LT3651-4.1 [Linear]
Monolithic 4A High Voltage Monolithic 4A High Voltage; 4A单片高电压4A单片高电压
| 型号： | LT3651-4.1 |
| 厂家： | 
Linear |
| 描述： | Monolithic 4A High Voltage Monolithic 4A High Voltage |
| 文件： | 总22页 (文件大小：210K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT3651-4.1/LT3651-4.2
Monolithic 4A High Voltage
1 Cell Li-Ion Battery Charger
FEATURES
DESCRIPTION
The LT®3651 is a 1 cell 4A Li-Ion/Polymer battery charger
that operates over a 4.8V to 32V input voltage range. An
efficient monolithic average current mode synchronous
switching regulator provides constant current, constant
voltage charging with programmable maximum charge
current. A charging cycle starts with battery insertion
or when the battery voltage drops 2.5% below the float
voltage. Charger termination is selectable as either charge
current or internal safety timer timeout. Charge current
termination occurs when the charge current falls to one-
tenth the programmed maximum current (C/10). Timer
based termination is typically set to three hours and is
user programmable (charging continues below C/10 until
timeout). Once charging is terminated, the LT3651 supply
current drops to 85μA into a standby mode.
n
Wide Input Voltage Range: 4.8V to 32V
(40V Absolute Maximum)
n
Programmable Charge Current Up to 4A
n
Selectable C/10 or Onboard Timer Termination
n
Dynamic Charge Rate Programming/Soft-Start
n
Programmable Input Current Limit
n
0.5% Float Voltage Accuracy
n
7.5% Charge Current Accuracy
n
4% C/10 Detection Accuracy
n
NTC Resistor Temperature Monitor
n
Auto-Recharge at 97.5% Float Voltage
n
Auto-Precondition <70% Float Voltage
n
Bad Battery Detection with Auto-Reset
n
Average Current Mode, Synchronous Switcher
n
User Programmable Frequency
n
Low Profile (0.75mm) 5mm × 6mm 36-Pin
The LT3651 offers several safety features. A discharged
battery is preconditioned with a small trickle charge and
generates a signal if unresponsive. A thermistor monitors
battery temperature, halting charging if out of range. Ex-
cessive die temperature reduces charge current. Charge
current is also reduced to maintain constant input current
to prevent excessive input loading.
QFN Package
APPLICATIONS
n
Industrial Handheld Instruments
n
12V to 24V Automotive and Heavy Equipment
n
Desktop Cradle Chargers
Notebook Computers
n
The LT3651 is available in a 5mm × 6mm 36-pin QFN
package.
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.
TYPICAL APPLICATION
Efficiency, Power Loss vs VIN
6.5V to 32V Single Cell 4A Charger
86
85
84
83
82
81
80
4.4
4.0
3.6
3.2
2.8
2.4
2.0
V
= 3.9
BAT
TO
SYSTEM
LOAD
V
IN
E
FF
6.5V TO
32V
22μF
100k
100k
10V
CLP
SHDN
ACPR
FAULT
CHRG
CLN
V
IN
SW
Si7611DN
1μF
1N5819
6.5μH
WÜRTH 744314650
BOOST
LT3651-4.2
SENSE
RT
24mΩ
301k
P
LOSS
TIMER
BAT
NTC
+
100μF
BATTERY
I
RNG/SS GND
20
5
10
15
25
30
LIM
365142 TA01a
365142 TA01b
V
(V)
IN
365142fb
1
LT3651-4.1/LT3651-4.2
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
TOP VIEW
V
.......................................................................... 40V
IN
CLN, CLP, SHDN
, CHRG,
FAULT ACPR ............................... V + 0.5V Up to 40V
,
IN
36 35 34 33 32 31 30 29
CLP – CLN ............................................................. 0.5V
SW ...........................................................................40V
NTC
ACPR
BAT
1
2
3
4
5
6
7
8
9
28
I
LIM
27 SHDN
CHRG
FAULT
26
25
SW – V ..................................................................4.5V
IN
37
38
SENSE
BOOST
GND
SW
BOOST ......................................... SW + 10V Up to 50V
SENSE, BAT ............................................................ 10V
SENSE-BAT ............................................. –0.5V to 0.5V
24 TIMER
GND
23
22 SW
21 NC
20 NC
19 NC
NC
TIMER, RNG/SS, I , NTC, RT .............................. 2.5V
LIM
NC
Operating Junction Temperature Range
NC 10
(Notes 2, 3)................................................–40 to 125°C
Storage Temperature Range.......................–65 to 150°C
11 12 13 14 15 16 17 18
UHE PACKAGE
36-LEAD (5mm w 6mm) PLASTIC QFN
T
= 125°C, θ = 43°C/W
JMAX
JA
EXPOSED PAD (PIN 37) IS GND, MUST BE SOLDERED TO PCB
EXPOSED PAD (PIN 38) IS SW, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3651EUHE-4.1#PBF
LT3651IUHE-4.1#PBF
LT3651EUHE-4.2#PBF
LT3651IUHE-4.2#PBF
LT3651EUHE-4.1#TRPBF 365141
LT3651IUHE-4.1#TRPBF 365141
LT3651EUHE-4.2#TRPBF 365142
LT3651IUHE-4.2#TRPBF 365142
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
36-Lead (5mm × 6mm) Plastic QFN
36-Lead (5mm × 6mm) Plastic QFN
36-Lead (5mm × 6mm) Plastic QFN
36-Lead (5mm × 6mm) Plastic QFN
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/
365142fb
2
LT3651-4.1/LT3651-4.2
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = 20V, SHDN = 2V, SENSE = BAT = VBAT(FLT)
,
CTIMER = 0.68μF, RT = 50k, CLP = CLN = VIN, BOOST – SW = 4V.
PARAMETER
CONDITIONS
MIN
4.8
32
TYP
MAX
32
UNITS
l
l
V
IN
V
IN
V
IN
V
IN
V
IN
Operating Range
OVLO Threshold
OVLO Hysteresis
UVLO Threshold
UVLO Hysteresis
V
V
V
V
V
V
V
V
Rising
Rising
35
1.1
4.6
0.2
4.1
40
IN
l
4.8
IN
Battery Float Voltage, V
LT3651-4.1
4.08
4.06
4.12
4.14
BAT(FLT)
l
l
LT3651-4.2
4.18
4.16
4.2
4.22
4.24
V
Battery Recharge Voltage Hysteresis
Threshold Voltage Relative to V
–105
mV
BAT(FLT)
Battery Precondition Threshold Voltage, V
LT3651-4.1 V Rising
2.83
2.9
V
V
BAT(PRE)
BAT
LT3651-4.2 V Rising
BAT
Battery Precondition Threshold Hysteresis
Threshold Voltage Relative to V
70
mV
BAT(PRE)
Operating V Supply Current
CC/CV Mode, Top Switch On, I = 0
8.6
80
17
mA
μA
μA
IN
SW
Standby Mode
Shutdown (SHDN = 0)
Top Switch On Voltage
V
V
– V , I = 4A
480
–140
40
mV
mV
mA
mA/A
mV
mV
nA
IN
SW SW
Bottom Switch On Voltage
BOOST Supply Current
BOOST Switch Drive
, I = 4A
SW SW
Switch High, I = 0, 2.5 < (V
– V ) < 4.5
SW
BOOST
SW
I
/I , I = 4A
25
BOOST SW SW
Precondition Current Sense Voltage
Input Current Limit Voltage
CLP Input Bias Current
CLN Input Bias Current
V
V
– V , V = 2.5
14
SENSE
BAT BAT
l
l
– V , I Open
70
43
95
115
57
CLP
CLN LIM
120
36
μA
I
Bias Current
50
μA
LIM
System Current Limit Programming Gain
Maximum Charge Current Sense Voltage
C/10 Trigger Sense Voltage
BAT Input Bias Current
V
V
V
/(V
– V ), V = 0.5V
ILIM
11.5
95
V/V
mV
mV
μA
ILIM CLP
CLN
l
l
– V , V = 3.5, V
> 1.1V
88
103
12.3
1
SENSE
SENSE
BAT BAT
RNG/SS
– V
5.0
8.6
0.1
0.1
50
BAT
Charging Terminated
Charging Terminated
SENSE Input Bias Current
RNG/SS Bias Current
1
μA
l
l
l
l
44
56
μA
Charge Current Limit Programming Gain
NTC Range Limit (High)
NTC Range Limit (Low)
V
V
V
/(V
– V ), V = 0.5V
RNG/SS
8.5
10.8
1.36
0.29
10
12.5
1.45
0.31
V/V
V
RNG/SS SENSE
BAT
Rising
Falling
1.25
0.27
NTC
NTC
V
NTC Threshold Hysteresis
NTC Disable Impedance
NTC Bias Current
% of Threshold
Minimum External Impedance to GND
%
l
l
l
150
46.5
1.16
470
50
kꢀ
μA
V
V
= 0.75V
53.5
1.23
NTC
Shutdown Threshold
Rising
1.20
95
V
SHDN
Shutdown Hysteresis
mV
nA
SHDN Input Bias Current
Status Low Voltage
–10
l
V
, V
, V
, Load = 10mA
0.45
V
CHRG FAULT ACPR
365142fb
3
LT3651-4.1/LT3651-4.2
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = 20V, SHDN = 2V, SENSE = BAT = VBAT(FLT)
CTIMER = 0.68μF, RT = 50k, CLP = CLN = VIN, BOOST – SW = 4V.
