Datasheet

LTC3101
13
3101fb
OPERATION
INTRODUCTION
The LTC3101 provides a complete power management
solution for low power portable devices. It generates a
total of six output voltage rails and provides a seamless,
automatic transition between two input power sources.
The LTC3101 contains three high effi ciency synchronous
DC/DC converters: a 5-switch buck-boost DC/DC con-
verter and two synchronous 3-switch step-down DC/DC
converters. The buck-boost DC/DC converter is typically
utilized to provide a 3V or 3.3V rail that lies within the
input voltage range. The two step-down converters can
be confi gured to provide two lower voltage output rails,
such as a 1.8V rail for SDRAM and a 1.2V rail to supply
the system microprocessor.
The LTC3101 can operate from any power source over the
wide input voltage range of 1.8V to 5.5V. All three switching
DC/DC converters operate from a common 1.27MHz oscil-
lator and a single pin can be used to place all three DC/DC
converters into Burst Mode operation to reduce the total
no-load quiescent current with all six output voltage rails
active to only 38µA (typical). In standby operation, with
only the LDO and MAX outputs active, the input current
is reduced to 15µA (typical).
The 5-switch buck-boost DC/DC converter generates a
user-programmable output voltage rail that can lie within
the voltage range of the input power sources. Utilizing
a proprietary switching algorithm, the buck-boost con-
verter maintains high effi ciency and low noise operation
with input voltages that are above, below, or even equal
to the required output rail. A protected Hot Swap output
powered by the buck-boost output voltage rail is enabled
once the buck-boost reaches regulation. This provides a
current-limited output that can be shorted without affecting
the primary buck-boost output. One use of the Hot Swap
output is to power external fl ash memory cards that need
to be hot-plugged without disrupting the primary buck-
boost output rail.
The synchronous buck converters are typically used to
provide two high effi ciency lower voltage rails and sup-
port 100% duty cycle operation to extend battery life. The
output voltage of each buck converter is independently
user programmable and can be set as low as 0.6V.
An always-alive LDO provides a fi xed 1.8V output at 50mA
which can be utilized to power critical functions such as a
real time clock. Reverse blocking allows the LDO to be used
to charge a supercapacitor for memory retention when both
power sources are removed. The MAX output generates
a secondary always-alive, current-limited output rail that
tracks the higher voltage input power source (battery or
USB) and is convenient for powering additional external
LDOs and circuitry that can function directly from a wide
input voltage range.
A pushbutton interface and internal supply sequencing
complete the LTC3101 as a total power supply solution
while requiring only a minimal number of supporting
external components. Integral to the pushbutton control
is an internal microprocessor reset generator with a reset
duration that can be easily programmed using a single
external capacitor allowing the interface to be customized
to each particular application.
The extensive functionality and fl exibility of the LTC3101,
along with its small size and high effi ciency, make it an
excellent power solution for a wide variety of low power
portable electronic products.
PUSHBUTTON INTERFACE
The LTC3101 includes a pushbutton interface that allows
a single momentary pushbutton to control the sequenced
power-up and power-down of all output rails in coordina-
tion with an external microprocessor. In addition, three
independent enable pins allow an unused DC/DC converter
to be independently disabled and also provide the means
to manually implement an alternate power-up sequence.
The LTC3101 can be enabled by either forcing PWRON
high or by forcing PWRKEY low. In either case, the DC/DC
converters (if enabled by their respective enable pin)
will power up in the internally fi xed default sequence:
buck converter 1, buck converter 2, and fi nally the buck-
boost converter. In the typical application, the power-on
sequence is initiated when the PWRKEY is driven low by an
external momentary pushbutton. Once the microproces-
sor is powered up it must assert PWRON high before the
pushbutton is released, thereby forcing the LTC3101 to