8
13.6
13.4
13.2
13.0
12.8
12.6
PROGRAMMED V
13.0
12.8
–19.8mV/°C
–10
0
10
20
30
40
50
60
TEMPERATURE (°C)
3652 F10b
Figure 10. Thermistor-Based Temperature Compensation
Network Programs VFLOAT to Closely Match Ideal Lead-Acid
Float Charge Voltage for 6-Cell Charger
–10
0
10
20
30
40
50
60
TEMPERATURE (°C)
3652 F09b
Figure 9. Lead-Acid 6-Cell Float Charge Voltage vs
Temperature Has –19.8mV/°C Characteristic Using LM234 with
Feedback Network
3652fb
18
LT3652
APPLICATIONS INFORMATION
Status Pins
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.
The LT3652 reports charger status through two open
collector outputs, the CHRG and FAULT pins. These pins
can accept voltages as high as V , and can sink up to
IN
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-
grammedmaximumchargecurrent.TheFAULTpinsignals
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 V
drops below 97.5% of the full-charged float
BAT
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.
STATUS PINS STATE
CHRG
FAULT
CHARGER STATUS
Timer Termination
OFF
OFF
OFF
ON
Not Charging — Standby or Shutdown Mode
Bad Battery Fault (Precondition Timeout / EOC
Failure)
TheLT3652supportsatimerbasedterminationscheme,in
which a battery charge cycle is terminated after a specific
amount of time elapses. Timer termination is engaged
ON
ON
OFF
ON
Normal Charging at C/10 or Greater
NTC Fault (Pause)
when a capacitor (C
) is connected from the TIMER
TIMER
pin to ground. The timer cycle EOC (T ) occurs based
EOC
on C
following the relation:
TIMER
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.
–7
C
= T
• 2.27 x 10
(Hours)
TIMER
EOC
Timer EOC is typically set to 3 hours, which requires a
0.68μF capacitor.
TheCHRGstatuspincontinuestosignalchargingataC/10
rate,regardlessofwhatterminationschemeisused.When
timer termination is used, the CHRG status pin is pulled
low during a charging cycle until the charger output cur-
rent 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.
C/10 Termination
The LT3652 supports a low-current based termination
scheme,whereabatterychargecycleterminateswhenthe
current output from the charger falls to below one-tenth
of the maximum current, as programmed with R
.
SENSE
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
The C/10 threshold current corresponds to 10mV across
. This termination mode is engaged by shorting
R
SENSE
the TIMER pin to ground.
3652fb
19
LT3652
APPLICATIONS INFORMATION
full-chargefloatvoltage. Ifachargecycleisnotsuccessful
at EOC, the timer cycle resets and charging continues for
another full timer cycle.
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.
When V
drops below 97.5% of the full-charge float
BAT
voltage, whether by battery loading or replacement of the
battery, the charger automatically reengages and starts
charging.
Battery Temperature Monitor and Fault
The LT3652 can accommodate battery temperature moni-
toringbyusinganNTC(negativetemperatureco-efficient)
thermistor close to the battery pack. The temperature
monitoring function is enabled by connecting a 10kΩ,
B=3380NTCthermistorfromtheNTCpintoground.Ifthe
NTC function is not desired, leave the pin unconnected.
Preconditioning and Bad Battery Fault
A LT3652 has a precondition mode, where charge current
is limited to 15% of the programmed I
, as set by
CHG(MAX)
R
. The precondition current corresponds to 15mV
SENSE
across R
.
SENSE
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 LT3652
triggersanNTCfault.TheNTCfaultconditionremainsuntil
the voltage on the NTC pin corresponds to a temperature
withinthe0°Cto40°Crange. Bothhotandcoldthresholds
incorporate hysteresis that correspond to 5°C.
Precondition mode is engaged while the voltage on the
pin is below the precondition threshold (2.3V, or
V
FB
0.7 • V
). Once the V voltage rises above the
BAT(FLT)
FB
precondition threshold, normal full-current charging can
commence. The LT3652 incorporates 70mV of threshold
hysteresis to prevent mode glitching.
