LT3651-8.2 [Linear]
Monolithic 4A HIgh Voltage 2-Cell Li-Ion Battery Charger; 4A单片高电压2节锂离子电池充电器
| 型号： | LT3651-8.2 |
| 厂家： | 
Linear |
| 描述： | Monolithic 4A HIgh Voltage 2-Cell Li-Ion Battery Charger |
| 文件： | 总24页 (文件大小：332K) |
| 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
The LT®3651-802/LT3651-804 are 2-cell, 4A Li-Ion/Poly-
mer battery chargers that operate over a 9V to 32V input
voltage range0 An efficient monolithic average current
modesynchronousswitchingregulatorprovidesconstant
current, constant voltage charging with programmable
maximum charge current0 A charging cycle starts with
battery insertion or when the battery voltage drops 205ꢀ
below the float voltage0 Charger termination is selectable
as either charge current or internal safety timer timeout0
Charge current termination occurs when the charge cur-
rent falls to one-tenth the programmed maximum current
(C/1±)0 Timer based termination is typically set to three
hours and is user programmable (charging continues
below C/1± until timeout)0 Once charging is terminated,
theLT3651-802/LT3651-804supplycurrentdropsto85µA
into a standby mode0
n
Wide Input Voltage Range: 9V 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
±±05ꢀ Float Voltage Accuracy
n
±ꢁ05ꢀ Charge Current Accuracy
n
±4ꢀ C/1± Detection Accuracy
n
NTC Resistor Temperature Monitor
n
Auto-Recharge at 9ꢁ05ꢀ 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 (±0ꢁ5mm) 5mm × 6mm 36-Lead
QFN Package
The LT3651-802/LT3651-804 offer several safety features0
A discharged battery is preconditioned with a small trickle
chargeandgeneratesasignalifunresponsive0Athermistor
monitors battery temperature, halting charging if out of
range0 Excessive die temperature reduces charge current0
Charge current is also reduced to maintain constant input
current to prevent excessive input loading0
APPLICATIONS
n
Industrial Handheld Instruments
n
12V to 24V Automotive and Heavy Equipment
n
Desktop Cradle Chargers
Notebook Computers
n
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation0 All other trademarks are the property of their respective owners0
The LT3651-802/LT3651-804 are available in a 5mm ×
6mm 36-lead QFN package0
TYPICAL APPLICATION
9V to 32V 2-Cell 4A Charger
Efficiency, Power Loss vs VIN
90
89
88
87
6.0
5.5
5.0
4.5
TO
SYSTEM
LOAD
V
IN
9V TO 32V
V
= 7.8V
= 4A
BAT
BAT
I
22µF
100k
10k
EFFICIENCY
10V
CLP
SHDN
CLN
V
IN
SW
Si7611DN
1µF
LT3651-8.2/LT3651-8.4
10µH
ACPR
BOOST
TDK SLP12575T-100M5R4
CMPSH1-4
FAULT
CHRG
SENSE
24mΩ
POWER LOSS
RT
86
85
4.0
3.5
301k
BAT
NTC
RNG/SS GND
+
2-CELL
100µF
TIMER
Li-Ion
I
LIM
BATTERY
365188284 TA01a
10
15
20
25
30
1635 G07
V
IN
(V)
36518284f
1
LT3651-8.2/LT3651-8.4
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
TOP VIEW
V
00000000000000000000000000000000000000000000000000000000000000000000000000 4±V
IN
CLN, CLP, SHDN
, CHRG,
FAULT ACPR 0000000000000000000000000000000 V + ±05V Up to 4±V
,
IN
36 35 34 33 32 31 30 29
CLP – CLN 0000000000000000000000000000000000000000000000000000000000000±±05V
SW 0000000000000000000000000000000000000000000000000000000000000000000000000004±V
NTC
ACPR
BAT
1
2
3
4
5
6
7
8
9
28
I
LIM
27 SHDN
CHRG
FAULT
26
25
SW – V 000000000000000000000000000000000000000000000000000000000000000000405V
37
IN
GND
SENSE
BOOST
GND
SW
BOOST 000000000000000000000000000000000000000000 SW + 1±V Up to 5±V
SENSE, BAT 000000000000000000000000000000000000000000000000000000000000 1±V
SENSE-BAT 000000000000000000000000000000000000000000000 –±05V to ±05V
24 TIMER
GND
23
22 SW
21 NC
20 NC
19 NC
TIMER, RNG/SS, I , NTC, RT 000000000000000000000000000000 205V
38
SW
LIM
NC
Operating Junction Temperature Range
NC
NC 10
(Notes 2, 3)000000000000000000000000000000000000000000000000–4± to 125°C
Storage Temperature Range 0000000000000000000000–65 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-802#PBF
LT3651IUHE-802#PBF
LT3651EUHE-804#PBF
LT3651IUHE-804#PBF
LT3651EUHE-802#TRPBF 365182
LT3651IUHE-802#TRPBF 365182
LT3651EUHE-804#TRPBF 365184
LT3651IUHE-804#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 ranges0 *The temperature grade is identified by a label on the shipping
container0Consult LTC Marketing for information on non-standard lead based finish parts0
For more information on lead free part marking, go to: http://www0linear0com/leadfree/
For more information on tape and reel specifications, go to: http://www0linear0com/tapeandreel/
36518284f
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
90±
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
101
80ꢁ
±02
802
4±
IN
90±
IN
Battery Float Voltage, V
LT3651-802
8016
8012
8024
8028
V
V
BAT(FLT)
l
l
LT3651-804
8036
8032
804
8044
8048
V
V
Battery Recharge Voltage Hysteresis
Threshold Voltage Relative to V
–2±±
mV
BAT(FLT)
BAT(PRE)
Battery Precondition Threshold Voltage, V
LT3651-802, V Rising
5065
508±
V
V
BAT(PRE)
BAT
LT3651-804, 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 = ±
806
8±
1ꢁ
mA
µA
µA
IN
SW
Standby Mode
Shutdown (SHDN = ±)
Top Switch On Voltage
V
V
– V , I = 4A
48±
–14±
4±
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 = ±, 205V < (V
– V ) < 805V
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 = 50±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 = ±05V
ILIM
1105
95
V/V
mV
mV
µA
ILIM CLP
CLN
l
l
– V , V = ꢁ05V, V
> 101V
88
1±3
1203
1
SENSE
SENSE
BAT BAT
RNG/SS
– V
405
806
±01
±01
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 = ±05V
RNG/SS
805
1±08
1036
±029
1±
1205
1045
±031
V/V
V
RNG/SS SENSE
BAT
Rising
Falling
1025
±02ꢁ
NTC
NTC
V
NTC Threshold Hysteresis
NTC Disable Impedance
NTC Bias Current
ꢀ of Threshold
Minimum External Impedance to GND
ꢀ
l
l
l
15±
4605
1015
4ꢁ±
5±
kΩ
µA
V
V
= ±0ꢁ5V
5305
1023
NTC
Shutdown Threshold
Rising
102±
95
V
SHDN
Shutdown Hysteresis
mV
nA
SHDN Input Bias Current
Status Low Voltage
–1±
l
V
, V
, V
, Load = 1±mA
±045
V
CHRG FAULT ACPR
36518284f
3
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
±01
±025
3
V
Hour
Minute
ꢀ
2205
–13
13
