LTC4068X-4.2_15 [Linear]
Standalone Linear Li-Ion Battery Charger with Programmable Termination;型号: | LTC4068X-4.2_15 |
厂家: | Linear |
描述: | Standalone Linear Li-Ion Battery Charger with Programmable Termination 电池 |
文件: | 总12页 (文件大小:149K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
LTC4068-4.2/LTC4068X-4.2
Standalone Linear
Li-Ion Battery Charger with
Programmable Termination
U
FEATURES
DESCRIPTIO
■
Programmable Charge Current Up to 950mA
The LTC®4068 is a complete constant-current/constant-
voltage linear charger for single cell lithium-ion batteries.
Its DFN package and low external component count make
the LTC4068 ideally suited for portable applications. Fur-
thermore, the LTC4068 is designed to work within USB
power specifications.
■
Complete Linear Charger in DFN Package
■
No MOSFET, Sense Resistor or Blocking Diode
Required
■
Thermal Regulation Maximizes Charge Rate
Without Risk of Overheating*
■
Charges Directly from a USB Port
No external sense resistor or external blocking diode are
requiredduetotheinternalMOSFETarchitecture.Thermal
feedback regulates the charge current to limit the die
temperature during high power operation or high ambient
temperature conditions. The charge voltage is fixed at
4.2V and the charge current is programmed with a resis-
tor. The LTC4068 terminates the charge cycle when the
charge current drops below the programmed termination
threshold after the final float voltage is reached.
■
Programmable Charge Current Termination
■
Preset 4.2V Charge Voltage with ±1% Accuracy
■
Charge Current Monitor Output for Gas Gauging*
■
Automatic Recharge
■
Charge Status Output
■
“AC Present” Output
■
2.9V Trickle Charge Threshold (LTC4068)
■
Available Without Trickle Charge (LTC4068X)
■
Soft-Start Limits Inrush Current
■
When the input supply (wall adapter or USB supply) is
removed,theLTC4068entersalowcurrentstatedropping
the battery drain current to less than 2µA. Other features
include charge current monitor, undervoltage lockout,
automatic recharge and status pins to indicate charge
termination and the presence of adequate input voltage.
Low Profile (3mm × 3mm × 0.75mm) DFN Package
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APPLICATIO S
■
Cellular Telephones, PDAs, MP3 Players
Bluetooth Applications
■
, LTC and LT are registered trademarks of Linear Technology Corporation.
Protected by U.S. Patents, including 6522118.
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TYPICAL APPLICATIO
Complete Charge Cycle (750mAh Battery)
700
600
500
400
300
200
100
0
4.75
4.50
4.25
4.00
3.75
3.50
3.25
3.00
CONSTANT
CURRENT
Single Cell Li-Ion Battery Charger with C/5 Termination
CONSTANT
VOLTAGE
600mA
V
IN
V
CC
BAT
4.5V TO 6.5V
LTC4068-4.2
1-CELL
Li-Ion
BATTERY
+
CHRG
ACPR
EN
ITERM
PROG
V
= 5V
825Ω
CC
θ
= 40°C/W
GND
JA
1µF
1.65k
R
R
= 1.65k
PROG
TERM
= 825Ω
406842 TA01
T
A
= 25°C
0.25 0.5 0.75 1.0 1.25
1.75 2.0 2.25
0
1.5
406842 TA02
TIME (HOURS)
406842fa
1
LTC4068-4.2/LTC4068X-4.2
W W
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ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
(Note 1)
TOP VIEW
Input Supply Voltage (VCC) ....................... –0.3V to 10V
PROG, ITERM ................................ –0.3V to VCC + 0.3V
BAT............................................................. –0.3V to 7V
CHRG, ACPR, EN ...................................... –0.3V to 10V
BAT Short-Circuit Duration .......................... Continuous