Whentheinternaltimerisusedfortermination,badbattery
detection is engaged. There is no provision for bad battery
detection if C/10 termination is used. A bad battery fault
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.
is triggered when the voltage on V remains below the
FB
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.
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.
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.
Thermal Foldback
TheLT3652containsathermalfoldbackprotectionfeature
that reduces maximum charger output current if the IC
junction temperature approaches 125°C. In most cases,
on-chip temperatures servo such that any excessive tem-
peratureconditionsarerelievedwithonlyslightreductions
in maximum charger current.
Cycling the charger’s power or SHDN function initiates a
new charging cycle, but a LT3652 charger does not re-
quire a reset. Once a bad battery fault is detected, a new
timer charging cycle initiates when the V pin exceeds
FB
the precondition threshold voltage. During a bad battery
3652fb
20
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.
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
Layout Considerations
The LT3652 switch node has rise and fall times that are
typicallylessthan10nStomaximizeconversionefficiency.
The switch node (Pin SW) trace should be kept as short
as possible to minimize high frequency noise. The input
(C ) through the switch and inductor to the battery posi-
IN
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 (D ). In
F
capacitor(C )shouldbeplacedclosetotheICtominimize
IN
both cases, these switch currents return to ground via the
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
output bypass capacitor (C ).
BAT
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.
these and the V trace should be kept as short as pos-
FB
sible. Shielding these signals from switching noise with
a ground plane is recommended.
High current paths and transients should be kept iso-
lated from battery ground, to assure an accurate output
C
C
V
BAT
IN
BAT
R
SENSE
1
2
D
F
+
LT3652
SW
V
IN
SENSE
BAT
V
FB
3652 F11
Figure 11. Component Orientation Isolates High Current Paths
from Sensitive Nodes
3652fb
21
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
MBRS340
D3
AC ADAPTER INPUT
12V AT 1A
SW
V
V
IN
LT3652
330k
SH-DC121000
1μF
1N914
MBRS340
VISHAY
1HLP-2525CZ8R2M11
8.2μH
0.05
IN_REG
BOOST
SENSE
BAT
47k
SYSTEM
LOAD
SHDN
1μF
10k
CHRG
51k
+
10k
10μF
100μF
626k
NTC
FAULT
V
FB
TIMER
10μF
412k
0.68μF
+
R1 10k
B = 3380
REMOVABLE 2-CELL Li-Ion PACK
(8.3V FLOAT)
SH-DC121000
AC Adapter V vs I Characteristics
3652 TA02a
20
18
16
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
Basic 2A 1-Cell LiFePO4 Charger (3.6V Float) With C/10 Termination
CMSH3-40MA
V
IN
SW
V
IN
5V TO 32V (40V MAX)
LT3652
CMDSH2-4L
1μF
5.6μH
0.05
V
IN_REG
BOOST
SENSE
BAT
SYSTEM
LOAD
SHDN
CHRG
FAULT
TIMER
10μF
C3
10μF
30k
NTC
+
V
FB
223k
3652 TA03
330k
LiFePO CELL
4
3652fb
22
LT3652
PACKAGE DESCRIPTION
DD Package
12-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1725 Rev A)
0.70 ±0.05
2.38 ±0.05
1.65 ±0.05
3.50 ±0.05
2.10 ±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
0.40 ± 0.10
TYP
7
12
2.38 ±0.10
3.00 ±0.10
(4 SIDES)
1.65 ±0.10
PIN 1 NOTCH
PIN 1
TOP MARK
R = 0.20 OR
0.25 × 45°
CHAMFER
(SEE NOTE 6)
6
1
0.23 ± 0.05
0.45 BSC
0.75 ±0.05
0.200 REF
2.25 REF
(DD12) DFN 0106 REV A
0.00 – 0.05
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
3652fb
23
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 p 0.102
(.112 p .004)
2.845 p 0.102
(.112 p .004)
0.889 p 0.127
(.035 p .005)