Switcher Operating Frequency, f
R = 5±kΩ
T
101
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 device0 Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime0
Note 3: This IC includes overtemperature protection that is intended to
protect the device during momentary overload conditions0 The maximum
rated junction temperature will be exceeded when this protection is active0
Continuous operation above the specified absolute maximum operating
junction temperature may impair device reliability or permanently damage
the device0
Note 2: The LT3651-802/LT3651-804 are tested under pulse loaded
conditions such that T = T 0 The LT3651-802E/LT3651-804E are
J
A
guaranteed to meet performance specifications from ±°C to 85°C junction
temperature0 Specifications over the –4±°C to 125°C operating junction
temperature range are assured by design, characterization and correlation
with statistical process controls0 The LT3651-802I/LT3651-804I are
guaranteed over the full –4±°C to 125°C operating junction temperature
range0 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 impedance0
JA
36518284f
4
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
36518284f
5
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 Switch Drive
vs Switch Current
Switch Drive (IBST/ISW
)
Boost Drive vs Boost Voltage
vs Temperature
60
50
40
30
20
10
70
60
35
30
25
20
I
= 4A
I
= 4A
SW
SW
V
– V = 4V
BST
IN
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
I
(A)
– V (V)
IN
TEMPERATURE (°C)
SW
BST
36518284 G13
36518284 G14
26518284 G12
Oscillator Frequency
vs Temperature
Timer Resistor (RT)
vs Period and Frequency
1.0
0.5
0
400
R
= 54.9k
T
350
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
36518284f
6
LT3651-8.2/LT3651-8.4
PIN FUNCTIONS
NTC (Pin 1): Battery Temperature Monitor Pin0 This
pin is used to monitor battery temperature0 Typically a
1±kΩ NTC(negativetemperaturecoefficient)thermistor
(B = 338±) is embedded with the battery and connected
from the NTC pin to ground0 The pin sources 5±µA into
the resistor and monitors the voltage across the therm-
istor, regulating charging based on the voltage0 If this
function is not desired, leave the NTC pin unconnected0
GND (Pins 6, 23, 31, 37): Ground0 These pins are the
ground pins for the part0 Pins 31, 34 and 3ꢁ must be
connected together0 Pins 6 and 23 are connected via
the leadframe to the exposed backside Pin 3ꢁ0 Solder
the exposed backside to the PCB for good thermal and
electrical connection0
SW (Pins 7, 11-18, 22, 38): Switch Output Pin0 These
pins are the output of the charger switches0 An inductor is
connected between these pins and the SENSE pin0 When
the switcher is active, the inductor is charged by the high
ACPR (Pin 2): Open-Collector AC Present Status Pin0
This pin sinks current to indicate that V is valid and the
IN
charger is on0 Typically a resistor pull-up is used on this
side switch from V and discharged by the bottom side
IN
pin0 This pin can be pulled up to voltages as high as V
switch to GND0 Solder the exposed backside, Pin 38, to
IN
when disabled, and can sink currents up to 1±mA when
the PCB for good thermal connection0
enabled0
NC (Pins 8-10,19-21): No Connect0 These pins can be left
floating (not connected)0
BAT (Pin 3): Battery Voltage Monitor Pin0 This pin moni-
tors battery voltage0 A Kelvin connection is made to the
battery from this pin and a decoupling capacitor (C
is placed from this pin to ground0
TIMER (Pin 24): End-Of-Cycle Timer Programming Pin0
A capacitor on this pin to ground determines the full
charge end-of-cycle time0 Full charge end-of-cycle time is
programmed with this capacitor0 A 3 hour charge cycle is
obtained with a ±068µF capacitor0 This timer also controls
thebadbatteryfaultthatisgeneratedifthebatterydoesnot
reachthepreconditionthresholdvoltagewithinone-eighth
of a full cycle (2205 minutes for a 3 hour charge cycle)0
)
BAT
The charge function operates to achieve the final float
voltage at this pin0 The auto-restart feature initiates a new
charging cycle when the voltage at the BAT pin falls 205ꢀ
below this float voltage0 Once the charge cycle is termi-
nated, the input bias current of the BAT pin is reduced to
<±01µA to minimize battery discharge while the charger
remains connected0
The timer based termination is disabled by connecting the
TIMER pin to ground0 With the timer function disabled,
chargingterminateswhenthechargecurrentdropsbelowa
C/1±rate, orapproximately1±ꢀofmaximumchargerate0
SENSE (Pin 4): Charge Current Sense Pin0 The charge
current is monitored with a sense resistor (R
) con-
SENSE
nected between this pin and the BAT pin0 The inductor
current flows through R to the battery0 The voltage
FAULT (Pin 25): Open-Collector Fault Status Output0 This
pinindicateschargecyclefaultconditionsduringabattery
charging cycle0 Typically a resistor pull-up is used on this
pin0 This status pin can be pulled up to voltages as high
SENSE
across this resistor sets the average charge current0 The
maximum average charge current (I
95mV across the sense resistor0
) corresponds to
MAX
as V when disabled, and can sink currents up to 1±mA
IN
BOOST (Pin 5): Bootstrapped Supply Rail for Switch
Drive0 This pin facilitates saturation of the high side switch
transistor0 Connect a 1µF or greater capacitor from the
BOOST pin to the SW pin0 The operating range of this pin
is ±V to 805V, referenced to the SW pin when the switch is
high0 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 pin0
when enabled0 A temperature fault causes this pin to be
pulled low0 If the internal timer is used for termination,
a bad battery fault also causes this pin to be pulled low0
If no fault conditions exist, the FAULT pin remains high
impedance0
CHRG (Pin 26): Open-Collector Charger Status Output0
36518284f
7
LT3651-8.2/LT3651-8.4
PIN FUNCTIONS
This pin indicates the battery charging status0 Typically
CLP/CLN (Pin 29/Pin 30): System Current Limit Positive
