LTC3456 Datasheet, PDF (12/28 Pages) Linear Technology – 2-Cell, Multi-Output DC/DC Converter with USB Power Manager

LTC3456
U
OPERATIO
INTRODUCTION
The LTC3456 is a complete system-level power supply IC
used to power GPS portable navigators and other portable
systems. It takes power from one of three sources: battery,
USB or wall adapter. The device provides an integrated
standard solution resulting in a reduced parts count and
higher efficiency.
The LTC3456 generates two separate power supplies: a
Core supply for the processor and a Main supply for the
peripheral circuitry. The Main supply is a fixed 3.3V output
and the Core supply voltage can be adjusted from 0.8V to
V_BATT(MIN). In addition, the LTC3456 provides a Hot Swap
output which can be used for powering flash memory
cards. Both regulators utilize a 1MHz constant frequency
current mode architecture.
The device also incorporates a low-battery detector
(configurable as a low dropout regulator), USB power
manager and several protection features in a single pack-
age. The LTC3456’s control scheme allows 100% duty
cycle operation for the core output. It provides low dropout
operation when the core output is powered from the
battery, thereby extending battery life.
OPERATING MODES
The LTC3456 is powered from an AC wall adapter, USB or
battery, in that order of priority. It has onboard voltage
detectors to monitor the status of the wall adapter and USB
voltages. The unique control scheme of the LTC3456
allows seamless transition between battery, USB and wall
adapter input power sources.
Battery Powered
The LTC3456 is designed to accept an input battery
voltage range from 1.8V to 3.2V. This range is ideal for
2-cell Alkaline, NiCd or NiMH designs. Figure 2 shows an
LTC3456 being powered from two AA cells.
When enabled, the internal supply voltage V_INT (3.3V) is
generated via the boost regulator. V_INT is used to power
the bandgap reference, drivers and other internal circuitry.
Core output (1.8V) comes up next via the buck regulator.
Main output and the Hot Swap output are powered up with
a delay after the core output is in regulation.
V_BATT
2 AA CELLS ⁺
1.8V TO 3.2V
V_BATT
4
LTC3456
BUCK
L2
4.7µH
SW2_BST
14
BOOST
SW1
5
L1
10µH
V_INT
15
V_MAIN
16
R
–
+^VOS
HSO
17
3456 F02
Figure 2. Battery-Powered LTC3456
10µF
CORE OUTPUT
1.8V
200mA
V_INT
3.3V
22µF
MAIN OUTPUT
3.3V
1µF ^150mA
Hot Swap OUTPUT
3.3V
1µF ^50mA
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