1
LTC4068-4.2
406842f
Standalone Linear
Li-Ion Battery Charger with
Programmable Termination
s
Programmable Charge Current Up to 950mA
s
Complete Linear Charger in DFN Package
s
No MOSFET, Sense Resistor or Blocking Diode
Required
s
Thermal Regulation Maximizes Charge Rate
Without Risk of Overheating*
s
Charges Directly from a USB Port
s
Programmable Charge Current Termination
s
Preset 4.2V Charge Voltage with
1% Accuracy
s
Charge Current Monitor Output for Gas Gauging*
s
Automatic Recharge
s
Charge Status Output
s
"AC Present" Output
s
Soft-Start Limits Inrush Current
s
Low Profile (3mm
3mm
0.75mm) DFN Package
s
Cellular Telephones, PDAs, MP3 Players
s
Bluetooth Applications
, LTC and LT are registered trademarks of Linear Technology Corporation.
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.
No external sense resistor or external blocking diode are
required due to the internal MOSFET architecture. 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.
When the input supply (wall adapter or USB supply) is
removed, the LTC4068 enters a low current state dropping
the battery drain current to less than 2
A. Other features
include charge current monitor, undervoltage lockout,
automatic recharge and status pins to indicate charge
termination and the presence of adequate input voltage.
BAT
V
CC
CHRG
1.65k
406842 TA01
1
F
V
IN
4.5V TO 6.5V
1-CELL
Li-Ion
BATTERY
LTC4068-4.2
600mA
ACPR
EN
PROG
GND
+
ITERM
825
TIME (HOURS)
0
CHARGE CURRENT (mA)
1.5
406842 TA02
0.5
1.0
2.25
700
600
500
400
300
200
100
0
4.75
4.50
4.25
4.00
3.75
3.50
3.25
3.00
0.25
0.75
1.25
2.0
1.75
CONSTANT
VOLTAGE
CONSTANT
CURRENT
BATTERY VOLTAGE (V)
V
CC
= 5V
JA
= 40
C/W
R
PROG
= 1.65k
R
TERM
= 825
T
A
= 25
C
Complete Charge Cycle (750mAh Battery)
*US Patent 6,522,118
Single Cell Li-Ion Battery Charger with C/5 Termination
DESCRIPTIO
U
FEATURES
APPLICATIO S
U
TYPICAL APPLICATIO
U
2
LTC4068-4.2
406842f
(Note 1)
Input Supply Voltage (V
CC
) ....................... 0.3V to 10V
PROG, ITERM ................................ 0.3V to V
CC
+ 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
T
JMAX
= 125
C,
JA
= 40
C/W (NOTE 3)
EXPOSED PAD IS GROUND (PIN 9)
MUST BE SOLDERED TO PCB
ORDER PART
NUMBER
DD PART MARKING
LBHZ
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
CC
Input Supply Voltage
q
4.25
6.5
V
I
CC
Input Supply Current
Charge Mode (Note 4), R
PROG
= 10k
q
0.4
1
mA
Standby Mode (Charge Terminated)
q
200
500
A
Shutdown Mode (EN = 5V, V
CC
< V
BAT
q
25
50
A
or V
CC
< V
UV
)
V
FLOAT
Regulated Output (Float) Voltage
0
C
T
A
85
C, 4.3V < V
CC
< 6.5V
4.158
4.2
4.242
V
I
