LT3651-8.4_15 [Linear]
Monolithic 4A High Voltage 2-Cell Li-Ion Battery Charger;
| 型号： | LT3651-8.4_15 |
| 厂家： | 
Linear |
| 描述： | Monolithic 4A High Voltage 2-Cell Li-Ion Battery Charger 电池 |
| 文件： | 总24页 (文件大小：351K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT3651-8.2/LT3651-8.4
Monolithic 4A High Voltage
2-Cell Li-Ion Battery Charger
FEATURES
DESCRIPTION
n
Wide Input Voltage Range: 9V to 32V
The LT®3651-8.2/LT3651-8.4 are 2-cell, 4A Li-Ion/Poly-
mer battery chargers that operate over a 9V to 32V input
voltage range. An efficient monolithic average current
modesynchronousswitchingregulatorprovidesconstant
current, constant voltage charging with programmable
maximum charge current. A charging cycle starts with
battery insertion or when the battery voltage drops 2.5ꢀ
below the float voltage. Charger termination is selectable
as either charge current or internal safety timer timeout.
Charge current termination occurs when the charge cur-
rent falls to one-tenth the programmed maximum current
(C/1±). Timer based termination is typically set to three
hours and is user programmable (charging continues
below C/1± until timeout). Once charging is terminated,
theLT3651-8.2/LT3651-8.4supplycurrentdropsto85µA
into a standby mode.
(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
±±.5ꢀ Float Voltage Accuracy
n
±ꢁ.5ꢀ Charge Current Accuracy
n
±4ꢀ C/1± Detection Accuracy
n
NTC Resistor Temperature Monitor
n
Auto-Recharge at 9ꢁ.5ꢀ Float Voltage
n
Auto-Precondition at <ꢁ±ꢀ Float Voltage
n
Bad Battery Detection with Auto-Reset
n
Average Current Mode, Synchronous Switcher
n
User Programmable Frequency
n
Low Profile (±.ꢁ5mm) 5mm × 6mm 36-Lead
QFN Package
The LT3651-8.2/LT3651-8.4 offer several safety features.
A discharged battery is preconditioned with a small trickle
chargeandgeneratesasignalifunresponsive.Athermistor
monitors battery temperature, halting charging if out of
range. Excessive die temperature reduces charge current.
Charge current is also reduced to maintain constant input
current to prevent excessive input loading.
APPLICATIONS
n
Industrial Handheld Instruments
n
12V to 24V Automotive and Heavy Equipment
n
Desktop Cradle Chargers
Notebook Computers
n
The LT3651-8.2/LT3651-8.4 are available in a 5mm ×
6mm 36-lead QFN package.
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.
TYPICAL APPLICATION
12V to 32V 2-Cell 4A Charger
Efficiency, Power Loss vs VIN
91
90
89
88
87
5.0
4.5
4.0
3.5
3.0
TO
SYSTEM
LOAD
V
IN
12V TO 32V
V
BAT
= 7.8V
BAT
EFFICIENCY
I
= 4A
22µF
100k
10k
10V
CLP
SHDN
CLN
V
IN
SW
Si7611DN
1µF
LT3651-8.2/LT3651-8.4
10µH
WÜRTH 74477010
ACPR
BOOST
CMPSH1-4
FAULT
CHRG
SENSE
24mΩ
RT
301k
BAT
NTC
RNG/SS GND
POWER LOSS
+
2-CELL
100µF
TIMER
Li-Ion
I
LIM
BATTERY
365188284 TA01a
10
15
20
25
30
35
V
(V)
IN
36518284 TA01b
36518284fa
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For more information www.linear.com/LT3651-8.2
LT3651-8.2/LT3651-8.4
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
TOP VIEW
V
.......................................................................... 4±V
IN
CLN, CLP, SHDN
, CHRG,
FAULT ACPR ............................... V + ±.5V Up to 4±V
,
IN
36 35 34 33 32 31 30 29
CLP – CLN .............................................................±±.5V
SW ...........................................................................4±V
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
37
IN
GND
SENSE
BOOST
GND
SW
BOOST .......................................... SW + 1±V Up to 5±V
SENSE, BAT ............................................................ 1±V
SENSE-BAT ............................................. –±.5V to ±.5V
24 TIMER
GND
23
22 SW
21 NC
20 NC
19 NC
TIMER, RNG/SS, I , NTC, RT .............................. 2.5V
38
SW
LIM
NC
Operating Junction Temperature Range
NC
NC 10
(Notes 2, 3)................................................–4± to 125°C
Storage Temperature Range ......................–65 to 15±°C
11 12 13 14 15 16 17 18
UHE PACKAGE
36-LEAD (5mm × 6mm) PLASTIC QFN
= 125°C, θ = 43°C/W
T
JMAX
JA
EXPOSED PAD (PIN 3ꢁ) IS GND, MUST BE SOLDERED TO PCB
EXPOSED PAD (PIN 38) IS SW, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3651EUHE-8.2#PBF
LT3651IUHE-8.2#PBF
LT3651EUHE-8.4#PBF
LT3651IUHE-8.4#PBF
LT3651EUHE-8.2#TRPBF 365182
LT3651IUHE-8.2#TRPBF 365182
LT3651EUHE-8.4#TRPBF 365184
LT3651IUHE-8.4#TRPBF 365184
–4±°C to 125°C
–4±°C to 125°C
–4±°C to 125°C
–4±°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/
36518284fa
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For more information www.linear.com/LT3651-8.2
LT3651-8.2/LT3651-8.4
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = 20V, SHDN = 2V, SENSE = BAT = VBAT(FLT)
CTIMER = 0.68µF, RT = 50k, CLP = CLN = VIN, BOOST – SW = 4V.