,
PARAMETER
CONDITIONS
MIN
TYP
25
MAX
UNITS
μA
TIMER Charge/Discharge Current
TIMER Disable Threshold
Full Charge Cycle Time-Out
Precondition Timeout
Timer Accuracy
l
l
0.1
0.25
3
V
Hour
Minute
%
22.5
–13
13
Switcher Operating Frequency, f
R = 50kΩ
T
1.1
250
MHz
kHz
O
T
R = 250kΩ
Minimum SW On-Time, t
150
ns
ON(MIN)
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
temperature range. The junction temperature (T in °C) is calculated from
J
the ambient temperature (T in °C) and power dissipation (P in Watts)
A
D
according to the formula:
T = T + P • θ
J
A
D
JA
Note 2: The LT3651 is tested under pulse loaded conditions such that
where θ (in °C/W) is the package thermal impedance.
JA
T = T . The LT3651E is guaranteed to meet performance specifications
J
A
Note 3: This IC includes overtemperature protection that is intended to
protect the device during momentary overload conditions. The maximum
rated junction temperature will be exceeded when this protection is active.
Continuous operation above the specified absolute maximum operating
junction temperature may impair device reliability or permanently damage
the device.
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
LT3651I is guaranteed over the full –40°C to 125°C operating junction
365142fb
4
LT3651-4.1/LT3651-4.2
TYPICAL PERFORMANCE CHARACTERISTICS
Battery Float Voltage
vs Temperature
VIN Standby Mode Current
vs Temperature
SENSE and BAT Pin Current
vs BAT Voltage, VSENSE = VBAT
1.0
0.5
150
100
95
90
85
80
75
70
65
60
55
50
LT3651-4.2
I
SENSE
100
50
I
BAT
0
–50
0
–100
–150
–200
–250
–300
–350
–0.5
–1.0
25
50
75 100
–50 –25
125
0
3.5
4.0 4.5
0
0.5 1.0 1.5 2.0 2.5 3.0
(V)
–50
–25
25
50
75
100
0
TEMPERATURE (°C)
V
TEMPERATURE (°C)
BAT
365142 G01
365142 G03
365142 G02
Maximum Charge Current vs
VRNG/SS as a Percentage of
Programmed IMAX
Thermal Foldback–Charge Current
vs Temperature as a Percentage
of Programmed ICHG(MAX)
IMAX Current Limit
(VSENSE – VBAT) vs Temperature
120
100
80
60
40
20
0
120
100
101.0
100.5
100.0
99.5
80
60
40
20
0
99.0
–50 –25
0
0.4
0.6
0.8
1.0
1.2
100
110
120
130
140
0.2
0
25
50
75 100 125
V
(V)
TEMPERATURE (°C)
TEMPERATURE (°C)
RNG/SS
365142 G04
365142 G06
365142 G05
Maximum Input Current vs VILIM
as a Percentage of Programmed
IIN(MAX)
Charge Current vs VBAT as a
Percentage of Programmed
ICHG(MAX)
Input Current Limit Voltage
Threshold vs Temperature
120
100
80
60
40
20
0
2.0
120
100
LT3651-4.2
1.5
1.0
R
OPEN
= 10k
ILIM
80
60
0.5
0
R
ILIM
–0.5
–1.0
–1.5
40
20
0
–2.0
–25
0
50
75 100 125
0
0.4
0.6
(V)
0.8
1.0
1.2
–50
25
2.5
3.0
3.5
(V)
4.0
4.5
0.2
V
V
TEMPERATURE (°C)
ILIM
BAT
365142 G07
365142 G08
365142 G09
365142fb
5
LT3651-4.1/LT3651-4.2
TYPICAL PERFORMANCE CHARACTERISTICS
C/10 Threshold (VSENSE –VBAT
vs Temperature
)
Top Side Switch VON
vs Temperature
Bottom Side VON vs Temperature
700
650
600
550
–50
–100
–150
–200
11
10
9
I
= 4A
I
= 4A
SW
SW
500
450
400
8
–250
7
50
TEMPERATURE (˚C)
100 125
–50 –25
0
25
75
–50 –25
0
25
50
75 100 125
–50 –25
0
25
50
75 100 125
TEMPERATURE (°C)
TEMPERATURE (°C)
365142 G11
365142 G12
365142 G10
Switch Drive (IBST/ISW
)
Boost Switch Drive
vs Switch Current
vs Temperature
Boost Drive vs Boost Voltage
60
50
40
30
20
10
70
60
35
30
25
20
I
= 4A
I
= 4A
SW
SW
50
40
30
20
10
15
2.5
3.5
4.5
V
5.5
6.5
7.5
0
1
2
3
4
5
–50 –25
0
25
50
75 100 125
TEMPERATURE (°C)
I
(A)
SW
– V (V)
IN
BST
365142 G14
365142 G15
365142 G13
Oscillator Frequency
vs Temperature
Timer Resistor (RT)
vs Period and Frequency
400
350
1.0
0.5
0
R
= 54.9k
T
300
250
200
150
100
50
–0.5
–1.0
2
500
3
4
6
167
1
1000
5
200
–50 –25
0
25
50
75 100 125
333
250
TEMPERATURE (°C)
PERIOD (μs)
365142 G16
FREQUENCY (kHz)
365142 G17
365142fb
6
LT3651-4.1/LT3651-4.2
PIN FUNCTIONS
NTC (Pin 1): Battery Temperature Monitor Pin. This
pin is used to monitor battery temperature. Typically a
10kꢀ NTC(negativetemperaturecoefficient)thermistor
(B = 3380) is embedded with the battery and connected
from the NTC pin to ground. The pin sources 50μA into
the resistor and monitors the voltage across the therm-
istor, regulating charging based on the voltage. If this
function is not desired, leave the NTC pin unconnected.
GND (Pins 6, 23, 31, 37): Ground. These pins are the
groundpinsforthepart.Pins31and37mustbeconnected
together. Pins 6 and 23 are connected via the leadframe to
theexposedbacksidePin37. Soldertheexposedbackside
to the PCB for good thermal and electrical connection.
SW (Pins 7, 11-18, 22, 38): Switch Output Pin. These
pins are the output of the charger switches. An inductor
is connected between this pin and the SENSE pin. When
the switcher is active, the inductor is charged by the high
ACPR (Pin 2): Open-Collector AC Present Status Pin.
