LTC4064
1
sn4064 4064fs
APPLICATIO S
U
FEATURES
TYPICAL APPLICATIO
U
DESCRIPTIO
U
■
File Servers, RAID Systems
■
Storage Products
■
Li-Ion Battery Back-Up
■
Preset 4V Charge Voltage with 1% Accuracy
Prolongs 4.2V Li-Ion Battery Lifetime
■
Automatic Recharge
■
Thermal Regulation Maximizes Charging Rate
without Risk of Overheating*
■
No MOSFET, Sense Resistor or Blocking Diode
Required
■
Programmable Charge Termination Timer
■
Thermistor Input for Temperature Qualified Charging
■
Programmable Charge Current with 7% Accuracy
■
C/10 Charge Current Detection Output
■
25µA Supply Current in Shutdown Mode
■
Charge Current Monitor Useful for Gas Gauging*
■
Charges Directly from USB Port
■
Tiny Thermally Enhanced 10-pin MSOP Package
Monolithic Linear Charger
for Back-Up Li-Ion Batteries
The LTC4064 is a standalone linear charger optimized for
prolonging the life of 1-cell Li-ion batteries in battery back-
up applications. By charging to a float voltage of 4V
instead of 4.2V or 4.1V, the LTC4064 decelerates the aging
process and capacity degradation when the battery is
unused for long periods of time but must be in a ready
state.
An external capacitor programs a safety timer to terminate
the charge cycle while the charge current is set externally
with a single resistor. When the input supply is removed,
the LTC4064 automatically enters a low current sleep
mode, dropping the battery drain current to less than 3µA.
Additional safety features designed to maximize battery
lifetime and reliability include NTC temperature sensing
and low battery charge conditioning (trickle charging).
The IC contains an on-chip power MOSFET and eliminates
the need for an external sense resistor and blocking diode.
The LTC4064 also includes C/10 detection circuitry, AC
present logic, and fault detection circuitry.
, LTC and LT are registered trademarks of Linear Technology Corporation.
BAT
PROG
TIMER
NTCGND 1.5k
1%
4.7µF
0.1µF
I
BAT
= 1A
4064TA01
SHDN
1-CELL
Li-Ion
BATTERY*
*AN OUTPUT CAPACITOR MAY BE REQUIRED
DEPENDING ON BATTERY LEAD LENGTH
V
CC
V
IN
= 5V
V
FLOAT
= 4V
8 2
9
7
5, 11 6
4LTC4064
Standalone Back-Up Li-Ion Battery Charger
*US Patent No. 6522118
LTC4064
2
sn4064 4064fs
Input Supply Voltage (V
CC
) ..................................... 10V
BAT ......................................................................... 10V
NTC, SHDN, TIMER, PROG ............ –0.3V to V
CC
+ 0.3V
CHRG, FAULT, ACPR ................................ –0.3V to 10V
BAT Short-Circuit Duration .......................... Continuous
BAT Current (Note 2) ............................................. 1.3A
PROG Current (Note 2) ....................................... 1.3mA
Junction Temperature.......................................... 125°C
Operating Temperature Range (Note 3) ...–40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ABSOLUTE AXI U RATI GS
W
WW
U
PACKAGE/ORDER I FOR ATIO
UUW
(Note 1)
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
CC
V
CC
Supply Voltage ●4.25 6.5 V
I
CC
V
CC
Supply Current Charger On; Current Mode; R
PROG
= 30k (Note 5) ●12 mA
Shutdown Mode; V
SHDN
= 0V ●25 50 µA
Sleep Mode V
CC
< V
BAT
or V
CC
≤ 4V ●25 50 µA
V
FLOAT
V
BAT
Regulated Float Voltage ●3.96 4.00 4.04 V
I
BAT
Battery Pin Current R
PROG
= 3k; Current Mode ●465 500 535 mA
R
PROG
= 15k; Current Mode ●93 100 107 mA
Shutdown Mode; V
SHDN
= 0V ±1±3µA
Sleep Mode V
CC
< V
BAT
or V
CC
< (V
UV
– ∆V
UV
)±1±3µA
I
TRIKL
Trickle Charge Current V
BAT
< 2V; R
PROG
= 3k ●35 50 65 mA
V
TRIKL
Trickle Charge Trip Threshold Voltage V
BAT
Rising 2.48 V
∆V
TRIKL
Trickle Charge Trip Hysteresis Voltage 100 mV
V
UV
V
CC
Undervoltage Lockout Voltage V
CC
Rising ●4 4.25 V
∆V
UV
V
CC
Undervoltage Lockout Hysteresis 200 mV
V
MSD
Manual Shutdown Threshold Voltage SHDN Pin Voltage 0.6 1.3 V
V
ASD
Automatic Shutdown Threshold Voltage (V
CC
- V
BAT
) High to Low 35 mV
(V
CC
- V
BAT
) Low to High 70 mV
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ORDER PART
NUMBER
LTC4064EMSE
T
JMAX
= 125°C, θ
JA
= 40°C/W (Note 4)
EXPOSED PAD IS GND, (PIN 11)
MUST BE SOLDERED TO PCB
1
2
3
4
5
CHRG
V
CC
FAULT
TIMER
GND
10
9
8
7
6
ACPR
BAT
SHDN
PROG
NTC
TOP VIEW
MSE EXPOSED PAD PACKAGE
10-LEAD PLASTIC MSOP
11
MSE PART MARKING
LTAHQ
LTC4064
3
sn4064 4064fs
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The Absolute Maximum BAT Current Rating of 1.3A is guaranteed
by design and current density calculations. The Absolute Maximum PROG
Current Rating is guaranteed to be 1/1000 of BAT current rating by design.