BAT Pin Current ........................................................ 1A
PROG Pin Current................................................... 1mA
Maximum Junction Temperature .......................... 125°C
Operating Temperature Range (Note 2) .. –40°C to 85°C
Storage Temperature Range ................. –65°C to 125°C
ORDER PART
NUMBER
ITERM
BAT
1
2
3
4
8
7
6
5
EN
ACPR
LTC4068EDD-4.2
LTC4068XEDD-4.2
9
CHRG
GND
V
CC
PROG
DD PART MARKING
DD PACKAGE
8-LEAD (3mm × 3mm) PLASTIC DFN
TJMAX = 125°C, θJA = 40°C/W (NOTE 3)
EXPOSED PAD IS GROUND (PIN 9)
MUST BE SOLDERED TO PCB
LBHZ
LBQB
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
Input Supply Voltage
Input Supply Current
●
4.25
6.5
V
CC
I
Charge Mode (Note 4), R
Standby Mode (Charge Terminated)
Shutdown Mode (EN = 5V, V < V
= 10k
●
●
●
0.4
200
25
1
500
50
mA
µA
µA
CC
PROG
CC
BAT
or V < V
)
CC
UV
V
Regulated Output (Float) Voltage
BAT Pin Current
0°C ≤ T ≤ 85°C, 4.3V < V < 6.5V
4.158
4.2
4.242
V
FLOAT
A
CC
I
R
R
= 10k, Current Mode
= 2k, Current Mode
●
●
●
92
465
100
500
–2.5
±1
105
535
–6
mA
mA
µA
BAT
PROG
PROG
Standby Mode, V
= 4.2V
BAT
Shutdown Mode (EN = 5V, V < V
or
±2
µA
CC
BAT
V
< V )
CC
UV
Sleep Mode, V = 0V
±1
45
±2
60
3
µA
mA
V
CC
I
Trickle Charge Current
V
< V , R = 2k (Note 5)
TRIKL PROG
●
30
TRIKL
BAT
V
V
V
V
V
V
Trickle Charge Threshold Voltage
Trickle Charge Hysteresis Voltage
R
R
= 10k, V Rising (Note 5)
BAT
2.8
2.9
80
TRIKL
TRHYS
UV
PROG
PROG
= 10k (Note 5)
mV
V
V
V
Undervoltage Lockout Voltage
Undervoltage Lockout Hysteresis
From V Low to High
●
●
●
●
●
3.7
150
0.4
3.8
200
0.7
0.7
2
3.92
300
CC
CC
CC
mV
V
UVHYS
EN(IL)
EN(IH)
EN Pin Input Low Voltage
EN Pin Input High Voltage
EN Pin Pull-Down Resistor
1
5
V
R
1.2
MΩ
EN
V
V
– V
Lockout Threshold
V
V
from Low to High
from High to Low
70
5
100
30
140
50
mV
mV
ASD
CC
BAT
CC
CC
I
Charge Termination Current Threshold
R
TERM
R
TERM
= 1k
= 5k
●
●
90
17.5
100
20
110
22.5
mA
mA
TERM
V
V
V
PROG Pin Voltage
R
= 10k, Current Mode
= 5mA
0.93
1
1.07
0.6
V
V
PROG
CHRG
ACPR
PROG
CHRG
CHRG Pin Output Low Voltage
ACPR Pin Output Low Voltage
Recharge Battery Threshold Voltage
I
I
0.35
0.35
100
= 5mA
0.6
V
ACPR
∆V
V
– V
, 0°C ≤ T ≤ 85°C
60
140
mV
RECHRG
FLOAT
RECHRG
A
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LTC4068-4.2/LTC4068X-4.2
ELECTRICAL CHARACTERISTICS The ● denotes specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
T
Junction Temperature in Constant
Temperature Mode
120
°C
LIM
R
ON
Power FET “ON” Resistance
600
mΩ
(Between V and BAT)
CC
t
t
t
Soft-Start Time
I
= 0 to I
=1000V/R
PROG
100
2
µs
ms
µs
SS
BAT
BAT
Recharge Comparator Filter Time
Termination Comparator Filter Time
V
High to Low
0.75
400
4.5
RECHARGE
TERM
BAT
BAT
I
Drops Below Charge Termination Threshold
1000
2500
Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 3: Failure to solder the exposed backside of the package to the PC
board will result in a thermal resistance much higher than 40°C/W.
Note 2: The LTC4068E-4.2/LTC4068XE-4.2 are guaranteed to meet
performance specifications from 0°C to 70°C. Specifications over the
–40°C to 85°C operating temperature range are assured by design,
characterization and correlation with statistical process controls.
Note 4: Supply current includes PROG pin current and ITERM pin current
(approximately 100µA each) but does not include any current delivered to
the battery through the BAT pin (approximately 100mA).
Note 5: This parameter is not applicable to the LTC4068X.