,
PARAMETER
CONDITIONS
MIN
9.±
32
TYP
MAX
32
UNITS
l
l
V
V
V
V
V
Operating Range
OVLO Threshold
OVLO Hysteresis
UVLO Threshold
UVLO Hysteresis
V
V
V
V
V
IN
IN
IN
IN
IN
V
V
Rising
Rising
35
1.1
8.ꢁ
±.2
8.2
4±
IN
9.±
IN
Battery Float Voltage, V
LT3651-8.2
8.16
8.12
8.24
8.28
V
V
BAT(FLT)
l
l
LT3651-8.4
8.36
8.32
8.4
8.44
8.48
V
V
Battery Recharge Voltage Hysteresis
Threshold Voltage Relative to V
–2±±
mV
BAT(FLT)
BAT(PRE)
Battery Precondition Threshold Voltage, V
LT3651-8.2, V Rising
5.65
5.8±
V
V
BAT(PRE)
BAT
LT3651-8.4, V Rising
BAT
Battery Precondition Threshold Hysteresis
Threshold Voltage Relative to V
9±
mV
Operating V Supply Current
CC/CV Mode, Top Switch On, I = ±
8.6
8±
1ꢁ
mA
µA
µA
IN
SW
Standby Mode
Shutdown (SHDN = ±)
Top Switch On Voltage
V
V
– V , I = 4A
48±
–14±
1ꢁ
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 = ±, 2.5V < (V
– V ) < 8.5V
SW
BOOST
SW
I
/I , I = 4A
22
BOOST SW SW
Precondition Current Sense Voltage
Input Current Limit Voltage
CLP Input Bias Current
CLN Input Bias Current
V
V
– V , V = 5.±V
14
SENSE
BAT BAT
l
l
– V , I Open
ꢁ±
43
95
115
5ꢁ
CLP
CLN LIM
12±
36
µA
I
Bias Current
5±
µA
LIM
System Current Limit Programming Gain
Maximum Charge Current Sense Voltage
C/1± Trigger Sense Voltage
BAT Input Bias Current
V
V
V
/(V
– V ), V = ±.5V
ILIM
11.5
95
V/V
mV
mV
µA
ILIM CLP
CLN
l
l
– V , V = ꢁ.5V, V
> 1.1V
88
1±3
12.3
1
SENSE
SENSE
BAT BAT
RNG/SS
– V
4.5
8.6
±.1
±.1
5±
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 = ±.5V
RNG/SS
8.5
1±.8
1.36
±.29
1±
12.5
1.45
±.31
V/V
V
RNG/SS SENSE
BAT
Rising
Falling
1.25
±.2ꢁ
NTC
NTC
V
NTC Threshold Hysteresis
NTC Disable Impedance
NTC Bias Current
ꢀ of Threshold
Minimum External Impedance to GND
ꢀ
l
l
l
15±
46.5
1.15
4ꢁ±
5±
kΩ
µA
V
V
= ±.ꢁ5V
53.5
1.23
NTC
Shutdown Threshold
Rising
1.2±
95
V
SHDN
Shutdown Hysteresis
mV
nA
SHDN Input Bias Current
Status Low Voltage
–1±
l
V
, V
, V
, Load = 1±mA
±.45
V
CHRG FAULT ACPR
36518284fa
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For more information www.linear.com/LT3651-8.2
LT3651-8.2/LT3651-8.4
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are at TA = 25°C (Note 2). VIN = 20V, SHDN = 2V, SENSE = BAT = VBAT(FLT)
CTIMER = 0.68µF, RT = 50k, CLP = CLN = VIN, BOOST – SW = 4V.
,
PARAMETER
CONDITIONS
MIN
TYP
25
MAX
UNITS
µA
TIMER Charge/Discharge Current
TIMER Disable Threshold
Full Charge Cycle Time-Out
Precondition Timeout
Timer Accuracy
l
l
±.1
±.25
3
V
Hour
Minute
ꢀ
22.5
–13
13
Switcher Operating Frequency, f
R = 5±kΩ
T
1.1
25±
MHz
kHz
O
T
R = 25±kΩ
Minimum SW On-Time, t
15±
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.
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.
Note 2: The LT3651-8.2/LT3651-8.4 are tested under pulse loaded
conditions such that T = T . The LT3651-8.2E/LT3651-8.4E are
J
A
guaranteed to meet performance specifications from ±°C to 85°C junction
temperature. Specifications over the –4±°C to 125°C operating junction
temperature range are assured by design, characterization and correlation
with statistical process controls. The LT3651-8.2I/LT3651-8.4I are
guaranteed over the full –4±°C to 125°C operating junction temperature
range. The junction temperature (T in °C) is calculated from the ambient
J
temperature (T in °C) and power dissipation (P in Watts) according to
A
D
the formula:
T = T + P • θ
JA
J
A
D
where θ (in °C/W) is the package thermal impedance.
JA
36518284fa
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For more information www.linear.com/LT3651-8.2
LT3651-8.2/LT3651-8.4
TYPICAL PERFORMANCE CHARACTERISTICS
SENSE and BAT Pin Currents
Battery Float Voltage
vs Temperature
VIN Standby Mode Current
vs Temperature
vs BAT Voltage (VSENSE = VBAT
)
150
100
1.0
0.5
100
95
90
85
80
75
70
65
60
55
50
LT3651-8.4
I
SENSE
50
I
BAT
0
–50
0
–100
–150
–200
–250
–300
–350
–0.5
–1.0
7
8
9
25
TEMPERATURE (°C)
50
75 100
0
1
2
3
4
5
6
–50 –25
125
0
–50
–25
25
50
75
100
0
V
(V)
TEMPERATURE (°C)
BAT
36518284 G03
36518284 G01
36518284 G02
Maximum Charge Current
vs VRNG/SS as a Percentage
of Programmed IIN(MAX)
ICHG Current Limit
(VSENSE – VBAT) vs Temperature
C/10 Threshold (VSENSE – VBAT
vs Temperature
)
120
100
80
60
40
20
0
11
10
9
101.0
100.5
100.0
99.5
8
7
99.0
–50 –25
0
25
50
75 100 125
0
0.4
0.6
0.8
1.0
1.2
0.2
–50 –25
0
25
50
75 100 125
TEMPERATURE (°C)
V
(V)
TEMPERATURE (°C)
RNG/SS
36518284 G04
36518284 G05
36518284 G06
Charge Current vs VBAT as a
Percentage of Programmed
ICHG(MAX)
Maximum Input Current
vs VILIM as a Percentage
of Programmed IIN(MAX)
120
100
120
100
80
60
40
20
0
LT3651-8.4
80
60
40
20
0
5
6
7
8
9
0
0.4
0.6
(V)
0.8
1.0
1.2
0.2
V
V
(V)
ILIM
BAT
36518284 G07
36518284 G08
36518284fa
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For more information www.linear.com/LT3651-8.2
LT3651-8.2/LT3651-8.4
TYPICAL PERFORMANCE CHARACTERISTICS
Input Current Limit Voltage
Threshold vs Temperature
Topside Switch VON
vs Temperature
Bottom Side Switch VON
vs Temperature
2.0
700
650
600
550
–50
–100
–150
–200
I
= 4A
I
= 4A
SW
SW
1.5
1.0
R
OPEN
= 10k
ILIM
0.5
0
R
ILIM
–0.5
–1.0
–1.5
500
450
400
–2.0
–250
–25
0
50
75 100 125
–50
25
50
TEMPERATURE (˚C)
100 125
–50 –25
0
25
75
–50 –25
0
25
50
75 100 125
TEMPERATURE (°C)
TEMPERATURE (°C)
36518284 G09
36518284 G10
26518284 G11
Boost Drive vs Switch Current
Boost Drive vs Boost Voltage
50
40
30
20
10
0
24
23
22
21
20
I
= 4A
SW
0
1
2
3
4
5
2
3
4
5
6
7
8
I
(A)
V
– V (V)
BST IN
SW
36518284 G14
36518284 G13
Oscillator Frequency
vs Temperature
Timer Resistor (RT)
vs Period and Frequency
1.0
0.5
0
400
350
R
= 54.9k
T
300
250
200
150
100
50
–0.5
–1.0
–50 –25
0
25
50
75 100 125
2
500
3
4
6
1
1000
5
333
250
167
200
TEMPERATURE (°C)
PERIOD (µs)
FREQUENCY (kHz)
26518284 G15
36518284 G16
36518284fa
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For more information www.linear.com/LT3651-8.2
LT3651-8.2/LT3651-8.4
PIN FUNCTIONS
NTC (Pin 1): Battery Temperature Monitor Pin. This
pin is used to monitor battery temperature. Typically a
1±kΩ NTC(negativetemperaturecoefficient)thermistor
(B = 338±) is embedded with the battery and connected
from the NTC pin to ground. The pin sources 5±µA 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.Pins31and3ꢁmustbeconnected
together. Pins 6 and 23 are connected via the leadframe to
theexposedbacksidePin3ꢁ. 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 these pins 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 1±mA when
NC (Pins 8-10,19-21): No Connect. These pins can be left
floating (not connected).