and Negative Input0 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
a resistor pull-up is used on this pin0 This status pin can
be pulled up to voltages as high as V when disabled,
IN
and can sink currents up to 1±mA when enabled0 CHRG
is pulled low during a battery charging cycle0 When the
charge cycle is terminated, the CHRG pin becomes high
impedance0 If the internal timer is used for termination,
thepinstayslowduringthechargingcycleuntilthecharge
current drops below a C/1± rate, or approximately 1±ꢀ
of the maximum charge current0 A temperature fault also
causes this pin to be pulled low0
CLP pin to the CLN pin and then connecting CLN to V 0
IN
The system load is then delivered from the CLN pin0 The
LT3651-802/LT3651-804 servo the maximum charge cur-
rent required to maintain programmed maximum system
current0 The system current limit is set as a function of
the voltage on the I
pin and the input current sense
LIM
resistor0 This function is disabled by shorting CLP, CLN
and V together0
IN
SHDN (Pin 27): Shutdown Pin0 This pin can be used for
precision UVLO functions0 When this pin rises above the
102±V threshold, the part is enabled0 The pin has 95mV of
voltage hysteresis0 When in shutdown mode, all charging
functionsaredisabled0WhentheSHDNpinispulledbelow
±04V, the IC enters a low current shutdown mode where
V (Pins 32, 33, 34): Charger Input Supply0 These pins
IN
provide power for the LT3651-802/LT3651-8040 Charge
current for the battery flows into these pins0 I is less
VIN
than 1±±µA after charge termination0 Connect the pins
together0
the V pin current is reduced to 1ꢁµA0 Typical SHDN pin
IN
RNG/SS (Pin 35): Charge Current Range and Soft-Start
Pin0 This pin allows for setting and dynamic adjustment
of the maximum charge current, and can be used to em-
ploy a soft-start function0 The voltage on this pin sets the
maximum charge current by setting the maximum voltage
input bias current is 1±nA0 Connect the pin to V if the
IN
shutdown function is not desired0
I
(Pin 28): Input Current Limit Programming0 This pin
LIM
allows for setting and dynamic adjustment of the system
input current limit, and can be used to employ a soft-start
function0 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 CLN0
across the charge current sense resistor, R
between SENSE and BAT0
, placed
SENSE
The effective range on the pin is ±V to 1V0 5±µA is sourced
from this pin usually to a resistor (R ) to ground0
RNG/SS
The effective range on the pin is ±V to 1V0 5±µA is sourced
from this pin usually to a resistor (R ) to ground0 V
V
represents approximately 1± times the maximum
RNG/SS
voltageacrossthechargecurrentsenseresistor0IfnoR
ILIM
IILIM
RNG/
represents approximately 11 times the maximum voltage
isusedthepartwilldefaulttomaximumchargecurrent0
SS
across the input current sense resistor0 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 current0
RNG/SS
Soft-start functionality for input current can be imple-
mented with a capacitor (C ) from I to ground0 The
to ground0 The soft-start capacitor and the programming
resistor can be implemented in parallel0 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 parallel0
recovery from faults if C
is used0
RNG/SS
RT (Pin 36): Switcher Oscillator Timer Set Pin0 A resis-
tor from this pin to ground sets the switcher oscillator
frequency0 Typically this is 5409k for f
= 1MHz0
OSC
36518284f
8
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
36518284f
9
LT3651-8.2/LT3651-8.4
OPERATION
Overview
205ꢀ from the full charge float voltage, the LT3651-802/
LT3651-804engageanautomaticchargecyclerestart0The
IC also automatically restarts a new charge cycle after a
bad battery fault once the failed battery is removed and
replaced with another battery0
The LT3651-802/LT3651-804 are complete Li-Ion battery
chargers, addressingwideinputvoltageandhighcurrents
(up to 4A)0 High charging efficiency is produced with a
constant frequency, average current mode synchronous
step-down switcher architecture0
After charging is completed the input bias currents on the
pins connecting to the battery are reduced to minimize
battery discharge0
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
termination0 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) switch0
The LT3651-802/LT3651-804 contain provisions for a bat-
tery temperature monitoring circuit0 Battery temperature
is monitored by using a NTC thermistor located with the
battery0 If the battery temperature moves outside a safe
chargingrangeof±°Cto4±°Cthechargingcyclesuspends
and signals a fault condition0
Maximum charge current is set with an external sense re-
sistor in series with the inductor and is adjustable through
the RNG/SS pin0 Total system input current is monitored
with an input sense resistor and is used to maintain con-
stant input current by regulating battery charge current0
The LT3651-802/LT3651-804 contain two digital open-
collectoroutputs, whichprovidechargerstatusandsignal
fault conditions0 These binary coded pins signal battery
charging,standbyorshutdownmodes,batterytemperature
faults and bad battery faults0
It is adjustable through the I pin0
LIM
Ifthebatteryvoltageislow,chargecurrentisautomatically
reduced to 15ꢀ of the programmed current to provide
safe battery preconditioning0 Once the battery voltage
climbs above the battery precondition threshold, the IC
automatically increases the maximum charge current to
the full programmed value0
A precision undervoltage lockout is possible by using a
resistor divider on the shutdown pin (SHDN)0 The input
supply current is 1ꢁµA when the IC is in shutdown0
General Operation (See Block Diagram)
TheLT3651-802/LT3651-804useanaveragecurrentmode
controllooparchitecturetocontrolaveragechargecurrent0
TheLT3651-802/LT3651-804sensechargeroutputvoltage
viatheBAT pin0Thedifferencebetweenthisvoltageandthe
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)0 Alternately, termination can
be time based through the use of an internal program-