Note 3: The LTC4064 is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
PROG
PROG Pin Voltage R
PROG
= 3k, I
PROG
= 500µA 1.5 V
I
CHRG
CHRG Pin Weak Pulldown Current V
CHRG
= 1V 15 30 50 µA
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
FAULT
FAULT Pin Output Low Voltage I
FAULT
= 5mA 0.35 0.6 V
I
C/10
End of Charge Indication Current Level R
PROG
= 3k 44 50 56 mA
t
TIMER
TIMER Accuracy C
TIMER
= 0.1µF10%
∆V
RECHRG
Recharge Threshold Voltage V
FLOAT
- V
RECHRG
, V
BAT
> V
TRIKL
●65 100 135 mV
Charge Termination Timer Expired
V
NTC-HOT
NTC Pin Hot Threshold Voltage V
NTC
Falling 2.5 V
V
HOT-HYS
NTC Pin Hot Hysteresis Voltage 80 mV
V
NTC-COLD
NTC Pin Cold Threshold Voltage V
NTC
Rising 4.375 V
V
COLD-HYS
NTC Pin Cold Hystersis Voltage 80 mV
V
NTC-DIS
NTC Pin Disable Threshold Voltage V
NTC
Rising 100 mV
V
DIS-HYS
NTC Pin Disable Hystersis Voltage 10 mV
T
LIM
Junction Temperature in 105 °C
Constant-Temperature Mode
R
ON
Power MOSFET “ON” Resistance 375 mΩ
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 4: 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 5: Supply current includes PROG pin current (approximately 50µA)
but does not include any current delivered to the battery through the BAT
pin (approximately 50mA).
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = 5V
LTC4064
4
sn4064 4064fs
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Battery Regulation Voltage
vs Battery Charge Current
I
BAT
(mA)
3.96
V
BAT
(V)
3.98
4.00
4.02
3.97
3.99
4.01
100 200 300 400
4064 G01
500500 150 250 350 450
V
CC
= 5V
T
A
= 25°C
R
PROG
= 3k
TEMPERATURE (°C)
–50
3.86
V
BAT
(V)
3.88
3.92
3.94
3.96
50
4.04
4064 G02
3.90
0
–25 75 100
25 125
3.98
4.00
4.02
V
CC
= 5V
R
PROG
= 3k
I
BAT
= 10mA
VCC (V)
4
VBAT (V)
4.5 55.5 6
4064 G03
6.5
4.010
4.008
4.006
4.004
4.002
4.000
3.998
3.996
3.994
3.992
3.990
7
VCC = 5V
TA = 25°C
RPROG = 3k
IBAT = 10mA
Battery Regulation Voltage
vs Temperature
Battery Regulation Voltage
vs VCC
Charge Current vs Input Voltage Charge Current vs Battery Voltage
Charge Current vs Ambient
Temperature with Thermal
Regulation
V
CC
(V)
4.0
I
BAT
(mA)
600
500
400
300
200
100
04.5 5.0
4064 G04
5.5
T
A
= 25°C
V
BAT
(V)
0
I
BAT
(mA)
150
450
500
550
122.5
4064 G05
50
350
250
100
400
0
300
200
0.5 1.5 3.5 4.5
34
V
CC
= 5V
T
A
= 25°C
R
PROG
= 3k
TEMPERATURE (°C)
–50
0
IBAT (mA)
200
400
600
–25 025 50
4064 G06
75
800
1000
100
300
500
700
900
100
THERMAL CONTROL
LOOP IN OPERATION
VCC = 5V
VBAT = 3.5V
RPROG = 1.5k
Undervoltage Lockout Voltage
vs Temperature
Shutdown Supply Current
vs Temperature and VCC
Manual Shutdown Threshold
Voltage vs Temperature and VCC
TEMPERATURE (°C)
–50
V
UV
(V)
3.95
3.97
3.98
3.99
4.05
4.02
050 75
4064 G07
3.96
4.03
4.04
4.01
4.00
–25 25 100 125
TEMPERATURE (°C)
–50
I
CC
(µA)
20
25
30
25 75
4064 G08
15
10
–25 0 50 100 125
5
0
V
SHDN
= 0V
V
CC
= 6.5V
V
CC
= 5.5V
V
CC
= 4.5V
TEMPERATURE (°C)
–50
VMSD (V)
0.80
0.90
0.95
1.00
1.30
1.15
050 75
4064 G09
0.85
1.20
1.25
1.10
1.05
–25 25 100 125
VCC = 6V
VCC = 5.5V
VCC = 4.5V
VCC = 5V
LTC4064
5
sn4064 4064fs
TYPICAL PERFOR A CE CHARACTERISTICS
UW
PROG Pin Voltage
vs Charge Current
PROG Pin Voltage vs VCC
Constant Current Mode
PROG Pin Voltage vs Temperature
Constant Current Mode
CHARGE CURRENT (mA)
0
V
PROG
(V)
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
400
4064 G10
100 200 300 50035050 150 250 450
V
CC
= 5V
T
A
= 25°C
R
PROG
= 3k
V
CC
(V)
4
1.485
V
PROG
(V)
1.490
1.495
1.500
1.505
1.515
4.5 5 5.5 6
4064 G11
6.5 7
1.510
V
BAT
= 3.5V
T
A
= 25°C
R
