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PDF LTC3400B Data sheet ( Hoja de datos )
| Número de pieza | LTC3400B | |
| Descripción | 600mA/ 1.2MHz Micropower Synchronous Boost Converter in ThinSOT | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3400/LTC3400B
600mA, 1.2MHz Micropower
Synchronous Boost Converter
in ThinSOT
FEATURES
s Up to 92% Efficiency
s Generates 3.3V at 100mA from a Single AA Cell
s Low Start-Up Voltage: 0.85V
s 1.2MHz Fixed Frequency Switching
s Internal Synchronous Rectifier
s 2.5V to 5V Output Range
s Automatic Burst Mode® Operation (LTC3400)
s Continuous Switching at Light Loads (LTC3400B)
s Logic Controlled Shutdown (< 1µA)
s Antiringing Control Minimizes EMI
s Tiny External Components
s Low Profile (1mm) ThinSOTTM Package
U
APPLICATIO S
s Pagers
s MP3 Players
s Digital Cameras
s LCD Bias Supplies
s Handheld Instruments
s Wireless Handsets
s GPS Receivers
DESCRIPTIO
The LTC®3400/LTC3400B are synchronous, fixed fre-
quency, step-up DC/DC converters delivering high effi-
ciency in a 6-lead ThinSOT package. Capable of supplying
3.3V at 100mA from a single AA cell input, the devices
contain an internal NMOS switch and PMOS synchronous
rectifier.
A switching frequency of 1.2MHz minimizes solution
footprint by allowing the use of tiny, low profile inductors
and ceramic capacitors. The current mode PWM design is
internally compensated, reducing external parts count.
The LTC3400 features automatic shifting to power saving
Burst Mode operation at light loads, while the LTC3400B
features continuous switching at light loads. Antiringing
control circuitry reduces EMI concerns by damping the
inductor in discontinuous mode, and the devices feature
low shutdown current of under 1µA.
Both devices are available in the low profile (1mm) ThinSOT
package.
, LTC, LT and Burst Mode are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
+ SINGLE
AA CELL
L1
4.7µH
C1
4.7µF
1
SW
65
VIN VOUT
OFF ON
LTC3400
43
SHDN FB
GND
2
C1, C2: TAIYO-YUDEN X5R EMK316BJ475ML
L1: COILCRAFT DO160C-472
R1
1.02M
1%
R2
604k
1%
VOUT
3.3V
100mA
C2
4.7µF
3400 F01
Figure 1. Single Cell to 3.3V Synchronous Boost Converter
Efficiency
100
VIN = 2.4V
90
80 VIN = 1.5V
70
60
50
FIGURE 1 CIRCUIT
WITH OPTIONAL SCHOTTKY DIODE
(SEE APPLICATIONS INFORMATION)
40
0.1 1 10 100
LOAD CURRENT (mA)
1000
3400 F01a
3400f
1
1 page  
U
OPERATIO
The LTC3400/LTC3400B are 1.2MHz, synchronous boost
converters housed in a 6-lead ThinSOT package. Able to
operate from an input voltage below 1V, the devices
feature fixed frequency, current mode PWM control for
exceptional line and load regulation. With its low RDS(ON)
and gate charge internal MOSFET switches, the devices
maintain high efficiency over a wide range of load current.
Detailed descriptions of the three distinct operating modes
follow. Operation can be best understood by referring to
the Block Diagram.
Low Voltage Start-Up
The LTC3400/LTC3400B will start up at a typical VIN volt-
age of 0.85V or higher. The low voltage start-up circuitry
controls the internal NMOS switch up to a maximum peak
inductor current of 850mA (typ), with an approximate
1.5µs off-time during start-up, allowing the devices to
start up into an output load. Once VOUT exceeds 2.3V, the
start-up circuitry is disabled and normal fixed frequency
PWM operation is initiated. In this mode, the LTC3400/
LTC3400B operate independent of VIN, allowing extended
operating time as the battery can droop to several tenths
of a volt without affecting output voltage regulation. The
limiting factor for the application becomes the ability of the
battery to supply sufficient energy to the output.