BAT
BAT Pin Current
R
PROG
= 10k, Current Mode
q
92
100
105
mA
R
PROG
= 2k, Current Mode
q
465
500
535
mA
Standby Mode, V
BAT
= 4.2V
q
2.5
6
A
Shutdown Mode (EN = 5V, V
CC
< V
BAT
or
1
2
A
V
CC
< V
UV
)
Sleep Mode, V
CC
= 0V
1
2
A
I
TRIKL
Trickle Charge Current
V
BAT
< V
TRIKL
, R
PROG
= 2k
q
30
45
60
mA
V
TRIKL
Trickle Charge Threshold Voltage
R
PROG
= 10k, V
BAT
Rising
2.8
2.9
3
V
V
TRHYS
Trickle Charge Hysteresis Voltage
R
PROG
= 10k
80
mV
V
UV
V
CC
Undervoltage Lockout Voltage
From V
CC
Low to High
q
3.7
3.8
3.92
V
V
UVHYS
V
CC
Undervoltage Lockout Hysteresis
q
150
200
300
mV
V
EN(IL)
EN Pin Input Low Voltage
q
0.4
0.7
V
V
EN(IH)
EN Pin Input High Voltage
q
0.7
1
V
R
EN
EN Pin Pull-Down Resistor
q
1.2
2
5
M
V
ASD
V
CC
V
BAT
Lockout Threshold
V
CC
from Low to High
70
100
140
mV
V
CC
from High to Low
5
30
50
mV
I
TERM
Charge Termination Current Threshold
R
TERM
= 1k
q
90
100
110
mA
R
TERM
= 5k
q
17.5
20
22.5
mA
V
PROG
PROG Pin Voltage
R
PROG
= 10k, Current Mode
0.93
1
1.07
V
V
CHRG
CHRG Pin Output Low Voltage
I
CHRG
= 5mA
0.35
0.6
V
V
ACPR
ACPR Pin Output Low Voltage
I
ACPR
= 5mA
0.35
0.6
V
V
RECHRG
Recharge Battery Threshold Voltage
V
FLOAT
V
RECHRG
, 0
C
T
A
85
C
60
100
140
mV
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25
C. V
CC
= 5V, unless otherwise noted.
ABSOLUTE AXI U RATI GS
W
W
W
U
PACKAGE/ORDER I FOR ATIO
U
U
W
ELECTRICAL CHARACTERISTICS
Consult LTC Marketing for parts specified with wider operating temperature ranges.
LTC4068EDD-4.2
TOP VIEW
9
DD PACKAGE
8-LEAD (3mm
3mm) PLASTIC DFN
5
6
7
8
4
3
2
1
ITERM
BAT
CHRG
GND
EN
ACPR
V
CC
PROG
3
LTC4068-4.2
406842f
Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2: The LTC4068E-4.2 is guaranteed to meet performance specifica-
tions 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.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
T
LIM
Junction Temperature in Constant
120
C
Temperature Mode
R
ON
Power FET "ON" Resistance
600
m
(Between V
CC
and BAT)
t
SS
Soft-Start Time
I
BAT
= 0 to I
BAT
=1000V/R
PROG
100
s
t
RECHARGE
Recharge Comparator Filter Time
V
BAT
High to Low
0.75
2
4.5
ms
t
TERM
Termination Comparator Filter Time
I
BAT
Drops Below Charge Termination Threshold
400
1000
2500
s
The
q
denotes specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25
C. V
CC
= 5V, unless otherwise noted.
ELECTRICAL CHARACTERISTICS
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 4: Supply current includes PROG pin current and ITERM pin current
(approximately 100
A each) but does not include any current delivered to
the battery through the BAT pin (approximately 100mA).