1
6
0.35
REF
5.23
(.206)
MIN
1.651 p 0.102
(.065 p .004)
3.20 – 3.45
(.126 – .136)
0.12 REF
DETAIL “B”
CORNER TAIL IS PART OF
THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
DETAIL “B”
12
4.039 p 0.102
7
NO MEASUREMENT PURPOSE
0.65
(.0256)
BSC
0.42 p 0.038
(.0165 p .0015)
(.159 p .004)
TYP
(NOTE 3)
0.406 p 0.076
RECOMMENDED SOLDER PAD LAYOUT
(.016 p .003)
12 11 10 9 8 7
REF
DETAIL “A”
0.254
(.010)
3.00 p 0.102
(.118 p .004)
(NOTE 4)
0o – 6o TYP
4.90 p 0.152
(.193 p .006)
GAUGE PLANE
0.53 p 0.152
(.021 p .006)
1
2 3 4 5 6
DETAIL “A”
0.86
(.034)
REF
1.10
(.043)
MAX
0.18
(.007)
SEATING
PLANE
0.22 – 0.38
(.009 – .015)
TYP
0.1016 p 0.0508
(.004 p .002)
MSOP (MSE12) 0608 REV B
0.650
(.0256)
BSC
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
3652fb
24
LT3652
REVISION HISTORY (Revision history begins at Rev B)
REV
DATE DESCRIPTION
PAGE NUMBER
B
2/10 Add MSOP-12 Package
1, 2, 24
3652fb
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However,noresponsibilityisassumedforitsuse.LinearTechnologyCorporationmakesnorepresenta-
t ion t h a t t he in ter c onne c t ion o f i t s cir cui t s a s de s cr ib e d her ein w ill no t in fr inge on ex is t ing p a ten t r igh t s.
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; 0°C to 45°C Battery Temperature Charging Range
MBRS140
SOLAR PANEL INPUT
<40V OC VOLTAGE
16V PEAK POWER VOLTAGE
10μF
499k
SW
V
V
IN
LT3652
1μF
1N914 BZX84C6V2L
WURTH
7447779122
MBRS340
22μH
0.1
IN_REG
BOOST
SENSE
BAT
SYSTEM
LOAD
SHDN
CHRG
100k
+
910
10μF
100μF
309k
100k
NTC
FAULT
174k
V
+
FB
TIMER
4.7μF
12V LEAD
ACID BATTERY
1M
1N4148
10k
B = 3380
muRata
NCP18XH103
3652 TA04
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT3650-4.1/LT3650-4.2 Monolithic 2A Switch Mode 1-Cell Li-Ion
Battery Charger
Standalone, 4.75V ≤ V ≤ 32V (40V Absolute Maximum), 1MHz, 2A
IN
Programmable Charge Current, Timer or C/10 Termination, Small and Few
External Components, 3mm × 3mm DFN12 Package, –4.1 for 4.1V Float Voltage
Batteries, –4.2 for 4.2V Float Voltage Batteries
LT3650-8.2/LT3650-8.4 Monolithic 2A Switch Mode 2-Cell Li-Ion
Battery Charger
Standalone, 9V ≤ V ≤ 32V (40V Absolute Maximum), 1MHz, 2A Programmable
IN
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 Standalone, 4V ≤ V ≤ 5.5V (6V Absolute Maximum, 7V Transient), 1.5MHz,
IN
Li-Ion Battery Charger
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
LTC4006
Switch Mode Lithium-Ion Battery Charger Standalone, 4.7V ≤ V ≤ 24V, 500kHz Frequency, 3 Hour Charge Termination
IN
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
LTC4008
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
Constant-Current/Constant-Voltage Switching Regulator Charger, Resistor
Voltage/Current Programming, AC Adapter Current Limit and Thermistor Sensor
and Indicator Outputs
LTC4009/LTC4009-1/
LTC4009-2
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 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
LTC40012/LTC40012-1/ 4A, High Efficiency, Multi-Chemistry
PowerPath Control, Constant-Current/Constant-Voltage Switching Regulator
LTC40012-2/ LTC4012-3 Battery Charger with PowerPath™ Control Charger, Resistor Voltage/Current Programming, AC Adapter Current Limit and
Thermistor Sensor and Indicator Outputs 1 to 4 Cell Li, Up to 18 Cell Ni, SLA and
Supercap Compatible; 4mm × 4mm QFN-20 Package –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
LT 0210 REV B • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
26
●
●
© LINEAR TECHNOLOGY CORPORATION 2010
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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