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TYPICAL PERFOR A CE CHARACTERISTICS
PROG Pin Voltage vs Supply
Voltage (Constant Current Mode)
PROG Pin Voltage
vs Temperature
Charge Current
vs PROG Pin Voltage
1.015
1.010
1.005
1.000
0.995
0.990
0.985
600
500
400
300
200
100
0
1.0100
1.0075
1.0050
1.0025
V
V
T
= 5V
V
V
= 5V
V
= 5V
CC
CC
CC
= 4V
= 4V
T
= 25°C
BAT
BAT
PROG
A
R
R
= 25°C
= 2k
= 2k
R
= 10k
A
R
PROG
TERM
= 10k
PROG
1.0000
0.9975
0.9950
0.9925
0.9900
4
5
5.5
(V)
6
6.5
7
–50
–25
0
50
75
100
0
0.4
0.6
(V)
PROG
0.8
1
1.2
4.5
25
0.2
V
V
TEMPERATURE (°C)
CC
405842 G01
405842 G02
405842 G03
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LTC4068-4.2/LTC4068X-4.2
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TYPICAL PERFOR A CE CHARACTERISTICS
Regulated Output (Float) Voltage
vs Charge Current
Regulated Output (Float) Voltage
vs Temperature
Regulated Output (Float) Voltage
vs Supply Voltage
4.26
4.215
4.210
4.205
4.200
4.195
4.190
4.185
4.215
4.210
4.205
4.200
4.195
4.190
4.185
V
A
R
= 5V
V
= 5V
PROG
T = 25°C
A
CC
CC
R
T
= 25°C
= 10k
R
= 10k
PROG
4.24
4.22
= 1.25k
PROG
4.20
4.18
4.16
4.14
4.12
4.10
100 200
400 500 600 700
(mA)
–50
0
25
50
75
100
4
5
5.5
(V)
6
6.5
7
0
300
–25
4.5
TEMPERATURE (°C)
V
I
CC
BAT
405842 G04
405842 G05
405842 G06
CHRG Pin I-V Curve
(Pull-Down State)
ACPR Pin I-V Curve
(Pull-Down State)
Trickle Charge Current
vs Temperature
30
25
20
15
30
25
20
15
60
50
40
30
20
10
0
V
V
= 5V
BAT
LTC4068 ONLY
CC
T
= –40°C
T
A
= –40°C
A
= 2.5V
T
T
= 25°C
= 90°C
T
T
= 25°C
= 90°C
A
A
A
R
= 2k
PROG
A
10
5
10
5
R
= 10k
50
PROG
25
V
V
= 5V
CC
BAT
V
V
= 5V
CC
BAT
= 4V
= 4V
0
0
4
6
7
4
6
7
–50
0
75
100
0
1
2
3
5
0
1
2
3
5
–25
TEMPERATURE (°C)
V
(V)
V
ACPR
(V)
CHRG
405842 G07
405842 G08
405842 G09
Trickle Charge Current
vs Supply Voltage
Trickle Charge Threshold Voltage
vs Temperature
Charge Current vs Battery Voltage
60
50
40
30
20
10
0
600
500
400
300
3.000
2.975
2.950
2.925
V
T
= 2.5V
LTC4068 ONLY
LTC4068 ONLY
V
= 5V
PROG
LTC4068 ONLY
BAT
A
CC
= 25°C
R
= 10k
R
= 2k
PROG
2.900
2.875
200
100
0
2.850
2.825
2.800
R
= 10k
6
PROG
V
= 5V
CC
JA
θ
= 40°C/W
R
= 2k
PROG
3.3 3.6 3.9
(V)
4
5
5.5
(V)
6.5
7
–50
–25
0
50
75
100
2.4 2.7
3
4.2 4.5
4.5
25
V
TEMPERATURE (°C)
V
BAT
CC
405842 G10
405842 G11
405842 G12
406842fa
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LTC4068-4.2/LTC4068X-4.2
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TYPICAL PERFOR A CE CHARACTERISTICS
Charge Current
vs Ambient Temperature
Charge Current vs Supply Voltage
600
500
400
300
200
100
0
600
ONSET OF THERMAL REGULATION
R
= 2k
PROG
500
400
300
R
PROG
= 2k
V
T
JA
= 4V
V
V
θ
= 5V
= 4V
BAT
A
CC
= 25°C
BAT
θ
= 40°C/W
= 40°C/W
JA
200
100
0
R
= 10k
50
R
= 10k
PROG
PROG
4
5
5.5
6
6.5
7
–50 –25
0
25
75
100 125
4.5
V
(V)
TEMPERATURE (°C)
CC
405842 G13
405842 G14
Power FET “ON” Resistance
vs Temperature
Recharge Threshold Voltage
vs Temperature
700
650
600
550
500
450
400
350
4.16
4.14
4.12
4.10
4.08
4.06
4.04
V
I
= 4.2V
V
= 5V
PROG
CC
BAT
R
CC
= 100mA
R
= 10k
= 2k
PROG
–50
0
25
50
75 100 125
–25
–50
0
25
50
75
100
–25
TEMPERATURE (°C)
TEMPERATURE (°C)
405842 G17
405842 G15
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PI FU CTIO S
ITERM (Pin 1): Charge Termination Program. The charge voltage. Thisdividerisdisconnectedinshutdownmodeto
termination current threshold current is programmed by minimize current drain from the battery.
connecting a 1% resistor, RTERM, to ground. The current
CHRG (Pin 3): Charge Status Open-Drain Output. When
threshold ITERM, is set by the following formula:
the battery is charging, the CHRG pin is pulled low by an
internal N-channel MOSFET. When the charge cycle is
completed, CHRG becomes high impedance.