This pin sinks current to indicate that V is valid and the
side switch from V and discharged by the bottom side
IN
IN
charger is on. Typically a resistor pull-up is used on this
switch to GND. Solder the exposed backside, Pin 38, to
pin. This pin can be pulled up to voltages as high as V
the PCB for good thermal connection.
IN
when disabled, and can sink currents up to 10mA when
TIMER (Pin 24): End-Of-Cycle Timer Programming Pin.
A capacitor on this pin to ground determines the full
charge end-of-cycle time. Full charge end-of-cycle time is
programmed with this capacitor. A 3 hour charge cycle is
obtained with a 0.68μF capacitor. This timer also controls
thebadbatteryfaultthatisgeneratedifthebatterydoesnot
reachthepreconditionthresholdvoltagewithinone-eighth
of a full cycle (22.5 minutes for a 3 hour charge cycle).
enabled.
BAT (Pin 3): Battery Voltage Monitor Pin. This pin moni-
tors battery voltage. A Kelvin connection is made to the
battery from this pin and a decoupling capacitor (C
is placed from this pin to ground.
)
BAT
The charge function operates to achieve the final float
voltage at this pin. The auto-restart feature initiates a new
charging cycle when the voltage at the BAT pin falls 2.5%
below this float voltage. Once the charge cycle is termi-
nated, the input bias current of the BAT pin is reduced to
<0.1μA to minimize battery discharge while the charger
remains connected.
The timer based termination is disabled by connecting the
TIMER pin to ground. With the timer function disabled,
chargingterminateswhenthechargecurrentdropsbelowa
C/10rate, orapproximately10%ofmaximumchargerate.
FAULT (Pin 25): Open-Collector Fault Status Output. This
pinindicateschargecyclefaultconditionsduringabattery
charging cycle. Typically a resistor pull-up is used on this
pin. This status pin can be pulled up to voltages as high
SENSE (Pin 4): Charge Current Sense Pin. The charge
current is monitored with a sense resistor (R
) con-
SENSE
nected between this pin and the BAT pin. The inductor
current flows through R to the battery. The voltage
as V when disabled, and can sink currents up to 10mA
SENSE
IN
across this resistor sets the average charge current. The
maximum average charge current (I
95mV across the sense resistor.
when enabled. A temperature fault causes this pin to be
pulled low. If the internal timer is used for termination,
a bad battery fault also causes this pin to be pulled low.
If no fault conditions exist, the FAULT pin remains high
impedance.
) corresponds to
MAX
BOOST (Pin 5): Bootstrapped Supply Rail for Switch
Drive. This pin facilitates saturation of the high side switch
transistor. Connect a 1μF or greater capacitor from the
BOOST pin to the SW pin. The operating range of this pin
is 0V to 4.5V, referenced to the SW pin when the switch is
high. The voltage on the decoupling capacitor is refreshed
through a rectifying diode, with the anode connected to
either the battery output voltage or an external source,
and the cathode connected to the BOOST pin.
365142fb
7
LT3651-4.1/LT3651-4.2
PIN FUNCTIONS
CHRG (Pin 26): Open-Collector Charger Status Output.
This pin indicates the battery charging status. Typically
a resistor pull-up is used on this pin. This status pin can
CLP/CLN (Pin 29/Pin 30): System Current Limit Positive
and Negative Input. System current levels are monitored
by connecting a sense resistor from the input power sup-
ply to the CLP pin, connecting a sense resistor from the
be pulled up to voltages as high as V when disabled,
IN
and can sink currents up to 10mA when enabled. CHRG
is pulled low during a battery charging cycle. When the
charge cycle is terminated, the CHRG pin becomes high
impedance. If the internal timer is used for termination,
thepinstayslowduringthechargingcycleuntilthecharge
current drops below a C/10 rate, or approximately 10%
of the maximum charge current. A temperature fault also
causes this pin to be pulled low.
CLP pin to the CLN pin and then connecting CLN to V .
IN
The system load is then delivered from the CLN pin. The
LT3651 servos the maximum charge current required to
maintain programmed maximum system current. The
system current limit is set as a function of the voltage
on the I
pin and the input current sense resistor. This
LIM
function is disabled by shorting CLP, CLN and V together.
IN
V (Pins 32, 33, 34): Charger Input Supply. These pins
IN
SHDN (Pin 27): Shutdown Pin. This pin can be used for
precision UVLO functions. When this pin rises above the
1.20V threshold, the part is enabled. The pin has 95mV of
voltage hysteresis. When in shutdown mode, all charging
functionsaredisabled.WhentheSHDNpinispulledbelow
0.4V, the IC enters a low current shutdown mode where
provide power for the LT3651. Charge current for the
battery flows into this pin. I is less than 100μA after
VIN
charge termination. Connect both pins together.
RNG/SS (Pin 35): Charge Current Range and Soft-Start
Pin. This pin allows for setting and dynamic adjustment
of the maximum charge current, and can be used to em-
ploy a soft-start function. The voltage on this pin sets the
maximum charge current by setting the maximum voltage
the V pin current is reduced to 17μA. Typical SHDN pin
IN
input bias current is 10nA. Connect the pin to V if the
IN
shutdown function is not desired.
across the charge current sense resistor, R
between SENSE and BAT.
, placed
SENSE
I
(Pin 28): Input Current Limit Programming This pin
LIM
allows for setting and dynamic adjustment of the system
input current limit, and can be used to employ a soft-start
function. The voltage on this pin sets the maximum input
current by setting the maximum voltage across the input
current sense resistor, placed between CLP and CLN.
The effective range on the pin is 0V to 1V. 50μA is sourced
from this pin usually to a resistor (R ) to ground.
RNG/SS
RNG/SS
V
represents approximately 10 times the maximum
voltageacrossthechargecurrentsenseresistor.IfnoR
SS
RNG/
isusedthepartwilldefaulttomaximumchargecurrent.
The effective range on the pin is 0V to 1V. 50μA is sourced
Soft-start functionality for charge current can be imple-
mentedbyconnectingacapacitor(C )fromRNG/SS
from this pin usually to a resistor (R ) to ground. V
ILIM
IILIM
RNG/SS
represents approximately 11 times the maximum voltage
to ground. The soft-start capacitor and the programming
resistor can be implemented in parallel. The RNG/SS pin
is pulled low during fault conditions, allowing graceful
across the input current sense resistor. If no R is used
ILIM
the part will default to maximum input current.
Soft-start functionality for input current can be imple-
mented with a capacitor (C ) from I to ground. The
recovery from faults if C
is used.
RNG/SS
ILIM
LIM
RT (Pin 36): Switcher Oscillator Timer Set Pin. A resis-
soft-start capacitor and the programming resistor can be
implemented in parallel.
tor from this pin to ground sets the switcher oscillator
frequency. Typically this is 54.9k for f
= 1MHz.
OSC
365142fb
8
LT3651-4.1/LT3651-4.2
BLOCK DIAGRAM
STANDBY
–
+
BOOST
5
UVLO
50μA
+
–
+
–
V
4.6V
IN
32, 33, 34
I
LIM
35V
28
OVLO
CLN
CLP
+
+
–
30
29
R
+
LATCH
A13
S
Q
A12
RT
OSC
A10
36
24
0.2V
TIMER
+
–
–
+
SW
7, 11-18, 22, 38
TIMER OSC
A14
A11
V
IN
+
125°C
V
C
T
J
–
REV CUR
INHIBIT
RIPPLE COUNTER
R
C-EA
S
SENSE
BAT
–
COUNT
RESET
STANDBY
4
3
R
S
+
COUNT
A9
V-EA
+
–
–
+
COUNT
+
RESET
MODE
0.3V
ENABLE (TIMER
OR C/10)
I
TH
RNG/SS
CHRG
FAULT
10R
26
25
CONTROL LOGIC
35
S
TERMINATE
SS/RESET
STATUS
SS/RESET
0.15V
50μA
A7
A8
–
+
C/10
0.1V
+
+
+
1V
–
+
PRECONDITION
NTC
2.9V
V
INT
2.7V
SHDN
A6
–
+
27
×2.25
+
+
A1
STANDBY
+
–
1.2V
4.2V
4.1V
1.36V
0.29V
A4
50μA
+
–
TERMINATE
A2
–
+
ACPR
2
A3
+ –
NTC
A5
1
+
–
1.3V
2.4V
0.7V
46μA
GND
6, 23, 31, 37
365142 BD
V
V
V
: 4.1V FOR LT3651-4.1, 4.2V FOR LT3651-4.2
BAT(FLT)
-V
: 4.0V FOR LT3651-4.1, 4.1V FOR LT3651-4.2
BAT(FLT) RECHRG
: 2.85V FOR LT3651-4.1, 2.9V FOR LT3651-4.2
BAT(PRE)
365142fb
9
LT3651-4.1/LT3651-4.2
OPERATION
Overview
cycle after a bad battery fault once the failed battery is
removed and replaced with another battery.
