LTC3114-1_15 Datasheet, PDF (10/34 Pages) Linear Technology – 40V, 1A Synchronous Buck-Boost DC/DC Converter with Programmable Output Current

LTC3114-1
PIN FUNCTIONS
PV_IN (Pin 14): Power Input for the Buck-Boost Converter.
A 10µF or larger capacitor must be connected between
PV_IN and GND as close to the IC as possible. The bypass
capacitor ground connection should via directly down to
the PCB ground plane. Pins PV_IN and V_IN must be con-
nected together in the application.
SW1 (Pin 15): Buck-Boost Power Converter Switch Pin.
This pin is connected to one side of the buck-boost inductor.
MODE (Pin 16): Burst Mode/PWM Mode Control Pin.
Forcing MODE high causes the IC to operate in continu-
ous fixed frequency PWM mode. The nominal switching
frequency in PWM mode is 1.2MHz. Forcing MODE low
enables Burst Mode operation. Burst Mode operation
improves efficiency at light loads by only activating the
buck-boost converter as needed to maintain the nominal
regulated output voltage. If MODE is low, the converter
will automatically transition to PWM mode if the load
current increases.
OPERATION
INTRODUCTION
The LTC3114-1 is a monolithic, current mode, buck-boost
DC/DC converter that can operate over a wide voltage
range of 2.2V to 40V and provide up to 1A to the load.
Internal, low R_DS(ON) N-channel DMOS power switches
reduce solution complexity and maximize efficiency. A
proprietary switch control algorithm allows the buck-boost
converter to maintain output voltage regulation with input
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 LTC3114-1 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 capability
is also included in the LTC3114-1 and is user selected
via the MODE input pin. In Burst Mode operation, the
LTC3114-1 provides exceptional efficiency at light output
loading conditions by operating the converter only when
necessary to maintain voltage regulation. At higher loads,
the LTC3114-1 automatically switches to fixed frequency
PWM mode when Burst Mode operation is selected. For
5V V_OUT applications, the quiescent current in Burst Mode
operation can be as low as 20µA with the internal LDO
regulator bootstrapped to the output voltage. If the ap-
plication requires extremely low noise, continuous PWM
operation can also be selected via the MODE pin. The
LTC3114-1 also features an accurate RUN comparator
threshold with hysteresis. This allows the buck-boost
DC/DC converter to turn on and off at user-selected
V_IN voltage thresholds. With a wide voltage range and
programmable output current or monitoring capabilities,
the LTC3114-1 is well suited for many demanding power
conversion needs.
PROGRAMMABLE AVERAGE OUTPUT CURRENT
The LTC3114-1 includes the ability to program an accu-
rate average output current from the buck-boost DC/DC
converter. Whether the application is driving high power
LEDs, charging batteries, a wide compliance range current
source or just providing a well controlled current limit, the
LTC3114-1 programmable average output current capabil-
ity delivers high efficiency and maximum flexibility. The
output current limit level is independent of operating mode,
(buck or boost), and is active down to approximately 2V
on V_OUT. Below 2V on V_OUT, a secondary foldback current
limit circuit is activated to reduce power dissipation. The
desired average output current level is programmed with
a standard low wattage resistor from PROG to ground.
A low loss current sense resistor and accurate current
sense amplifier are integrated within the IC, greatly sim-
plifying the PCB layout and design. Factory trimming of
the output current limit offset and gain provide a high
degree of accuracy, typically within ±5% of the setpoint.
The applications section provides details on how to select
the programming resistor, R_PROG, for the desired average
output current level from the LTC3114-1.
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