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.
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 ±.68µF capacitor. This timer also controls
thebadbatteryfaultthatisgeneratedifthebatterydoesnot
reachthepreconditionthresholdvoltagewithinone-eighth
of a full cycle (22.5 minutes for a 3 hour charge cycle).
)
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 2.5ꢀ
below this float voltage. Once the charge cycle is termi-
nated, the input bias current of the BAT pin is reduced to
<±.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/1±rate, orapproximately1±ꢀofmaximumchargerate.
SENSE (Pin 4): Charge Current Sense Pin. The charge
current is monitored with a sense resistor (R
) con-
SENSE
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
nected between this pin and the BAT pin. The inductor
current flows through R to the battery. The voltage
SENSE
across this resistor sets the average charge current. The
maximum average charge current (I
95mV across the sense resistor.
) corresponds to
MAX
as V when disabled, and can sink currents up to 1±mA
IN
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.
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 ±V to 8.5V, referenced to the SW pin when the switch is
high. The voltage on the decoupling capacitor is refreshed
through a rectifying diode, with the anode connected to
either the battery output voltage or an external source,
and the cathode connected to the BOOST pin.
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
be pulled up to voltages as high as V when disabled,
IN
36518284fa
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For more information www.linear.com/LT3651-8.2
LT3651-8.2/LT3651-8.4
PIN FUNCTIONS
and can sink currents up to 1±mA 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/1± rate, or approximately 1±ꢀ
of the maximum charge current. A temperature fault also
causes this pin to be pulled low.
ply to the CLP pin, connecting a sense resistor from the
CLP pin to the CLN pin and then connecting CLN to V .
IN
The system load is then delivered from the CLN pin. The
LT3651-8.2/LT3651-8.4 servo the maximum charge cur-
rent 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
LIM
resistor. This function is disabled by shorting CLP, CLN
and V together.
IN
SHDN (Pin 27): Shutdown Pin. This pin can be used for
precision UVLO functions. When this pin rises above the
1.2±V threshold, the part is enabled. The pin has 95mV of
voltage hysteresis. When in shutdown mode, all charging
functionsaredisabled.WhentheSHDNpinispulledbelow
±.4V, the IC enters a low current shutdown mode where
V (Pins 32, 33, 34): Charger Input Supply. These pins
IN
provide power for the LT3651-8.2/LT3651-8.4. Charge
current for the battery flows into these pins. I is less
VIN
than 1±±µA after charge termination. Connect the pins
together.
the V pin current is reduced to 1ꢁµA. Typical SHDN pin
IN
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
input bias current is 1±nA. Connect the pin to V if the
IN
shutdown function is not desired.
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.
across the charge current sense resistor, R
between SENSE and BAT.
, placed
SENSE
The effective range on the pin is ±V to 1V. 5±µA is sourced
from this pin usually to a resistor (R ) to ground.
RNG/SS
The effective range on the pin is ±V to 1V. 5±µA is sourced
from this pin usually to a resistor (R ) to ground. V
V
represents approximately 1± times the maximum
RNG/SS
voltageacrossthechargecurrentsenseresistor.IfnoR
ILIM
IILIM
RNG/
represents approximately 11 times the maximum voltage
isusedthepartwilldefaulttomaximumchargecurrent.
SS
across the input current sense resistor. If no R is used
ILIM
Soft-start functionality for charge current can be imple-
mentedbyconnectingacapacitor(C )fromRNG/SS
the part will default to maximum input current.
RNG/SS
Soft-start functionality for input current can be imple-
mented with a capacitor (C ) from I to ground. The
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
ILIM
LIM
soft-start capacitor and the programming resistor can be
implemented in parallel.
recovery from faults if C
is used.
RNG/SS
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-
RT (Pin 36): Switcher Oscillator Timer Set Pin. A resis-
tor from this pin to ground sets the switcher oscillator
frequency. Typically this is 54.9k for f
= 1MHz.
OSC
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For more information www.linear.com/LT3651-8.2
LT3651-8.2/LT3651-8.4
BLOCK DIAGRAM
STANDBY
–
+
BOOST
5
UVLO
50µA
+
–
+
–
V
IN
8.7V
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
†
5.65V
V
INT
2.7V
SHDN
A6
–
+
27
×2.25
+
+
A1
STANDBY
+
–
1.2V
8.2V*
8.0V**
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
365148284 BD
*V
: 8.2V FOR LT3651-8.2, 8.4V FOR LT3651-8.4
BAT(FLT)
BAT(FLT)
BAT(PRE)
**V
– ∆V
: 8V FOR LT3651-8.2, 8.2V FOR LT3651-8.4
RECHRG
†
V
: 5.65V FOR LT3651-8.2, 5.8V FOR LT3651-8.4
36518284fa
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For more information www.linear.com/LT3651-8.2
LT3651-8.2/LT3651-8.4
OPERATION
Overview
2.5ꢀ from the full charge float voltage, the LT3651-8.2/
LT3651-8.4engageanautomaticchargecyclerestart.The
IC also automatically restarts a new charge cycle after a
bad battery fault once the failed battery is removed and
replaced with another battery.
