LTC3101
OPERATION
INTRODUCTION
An always-alive LDO provides a fixed 1.8V output at 50mA
which can be utilized to power critical functions such as a
realtimeclock.ReverseblockingallowstheLDOtobeused
tochargeasupercapacitorformemoryretentionwhenboth
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.
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 efficiency 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 configured 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.
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 LTC3101 can operate from any power source over the
wideinputvoltagerangeof1.8Vto5.5V.Allthreeswitching
DC/DCconvertersoperatefromacommon1.27MHzoscil-
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 extensive functionality and flexibility of the LTC3101,
along with its small size and high efficiency, make it an
excellent power solution for a wide variety of low power
portable electronic products.
PUSHBUTTON INTERFACE
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 efficiency 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-limitedoutputthatcanbeshortedwithoutaffecting
the primary buck-boost output. One use of the Hot Swap
output is to power external flash memory cards that need
to be hot-plugged without disrupting the primary buck-
boost output rail.
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
independentenablepinsallowanunusedDC/DCconverter
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
highorbyforcingPWRKEYlow. Ineithercase, theDC/DC
converters (if enabled by their respective enable pin)
will power up in the internally fixed default sequence:
buck converter 1, buck converter 2, and finally the buck-
boost converter. In the typical application, the power-on
sequenceisinitiatedwhenthePWRKEYisdrivenlowbyan
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
The synchronous buck converters are typically used to
provide two high efficiency 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.
3101f
13
Linear [ Linear ]
