LTC3118_15 Datasheet, PDF (12/38 Pages) Linear Technology – 18V, 2A Buck-Boost DC/DC Converter with Low-Loss Dual Input PowerPath

LTC3118
Operation
Introduction
The LTC3118 is a dual-input, current mode, monolithic
buck-boost DC/DC converter that can operate over a wide
input voltage range of 2.2V to 18V. The output voltage
can be programmed between 2V to 18V and deliver more
than 2A of load current. The LTC3118 operates from either
V_IN1 or V_IN2 depending on the state of the SEL pin. If SEL
is commanded to be a logic high, V_OUT will be powered
from the highest valid input voltage. If SEL is a logic low,
V_OUT will be powered from V_IN1 (priority mode) assuming
sufficient input voltage is present. Internal, low R_DS(ON)
N-channel power switches reduce the solution complexity
and maximize efficiency.
A proprietary switch algorithm allows the buck-boost
converter to maintain output voltage regulation with in-
put voltages that are above, below or equal to the output
voltage. Transitions between the step-up or step-down
operating modes are seamless and free of transients and
subharmonic switching, making this product ideal for noise
sensitive applications. The LTC3118 operates at a fixed
nominal switching frequency of 1.2MHz, which provides
an ideal trade-off between small solution size and high
efficiency. Current mode control provides inherent input
line voltage rejection, simplified compensation and rapid
response to load transients. Burst Mode operation capabil-
ity is also included in the LTC3118 and is user-selected
via the MODE input pin. In Burst Mode operation, the
LTC3118 provides exceptional efficiency at light output
loads by operating the converter only when necessary to
maintain voltage regulation. At higher loads, the LTC3118
automatically transitions to fixed frequency PWM mode
when Burst Mode operation is selected.
For 5V V_OUT applications, the input quiescent currents in
Burst Mode operation can be reduced with the internal
LDO regulator bootstrapped to the output voltage. If the
application requires extremely low noise, continuous PWM
operation can also be selected via the MODE pin. The
LTC3118 also features accurate, resistor programmable
RUN comparator thresholds with hysteresis for each V_IN.
This allows the buck-boost DC/DC converter to turn on
and off at user-selected voltage thresholds depending on
the power source for each V_IN. With a wide voltage range
and high efficiency, the LTC3118 is well suited for many
demanding power systems.
Power Stage Topology
Figure 1 shows the topology of the dual-input LTC3118
power stage switches and their associated gate drivers.
The LTC3118 integrates independent switch paths from
V_IN1 to SW1 and V_IN2 to SW1 to provide isolation between
the selected input and the inactive input. This configuration
allows conversion from either input source, regardless of
their respective voltage levels, enabling ideal diode or V_IN1
priority modes (see SEL pin description).
PUMP1
V_IN1
PUMP2
V_IN2
BST1
A1_ON
CM1
A1
BST1
CM2
A2
A2_ON
SW1
V_CC
B_ON
B
V_OUT
BST2
D
D_ON
L
SW2
V_CC
C
C_ON
12
PGND
3118 F01
Figure 1. LTC3118 Dual-Input Power Stage
3118f
For more information www.linear.com/LTC3118