LTC4054L-4.2
150mA Standalone Linear
Li-Ion Battery Charger in ThinSOT
Description
Features
Programmable Charge Current Range:
10mA to 150mA
n No External MOSFET, Sense Resistor or Blocking
Diode Required
n Complete Linear Charger in ThinSOT™ Package for
Single Cell/Coin Cell Lithium-Ion Batteries
n Constant-Current/Constant-Voltage Operation with
Thermal Regulation* to Maximize Charge Rate
without Risk of Overheating
n Charges Single Cell Li-Ion Batteries Directly from
USB Port
n Preset 4.2V Charge Voltage with ±1% Accuracy
n Charge Current Monitor Output for Gas Gauging*
n Automatic Recharge
n Charge Status Output Pin
n C/10 Charge Termination
n 25µA Max Supply Current in Shutdown Mode
n 2.9V Trickle Charge Threshold
n Soft-Start Limits Inrush Current
n Available in a 5-Lead Low Profile (1mm)
SOT-23 Package
The LTC®4054L is a complete, constant-current/constantvoltage linear charger for single cell lithium-ion batteries.
Its small size and ability to regulate low charge currents
make the LTC4054L especially well-suited for portable applications using low capacity rechargeable lithium-ion coin
cells. Furthermore, the LTC4054L is specifically designed
to work within USB power specifications.
Applications
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.
n
n
Charger for Li-Ion Coin Cell Batteries
Portable MP3 Players, Wireless Headsets
Bluetooth Applications
Multifunction Wristwatches
Typical Application
When the input supply (wall adapter or USB supply) is
removed, the LTC4054L automatically enters a low current
state, dropping the battery drain current to less than 2µA.
The LTC4054L can be put into shutdown mode, reducing
the supply current to 25µA.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the property
of their respective owners. *Protected by U.S. Patents including 6,522,118.
Complete Charge Cycle (130mAh Battery)
100
90mA Li-Ion Single Coin Cell Charger
80
4
VCC
BAT
LTC4054L-4.2
PROG
GND
2
3
90mA
5
1.69k
4.2V
COIN CELL
Li-Ion
BATTERY
4054l42 TA01
4.4
CONSTANT
CURRENT
70
4.3
CONSTANT
VOLTAGE
4.2
4.1
60
4.0
50
3.9
40
3.8
30
20
10
0
3.7
VCC = 5V
θJA = 130°C/W
RPROG = 1.69k
TA = 25°C
BATTERY VOLTAGE (V)
VIN
4.5V TO 6.5V
1µF
90
CHARGE CURRENT (mA)
n
n
n
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 eliminate
thermal overdesign. The charge voltage is fixed at 4.2V, and
the charge current can be programmed externally with a
single resistor. The LTC4054L automatically terminates a
charge cycle when the charge current drops to 1/10th the
programmed value after the final float voltage is reached.
3.6
3.5
3.4
0 0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0 2.25
TIME (HOURS)
4054l42 TA01b
4054l42fa
1
LTC4054L-4.2
Absolute Maximum Ratings
Pin Configuration
(Note 1)
TOP VIEW
Input Supply Voltage (VCC)......................... –0.3V to 10V
PROG................................................–0.3V to VCC + 0.3V
CHRG.......................................................... –0.3V to 10V
BAT............................................................... –0.3V to 7V
BAT Short-Circuit Duration............................ Continuous
BAT Pin Current................................................... 200mA
PROG Pin Current..................................................1.5mA
Maximum Junction Temperature........................... 125°C
Operating Temperature Range (Note 2)....–40°C to 85°C
Storage Temperature Range................... –65°C to 125°C
