LTC4054-4.2/LTC4054X-4.2
Standalone Linear
Li-Ion Battery Charger with
Thermal Regulation in ThinSOT
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FEATURES
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Programmable Charge Current Up to 800mA
No MOSFET, Sense Resistor or Blocking
Diode Required
Complete Linear Charger in ThinSOTTM Package for
Single Cell Lithium-Ion Batteries
Constant-Current/Constant-Voltage Operation with
Thermal Regulation* to Maximize Charge Rate
Without Risk of Overheating
Charges Single Cell Li-Ion Batteries Directly
from USB Port
Preset 4.2V Charge Voltage with ±1% Accuracy
Charge Current Monitor Output for Gas
Gauging*
Automatic Recharge
Charge Status Output Pin
C/10 Charge Termination
25µA Supply Current in Shutdown
2.9V Trickle Charge Threshold (LTC4054)
Available Without Trickle Charge (LTC4054X)
Soft-Start Limits Inrush Current
Available in 5-Lead SOT-23 Package
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APPLICATIO S
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Cellular Telephones, PDAs, MP3 Players
Charging Docks and Cradles
Bluetooth Applications
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The LTC®4054 is a complete constant-current/constantvoltage linear charger for single cell lithium-ion batteries.
Its ThinSOT package and low external component count
make the LTC4054 ideally suited for portable applications.
Furthermore, the LTC4054 is specifically designed to work
within USB power specifications.
No external sense resistor is needed, and no blocking
diode is 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. The charge voltage is fixed at 4.2V,
and the charge current can be programmed externally with
a single resistor. The LTC4054 automatically terminates
the charge cycle when the charge current drops to 1/10th
the programmed value after the final float voltage is
reached.
When the input supply (wall adapter or USB supply) is
removed, the LTC4054 automatically enters a low current
state, dropping the battery drain current to less than 2µA.
The LTC4054 can be put into shutdown mode, reducing
the supply current to 25µA.
Other features include charge current monitor, undervoltage
lockout, automatic recharge and a status pin to indicate
charge termination and the presence of an input voltage.
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
*U.S.Patent No. 6,522,118
Complete Charge Cycle (750mAh Battery)
TYPICAL APPLICATIO
700
600mA Single Cell Li-Ion Charger
1µF
4
VCC
BAT
LTC4054-4.2
PROG
GND
3
600mA
5
1.65k
4.2V
Li-Ion
BATTERY
2
CONSTANT
POWER
500
4.25
400
4.00
300
3.75
3.50
200
VCC = 5V
θJA = 130°C/W
RPROG = 1.65k
TA = 25°C
100
0
405442 TA01a
4.50
CONSTANT
VOLTAGE
0
CHARGE
TERMINATED
BATTERY VOLTAGE (V)
VIN
4.5V TO 6.5V
4.75
CONSTANT
CURRENT
600
CHARGE CURRENT (mA)
■
DESCRIPTIO
3.25
3.00
0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0
TIME (HOURS)
405442 TAO1b
405442xf
1
LTC4054-4.2/LTC4054X-4.2
W W
W
AXI U
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ABSOLUTE
RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
Input Supply Voltage (VCC) ....................... –0.3V to 10V
PROG ............................................. – 0.3V to VCC + 0.3V
BAT .............................................................. –0.3V to 7V