The LT3651-8.2/LT3651-8.4 are complete Li-Ion battery
chargers, addressingwideinputvoltageandhighcurrents
(up to 4A). High charging efficiency is produced with a
constant frequency, average current mode synchronous
step-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 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 LT3651-8.2/LT3651-8.4 contain provisions for a bat-
tery temperature monitoring circuit. Battery temperature
is monitored by using a NTC thermistor located with the
battery. If the battery temperature moves outside a safe
chargingrangeof±°Cto4±°Cthechargingcyclesuspends
and signals a fault condition.
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.
The LT3651-8.2/LT3651-8.4 contain two digital open-
collectoroutputs, whichprovidechargerstatusandsignal
fault conditions. These binary coded pins signal battery
charging,standbyorshutdownmodes,batterytemperature
faults and bad battery faults.
It is adjustable through the I pin.
LIM
Ifthebatteryvoltageislow,chargecurrentisautomatically
reduced to 15ꢀ 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.
A precision undervoltage lockout is possible by using a
resistor divider on the shutdown pin (SHDN). The input
supply current is 1ꢁµA when the IC is in shutdown.
General Operation (See Block Diagram)
TheLT3651-8.2/LT3651-8.4useanaveragecurrentmode
controllooparchitecturetocontrolaveragechargecurrent.
TheLT3651-8.2/LT3651-8.4sensechargeroutputvoltage
viatheBAT pin.Thedifferencebetweenthisvoltageandthe
internal float voltage reference is integrated by the voltage
Charge termination can occur when charge current de-
creases to one-tenth the programmed maximum charge
current (C/1± 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/1± 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.
error amplifier (V-EA). The amplifier output voltage (I )
TH
corresponds to the desired average voltage across the
inductor sense resistor, R
, connected between the
SENSE
SENSE and BAT pins. The I voltage is divided down by
TH
a factor of 1±, and provides a voltage offset on the input
of the current error amplifier (C-EA). The difference be-
tween this imposed voltage and the current sense resistor
voltage is integrated by C-EA. The resulting voltage (V )
C
Once charging is terminated and the LT3651-8.2/
LT3651-8.4 are not actively charging, the IC automatically
enters a low current standby mode in which supply bias
currentsarereducedto<85µA.Ifthebatteryvoltagedrops
provides a voltage that is compared against an internally
generated ramp and generates the switch duty cycle that
controls the charger’s switches.
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LT3651-8.2/LT3651-8.4
OPERATION
The I error voltage corresponds linearly to average cur-
Use of the timer function also enables bad battery detec-
tion. This fault condition is achieved if the battery does
not respond to preconditioning and the charger remains
in (or enters) precondition mode after one-eighth of the
programmed charge cycle time. A bad battery fault halts
the charging cycle, the CHRG status pin goes high imped-
ance and the FAULT pin is pulled low.
TH
rent 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
current sense voltage (voltage across R
TH
) to 95mV
SENSE
setting the maximum charge current. Manipulation of
maximum charge current is possible through the RNG/SS
and I pins (see the RNG/SS: Dynamic Charge Current
LIM
When the LT3651-8.2/LT3651-8.4 terminate a charging
cycle, whether through C/1± 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 2.5ꢀ. Because the voltage on a successfully
charged battery is at the full float voltage, the voltage er-
ror amp detects an overvoltage condition and rails low.
When the voltage error amp output drops below ±.3V,
the IC enters standby mode, where most of the internal
Adjust, RNG/SS: Soft-Start and I Control sections).
LIM
If the voltage on the BAT pin (V ) is below V
, Aꢁ
BAT(PRE)
BAT
initiates the precondition mode. During the precondition
interval, the charger continues to operate in constant cur-
rent mode, but the I clamp is reduced to ±.15V reducing
TH
chargecurrentto15ꢀofthemaximumprogrammedvalue.
As V approaches the float voltage (V
) the voltage
FLOAT
BAT
errorampV-EA takescontrolofI and thechargertransi-
TH
circuitry is disabled and the V bias current is reduced
IN
tions into constant voltage (CV) mode. As this occurs, the
to <1±±µA. When the voltage on the BAT pin drops below
the reduced float reference level, the output of the voltage
error amp will climb, at which point the IC comes out of
standby mode and a new charging cycle is initiated.
I
voltage falls from the limit clamp and charge current is
TH
reduced from the maximum value. When the I voltage
TH
falls below ±.1V, A8 signals C/1±. If the charger is config-
ured for C/1± 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.
Input current is measured via a resistor (R ) that is
CL
placed between the CLP and CLN pins. Power is applied
The LT3651-8.2/LT3651-8.4 contain an internal charge
cycle timer that terminates a successful charge cycle af-
ter a programmed amount of time. This timer is typically
programmed to achieve end-of-cycle in three hours, but
can be configured for any amount of time by setting an
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
achieved, I is reduced, lowering the charge current thus
TH
maintaining the maximum input current.
appropriate timing capacitor value (C
). When timer
TIMER
termination is used, the charge cycle does not terminate
after C/1± is achieved. Because the CHRG status pin re-
sponds to the C/1± current level, the IC will indicate a fully
charged battery status, but the charger will continue to
source low currents. At the programmed end of the cycle
time the charge cycle stops and the part enters standby
mode. If the battery did not achieve at least 9ꢁ.5ꢀ of the
full float voltage at the end-of-cycle, charging is deemed
unsuccessful and another full-timer cycle is initiated.
5±µA 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,
A1± activates decreasing I and reduces charge current.
TH
This reduces on-chip power dissipation to safe levels but
continues charging.
36518284fa
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For more information www.linear.com/LT3651-8.2
LT3651-8.2/LT3651-8.4
APPLICATIONS INFORMATION
OSC Frequency
which has a maximum at V = 2 • V , where I
CVIN(RMS)
CHG(MAX)
tor RMS rating of 2A.
IN
BAT
=I
/2.Intheexampleabovethatrequiresacapaci-
A precision resistor to ground sets the LT3651-8.2/
LT3651-8.4 switcher oscillator frequency, f , permit-
OSC
ting user adjustability of the frequency value. Typically
this frequency is in the 2±±kHz to 1MHz range. Power
consideration may necessitate lower frequency operation
especiallyifthechargerisoperatedwithveryhighvoltages.
Adjustability also allows the user to position switching
harmonics if their system requires.
Boost Supply
The BOOST bootstrapped supply rail drives the internal
switch and facilitates saturation of the high side switch
transistor. The BOOST voltage is normally created by
connecting a 1µF capacitor from the BOOST pin to the
SW pin. Operating range of the BOOST pin is 2V to 8.5V,
as referenced to the SW pin.