TheLT3651isacompleteLi-Ionbatterycharger,addressing
wide input voltage (4.8V to 32V) and high currents (up to
4A). High charging efficiency is produced with a constant
frequency,averagecurrentmodesynchronousstep-down
switcher architecture.
After charging is completed the input bias currents on the
pins connecting to the battery are reduced to minimize
battery discharge.
The LT3651 contains provisions for a battery temperature
monitoring circuit. Battery temperature is monitored by
using a NTC thermistor located with the battery. If the
battery temperature moves outside a safe charging range
of 0°C to 40°C the charging cycle suspends and signals
a fault condition.
The charger includes the necessary circuitry to allow for
programming and control of constant current, constant
voltage (CC/CV) charging with both current only and timer
termination. High charging efficiency is achieved by the
switcher by using a bootstrapped supply for low switch
drop for the high side driver and a MOSFET for the low
side (synchronous) switch.
The LT3651 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.
Maximum charge current is set with an external sense re-
sistor in series with the inductor and is adjustable through
the RNG/SS pin. Total system input current is monitored
with an input sense resistor and is used to maintain con-
stant input current by regulating battery charge current.
A precision undervoltage lockout is possible by using a
resistor divider on the shutdown pin (SHDN). The input
supply current is 17μA when the IC is in shutdown.
It is adjustable through the I pin.
LIM
Ifthebatteryvoltageislow,chargecurrentisautomatically
reduced to 15% of the programmed current to provide
safe battery preconditioning. Once the battery voltage
climbs above the battery precondition threshold, the IC
automatically increases the maximum charge current to
the full programmed value.
General Operation (See Block Diagram)
The LT3651 uses an average current mode control loop
architecturetocontrolaveragechargecurrent.TheLT3651
senses charger output voltage via the BAT pin. The dif-
ference between this voltage and the internal float volt-
age reference is integrated by the voltage error amplifier
Charge termination can occur when charge current de-
creases to one-tenth the programmed maximum charge
current (C/10 termination). Alternately, termination can
be time based through the use of an internal program-
mable charge cycle control timer. When using the timer
termination, charging continues beyond the C/10 level to
“top-off” a battery. Charging typically terminates three
hours after initiation. When the timer-based scheme is
used, bad battery detection is also supported. A system
fault is triggered if a battery stays in precondition mode
for more than one-eighth of the total charge cycle time.
(V-EA). The amplifier output voltage (I ) corresponds
TH
to the desired average voltage across the inductor sense
resistor, R
, connected between the SENSE and BAT
SENSE
pins. The I voltage is divided down by a factor of 10,
TH
and provides a voltage offset on the input of the current
error amplifier (C-EA). The difference between this im-
posed voltage and the current sense resistor voltage is
integrated by C-EA. The resulting voltage (V ) provides a
C
voltage that is compared against an internally generated
ramp and generates the switch duty cycle that controls
the charger’s switches.
Once charging is terminated and the LT3651 is not actively
charging,theICautomaticallyentersalowcurrentstandby
mode in which supply bias currents are reduced to <85μA.
If the battery voltage drops 2.5% from the full charge float
voltage, the LT3651 engages an automatic charge cycle
restart. The IC also automatically restarts a new charge
The I error voltage corresponds linearly to average
TH
current sensed across the inductor current sense resistor.
Maximum charge current is controlled by clamping the
maximum voltage of I to 1V. This limits the maximum
TH
current sense voltage (voltage across R
) to 95mV
SENSE
365142fb
10
LT3651-4.1/LT3651-4.2
OPERATION
setting the maximum charge current. Manipulation of
maximum charge current is possible through the RNG/SS
not respond to preconditioning and the charger remains
in (or enters) precondition mode after one-eighth of the
programmed charge cycle time. A bad battery fault halts
the charging cycle, the CHRG status pin goes high imped-
ance and the FAULT pin is pulled low.
and I pins (see the RNG/SS: Dynamic Charge Current
LIM
Adjust, RNG/SS: Soft-Start and I Control sections).
LIM
If the voltage on the BAT pin (V ) is below V
,
BAT(PRE)
BAT
A7 initiates the precondition mode. During the pre-
When the LT3651 terminates a charging cycle, whether
through C/10 detection or by reaching timer end-of-cycle,
the average current mode analog loop remains active but
the internal float voltage reference is reduced by 2.5%.
Because the voltage on a successfully charged battery is
at the full float voltage, the voltage error amp detects an
overvoltageconditionandrailslow.Whenthevoltageerror
ampoutputdropsbelow0.3V, theICentersstandbymode,
where most of the internal circuitry is disabled and the
condition interval, the charger continues to operate in
constant current mode, but the I clamp is reduced to
TH
0.15V reducing charge current to 15% of the maximum
programmed value.
As V approaches the float voltage (V
) the voltage
BAT
FLOAT
error amp V-EA takes control of I and the charger transi-
TH
tions into constant voltage (CV) mode. As this occurs, the
I
voltage falls from the limit clamp and charge current is
TH
V bias current is reduced to <100μA. When the voltage
IN
reduced from the maximum value. When the I voltage
TH
on the BAT pin drops below the reduced float reference
level, the output of the voltage error amp will climb, at
which point the IC comes out of standby mode and a new
charging cycle is initiated.
falls below 0.1V, A8 signals C/10. If the charger is config-
ured for C/10 termination the charge cycle is terminated.
Once the charge cycle is terminated, the CHRG status
pin becomes high impedance and the charger enters low
current standby mode.
The system current limit allows charge current to be
reduced in order to maintain a constant input current.
The LT3651 contains an internal charge cycle timer that
terminates a successful charge cycle after a programmed
amount of time. This timer is typically programmed to
achieveend-of-cycleinthreehours, butcanbeconfigured
for any amount of time by setting an appropriate timing
Input current is measured via a resistor (R ) that is
CL
placed between the CLP and CLN pins. Power is applied
through this resistor and is used to supply both V of the
IN
chip and other system loads. An offset produced on the
inputs of A12 sets the threshold. When that threshold is
capacitor value (C
). When timer termination is used,
TIMER
achieved, I is reduced, lowering the charge current thus
TH
the charge cycle does not terminate after C/10 is achieved.
BecausetheCHRGstatuspinrespondstotheC/10current
level, the IC will indicate a fully charged battery status,
but the charger will continue to source low currents. At
the programmed end of the cycle time the charge cycle
stops and the part enters standby mode. If the battery
did not achieve at least 97.5% of the full float voltage at
the end-of-cycle, charging is deemed unsuccessful and
another full-timer cycle is initiated.
maintaining the maximum input current.
50μA of current is sourced from I to a resistor (R
)
LIM
LIM
LIM
ILIM
that is placed from that pin to ground. The voltage on I
determines the regulating voltage across R . 1V on I
CL
LIM
corresponds to 95mV across R . The I
pin clamps
CL
internally to 1V maximum.
If the junction temperature of the die becomes excessive,
A10 activates decreasing I and reduces charge current.