CHRG ........................................................ –0.3V to 10V
BAT Short-Circuit Duration .......................... Continuous
BAT Pin Current ................................................. 800mA
PROG Pin Current ................................................ 800µA
Maximum Junction Temperature .......................... 125°C
Operating Ambient Temperature Range
(Note 2) .............................................. – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 125°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
TOP VIEW
CHRG 1
5 PROG
LTC4054ES5-4.2
LTC4054XES5-4.2
GND 2
BAT 3
4 VCC
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
S5 PART MARKING
TJMAX = 125°C, (θJA = 80°C/ W TO
150°C/W DEPENDING ON PC BOARD LAYOUT)
(N0TE 3)
LTH7
LTADY
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
VCC
Input Supply Voltage
ICC
Input Supply Current
Charge Mode (Note 4), RPROG = 10k
Standby Mode (Charge Terminated)
Shutdown Mode (RPROG Not Connected,
VCC < VBAT, or VCC < VUV)
VFLOAT
Regulated Output (Float) Voltage
0°C ≤ TA ≤ 85°C, IBAT = 40mA
IBAT
BAT Pin Current
RPROG = 10k, Current Mode
RPROG = 2k, Current Mode
Standby Mode, VBAT = 4.2V
Shutdown Mode (RPROG Not Connected)
Sleep Mode, VCC = 0V
ITRIKL
Trickle Charge Current
VBAT < VTRIKL, RPROG = 2k (Note 5)
VTRIKL
Trickle Charge Threshold Voltage
RPROG = 10k, VBAT Rising (Note 5)
VTRHYS
Trickle Charge Hysteresis Voltage
RPROG = 10k (Note 5)
VUV
VCC Undervoltage Lockout Threshold
From VCC Low to High
VUVHYS
VCC Undervoltage Lockout Hysteresis
VMSD
Manual Shutdown Threshold Voltage
PROG Pin Rising
PROG Pin Falling
VASD
VCC – VBAT Lockout Threshold Voltage
VCC from Low to High
VCC from High to Low
ITERM
C/10 Termination Current Threshold
RPROG = 10k (Note 6)
RPROG = 2k
VPROG
PROG Pin Voltage
RPROG = 10k, Current Mode
ICHRG
CHRG Pin Weak Pull-Down Current
VCHRG = 5V
VCHRG
CHRG Pin Output Low Voltage
ICHRG = 5mA
∆VRECHRG
Recharge Battery Threshold Voltage
VFLOAT - VRECHRG
MIN
TYP
MAX
6.5
V
300
200
25
2000
500
50
µA
µA
µA
4.158
4.2
4.242
V
●
●
●
93
465
0
100
500
–2.5
±1
±1
107
535
–6
±2
±2
mA
mA
µA
µA
µA
●
20
45
70
mA
2.8
2.9
3.0
V
●
4.25
●
●
●
UNITS
60
80
110
mV
●
3.7
3.8
3.92
V
●
150
200
300
mV
●
●
1.15
0.9
1.21
1.0
1.30
1.1
V
V
70
5
100
30
140
50
mV
mV
●
●
0.085
0.085
0.10
0.10
0.115
0.115
mA/mA
mA/mA
●
0.93
1.0
1.07
V
8
100
20
35
µA
0.35
0.6
V
150
200
mV
405442xf
2
LTC4054-4.2/LTC4054X-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
TLIM
Junction Temperature in Constant
Temperature Mode
120
°C
RON
Power FET “ON” Resistance
(Between VCC and BAT)
600
mΩ
tSS
Soft-Start Time
IBAT = 0 to IBAT =1000V/RPROG
tRECHARGE
Recharge Comparator Filter Time
VBAT High to Low
0.75
2
4.5
ms
tTERM
Termination Comparator Filter Time
IBAT Falling Below ICHG/10
400
1000
2500
µs
IPROG
PROG Pin Pull-Up Current
µs
100
µA
3
Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2: The LTC4054E-4.2 and the LTC4054XE-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 3: See Thermal Considerations.
Note 4: Supply current includes PROG pin current (approximately 100µA)
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 LTC4054X.
Note 6: ITERM is expressed as a fraction of measured full charge current
with indicated PROG resistor.