mable charge cycle control timer0 When using the timer
termination, charging continues beyond the C/1± level to
“top-off” a battery0 Charging typically terminates three
hours after initiation0 When the timer-based scheme is
used, bad battery detection is also supported0 A system
fault is triggered if a battery stays in precondition mode
for more than one-eighth of the total charge cycle time0
error amplifier (V-EA)0 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 pins0 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)0 The difference be-
tween this imposed voltage and the current sense resistor
voltage is integrated by C-EA0 The resulting voltage (V )
C
Once charging is terminated and the LT3651-802/
LT3651-804 are not actively charging, the IC automatically
enters a low current standby mode in which supply bias
currentsarereducedto<85µA0Ifthebatteryvoltagedrops
provides a voltage that is compared against an internally
generated ramp and generates the switch duty cycle that
controls the charger’s switches0
36518284f
10
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-
tion0 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 time0 A bad battery fault halts
the charging cycle, the CHRG status pin goes high imped-
ance and the FAULT pin is pulled low0
TH
rent sensed across the inductor current sense resistor0
Maximum charge current is controlled by clamping the
maximum voltage of I to 1V0 This limits the maximum
current sense voltage (voltage across R
TH
) to 95mV
SENSE
setting the maximum charge current0 Manipulation of
maximum charge current is possible through the RNG/SS
and I pins (see the RNG/SS: Dynamic Charge Current
LIM
When the LT3651-802/LT3651-804 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 205ꢀ0 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 low0
When the voltage error amp output drops below ±03V,
the IC enters standby mode, where most of the internal
Adjust, RNG/SS: Soft-Start and I Control sections)0
LIM
If the voltage on the BAT pin (V ) is below V
, Aꢁ
BAT(PRE)
BAT
initiates the precondition mode0 During the precondition
interval, the charger continues to operate in constant cur-
rent mode, but the I clamp is reduced to ±015V reducing
TH
chargecurrentto15ꢀofthemaximumprogrammedvalue0
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) mode0 As this occurs, the
to <1±±µA0 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 initiated0
I
voltage falls from the limit clamp and charge current is
TH
reduced from the maximum value0 When the I voltage
TH
falls below ±01V, A8 signals C/1±0 If the charger is config-
ured for C/1± termination the charge cycle is terminated0
Once the charge cycle is terminated, the CHRG status
pin becomes high impedance and the charger enters low
current standby mode0
The system current limit allows charge current to be
reduced in order to maintain a constant input current0
Input current is measured via a resistor (R ) that is
CL
placed between the CLP and CLN pins0 Power is applied
The LT3651-802/LT3651-804 contain an internal charge
cycle timer that terminates a successful charge cycle af-
ter a programmed amount of time0 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 loads0 An offset produced on the
inputs of A12 sets the threshold0 When that threshold is
achieved, I is reduced, lowering the charge current thus
TH
maintaining the maximum input current0
appropriate timing capacitor value (C
)0 When timer
TIMER
termination is used, the charge cycle does not terminate
after C/1± is achieved0 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 currents0 At the programmed end of the cycle
time the charge cycle stops and the part enters standby
mode0 If the battery did not achieve at least 9ꢁ05ꢀ of the
full float voltage at the end-of-cycle, charging is deemed
unsuccessful and another full-timer cycle is initiated0
5±µA of current is sourced from I to a resistor (R
)
LIM
LIM
LIM
ILIM
that is placed from that pin to ground0 The voltage on I
determines the regulating voltage across R 0 1V on I
CL
LIM
corresponds to 95mV across R 0 The I
pin clamps
CL
internally to 1V maximum0
If the junction temperature of the die becomes excessive,
A1± activates decreasing I and reduces charge current0
TH
This reduces on-chip power dissipation to safe levels but
continues charging0
36518284f
11
LT3651-8.2/LT3651-8.4
APPLICATIONS INFORMATION
OSC Frequency
Thecapacitormusthaveanadequateripplecurrentrating0
RMS ripple current, I
is approximated by:
CVIN(RMS)
A precision resistor to ground sets the LT3651-802/
LT3651-804 switcher oscillator frequency, f , permit-
OSC
VBAT
V
IN
VBAT
ICVIN(RMS) ≈ ICHG(MAX)
•
•
–1
ting user adjustability of the frequency value0 Typically
this frequency is in the 2±±kHz to 1MHz range0 Power
consideration may necessitate lower frequency operation
especiallyifthechargerisoperatedwithveryhighvoltages0
Adjustability also allows the user to position switching
harmonics if their system requires0
V
IN
which has a maximum at V = 2 • V , where I
CVIN(RMS)
IN
BAT
=I
/20Intheexampleabovethatrequiresacapaci-
CHG(MAX)
tor RMS rating of 2A0
Boost Supply
The timing resistor, R , value is set by the following:
T
The BOOST bootstrapped supply rail drives the internal
switch and facilitates saturation of the high side switch
transistor0 The BOOST voltage is normally created by
connecting a 1µF capacitor from the BOOST pin to the
SW pin0 Operating range of the BOOST pin is 2V to 805V,
as referenced to the SW pin0
54.9
RT =
kΩ
(
)
fOSC MHz
(
)
Set R to 5409k for 1MHz operation0
T
V Input Supply
IN
The boost capacitor is normally charged via a diode con-
nected from the battery or an external source through the
low side switch0 Rate the diode average current greater
The LT3651-802/LT3651-804 are biased directly from the
charger input supply through the V pin0 This supply
IN
provides large switched currents, so a high quality, low
than ±01A and its reverse voltages greater than V