100V
RTERM
100V
ITERM
ITERM
=
, RTERM =
GND (Pins 4, 9): Ground/Exposed Pad. The exposed
backside package pad (Pin 9) is electrical ground and
must be soldered to the PC board for maximum heat
transfer.
BAT (Pin 2): Charge Current Output. Provides charge
currenttothebatteryfromtheinternalP-channelMOSFET,
and regulates the final float voltage to 4.2V. An internal
precision resistor divider from this pin sets the float
406842fa
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LTC4068-4.2/LTC4068X-4.2
U
U
U
PI FU CTIO S
PROG (Pin 5): Charge Current Program and Charge Cur-
rent Monitor. Charge current is programmed by connect-
ing a 1% resistor, RPROG, to ground. When charging in
constant-currentmode,thispinservosto1V.Inallmodes,
the voltage on this pin can be used to measure the charge
current using the following formula:
When VCC is within 100mV of the BAT pin voltage, the
LTC4068 enters shutdown mode dropping the battery
drain current to less than 2µA.
ACPR (Pin 7): Power Supply Status Open-Drain Output.
WhenVCC isgreaterthantheundervoltagelockoutthresh-
old and at least 100mV above VBAT, the ACPR pin is pulled
to ground; otherwise, the pin is high impedance.
IBAT = (VPROG/RPROG) • 1000
Thispinisclampedtoapproximately2.4V. Drivingthispin
to voltages beyond the clamp voltage can draw large
currents and should be avoided.
EN(Pin8):EnableInput. AlogichighontheENpinwillput
the LTC4068 into shutdown mode where the battery drain
current is reduced to less than 2µA and the supply current
is reduced to less than 50µA. A logic low or floating the EN
pin (allowing an internal 2MΩ pull-down resistor to pull
this pin low) enables charging.
VCC (Pin 6): Positive Input Supply Voltage. Provides
power to the charger. VCC can range from 4.25V to 6.5V.
This pin should be bypassed with at least a 1µF capacitor.
W
BLOCK DIAGRA
6
V
CC
120°C
T
A
1×
1×
T
DIE
1000×
–
+
BAT
2
5µA
MA
R1
R2
ACPR
CHRG
+
7
3
VA
–
CA
+
REF
1.211V
–
R3
1V
*
CHARGE ACPR
LOGIC
R4
0.1V
R5
+
–
TERM
C1
EN
SHDN
EN
8
*TRICKLE
CHARGE
DISABLED
ON THE
LTC4068X
C2*
+
–
2.9V
TO BAT
ITERM
PROG
GND
4, 9
1
5
R
R
PROG
TERM
406842 BD
406842fa
6
LTC4068-4.2/LTC4068X-4.2
U
OPERATIO
The LTC4068 is a single cell lithium-ion battery charger
using a constant-current/constant-voltage algorithm. It
can deliver up to 950mA of charge current (using a good
thermal PCB layout) with a final float voltage accuracy of
±1%. The LTC4068 includes an internal P-channel power
MOSFET and thermal regulation circuitry. No blocking
diode or external current sense resistor is required; thus,
the basic charger circuit requires only two external com-
ponents. Furthermore, the LTC4068 is capable of operat-
ing from a USB power source.
Programming Charge Termination
The charge cycle terminates when the charge current
falls below the programmed termination threshold. This
threshold is set by connecting an external resistor, RTERM
from the ITERM pin to ground. The charge termination
current threshold (ITERM) is set by the following equation:
,
100V ICHG
R
100V
ITERM
ITERM
=
=
•
PROG ,RTERM
RTERM 10 RTERM
=
The termination condition is detected by using an internal
filtered comparator to monitor the ITERM pin. When the
ITERM pin voltage drops below 100mV* for longer than
tTERM (typically 1ms), charging is terminated. The charge
current is latched off and the LTC4068 enters standby
mode where the input supply current drops to 200µA.
(Note: Termination is disabled in trickle charging and
thermal limiting modes.)