TH
Use of the timer function also enables bad battery detec-
tion. This fault condition is achieved if the battery does
This reduces on-chip power dissipation to safe levels but
continues charging.
365142fb
11
LT3651-4.1/LT3651-4.2
APPLICATIONS INFORMATION
OSC Frequency
Boost Supply
A precision resistor to ground sets the LT3651 switcher
The BOOST bootstrapped supply rail drives the internal
switch and facilitates saturation of the high side switch
transistor. The BOOST voltage is normally created by con-
necting a 1μF capacitor from the BOOST pin to the SW
pin. Operating range of the BOOST pin is 2V to 4.5V, as
referenced to the SW pin.
oscillator frequency, f , permitting user adjustability
OSC
of the frequency value. Typically this frequency is in the
200kHz to 1MHz range. Power consideration may neces-
sitate lower frequency operation especially if the charger
is operated with very high voltages. Adjustability also
allows the user to position switching harmonics if their
system requires.
The boost capacitor is normally charged via a diode con-
nected from the battery or an external source through the
low side switch. Rate the diode average current greater
The timing resistor, R , value is set by the following:
T
than 0.1A and its reverse voltages greater than V
.
54.9
IN(MAX)
RT =
kΩ t
(
)
fOSC MHz
(
)
If an external supply that is greater than the input is avail-
able (V – V > 2V), it may be used in place of the
BOOST
IN
Set R to 54.9k for 1MHz operation.
T
bootstrap capacitor and diode.
V Input Supply
IN
V ,V Start-Up Requirement
IN BOOST
TheLT3651isbiaseddirectlyfromthechargerinputsupply
The LT3651 operates with a V range of 4.8V to 32V. The
IN
through the V pin. This supply provides large switched
IN
charger begins a charging cycle when the detected battery
voltage is below the 4.0V/4.1V auto-restart float voltage
and the part is enabled.
currents, so a high quality, low ESR decoupling capacitor
is required to minimize voltage glitches on V . The V
IN
IN
decoupling capacitor (C ) absorbs all input switching
VIN
When V is below 6.3V and the BOOST capacitor is un-
ripple current in the charger. Size is determined by input
IN
charged, the high side switch would normally not have
sufficient head room to start switching. During normal
operation the low side switch is deactivated when charge
current is very low to prevent reverse current in the in-
ductor. However in order to facilitate start-up, the LT3651
ripple voltage with the following equation:
I
MAX • V
BAT
CIN(BULK)
=
μF
( )
fOSC MHz • ΔV • V
(
)
IN
IN
where ΔV is the input ripple, I
is the maximum
MAX
IN
enables the switch if V
voltage is low. This allows
BOOST
charge current and f is the oscillator frequency. A good
initialchargingoftheBOOSTcapacitorwhichthenpermits
thehighsideswitchtosaturateandefficientlyoperate.The
boost capacitor charges to full potential after a few cycles.
starting point for ΔV is 0.1V. Worst-case conditions are
IN
IN
with V high and V at minimum. So for a 8V V ,
BAT
IN(MIN)
I
= 4A and a 1MHz oscillator frequency:
MAX
The design should consider that as the switcher turns on
and input current increases, input voltage drops due to
source input impedance and input capacitance. This po-
tentially allows the input voltage to drop below the internal
4 • 4.2
1• 0.1• 8
CIN(BULK)
=
= 21μF
Thecapacitormusthaveanadequateripplecurrentrating.
RMS ripple current, I is approximated by:
V UVLO turn-on and thus disrupt normal behavior and
IN
CVIN(RMS)
potentially stall start-up. If an input current sense resis-
tor is used, its drop must be considered as well. These
problems are worsened because input current is largest
at low input voltage. Pay careful attention to drops in the
power path. Adding a soft-start capacitor to the RNG/SS
pinandsettingUVLOto4.8VwiththeSHDNpinisrequired
⎛
⎜
⎞
V
V
IN
V
BAT
BAT
ICVIN(RMS) ≈ ICHARGE(MAX)
•
•
– 1
⎟
⎠
⎝ V
IN
which has a maximum at V = 2 • V , where I
IN
BAT
CVIN(RMS)
= I
/2. In the example above that requires a
CHARGE(MAX)
capacitor RMS rating of 2A.
at low V .
IN
365142fb
12
LT3651-4.1/LT3651-4.2
APPLICATIONS INFORMATION
BAT Output Decoupling
Inductor Selection
The primary criteria for inductor value selection in the
LT3651chargeristheripplecurrentcreatedduringswitch-
It is recommended that the LT3651 charger output have
a decoupling capacitor. If the battery can be disconnected
from the charger output this capacitor is required. The
ing. Ripple current, ΔI
, is typically set within a range of
MAX
25% to 35% of the maximum charge current, I
. This
value of this capacitor (C ) is related to the minimum
MAX
BAT
percentage typically gives a good compromise between
losses due to ripple and inductor size. An approximate
formula for inductance is:
operational V voltage such that:
IN
⎛
⎞
350μF
CBAT ≈ 20μF +
⎜
⎟
V
⎝
⎠
IN(MIN)
⎛
⎞
⎟
VBAT + VF
VBAT + VF
V + VF ⎠
IN
L =
• 1–
μH
(
)
⎜
⎝
ΔIMAX • fOSC MHz
(
)
The voltage rating on C must meet or exceed the bat-
BAT
tery float voltage.
Worse-case ripple is at high V and high V . V is the
IN
BAT
F
forwardvoltageofthesynchronousswitch(approximately
0.14V at 4A). Figure 2 shows inductance for the case of a
4A charger. The inductor must have a saturation current
equal to or exceeding the maximum peak current in the
R
: Charge Current Programming
SENSE
The LT3651 charger is configurable to charge at average
currentsashighas4A(seeFigure1).IfRNG/SSmaximum
voltage is not limited, the inductor sense resistor, R
has 95mV across it at maximum charge current so:
inductor. Peak current is I
+ ΔI
/2.
MAX
MAX
,
SENSE
Magnetics vendors typically specify inductors with maxi-
mumRMSandsaturationcurrentratings.Selectaninduc-
tor that has a saturation current rating at or above peak
0.095V
RSENSE
=
IMAX(AVG)
is the maximum average charge current.
current, and an RMS rating above I
. Inductors must
MAX
also meet a maximum volt-second product requirement.
If this specification is not in the data sheet of an inductor,
consultthevendortomakesurethemaximumvolt-second
productisnotbeingexceededbyyourdesign.Theminimum
required volt-second product is approximately:
where I
R
MAX(AVG)
is 24mꢀ for a 4A charger.
SENSE
SW
BOOST
LT3651
SENSE
⎛
⎞
VBAT
fOSC(MHz)
VBAT
V
IN(MAX)
• 1–
V •µs
(
)
⎜
⎟
⎝
⎠
R
SENSE
BAT
4
+
365142 F01
3
2
1
0
Figure 1. Programming Maximum Charge Current Using RSENSE
I
f
= 4A
MAX
OSC
= 1MHz
25% TO 35% RIPPLE
5
10
15
20
25
30
V
(V)
IN(MAX)
365142 F02
Figure 2. Inductance (L) vs Maximum VIN
365142fb
13
LT3651-4.1/LT3651-4.2
APPLICATIONS INFORMATION
System Input Current Limit
TheprogrammingrangeforI is0Vto1V.Voltageshigher
LIM
than 1V have no effect on the maximum input current. The
The LT3651 contains a PowerPathTM control feature to
help manage supply load currents. The charger adjusts
charger output current in response to a system load so as
to maintain a constant input supply load. If overall input
supply current exceeds the programmed maximum value
the charge current is diminished in an attempt to keep
supply current constant. One application where this is
helpfulisifyouhaveacurrentlimitedinputsupply. Setting
the maximum input current limit below the supply limit
prevents supply collapse.
default maximum sense voltage is 95mV and is obtained
if R
is greater than 20k or if the pin is left open.
