LTC3550
Dual Input USB/AC Adapter
Li-Ion Battery Charger with
600mA Buck Converter
U
DESCRIPTIO
FEATURES
TheLTC®3550isastandalonelinearchargerwitha600mA
monolithic synchronous buck converter. It is capable of
chargingasingle-cellLi-Ionbatteryfrombothwalladapter
and USB inputs. The charger automatically selects the
appropriate power source for charging.
■
Charges Single-Cell Li-Ion Battery from Wall
Adapter and USB Inputs
■
Automatic Input Power Detection and Selection
■
Charge Current Programmable Up to 950mA from
Wall Adapter Input
■
Adjustable Output, High Efficiency 600mA
Internal thermal feedback regulates the battery charge
currenttomaintainaconstantdietemperatureduringhigh
power operation or high ambient temperature conditions.
The float voltage is fixed at 4.2V and the charge currents
are programmed with external resistors. The LTC3550
terminates the charge cycle when the charge current
drops below the programmed termination threshold after
the final float voltage is reached. With power applied to
both inputs, the LTC3550 can be put into shutdown mode
reducing the DCIN supply current to 20μA, the USBIN
supply current to 10μA, and the battery drain current to
less than 2μA.
Synchronous DC/DC Converter
■
No External MOSFET, Sense Resistor or Blocking
Diode Needed
■
Thermal Regulation Maximizes Charge Rate Without
Risk of Overheating*
■
Preset Charge Voltage with 0.6ꢀ Accuracy
■
Programmable Charge Current Termination
■
1.5MHz Constant Frequency Operation (Step-Down
Converter)
18μA USB Suspend Current in Shutdown
■
■
“Power Present” Status Output
Charge Status Output
Automatic Recharge
■
■
■
The DC/DC converter switching frequency is internally
set at 1.5MHz, allowing the use of small surface mount
inductors and capacitors.
, 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, includng 6522118, 6700364, 6580258, 5481178, 6304066,
6127815, 6498466, 6611131
Available in a Thermally Enhanced, Low Profile
(0.75mm) 16-LeUad (5mm × 3mm) DFN Package
APPLICATIO S
■
Cellular Telephones
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TYPICAL APPLICATIO
Complete Charge Cycle
(1100mA Battery)
1000
800
Dual Input Battery Charger and DC/DC Converter
600
2.2µH
V
OUT
400
200
0
4.2
4.0
3.8
3.6
3.4
1.2V
SW
600mA
C
OUT
10µF
CONSTANT VOLTAGE
USBIN = 5V
LTC3550
22pF
301k
301k
CER
WALL
DCIN
V
FB
ADAPTER
RUN
T
= 25°C
A
IDC
IUSB
USB
PORT
R
R
= 1.24k
800mA (WALL)
500mA (USB)
USBIN
IUSB
IDC
V
CC
= 2k
1µF
BAT
5.0
2.5
0
2k
1%
4.7µF
ITERM
4.2V
+
1µF
GND
2k
1%
1.24k
1%
SINGLE-CELL
Li-Ion BATTERY
0
0.5
1.0
1.5
2.0
2.5
3.0
TIME (HR)
3550 TA01
3550 TA02
3550fa
1