Normal Charge Cycle
AchargecyclebeginswhenthevoltageattheVCC pinrises
abovetheUVLOthresholdlevelanda1%programresistor
is connected from the PROG pin to ground. If the BAT pin
is less than 2.9V, the charger enters trickle charge mode.
In this mode, the LTC4068 supplies approximately 1/10th
the programmed charge current to bring the battery volt-
age up to a safe level for full current charging. (Note: The
LTC4068X does not include this trickle charge feature.)
ITERMcanbesettobe1/10thofICHG byshortingtheITERM
pin to the PROG pin, thus eliminating the need for external
resistor RTERM. When configured in this way, ITERM is
alwayssettoICHG/10,andtheprogrammedchargecurrent
is set by the equation:
When the BAT pin voltage rises above 2.9V, the charger
enters constant-current mode where the programmed
chargecurrentissuppliedtothebattery.WhentheBATpin
approaches the final float voltage (4.2V), the LTC4068
enters constant-voltage mode and the charge current
begins to decrease. When the charge current drops to the
programmed termination threshold (set by the external
resistor RTERM), the charge cycle ends.
500V
RPROG
500V**
ICHG
ICHG
=
,RPROG =
When charging, transient loads on the BAT pin can cause
the ITERM pin to fall below 100mV for short periods of
time before the DC charge current has dropped to 10% of
the programmed value. The 1ms filter time (tTERM) on the
termination comparator ensures that transient loads of
this nature do not result in premature charge cycle termi-
nation. Once the average charge current drops below the
programmed termination threshold, the LTC4068 termi-
nates the charge cycle and ceases to provide any current
out of the BAT pin. In this state, any load on the BAT pin
must be supplied by the battery.
Programming Charge Current
The charge current is programmed using a single resistor
from the PROG pin to ground. The charge current out of
the BAT pin is 1000 times the current out of the PROG pin.
The program resistor and the charge current are calcu-
lated using the following equations:
1000V
ICHG
1000V
RPROG
RPROG
=
, ICHG =
ChargecurrentoutoftheBATpincanbedeterminedatany
time by monitoring the PROG pin voltage and using the
following equation:
The LTC4068 constantly monitors the BAT pin voltage in
standbymode.Ifthisvoltagedropsbelowthe4.1Vrecharge
*
Any external sources that hold the ITERM pin above 100mV will prevent the LTC4068 from
terminating a charge cycle.
VPROG
RPROG
IBAT
=
•1000
**
These equations apply only when the ITERM pin is shorted to the PROG pin.
406842fa
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LTC4068-4.2/LTC4068X-4.2
U
OPERATIO
Thermal Limiting
threshold (VRECHRG), another charge cycle begins and
charge current is once again supplied to the battery. To
manuallyrestartachargecyclewheninstandbymode, the
inputvoltagemustberemovedandreappliedorthecharger
mustbeshutdownandrestartedusingtheENpin.Figure 1
shows the state diagram of a typical charge cycle.
Aninternalthermalfeedbackloopreducestheprogrammed
chargecurrentifthedietemperatureattemptstoriseabove
apresetvalueofapproximately120°C.Thisfeatureprotects
the LTC4068 from excessive temperature and allows the
user to push the limits of the power handling capability of
agivencircuitboardwithoutriskofdamagingtheLTC4068.
Thechargecurrentcanbesetaccordingtotypical(notworst
case) ambient temperature with the assurance that the
chargerwillautomaticallyreducethecurrentinworst-case
conditions. DFN power considerations are discussed fur-
ther in the Applications Information section.
POWER ON
BAT < 2.9V
TRICKLE CHARGE
MODE
EN DRIVEN LOW
OR
UVLO CONDITION
STOPS
LTC4068
ONLY
1/10TH FULL CURRENT
CHRG: STRONG
PULL-DOWN
BAT > 2.9V
Undervoltage Lockout (UVLO)
BAT > 2.9V
SHUTDOWN MODE
CHARGE MODE
Aninternalundervoltagelockoutcircuitmonitorstheinput
voltageandkeepsthechargerinshutdownmodeuntilVCC
risesabovetheundervoltagelockoutthreshold. TheUVLO
circuit has a built-in hysteresis of 200mV. Furthermore, to
protect against reverse current in the power MOSFET, the
UVLO circuit keeps the charger in shutdown mode if VCC
falls to within 30mV of the BAT voltage. If the UVLO com-
parator is tripped, the charger will not come out of shut-
down mode until VCC rises 100mV above the BAT voltage.