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
PROG Pin Voltage vs Supply
Voltage (Constant Current Mode)
V
CC
(V)
4
0.985
V
PROG
(V)
0.990
0.995
1.000
1.005
1.015
4.5
5
5.5
6
405842 G01
6.5
7
1.010
V
CC
= 5V
V
BAT
= 4V
T
A
= 25
C
R
PROG
= 10k
TEMPERATURE (
C)
50
V
PROG
(V)
0.9975
1.0000
1.0025
25
75
405842 G02
0.9950
0.9925
0.9900
25
0
50
1.0050
1.0075
1.0100
100
V
CC
= 5V
V
BAT
= 4V
R
PROG
= 10k
V
PROG
(V)
0
0
I
BAT
(mA)
100
200
300
400
600
0.2
0.4
0.6
0.8
405842 G03
1
1.2
500
V
CC
= 5V
T
A
= 25
C
R
PROG
= 2k
R
TERM
= 2k
PROG Pin Voltage
vs Temperature
Charge Current
vs PROG Pin Voltage
4
LTC4068-4.2
406842f
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Regulated Output (Float) Voltage
vs Charge Current
I
BAT
(mA)
0
V
FLOAT
(V)
4.24
300
405842 G04
4.18
4.14
100
200
400
4.12
4.10
4.26
4.22
4.20
4.16
500
600
700
V
CC
= 5V
T
A
= 25
C
R
PROG
= 1.25k
Regulated Output (Float) Voltage
vs Temperature
TEMPERATURE (
C)
50
4.185
V
FLOAT
(V)
4.190
4.195
4.200
4.205
4.215
25
0
25
50
405842 G05
75
100
4.210
V
CC
= 5V
R
PROG
= 10k
Regulated Output (Float) Voltage
vs Supply Voltage
V
CC
(V)
4
4.185
V
FLOAT
(V)
4.190
4.195
4.200
4.205
4.215
4.5
5
5.5
6
405842 G06
6.5
7
4.210
T
A
= 25
C
R
PROG
= 10k
CHRG Pin I-V Curve
(Pull-Down State)
Trickle Charge Current
vs Temperature
ACPR Pin I-V Curve
(Pull-Down State)
V
CHRG
(V)
0
I
CHRG
(mA)
20
25
30
3
5
405842 G07
15
10
1
2
4
6
7
5
0
T
A
= 40
C
T
A
= 25
C
T
A
= 90
C
V
CC
= 5V
V
BAT
= 4V
V
ACPR
(V)
0
I
ACPR
(mA)
20
25
30
3
5
405842 G08
15
10
1
2
4
6
7
5
0
T
A
= 40
C
T
A
= 25
C
T
A
= 90
C
V
CC
= 5V
V
BAT
= 4V
TEMPERATURE (
C)
50
0
I
TRKL
(mA)
10
20
30
40
60
25
0
25
50
405842 G09
75
100
50
V
CC
= 5V
V
BAT
= 2.5V
R
PROG
= 2k
R
PROG
= 10k
Trickle Charge Current
vs Supply Voltage
Charge Current vs Battery Voltage
V
CC
(V)
4
0
I
TRKL
(mA)
10
20
30
40
60
4.5
5
5.5
6
405842 G10
6.5
7
50
V
BAT
= 2.5V
T
A
= 25
C
R
PROG
= 2k
R
PROG
= 10k
Trickle Charge Threshold Voltage
vs Temperature
TEMPERATURE (
C)
50
V
TRKL
(V)
2.875
2.900
2.925
25
75
405842 G11
2.850
2.825
2.800
25
0
50
2.950
2.975
3.000
100
V
CC
= 5V
R
PROG
= 10k
V
BAT
(V)
2.4
I
BAT
(mA)
400
500
600
3.3
3.9
405842 G08
300
200
2.7
3
3.6
4.2
4.5
100
0
V
CC
= 5V
JA
= 40
C/W
R
PROG
= 2k
5
LTC4068-4.2
406842f
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Charge Current vs Supply Voltage
Charge Current
vs Ambient Temperature
Recharge Threshold Voltage
vs Temperature
Power FET "ON" Resistance
vs Temperature
V
CC
(V)
4
0
I
BAT
(mA)
100
200
300
400
600
4.5
5
5.5
6
405842 G13
6.5
7
500
V
BAT
= 4V
T
A
= 25
C
JA
= 40
C/W
R
PROG
= 2k
R
PROG
= 10k
TEMPERATURE (
C)
50
I
BAT
(mA)
400
500
600
25
75
405842 G14
300
200
25
0
50
100
125
100
0
V
CC
= 5V
V
BAT
= 4V
JA
= 40
C/W
R
PROG
= 2k
ONSET OF THERMAL REGULATION
R
PROG
= 10k
TEMPERATURE (
C)
50
4.04
V
RECHRG
(V)
4.06
4.08
4.10
4.12
4.16
25
0
25
50
405842 G15
75
100
4.14
V
CC
= 5V
R
PROG
= 10k
TEMPERATURE (
C)
50
R
DS(ON)
(m
)
700
650
600
550
500
450
400
350
25
0
25
50
405842 G17
75
125
100
V
CC
= 4.2V
I
BAT
= 100mA
R
PROG
= 2k
U
U
U
PI FU CTIO S
ITERM (Pin 1): Charge Termination Program. The charge
termination current threshold current is programmed by
connecting a 1% resistor, R
TERM
, to ground. The current
threshold I
TERM
, is set by the following formula:
I
V
R
R
V
I
TERM
TERM
TERM
TERM
=
=
100
100
,
BAT (Pin 2): Charge Current Output. Provides charge
current to the battery from the internal P-channel MOSFET,
and regulates the final float voltage to 4.2V. An internal
precision resistor divider from this pin sets the float
voltage which is disconnected in shutdown mode.