Lead Temperature (Soldering, 10 sec).................... 300°C
CHRG 1
5 PROG
GND 2
BAT 3
4 VCC
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
TJMAX = 125°C, θJA = 80°C/W TO 150°C/W
DEPENDING ON PCB BOARD LAYOUT (NOTE 3)
Order Information
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
LTC4054LES5-4.2#PBF
LTC4054LES5-4.2#TRPBF LTAFA
PACKAGE DESCRIPTION
TEMPERATURE RANGE
5-Lead Plastic TSOT-23
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
Electrical
Characteristics
The
l denotes the 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
VCC
Supply Voltage
ICC
Supply Current
Charge Mode (Note 4), RPROG = 1k
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 = 15k, Current Mode
RPROG = 1k, Current Mode
Standby Mode, VBAT = 4.2V
Shutdown Mode (RPROG Not Connected)
Sleep Mode, VCC = 0V
l
l
l
l
l
ITRIKL
Trickle Charge Current
VBAT < VTRIKL, RPROG = 1k (IBAT = 150mA)
VTRIKL
Trickle Charge Threshold Voltage
RPROG = 15k, VBAT Rising
VTRHYS
Trickle Charge Hysteresis Voltage
RPROG = 15k
From VCC Low to High
VUV
VCC Undervoltage Lockout Threshold Voltage
VUVHYS
VCC Undervoltage Lockout Hysteresis Voltage
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
TYP
MAX
6.5
V
1200
200
25
2000
500
50
µA
µA
µA
4.158
4.2
4.242
V
9.3
142.5
0
10
150
–2.5
±1
±1
10.7
157.5
–6
±2
±2
mA
mA
µA
µA
µA
4.25
l
l
l
UNITS
5
15
25
mA
2.8
2.9
3
V
60
80
110
mV
l
3.7
3.8
3.92
V
l
150
200
300
mV
l
l
1.15
0.9
1.21
1.0
1.30
1.1
V
V
70
5
100
30
140
50
mV
mV
4054l42fa
2
LTC4054L-4.2
Electrical
Characteristics
The
l denotes the 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
ITERM
C/10 Termination Current Threshold
RPROG = 15k (IBAT = 10mA) (Note 5)
RPROG = 1k (IBAT = 150mA) (Note 5)
l
l
0.085
0.088
0.10
0.10
0.115
0.112
mA/mA
mA/mA
VPROG
PROG Pin Voltage
RPROG = 1k, Current Mode
l
0.93
1
1.07
V
ICHRG
CHRG Pin Weak Pull-Down Current
VCHRG = 5V
8
20
35
µA
VCHRG
CHRG Pin Output Low Voltage
ICHRG = 5mA
∆VRECHRG
Recharge Battery Hysteresis Voltage
VFLOAT – VRECHRG
TLIM
Junction Temperature in Constant
Temperature Mode
120
°C
RON
Power FET “ON” Resistance
(Between VCC and BAT)
1.5
Ω
tSS
Soft-Start Time
IBAT = 0 to IBAT =150V/RPROG
100
µs
100
0.35
0.6
V
150
200
mV
tRECHARGE
Recharge Comparator Filter Time
VBAT High to Low
0.75
2
4.5
ms
tTERM
Termination Comparator Filter Time
IBAT Drops Below ICHG/10
400
1000
2500
µs
IPROG
PROG Pin Pull-Up Current
1.5
3
5
µA
Note 3: See Thermal Considerations.
Note 4: Supply current includes PROG pin current (≈1mA) but does not
include any current delivered to the battery through the BAT pin.
Note 5: ITERM is expressed as a fraction of measured full charge current
with indicated PROG resistor.
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LTC4054LE-4.2 is 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.
Typical Performance Characteristics
PROG Pin Voltage vs Supply
Voltage (Constant Current Mode)
1.0100
PROG Pin Voltage vs Temperature
(Constant Current Mode)
1.0100
VCC = 5V
VBAT = 4V
TA = 25°C
1.0075
1.0075
1.0050
180
VCC = 5V
VBAT = 4V
RPROG = 1k
VCC = 5V
RPROG = 1k
TA = 25°C
150
1.0050
RPROG = 1k
1.0000
RPROG = 15k
0.9975
0.9975
0.9950
0.9950
0.9925
0.9925
4
4.5
5
5.5
VCC (V)
IBAT (mA)
1.0000
120
1.0025
VPROG (V)
VPROG (V)
1.0025
0.9900
Charge Current
vs PROG Pin Voltage
6
6.5
7
0.9900
–50
90
60
30
–25
0
50
25
TEMPERATURE (°C)
75
100
4054L G02
0
0
0.25
0.5
0.75
VPROG (V)
1
1.25
4054L G03
4054L G01
4054l42fa
3
LTC4054L-4.2
Typical Performance Characteristics
PROG Pin Pull-Up Current vs