The timing resistor, R , value is set by the following:
T
54.9
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
RT =
kΩ
(
)
fOSC MHz
Set R to 54.9k for 1MHz operation.
T
than ±.1A and its reverse voltages greater than V
.
IN(MAX)
If an external supply that is greater than the input is avail-
able (V – V > 2V), it may be used in place of the
V Input Supply
IN
BOOST
IN
The LT3651-8.2/LT3651-8.4 are biased directly from the
charger input supply through the V pin. This supply
bootstrap capacitor and diode.
IN
provides large switched currents, so a high quality, low
ESR decoupling capacitor is required to minimize volt-
V ,V Start-Up Requirement
IN BOOST
The LT3651-8.2/LT3651-8.4 operate with a V range of
age glitches on V . The V decoupling capacitor (C )
IN
IN
IN
VIN
9V to 32V. The charger begins a charging cycle when the
detected battery voltage is below the auto-restart float
voltage and the part is enabled.
absorbs all input switching ripple current in the charger.
Size is determined by input ripple voltage with the fol-
lowing equation:
When V is below 1±.5V and the BOOST capacitor is
IN
ICHG(MAX) • VBAT
CIN(BULK)
µF
( )
uncharged, the high side switch would normally not have
sufficient head room to start switching. During normal
operation the low side switch is deactivated when charge
current is very low to prevent reverse current in the induc-
tor. However in order to facilitate start-up, the LT3651-
fOSC MHz • ∆V • V
IN
IN
where ∆V is the input ripple, I
is the maximum
IN
CHG(MAX)
charge current and f is the oscillator frequency. A good
starting point for ∆V is ±.1V. Worst-case conditions
IN
8.2/LT3651-8.4 enable the switch if V
voltage is
BOOST
are with V
IN(MIN) MAX
high and V at minimum. So for a 15V
BAT
IN
low. This allows initial charging of the BOOST capacitor
which then permits the high side switch to saturate and
efficiently operate. The boost capacitor charges to full
potential after a few cycles.
V
, I
= 4A and a 1MHz oscillator frequency:
4•8.2
= = 22µF
CIN(BULK)
1•0.1•15
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
Thecapacitormusthaveanadequateripplecurrentrating.
RMS ripple current, I
is approximated by:
CVIN(RMS)
VBAT
V
IN
VBAT
ICVIN(RMS) ≈ICHG(MAX)
•
•
–1
V UVLO turn-on and thus disrupt normal behavior and
IN
V
IN
potentially stall start-up. If an input current sense resis-
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LT3651-8.2/LT3651-8.4
APPLICATIONS INFORMATION
Inductor Selection
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
pin and setting UVLO to 9V with the SHDN pin is required
The primary criteria for inductor value selection in the
LT3651-8.2/LT3651-8.4 charger is the ripple current cre-
ated during switching. Ripple current, ∆I
, is typically
MAX
set within a range of 25ꢀ to 35ꢀ of the maximum charge
current, I . This percentage typically gives a good com-
at low V .
IN
MAX
promise between losses due to ripple and inductor size.
An approximate formula for inductance is:
BAT Output Decoupling
It is recommended that the LT3651-8.2/LT3651-8.4 char-
ger output have a decoupling capacitor. If the battery can
be disconnected from the charger output this capacitor is
VBAT + VF
VBAT + VF
V + VF
IN
L =
• 1–
µH
(
)
∆IMAX • fOSC MHz
(
)
required. The value of this capacitor (C ) is related to
BAT
Worse-case ripple is at high V and high V . V is the
IN
BAT
F
the minimum operational V voltage such that:
IN
forwardvoltageofthesynchronousswitch(approximately
±.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
350µF
CBAT ≈20µF +
V
IN(MIN)
inductor. Peak current is I
+ ∆I
/2.
CHG(MAX)
CHG(MAX)
The voltage rating on C must meet or exceed the bat-
BAT
tery float voltage.
Magnetics vendors typically specify inductors with maxi-
mumRMSandsaturationcurrentratings.Selectaninductor
thathasasaturationcurrentratingatorabovepeakcurrent,
R : Charge Current Programming
SENSE
and an RMS rating above I
. Inductors must also
CHG(MAX)
The LT3651-8.2/LT3651-8.4 charger is configurable to
charge at average currents as high as 4A (see Figure 1).
If RNG/SS maximum voltage is not limited, the inductor
meet a maximum volt-second product requirement. If this
specificationisnotinthedatasheetofaninductor,consult
the vendor to make sure the maximum volt-second prod-
uct is not being exceeded by your design. The minimum
required volt-second product is approximately:
sense resistor, R
, has 95mV across it at maximum
SENSE
charge current so:
0.095V
ICHG(MAX)
RSENSE
=
VBAT
VBAT
• 1–
V •µs
(
)
fOSC(MHz)
V
IN(MAX)
where I
SENSE
is the maximum average charge current.
CHG(MAX)
is 24mΩ for a 4A charger.
R
4
SW
3
2
1
0
BOOST
LT3651-8.2
LT3651-8.4
SENSE
R
SENSE
BAT
I
= 4A
MAX
OSC
+
f
= 1MHz
25% TO 35% RIPPLE
365142 F01
9 10
15
20
25
30
V
(V)
IN(MAX)
Figure 1. Programming Maximum Charge Current Using RSENSE
36512 F02
Figure 2. Inductance (L) vs Maximum VIN
36518284fa
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LT3651-8.2/LT3651-8.4
APPLICATIONS INFORMATION
Acceptable power inductors are available from several
manufacturers such a Würth Elektronik, Vishay, Coilcraft
and TDK.
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 times duty
IN
cycle). Using the full I
range, the maximum voltage
across R is 95mV. So R is set at 95mV/2A = 48mΩ.
LIM
System Input Current Limit
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 ±.
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 ±A. When
the input limiter reduces charge current it does not impact
the internal system timer if used. See Figure 4.
TheLT3651-8.2/LT3651-8.4containaPowerPath control
feature to help manage supply load currents. The charger
adjusts charger output current in response to a system
load so as to maintain a constant input supply load. If
overall input supply current exceeds the programmed
maximum value the charge current is diminished in an
attempt to keep supply current constant. One application
where this is helpful is if you have a current limited input
supply. Setting the maximum input current limit below
the supply limit prevents supply collapse.
A resistor, R , is placed between the input supply and the
CL
3
system and charger loads as shown in Figure 3.