0
ESR decoupling capacitor is required to minimize volt-
IN(MAX)
age glitches on V 0 The V decoupling capacitor (C )
VIN
IN
IN
If an external supply that is greater than the input is avail-
able (V – V > 2V), it may be used in place of the
absorbs all input switching ripple current in the charger0
Size is determined by input ripple voltage with the fol-
lowing equation:
BOOST
IN
bootstrap capacitor and diode0
V ,V Start-Up Requirement
IN BOOST
ICHG(MAX) • VBAT
CIN(BULK)
µF
( )
The LT3651-802/LT3651-804 operate with a V range of
fOSC MHz • ∆V • V
IN
(
)
IN
IN
9V to 32V0 The charger begins a charging cycle when the
detected battery voltage is below the auto-restart float
voltage and the part is enabled0
where ∆V is the input ripple, I
is the maximum
IN
CHG(MAX)
charge current and f is the oscillator frequency0 A good
starting point for ∆V is ±01V0 Worst-case conditions
IN
are with V
IN(MIN) MAX
high and V at minimum0 So for a 15V
BAT
IN
V
, I
= 4A and a 1MHz oscillator frequency:
4•8.2
= = 22µF
CIN(BULK)
1•0.1•15
36518284f
12
LT3651-8.2/LT3651-8.4
APPLICATIONS INFORMATION
BAT Output Decoupling
When V is below 1±05V and the BOOST capacitor is
IN
uncharged, the high side switch would normally not have
sufficient head room to start switching0 During normal
operation the low side switch is deactivated when charge
current is very low to prevent reverse current in the induc-
tor0 However in order to facilitate start-up, the LT3651-
It is recommended that the LT3651-802/LT3651-804 char-
ger output have a decoupling capacitor0 If the battery can
be disconnected from the charger output this capacitor is
required0 The value of this capacitor (C ) is related to
BAT
the minimum operational V voltage such that:
IN
802/LT3651-804 enable the switch if V
voltage is
BOOST
low0 This allows initial charging of the BOOST capacitor
which then permits the high side switch to saturate and
efficiently operate0 The boost capacitor charges to full
potential after a few cycles0
350µF
CBAT ≈ 20µF +
V
IN(MIN)
The voltage rating on C must meet or exceed the bat-
BAT
tery float voltage0
The design should consider that as the switcher turns on
and input current increases, input voltage drops due to
source input impedance and input capacitance0 This po-
tentially allows the input voltage to drop below the internal
R : Charge Current Programming
SENSE
The LT3651-802/LT3651-804 charger is configurable to
charge at average currents as high as 4A (see Figure 1)0
If RNG/SS maximum voltage is not limited, the inductor
V UVLO turn-on and thus disrupt normal behavior and
IN
potentially stall start-up0 If an input current sense resis-
tor is used, its drop must be considered as well0 These
problems are worsened because input current is largest
at low input voltage0 Pay careful attention to drops in the
power path0 Adding a soft-start capacitor to the RNG/SS
pin and setting UVLO to 9V with the SHDN pin is required
sense resistor, R
, has 95mV across it at maximum
SENSE
charge current so:
0.095V
ICHG(MAX)
RSENSE
=
at low V 0
IN
where I
SENSE
is the maximum average charge current0
CHG(MAX)
is 24mΩ for a 4A charger0
R
SW
BOOST
LT3651-8.2
LT3651-8.4
SENSE
R
SENSE
BAT
+
365142 F01
Figure 1. Programming Maximum Charge Current Using RSENSE
36518284f
13
LT3651-8.2/LT3651-8.4
APPLICATIONS INFORMATION
Inductor Selection
specificationisnotinthedatasheetofaninductor,consult
the vendor to make sure the maximum volt-second prod-
uct is not being exceeded by your design0 The minimum
required volt-second product is approximately:
The primary criteria for inductor value selection in the
LT3651-802/LT3651-804 charger is the ripple current cre-
ated during switching0 Ripple current, ∆I
, is typically
MAX
set within a range of 25ꢀ to 35ꢀ of the maximum charge
current, I 0 This percentage typically gives a good com-
VBAT
fOSC(MHz)
VBAT
• 1–
V •µs
(
)
MAX
V
IN(MAX)
promise between losses due to ripple and inductor size0
An approximate formula for inductance is:
Acceptable power inductors are available from several
manufacturers such a Würth Elektronik, Vishay, Coilcraft
and TDK0
VBAT + VF
VBAT + VF
V + VF
IN
L =
• 1–
µH
(
)
∆IMAX • fOSC MHz
(
)
Worse-case ripple is at high V and high V 0 V is the
System Input Current Limit
IN
BAT
F
forwardvoltageofthesynchronousswitch(approximately
±014V at 4A)0 Figure 2 shows inductance for the case of a
4A charger0 The inductor must have a saturation current
equal to or exceeding the maximum peak current in the
TheLT3651-802/LT3651-804containaPowerPath control
feature to help manage supply load currents0 The charger
adjusts charger output current in response to a system
load so as to maintain a constant input supply load0 If
overall input supply current exceeds the programmed
maximum value the charge current is diminished in an
attempt to keep supply current constant0 One application
where this is helpful is if you have a current limited input
supply0 Setting the maximum input current limit below
the supply limit prevents supply collapse0
inductor0 Peak current is I
+ ∆I
/20
CHG(MAX)
CHG(MAX)
Magnetics vendors typically specify inductors with maxi-
mumRMSandsaturationcurrentratings0Selectaninductor
thathasasaturationcurrentratingatorabovepeakcurrent,
and an RMS rating above I
0 Inductors must also
CHG(MAX)
meet a maximum volt-second product requirement0 If this
4
A resistor, R , is placed between the input supply and the
CL
system and charger loads as shown in Figure 30
3
2
1
INPUT
SUPPLY
CLP
LT3651-8.2
LT3651-8.4
R
CL
CLN
SYSTEM LOAD
V
IN
I
f
= 4A
MAX
OSC
= 1MHz
I
25% TO 35% RIPPLE
LIM
0
R
LIM
9 10
15
20
25
30
V
(V)
365142 F03
IN(MAX)
36512 F02
Figure 2. Inductance (L) vs Maximum VIN
Figure 3. Input Current Limit Configuration
36518284f
14
LT3651-8.2/LT3651-8.4
APPLICATIONS INFORMATION
is designed, the input current exceeds the maximum
desired, though the charge current reduces to ±A0 When
the input limiter reduces charge current it does not impact