ILIM
For example, say you want a maximum input current of
2A and the charger is designed for 4A maximum average
charge current, which is 1A V referred (4A time duty
IN
cycle). Using the full I
range, the maximum voltage
across R is 95mV. So R is set at 95mV/2A = 48mΩ.
LIM
CL
CL
When the system load exceeds 1A (= 2A – 1A) charge
current is reduced such that the total input current stays
at 2A. When the system load is 2A the charge current is 0.
This feature only controls charge current so if the system
load exceeds the maximum limit and no other limitation
is designed, the input current exceeds the maximum
desired, though the charge current reduces to 0A. When
the input limiter reduces charge current it does not impact
the internal system timer if used. See Figure 4.
A resistor, R , is placed between the input supply and the
CL
system and charger loads as shown in Figure 3.
The LT3651 sources 50μA from the I pin, so a voltage
LIM
is developed by simply connecting a resistor to ground.
The voltage on the I pin corresponds to 11.5 times the
LIM
maximum voltage across the input sense resistor (R ).
CL
Input current limit is defined by:
Ifreducedvoltageoverheadorbetterefficiencyisrequired
V
50μA •RILIM
11.5 •RCL
ILIM
then reduce the maximum voltage across R . So for
CL
IINPUT(MAX)
=
=
11.5 •RCL
instance, a 10k R
sets the maximum R voltage to
43mV. This reduction comes at the expense of slightly
ILIM
CL
increased limit variation.
INPUT
SUPPLY
CLP
LT3651
CLN
R
3
CL
SYSTEM LOAD
V
IN
INPUT CURRENT
2
I
LIM
R
LIM
365142 F03
CHARGE
1
0
CURRENT
(V REFERRED)
IN
Figure 3. Input Current Limit Configuration
365142 F04
0
1
2
SYSTEM LOAD CURRENT (A)
Figure 4. Input Current Limit for 4A Maximum Charger
and 6A System Current Limit
365142fb
14
LT3651-4.1/LT3651-4.2
APPLICATIONS INFORMATION
Note the LT3651 internally integrates the input limit
signals. This should normally provide sufficient filtering
and reduce the sensitivity to current spikes. For the best
accuracy take care in provide good Kelvin connections
LT3651
RNG/SS
10k
LOGIC HIGH = HALF CURRENT
from R to CLP, CLN.
CL
365142 F05
Further flexibility is possible by dynamically altering the
I
pin. Different resistor values could be switched in
Figure 5. Using the RNG/SS Pin for
Digital Control of Maximum Charge Current
LIM
to create unique input limit conditions. The I
pin can
LIM
also be tied to a servo amplifier for other options. See the
information in the following section concerning I
programming for examples.
RNG/SS
LT3651
RNG/SS
RNG/SS: Dynamic Current Adjust
+
SERVO
–
The RNG/SS pin gives the user the capability to adjust
maximum charge current dynamically. The part sources
50μA from the pin, so connecting a resistor to ground
develops a voltage. The voltage on the RNG/SS pin cor-
responds to ten times the maximum voltage across the
REFERENCE
365142 F06
Figure 6. Driving the RNG/SS Pin
with a Current-Sink Active Servo Amplifier
charge current sense resistor, R
tions for charge current are:
. The defining equa-
SENSE
RNG/SS: Soft-Start
Soft-start functionality is also supported by the RNG/SS
pin. The 50μA sourced from the RNG/SS pin can linearly
VRNG/SS
10.8 •RSENSE
50μA •RRNG/SS
10.8 •RSENSE
IMAX(RNG/SS)
=
=
charge a capacitor, C
, connected from the RNG/SS
RNG/SS
pintoground(seeFigure7).Themaximumchargecurrent
follows this voltage. Thus, the charge current increases
from zero to the fully programmed value as the capacitor
I
is the maximum charge current.
MAX(RNG/SS)
The programming range for RNG/SS is 0V to 1V. Voltages
higher than 1V have no effect on the maximum charge
current. The default maximum sense voltage is 95mV
and is obtained if R
pin is left open.
charges from 0V to 1V. The value of C
is calculated
RNG/SS
based on the desired time to full current (t ) following
SS
is greater than 20k or if the
RNG/SS
the relation:
C
= 50μA • t
SS
RNG/SS
For example, say you want to reduce the maximum charge
currentto50%ofthemaximumvalue.SetRNG/SSto0.5V
(50% of 1V), imposing a 46mV maximum sense voltage.
Per the above equation, 0.5V on RNG/SS requires a 10k
resistor. If the charge current needs to be dynamically
adjustable then Figure 5 shows one method.
TheRNG/SSpinispulledtogroundinternallywhencharg-
ing is terminated so each new charging cycle begins with
a soft-start cycle. RNG/SS is also pulled to ground during
badbatteryandNTCfaultconditions,soagracefulrecovery
from these faults is possible.
Active servos can also be used to impose voltages on the
RNG/SS pin, provided they can only sink current. Active
circuits that source current cannot be used to drive the
RNG/SS pin. An example is shown in Figure 6.
LT3651
RNG/SS
C
RNG/SS
365142 F07
Figure 7. Using the RNG/SS Pin for Soft-Start
365142fb
15
LT3651-4.1/LT3651-4.2
APPLICATIONS INFORMATION
Status Pins
Timer Termination
The LT3651 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
TheLT3651supportsatimer-basedterminationscheme,in
which a battery charge cycle is terminated after a specific
amount of time elapses. Timer termination is engaged
10mA when enabled
.
when a capacitor (C
) is connected from the TIMER
TIMER
pin to ground. The timer cycle end-of-cycle (t ) occurs
EOC
The CHRG pin indicates that the charger is delivering cur-
rent at greater than a C/10 rate, or one-tenth of the pro-
grammedmaximumchargecurrent.TheFAULTpinsignals
bad battery and NTC faults. These pins are binary coded,
and signal state following the table below. On indicates
the pin pulled low, and Off indicates pin high impedance.
based on C
following the relation:
TIMER
t
EOC(Hrs)
CTIMER
=
• 0.68 μF
( )
3
so a typical 3 hour timer end-of-cycle would use a 0.68μF
capacitor.
Table 1. Status Pins State Table
STATUS PINS STATE
The CHRG status pin continues to signal charging at a
C/10 rate, regardless of which termination scheme is
used. When timer termination is used, the CHRG status
pin is pulled low during a charge cycle until the charger
output current falls below the C/10 threshold. The charger
continues to “top off” the battery until timer end-of-cycle,
when the LT3651 terminates the charge cycle and enters
standby mode.
CHARGER STATUS
CHRG
Off
FAULT
Off
Not Charging—Standby or Shutdown Mode
Off
On
Bad Battery Fault
(Precondition Timeout/EOC Failure)
On
On
Off
On
Normal Charging at C/10 or Greater
NTC Fault (Pause)
C/10 Termination
Termination at the end of the timer cycle only occurs if the
charge cycle was successful. A successful charge cycle
occurs when the battery is charged to within 2.5% of the
full-charge float voltage. If a charge cycle is not success-
ful at end-of-cycle, the timer cycle resets and charging
continues for another full-timer cycle.
The LT3651 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 the maximum current, as programmed with R
The C/10 threshold current corresponds to 9mV across
.
SENSE
R
. This termination mode is engaged by shorting
When V
drops below 97.5% of the full-charge float
SENSE
BAT
the TIMER pin to ground.
voltage, whether by battery loading or replacement of the
battery, the charger automatically re-engages and starts
charging.
When C/10 termination is used, a LT3651 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 LT3651 enters standby mode.
The CHRG status pin follows the charge cycle and is high
impedance when the charger is not actively charging.
Precondition and Bad Battery Fault
A LT3651 charger has a precondition mode, in which
charge current is limited to 15% of the programmed I
,
MAX
as set by R
. The precondition current corresponds
SENSE
to 14mV across R
.
SENSE
PreconditionmodeisengagedwhilethevoltageontheBAT
pin is below the precondition threshold (V ). Once
the BAT voltage rises above the precondition threshold,
normal full-current charging can commence. The LT3651
incorporates 2.5% of threshold for hysteresis to prevent
mode glitching.