U W
TYPICAL PERFOR A CE CHARACTERISTICS
PROG Pin Voltage vs Supply
Voltage(Constant Current Mode)
1.015
1.0100
VCC = 5V
VBAT = 4V
TA = 25°C
RPROG = 10k
1.0075
VCC = 5V
TA = 25°C
500 RPROG = 2k
1.0050
VPROG (V)
1.005
VPROG (V)
600
VCC = 5V
VBAT = 4V
RPROG = 10k
1.000
400
1.0025
IBAT (mA)
1.010
Charge Current vs
PROG Pin Voltage
PROG Pin Voltage vs
Temperature
1.0000
0.9975
0.995
300
200
0.9950
0.990
0.985
100
0.9925
4.0
4.5
5.0
5.5
VCC (V)
6.0
6.5
7.0
4054 G01
0.9900
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
4054 G02
0
0
0.25
0.50
0.75
VPROG (V)
1.00
1.25
4054 G03
405442xf
3
LTC4054-4.2/LTC4054X-4.2
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TYPICAL PERFOR A CE CHARACTERISTICS
PROG Pin Pull-Up Current vs
Temperature and Supply Voltage
3.7
PROG Pin Current vs PROG Pin
Voltage (Clamp Current)
PROG Pin Current vs PROG Pin
Voltage (Pull-Up Current)
VBAT = 4.3V
VPROG = 0V
3.5
VCC = 4.2V
3.5
0
3.0
–50
–100
2.5
3.1
VCC = 6.5V
2.9
IPROG (µA)
IPROG (µA)
IPROG (µA)
3.3
2.0
1.5
1.0
2.7
0.5
2.5
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
2.2
2.1
2.3
2.4
2.5
–400
2.0
2.6
2.5
3.0
4.210
5.5
TA = 25°C
RPROG = 10k
4.210
4.205
VFLOAT (V)
VFLOAT (V)
5.0
4.215
VCC = 5V
RPROG = 10k
4.205
4.16
4.5
Regulated Output (Float) Voltage
vs Supply Voltage
4.215
VCC = 5V
TA = 25°C
RPROG = 1.25k
4.18
4.0
4054 G06
Regulated Output (Float) Voltage
vs Temperature
4.20
3.5
VPROG (V)
4054 G05
4.26
VFLOAT (V)
VCC = 5V
VBAT = 4.3V
TA = 25°C
VPROG (V)
Regulated Output (Float) Voltage
vs Charge Current
4.22
–250
–350
4054 G04
4.24
–200
–300
VCC = 5V
VBAT = 4.3V
TA = 25°C
0
2.0
125
–150
4.200
4.200
4.195
4.195
4.190
4.190
4.14
4.12
4.10
0
100
200
300 400
IBAT (mA)
500
600
700
4.185
–50
0
–25
50
25
75
100
4.185
4054 G07
18
20
18
14
ICHRG (µA)
ICHRG (mA)
ICHRG (mA)
VCC = 5V
VBAT = 4V
TA = 25°C
12
10
2
4
3
VCHRG (V)
5
6
7
4
–50 –25
14
VCC = 5V
VBAT = 4.3V
TA = 25°C
10
8
0
25
50
75
100
125
TEMPERATURE (°C)
4054 G10
16
12
6
0
7.0
20
8
5
6.5
22
VCC = 5V
VBAT = 4V
VCHRG = 1V
16
10
6.0
CHRG Pin I-V Curve
(Weak Pull-Down State)
20
15
5.5
VCC (V)
4054 G09
CHRG Pin Current vs Temperature
(Strong Pull-Down State)
25
1
5.0
4.5
4054 G08
CHRG Pin I-V Curve
(Strong Pull-Down State)
0
4.0
TEMPERATURE (°C)
4054 G11
0
1
2
4
3
VCHRG (V)
5
6
7
4054 G12
405442xf
4
LTC4054-4.2/LTC4054X-4.2
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TYPICAL PERFOR A CE CHARACTERISTICS
CHRG Pin Current vs Temperature
(Weak Pull-Down State)
28
25
Trickle Charge Current vs
Supply Voltage
Trickle Charge Current
vs Temperature
50
VCC = 5V
VBAT = 4.3V
VCHRG = 5V
50
RPROG = 2k
RPROG = 2k
40
40
19
ITRIKL (mA)
ITRIKL (mA)
ICHRG (µA)
23
30
VCC = 5V
VBAT = 2.5V
20
30
VBAT = 2.5V
TA = 25°C
20
16
10
13
10
–50
–25
0
25
50
TEMPERATURE (°C)
75
0
–50
100
10
RPROG = 10k
–25
0
25
50
TEMPERATURE (°C)
75
4054 G13
0
100
4.0
4.5
5.0
5.5
VCC (V)
6.0
6.5
4054 G14
Trickle Charge Threshold vs
Temperature
Charge Current vs Supply Voltage
Charge Current vs Battery Voltage
VCC = 5V
RPROG = 10k
7.0
4054 G15
600
600
3.000
2.975
RPROG = 10k
RPROG = 2k
TA = 0°C
500
500
TA = 40°C
2.900
2.875
TA = 25°C
300
VBAT = 4V
TA = 25°C
θJA = 80°C/W
300
200
200
2.850
VCC = 5V
θJA = 125°C/W
RPROG = 2k
100
2.825
2.800
–50
–25
0
25
50
TEMPERATURE (°C)
75
0
2.7
100
3.0
3.3
3.6
3.9
VBAT (V)
4.2
400
4.07
650
4.03
50
25
75
0
TEMPERATURE (°C)
100
125
4054 G19
6.0
6.5
3.99
–50
7.0
VCC = 4.2V
IBAT = 100mA
RPROG = 2k
550
500
450
4.01
100
5.5
VCC (V)
600
4.05
RPROG = 10k