CHRG (Pin 3): Charge Status Open-Drain Output. When
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.
GND (Pins 4, 9): Ground/Exposed Pad. The exposed
backside of the package (Pin 9) is also ground and must
be soldered to the PC board for maximum heat transfer.
PROG (Pin 5): Charge Current Program and Charge Cur-
rent Monitor. Charge current is programmed by connect-
ing a 1% resistor, R
PROG
, to ground. When charging in
constant-current mode, this pin servos to 1V. In all modes,
6
LTC4068-4.2
406842f
ACPR (Pin 7): Power Supply Status Open-Drain Output.
When V
CC
is greater than the undervoltage lockout thresh-
old and at least 100mV above V
BAT
, the ACPR pin is pulled
to ground; otherwise, the pin is high impedance.
EN (Pin 8): Enable Input . A logic high on the EN pin will put
the LTC4068 into shutdown mode where the battery drain
current is reduced to less than 2
A and the supply current
is reduced to less than 50
A. A logic low or floating the EN
pin (allowing an internal 2M
pull-down resistor to pull
this pin low) enables charging.
U
U
U
PI FU CTIO S
the voltage on this pin can be used to measure the charge
current using the following formula:
I
BAT
= (V
PROG
/R
PROG
) 1000
This pin is clamped to approximately 2.4V. Driving this pin
to voltages beyond the clamp voltage can draw large
currents and should be avoided.
V
CC
(Pin 6): Positive Input Supply Voltage. Provides
power to the charger. V
CC
can range from 4.25V to 6.5V.
This pin should be bypassed with at least a 1
F capacitor.
When V
CC
is within 100mV of the BAT pin voltage, the
LTC4068 enters shutdown mode dropping the battery
drain current to less than 2
A.
BLOCK DIAGRA
W
+
+
+
2
6
+
120
C
T
DIE
T
A
MA
CA
C1
1
1000
VA
R1
BAT
R2
R3
1V
0.1V
R4
R5
PROG
5
A
R
PROG
REF
1.211V
V
CC
CHRG
3
EN
8
GND
4, 9
406842 BD
+
C2
2.8V
TO BAT
TERM
ACPR
CHARGE
SHDN
EN
LOGIC
ACPR
7
5
1
ITERM
R
TERM
1
7
LTC4068-4.2
406842f
OPERATIO
U
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.
Normal Charge Cycle
A charge cycle begins when the voltage at the V
CC
pin rises
above the UVLO threshold level and a 1% program resistor
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.
When the BAT pin voltage rises above 2.9V, the charger
enters constant-current mode where the programmed
charge current is supplied to the battery. When the BAT pin
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 R
TERM
) the charge cycle ends.
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:
R
V
I
I
V
R
PROG
CHG
CHG
PROG
=
=
1000
1000
,
Charge current out of the BAT pin can be determined at any
time by monitoring the PROG pin voltage and using the
following equation:
I
V
R
BAT
PROG
PROG
=
1000
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, R
TERM
,
from the ITERM pin to ground. The charge termination
current threshold (I
TERM)
is set by the following equation:
I
V
R
I
R
R
R
V
I
TERM
TERM
CHG
PROG
TERM
TERM
TERM
=
=
=
100
10
100
,
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
t
TERM
(typically 1ms), charging is terminated. The charge
current is latched off and the LTC4068 enters standby
mode where the input supply current drops to 200
A.
(Note: termination is disabled in trickle charging and
thermal limiting modes.)