Low Noise Fixed Frequency Operation
Oscillator: The frequency of operation is internally set to
1.2MHz.
Error Amp: The error amplifier is an internally compensated
transconductance type (current output) with a transconduc-
tance (gm) = 33 microsiemens. The internal 1.23V reference
voltage is compared to the voltage at the FB pin to generate
an error signal at the output of the error amplifier. A volt-
age divider from VOUT to ground programs the output
voltage via FB from 2.5V to 5V using the equation:
VOUT = 1.23V • [1 + (R1/R2)]
Current Sensing: A signal representing NMOS switch
current is summed with the slope compensator. The
summed signal is compared to the error amplifier output
to provide a peak current control command for the PWM.
Peak switch current is limited to approximately 850mA
LTC3400/LTC3400B
independent of input or output voltage. The current signal
is blanked for 40ns to enhance noise rejection.
Zero Current Comparator: The zero current comparator
monitors the inductor current to the output and shuts off
the synchronous rectifier once this current reduces to ap-
proximately 20mA. This prevents the inductor current from
reversing in polarity improving efficiency at light loads.
Antiringing Control: The antiringing control circuitry pre-
vents high frequency ringing of the SW pin as the inductor
current goes to zero by damping the resonant circuit
formed by L and CSW (capacitance on SW pin).
Burst Mode Operation
Portable devices frequently spend extended time in low
power or standby mode, only switching to high power
drain when specific functions are enabled. In order to
improve battery life in these types of products, high power
converter efficiency needs to be maintained over a wide
output power range. In addition to its high efficiency at
moderate and heavy loads, the LTC3400 includes auto-
matic Burst Mode operation that improves efficiency of
the power converter at light loads. Burst mode operation
is initiated if the output load current falls below an
internally programmed threshold (see Typical Perfor-
mance graph, Output Load Burst Mode Threshold vs VIN).
Once initiated, the Burst Mode operation circuitry shuts
down most of the device, only keeping alive the circuitry
required to monitor the output voltage. This is referred to
as the sleep state. In sleep, the LTC3400 draws only 19µA
from the output capacitor, greatly enhancing efficiency.
When the output voltage has drooped approximately 1%
from nominal, the LTC3400 wakes up and commences
normal PWM operation. The output capacitor recharges
and causes the LTC3400 to reenter sleep if the output load
remains less than the sleep threshold. The frequency of
this intermittent PWM or burst operation is proportional to
load current; that is, as the load current drops further
below the burst threshold, the LTC3400 turns on less
frequently. When the load current increases above the
burst threshold, the LTC3400 will resume continuous
PWM operation seamlessly. The LTC3400B does not use
Burst Mode operation and features continous operation at
light loads, eliminating low frequency output voltage ripple
at the expense of light load efficiency.
3400f
5
5 Page 
PACKAGE DESCRIPTIO
LTC3400/LTC3400B
S6 Package
6-Lead Plastic SOT-23
(Reference LTC DWG # 05-08-1636)
0.754
0.854 ± 0.127
2.90 BSC
(NOTE 4)
3.254
0.95 BSC
2.80 BSC 1.50 – 1.75
(NOTE 4)
PIN ONE ID
1.9 BSC
RECOMMENDED SOLDER PAD LAYOUT
0.20 BSC
DATUM ‘A’
0.95 BSC
0.80 – 0.90
1.00 MAX
0.30 – 0.50 REF
0.09 – 0.20
NOTE:
(NOTE 3)
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
1.90 BSC
0.30 – 0.45 TYP
6 PLCS (NOTE 3)
0.01 – 0.10
S6 TSOT-23 0801
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
3400f
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11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet LTC3400B.PDF ] | |
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