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PDF LTC3111 Data sheet ( Hoja de datos )
| Número de pieza | LTC3111 | |
| Descripción | 1.5A Synchronous Buck-Boost DC/DC Converter | |
| Fabricantes | Linear | |
| Logotipo |  |
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FEATURES
n Regulated Output with VIN Above, Below
or Equal to VOUT
n 2.5V to 15V Input and Output Voltage Range
n 1.5A Continuous Output Current: VIN ≥ 5V,
VOUT = 5V, PWM Mode
n Single Inductor
n Accurate RUN Threshold
n Up to 95% Efficiency
n 800kHz Switching Frequency, Synchronizable
Between 600kHz and 1.5MHz
n 49µA No-Load Quiescent Current in Burst Mode®
Operation
n Output Disconnect in Shutdown
n Shutdown Current < 1µA
n Internal Soft-Start
n Small, Thermally Enhanced 14-Lead (3mm × 4mm ×
0.75mm) DFN and 16-Lead MSOP Packages
APPLICATIONS
n 3.3V or 5V from 1, 2 or 3 Li-Ion, Multiple-Cell
Alkaline/NiMH Batteries
n RF Transmitters
n Military, Industrial Power Systems
LTC3111
15V, 1.5A Synchronous
Buck-Boost DC/DC
Converter
DESCRIPTION
The LTC®3111 is a fixed frequency, synchronous buck-
boost DC/DC converter with 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 and output range of 2.5V to 15V, the LTC3111
is well suited for a wide variety of single or multiple-cell
batteries, back-up capacitor or wall adapter source applica-
tions. Low RDS(ON) internal N-channel MOSFET switches
and selectable PWM or Burst Mode operation produce
high efficiency over a wide range of operating conditions.
An accurate RUN pin allows the user to program the
turn-on threshold voltage of the converter. Other features
include: short-circuit protection, internal soft-start and
thermal shutdown.
The LTC3111 is offered in both thermally enhanced
14-lead (3mm × 4mm × 0.75mm) DFN and 16-lead MSOP
packages.
L, LT, LTC, LTM, Linear Technology, the Linear logo, Burst Mode, LTspice 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 6404251, 6166527, 5481178, 6304066, 6580258.
TYPICAL APPLICATION
5V, 800kHz Wide Input Voltage Buck-Boost Regulator
4.7µH
0.1µF
VIN
2.5V TO 15V
10µF
SW1
BST1
VIN
SW2
BST2
VOUT
LTC3111
COMP
BURST PWM
OFF ON
PWM/SYNC
RUN
FB
SNSGND
SGND
VCC
PGND
0.1µF
680pF
26.1k
27pF
1µF
1M 20k
VOUT
5V
22µF
1.5A
(VIN > 5V)
33pF
191k
3111 TA01a
For more information www.linear.com/LTC3111
Efficiency at 5VOUT
100 PWM
90
BURST
80
70
60
50
40
30
0.0001
VIN = 2.7V
VIN = 5V
VIN = 12V
0.001 0.01 0.1
1
LOAD CURRENT (A)
10
3111 TA01b
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1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, VIN = 5V, VOUT = 5V, unless otherwise specified
Wide VIN to 12VOUT Efficiency
100 PWM
90 BURST
80
70
60
50
40
30
0.0001
VIN = 2.7V
VIN = 5V
VIN = 12V
0.001 0.01
0.1
LOAD CURRENT (A)
1
3111 G07
800kHz PWM Mode No-Load Input
Current
20
18
16
14
12
10
8
6
4
2
0
2 3 4 5 6 7 8 9 10 11 12 13 14 15
VIN (V)
31111 G10
VCC Voltage vs VCC Current
4.2
4.1
4.0
3.9
3.8
3.7
3.6
3.5
0
10 20 30 40 50 60 70 80
CURRENT FROM VCC (mA)
3111 G13
Wide VIN to 12VOUT Power Loss
10
PWM
1
0.1
0.01 BURST
0.001
0.0001
0.0001
VIN = 2.7V
VIN = 5V
VIN = 12V
0.001 0.01 0.1
1
LOAD CURRENT (A)
10
3111 G08
Burst Mode No-Load Current with
VVCOCUTfrwomithVaINn
or Back-Fed from
Optional Diode
450 VOUT = 5V
400
350
300
250
200
150
100 VCC FROM VIN
50
VCC FROM VOUT
0
2 3 4 5 6 7 8 9 10 11 12 13 14 15
VIN (V)
3111 G11
Normalized N-Channel MOSFET
Resistance vs VCC
1.30
1.25
1.20
1.15
1.10
1.05
1.00
0.95
0.90
2.5 3.0 3.5 4.0 4.5 5.0
VCC (V)
3111 G14
For more information www.linear.com/LTC3111