I
TERM
can be set to be 1/10th of I
CHG
by shorting the ITERM
pin to the PROG pin, thus eliminating the need for external
resistor R
TERM
. When configured in this way, I
TERM
is
always set to I
CHG
/10, and the programmed charge current
is set by the equation:
I
V
R
R
V
I
CHG
PROG
PROG
CHG
=
=
500
500
,
**
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 (t
TERM
) 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.
The LTC4068 constantly monitors the BAT pin voltage in
standby mode. If this voltage drops below the 4.1V recharge
Any external sources that hold the ITERM pin above 100mV will prevent the LTC4068 from
terminating a charge cycle.
These equations apply only when the ITERM pin is shorted to the PROG pin.
*
**
8
LTC4068-4.2
406842f
OPERATIO
U
threshold (V
RECHRG
), another charge cycle begins and
charge current is once again supplied to the battery. To
manually restart a charge cycle when in standby mode, the
input voltage must be removed and reapplied or the charger
must be shut down and restarted using the EN pin. Figure 1
shows the state diagram of a typical charge cycle.
Thermal Limiting
An internal thermal feedback loop reduces the programmed
charge current if the die temperature attempts to rise above
a preset value of approximately 120
C. This feature protects
the LTC4068 from excessive temperature and allows the
user to push the limits of the power handling capability of
a given circuit board without risk of damaging the LTC4068.
The charge current can be set according to typical (not worst
case) ambient temperature with the assurance that the
charger will automatically reduce the current in worst-case
conditions. DFN power considerations are discussed fur-
ther in the Applications Information section.
Undervoltage Lockout (UVLO)
An internal undervoltage lockout circuit monitors the input
voltage and keeps the charger in shutdown mode until V
CC
rises above the undervoltage lockout threshold. The UVLO
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 V
CC
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 V
CC
rises 100mV above the BAT voltage.
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 2
A and the
supply current to less than 50
A. 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.
Automatic Recharge
Once the charge cycle is terminated, the LTC4068 continu-
ously monitors the voltage on the BAT pin using a com-
parator with a 2ms filter time (t
RECHARGE
). 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
Figure 1. State Diagram of a Typical Charge Cycle
TRICKLE CHARGE
MODE
1/10TH FULL CURRENT
BAT > 2.9V
BAT < 2.9V
BAT > 2.9V
CHRG: STRONG
PULL-DOWN
CHARGE MODE
FULL CURRENT
CHRG: STRONG
PULL-DOWN
SHUTDOWN MODE
CHRG: Hi-Z
EN DRIVEN LOW
OR
UVLO CONDITION
STOPS
EN DRIVEN HIGH
OR
UVLO CONDITION
I
CC
DROPS TO <25
A
POWER ON
ITERM < 100mV
STANDBY MODE
NO CHARGE CURRENT
CHRG: Hi-Z
2.9V < BAT < 4.1V
406842 F01
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)
The power supply status output has two states: pull-down
and high impedance. The pull-down state indicates that
V
CC
is above the UVLO threshold (3.8V) and is also 100mV
above the battery voltage. If these conditions are not met,
the ACPR pin is high impedance indicating that the LTC4068
is unable to charge the battery.
9
LTC4068-4.2
406842f
APPLICATIO S I FOR ATIO
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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 1
resistor in series with
the capacitor. No series resistor is needed if tantalum
capacitors are used.
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, C
PROG
, the
following equation can be used to calculate the maximum
resistance value for R
PROG
:
R
C
PROG
PROG
1
2
10
5
Average, rather than instantaneous charge current may be
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
LTC4068-4.2
GND
PROG
R
PROG
10k
C
FILTER
406842 F02
CHARGE
CURRENT
MONITOR
CIRCUITRY
Figure 2. Isolating Capacitive Load on PROG Pin and Filtering
Power Dissipation
It is not necessary to design for worst-case power dissi-
pation scenarios because the LTC4068 automatically re-
duces the charge current during high power conditions.