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.
BAT(PRE)
There is no provision for bad battery detection if C/10
termination is used.
365142fb
16
LT3651-4.1/LT3651-4.2
APPLICATIONS INFORMATION
timer count is suspended and held until the fault condition
is relieved. The RNG/SS pin is also pulled low during this
fault, to accommodate a graceful restart in the event that
a soft-start function is being incorporated (see the RNG/
SS: Soft-Start section).
When the internal timer is used for termination, bad bat-
tery detection is engaged. This fault detection feature
is designed to identify failed cells. A bad battery fault is
triggered when the voltage on BAT remains below the
preconditionthresholdforgreaterthanone-eighthofafull
timer cycle (one-eighth end-of-cycle). A bad battery fault
is also triggered if a normally charging battery re-enters
precondition mode after one-eighth end-of-cycle.
If higher operational charging temperatures are desired,
the temperature range can be expanded by adding series
resistance to the 10k NTC resistor. Adding a 0.91k (0TC)
resistor will increase the effective temperature threshold
to 45°C.
When a bad battery fault is triggered, the charge cycle
is suspended, so the CHRG status pin becomes high
impedance. The FAULT pin is pulled low to signal a fault
detection. The RNG/SS pin is also pulled low during this
fault, to accommodate a graceful restart, in the event that
a soft-start function is incorporated (see the RNG/SS:
Soft-Start section).
Thermal Foldback
The LT3651 contains a thermal foldback protection fea-
ture that reduces maximum charger output current if the
internal IC junction temperature approaches 125°C. In
most cases, on-chip temperature servos such that any
overtemperature conditions are relieved with only slight
reductions in maximum charge current.
Cycling the charger’s power or SHDN function initiates a
new charge cycle, but a LT3651 charger does not require
a reset. Once a bad battery fault is detected, a new timer
charge cycle initiates when the BAT pin exceeds the pre-
condition threshold voltage. During a bad battery fault,
1mA is sourced from the charger. Removing the failed
batteryallowsthechargeroutputvoltagetoriseandinitiate
a charge cycle reset. In that way removing a bad battery
resets the LT3651. A new charge cycle is started by con-
necting another battery to the charger output.
In some cases, the thermal foldback protection feature
can reduce charge currents below the C/10 threshold. In
applications that use C/10 termination (TIMER = 0V), the
LT3651 will suspend charging and enter standby mode
until the overtemperature condition is relieved.
Layout Considerations
The LT3651 switch node has rise and fall times that are
typicallylessthan10nstomaximizeconversionefficiency.
These fast switch times require care in the board layout
to minimize noise problems. The philosophy is to keep
the physical area of high current loops small (the inductor
charge/discharge paths) to minimize magnetic radiation.
Keeptraceswideandshorttominimizeparasiticinductance
and resistance and shield fast switching voltage nodes
(SW, BOOST) to reduce capacitive coupling.
Battery Temperature Fault: NTC
The LT3651 can accommodate battery temperature moni-
toring by using an NTC (negative temperature coefficient)
thermistor close to the battery pack. The temperature
monitoring function is enabled by connecting a 10kΩ,
B = 3380 NTC thermistor from the NTC pin to ground. If
theNTCfunctionisnotdesired,leavethepinunconnected.
The NTC pin sources 50μA and monitors the voltage
dropped across the 10kΩ thermistor. When the voltage
on this pin is above 1.36V (0°C) or below 0.29V (40°C),
the battery temperature is out of range, and the LT3651
triggersanNTCfault.TheNTCfaultconditionremainsuntil
the voltage on the NTC pin corresponds to a temperature
withinthe0°Cto40°Crange. Bothhotandcoldthresholds
incorporate hysteresis that corresponds to 2.5°C.
The switched node (SW pin) trace should be kept as
short as possible to minimize high frequency noise. The
V
capacitor (C ) should be placed close to the IC to
IN
IN
minimize this switching noise. Short, wide traces on these
nodes minimize stray inductance and resistance. Keep the
BOOSTdecouplingcapacitorincloseproximitytotheICto
minimize ringing from trace inductance. Route the SENSE
and BAT traces together and keep the traces as short as
During an NTC fault, charging is halted and both status
pins are pulled low. If timer termination is enabled, the
possible. Shielding these signals from switching noise
365142fb
17
LT3651-4.1/LT3651-4.2
APPLICATIONS INFORMATION
with ground is recommended. Make Kelvin connections
to the battery and sense resistor.
Transition losses are adjustable by changing switcher
frequency. Higher input voltages cause an increase in
transition losses, decreasing overall efficiency. However
transition losses are inversely proportional to switcher
oscillator frequency so lowering operating frequency
reduces these losses. But lower operating frequency
usually requires higher inductance to maintain inductor
ripple current (inversely proportional). Inductors with
larger values typically have more turns, increasing ESR
unlessyouincreasewirediametermakingthemphysically
larger. So there is an efficiency and board size trade-off.
Secondarily, inductor AC losses increase with frequency
and lower ripple reduces AC capacitor losses.
Keep high current paths and transients isolated from
battery ground, to assure an accurate output voltage
reference. Effective grounding is achieved by considering
switched current in the ground plane, and careful compo-
nent placement and orientation can effectively steer these
high currents such that the battery reference does not get
corrupted. Figure8illustratesthehighcurrent, highspeed
current loops. When the top switch is enabled (charge
loop), current flows from the input bypass capacitor (C )
IN
through the switch and inductor to the battery positive
terminal.Whenthetopswitchisdisabled(dischargeloop),
current to the battery positive terminal is provided from
ground through the synchronous switch. In both cases,
these switched currents return to ground via the output
The following simple rules of thumb assume a charge
current of 4A and battery voltage of 3.6V, with 1MHz os-
cillator, 24mΩ sense resistor and 3.3μH/20mΩ inductor.
bypass capacitor (C ).
BAT
A 1% increase in efficiency represents a 0.2W reduction
in power loss at 85% overall efficiency. One way to do
this is to decrease resistance in the high current path. A
reduction of 0.2W at 4A requires a 12.5mΩ reduction in
resistance. This can be done by reducing inductor ESR.
It is also possible to lower the sense resistance (with a
Power Considerations
The LT3651 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.
reduction in R
as well), with a trade-off of slightly
RNG/SS
less accurate current accuracy. All high current board
tracesshouldhavethelowestresistancepossible.Addition
of input current limit sense resistance reduces efficiency.
Consideration should be given for power dissipation and
overall efficiency in a LT3651 charger. A detailed analysis
is beyond the scope of the data sheet, however following
are general guidelines.
Charger efficiency drops approximately linearly with in-
creasing frequency all other things constant. At 15V V
IN
there is a 1% improvement in efficiency for every 200kHz
reduction in frequency (100kHz to 1MHz); At 28V V , 1%
IN
The major components of power loss are: conduction
and transition losses of the LT3651 switches; losses in
the inductor and sense resistors; and AC losses in the
decoupling capacitors. Switch conduction loss is fixed.
for every 100kHz.
Of course all of these must be experimentally confirmed
in the actual charger.