the internal system timer if used0 See Figure 40
TheLT3651-802/LT3651-804source5±µAfromtheI pin,
LIM
so a voltage is developed by simply connecting a resistor
to ground0 The voltage on the I
pin corresponds to
LIM
1105 times the maximum voltage across the input sense
resistor (R )0 Input current limit is defined by:
CL
Ifreducedvoltageoverheadorbetterefficiencyisrequired
then reduce the maximum voltage across R 0 So for
VILIM
11.5•RCL
50µA •RILIM
11.5•RCL
CL
IINPUT(MAX)
=
=
instance, a 1±k R
sets the maximum R voltage to
43mV0 This reduction comes at the expense of slightly
ILIM
CL
increased limit variation0
TheprogrammingrangeforI is±Vto1V0Voltageshigher
LIM
than 1V have no effect on the maximum input current0 The
Note the LT3651-802/LT3651-804 internally integrate the
inputlimitsignals0Thisshouldnormallyprovidesufficient
filtering and reduce the sensitivity to current spikes0 For
the best accuracy take care to provide good Kelvin con-
default maximum sense voltage is 95mV and is obtained
if R
is greater than 2±k or if the pin is left open0
ILIM
For example, say you want a maximum input current of
2A and the charger is designed for 4A maximum average
nections from R to CLP, CLN0
CL
charge current, which is 1A V referred (4A times duty
IN
Further flexibility is possible by dynamically altering the
cycle)0 Using the full I
range, the maximum voltage
across R is 95mV0 So R is set at 95mV/2A = 48mΩ0
LIM
I
pin0 Different resistor values could be switched in
LIM
CL
CL
to create unique input limit conditions0 The I
pin can
LIM
When the system load exceeds 1A (= 2A – 1A) charge
current is reduced such that the total input current stays
at 2A0 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
also be tied to a servo amplifier for other options0 See the
information in the following section concerning I
programming for examples0
RNG/SS
3
INPUT CURRENT
2
1
CHARGE
CURRENT
(V REFERRED)
IN
0
365142 F04
0
1
2
SYSTEM LOAD CURRENT (A)
Figure 4. Input Current Limit for 4A Maximum Charger
and 6A System Current Limit
36518284f
15
LT3651-8.2/LT3651-8.4
APPLICATIONS INFORMATION
RNG/SS: Dynamic Current Adjust
Active servos can also be used to impose voltages on the
RNG/SS pin, provided they can only sink current0 Active
circuits that source current cannot be used to drive the
RNG/SS pin0 An example is shown in Figure 60
The RNG/SS pin gives the user the capability to adjust
maximum charge current dynamically0 The part sources
5±µA from the pin, so connecting a resistor to ground
develops a voltage0 The voltage on the RNG/SS pin cor-
responds to ten times the maximum voltage across the
RNG/SS: Soft-Start
Soft-start functionality is also supported by the RNG/SS
pin0 The 5±µA sourced from the RNG/SS pin can linearly
charge current sense resistor, R
tions for charge current are:
0 The defining equa-
SENSE
charge a capacitor, C , connected from the RNG/
RNG/SS
VRNG/SS
10.8•RSENSE 10.8•RSENSE
50µA •RRNG/SS
SS pin to ground (see Figure ꢁ)0 The maximum charge
current follows this voltage0 Thus, the charge current
increases from zero to the fully programmed value as the
IMAX(RNG/SS)
=
=
I
is the maximum charge current0
MAX(RNG/SS)
capacitor charges from ±V to 1V0 The value of C
is
SS
RNG/SS
calculated based on the desired time to full current (t )
The programming range for RNG/SS is ±V to 1V0 Voltages
higher than 1V have no effect on the maximum charge
current0 The default maximum sense voltage is 95mV
following the relation:
C
= 5±µA • t
SS
RNG/SS
and is obtained if R
pin is left open0
is greater than 2±k or if the
RNG/SS
TheRNG/SSpinispulledtogroundinternallywhencharg-
ing is terminated so each new charging cycle begins with
a soft-start cycle0 RNG/SS is also pulled to ground during
badbatteryandNTCfaultconditions,soagracefulrecovery
from these faults is possible0
For example, say you want to reduce the maximum charge
currentto5±ꢀofthemaximumvalue0SetRNG/SSto±05V
(5±ꢀ of 1V), imposing a 46mV maximum sense voltage0
Per the above equation, ±05V on RNG/SS requires a 1±k
resistor0 If the charge current needs to be dynamically
adjustable then Figure 5 shows one method0
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
36518284f
16
LT3651-8.2/LT3651-8.4
APPLICATIONS INFORMATION
Status Pins
the charger terminates and the LT3651-802/LT3651-804
enter standby mode0 The CHRG status pin follows the
charge cycle and is high impedance when the charger is
not actively charging0
TheLT3651-802/LT3651-804reportchargerstatusthrough
two open-collector outputs, the CHRG and FAULT pins0
These pins can accept voltages as high as VIN, and can
When V
drops below 9ꢁ05ꢀ of the full-charged float
sink up to 1±mA when enabled
0
BAT
voltage, whether by battery loading or replacement of the
battery, the charger automatically re-engages and starts
charging0
The CHRG pin indicates that the charger is delivering cur-
rent at greater than a C/1± rate, or one-tenth of the pro-
grammedmaximumchargecurrent0TheFAULTpinsignals
bad battery and NTC faults0 These pins are binary coded,
and signal state following the table below0 On indicates
the pin pulled low, and Off indicates pin high impedance0
There is no provision for bad battery detection if C/1±
termination is used0
Timer Termination
Table 1. Status Pins State Table
STATUS PINS STATE
TheLT3651-802/LT3651-804supportatimer-basedtermi-
nationscheme,inwhichabatterychargecycleisterminated
after a specific amount of time elapses0 Timer termination
CHARGER STATUS
CHRG
Off
FAULT
Off
Not Charging—Standby or Shutdown Mode
is engaged when a capacitor (C
) is connected from
TIMER
Off
On
Bad Battery Fault
(Precondition Timeout/EOC Failure)
the TIMER pin to ground0 The timer cycle end-of-cycle
(t ) occurs based on C
following the relation:
On
On
Off
On
Normal Charging at C/1± or Greater
NTC Fault (Pause)
EOC
TIMER
tEOC Hrs
(
)
CTIMER
=
•0.68 µF
( )
3
C/10 Termination
so a typical 3 hour timer end-of-cycle would use a ±068µF
capacitor0