I
CC
DROPS TO <25µA
FULL CURRENT
CHRG: Hi-Z
CHRG: STRONG
PULL-DOWN
ITERM < 100mV
STANDBY MODE
NO CHARGE CURRENT
CHRG: Hi-Z
EN DRIVEN HIGH
OR
UVLO CONDITION
2.9V < BAT < 4.1V
406842 F01
Figure 1. State Diagram of a Typical Charge Cycle
Manual Shutdown
At any point in the charge cycle, the LTC4068 can be put
into shutdown mode by driving the EN pin high. This
reduces the battery drain current to less than 2µA and the
supply current to less than 50µA. When in shutdown
mode, the CHRG pin is in the high impedance state. A new
charge cycle can be initiated by driving the EN pin low. An
internal resistor pull-down on this pin forces the LTC4068
to be enabled if the pin is allowed to float.
Charge Status Indicator (CHRG)
The charge status output has two states: pull-down and
high impedance. The pull-down state indicates that the
LTC4068 is in a charge cycle. Once the charge cycle has
terminated or the LTC4068 is disabled, the pin state
becomes high impedance.
Power Supply Status Indicator (ACPR)
Automatic Recharge
The power supply status output has two states: pull-down
and high impedance. The pull-down state indicates that
Oncethechargecycleisterminated,theLTC4068continu-
ously monitors the voltage on the BAT pin using a com-
parator with a 2ms filter time (tRECHARGE). A charge cycle
restarts when the battery voltage falls below 4.10V (which
corresponds to approximately 80% to 90% battery capac-
ity). This ensures that the battery is kept at, or near, a fully
V
CC isabovetheUVLOthreshold(3.8V)andisalso100mV
above the battery voltage. If these conditions are not met,
theACPRpinishighimpedanceindicatingthattheLTC4068
is unable to charge the battery.
406842fa
8
LTC4068-4.2/LTC4068X-4.2
U
W U U
APPLICATIO S I FOR ATIO
charged condition and eliminates the need for periodic filter can be used on the PROG pin to measure the average
charge cycle initiations. The CHRG output enters a pull- battery current, as shown in Figure 2. A 10k resistor has
down state during recharge cycles.
been added between the PROG pin and the filter capacitor
to ensure stability.
If the battery is removed from the charger, a sawtooth
waveformofapproximately100mVappearsatthecharger
output. This is caused by the repeated cycling between
termination and recharge events. This cycling results in
pulsing at the CHRG output; an LED connected to this pin
will exhibit a blinking pattern, indicating to the user that a
battery is not present. The frequency of the sawtooth is
dependent on the amount of output capacitance.
LTC4068-4.2
CHARGE
10k
CURRENT
PROG
MONITOR
CIRCUITRY
R
PROG
C
FILTER
GND
406842 F02
Figure 2. Isolating Capacitive Load on PROG Pin and Filtering
Stability Considerations
The constant-voltage mode feedback loop is stable with-
out an output capacitor, provided a battery is connected to
the charger output. With no battery present, an output
capacitor on the BAT pin is recommended to reduce ripple
voltage. When using high value, low ESR ceramic capaci-
tors, it is recommended to add a 1Ω resistor in series with
the capacitor. No series resistor is needed if tantalum
capacitors are used.
Power Dissipation
It is not necessary to design for worst-case power dissi-
pation scenarios because the LTC4068 automatically
reducesthechargecurrentduringhighpowerconditions.
The conditions that cause the LTC4068 to reduce charge
current through thermal feedback can be approximated
by considering the power dissipated in the IC. Nearly all
of this power dissipation is generated by the internal
MOSFET—this is calculated to be approximately:
In constant-current mode, the PROG pin is in the feedback
loop, not the battery. The constant-current mode stability
is affected by the impedance at the PROG pin. With no
additional capacitance on the PROG pin, the charger is
stable with program resistor values as high as 20k; how-
ever, additional capacitance on this node reduces the
maximum allowed program resistor. The pole frequency
at the PROG pin should be kept above 100kHz. Therefore,
if the PROG pin is loaded with a capacitance, CPROG, the
following equation can be used to calculate the maximum
PD = (VCC – VBAT) • IBAT
where PD is the power dissipated, VCC is the input supply
voltage, VBAT is the battery voltage and IBAT is the charge
current. The approximate ambient temperature at which
the thermal feedback begins to protect the IC is:
TA = 120°C – PDθJA
TA = 120°C – (VCC – VBAT) • IBAT • θJA
Example: An LTC4068 operating from a 5V supply is
programmed to supply 800mA full-scale current to a
dischargedLi-Ionbatterywithavoltageof3.3V.Assuming
θJA is 50°C/W (see Thermal Considerations), the ambient
temperatureatwhichtheLTC4068willbegintoreducethe
charge current is approximately:
resistance value for RPROG
:
1
RPROG
≤
2π •105 •CPROG
Average, ratherthaninstantaneouschargecurrentmaybe
of interest to the user. For example, if a switching power
supply operating in low current mode is connected in
parallel with the battery, the average current being pulled
out of the BAT pin is typically of more interest than the
instantaneous current pulses. In such a case, a simple RC
TA = 120°C – (5V – 3.3V) • (800mA) • 50°C/W
TA = 120°C – 1.36W • 50°C/W = 120°C – 68°C
TA = 52°C
406842fa
9
LTC4068-4.2/LTC4068X-4.2
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APPLICATIO S I FOR ATIO
The LTC4068 can be used above 52°C ambient but the
charge current will be reduced from the programmed
800mA. The approximate current at a given ambient
temperature can be approximated by:
ceramiccapacitors. Becauseoftheself-resonantandhigh
Q characteristics of some types of ceramic capacitors,
high voltage transients can be generated under some
start-up conditions such as connecting the charger input
to a live power source. Adding a 1.5Ω resistor in series
with an X5R ceramic capacitor will minimize start-up
voltage transients. For more information, see Application
Note 88.