0
–50 –25
700
VCC = 5V
RPROG = 10k
RDS(ON) (mΩ)
4.09
200
5.0
Power FET “ON” Resistance
vs Temperature
VRECHRG (V)
500
ONSET OF
THERMAL
REGULATION
4.5
4054 G18
4.11
VCC = 5V
VBAT = 4V
θJA = 80°C/W
4.0
Recharge Voltage Threshold
vs Temperature
RPROG = 2k
IBAT (mA)
0
4.5
4054 G17
Charge Current vs Ambient
Temperature
300
RPROG = 10k
100
4054 G16
600
ONSET OF
THERMAL
REGULATION
400
IBAT (mA)
400
2.925
IBAT (mA)
VTRIKL (V)
2.950
400
–25
50
25
0
TEMPERATURE (°C)
75
100
4054 G20
350
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
4054 G21
405442xf
5
LTC4054-4.2/LTC4054X-4.2
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PI FU CTIO S
CHRG (Pin 1): Open-Drain Charge Status Output. When
the battery is charging, the CHRG pin is pulled low by an
internal N-channel MOSFET. When the charge cycle is
completed, a weak pull-down of approximately 20µA is
connected to the CHRG pin, indicating an “AC present”
condition. When the LTC4054 detects an undervoltage
lockout condition, CHRG is forced high impedance.
PROG (Pin 5): Charge Current Program, Charge Current
Monitor and Shutdown Pin. The charge current is programmed by connecting a 1% resistor, RPROG, to ground.
When charging in constant-current mode, this pin servos
to 1V. In all modes, the voltage on this pin can be used to
measure the charge current using the following formula:
GND (Pin 2): Ground.
The PROG pin can also be used to shut down the charger.
Disconnecting the program resistor from ground allows
a 3µA current to pull the PROG pin high. When it reaches
the 1.21V shutdown threshold voltage, the charger enters
shutdown mode, charging stops and the input supply
current drops to 25µA. This pin is also clamped to
approximately 2.4V. Driving this pin to voltages beyond
the clamp voltage will draw currents as high as 1.5mA.
Reconnecting RPROG to ground will return the charger to
normal operation.
BAT (Pin 3): Charge Current Output. Provides charge
current to the battery 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.
VCC (Pin 4): Positive Input Supply Voltage. Provides
power to the charger. VCC can range from 4.25V to 6.5V
and should be bypassed with at least a 1µF capacitor.
When VCC drops to within 30mV of the BAT pin voltage, the
LTC4054 enters shutdown mode, dropping IBAT to less
than 2µA.
IBAT = (VPROG/RPROG) • 1000
405442xf
6
LTC4054-4.2/LTC4054X-4.2
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BLOCK DIAGRA
4
VCC
120°C
1×
TA
1000×
TDIE
BAT
–
+
5µA
3
MA
R1
+
VA
CA
–
R2
–
+
–
SHDN
REF
1.21V
C1
+
R3
1V
R4
+
0.1V
C2
CHRG
1
R5
–
STANDBY
3µA
TRICKLE CHARGE
DISABLED ON
LTC4054X
+
TO
BAT
–
2.9V
VCC
C3
PROG
5
GND
RPROG
2
405442 BD
405442xf
7
LTC4054-4.2/LTC4054X-4.2
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OPERATIO
The LTC4054 is a single cell lithium-ion battery charger
using a constant-current/constant-voltage algorithm. It
can deliver up to 800mA of charge current (using a good
thermal PCB layout) with a final float voltage accuracy of
±1%. The LTC4054 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 components. Furthermore, the LTC4054 is capable of operating from a USB power source.
Normal Charge Cycle
A charge cycle begins when the voltage at the VCC pin rises
above the UVLO threshold level and a 1% program resistor
is connected from the PROG pin to ground or when a
battery is connected to the charger output. If the BAT pin
is less than 2.9V, the charger enters trickle charge mode.