The LT3651-802/LT3651-804 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
The CHRG status pin continues to signal charging at a
C/1± rate, regardless of which termination scheme is
used0 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± threshold0 The charger
continues to “top off” the battery until timer end-of-cycle,
when the LT3651-802/LT3651-804 terminate the charge
cycle and enters standby mode0
with R
0 The C/1± threshold current corresponds to
SENSE
9mV across R
by shorting the TIMER pin to ground0
0 This termination mode is engaged
SENSE
WhenC/1±terminationisused,aLT3651-802/LT3651-804
chargersourcesbatterychargecurrentaslongastheaver-
age current level remains above the C/1± threshold0 As the
full-charge float voltage is achieved, the charge current
falls until the C/1± threshold is reached, at which time
Termination at the end of the timer cycle only occurs if the
36518284f
17
LT3651-8.2/LT3651-8.4
APPLICATIONS INFORMATION
triggered when the voltage on BAT remains below the
preconditionthresholdforgreaterthanone-eighthofafull
timer cycle (one-eighth end-of-cycle)0 A bad battery fault
is also triggered if a normally charging battery re-enters
precondition mode after one-eighth end-of-cycle0
charge cycle was successful0 A successful charge cycle
occurs when the battery is charged to within 205ꢀ of the
full-charge float voltage0 If a charge cycle is not success-
ful at end-of-cycle, the timer cycle resets and charging
continues for another full-timer cycle0
When a bad battery fault is triggered, the charge cycle
is suspended, so the CHRG status pin becomes high
impedance0 The FAULT pin is pulled low to signal a fault
detection0 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)0
When V
drops below 9ꢁ05ꢀ of the full-charge float
BAT
voltage, whether by battery loading or replacement of the
battery, the charger automatically re-engages and starts
charging0
Precondition and Bad Battery Fault
A LT3651-802/LT3651-804 charger has a precondition
mode, in which charge current is limited to 15ꢀ of the
programmed I
current corresponds to 14mV across R
Cycling the charger’s power or SHDN function initiates a
new charge cycle, but a LT3651-802/LT3651-804 charger
does not require a reset0 Once a bad battery fault is de-
tected, a new timer charge cycle initiates when the BAT pin
exceeds the precondition threshold voltage0 During a bad
battery fault, 1mA is sourced from the charger0 Removing
the failed battery allows the charger output voltage to rise
and initiate a charge cycle reset0 In that way removing a
bad battery resets the LT3651-802/LT3651-8040 A new
charge cycle is started by connecting another battery to
the charger output0
, as set by R
0 The precondition
SENSE
MAX
SENSE
0
Precondition mode is engaged while the voltage on the
BAT pin is below the precondition threshold (V )0
Once the BAT voltage rises above the precondition thresh-
old, normal full-current charging can commence0 The
LT3651-802/LT3651-804 incorporate 205ꢀ of threshold
for hysteresis to prevent mode glitching0
BAT(PRE)
When the internal timer is used for termination, bad bat-
tery detection is engaged0 This fault detection feature
is designed to identify failed cells0 A bad battery fault is
36518284f
18
LT3651-8.2/LT3651-8.4
APPLICATIONS INFORMATION
Battery Temperature Fault: NTC
Thermal Foldback
TheLT3651-802/LT3651-804canaccommodatebatterytem-
peraturemonitoringbyusinganNTC(negativetemperature
coefficient)thermistorclosetothebatterypack0Thetemper-
aturemonitoringfunctionisenabledbyconnectinga1±kΩ,
B = 338± NTC thermistor from the NTC pin to ground0 If
theNTCfunctionisnotdesired,leavethepinunconnected0
The LT3651-802/LT3651-804 contain a thermal foldback
protection feature that reduces maximum charger output
current if the internal IC junction temperature approaches
125°C0 In most cases, on-chip temperature servos such
thatanyovertemperatureconditionsarerelievedwithonly
slight reductions in maximum charge current0
The NTC pin sources 5±µA and monitors the voltage
droppedacrossthe1±kΩthermistor0Whenthevoltageon
this pin is above 1036V (±°C) or below ±029V (4±°C), the
battery temperature is out of range, and the LT3651-802/
LT3651-804 trigger an NTC fault0 The NTC fault condition
remains until the voltage on the NTC pin corresponds to
a temperature within the ±°C to 4±°C range0 Both hot and
cold thresholds incorporate hysteresis that corresponds
to 205°C0
In some cases, the thermal foldback protection feature
can reduce charge currents below the C/1± threshold0 In
applications that use C/1± termination (TIMER = ±V), the
LT3651-802/LT3651-804 suspend charging and enters
standby mode until the overtemperature condition is
relieved0
Layout Considerations
The LT3651-802/LT3651-804 switch node has rise and fall
times that are typically less than 1±nsto maximize conver-
sion efficiency0 These fast switch times require care in the
board layout to minimize noise problems0 The philosophy
istokeepthephysicalareaofhighcurrentloopssmall(the
inductor charge/discharge paths) to minimize magnetic
radiation0Keeptraceswideandshorttominimizeparasitic
inductance and resistance and shield fast switching volt-
age nodes (SW, BOOST) to reduce capacitive coupling0
During an NTC fault, charging is halted and both status
pins are pulled low0 If timer termination is enabled, the
timer count is suspended and held until the fault condition
is relieved0 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)0
If higher operational charging temperatures are desired,
the temperature range can be expanded by adding series
resistance to the 1±k NTC resistor0 Adding a ±091k (±TC)
resistor will increase the effective temperature threshold
to 45°C0
36518284f
19
LT3651-8.2/LT3651-8.4
APPLICATIONS INFORMATION
Power Considerations
The switched node (SW pin) trace should be kept as
short as possible to minimize high frequency noise0 The
