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PDF LTC3400-1 Data sheet ( Hoja de datos )
| Número de pieza | LTC3400-1 | |
| Descripción | 1.2MHz Micropower Synchronous Boost Converter | |
| Fabricantes | Linear | |
| Logotipo |  |
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LTC3400-1
600mA, 1.2MHz Micropower
Synchronous Boost Converter
in ThinSOT
FEATURES
■ Up to 92% Efficiency
■ Generates 3.3V at 100mA from a Single AA Cell
■ Low Start-Up Voltage: 0.85V
■ VOUT Connected to VIN in Shutdown
■ Internal Synchronous Rectifier
■ 2.5V to 5V Output Range
■ Automatic Burst Mode® Operation
■ Logic Controlled Shutdown (< 1µA)
■ Antiringing Control Minimizes EMI
■ Tiny External Components
■ Low Profile (1mm) SOT-23 Package
U
APPLICATIO S
■ Pagers
■ MP3 Players
■ Digital Cameras
■ LCD Bias Supplies
■ Handheld Instruments
■ Wireless Handsets
■ GPS Receivers
DESCRIPTIO
The LTC®3400-1 is a synchronous, fixed frequency, step-
up DC/DC converter delivering high efficiency in a 6-lead
ThinSOT™ package. Capable of supplying 3.3V at 100mA
from a single AA cell input, the device contains 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 LTC3400-1 features automatic shifting to power sav-
ing Burst Mode operation at light loads. In shutdown, VOUT
and VIN are connected, which allows the input battery to be
used for backup power. The LTC3400-1 features low
shutdown current of under 1µA.
The LTC3400-1 is offered in the low profile (1mm)
SOT-23 package.
, LTC, LT and Burst Mode are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
US Patent Numbers 5,481,178; 6,580,258; 6,304,066; 6,127,815; 6,498,466; 6,611,131.
TYPICAL APPLICATIO
Single Cell to 3.3V Synchronous Boost Converter
+ SINGLE
AA CELL
4.7µH
4.7µF
OFF ON
SW
VIN VOUT
LTC3400-1
SHDN FB
GND
1.02M
1%
604k
1%
VOUT
3.3V
100mA
4.7µF
34001 F01
Efficiency
100
90 VIN = 2.4V
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
34001 F01a
34001f
1
1 page  
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OPERATIO
The LTC3400-1 is a1.2MHz, synchronous boost converter
housed in a 6-lead ThinSOT package. Able to operate from
an input voltage below 1V, the device features fixed
frequency, current mode PWM control for exceptional line
and load regulation. With its low RDS(ON) and gate charge
internal MOSFET switches, the device maintains 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 LTC3400-1 will start up at a typical VIN voltage 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 device to start up into an
output load. Once VOUT exceeds 2.3V, the start-up cir-
cuitry is disabled and normal fixed frequency PWM opera-
tion is initiated. In this mode, the LTC3400-1 operates
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
LTC3400-1
to provide a peak current control command for the PWM.
Peak switch current is limited to approximately 850mA
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 LTC3400-1 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 LTC3400-1 draws only
19µA from the output capacitor, greatly enhancing effi-
ciency. When the output voltage has drooped approxi-
mately 1% from nominal, the LTC3400-1 wakes up and
commences normal PWM operation. The output capacitor
recharges and causes the LTC3400-1 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 LTC3400-1
turns on less frequently. When the load current increases
34001f
5
5 Page 
PACKAGE DESCRIPTIO
S6 Package
6-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1636)
0.62 0.95
MAX REF
1.22 REF
LTC3400-1
2.90 BSC
(NOTE 4)
3.85 MAX 2.62 REF
1.4 MIN
2.80 BSC 1.50 – 1.75
(NOTE 4)
PIN ONE ID
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
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
6 PLCS (NOTE 3)
0.01 – 0.10
S6 TSOT-23 0302
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.
34001f
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11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet LTC3400-1.PDF ] | |
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