INPUT CURRENT
2
TheLT3651-8.2/LT3651-8.4source5±µAfromtheI pin,
LIM
so a voltage is developed by simply connecting a resistor
to ground. The voltage on the I
pin corresponds to
LIM
11.5 times the maximum voltage across the input sense
resistor (R ). Input current limit is defined by:
CHARGE
1
0
CURRENT
CL
(V REFERRED)
IN
VILIM
11.5•RCL
50µA •RILIM
11.5•RCL
IINPUT(MAX)
=
=
365142 F04
0
1
2
SYSTEM LOAD CURRENT (A)
TheprogrammingrangeforI is±Vto1V.Voltageshigher
LIM
Figure 4. Input Current Limit for 4A Maximum Charger
and 6A System Current Limit
than 1V have no effect on the maximum input current. The
default maximum sense voltage is 95mV and is obtained
Ifreducedvoltageoverheadorbetterefficiencyisrequired
if R
is greater than 2±k or if the pin is left open.
ILIM
then reduce the maximum voltage across R . So for
CL
INPUT
SUPPLY
instance, a 1±k R
sets the maximum R voltage to
43mV. This reduction comes at the expense of slightly
ILIM
CL
CLP
increased limit variation.
LT3651-8.2
LT3651-8.4
R
CL
CLN
SYSTEM LOAD
Note the LT3651-8.2/LT3651-8.4 internally integrate the
inputlimitsignals. Thisshouldnormallyprovidesufficient
filtering and reduce the sensitivity to current spikes. For
the best accuracy take care to provide good Kelvin con-
V
IN
I
LIM
R
LIM
nections from R to CLP, CLN.
365142 F03
CL
Figure 3. Input Current Limit Configuration
36518284fa
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LT3651-8.2/LT3651-8.4
APPLICATIONS INFORMATION
Further flexibility is possible by dynamically altering the
current. The default maximum sense voltage is 95mV
and is obtained if R
pin is left open.
is greater than 2±k or if the
I
pin. Different resistor values could be switched in
RNG/SS
LIM
to create unique input limit conditions. The I
pin can
LIM
also be tied to a servo amplifier for other options. See the
For example, say you want to reduce the maximum charge
currentto5±ꢀofthemaximumvalue.SetRNG/SSto±.5V
(5±ꢀ of 1V), imposing a 46mV maximum sense voltage.
Per the above equation, ±.5V on RNG/SS requires a 1±k
resistor. If the charge current needs to be dynamically
adjustable then Figure 5 shows one method.
information in the following section concerning I
programming for examples.
RNG/SS
RNG/SS: Dynamic Current Adjust
The RNG/SS pin gives the user the capability to adjust
maximum charge current dynamically. The part sources
5±µA 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
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.
charge current sense resistor, R . The defining equa-
SENSE
tions for charge current are:
RNG/SS: Soft-Start
VRNG/SS
10.8•RSENSE 10.8•RSENSE
50µA •RRNG/SS
Soft-start functionality is also supported by the RNG/SS
pin. The 5±µA sourced from the RNG/SS pin can linearly
IMAX(RNG/SS)
=
=
charge a capacitor, C
, connected from the RNG/
RNG/SS
I
is the maximum charge current.
MAX(RNG/SS)
SS pin to ground (see Figure ꢁ). The maximum charge
current follows this voltage. Thus, the charge current
increases from zero to the fully programmed value as the
The programming range for RNG/SS is ±V to 1V. Voltages
higher than 1V have no effect on the maximum charge
LT3651-8.2
LT3651-8.4
LT3651-8.2
LT3651-8.4
RNG/SS
RNG/SS
10k
+
SERVO
–
LOGIC HIGH = HALF CURRENT
REFERENCE
365142 F06
365142 F05
Figure 5. Using the RNG/SS Pin for
Digital Control of Maximum Charge Current
Figure 6. Driving the RNG/SS Pin
with a Current-Sink Active Servo Amplifier
LT3651-8.2
LT3651-8.4
RNG/SS
C
RNG/SS
365142 F07
Figure 7. Using the RNG/SS Pin for Soft-Start
36518284fa
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LT3651-8.2/LT3651-8.4
APPLICATIONS INFORMATION
capacitor charges from ±V to 1V. The value of C
is
SS
WhenC/1±terminationisused,aLT3651-8.2/LT3651-8.4
chargersourcesbatterychargecurrentaslongastheaver-
age current level remains above the C/1± threshold. As the
full-charge float voltage is achieved, the charge current
falls until the C/1± threshold is reached, at which time
the charger terminates and the LT3651-8.2/LT3651-8.4
enter standby mode. The CHRG status pin follows the
charge cycle and is high impedance when the charger is
not actively charging.
RNG/SS
calculated based on the desired time to full current (t )
following the relation:
C
= 5±µA • t
SS
RNG/SS
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.
When V
drops below 9ꢁ.5ꢀ of the full-charged float
BAT
voltage, whether by battery loading or replacement of the
battery, the charger automatically re-engages and starts
charging.
Status Pins
TheLT3651-8.2/LT3651-8.4reportchargerstatusthrough
two open-collector outputs, the CHRG and FAULT pins.
These pins can accept voltages as high as VIN, and can
There is no provision for bad battery detection if C/1±
termination is used.
sink up to 1±mA when enabled
.
The CHRG pin indicates that the charger is delivering cur-
rent at greater than a C/1± 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.
Timer Termination
TheLT3651-8.2/LT3651-8.4supportatimer-basedtermi-
nationscheme,inwhichabatterychargecycleisterminated
after a specific amount of time elapses. Timer termination
is engaged when a capacitor (C
) is connected from
TIMER
the TIMER pin to ground. The timer cycle end-of-cycle
Table 1. Status Pins State Table
STATUS PINS STATE
(t ) occurs based on C
EOC
following the relation:
TIMER
tEOC Hrs
(
)
CHARGER STATUS
CHRG
Off
FAULT
Off
CTIMER
=
•0.68 µF
( )
3
Not Charging—Standby or Shutdown Mode
Off
On
Bad Battery Fault
so a typical 3 hour timer end-of-cycle would use a ±.68µF
capacitor.
(Precondition Timeout/EOC Failure)
On
On
Off
On
Normal Charging at C/1± or Greater
NTC Fault (Pause)
The CHRG status pin continues to signal charging at a
C/1± 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/1± threshold. The charger
continues to “top off” the battery until timer end-of-cycle,
when the LT3651-8.2/LT3651-8.4 terminate the charge
cycle and enters standby mode.
C/10 Termination
The LT3651-8.2/LT3651-8.4 support a low current based
termination scheme, where a battery charge cycle termi-
nates when the current output from the charger falls to
below one-tenth the maximum current, as programmed
with R
9mV across R
by shorting the TIMER pin to ground.