BOOST
V
IN
C
BOOST
C
IN
R
SENSE
LT3651
CHARGE
SW
+
C
BATTERY
DISCHARGE
BAT
365142 F08
Figure 8
365142fb
18
LT3651-4.1/LT3651-4.2
TYPICAL APPLICATIONS
6.5V to 32V 4A Charger with High Voltage Current Foldback
Maximum Charge Current vs VIN
5
SBM540
R
IL
120k
SMAZ24
1k
V
IN
C
IN
22μF
4
3
2
18.2V
CLP
CLN
V
IN
SHDN
ACPR
FAULT
CHRG
SW
BOOST
SENSE
1μF
3.3μH
1N5819
LT3651
RT
1
0
R
SENSE
R
T
24mΩ
54.9k
BAT
NTC
RNG/SS GND
TIMER
C
BAT
+
BATTERY
365142 TA02a
5
15
20
(V)
25
30
35
10
100μF
I
LIM
V
IN
365142 TA02b
12V to 32V 4A Charger with Low Voltage Current Foldback
Using the RNG/SS Pin
Maximum Charge Current vs VIN
5
4
3
2
0
SBM540
TO
V
IN
SYSTEM
LOAD
C
IN
SMAZ9V1
9.1V
22μF
CLP
CLN
V
IN
SHDN
ACPR
FAULT
CHRG
SW
BOOST
SENSE
1μF
1N5819
3.3μH
LT3651
RT
R
SENSE
R
T
24mΩ
54.9k
BAT
NTC
RNG/SS GND
TIMER
C
BAT
+
10
15
20
25
(V)
30
35
BATTERY
100μF
I
LIM
V
68k
365142 TA03a
IN
365142 TA03b
5.1k
1μF
6.5V to 32V 4A Charger with Approximately Constant Input Power
Input Power vs VIN
25
24
23
22
21
20
19
18
17
16
15
R
SENSE
SBM540
TO
SYSTEM
LOAD
50mΩ
V
IN
C
IN
8.2V
22μF
CLP
CLN
V
IN
SHDN
ACPR
FAULT
CHRG
SW
1μF
1N5819
180k
180k
3.3μH
BOOST
SENSE
LT3651
20k
6.2V
RT
R
SENSE
24mΩ
R
T
54.9k
BAT
NTC
TIMER
C
+
BAT
BATTERY
100μF
I
RNG/SS GND
LIM
5
10
20
(V)
25
30
35
15
365142 TA05a
V
IN
0.1μF
22k
365142 TA05b
365142fb
19
LT3651-4.1/LT3651-4.2
PACKAGE DESCRIPTION
UHE Package
Variation: UHE36MA
36-Lead Plastic QFN (5mm × 6mm)
(Reference LTC DWG # 05-08-1753 Rev A)
0.70 p 0.05
1.52
2.54 p 0.05
5.50 p 0.05
p 0.05
0.25 p 0.05
4.10 p 0.05
3.50 REF
3.45 p 0.05
0.76 p 0.05
3.45 p 0.05
PACKAGE
OUTLINE
0.25 p 0.05
0.50 BSC
4.50 REF
5.10 p 0.05
6.50 p 0.05
RECOMMENDED SOLDER PAD LAYOUT
PIN 1 NOTCH
R = 0.30 TYP
OR 0.35 s 45o
CHAMFER
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
R = 0.10
3.50 REF
5.00 p 0.10
0.00 – 0.05
TYP
35
36
0.200 REF
0.40 p0.10
PIN 1
1
2
TOP MARK
(SEE NOTE 6)
2.54 p 0.10
3.45
p 0.10
6.00 p 0.10
4.50 REF
1.52 p 0.10
3.45
p 0.10
(UHE36MA) QFN 0410 REV A
0.25 p 0.05
0.50 BSC
R = 0.125
TYP
0.75 p 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE
2. DRAWING NOT TO SCALE
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.20mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
3. ALL DIMENSIONS ARE IN MILLIMETERS
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON THE TOP AND BOTTOM OF PACKAGE
365142fb
20
LT3651-4.1/LT3651-4.2
REVISION HISTORY
REV
DATE
DESCRIPTION
PAGE NUMBER
2, 6, 7, 8
1-22
A
01/11 Revised Pin 34 to V in Pin Configuration, Pin Functions and Block Diagram
IN
B
03/11 Revised entire data sheet to add LT3651-4.1
365142fb
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
21
LT3651-4.1/LT3651-4.2
TYPICAL APPLICATION
6.5V to 32V 4A Charger with 3-Hour Charge Timeout, 6.3A Input
Current Limit, 10ms Soft-Start and Battery Temperature Monitoring
R
IL
16mΩ
SBM540
TO
V
IN
SYSTEM
LOAD
C
IN
1μF
V
22μF
LOGIC
50k 50k 50k 50k
CLP
CLN
V
IN
SHDN
SW
LT3651
1μF
ACPR
FAULT
CHRG
RT
3.3μH
BOOST
SENSE
TO
CONTROLLER
1N5819
R
SENSE
24mΩ
R
T
54.9k
BAT
NTC
RNG/SS GND
TIMER
C
BAT
C
TIMER
0.68μF
100μF
I
LIM
0.47μF
NTC B +
BATTERY
10k
365142 TA04
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1511
3A Constant Current/Constant Voltage
Battery Charger
High Efficiency, Minimum External Components to Fast Charge Lithium,
NIMH and NiCd Batteries, 24-Lead SO Package
LT1513
LT3650
SEPIC Constant or Programmable
Charger Input Voltage May Be Higher, Equal to or Lower Than Battery Voltage,
Current/Constant Voltage Battery Charger 500kHz Switching Frequency, DD-Pak and TO-220 Packages
2A Monolithic Li-Ion Battery Charger
High Efficiency, Wide Input Voltage Range Charger, Time or Charge Current
Termination, Automatic Restart, Temperature Monitoring, Programmable Charge
Current, Input Current Limit, 12-Lead DFN and MSOP Packages
LT3651-8.2/LT3651-8.4 Monolithic 4A High Voltage 2 Cell Li-Ion Standalone 9.0 ≤ V ≤ 32V, 40V Abs Max, 1MHz, Programmable Charge Current,
IN
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Timer or C/10 Termination, 5mm × 6mm QFN-36 Package
LT3652
Power Tracking 2A Battery Charger
Input Supply Voltage Regulation Loop for Peak Power Tracking in (MPPT)
Solar Applications, Standalone, 4.95V ≤ V ≤ 32V (40V Abs Max), 1MHz, 2A
IN
Programmable Charge Current, Timer or C/10 Termination, 3mm × 3mm DFN-12
Package and MSOP-12 Packages
LTC4002
LTC4006
LTC4007
LTC4008
Standalone Li-Ion Switch Mode
Battery Charger
Complete Charger for 1- or 2-Cell Li-Ion Batteries, Onboard Timer Termination,
Up to 4A Charge Current, 10-Lead DFN and SO-8 Packages
Small, High Efficiency, Fixed Voltage
Li-Ion Battery Charger with Termination
Complete Charger for 2-, 3- or 4-Cell Li-Ion Batteries, AC Adapter Current Limit
and Thermistor Sensor, 16-Lead Narrow SSOP Package
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, 24-Lead SSOP Package
4A, High Efficiency, Multi-Chemistry
Battery Charger
Complete Charger for 2- to 6-Cell Li-Ion Batteries or 4- to 18-Cell Nickel Batteries,
Up to 96% Efficiency, 20-Lead SSOP Package
LTC4009/LTC4009-1
LTC4009-2
High Efficiency, Multi-Chemistry
Battery Charger
Complete Charger for 1- to 4-Cell Li-Ion Batteries or 4- to 18-Cell Nickel Batteries,
Up to 93% Efficiency, 20-Lead (4mm × 4mm) QFN Package, LTC4009-1 for 4.1V
Float Voltage, LTC4009-2 for 4.2V Float Voltage
LTC4012/LTC4012-1/
4A, High Efficiency, Multi-Chemistry
PowerPath Control, Constant-Current/Constant-Voltage Switching Regulator Charger,
LTC4012-2/LTC4012-3 Battery Charger with PowerPath Control Resistor, Voltage/Current Programming, AC Adapter Current Limit and Thermistor
Sensor and Indicator Outputs, 1 to 4-Cell Li, Up to 18-Cell Ni, SLA and SuperCap
Compatible; 4mm × 4mm QFN-20 Package; LTC4012-1 Version for 4.1V Li Cells,
LTC4012-2 Version for 4.2V Li Cells, LTC4012-3 Version Has Extra GND Pin
365142fb
LT 0311 REV B • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
22
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© LINEAR TECHNOLOGY CORPORATION 2010
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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