Temperature and Supply Voltage
3.7
PROG Pin Current vs PROG Pin
Voltage (Pull-Up Current)
3.5
VBAT = 4.3V
VPROG = 0V
3.5
0
VCC = 5V
VBAT = 4.3V
TA = 25°C
3.0
–100
2.9
VCC = 4.2V
IPROG (µA)
VCC = 6.5V
IPROG (µA)
3.1
2.0
1.5
1.0
2.7
50
25
75
0
TEMPERATURE (°C)
100
2.1
2.2
2.3
2.4
VPROG (V)
4054L G04
Regulated Output (Float) Voltage
vs Charge Current
–200
–250
–350
0
2.0
125
–150
–300
0.5
2.5
–50 –25
–400
2.6
2.5
4.215
VCC = 5V
RPROG = 600Ω
4.24 TA = 25°C
4.210
4.215
VCC = 5V
RPROG = 1k
4.200
4.195
4.16
4.190
4.190
60
30
90
120
IBAT (mA)
150
180
4.185
–50
75
100
CHRG Pin Current vs Temperature
(Strong Pull-Down State)
1
2
4
3
VCHRG (V)
5
6
7
4054L G10
5
4.5
12
10
4
– 50 – 25
5.5
VCC (V)
6.5
6
7
4054L G09
18
14
16
14
12
VCC = 5V
VBAT = 4.3V
TA = 25°C
10
6
0
4
20
8
5
4054L G06
22
VCC = 5V
18 VBAT = 4V
VCHRG = 1V
16
10
5.5
CHRG Pin I-V Curve
(Weak Pull-Down State)
20
VCC = 5V
VBAT = 4V
TA = 25°C
15
0
4.185
4054L G08
ICHRG (mA)
ICHRG (mA)
20
0
25
50
TEMPERATURE (°C)
ICHRG (µA)
25
–25
4054L G07
CHRG Pin I-V Curve
(Strong Pull-Down State)
5
4.200
4.195
0
4.5
4
3.5
VPROG (V)
4.205
4.18
4.14
3
RPROG = 1k
TA = 25°C
4.210
VFLOAT (V)
VFLOAT (V)
4.20
2.5
Regulated Output (Float) Voltage
vs Supply Voltage
4.205
VFLOAT (V)
4.22
2
4054L G05
Regulated Output (Float) Voltage
vs Temperature
4.26
VCC = 5V
VBAT = 4.3V
TA = 25°C
–50
2.5
3.3
IPROG (µA)
PROG Pin Current vs PROG Pin
Voltage (Clamp Current)
75
50
25
TEMPERATURE (°C)
0
100
125
4054L G11
8
0
1
2
4
3
VCHRG (V)
5
6
7
4054L G12
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4
LTC4054L-4.2
Typical Performance Characteristics
CHRG Pin Current vs Temperature
(Weak Pull-Down State)
Trickle Charge Current
vs Temperature
28
Trickle Charge Current
vs Supply Voltage
15
VCC = 5V
VBAT = 4.3V
25 VCHRG = 5V
15
RPROG = 1k
12
RPROG = 1k
12
19
16
9
6
ITRKL (mA)
ITRKL (mA)
ICHRG (µA)
22
VCC = 5V
VBAT = 2.5V
3
13
9
VBAT = 2.5V
TA = 25°C
6
3
RPROG = 15k
10
–50
0
25
50
TEMPERATURE (°C)
–25
75
0
–50
100
–25
0
25
50
TEMPERATURE (°C)
RPROG = 15k
75
100
Trickle Charge Threshold
vs Temperature
Charge Current vs Battery Voltage
160
2.950
120
VCC = 5V
2.975 RPROG = 1k
IBAT (mA)
2.900
2.875
5
5.5
VCC (V)
6
6.5
7
4054L G15
VBAT = 4V
TA = 25°C
θJA = 125°C/W
160
RPROG = 1k
VCC = 5V
RPROG = 1k
TA = 25°C
θJA = 125°C/W
80
120
80
40
2.850
40
2.825
RPROG = 15k
–25
0
50
25
TEMPERATURE (°C)
75
0
100
2.7
4054L G16
Charge Current
vs Ambient Temperature
4.11
RPROG = 1k
4.09
VRECHRG (V)
ONSET OF
THERMAL
REGULATION
120
3.3
3.6
3.9
VBAT (V)
4.2
4.5
VBAT = 4V
90 VCC = 5V
θJA = 125°C/W
30
4.5
5
5.5
VCC (V)
6
6.5
7
4054L G18
Power FET “ON” Resistance
vs Temperature
1.8
VCC = 5V
RPROG = 1k
1.6
4.07
4.05
4.03
60
4
4054L G17
Recharge Voltage Threshold
vs Temperature
180
150
3.0
0
RDS(ON) (mΩ)
2.800
–50
IBAT (mA)
4.5
Charge Current vs Supply Voltage
200
IBAT (mA)
3.000
2.925
4
4054L G14
4054L G13
VTRKL (V)
0
VCC = 4.1V
VBAT = 4V
RPROG = 1k
1.4
1.2
1.0
4.01
RPROG = 15k
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
4054L G19
3.99
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
4054L G20
0.8
–50
–25
50
0
75
25
TEMPERATURE (°C)
100
125
4054L G21
4054l42fa
5
LTC4054L-4.2
Pin Functions
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 LTC4054L 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 is also 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
this float voltage and 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 LTC4054L enters shutdown mode, dropping IBAT to
less than 2µA.
