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LTC3114EDHC-1#TRPBF

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P30P31-P33P34-P34
LTC3114-1
10
31141fb
For more information www.linear.com/LTC3114-1
pin FuncTions
BST1 (Pin 13): Flying Capacitor Pin for SW1. This pin must
be connected to SW1 through a 68nF capacitor. BST1 is
used to generate the gate driver rail for power switch A.
Make the PCB trace from BST2 to the boost capacitor as
short and direct as possible.
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 pro-
grammable output current or monitoring capabilities,
the LT
C3114
-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
-
LTC3114-1
11
31141fb
For more information www.linear.com/LTC3114-1
operaTion
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.
PWM Mode Operation
If the MODE pin is high or if the load current on the
converter is high enough to command PWM mode opera
-
tion with MODE low, the LTC3114-1 operates in a fixed
1.2MHz
P
WM mode using a current mode control loop.
PWM mode minimizes output voltage ripple and yields a
low noise switching frequency spectrum. A proprietary
switching algorithm provides seamless transitions be
-
tween operating modes and eliminates discontinuities 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 LTC3114-1 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.
A
PLDO
BST1
C
BST1
C
BST2
L
BST2PV
IN
PV
OUT
SW1 SW2
PLDO
PLDO
PLDO
LTC3114-1
PGND PGND
31141 F01
B
D
C
Figure 1. Power Stage Schematic
When stepping down from a high input voltage to a lower
output voltage, the converter operates in buck mode and
switch D remains on for the entire switching cycle except
for the minimum switch low duration (typically 50ns). Dur
-
ing the switch low duration, switch C is turned on which
forces SW2 low and charges the flying capacitor
, C
BST2
.
This ensures that the switch D gate driver power supply
rail on BST2 is maintained. The duty cycle of switches A
and B are adjusted by the PWM to maintain output voltage
regulation in buck mode.
If the input voltage is lower than the output voltage, the
converter operates in boost mode. Switch A remains on
for the entire switching cycle except for the minimum
switch low duration (typically 100ns). During the switch
low duration, switch B is turned on which forces SW1
low and charges the flying capacitor, C
BST1
. This ensures
that the switch A gate driver power supply rail on BST1
is maintained. The duty cycle of switches C and D are
adjusted by the PWM to maintain output voltage regula
-
tion in boost mode.
Oscillator
The LTC3114
-1 operates from an internal oscillator with
a nominal fixed frequency of 1.2MHz. This allows the
DC/DC converter efficiency to be maximized while still
using small external components.
LTC3114-1
12
31141fb
For more information www.linear.com/LTC3114-1
operaTion
Current Mode Control
The LTC3114-1 utilizes average current mode control for
the pulse width modulator as shown in Figure 2. Current
mode control, both average and the better known peak
method, enjoy some benefits compared to other control
methods including: simplified loop compensation, rapid
response to load transients and improved rejection of line
voltage transients.
Referring to Figure 2, an internal high gain transconduc
-
tance error amplifier monitors V
OUT
through a voltage
divider connected to the FB pin and provides an output, VC,
that is used by the current mode control loop to command
the appropriate inductor current level. To ensure stability,
external frequency compensation components (C
P1
, C
P2
and R
Z
) must be installed between VC and ground. The
procedure for determining these components is provided
in the Applications Information section of this data sheet.
VC is internally connected to the noninverting input of a
high gain, integrating, operational amplifier, referred to
in Figure 2, as the average current amp. The inverting
input of the average current amplifier is connected to
the inductor current sense circuit through a gain setting
resistor (R
CS1
) and to its output (VIA) through an internal
frequency compensation network comprised of R
CS2
,
C
CS1
and C
CS2
. The average current amplifier’s output
provides the cycle-by-cycle duty cycle command into the
buck-boost PWM circuitry.
The noninverting reference level input to the average cur
-
rent amplifier is VC and the feedback or inverting input
is driven from the inductor current sensing circuitr
y. The
inductor current sensing circuitry alternately measures
the current through switches A and B. The output of the
PWM
A B C D
CONTROL
LOGIC
VIA
AVERAGE
CURRENT
AMP
VOLTAGE
ERROR
AMP
ACTIVE RANGE OF
VC = 135mV TO 1V
SOFT-START
1V
R
CS1
C
CS2
R
CS2
C
CS1
R
Z
R
BOT
R
TOP
C
P1
+
–
C
P2
R
COESR
R
LOAD
V
OUT
C
OUT
R
X
g
m
= 111µA/V
V
IN
SWB
SWC
SWD
PV
OUT
SWA
R
A
250mΩ
V
DS
SENSE
L1
V
DS
SENSE
1V
g
m
= 120µS
R
O
= 3.6M
FB
VC
GND
31141 F02
+
–
g
m
INDUCTOR
I
SENSE
Figure 2. Average Current Mode Control Loop
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LTC3114EDHC-1#TRPBF

Mfr. #:
Buy LTC3114EDHC-1#TRPBF
Manufacturer:
Analog Devices / Linear Technology
Description:
Switching Voltage Regulators 40V, 1A Sync. Buck-Boost Converter with Programmable Current Limit
Lifecycle:
New from this manufacturer.
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