PROG
= 3k
TEMPERATURE (°C)
–50
1.485
V
PROG
(V)
1.490
1.495
1.500
1.505
1.515
–25 02550
4064 G12
75 100
1.510
V
CC
= 5V
V
BAT
= 4V
R
PROG
= 3k
Trickle Charge Current
vs Temperature
CHRG Pin Weak Pull-Down
Current vs Temperature
CHRG Pin Output Low Voltage
vs Temperature
TEMPERATURE (°C)
–50 –25
7
I
BAT
(% OF PROGRAMMED CURRENT)
9
12
050 75
4064 G13
8
11
10
25 100 125
V
BAT
= 2V
T
A
= 25°C
R
PROG
= 3k
TEMPERATURE (°C)
–50
25
ICHRG (µA)
26
28
29
30
35
32
050 75
4064 G14
27
33
34
31
–25 25 100 125
VCC = 5V
IBAT < C/10
TEMPERATURE (°C)
–50
V
CHRG
(V)
0.4
0.5
0.6
25 75
4064 G15
0.3
0.2
–25 0 50 100 125
0.1
0
V
CC
= 5V
I
CHRG
= 5mA
Timer Error vs Temperature
TEMPERATURE (°C)
–50
–5
tTIMER (%)
–4
–2
–1
0
5
2
050 75
4064 G16
–3
3
4
1
–25 25 100 125
VCC = 5V
CTIMER = 0.1µF
Timer Error vs VCC
VCC (V)
4
–5
tTIMER (%)
–3
–1
1
4.5 55.5 6
4064 G17
6.5
3
5
–4
–2
0
2
4
7
TA = 25°C
CTIMER = 0.1µF
LTC4064
6
sn4064 4064fs
UU
U
PI FU CTIO S
CHRG (Pin 1): Open-Drain Charge Status Output. When
the battery is being charged, the CHRG pin is pulled low by
an internal N-channel MOSFET. When the charge current
drops to 10% of the full-scale current, the N-channel
MOSFET latches off and a 30µA current source is con-
nected from the CHRG pin to ground. The C/10 latch can
be cleared by grounding the SHDN pin, momentarily, or
toggling V
CC
. When the timer runs out or the input supply
is removed, the current source is disconnected and the
CHRG pin is forced high impedance.
V
CC
(Pin 2): Positive Input Supply Voltage. When V
CC
is
within 35mV of V
BAT
or less than the undervoltage lockout
threshold, the LTC4064 enters sleep mode, dropping I
BAT
to less than 3µA. V
CC
can range from 4.25V to 6.5V.
Bypass this pin with at least a 4.7µF ceramic capacitor to
ground.
FAULT (Pin 3): Open-Drain Fault Status Output. The
FAULT open-drain logic signal indicates that the charger
has timed out under trickle charge conditions or the NTC
comparator is indicating an out-of-range battery tempera-
ture condition. If V
BAT
is less that 2.48V, trickle charging
begins whereby the charge current drops to one tenth of
its programmed value and the timer period is reduced by
a factor of four. When one fourth of the timing period has
elapsed, if V
BAT
is still less than 2.48V, trickle charging
stops and the FAULT pin latches to ground. The fault can
be cleared by toggling V
CC
, momentarily grounding the
SHDN pin or pulling the BAT pin above 2.48V. If the NTC
comparator is indicating an out-of-range battery tempera-
ture condition, the FAULT pin will pull to ground until the
temperature returns to the acceptable range.
TIMER (Pin 4): Timer Capacitor. The timer period is set by
placing a capacitor, C
TIMER
, to ground. The timer period is:
Time (Hours) = (C
TIMER
• 3 hr)/(0.1µF)
Short the TIMER pin to ground to disable the internal timer
function.
GND (Pins 5, 11): Ground. The exposed backside of the
package is also ground and must be soldered to the PC
board for maximum heat transfer.
NTC (Pin 6): Input to the NTC (Negative Temperature
Coefficient) Thermistor Temperature Monitoring Circuit.
With an external 10kΩ NTC thermistor to ground and a 1%
resistor to V
CC
, this pin can sense the temperature of the
battery pack and stop charging when it is out of range.
When the voltage at this pin drops below (0.5)•(V
CC
) at hot
temperatures or rises above (0.875)•(V
CC
) at cold, charg-
ing is suspended and the internal timer is frozen. The
CHRG pin output status is not affected in this hold state.