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:
P
D
= (V
CC
V
BAT
) I
BAT
where P
D
is the power dissipated, V
CC
is the input supply
voltage, V
BAT
is the battery voltage and I
BAT
is the charge
current. The approximate ambient temperature at which
the thermal feedback begins to protect the IC is:
T
A
= 120
C P
D
JA
T
A
= 120
C (V
CC
V
BAT
) I
BAT
JA
Example: An LTC4068 operating from a 5V supply is
programmed to supply 800mA full-scale current to a
discharged Li-Ion battery with a voltage of 3.3V. Assuming
JA
is 50
C/W (see Thermal Considerations), the ambient
temperature at which the LTC4068 will begin to reduce the
charge current is approximately:
T
A
= 120
C (5V 3.3V) (800mA) 50
C/W
T
A
= 120
C 1.36W 50
C/W = 120
C 68
C
T
A
= 52
C
charged condition and eliminates the need for periodic
charge cycle initiations. The CHRG output enters a pull-
down state during recharge cycles.
If the battery is removed from the charger, a sawtooth
waveform of approximately 100mV appears at the charger
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.
filter can be used on the PROG pin to measure the average
battery current, as shown in Figure 2. A 10k resistor has
been added between the PROG pin and the filter capacitor
to ensure stability.
10
LTC4068-4.2
406842f
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:
I
C T
V
V
BAT
A
CC
BAT
JA
=
(
)
120
Using the previous example with an ambient temperature
of 60
C, the charge current will be reduced to
approximately:
I
C
C
V
V
C W
C
C A
I
mA
BAT
BAT
=
(
)
=
=
120
60
5
3 3
50
60
85
706
.
/
/
Moreover, when thermal feedback reduces the charge cur-
rent the voltage at the PROG pin is also reduced proportion-
ally as discussed in the Operation section. It is important
to remember that LTC4068 applications do not need to be
designed for worst-case thermal conditions since the IC will
automatically reduce power dissipation when the junction
temperature reaches approximately 120
C.
Thermal Considerations
In order to deliver maximum charge current under all
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 2500mm
2
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.
V
CC
Bypass Capacitor
Many types of capacitors can be used for input bypassing,
however, caution must be exercised when using multilayer
ceramic capacitors. Because of the self-resonant and high
APPLICATIO S I FOR ATIO
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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 1.5
resistor in series
with an X5R ceramic capacitor will minimize start-up
voltage transients. For more information, see Application
Note 88.
Charge Current Soft-Start
The LTC4068 includes a soft-start circuit to minimize the
inrush current at the start of a charge cycle. When a charge
cycle is initiated, the charge current ramps from zero to
full-scale current over a period of approximately 100
s.
This has the effect of minimizing the transient current load
on the power supply during start-up.
USB and Wall Adapter Power
The LTC4068 allows charging from both a wall adapter
and a USB port. Figure 3 shows an example of how to
combine wall adapter and USB power inputs. A P-channel
MOSFET, MP1, is used to prevent back conducting into
the USB port when a wall adapter is present and a
Schottky diode, D1, is used to prevent USB power loss
through the 1k pull-down resistor.
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
wall adapter is present. The charge termination threshold
remains fixed at 80mA.
+
LTC4068-4.2
BAT
ITERM
PROG
V
CC
GND
D1
5V WALL
ADAPTER
800mA I
CHG
USB POWER
500mA I
CHG
I
CHG
SYSTEM
LOAD
Li-Ion
BATTERY
MP1
1k
3.3k
2k
MN1
6
4, 9
2
1
5
406842 F03
1.25k
Figure 3. Combining Wall Adapter and USB Power
11
LTC4068-4.2
406842f
DD Package
8-Lead Plastic DFN (3mm
3mm)
(Reference LTC DWG # 05-08-1698)
U
PACKAGE DESCRIPTIO
3.00
0.10
(4 SIDES)
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
0.38
0.10
BOTTOM VIEW--EXPOSED PAD
1.65
0.10
(2 SIDES)
0.75
0.05
R = 0.115
TYP
2.38
0.10
(2 SIDES)
1
4
8
5
PIN 1
TOP MARK
0.200 REF
0.00 0.05
(DD8) DFN 0203
0.28
0.05
2.38
0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
1.65
0.05
(2 SIDES)
2.15
0.05
0.50
BSC
0.675
0.05
3.5
0.05
PACKAGE
OUTLINE
0.28
0.05
0.50 BSC
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-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
APPLICATIO S I FOR ATIO
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IN
V
CC
LTC4068
DRAIN-BULK
DIODE OF FET
405842 F04
Figure 4. Low Loss Input Reverse Polarity Protection
Reverse Polarity Input Voltage Protection
In some applications, protection from reverse polarity
voltage on V
CC
is desired. If the supply voltage is high
enough, a series blocking diode can be used. In other
cases, where the voltage drop must be kept low, a P-channel
MOSFET can be used (as shown in Figure 4).
