LTC3129_15 Datasheet, PDF (10/30 Pages) Linear Technology – 15V, 200mA Synchronous Buck-Boost DC/DC Converter with 1.3A Quiescent Current

LTC3129
OPERATION
INTRODUCTION
The LTC3129 is a 1.3µA quiescent current, monolithic, cur-
rent mode, buck-boost DC/DC converter that can operate
over a wide input voltage range of 1.92V to 15V and provide
up to 200mA to the load. Internal, low R_DS(ON) N-channel
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 sub-harmonic switching, making this product ideal
for noise sensitive applications. The LTC3129 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 LTC3129 and
is user-selected via the PWM input pin. In Burst Mode
operation, the LTC3129 provides exceptional efficiency at
light output loading conditions by operating the converter
only when necessary to maintain voltage regulation. The
Burst Mode quiescent current is a miserly 1.3µA. At higher
loads, the LTC3129 automatically switches to fixed fre-
quency PWM mode when Burst Mode operation is selected.
(Please refer to the Typical Performance Characteristics
curves for the mode transition point at different input and
output voltages.) If the application requires extremely low
noise, continuous PWM operation can also be selected
via the PWM pin.
A MPPC (maximum power point control) function is also
provided that allows the input voltage to the converter to
be servo'd to a programmable point for maximum power
when operating from various non-ideal power sources
such as photovoltaic cells. The LTC3129 also features
an accurate RUN comparator threshold with hysteresis,
allowing the buck-boost DC/DC converter to turn on and
off at user-selected V_IN voltage thresholds. With a wide
voltage range, 1.3µA Burst Mode current and program-
mable RUN and MPPC pins, the LTC3129 is well suited
for many diverse applications.
PWM MODE OPERATION
If the PWM pin is high or if the load current on the converter
is high enough to command PWM mode operation with
PWM low, the LTC3129 operates in a fixed 1.2MHz PWM
mode using an internally compensated average current
mode control loop. PWM mode minimizes output voltage
ripple and yields a low noise switching frequency spec-
trum. A proprietary switching algorithm provides seamless
transitions between operating modes and eliminates dis-
continuities in the average inductor current, inductor ripple
current and loop transfer function throughout all modes of
operation. These advantages result in increased efficiency,
improved loop stability and lower output voltage ripple in
comparison to the traditional buck-boost converter.
Figure 1 shows the topology of the LTC3129 power stage
which is comprised of four N-channel DMOS switches and
their associated gate drivers. In PWM mode operation
both switch pins transition on every cycle independent of
the input and output voltages. In response to the internal
control loop command, an internal pulse width modulator
generates the appropriate switch duty cycle to maintain
regulation of the output voltage.
C_BST1
L
C_BST2
BST1
V_IN SW1
SW2 V_OUT
BST2
V_CC
V_CC
A
D
V_CC
V_CC
B
C
PGND
PGND
Figure 1. Power Stage Schematic
LTC3129
3129 F01
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