The LT3651-802/LT3651-804 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 PCB0 This footprint should be made as
large as possible to reduce the thermal resistance of the
IC case to ambient air0
V
IN
capacitor (C ) should be placed close to the IC to
IN
minimize this switching noise0 Short, wide traces on these
nodes minimize stray inductance and resistance0 Keep the
BOOSTdecouplingcapacitorincloseproximitytotheICto
minimize ringing from trace inductance0 Route the SENSE
and BAT traces together and keep the traces as short as
possible0 Shielding these signals from switching noise
with ground is recommended0 Make Kelvin connections
to the battery and sense resistor0
Consideration should be given for power dissipation and
overall efficiency in a LT3651-802/LT3651-804 charger0 A
detailed analysis is beyond the scope of the data sheet,
however following are general guidelines0
Keep high current paths and transients isolated from
battery ground, to assure an accurate output voltage
reference0 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
corrupted0Figure8illustratesthehighcurrent, highspeed
current loops0 When the top switch is enabled (charge
The major components of power loss are: conduction and
transition losses ofthe LT3651-802/LT3651-804 switches;
losses in the inductor and sense resistors; and AC losses
in the decoupling capacitors0 Switch conduction loss is
fixed0Transitionlossesareadjustablebychangingswitcher
frequency0 Higher input voltages cause an increase in
transition losses, decreasing overall efficiency0 However
transition losses are inversely proportional to switcher
oscillator frequency so lowering operating frequency
reduces these losses0 But lower operating frequency
usually requires higher inductance to maintain inductor
ripple current (inversely proportional)0 Inductors with
larger values typically have more turns, increasing ESR
unlessyouincreasewirediametermakingthemphysically
loop), current flows from the input bypass capacitor (C )
IN
through the switch and inductor to the battery positive
terminal0Whenthetopswitchisdisabled(dischargeloop),
current to the battery positive terminal is provided from
ground through the synchronous switch0 In both cases,
these switched currents return to ground via the output
bypass capacitor (C )0
BAT
BOOST
V
IN
C
BOOST
C
IN
R
SENSE
LT3651-8.2
LT3651-8.4
SW
+
C
BATTERY
DISCHARGE
BAT
CHARGE
365142 F08
Figure 8
36518284f
20
LT3651-8.2/LT3651-8.4
APPLICATIONS INFORMATION
larger0 So there is an efficiency and board size trade-off0
Secondarily, inductor AC losses increase with frequency
and lower ripple reduces AC capacitor losses0
reduction in R
as well), with a trade-off of slightly
RNG/SS
less accurate current accuracy0 All high current board
tracesshouldhavethelowestresistancepossible0Addition
of input current limit sense resistance reduces efficiency0
The following simple rules of thumb assume a charge
current of 4A and battery voltage of ꢁ05V, with 1MHz os-
cillator, 24mΩ sense resistor and 303µH/2±mΩ inductor0
Charger efficiency drops approximately linearly with in-
creasing frequency all other things constant0 At 15V V
IN
there is a 1ꢀ improvement in efficiency for every 2±±kHz
A 1ꢀ increase in efficiency represents a ±035W reduction
in power loss at 85ꢀ overall efficiency0 One way to do
this is to decrease resistance in the high current path0 A
reduction of ±02W at 4A requires a 22mΩ reduction in
resistance0 This can be done by reducing inductor ESR0
It is also possible to lower the sense resistance (with a
reduction in frequency (1±±kHz to 1MHz); At 28V V , 1ꢀ
IN
for every 1±±kHz0
Of course all of these must be experimentally confirmed
in the actual charger0
TYPICAL APPLICATIONS
9V to 32V 4A Charger with High Voltage Current Foldback
Maximum Charge Current vs VIN
SBM540
5
R
IL
1k
120k
SMAZ24
V
IN
C
IN
22µF
4
3
2
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
36518284f
21
LT3651-8.2/LT3651-8.4
TYPICAL APPLICATIONS
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
SYSTEM
LOAD
V
IN
C
IN
22µF
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
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
36518284f
22
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
36518284f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable0
However, no responsibility is assumed for its use0 Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights0
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
LT3651-401/LT3651-402 Monolithic 4A Switch Mode Synchronous Standalone, 40ꢁ5 ≤ V ≤ 32V (4±V Abs Max), 1MHz, 4A, Programmable Charge
IN
1-Cell Li-Ion Battery Charger
Current Timer or V/1± Termination 5mm × 6mm QFN-36 Package
LT365±
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, 4095V ≤ V ≤ 32V (4±V Abs Max), 1MHz, 2A
IN
Programmable Charge Current, Timer or C/1± Termination, 3mm × 3mm DFN-12
Package and MSOP-12 Packages0 LT3652HV Version Up to V = 34V
IN
LTC4±±±
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 6±V ±±025ꢀ 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
LTC4±±2
LTC4±±6
LTC4±±ꢁ
LTC4±±8
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, 1±-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 96ꢀ Efficiency, 2±-Lead SSOP Package
LTC4±±9/LTC4±±9-1
LTC4±±9-2
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 93ꢀ Efficiency, 2±-Lead (4mm × 4mm) QFN Package, LTC4±±9-1 for 401V
Float Voltage, LTC4±±9-2 for 402V Float Voltage
LTC4±12/LTC4±12-1/
4A, High Efficiency, Multi-Chemistry
PowerPath Control, Constant-Current/Constant-Voltage Switching Regulator
LTC4±12-2/LTC4±12-3 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-2± Package; LTC4±12-1 Version for 401V
Li Cells, LTC4±12-2 Version for 402V Li Cells, LTC4±12-3 Version Has Extra GND Pin
36518284f
LT 1212 • PRINTED IN USA
24 LinearTechnology Corporation
163± McCarthy Blvd0, Milpitas, CA 95±35-ꢁ41ꢁ
●
●
LINEAR TECHNOLOGY CORPORATION 2012
(4±8) 432-19±± FAX: (4±8) 434-±5±ꢁ www0linear0com
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