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PDF LTC3411EMS Data sheet ( Hoja de datos )
| Número de pieza | LTC3411EMS | |
| Descripción | 1.25A/ 4MHz/ Synchronous Step-Down DC/DC Converter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
s Small 10-Lead MSOP or DFN Package
s Uses Tiny Capacitors and Inductor
s High Frequency Operation: Up to 4MHz
s High Switch Current: 1.6A
s Low RDS(ON) Internal Switches: 0.110Ω
s High Efficiency: Up to 95%
s Stable with Ceramic Capacitors
s Current Mode Operation for Excellent Line
and Load Transient Response
s Short-Circuit Protected
s Low Dropout Operation: 100% Duty Cycle
s Low Shutdown Current: IQ ≤ 1µA
s Low Quiescent Current: 60µA
s Output Voltages from 0.8V to 5V
s Selectable Burst Mode® Operation
s Sychronizable to External Clock
U
APPLICATIO S
s Notebook Computers
s Digital Cameras
s Cellular Phones
s Handheld Instruments
s Board Mounted Power Supplies
LTC3411
1.25A, 4MHz, Synchronous
Step-Down DC/DC Converter
DESCRIPTIO
The LTC®3411 is a constant frequency, synchronous,
step- down DC/DC converter. Intended for medium power
applications, it operates from a 2.63V to 5.5V input voltage
range and has a user configurable operating frequency up
to 4MHz, allowing the use of tiny, low cost capacitors and
inductors 2mm or less in height. The output voltage is
adjustable from 0.8V to 5V. Internal sychronous 0.11Ω
power switches with 1.6A peak current ratings provide
high efficiency. The LTC3411’s current mode architecture
and external compensation allow the transient response
to be optimized over a wide range of loads and output
capacitors.
The LTC3411 can be configured for automatic power
saving Burst Mode operation to reduce gate charge losses
when the load current drops below the level required for
continuous operation. For reduced noise and RF interfer-
ence, the SYNC/MODE pin can be configured to skip
pulses or provide forced continuous operation.
To further maximize battery life, the P-channel MOSFET is
turned on continuously in dropout (100% duty cycle) with
a low quiescent current of 60µA. In shutdown, the device
draws <1µA.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
13k
1000pF
VIN
2.63V TO 5.5V
VIN SYNC/MODE
PVIN
PGOOD
SVIN
SW
LTC3411
ITH
SHDN/RT
VFB
SGND PGND
324k
C1
22µF
L1
2.2µH
887k
412k
VOUT
2.5V/1.25A
C2
22µF
NOTE: IN DROPOUT, THE OUTPUT TRACKS
THE INPUT VOLTAGE
C1, C2: TAIYO YUDEN JMK325BJ226MM
L1: TOKO A914BYW-2R2M (D52LC SERIES)
3411 F01
Figure 1. Step-Down 2.5V/1.25A Regulator
Efficiency vs Load Current
100
95
90
85
80
VIN = 3.3V
75 VOUT = 2.5V
fO = 1MHz
Burst Mode OPERATION
70
1 10 100
LOAD CURRENT (mA)
1000
3411 TA01
sn3411 3411fs
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LTC3411
Load Regulation
0.4
0.3
Burst Mode
0.2 OPERATION
0.1 PULSE SKIP
VIN = 3.3V
VOUT = 2.5V
0 FORCED
–0.1 CONTINUOUS
–0.2
–0.3
–0.4
–0.5
1
10 100 1000
LOAD CURRENT (mA)
10000
3411 G07
Frequency Variation
vs Temperature
10
8
6
4
2
0
–2
–4
–6
–8
–10
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3411 G10
Line Regulation
0.50
VOUT = 1.8V
0.45 TA = 25°C
0.40
0.35
0.30
0.25
0.20 IOUT = 1.25A
0.15
0.10 IOUT = 400mA
0.05
0
23456
VIN (V)
3411 G08
Efficiency vs Frequency
100
VIN = 3.3V
VOUT = 2.5V
IOUT = 500mA
TA = 25°C
95
90
85
0
123
FREQUENCY (MHz)
4
3411 G11
Frequency vs VIN
10
VOUT = 1.8V
8 IOUT = 1.25A
6 TA = 25°C
4
2
0
–2
–4
–6
–8
–10
2
34
VIN (V)
56
3411 G09
RDS(ON) vs VIN
120
TA = 25°C
115
110
SYNCHRONOUS SWITCH
105
MAIN SWITCH
100
95
90
2.5 3 3.5 4 4.5 5 5.5 6
VIN (V)
3411 G12
sn3411 3411fs
5
5 Page 
LTC3411
APPLICATIO S I FOR ATIO
Setting the Output Voltage
The LTC3411 develops a 0.8V reference voltage between
the feedback pin, VFB, and the signal ground as shown in
Figure 5. The output voltage is set by a resistive divider
according to the following formula:
VOUT ≈ 0.8V 1+ RR21
Keeping the current small (<5µA) in these resistors maxi-
mizes efficiency, but making them too small may allow
stray capacitance to cause noise problems and reduce the
phase margin of the error amp loop.
To improve the frequency response, a feed-forward ca-
pacitor CF may also be used. Great care should be taken to
route the VFB line away from noise sources, such as the
inductor or the SW line.
Shutdown and Soft-Start
The SHDN/RT pin is a dual purpose pin that sets the
oscillator frequency and provides a means to shut down
the LTC3411. This pin can be interfaced with control logic
in several ways, as shown in Figure 3(a) and Figure 3(b).
The ITH pin is primarily for loop compensation, but it can
also be used to increase the soft-start time. Soft start
reduces surge currents from VIN by gradually increasing
the internal peak inductor current. Power supply sequenc-
ing can also be accomplished using this pin. The LTC3411
has an internal digital soft-start which steps up a clamp on
ITH over 1024 clock cycles, as can be seen in Figure 4.
The soft-start time can be increased by ramping the
voltage on ITH during start-up as shown in Figure 3(c). As
the voltage on ITH ramps through its operating range the
internal peak current limit is also ramped at a proportional
linear rate.
Mode Selection and Frequency Synchronization
The SYNC/MODE pin is a multipurpose pin which provides
mode selection and frequency synchronization. Connect-
ing this pin to VIN enables Burst Mode operation, which
provides the best low current efficiency at the cost of a
higher output voltage ripple. When this pin is connected to
ground, pulse skipping operation is selected which pro-
vides the lowest output voltage and current ripple at the
cost of low current efficiency. Applying a voltage within 1V
of the supplies, results in forced continuous mode, which
creates a fixed output ripple and is capable of sinking some
current (about 1/2∆IL). Since the switching noise is con-
stant in this mode, it is also the easiest to filter out. In many
cases, the output voltage can be simply connected to the
SYNC/MODE pin, giving the forced continuous mode,
except at startup.
RUN
SHDN/RT
RT
SHDN/RT SVIN
RT 1M
3411 F03a
RUN
(3a)
RUN OR VIN ITH
R1 D1
RC
(3b)
3411 F03b
C1
(3c)
CC
3411 F03c
Figure 3. SHDN/RT Pin Interfacing and External Soft-Start
VIN
2V/DIV
VOUT
2V/DIV
IL
500mA/DIV
VIN = 3.3V
VOUT = 2.5V
RL = 1.4Ω
200µs/DIV
Figure 4. Digital Soft-Start
3411 F04.eps
sn3411 3411fs
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LTC3411EMS.PDF ] | |
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