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PDF LTC3112 Data sheet ( Hoja de datos )
| Número de pieza | LTC3112 | |
| Descripción | 2.5A Synchronous Buck-Boost DC/DC Converter | |
| Fabricantes | Linear Technology Corporation | |
| Logotipo |  |
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Features
n Regulated Output with VIN Above, Below or Equal to VOUT
n 2.7V to 15V Input Voltage Range
n 2.5V to 14V Output Voltage Range
n 2.5A Continuous Output Current: VIN ≥ 5V,
VOUT = 5V, PWM Mode
n Output Current Monitor
n Up to 95% Efficiency
n 750kHz Switching Frequency, Synchronizable
Between 300kHz and 1.5MHz
n Internal N-Channel MOSFETs
n Selectable Burst Mode® Operation, IQ = 50µA
n Shutdown Current < 1µA
n Overvoltage Protection
n Output Disconnect in Shutdown
n Internal Soft-Start
n Small, Thermally Enhanced 16-Lead (4mm × 5mm ×
0.75mm) DFN and 20-Lead TSSOP Package
Applications
n 3.3V or 5V from 1, 2 or 3 Li-Ion, Backup Capacitor Stack
n Hand Held Inventory Terminals
n RF Transmitters
n 12V Synchronous Boost Converter
n Multiple Power Input Systems
n LED Lighting with Current Regulation
n 12V Lead Acid Battery to 12V
LTC3112
15V, 2.5A Synchronous
Buck-Boost DC/DC
Converter
Description
The LTC®3112 is a fixed frequency synchronous buck-boost
DC/DC converterwith an extended input and output range.
The unique 4-switch, single inductor architecture provides
low noise and seamless operation from input voltages
above, below or equal to the output voltage.
With an input range of 2.7V to 15V, the LTC3112 is well-
suited for a wide variety of single or multiple cell battery,
backup capacitor or wall adapter source applications. Low
RDS(ON) internal N-Channel MOSFET switches provide
highly efficient operation in applications with higher load
current requirements.
The LTC3112 features selectable PWM or Burst Mode
operation, an easily synchronized oscillator and output
disconnect in shutdown. An output current monitor circuit
allows the load current to be controlled or measured. Other
features include <1µA shutdown current, short circuit
protection, soft-start, current limit and thermal shutdown.
The LTC3112 is offered in both a 16-pin (4mm × 5mm ×
0.75mm) DFN and 20-pin TSSOP packages.
L, LT, LTC, LTM, Linear Technology Burst Mode, LTSpice and the Linear logo are registered
trademarks and No RSENSE and PowerPath are trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Protected by U.S. Patents,
including 5481178.
Typical Application
5V, 750kHz Wide Input Voltage Range Buck-Boost Regulator
4.7µH
0.1µF
2.7V TO 15V
VIN
BURST PWM
10µF
OFF ON
1µF
SW1 SW2
BST1
BST2
VIN VOUT
VCC LTC3112 COMP
PWM/SYNC
RUN
GND
FB
IOUT
OVP
0.1µF
680pF 33k
22pF
845k
5V/2.5A, VIN > 5V
47pF
VOUT
10k
100pF
TO ADC
1V PER AMP
42.2k
158k
47µF
3112 TA01
For more information www.linear.com/LTC3112
Efficiency at 5VOUT
100 PWM
90
BURST
80
70
60
50
40
30
0.0001 0.001 0.01
0.1
LOAD CURRENT (A)
251..270VVVINIINN
1
3112 TA02
3112fc
1
1 page  
Typical Performance Characteristics
TA = 25°C, VIN = 5.0V, VOUT = 5.0V unless otherwise specified
Maximum Output Current
PWM Mode
4.8
Maximum Output Current
Burst Mode Operation
560
4.0
3.2
2.4
1.6
0.8 351..230VVVOOOUUUTTT
0
2 3 4 5 6 7 8 9 10 11 12 13 14 15
VIN (V)
3112 G04
480
400
320
240
160
80 351..230VVVOOOUUUTTT
0
2 3 4 5 6 7 8 9 10 11 12 13 14 15
VIN (V)
3112 G05
750kHz PWM Mode No-Load Input
Current
25
VOUT = 5V
20
15
Burst Mode No-Load Input Current
with
from
VVCOCUfTrowmithVOINpotiroBnaacl kD-iFoedde
350
VOUT = 5V
300
VVCCCC
FROM
FROM
VVIONUT
250
200
10 150
100
5
50
0
2 3 4 5 6 7 8 9 10 11 12 13 14 15
VIN (V)
3112 G07
0
3 5 7 9 11 13 15
VIN (V)
3112 G08
VCC Voltage vs VCC Current
4.4
VIN = 5V
4.3
4.2
4.1
4.0
3.9
0 20 40 60 80 100 120 140
CURRENT FROM VCC (mA)
3112 G10
Boost Mode Minimum SW1
Low Time vs VCC Voltage
275
250
225
200
175
150
125
2.5
3 3.5 4 4.5 5
VCC VOLTAGE (V)
3112 G11
For more information www.linear.com/LTC3112
LTC3112
v1s2VFIrNeqtoue1n2cVyOUwTitEhff4ic.7ieµnHcy
100
90
80
70
60
50
40
30
0.01
0.1 1
LOAD CURRENT (mA)
500kHz
750KHz
1000kHz
1500kHz
10
3112 G06
PVWCCMVoMltoadgee
vs
No
VLIoNad
4.5
4.0
3.5
3.0
2.5
2.0
2 3 4 5 6 7 8 9 10 11 12 13 14 15
VIN (V)
3112 G09
Normalized N-Channel MOSFET