IBAT = (VPROG/RPROG) • 150
4054l42fa
6
LTC4054L-4.2
Block Diagram
4
VCC
120°C
TA
TDIE
1×
150×
–
+
BAT
5µA
MA
3
R1
+
VA
R2
–
CA
+
–
REF
1.21V
–
SHDN
C1
R3
+
1V
R4
+
1
0.1V
C2
CHRG
R5
–
STANDBY
VCC
3µA
C3
–
+
2.9V
TO BAT
5
PROG
GND
2
RPROG
4054L42 BD
4054l42fa
7
LTC4054L-4.2
Operation
The LTC4054L is a single cell lithium-ion battery charger
using a constant-current/constant-voltage algorithm. Its
ability to control charge currents as low as 10mA make it
well-suited for charging low capacity lithium-ion coin cell
batteries. The LTC4054L includes an internal P-channel
power MOSFET and thermal regulation circuitry. No blocking diode or external sense resistor is required; thus, the
basic charger circuit requires only three external components. Furthermore, the LTC4054L is capable of operating
from a USB power source.
Normal Charge Cycle
The charge cycle begins when the voltage at the VCC pin
rises above the UVLO 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 LTC4054L supplies approximately 1/10 the
programmed charge current in order to bring the battery
voltage 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 LTC4054L
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 150 times the current out of the PROG pin. The program
resistor and the charge current are calculated using the
following equations:
RPROG =
150V
150V
, I CHG =
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
•150
RPROG
Charge Termination
The 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 LTC4054L enters standby
mode, where the input supply current drops to 200µA.
(Note: C/10 termination is disabled in trickle charging and
thermal limiting modes.)
While 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 for longer than tTERM , the LTC4054L
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 LTC4054L 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.
1Any external sources that hold the PROG pin above 100mV will prevent the LTC4054L from
terminating a charge cycle.
4054l42fa
8
LTC4054L-4.2
Operation
POWER ON
BAT < 2.9V
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
PROG FLOATED
OR
UVLO CONDITION
NO CHARGE CURRENT
CHRG: WEAK
PULL-DOWN
2.9V < BAT < 4.05V
4054L42 F01
Figure 1. 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
LTC4054L is in a charge cycle. Once the charge cycle has
terminated, the pin state is determined by undervoltage
lockout conditions. A weak pull-down indicates that VCC
meets the UVLO conditions and the LTC4054L is ready
to charge. High impedance indicates that LTC4054L is in
undervoltage lock-out mode: either VCC is within 100mV
of 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 LTC4054L 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 LTC4054L. 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.
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.
4054l42fa
9
LTC4054L-4.2
Operation
Manual Shutdown
Automatic Recharge
At any point in the charge cycle, the LTC4054L can be put
into shutdown mode by removing RPROG thus floating
the PROG pin. This reduces the battery drain current to
less than 2µA and the supply current to less than 50µA.
A new charge cycle can be initiated by reconnecting the
program resistor.
Once the charge cycle is terminated, the LTC4054L 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 pull-down state during recharge cycles.
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 LTC4054L is in undervoltage lockout mode: either
VCC is within 100mV of the BAT pin voltage or insufficient
voltage is applied to the VCC pin.
4054l42fa
10
LTC4054L-4.2
Applications Information
Stability Considerations
Power Dissipation
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.
The conditions that cause the LTC4054L 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 from the internal
MOSFET—this is calculated to be approximately:
In constant-current mode, the PROG pin is in the feedback
loop, not the battery. The constant-current mode stability is affected by the impedance at the PROG pin. With
no additional capacitance on the PROG pin, the charger
is stable with program resistor values as high as 20k.