The FAULT pin will be pulled to ground, but not latched.
When the temperature returns to an acceptable range,
charging will resume and the FAULT pin is released. The
NTC feature can be disabled by grounding the NTC pin.
PROG (Pin 7): Charge Current Program and Charge Cur-
rent Monitor Pin. The charge current is programmed by
connecting a resistor, R
PROG
to ground. When in con-
stant-current mode, the LTC4064 servos the PROG pin
voltage to 1.5V. In all modes the voltage on the PROG pin
can be used to measure the charge current as follows:
I
BAT
= (V
PROG
/R
PROG
) • 1000.
SHDN (Pin 8): Shutdown Input Pin. Pulling the SHDN pin
to ground will put the LTC4064 into standby mode where
the BAT drain current is reduced to less than 3µA, and the
supply current is reduced to less than 25µA. For normal
operation, pull the SHDN pin up to V
CC
.
BAT (Pin 9): Charge Current Output. A bypass capacitor of
at least 1µF with a 1Ω series resistor is required to keep the
loop stable when the battery is not present. A precision
internal resistor divider sets the final float potential on this
pin. The internal resistor divider is disconnected in sleep
and shutdown mode.
ACPR (Pin 10): Open-Drain Power Supply Status Output.
When V
CC
is greater than the undervoltage lockout thresh-
old and at least 35mV above V
BAT
, the ACPR pin will pull
to ground. Otherwise, the pin is high impedance.
LTC4064
7
sn4064 4064fs
SI PLIFIED
W
BLOCK DIAGRA
W
Figure 1
2.485V
–
+
–
+
–
+
–
+
–+
4064 BD
HOT COLD DISABLE
STOP
FAULT
CHARGE
OSCILLATOR
COUNTER
TIMER
C
TIMER
NTC
NTC
CHRG
ACPR
FAULT
30µA
2.485V TO BAT
REF
–
+
C/10
ACPR
TA
CA
C2
C3
VA
MA
PROG
BAT
V
CC
GND
R1
R3
R4
R5
R2
30µA
1.5V
0.15V
105°C
T
DIE
D1
D2
D3
M2
×1M1
×1000
MP
R
PROG
SHDN
LOGIC
SHDN
2
6
1
10
3
4 7 5, 11
8
9
C/10
LTC4064
8
sn4064 4064fs
The LTC4064 is a linear battery charger designed primarily
for charging single cell lithium-ion batteries used in back-
up applications. With a 4V final float voltage accuracy of
±1%, the LTC4064 maximizes the lifetime of 4.2V chem-
istry lithium-ion batteries. A precision, automatic recharge
feature ensures that the battery voltage remains within
100mV of this 4V float voltage at all times.
Featuring an internal P-channel power MOSFET, the charger
uses a constant-current/constant-voltage charge algo-
rithm with programmable current and a programmable
timer for charge termination. Charge current can be
programmed up to 1.25A with an accuracy of ±7%. No
blocking diode or sense resistor is required thus dropping
the external component count to three for the basic
charger circuit. The CHRG, ACPR, and FAULT open-drain
status outputs provide information regarding the status of
the LTC4064 at all times. An NTC thermistor input
provides the option of charge qualification using battery
temperature.
An internal thermal limit reduces the programmed charge
current if the die temperature attempts to rise above a
preset value of approximately 105°C. This feature protects
the LTC4064 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 LTC4064
or the external components. Another benefit of the LTC4064
thermal limit is that charge current can be set according to
typical, not worst-case, ambient temperatures for a given
application with the assurance that the charger will auto-
matically reduce the current in worst-case conditions.
The charge cycle begins when the voltage at the V
CC
pin
rises above the UVLO level, a program resistor is con-
nected from the PROG pin to ground, and the SHDN pin is
pulled above the shutdown threshold. At the beginning of
the charge cycle, if the battery voltage is below 2.48V, the
charger goes into trickle charge mode to bring the cell
voltage up to a safe level for charging. The charger goes
into the fast charge constant-current mode once the
voltage on the BAT pin rises above 2.48V. In constant-
current mode, the charge current is set by R
PROG
.
When the battery approaches the final float voltage, the
charge current begins to decrease as the LTC4064 enters
the constant-voltage mode. When the current drops to
10% of the full-scale charge current, an internal compara-
tor latches off the MOSFET on the CHRG pin and connects
a weak current source to ground (30µA) to indicate a near
end-of-charge (C/10) condition. The C/10 latch can be
cleared by grounding the SHDN pin momentarily, or
momentarily removing and reapplying V
CC
.
An external capacitor on the TIMER pin sets the total
charge time. When this time elapses, the charge cycle
terminates and the CHRG pin assumes a high impedance
state. To restart the charge cycle, remove the input voltage
and reapply it, or momentarily force the SHDN pin to 0V.
The charge cycle will also restart if the BAT pin voltage falls
below the recharge threshold.
When the input voltage is not present, the charger goes
into a sleep mode, dropping battery drain current, I
BAT
, to
less than 3µA. This greatly reduces the current drain on the
battery and increases the standby time. The charger can be
shut down (I
CC
= 25µA) by forcing the SHDN pin to 0V.
