n General Purpose Battery Charger Controller
n Efﬁcient 550kHz Synchronous Buck PWM Topology
n ±0.5% Output Float Voltage Accuracy
n Programmable Charge Current: 4% Accuracy
n Programmable AC Adapter Current Limit:
wwwn.DaNtoaSAhueedti4bUl.ecoNmoise with Ceramic Capacitors
n Wide Input Voltage Range: 6V to 28V
n Wide Output Voltage Range: 2V to 28V
n Indicator Outputs for AC Adapter Present, Charging,
C/10 Current Detection and Input Current Limiting
n Analog Charge Current Monitor
n Micropower Shutdown
n Thermally Enhanced 20-Pin 4mm × 4mm × 0.75mm
n Notebook Computers
n Portable Instruments
n Battery Backup Systems
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents including 5723970.
The LTC4009 is a constant-current/constant-voltage battery
charger controller. It uses a synchronous quasi-constant
frequency PWM control architecture that will not generate
audible noise with ceramic bulk capacitors. Charge cur-
rent is set by the combination of external sense, input and
programming resistors. With no built-in termination, the
LTC4009 family charges a wide range of batteries under
The LTC4009 features a fully adjustable output voltage, while
the LTC4009-1 and LTC4009-2 can be pin-programmed for
lithium-ion/polymer battery packs of 1-, 2-, 3- or 4-series
cells. The LTC4009-1 provides output voltage of 4.1V/cell,
and the LTC4009-2 is a 4.2V/cell version.
The device includes AC adapter input current limiting which
maximizes the charge rate for a ﬁxed input power level. An
external sense resistor programs the input current limit, and
the ICL status pin indicates when the battery charge current
is being reduced as a result of AC adapter current limiting.
The CHRG status pin is active during all charging modes,
including special indication for low charge current.
13V TO 20V
Efﬁciency at DCIN = 20V
VFLOAT = 12.3V
RSENSE = 33mΩ
RIN = 3.01k
RPROG = 26.7k
DIN = SSB44
L = IHLP-2525CZ 6.8μH
0.5 1.0 1.5 2.0 2.5 3.0
CHARGE CURRENT (A)