In this mode, the LTC4054 supplies approximately 1/10
the programmed charge current to bring the battery voltage up to a safe level for full current charging. (Note: The
LTC4054X does not include this trickle charge feature).
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 LTC4054
enters constant-voltage mode and the charge current
begins to decrease. When the charge current drops to
1/10 of the programmed value, the charge cycle ends.
Programming Charge Current
The charge current is programmed using a single resistor
from the PROG pin to ground. The battery charge current
is 1000 times the current out of the PROG pin. The
program resistor and the charge current are calculated
using the following equations:
1000V
1000V
RPROG =
, ICHG =
ICHG
RPROG
The charge current out of the BAT pin can be determined
at any time by monitoring the PROG pin voltage using the
following equation:
IBAT =
VPROG
•1000
RPROG
Charge Termination
A charge cycle is terminated when the charge current falls
to 1/10th the programmed value after the final float voltage
is reached. This condition is detected by using an internal,
filtered comparator to monitor the PROG pin. When the
PROG pin voltage falls below 100mV1 for longer than
tTERM (typically 1ms), charging is terminated. The charge
current is latched off and the LTC4054 enters standby
mode, where the input supply current drops to 200µA.
(Note: C/10 termination is disabled in trickle charging and
thermal limiting modes).
When charging, transient loads on the BAT pin can cause
the PROG pin to fall below 100mV for short periods of time
before the DC charge current has dropped to 1/10th 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 termination. Once the average charge current drops below
1/10th the programmed value, the LTC4054 terminates
the charge cycle and ceases to provide any current through
the BAT pin. In this state, all loads on the BAT pin must be
supplied by the battery.
The LTC4054 constantly monitors the BAT pin voltage in
standby mode. If this voltage drops below the 4.05V
recharge threshold (VRECHRG), another charge cycle begins and 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 PROG
pin. Figure 1 shows the state diagram of a typical charge
cycle.
Charge Status Indicator (CHRG)
The charge status output has three different states: strong
pull-down (~10mA), weak pull-down (~20µA) and high
impedance. The strong pull-down state indicates that the
LTC4054 is in a charge cycle. Once the charge cycle has
terminated, the pin state is determined by undervoltage
Note 1: Any external sources that hold the PROG pin above 100mV will prevent the LTC4054
from terminating a charge cycle.
405442xf
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LTC4054-4.2/LTC4054X-4.2
U
OPERATIO
lockout conditions. A weak pull-down indicates that VCC
meets the UVLO conditions and the LTC4054 is ready to
charge. High impedance indicates that the LTC4054 is in
undervoltage lockout mode: either VCC is less than 100mV
above the BAT pin voltage or insufficient voltage is applied
to the VCC pin. A microprocessor can be used to distinguish between these three states—this method is discussed in the Applications Information section.
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 LTC4054 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 LTC4054. 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. ThinSOT power considerations are discussed further in the Applications Information section.
than 2µA and the supply current to less than 50µA. A new
charge cycle can be initiated by reconnecting the program
resistor.
In manual shutdown, the CHRG pin is in a weak pull-down
state as long as VCC is high enough to exceed the UVLO
conditions. The CHRG pin is in a high impedance state if
the LTC4054 is in undervoltage lockout mode: either VCC
is within 100mV of the BAT pin voltage or insufficient voltage
is applied to the VCC pin.
Automatic Recharge
Once the charge cycle is terminated, the LTC4054 continuously monitors the voltage on the BAT pin using a comparator with a 2ms filter time (tRECHARGE). A charge cycle
restarts when the battery voltage falls below 4.05V (which
corresponds to approximately 80% to 90% battery capacity). This ensures that the battery is kept at or near a fully
charged condition and eliminates the need for periodic
charge cycle initiations. CHRG output enters a strong pulldown state during recharge cycles.
POWER ON
BAT < 2.9V
Undervoltage Lockout (UVLO)
An internal undervoltage lockout circuit monitors the input
voltage and keeps the charger in shutdown mode until VCC
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 VCC
falls to within 30mV of the battery voltage. If the UVLO
comparator is tripped, the charger will not come out of
shutdown mode until VCC rises 100mV above the battery
voltage.