OPERATIO
U
LTC4064
9
sn4064 4064fs
For example, if 500mA charge current is required,
calculate:
R
PROG
= 1500V/0.5A = 3kΩ
For best stability over temperature and time, 1% metal-
film resistors are recommended.
If the charger is in constant-temperature or constant-
voltage mode, the battery current can be monitored by
measuring the PROG pin voltage as follows:
I
BAT
= (V
PROG
/ R
PROG
) • 1000
USB and Wall Adapter Power
Although the LTC4064 allows charging from a USB port,
a wall adapter can also be used to charge Li-Ion batteries.
Figure 2 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 Schottky diode, D1, is used
to prevent USB power loss through the 1k pull-down
resistor.
Typically a wall adapter can supply significantly more
current than the 500mA-limited USB port. Therefore, an N-
channel MOSFET, MN1 and an extra 3k program resistor
can be used to increase the charge current to 1A when the
wall adapter is present.
APPLICATIO S I FOR ATIO
WUUU
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 35mV of the battery voltage. If the UVLO
comparator is tripped, the charger will not come out of
shutdown until V
CC
rises 70mV above the battery voltage.
Trickle Charge And Defective Battery Detection
At the beginning of a charge cycle, if the battery voltage is
low (below 2.48V) the charger goes into trickle charge
reducing the charge current to 10% of the full-scale
current. If the low battery voltage persists for one quarter
of the total charge time, the battery is assumed to be
defective, the charge cycle is terminated, the CHRG pin
output assumes a high impedance state, and the FAULT
pin pulls low. The fault can be cleared by toggling V
CC
,
temporarily forcing the SHDN pin to 0V, or temporarily
forcing the BAT pin voltage above 2.48V.
Shutdown
The LTC4064 can be shut down (I
CC
= 25µA) by pulling the
SHDN pin to 0V. For normal operation, pull the SHDN pin
above the manual shutdown threshold voltage level. Do
not leave this pin open. In shutdown the internal linear
regulator is turned off, and the internal timer is reset.
Programming Charge Current
The formula for the battery charge current (see Figure 1)
is:
I
CHG
= (I
PROG
) • 1000
= (1.5V / R
PROG
) • 1000 or
R
PROG
= 1500V/I
CHG
where R
PROG
is the total resistance from the PROG pin to
ground. Under trickle charge conditions, this current is
reduced to 10% of the full-scale value.
Figure 2. Combining Wall Adapter and USB Power
4064 F02
1k 3k
Li-Ion
BATTERY
5V WALL
ADAPTER
1A I
CHG
3k
LTC4064
BAT
V
CC
2
9
7
I
CHG
PROG +
SYSTEM
LOAD
USB
POWER
500mA I
CHG
D1
MN1
MP1
LTC4064
10
sn4064 4064fs
Programming The Timer
The programmable timer is used to terminate the charge
cycle. The timer duration is programmed by an external
capacitor at the TIMER pin. The total charge time is:
Time (Hours) = (3 Hours) • (C
TIMER
/0.1µF) or
C
TIMER
= 0.1µF • Time (Hours)/3 (Hours)
The timer starts when an input voltage greater than the
undervoltage lockout threshold level is applied and the
SHDN pin is greater than the manual shutdown threshold
voltage level. After a time-out occurs, the charge current
stops, and the CHRG output assumes a high impedance
state to indicate that the charging has stopped. Connect-
ing the TIMER pin to ground disables the timer function.
Recharge
After a charge cycle has terminated, if the battery voltage
drops below the recharge threshold of 3.90V a new charge
cycle will begin. The recharge circuit integrates the BAT
pin voltage for a few milliseconds to prevent a transient
from restarting the charge cycle.
If the battery voltage remains below 2.48V during trickle
charge for 1/4 of the programmed time, the battery may be
defective and the charge cycle will end. In addition, the
recharge comparator is disabled and a new charge cycle
will not begin unless the input voltage is toggled off-then-
on, the SHDN pin is momentarily pulled to ground, or the
BAT pin is pulled above the 2.48V trickle charge threshold.
Open-Drain Status Outputs
The LTC4064 has three open-drain status outputs: ACPR,
CHRG and FAULT. The ACPR pin pulls low when an input
voltage greater than the undervoltage lockout threshold is
applied and becomes high impedance when power (V
IN
<
V
UV
) is removed. CHRG and FAULT work together to
indicate the status of the charge cycle. Table 1 describes
the status of the charge cycle based on the CHRG and
FAULT outputs.
APPLICATIO S I FOR ATIO
WUUU
Table 1.
FAULT CHRG Description
High Low Charge cycle has started, C/10 has not been
reached and charging is proceeding normally.
Low Low Charge cycle has started, C/10 has not been
reached, but the charge current and timer
have been paused due to an NTC out-of-
temperature condition.
High 30µA C/10 has been reached and charging is
pull-down proceeding normally.
Low 30µA C/10 has been reached but the charge current
pull-down and timer have paused due to an NTC out-of-
temperature condition.
High High Normal timeout (charging has terminated).
Low High If FAULT goes low and CHRG goes high
impedance simultaneously, then the LTC4064
has timed out due to a bad cell (V
BAT
<2.48V
after one-quarter the programmed charge time).