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:
RPROG ≤
1
5
2π •10 •CPROG
CHARGE
CURRENT
MONITOR
CIRCUITRY
10k
PROG
RPROG
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 LTC4054L operating from a 6V wall adapter
is programmed to supply 150mA full-scale current to a
discharged Li-Ion battery with a voltage of 3.75V. Assuming θJA is 200°C/W, the ambient temperature at which
the LTC4054L will begin to reduce the charge current is
approximately:
TA = 120°C – (6V – 3.75V) • (150mA) • 200°C/W
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.
LTC4054L
PD = (VCC – VBAT) • IBAT
CFILTER
GND
4054L42 F02
Figure 2. Isolating Capacitive Load on PROG Pin and Filtering
TA = 120°C – 0.3375W • 200°C/W = 120°C – 67.5°C
TA = 52.5°C
The LTC4054L can be used above 52.5°C, but the charge
current will be reduced from 150mA. 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 =
120°C – 60°C
60°C
=
(6V – 3.75V ) • 200°C/W 450°C/A
IBAT = 133mA
4054l42fa
11
LTC4054L-4.2
Applications Information
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 LTC4054L 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
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
VCC 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 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.
Charge Current Soft-Start
The LTC4054L 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.
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.
*Each layer uses one ounce copper
4054l42fa
12
LTC4054L-4.2
Applications Information
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 3 shows that by using two different value pull-up resistors, a microprocessor can detect
all three states from this pin.
To detect when the LTC4054L 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.
V+
VCC
LTC4054L
CHRG
VDD
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 P‑channel MOSFET
can be used (as shown in Figure 4).
USB and Wall Adapter Power
The LTC4054L allows charging from both a wall adapter
and a USB port. Figure 5 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.
DRAIN-BULK
DIODE OF FET
LTC4054L
VCC
VIN
4054L42 F04
Figure 4. Low Loss Input Reverse Polarity Protection
5V WALL
ADAPTER
BAT
LTC4054L-4.2
D1
800k
2k
µPROCESSOR
USB
POWER
4
MP1
1k
OUT
IN
3
VCC
PROG
5
100mA
+
SYSTEM
LOAD
Li-Ion
BATTERY
1.5k
4054l42 F05
4054L42 F03
Figure 3. Using a Microprocessor to Determine CHRG State
Figure 5. Combining Wall Adapter and USB Power
4054l42fa
13
LTC4054L-4.2
Package Description
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
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 REV B
4054l42fa
14
LTC4054L-4.2
Revision History
REV
DATE
DESCRIPTION
A
8/11
Corrected lead count on last bullet item in Features.
PAGE NUMBER
1
4054l42fa
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.
15
LTC4054L-4.2
Typical Application
Full Featured Single Cell Li-Ion Charger
Basic Li-Ion Battery Charger with
Reverse Polarity Input Protection
VIN = 5V
CHARGING
4
VCC
330Ω
1
BAT
LTC4054L-4.2
CHRG
GND
2
PROG
3
4
5V WALL
ADAPTER
1µF
100mA
BAT
LTC4054L-4.2
1µF
5
VCC
+
GND
2
1.5k
PROG
3
5
100mA
+
1.5k
4054L42 TA03
SHDN
4054L42 TA02
USB/Wall Adapter Power Li-Ion Charger
5V WALL
ADAPTER
BAT
4
USB
POWER
1µF
1k
3
+
LTC4054L-4.2
VCC
PROG
GND
2
100mA
Li-Ion
CELL
5
1.5k
4054L42 TA05
Related Parts
PART NUMBER
DESCRIPTION
COMMENTS
LTC1731
Lithium-Ion Linear Battery Charger Controller
Simple Charger uses External FET, Features Preset Voltages, C/10 Charger
Detection and Programmable Timer
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
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, Safety Current Limit
LTC4053
USB Compatible Monolithic Li-Ion Battery Charger
Standalone Charger with Programmable Timer, Up to 1.25A Charge Current
LTC4054
800mA Standalone Linear Li-Ion Battery Charger with
Thermal Regulation in ThinSOT
No External MOSFET, Sense Resistor or Blocking Diode Required, Charge
Current Monitor for Gas Gauging, C/10 Charge Termination
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
LTC4058
950mA Standalone Li-Ion Charger in 3mm × 3mm DFN
USB Compatible, Thermal Regulation Protects Against Overheating
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
4054l42fa
16 Linear Technology Corporation
LT 0811 REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
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