Resistance vs VCC
1.3
1.2
1.1
1.0
0.9
0.8
0.7
2.5 2.75 3 3.25 3.5 3.75 4 4.25 4.5 4.75 5
VCC (V)
3112 G12
3112fc
5
5 Page 
LTC3112
Operation
INTRODUCTION
The LTC3112 is an extended input and output range,
high current synchronous buck-boost DC/DC converter
optimized for a variety of demanding applications. The
LTC3112 utilizes a proprietary switching algorithm, which
allows its output voltage to be regulated above, below or
equal to the input voltage. The error amplifier output on
COMP determines the output duty cycle of the switches.
The low RDS(ON), low gate charge synchronous switches
provide high efficiency pulse width modulation control.
High efficiency is achieved at light loads when Burst Mode
operation is commanded.
LOW NOISE FIXED FREQUENCY OPERATION
Oscillator, Phase-Locked Loop
An internal oscillator circuit sets the normal frequency of
operation to 750kHz. A pulse train applied to the PWM/
SYNC pin allows the operating frequency to be programmed
between 300kHz to 1.5MHz via an internal phase-locked
loop circuit. The pulse train must have a minimum high or
low state of at least 100ns to guarantee operation (Note 7).
Error Amplifier
The error amplifier is a high gain voltage mode ampli-
fier. The loop compensation components are configured
around the amplifier (from FB to COMP and VOUT to FB)
to obtain stability of the converter and rapid response
to load transients. Refer to the Applications Information
section of this data sheet under Closing the Feedback
Loop for information on selecting compensation type
and components.
Current Limit Operation
The buck-boost converter has two current limit circuits.
The primary current limit is an average current limit circuit
which sources current into the feedback divider network
proportional to the extent that switch A current exceeds
6A typical. Due to the high gain of the feedback loop, the
injected current forces theerroramplifier output todecrease
until the average current through switch A decreases ap-
proximately to the current limit value. The average cur-
rent limit utilizes the error amplifier in an active state and
thereby provides a smooth recovery with little overshoot
once the current limit fault condition is removed. Since
the current limit is based on the average current through
switch A, the peak inductor current in current limit will
have a dependency on the duty cycle (i.e. on the input
and output voltages) in the overcurrent condition. For this
current limit feature to be most effective, the Thevenin
resistance from the FB to ground should exceed 100kΩ.
The speed of the average current limit circuit is limited by
the dynamics of the error amplifier. On a hard output short,
it would be possible for the inductor current to increase
substantially beyond current limit before the average cur-
rent limit circuit would react. For this reason, there is a
second current limit circuit which turns off switch A if the
current ever exceeds approximately 160% of the average
current limit value. This provides additional protection in
the case of an instantaneous hard output short.
Should the output become shorted, the average current
limit is reduced to approximately one half of the normal
operating current limit.
Reverse Current Limit
During fixed frequency operation, a reverse current com-
parator on switch D monitors the current entering the
VOUT pin. When this reverse current exceeds 1A (typical)
switch D will be turned off for the remainder of the switch-
ing cycle. This feature protects the buck-boost converter
from excessive reverse current if the buck-boost output
is above the regulation voltage.
Internal Soft-Start
The LTC3112 buck-boost converter has an independent
internal soft-start circuit with a nominal duration of 2ms.
The converter remains in regulation during soft-start and
will therefore respond to output load transients which
occur during this time. In addition, the output voltage rise
time has minimal dependency on the size of the output
capacitor or load current during start-up.
For more information www.linear.com/LTC3112
3112fc
11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LTC3112.PDF ] | |
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