If CHRG goes high impedance first, then
the LTC4064 has timed out normally (charging
has terminated), but NTC is indicating an out-
of-temperature condition.
CHRG Status Output Pin
When the charge cycle starts, the CHRG pin is pulled to
ground by an internal N-channel MOSFET capable of
driving an LED. When the charge current drops to 10% of
the full-scale current (C/10), the N-channel MOSFET is
latched off and a weak 30µA current source to ground is
connected to the CHRG pin. After a time-out occurs,
the pin assumes a high impedance state. By using two
different value pull-up resistors a microprocessor can
detect three states from this pin (charging, C/10 and time-
out). See Figure 3.
When the LTC4064 is in charge mode, the CHRG pin is
pulled low by the internal N-channel MOSFET. To detect
this mode, force the digital output pin, OUT, high and
measure the voltage at the CHRG pin. The N-channel
MOSFET will pull the pin low even with the 2k pull-up
resistor. Once the charge current drops to 10% of the
LTC4064
11
sn4064 4064fs
–
+
–
+
–
+
4064 F04
R
NTC
10k
R
HOT
1%
7/8 V
CC
1/2 V
CC
3/160 V
CC
TOO COLD
TOO HOT
DISABLE NTC
LTC4064
V
CC
NTC
Thermistors
The LTC4064 NTC trip points were designed to work with
thermistors whose resistance-temperature characteris-
tics follow Vishay Dale’s “R-T Curve 2”. The Vishay
NTHS0603N02N1002J is an example of such a ther-
mistor. However, Vishay Dale has many thermistor prod-
ucts that follow the “R-T Curve 2” characteristic in a variety
of sizes. Futhermore, any thermistor whose ratio of R
COLD
to R
HOT
is about 7.0 will also work (Vishay Dale R-T Curve
2 shows a ratio of R
COLD
to R
HOT
of 2.816/0.4086 = 6.9).
NTC Layout Considerations
It is important that the NTC thermistor not be in close
thermal contact with the LTC4064. Because the LTC4064
package can reach temperatures in excess of the 50°C trip
point, the NTC function can cause a hysteretic oscillation
which turns the charge current on and off according to the
package temperature rather than the battery temperature.
This problem can be eliminated by thermally coupling the
NTC thermistor to the battery and not to the LTC4064.
Furthermore, it is essential that the V
CC
connection to
R
HOT
is made according to standard Kelvin sense tech-
niques. Since V
CC
is a high current path into the LTC4064,
it is essential to minimize voltage drops between the V
CC
input pin and the top of R
HOT
.
APPLICATIO S I FOR ATIO
WUUU
Figure 4
Figure 3. Microprocessor Interface
4064 F03
400k
2k
3
8
LTC4064
IN
V
CC
V
DD
OUT
CHRG
V
+
µPROCESSOR
full-scale current (C/10), the N-channel MOSFET is turned
off and a 30µA current source is connected to the CHRG
pin. The IN pin will then be pulled high by the 2k pull-up.
By forcing the OUT pin to a high impedance state, the
current source will pull the pin low through the 400k
resistor. When the internal timer has expired, the CHRG
pin will assume a high impedance state and the 400k
resistor will then pull the pin high to indicate that charging
has terminated.
NTC Thermistor
The battery temperature is measured by placing a negative
temperature coefficient (NTC) thermistor close to the
battery pack. The NTC circuitry is shown in Figure 4. To use
this feature, connect a 10k NTC thermistor between the
NTC pin and ground and a resistor (R
HOT
) from the NTC pin
to V
CC
. R
HOT
should be a 1% resistor with a value equal to
the value of the chosen NTC thermistor at 50°C (this value
is 4.1k for a Vishay NTHS0603N02N1002J thermistor).
The LTC4064 goes into hold mode when the resistance of
the NTC thermistor drops below 4.1k which should be
approximately 50°C. The hold mode freezes the timer and
stops the charge cycle until the thermistor indicates a
return to a valid temperature. As the temperature drops,
the resistance of the NTC thermistor rises. The LTC4064
is designed to go into hold mode when the value of the NTC
thermistor increases to seven times the value of R
HOT
. For
a Vishay NTHS0603N02N1002J thermistor, this value is
28.7k which corresponds to approximately 0°C. The hot
and cold comparators each have approximately 2°C of
hysteresis to prevent oscillation about the trip point. The
NTC function can be disabled by grounding the NTC pin.
LTC4064
12
sn4064 4064fs
Constant-Current/Constant-Voltage/
Constant-Temperature
The LTC4064 uses a unique architecture to charge a
battery in a constant-current, constant-voltage, constant-
temperature fashion. Figure 1 shows a simplified block
diagram of the LTC4064. Three of the amplifier feedback
loops shown control the constant-current, CA, constant-
voltage, VA, and constant-temperature, TA modes. A
fourth amplifier feedback loop, MA, is used to increase the
output impedance of the current source pair, M1 and M2
(note that M1 is the internal P-channel power MOSFET). It
ensures that the drain current of M1 is exactly 1000 times
greater than the drain current of M2.
