LTC4081 Datasheet, PDF (1/24 Pages) Linear Technology – 500mA Li-Ion Charger with NTC Input and 300mA Synchronous Buck

FEATURES
Battery Charger:
■ _{Constant-Current/Constant-Voltage Operation}
with Thermal Feedback to Maximize Charge Rate
Without Risk of Overheating
■ _{Internal 4.5 Hour Safety Timer for Termination}
■ _{Charge Current Programmable Up to 500mA with}
5% Accuracy
■ _{NTC Thermistor Input for Temperature Qualified}
Charging
■ _{C/10 Charge Current Detection Output}
■ _{5μA Supply Current in Shutdown Mode}
Switching Regulator:
■ _{High Efficiency Synchronous Buck Converter}
■ _{300mA Output Current (Constant-Frequency Mode)}
■ _{2.7V to 4.5V Input Range (Powered from BAT Pin)}
■ _{0.8V to VBAT Output Range}
■ _{MODE Pin Selects Fixed (2.25MHz) Constant-Frequency}
PWM Mode or Low I_CC (23μA) Burst Mode^® Operation
■ _{2μA BAT Current in Shutdown Mode}
■ _{10-lead, low profile (0.75 mm) 3mm × 3mm DFN}
package
U
APPLICATIO S
■ _{Wireless Headsets}
■ _{Bluetooth Applications}
■ _{Portable MP3 Players}
■ _{Multifunction Wristwatches}
LTC4081
500mA Li-Ion Charger
with NTC Input and
300mA Synchronous Buck
DESCRIPTIO
The LTC4081 is a complete constant-current/constant-
voltage linear battery charger for a single-cell 4.2V
lithium-ion/polymer battery with an integrated 300mA
synchronous buck converter. A 3mm × 3mm DFN pack-
age and low external component count make the LTC4081
especially suitable for portable applications. Furthermore,
the LTC4081 is specifically designed to work within USB
power specifications.
The ^⎯C^⎯H^⎯R^⎯G pin indicates when charge current has
dropped to ten percent of its programmed value (C/10).
An internal 4.5 hour timer terminates the charge cycle.
The full-featured LTC4081 battery charger also includes
trickle charge, automatic recharge, soft-start (to limit inrush
current) and an NTC thermistor input used to monitor
battery temperature.
The LTC4081 integrates a synchronous buck converter
that is powered from the BAT pin. It has an adjustable
output voltage and can deliver up to 300mA of load cur-
rent. The buck converter also features low-current high-
efficiency Burst Mode operation that can be selected by
the MODE pin.
The LTC4081 is available in a 10-lead, low profile (0.75
mm) 3mm × 3mm DFN package.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Protected by U.S. Patents,
including 6522118.
TYPICAL APPLICATIO
Li-Ion Battery Charger with 1.8V Buck Regulator
V_CC
(3.75V
TO 5.5V)
100k
4.7μF
100k T
510Ω
V_CC
CHRG
EN_BUCK BAT
LTC4081
NTC
SW
1OμH
EN_CHRG
FB
500mA
10pF 1M
MODE GND PROG
806Ω
806k
+
4.7μF
4.2V
Li-Ion/
POLYMER
BATTERY
V_OUT
(1.8V/300mA)
4.7μF
4081 TA01a
Buck Efficiency vs Load Current
(V_OUT = 1.8V)
100
1000
EFFICIENCY
80 _(Burst)
EFFICIENCY
(PWM)
60
100
POWER
LOSS 10
(PWM)
40
20
0
0.01
POWER LOSS
1
(Burst)
V_BAT = 3.8V
V_OUT = 1.8V
0.1
L = 10μH
C = 4.7μF
0.01
0.1
1
10 100 1000
LOAD CURRENT (mA)
4081 TA01b
4081f
1