Manual Shutdown
At any point in the charge cycle, the LTC4054 can be put
into shutdown mode by removing RPROG thus floating the
PROG pin. This reduces the battery drain current to less
PROG
RECONNECTED
OR
UVLO CONDITION
STOPS
TRICKLE CHARGE
MODE
1/10TH FULL CURRENT
CHRG: STRONG
PULL-DOWN
BAT > 2.9V
SHUTDOWN MODE
CHARGE MODE
ICC DROPS TO 2.9V
PROG < 100mV
STANDBY MODE
NO CHARGE CURRENT
PROG FLOATED
OR
UVLO CONDITION
CHRG: WEAK
PULL-DOWN
2.9V < BAT < 4.05V
405442 F01
Figure 1. State Diagram of a Typical Charge Cycle
405442xf
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Stability Considerations
CHARGE
CURRENT
MONITOR
CIRCUITRY
10k
PROG
The constant-voltage mode feedback loop is stable without an output capacitor provided a battery is connected to
the charger output. With no battery present, an output
capacitor is recommended to reduce ripple voltage. When
using high value, low ESR ceramic capacitors, it is recommended to add a 1Ω 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. However, 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
resistance value for RPROG:
1
RPROG ≤
5
2π • 10 • CPROG
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
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.
LTC4054
RPROG
CFILTER
GND
405442 F02
Figure 2. Isolating Capacitive Load on PROG Pin and Filtering
Power Dissipation
The conditions that cause the LTC4054 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:
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 LTC4054 operating from a 5V USB supply is
programmed to supply 400mA full-scale current to a
discharged Li-Ion battery with a voltage of 3.75V. Assuming θJA is 150°C/W (see Board Layout Considerations), the
ambient temperature at which the LTC4054 will begin to
reduce the charge current is approximately:
TA = 120°C – (5V – 3.75V) • (400mA) • 150°C/W
TA = 120°C – 0.5W • 150°C/W = 120°C – 75°C
TA = 45°C
405442xf
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LTC4054-4.2/LTC4054X-4.2
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The LTC4054 can be used above 45°C ambient, but the
charge current will be reduced from 400mA. The approximate current at a given ambient temperature can be
approximated by:
IBAT =
120°C – TA
(VCC – VBAT ) • θJA
Using the previous example with an ambient temperature
of 60°C, the charge current will be reduced to approximately:
IBAT
60°C
=
=
5V – 3.75V • 150°C /W 187.5°C /A
(
120°C – 60°C
IBAT = 320mA
)
Moreover, when thermal feedback reduces the charge
current, the voltage at the PROG pin is also reduced
proportionally as discussed in the Operation section.
It is important to remember that LTC4054 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
Because of the small size of the ThinSOT package, it is very
important to use a good thermal PC board layout to
maximize the available charge current. The thermal path
for the heat generated by the IC is from the die to the
copper lead frame, through the package leads, (especially
the ground lead) to the PC board copper. The PC board
copper is the heat sink. The footprint copper pads should
be as wide as possible and expand out to larger copper
areas to spread and dissipate the heat to the surrounding
ambient. Feedthrough vias to inner or backside copper
layers are also useful in improving the overall thermal
performance of the charger. Other heat sources on the
board, not related to the charger, must also be considered
when designing a PC board layout because they will affect
overall temperature rise and the maximum charge current.
The following table lists thermal resistance for several
different board sizes and copper areas. All measurements
were taken in still air on 3/32" FR-4 board with the device
mounted on topside.
Table 1. Measured Thermal Resistance (2-Layer Board*)
COPPER AREA
TOPSIDE
BACKSIDE
BOARD
AREA
THERMAL RESISTANCE
JUNCTION-TO-AMBIENT
2500mm2
2500mm2
2500mm2
125°C/W
1000mm2
2500mm2
2500mm2
125°C/W
225mm2
2500mm2
2500mm2
130°C/W
100mm2
2500mm2
2500mm2
135°C/W
50mm2
2500mm2
2500mm2
150°C/W
*Each layer uses one ounce copper
Table 2. Measured Thermal Resistance (4-Layer Board**)
COPPER AREA
(EACH SIDE)
BOARD
AREA
THERMAL RESISTANCE
JUNCTION-TO-AMBIENT
2500mm2***
2500mm2
80°C/W
*Top and bottom layers use two ounce copper, inner layers use one ounce copper.
**10,000mm2 total copper area
Increasing Thermal Regulation Current
Reducing the voltage drop across the internal MOSFET
can significantly decrease the power dissipation in the IC.