Amplifiers CA, TA, and VA are used in three separate
feedback loops to force the charger into constant-current,
temperature, or voltage mode, respectively. Diodes, D1,
D2, and D3 provide priority to whichever loop is trying to
reduce the charge current the most. The outputs of the
other two amplifiers saturate low which effectively re-
moves their loops from the system. When in constant-
current mode, CA servos the voltage at the PROG pin to be
precisely 1.50V (or 0.15V when in trickle-charge mode).
TA limits the die temperature to approximately 105°C
when in constant-temperature mode and the PROG pin
voltage gives an indication of the charge current as dis-
cussed in “Programming Charge Current”. VA servos its
inverting input to precisely 2.485V when in constant-
voltage mode and the internal resistor divider made up of
R1 and R2 ensures that the battery voltage is maintained
at 4V. Again, the PROG pin voltage gives an indication of
the charge current.
In typical operation, the charge cycle begins in constant-
current mode with the current delivered to the battery
equal to 1500V/R
PROG
. If the power dissipation of the
LTC4064 results in the junction temperature approaching
105°C, the amplifier (TA) will begin decreasing the charge
current to limit the die temperature to approximately
105°C. As the battery voltage rises, the LTC4064 either
returns to constant-current mode or it enters constant-
voltage mode straight from constant-temperature mode.
APPLICATIO S I FOR ATIO
WUUU
NTC Trip Point Errors
When a 1% resistor is used for R
HOT
, the major error in
the 50°C trip point is determined by the tolerance of
the NTC thermistor. A typical 10k NTC thermistor has
a ±10% tolerance. By looking up the temperature
coefficient of the thermistor at 50°C, the tolerance error
can be calculated in degrees centigrade. Consider the
Vishay NTHS0603N02N1002J thermistor which has a
temperature coefficient of –3.3%/°C at 50°C. Dividing
the tolerance by the temperature coefficient, ±10%/
(3.3%/°C) = ±3°C, gives the temperature error of the hot
trip point.
The cold trip point is a little more complicated because its
error depends on the tolerance of the NTC thermistor and
the degree to which the ratio of its value at 0°C and its value
at 50°C varies from 7 to 1. Therefore, the cold trip point
error can be calculated using the tolerance, TOL, the
temperature coefficient of the thermistor at 0°C, TC
(in %/°C), the value of the thermistor at 0°C, R
COLD
, and
the value of the thermistor at 50°C, R
HOT
. The formula is:
Temperature Error (°C) =
1
71 100
+
⎛
⎝
⎜
⎞
⎠
⎟
TOL R
R
TC
COLD
HOT
•–•
For example, the Vishay NTHS0603N02N1002J thermistor
with a tolerance of ±10%, TC of –4.5%/°C, and R
COLD
/
R
HOT
of 6.89, has a cold trip point error of:
Temperature Error (°C) =
1010
76 89 1 100
45
±
⎛
⎝
⎜
⎞
⎠
⎟
.•. – •
–.
= –1.8°C, +2.5°C
If a thermistor with a tolerance less than ±10% is used, the
trip point errors begin to depend on errors other than
thermistor tolerance including the input offset voltage of
the internal comparators of the LTC4064 and the effects of
internal voltage drops due to high charging currents.
LTC4064
13
sn4064 4064fs
Regardless of mode, the voltage at the PROG pin is
proportional to the current being delivered to the battery.
Power Dissipation
The conditions that cause the LTC4064 to reduce charge
current due to the thermal protection feedback can be
approximated by considering the power dissipated in the
IC. For high charge currents, the LTC4064 power dissipa-
tion is 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 battery
charge current. It is not necessary to perform any worst-
case power dissipation scenarios because the LTC4064
will automatically reduce the charge current to maintain
the die temperature at approximately 105°C. However, the
approximate ambient temperature at which the thermal
feedback begins to protect the IC is:
T
A
= 105°C – P
D
θ
JA
T
A
= 105°C – (V
CC
– V
BAT
) • I
BAT
•
θ
JA
Example: Consider an LTC4064 operating from a 5V wall
adapter providing 1.2A to a 3.75V Li-Ion battery. The
ambient temperature above which the LTC4064 will begin
to reduce the 1.2A charge current is approximately:
T
A
= 105°C – (5V – 3.75V) • 1.2A • 40°C/W
T
A
= 105°C – 1.5W • 40°C/W = 105°C – 60°C = 45°C
The LTC4064 can be used above 45°C, but the charge
current will be reduced below 1.2A. The approximate
charge current at a given ambient temperature can be
approximated by:
ICT
VV
BAT A
CC BAT JA
=°105 –
(– )•θ
Consider the above example with an ambient temperature
of 55°C. The charge current will be reduced to approxi-
mately:
ICC
VVCW
C
CA A
BAT =°°
°=°
°=
105 55
5 3 75 40
50
50 1
–
(–. )• / /
APPLICATIO S I FOR ATIO
WUUU
Furthermore, the voltage at the PROG pin will change
proportionally with the charge current as discussed in the
Programming Charge Current section.
It is important to remember that LTC4064 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
105°C.
