LTC4008
4A, High Efficiency,
Multi-Chemistry Battery Charger
FEATURES
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DESCRIPTIO
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General Purpose Charger Controller
High Conversion Efficiency: Up to 96%
Output Currents Exceeding 4A
±0.8%
Voltage Accuracy
AC Adapter Current Limiting Maximizes
Charge Rate*
Thermistor Input for Temperature Qualified Charging
Wide Input Voltage Range: 6V to 28V
Wide Output Voltage: 3V to 28V
0.5V Dropout Voltage; Maximum Duty Cycle: 98%
Programmable Charge Current:
±4%
Accuracy
Indicator Outputs for Charging, C/10 Current
Detection, AC Adapter Present, Input Current
Limiting and Faults
Charging Current Monitor Output
Available in a 20-Pin Narrow SSOP Package
The LTC
®
4008 is a constant-current/constant-voltage
charger controller. The PWM controller uses a synchro-
nous, quasi-constant frequency, constant off-time archi-
tecture that will not generate audible noise even when
using ceramic capacitors. Charging current is program-
mable with a sense resistor and programming resistor to
±4%
typical accuracy. Charging current can be monitored
as a voltage across the programming resistor. An external
resistor divider and precision internal reference set the
final float voltage.
The LTC4008 includes a thermistor sensor input that will
suspend charging if an unsafe temperature condition is
detected and will automatically resume charging when
battery temperature returns to within safe limits; a FAULT
pin indicates this condition. A FLAG pin indicates when
charging current has decreased below 10% of the pro-
grammed current. An external sense resistor programs
AC adapter current limiting. The I
CL
pin indicates when the
charging current is being reduced by input current limiting
so that the charging algorithm can adapt.
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
*Protected by U.S. Patents including 5723970
APPLICATIO S
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Notebook Computers
Portable Instruments
Battery Backup Systems
TYPICAL APPLICATIO
DCIN
0V TO 28V
12.3V, 4A Li-Ion Charger
INPUT SWITCH
0.1µF
140k*
V
LOGIC
100k
I
CL
ACP
FAULT
FLAG
32.4k
100k
LTC4008
BATMON
DCIN
V
FB
I
CL
ACP/SHDN
FAULT
FLAG
NTC
R
T
INFET
CLP
CLN
TGATE
BGATE
PGND
CSP
BAT
PROG
3.01k
3.01k
CHARGING
CURRENT
MONITOR
Q2
20µF
Li-Ion
BATTERY
Q1
0.1µF
4.99k
20µF
10µH
0.025Ω
0.02Ω
SYSTEM
LOAD
15k*
THERMISTOR
10k
NTC
150k
0.47µF
6.04k
0.12µF
I
TH
GND
0.0047µF
26.7k
Q1: Si4431BDY
Q2: FDC645N
4008 TA01
NOTE: * 0.25% TOLERANCE
ALL OTHER RESISTORS ARE 1% TOLERANCE
U
4008fa
U
U
1
LINER [ LINEAR TECHNOLOGY ]
