LTC3455
Dual DC/DC Converter
with USB Power Manager
and Li-Ion Battery Charger
U
DESCRIPTIO
FEATURES
The LTC®3455 is a complete power management solution
for a variety of portable applications. The device contains
two synchronous step-down DC/DC converters, a USB
power controller, a full-featured Li-Ion battery charger, a
Hot Swap output, a low-battery indicator, and numerous
internal protection features. The LTC3455 provides a
small, simple solution for obtaining power from three
differentpowersources:asingle-cellLi-Ionbattery, aUSB
port, and a wall adapter. Current drawn from the USB bus
isaccuratelylimitedunderallconditions. WheneveraUSB
or a wall adapter is present, the battery charger is enabled
and all internal power for the device is drawn from the
appropriate external power source. All outputs are dis-
charged to ground during shutdown to provide complete
output disconnect. The device is available in a
4mm × 4mm 24-pin exposed-pad QFN package.
■
Seamless Transition between Input Power Sources:
Li-Ion Battery, USB, and 5V Wall Adapter
■
Accurate USB Current Limiting (500mA/100mA)
■
Two High Efficiency DC/DC Converters: Up to 96%
■
Thermal Regulation Maximizes Battery Charge
Rate without Risk of Overheating*
Full-Featured Li-Ion Battery Charger
■
■
Hot Swap™ Output for SDIO and Memory Cards
Pin-Selectable Burst Mode® Operation
■
■
Output Disconnect: All Outputs Discharged to
Ground During Shutdown
■
Available in a 4mm × 4mm × 0.8mm 24-Pin
QFN Package
U
APPLICATIO S
■
Handheld Computers
Digital Cameras
MP3 Players
, LTC and LT are registered trademarks of Linear Technology Corporation.
■
Hot Swap is a trademark of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
*U.S. Patent 6,522,118
■
U
TYPICAL APPLICATIO
8
21
15
19
22
20
23
USB 5V
1Ω
USB
MODE
HSON
ON2
6
SUSPEND
USB
Efficiency
5
4.7µF
CONTROLLER
µC
USBHP
PWRON
RST
100
10
SWITCHER 2
OUT2
WALL 5V
V
MAX
V
= 3.3V
95
90
85
80
75
70
65
60
PBSTAT
10µF
1Ω
1µF
1M
1M
ON/OFF
LTC3455
3.32k
1k
1.8V
4
SWITCHER 1
V = 1.8V
OUT1
CHRG
24
14
11
ON
WALLFB
0.1µF
3.3V, HS
HSO
3
2
1.24k
1µF
TIMER
PROG
13
12
HSI
2.49k
4.7µH
9
3.3V
0.5A
SW2
V
BAT
10pF
249k
4.7µF
1M
18
7
SINGLE
CELL Li-ION
3.3V TO 4.2V
1.8V
10µF
FB2
+
V
= 3.6V
BAT
80.6k
17
16
LBO
AO
AI
1
10
100
1000
4.7µH
10pF
V
BAT
1.8V
0.4A
SW1
LOAD CURRENT (mA)
2.49M
100k
3455 TA01b
1
10µF
FB1
25
806k
80.6k
GND
3455 TA01a
3455f
1