. The C/1± threshold current corresponds to
SENSE
. This termination mode is engaged
SENSE
36518284fa
16
For more information www.linear.com/LT3651-8.2
LT3651-8.2/LT3651-8.4
APPLICATIONS INFORMATION
Cycling the charger’s power or SHDN function initiates a
new charge cycle, but a LT3651-8.2/LT3651-8.4 charger
does not require a reset. Once a bad battery fault is de-
tected, a new timer charge cycle initiates when the BAT pin
exceeds the precondition threshold voltage. During a bad
battery fault, 1mA is sourced from the charger. Removing
the failed battery allows the charger output voltage to rise
and initiate a charge cycle reset. In that way removing a
bad battery resets the LT3651-8.2/LT3651-8.4. A new
charge cycle is started by connecting another battery to
the charger output.
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 2.5ꢀ 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.
When V
drops below 9ꢁ.5ꢀ of the full-charge float
BAT
voltage, whether by battery loading or replacement of the
battery, the charger automatically re-engages and starts
charging.
Precondition and Bad Battery Fault
Battery Temperature Fault: NTC
A LT3651-8.2/LT3651-8.4 charger has a precondition
mode, in which charge current is limited to 15ꢀ of the
TheLT3651-8.2/LT3651-8.4canaccommodatebatterytem-
peraturemonitoringbyusinganNTC(negativetemperature
coefficient)thermistorclosetothebatterypack.Thetemper-
aturemonitoringfunctionisenabledbyconnectinga1±kΩ,
B = 338± NTC thermistor from the NTC pin to ground. If
theNTCfunctionisnotdesired,leavethepinunconnected.
programmed I
, as set by R
. The precondition
SENSE
MAX
SENSE
current corresponds to 14mV across R
.
Precondition mode is engaged while the voltage on the
BAT pin is below the precondition threshold (V ).
BAT(PRE)
Once the BAT voltage rises above the precondition thresh-
old, normal full-current charging can commence. The
LT3651-8.2/LT3651-8.4 incorporate 2.5ꢀ of threshold
for hysteresis to prevent mode glitching.
The NTC pin sources 5±µA and monitors the voltage
droppedacrossthe1±kΩthermistor.Whenthevoltageon
this pin is above 1.36V (±°C) or below ±.29V (4±°C), the
battery temperature is out of range, and the LT3651-8.2/
LT3651-8.4 trigger an NTC fault. The NTC fault condition
remains until the voltage on the NTC pin corresponds to
a temperature within the ±°C to 4±°C range. Both hot and
cold thresholds incorporate hysteresis that corresponds
to 2.5°C.
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.
During an NTC fault, charging is halted and both status
pins are pulled low. If timer termination is enabled, the
timer count is suspended and held until the fault condition
is relieved. The RNG/SS pin is also pulled low during this
fault, to accommodate a graceful restart in the event that
a soft-start function is being incorporated (see the RNG/
SS: Soft-Start section).
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).
36518284fa
17
For more information www.linear.com/LT3651-8.2
LT3651-8.2/LT3651-8.4
APPLICATIONS INFORMATION
and BAT traces together and keep the traces as short as
possible. Shielding these signals from switching noise
with ground is recommended. Make Kelvin connections
to the battery and sense resistor.
If higher operational charging temperatures are desired,
the temperature range can be expanded by adding series
resistance to the 1±k NTC resistor. Adding a ±.91k (±TC)
resistor will increase the effective temperature threshold
to 45°C.
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
Thermal Foldback
The LT3651-8.2/LT3651-8.4 contain a thermal foldback
protection feature that reduces maximum charger output
current if the internal IC junction temperature approaches
125°C. In most cases, on-chip temperature servos such
thatanyovertemperatureconditionsarerelievedwithonly
slight reductions in maximum charge current.
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
In some cases, the thermal foldback protection feature
can reduce charge currents below the C/1± threshold. In
applications that use C/1± termination (TIMER = ±V), the
LT3651-8.2/LT3651-8.4 suspend charging and enters
standby mode until the overtemperature condition is
relieved.
bypass capacitor (C ).
BAT
BOOST
Layout Considerations
V
IN
C
BOOST
The LT3651-8.2/LT3651-8.4 switch node has rise and fall
times that are typically less than 1±ns to maximize conver-
sion efficiency. These fast switch times require care in the
board layout to minimize noise problems. The philosophy
istokeepthephysicalareaofhighcurrentloopssmall(the
inductor charge/discharge paths) to minimize magnetic
radiation.Keeptraceswideandshorttominimizeparasitic
inductance and resistance and shield fast switching volt-
age nodes (SW, BOOST) to reduce capacitive coupling.
C
IN
R
SENSE
LT3651-8.2
LT3651-8.4
SW
+
C
BATTERY
DISCHARGE
BAT
CHARGE
365142 F08
Figure 8
Power Considerations
The switched node (SW pin) trace should be kept as
short as possible to minimize high frequency noise. The
The LT3651-8.2/LT3651-8.4 packaging is designed to
efficiently remove heat from the IC via the exposed pad on
the backside of the package, which is soldered to a copper
footprint on the PCB. This footprint should be made as
large as possible to reduce the thermal resistance of the
IC case to ambient air.
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
36518284fa
18
For more information www.linear.com/LT3651-8.2
LT3651-8.2/LT3651-8.4
APPLICATIONS INFORMATION
Consideration should be given for power dissipation and
overall efficiency in a LT3651-8.2/LT3651-8.4 charger. A
detailed analysis is beyond the scope of the data sheet,
however following are general guidelines.
The following simple rules of thumb assume a charge
current of 4A and battery voltage of 7.5V, with 1MHz os-
cillator, 24mΩ sense resistor and 3.3µH/20mΩ inductor.
A 1% increase in efficiency represents a 0.35W reduction
in power loss at 85% overall efficiency. One way to do
this is to decrease resistance in the high current path. A
reduction of 0.2W at 4A requires a 22mΩ reduction in
resistance. This can be done by reducing inductor ESR.
It is also possible to lower the sense resistance (with a
The major components of power loss are: conduction and
transitionlossesoftheLT3651-8.2/LT3651-8.4 switches;
losses in the inductor and sense resistors; and AC losses
in the decoupling capacitors. Switch conduction loss is
fixed.Transitionlossesareadjustablebychangingswitcher
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.
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.
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
for every 100kHz.
Of course all of these must be experimentally confirmed
in the actual charger.