This has the effect of increasing the current delivered to
the battery during thermal regulation. One method is by
dissipating some of the power through an external component, such as a resistor or diode.
Example: An LTC4054 operating from a 5V wall adapter is
programmed to supply 800mA full-scale current to a
discharged Li-Ion battery with a voltage of 3.75V. Assuming θJA is 125°C/W, the approximate charge current at an
ambient temperature of 25°C is:
IBAT =
120°C – 25°C
= 608mA
(5V – 3.75V)• 125°C / W
By dropping voltage across a resistor in series with a 5V
wall adapter (shown in Figure 3), the on-chip power
dissipation can be decreased, thus increasing the thermally regulated charge current
IBAT =
120°C – 25°C
(VS – IBATRCC – VBAT )• θ JA
405442xf
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LTC4054-4.2/LTC4054X-4.2
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enough to put the LTC4054 into dropout. Figure 4 shows
how this circuit can result in dropout as RCC becomes
large.
VS
RCC
This technique works best when RCC values are minimized
to keep component size small and avoid dropout. Remember to choose a resistor with adequate power handling
capability.
VCC
BAT
1µF
LTC4054-4.2
Li-Ion
CELL
PROG
GND
RPROG
VCC Bypass Capacitor
405442 F03
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 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, refer to Application Note 88.
Figure 3. A Circuit to Maximize Thermal Mode Charge Current
Solving for IBAT using the quadratic formula2.
IBAT =
4R (120°C – TA )
(VS – VBAT ) – (VS – VBAT )2 CC
θ JA
2RCC
Using RCC = 0.25Ω, VS = 5V, VBAT = 3.75V, TA = 25°C and
θJA = 125°C/W we can calculate the thermally regulated
charge current to be:
Charge Current Soft-Start
The LTC4054 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 the
full-scale current over a period of approximately 100µs.
This has the effect of minimizing the transient current load
on the power supply during start-up.
IBAT = 708.4mA
While this application delivers more energy to the battery
and reduces charge time in thermal mode, it may actually
lengthen charge time in voltage mode if VCC becomes low
1000
VS = 5V
CONSTANT
CURRENT
CHARGE CURRENT (mA)
800
600
VS = 5.5V
400 THERMAL
MODE
VS = 5.25V
DROPOUT
VBAT = 3.75V
TA = 25°C
θJA = 125°C/W
RPROG = 1.25kΩ
200
0
0
0.25
0.5
0.75 1.0
RCC (Ω)
1.25
1.5
1.75
405442 F04
Figure 4. Charge Current vs RCC
Note 2: Large values of RCC will result in no solution for IBAT. This indicates that the LTC4054
will not generate enough heat to require thermal regulation.
405442xf
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LTC4054-4.2/LTC4054X-4.2
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CHRG Status Output Pin
The CHRG pin can provide an indication that the input
voltage is greater than the undervoltage lockout threshold
level. A weak pull-down current of approximately 20µA
indicates that sufficient voltage is applied to VCC to begin
charging. When a discharged battery is connected to the
charger, the constant current portion of the charge cycle
begins and the CHRG pin pulls to ground. The CHRG pin
can sink up to 10mA to drive an LED that indicates that a
charge cycle is in progress.
When the battery is nearing full charge, the charger enters
the constant-voltage portion of the charge cycle and the
charge current begins to drop. When the charge current
drops below 1/10 of the programmed current, the charge
cycle ends and the strong pull-down is replaced by the
20µA pull-down, indicating that the charge cycle has
ended. If the input voltage is removed or drops below the
undervoltage lockout threshold, the CHRG pin becomes
high impedance. Figure 5 shows that by using two
different value pull-up resistors, a microprocessor can
detect all three states from this pin.
V+
VCC
LTC4054
CHRG
To detect when the LTC4054 is in charge mode, force the
digital output pin (OUT) high and measure the voltage at
the CHRG pin. The N-channel MOSFET will pull the pin
voltage low even with the 2k pull-up resistor. Once the
charge cycle terminates, the N-channel MOSFET is turned
off and a 20µA current source is connected to the CHRG
pin. The IN pin will then be pulled high by the 2k pull-up
resistor. To determine if there is a weak pull-down current,
the OUT pin should be forced to a high impedance state.
The weak current source will pull the IN pin low through
the 800k resistor; if CHRG is high impedance, the IN pin
will be pulled high, indicating that the part is in a UVLO
state.