12
LTC4068-4.2
406842f
PART NUMBER
DESCRIPTION
COMMENTS
LTC1732
Lithium-Ion Linear Battery Charger Controller
Simple Charger uses External FET, Features Preset Voltages, C/10
Charger Detection and Programmable Timer, Input Power Good Indication
LTC1733
Monolithic Lithium-Ion Linear Battery Charger
Standalone Charger with Programmable Timer, Up to 1.5A Charge Current
LTC1734
Lithium-Ion Linear Battery Charger in ThinSOT
TM
Simple ThinSOT Charger, No Blocking Diode, No Sense Resistor Needed
LTC1734L
Lithium-Ion Linear Battery Charger in ThinSOT
Low Current Version of LTC1734; 50mA
I
CHRG
180mA
LTC1998
Lithium-Ion Low Battery Detector
1% Accurate 2.5
A Quiescent Current, SOT-23
LTC4007
4A Multicell Li-Ion Battery Charger
Standalone Charger, 6V
V
IN
28V, Up to 96% Efficiency,
0.8% Charging Voltage Accuracy
LTC4050
Lithium-Ion Linear Battery Charger Controller
C/10 Charger Detection and Programmable Timer, Thermistor Interface
LTC4052
Monolithic Lithium-Ion Battery Pulse Charger
No Blocking Diode or External Power FET Required,
1.5A Charge Current
LTC4053
USB Compatible Monolithic Li-Ion Battery Charger
Standalone Charger with Programmable Timer, Up to 1.25A Charge Current
LTC4054
Standalone Linear Li-Ion Battery Charger
Thermal Regulation Prevents Overheating, C/10 Termination,
in ThinSOT
C/10 Indicator, Up to 800mA Charge Current
LTC4057
Li-Ion Linear Battery Charger
Up to 800mA Charge Current, Thermal Regulation, ThinSOT Package
LTC4058
Standalone Li-Ion Linear Charger in DFN
Up to 950mA Charge Current, Kelvin Sense for High Accuracy,
LTC4058X
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
Low Loss PowerPath
TM
Controller in ThinSOT
Automatic Switching Between DC Sources, Load Sharing,
LTC4412
Replaces ORing Diodes
ThinSOT and PowerPath are trademarks of Linear Technology Corporation.
RELATED PARTS
TYPICAL APPLICATIO S
U
Full Featured Single Cell Li-Ion Charger
BAT
V
CC
CHRG
2k
5
8
3
7
4, 9
1
2
6
405642 TA03
1
F
1
F
V
IN
5V
1-CELL
Li-Ion
BATTERY
LTC4068-4.2
500mA
ACPR
EN
PROG
GND
1k
1k
1k
+
ITERM
Li-Ion Battery Charger with Reverse Polarity Input Protection
BAT
V
CC
ITERM
1k
5
8
4, 9
2
1
6
406842 TA04
1
F
5V
WALL
ADAPTER
LTC4068-4.2
500mA
EN
PROG
GND
1-CELL
Li-Ion
BATTERY
+
LT/TP 0304 1K PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 2004
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
q
FAX: (408) 434-0507
q
www.linear.com
USB/Wall Adapter Power Li-Ion Charger
+
LTC4068-4.2
PROG
V
CC
5V WALL
ADAPTER
USB
POWER
1-CELL
Li-Ion
BATTERY
1k
5k
1.25k
6
2
1
5
4, 9
406842 TA05
GND
1
F
100mA/
500mA
C
BAT
ITERM
I
BAT
PDF 
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