LTC3111
1f 2=V6I0N0tkoH1z2,V8O0U0TkEHfzf,ic1ieMnHczy
at
and
1.5MHz with L = 10µH
100
90
80
70
60
50
40
30
0.01
f = 600kHz
f = 800kHz
f = 1MHz
f = 1.5MHz
0.1
LOAD CURRENT (A)
1
3111 G09
VCC Voltage vs VIN PWM Mode
No Load
4.5
4.3
4.1
3.9
3.7
3.5
3.3
3.1
2.9
2.7
2.5
2 3 4 5 6 7 8 9 10 11 12 13 14 15
VIN (V)
3111 G12
Normalized N-Channel MOSFET
Resistance vs Temperature
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
–50
0 50 100
TEMPERATURE (°C)
150
3111 G15
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5 Page 
LTC3111
OPERATION
INTRODUCTION
The LTC3111 is an extended input and output range, syn-
chronous 1.5A buck-boost DC/DC converter optimized for
a variety of applications. The LTC3111 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 Lock Loop
An internal oscillator circuit sets the normal frequency of
operation to 800kHz. A pulse train applied to the PWM/
SYNC pin allows the operating frequency to be programmed
between 600kHz to 1.5MHz via an internal phase-lock-loop
circuit. The pulse train must have a minimum high or low
state of at least 100ns to guarantee operation (see Note 6
of the Electrical Characteristics).
Error Amplifier
The LTC3111 contains a high gain operational amplifier
which provides frequency compensation of the control
loop to maintain output voltage regulation. To ensure
loop stability, an external compensation network must be
installed in the application circuit. A Type III compensation
network, as shown in Figure 1, is recommended for most
applications since it provides the flexibility to optimize
the converter’s transient response while simultaneously
minimizing any DC error in the output voltage.
As shown in Figure 1, the error amplifier is followed by
an internal analog divider which adjusts the loop gain by
the reciprocal of the input voltage when the converter is in
buck mode and by the output voltage when the converter
is in boost mode which minimizes loop-gain variation
over changes in the input voltage. This simplifies design
of the compensation network and optimizes the transient
response over the entire range of input voltages. Details
VOUT
R1 RFF
CFF
RFB CFB
R2
CPOLE
LTC3111
0.8V
FB
COMP
+
–
VIN VOUT
÷
PWM
COMPARATORS
SW1
SW2
SGND
3111 F01
Figure 1. Error Amplifier and Compensation Network
on designing the compensation network for the LTC3111
applications can be found in the Applications Information
section of this data sheet.
Current Limit Operation
The buck-boost converter has two current limit circuits.
The input current limit sources current into the feedback
divider network whenever the current in switch A exceeds
3A 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 input current
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 input current limit circuit is limited by the
dynamics of the converter loop. On a hard output short, it
is possible for the inductor current to increase substantially
beyond the input current limit before the input current limit
circuit can react. For this reason, there is a peak current
limit circuit which turns off switch A if the current in switch
A exceeds approximately 190% of the input current limit
value. This provides additional protection in the case of
an instantaneous hard output short.
For more information www.linear.com/LTC3111
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11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LTC3111.PDF ] | |
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