36518284fa
19
For more information www.linear.com/LT3651-8.2
LT3651-8.2/LT3651-8.4
TYPICAL APPLICATIONS
9V to 32V 4A Charger with High Voltage Current Foldback
Maximum Charge Current vs VIN
SBM540
5
4
3
2
R
IL
1k
120k
SMAZ24
V
IN
C
IN
22µF
18.2V
CLP
CLN
V
IN
SW
SHDN
ACPR
FAULT
CHRG
1µF
3.3µH
BOOST
1N5819
LT3651-8.2/LT3651-84
NC
SENSE
RT
R
SENSE
24mΩ
1
0
R
T
54.9k
BAT
NTC
RNG/SS GND
TIMER
+
2-CELL
Li-Ion
C
BAT
100µF
5
15
20
(V)
25
30
35
10
I
LIM
BATTERY
V
IN
365142 TA02a
3651 TA02b
12V to 32V 4A Charger with Low Voltage Current Foldback
Using the RNG/SS Pin
Maximum Charge Current vs VIN
SBM540
5
4
3
2
0
TO
V
SYSTEM
IN
C
IN
22µF
LOAD
SMAZ9V1
9.1V
CLP
CLN
V
IN
SW
SHDN
ACPR
FAULT
CHRG
LT3651-82/LT3651-84
NC
1µF
1N5819
3.3µH
BOOST
SENSE
RT
R
SENSE
24mΩ
R
T
54.9k
BAT
NTC
RNG/SS GND
TIMER
C
+
2-CELL
Li-Ion
BAT
100µF
I
LIM
BATTERY
10
15
20
25
(V)
30
35
68k
365142 TA03a
V
IN
3651 TA03b
5.1k
1µF
36518284fa
20
For more information www.linear.com/LT3651-8.2
LT3651-8.2/LT3651-8.4
TYPICAL APPLICATIONS
9V to 32V 4A Charger with Approximately Constant Input Power
Input Power vs VIN
R
25
24
23
22
21
20
19
18
17
16
15
SENSE
50mΩ
SBM540
TO
SYSTEM
LOAD
V
IN
C
IN
22µF
8.2V
CLP
CLN
V
IN
SW
SHDN
ACPR
FAULT
CHRG
1µF
1N5819
180k
3.3µH
BOOST
LT3651-8.2/LT3651-8.4
20k
6.2V
NC
RT
SENSE
R
SENSE
24mΩ
R
T
54.9k
BAT
NTC
180k
TIMER
C
+
2-CELL
Li-Ion
BAT
100µF
I
RNG/SS GND
LIM
BATTERY
5
10
20
(V)
25
30
35
15
365142 TA05a
V
IN
365142 TA05b
0.1µF
22k
36518284fa
21
For more information www.linear.com/LT3651-8.2
LT3651-8.2/LT3651-8.4
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
UHE Package
Variation: UHE36MA
36-Lead Plastic QFN (5mm × 6mm)
(Reference LTC DWG # 05-08-1753 Rev A)
0.70 ±0.05
1.52
±0.05
2.54 ±0.05
5.50 ±0.05
0.25 ±0.05
4.10 ±0.05
3.50 REF
3.45 ±0.05
3.45 ±0.05
PACKAGE
OUTLINE
0.76 ±0.05
0.25 ±0.05
0.50 BSC
4.50 REF
5.10 ±0.05
6.50 ±0.05
RECOMMENDED SOLDER PAD LAYOUT
PIN 1 NOTCH
R = 0.30 TYP
OR 0.35 × 45°
CHAMFER
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
R = 0.10
3.50 REF
5.00 ±0.10
0.00 – 0.05
TYP
35
36
0.200 REF
0.40 ±0.10
PIN 1
1
2
TOP MARK
(SEE NOTE 6)
2.54 ±0.10
3.45
±0.10
6.00 ±0.10
4.50 REF
1.52 ±0.10
3.45
±0.10
(UHE36MA) QFN 0410 REV A
0.25 ±0.05
0.50 BSC
R = 0.125
TYP
0.75 ±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
36518284fa
22
For more information www.linear.com/LT3651-8.2
LT3651-8.2/LT3651-8.4
REVISION HISTORY
REV
DATE
DESCRIPTION
PAGE NUMBER
A
07/15 Modified Typical Application circuit.
Modified Efficiency/Power Loss curve.
1
1
3
6
7
Changed typical values of Boost Supply Current/ Switch Drive.
Modified Typical Performance Characteristic curves.
Clarified GND Pin Function description.
36518284fa
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.
23
LT3651-8.2/LT3651-8.4
TYPICAL APPLICATION
9V to 32V 4A Charger with 3-Hour Charge Timeout, 6.3A Input Current
Limit, 10ms Soft-Start and Battery Temperature Monitoring
R
IL
16mΩ
SBM540
TO
V
IN
SYSTEM
LOAD
C
IN
1µF
V
LOGIC
22µF
50k 50k 50k 50k
CLP
SHDN
CLN
V
IN
SW
LT3651-8.2
LT3651-8.4
NC
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
+
2-CELL
Li-Ion
BATTERY
NTC B
10k
3651 TA04
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT3651-4.1/LT3651-4.2 Monolithic 4A Switch Mode Synchronous Standalone, 4.75 ≤ V ≤ 32V (40V Abs Max), 1MHz, 4A, Programmable Charge
IN
1-Cell Li-Ion Battery Charger
Current Timer or V/10 Termination 5mm × 6mm QFN-36 Package
LT3650
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
LT3652/LT3652HV
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. LT3652HV Version Up to V = 34V
IN
LTC4000
High Voltage High Current Controller for Complete High Performance Battery Charger When Paired with a DC/DC Converter
Battery Charging and Power Management Wide Input and Output Voltage Range: 3V to 60V ±0.25% Accurate Programmable
Float Voltage, Programmable C/X or Timer Based Charge Termination NTC Input for
Temperature Qualified Charging, 28-Lead 4mm × 5mm QFN or SSOP Packages
LTC4002
LTC4006
LTC4007
LTC4008
Standalone Li-Ion Switch Mode
Battery Charger
Small, High Efficiency, Fixed Voltage
Li-Ion Battery Charger with Termination
High Efficiency, Programmable Voltage
Battery Charger with Termination
4A, High Efficiency, Multi-Chemistry
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
Complete Charger for 2-, 3- or 4-Cell Li-Ion Batteries, AC Adapter Current Limit
and Thermistor Sensor, 16-Lead Narrow SSOP Package
Complete Charger for 3- or 4-Cell Li-Ion Batteries, AC Adapter Current Limit,
Thermistor Sensor and Indicator Outputs, 24-Lead SSOP Package
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
LTC4012-2/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; LTC4012-1 Version for 4.1V
Li Cells, LTC4012-2 Version for 4.2V Li Cells, LTC4012-3 Version Has Extra GND Pin
36518284fa
LT 0715 REV A • PRINTED IN USA
24 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
●
LINEAR TECHNOLOGY CORPORATION 2012
(408)432-1900 FAX: (408) 434-0507 www.linear.com/LT3651-8.2
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