120°C – TA
IBAT
=
VCC – VBAT • θJA
(
)
Using the previous example with an ambient temperature
of 60°C, the charge current will be reduced to
approximately:
Charge Current Soft-Start
The LTC4068 includes a soft-start circuit to minimize the
inrushcurrentatthestartofachargecycle.Whenacharge
cycle is initiated, the charge current ramps from zero to
full-scale current over a period of approximately 100µs.
Thishastheeffectofminimizingthetransientcurrentload
on the power supply during start-up.
120°C – 60°C
60°C
85°C/A
IBAT
=
=
5V – 3.3V • 50°C/W
(
)
IBAT = 706mA
Moreover,whenthermalfeedbackreducesthechargecur-
rentthevoltageatthePROGpinisalsoreducedproportion-
ally as discussed in the Operation section. It is important
to remember that LTC4068 applications do not need to be
designedforworst-casethermalconditionssincetheICwill
automatically reduce power dissipation when the junction
temperature reaches approximately 120°C.
USB and Wall Adapter Power
The LTC4068 allows charging from both a wall adapter
and a USB port. Figure 3 shows how to combine wall
adapter and USB power inputs. A P-channel MOSFET,
MP1, isusedtopreventbackconductingintotheUSBport
when a wall adapter is present and a Schottky diode, D1,
is used to prevent USB power loss through the 1k pull-
down resistor.
Thermal Considerations
I
n order to deliver maximum charge current under all
Typically a wall adapter can supply more current than
the 500mA-limited USB port. Therefore, an N-channel
MOSFET, MN1, and an extra 3.3k program resistor are
used to increase the charge current to 800mA when the
walladapterispresent.Thechargeterminationthreshold
remains fixed at 80mA.
conditions, it is critical that the exposed metal pad on the
backside of the LTC4068 package is soldered to the PC
board ground. Correctly soldered to a 2500mm2 double-
sided 1oz copper board, the LTC4068 has a thermal
resistance of approximately 40°C/W. Failure to make
thermal contact between the exposed pad on the back-
side of the package and the copper board will result in
thermal resistances far greater than 40°C/W. As an
example, a correctly soldered LTC4068 can deliver over
800mA to a battery from a 5V supply at room tempera-
ture. Without a good backside thermal connection, this
number will drop considerably.
5V WALL
ADAPTER
I
CHG
800mA I
LTC4068-4.2
BAT
CHG
2
1
5
SYSTEM
LOAD
D1
6
USB POWER
V
CC
ITERM
500mA I
CHG
4, 9
MP1
GND PROG
1.25k
+
Li-Ion
BATTERY
3.3k
1k
2k
MN1
406842 F03
VCC Bypass Capacitor
Many types of capacitors can be used for input bypassing;
however,cautionmustbeexercisedwhenusingmultilayer
Figure 3. Combining Wall Adapter and USB Power
406842fa
10
LTC4068-4.2/LTC4068X-4.2
W U U
U
APPLICATIO S I FOR ATIO
DRAIN-BULK
DIODE OF FET
Reverse Polarity Input Voltage Protection
LTC4068
CC
In some applications, protection from reverse polarity
voltage on VCC is desired. If the supply voltage is high
enough, a series blocking diode can be used. In other
cases,wherethevoltagedropmustbekeptlow,aP-channel
MOSFET can be used (as shown in Figure 4).