Board Layout Considerations
The ability to deliver maximum charge current under all
conditions require that the exposed metal pad on the
backside of the LTC4064 package be soldered to the PC
board ground. Correctly soldered to a 2500mm
2
double-
sided 1oz. copper board the LTC4064 has a thermal
resistance of approximately 40°C/W. Failure to make
thermal contact between the exposed pad on the backside
of the package and the copper board will result in thermal
resistances far greater than 40°C/W. As an example, a
correctly soldered LTC4064 can deliver over 1250mA to a
battery from a 5V supply at room temperature. Without a
backside thermal connection, this number could drop to
less than 500mA.
V
CC
Bypass Capacitor
Many types of capacitors can be used for input bypassing.
However, caution must be exercised when using multi-
layer ceramic capacitors. Because of the self resonant and
high Q characteristics of some types of ceramic capaci-
tors, high voltage transients can be generated under some
start-up conditions, such as connecting the charger input
to a hot power source. For more information refer to
Application Note 88.
Stability
The constant-voltage mode feedback loop is stable
without any compensation provided that a battery is
connected. However, a 1µF capacitor with a 1Ω series
resistor to GND is recommended at the BAT pin to keep
ripple voltage low when the battery is disconnected.
In the constant-current mode it is the PROG pin that is in
the feedback loop and not the battery. The constant-
current mode stability is affected by the impedance at the
LTC4064
14
sn4064 4064fs
PROG pin. With no additional capacitance on the PROG
pin, stability is acceptable with program resistor values as
high as 50k. However, additional capacitance on this node
reduces the maximum allowed program resistor. The pole
frequency at the PROG pin should be kept above 500kHz.
Therefore, if the PROG pin is loaded with a capacitance, C,
the following equation should be used to calculate the
maximum resistance value for R
PROG
:
R
PROG
< 1/(6.283 • 5 × 10
5
• C)
5
7
R
PROG
C
FILTER
CHARGE
CURRENT
MONITOR
CIRCUITRY
10k
LTC4064
4064 F05
GND
PROG
Figure 5. Isolating Capacitive Load on PROG Pin and Filtering
APPLICATIO S I FOR ATIO
WUUU
Average, rather than instantaneous, battery 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
filter can be used on the PROG pin to measure the average
battery current as shown in Figure 5. A 10k resistor is
added between the PROG pin and the filter capacitor and
monitoring circuit to ensure stability.
LTC4064
15
sn4064 4064fs
PACKAGE DESCRIPTIO
U
MSE Package
10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1663)
MSOP (MSE) 0603
0.53 ± 0.152
(.021 ± .006)
SEATING
PLANE
0.18
(.007)
1.10
(.043)
MAX
0.17 – 0.27
(.007 – .011)
TYP
0.127 ± 0.076
(.005 ± .003)
0.86
(.034)
REF
0.50
(.0197)
BSC
12345
4.90 ± 0.152
(.193 ± .006)
0.497 ± 0.076
(.0196 ± .003)
REF
8910
10
1
76
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
0.254
(.010) 0° – 6° TYP
DETAIL “A”
DETAIL “A”
GAUGE PLANE
5.23
(.206)
MIN
3.20 – 3.45
(.126 – .136)
0.889 ± 0.127
(.035 ± .005)
RECOMMENDED SOLDER PAD LAYOUT
0.305 ± 0.038
(.0120 ± .0015)
TYP
2.083 ± 0.102
(.082 ± .004)
2.794 ± 0.102
(.110 ± .004)
0.50
(.0197)
BSC
BOTTOM VIEW OF
EXPOSED PAD OPTION
1.83 ± 0.102
(.072 ± .004)
2.06 ± 0.102
(.081 ± .004)
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.
LTC4064
16
sn4064 4064fs
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2001
LT/TP 0803 1K • PRINTED IN USA
Li-Ion Battery Charger with Reverse Polarity Input Protection
LTC4064
BAT
PROG
VCC
SHDN
TIMER
GND NTC
0.1µF
4.7µF
8
2
4
9
7
5
4064 TA03
6
IBAT = 1A
1-CELL
Li-Ion
BATTERY
5V WALL
ADAPTER
1.5k
1%
+
ACPR
FAULT
BAT
PROG
CHRG
NTC
TIMER
GND
V
IN
= 5V
4k
1%
3k
1%
R
NTC
10k
4.7µF
1µF
0.1µF
I
BAT
= 500mA
4064 TA04
1k
1k 1k
SHDN
Li-Ion
CELL
V
CC
82
10
3
9
7
5
4
6
1
1Ω
LTC4064
Full Featured Single Cell Li-Ion Charger
USB/Wall Adapter Power Li-Ion Battery Charger
SUSPEND
0.1µF15k
4.7µF
1µF
4064 TA02
1k
Li-Ion
CELL
USB
POWER
5V WALL
ADAPTER
100mA/
500mA
µC
3.74k
LTC4064
BAT
SHDN
V
CC
TIMER
GND
2
9
8
75
NTC
6
4
I
BAT
PROG
1Ω
+
TYPICAL APPLICATIO S
U
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ThinSOT is a trademark of Linear Technology Corporation.