Reverse Polarity Input Voltage Protection
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, where the voltage drop must be kept low a Pchannel MOSFET can be used (as shown in Figure 6).
VDD
DRAIN-BULK
DIODE OF FET
VIN
800k
2k
µPROCESSOR
LTC4054
VCC
4054 F06
OUT
IN
405442 F05
Figure 5. Using a Microprocessor to Determine CHRG State
Figure 6. Low Loss Input Reverse Polarity Protection
405442xf
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
13
LTC4054-4.2/LTC4054X-4.2
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USB and Wall Adapter Power
The LTC4054 allows charging from both a wall adapter
and a USB port. Figure 7 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 10k program resistor are used to
increase the charge current to 600mA when the wall
adapter is present.
5V WALL
ADAPTER
600mA ICHG
USB POWER
500mA ICHG
LTC4054-4.2
3
BAT
D1
4
VCC
MP1
PROG
5
ICHG
+
SYSTEM
LOAD
Li-Ion
BATTERY
10k
1k
MN1
2k
405442 F07
Figure 7. Combining Wall Adapter and USB Power
405442xf
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LTC4054-4.2/LTC4054X-4.2
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PACKAGE DESCRIPTIO
S5 Package
5-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1635)
0.62
MAX
0.95
REF
2.90 BSC
(NOTE 4)
1.22 REF
1.4 MIN
3.85 MAX 2.62 REF
2.80 BSC
1.50 – 1.75
(NOTE 4)
PIN ONE
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.30 – 0.45 TYP
5 PLCS (NOTE 3)
0.95 BSC
0.80 – 0.90
0.20 BSC
0.01 – 0.10
1.00 MAX
DATUM ‘A’
0.30 – 0.50 REF
0.09 – 0.20
(NOTE 3)
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
1.90 BSC
S5 TSOT-23 0302
405442xf
15
LTC4054-4.2/LTC4054X-4.2
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TYPICAL APPLICATIO S
USB/Wall Adapter Power Li-Ion Charger
5V WALL
ADAPTER
BAT
VCC
1µF
1k
VIN = 5V
IBAT
3
+
LTC4054-4.2
4
USB
POWER
Full Featured Single Cell Li-Ion Charger
Li-Ion
CELL
4
2.5k
5
PROG
GND
2
10k
VCC
330Ω
100mA/
500mA
3
LTC4054-4.2
1
µC
BAT
1µF
500mA
CHRG
405442 TA05
GND
2
PROG
5
+
2k
SHDN
800mA Li-Ion Charger with External Power Dissipation
405442 TA02
VIN = 5V
Basic Li-Ion Charger with Reverse Polarity Input Protection
0.25Ω
4
1µF
800mA
VCC
BAT
3
GND
2
PROG
4
5V WALL
ADAPTER
LTC4054-4.2
5
VCC
BAT
3
500mA
LTC4054-4.2
+
1µF
1.25k
GND
2
PROG
5
+
2k
405442 TA03
405442 TA04
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC1732
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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
Simple ThinSOT Charger, No Blocking Diode, No Sense Resistor Needed
LTC1734L
Lithium-Ion Linear Battery Charger in ThinSOT
Low Current Version of LTC1734
LTC1998
Lithium-Ion Low Battery Detector
1% Accurate 2.5µA Quiescent Current, SOT-23
LTC4050
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,
Thermistor Interface
LTC4052
Monolithic Lithium-Ion Battery Pulse Charger
No Blocking Diode or External Power FET Required
LTC4053
USB Compatible Monolithic Li-Ion Battery Charger
Standalone Charger with Programmable Timer, Up to 1.25A Charge Current
LTC4054L
10mA to 150mA Standalone Monolithic Lithium-Ion Low Current Version of LTC4054
Linear Battery Charger in ThinSOT
LTC4056
Standalone Lithium-Ion Linear Battery Charger
in ThinSOT
Standalone Charger with Programmable Timer, No Blocking Diode,
No Sense Resistor Needed
LTC4057
Monolithic Lithium-Ion Linear Battery Charger
with Thermal Regulation in ThinSOT
No External MOSFET, Sense Resistor or Blocking Diode Required,
Charge Current Monitor for Gas Gauging
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
405442xf
16
Linear Technology Corporation
LT/TP 0903 1K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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