V
V
IN
405842 F04
Figure 4. Low Loss Input Reverse Polarity Protection
U
PACKAGE DESCRIPTIO
DD Package
8-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1698)
0.675 ±0.05
3.5 ±0.05
2.15 ±0.05 (2 SIDES)
1.65 ±0.05
PACKAGE
OUTLINE
0.28 ± 0.05
0.50
BSC
2.38 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
R = 0.115
0.38 ± 0.10
TYP
5
8
3.00 ±0.10
(4 SIDES)
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(DD8) DFN 0203
4
1
0.28 ± 0.05
0.75 ±0.05
0.200 REF
0.50 BSC
2.38 ±0.10
(2 SIDES)
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-1)
2. ALL DIMENSIONS ARE IN MILLIMETERS
3. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
4. EXPOSED PAD SHALL BE SOLDER PLATED
406842fa
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 represen-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
11
LTC4068-4.2/LTC4068X-4.2
U
TYPICAL APPLICATIO S
Full Featured Single Cell Li-Ion Charger
Li-Ion Battery Charger with Reverse Polarity Input Protection
V
IN
5V
5V
WALL
ADAPTER
6
1k
1k
6
500mA
V
CC
2
500mA
V
CC
BAT
2
1
7
3
ACPR
BAT
LTC4068-4.2
ITERM
1
5
CHRG ITERM
LTC4068-4.2
1µF
1-CELL
Li-Ion
+
8
1µF
1k
EN
PROG
GND
4, 9
1µF
8
5
BATTERY
EN
PROG
GND
4, 9
1-CELL
Li-Ion
BATTERY
1k
+
2k
406842 TA04
405642 TA03
USB/Wall Adapter Power Li-Ion Charger
I
BAT
5V WALL
ADAPTER
2
BAT
1-CELL
Li-Ion
BATTERY
+
LTC4068-4.2
1
5
6
USB
POWER
V
ITERM
PROG
GND
4, 9
CC
1µF
1.25k
5k
1k
100mA/
500mA
µC
406842 TA05
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
Simple Charger uses External FET, Features Preset Voltages, C/10
LTC1732
Lithium-Ion Linear Battery Charger Controller
Charger Detection and Programmable Timer, Input Power Good Indication
Standalone Charger with Programmable Timer, Up to 1.5A Charge Current
Simple ThinSOT Charger, No Blocking Diode, No Sense Resistor Needed
LTC1733
LTC1734
LTC1734L
LTC1998
LTC4007
Monolithic Lithium-Ion Linear Battery Charger
Lithium-Ion Linear Battery Charger in ThinSOTTM
Lithium-Ion Linear Battery Charger in ThinSOT
Lithium-Ion Low Battery Detector
Low Current Version of LTC1734; 50mA ≤ I
≤ 180mA
CHRG
1% Accurate 2.5µA Quiescent Current, SOT-23
4A Multicell Li-Ion Battery Charger
Standalone Charger, 6V ≤ V ≤ 28V, Up to 96% Efficiency,
IN
±0.8% Charging Voltage Accuracy
LTC4050
LTC4052
LTC4053
LTC4054
Lithium-Ion Linear Battery Charger Controller
Monolithic Lithium-Ion Battery Pulse Charger
USB Compatible Monolithic Li-Ion Battery Charger
C/10 Charger Detection and Programmable Timer, Thermistor Interface
No Blocking Diode or External Power FET Required, ≤1.5A Charge Current
Standalone Charger with Programmable Timer, Up to 1.25A Charge Current
Standalone Linear Li-Ion Battery Charger
in ThinSOT
Thermal Regulation Prevents Overheating, C/10 Termination,
C/10 Indicator, Up to 800mA Charge Current
LTC4057
Li-Ion Linear Battery Charger
Up to 800mA Charge Current, Thermal Regulation, ThinSOT Package
LTC4058
LTC4058X
Standalone Li-Ion Linear Charger in DFN
Up to 950mA Charge Current, Kelvin Sense for High Accuracy,
C/10 Charge Termination
LTC4410
USB Power Manager
For Simultaneous Operation of USB Peripheral and Battery Charging from USB
Port, Keeps Current Drawn from USB Port Constant, Keeps Battery Fresh, Use
with the LTC4053, LTC1733, or LTC4054
LTC4411
LTC4412
Low Loss PowerPathTM Controller in ThinSOT
Automatic Switching Between DC Sources, Load Sharing,
Replaces ORing Diodes
ThinSOT and PowerPath are trademarks of Linear Technology Corporation.
406842fa
LT/TP 0904 1K REV A • PRINTED IN USA
12 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
●
●
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
©LINEAR TECHNOLOGY CORPORATION 2004
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