LTC3447 Просмотр технического описания (PDF) - Linear Technology
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LTC3447 Datasheet PDF : 16 Pages
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LTC3447
I2C Controllable Buck
Regulator in 3mm × 3mm DFN
FEATURES
■ I2C Programmable Output with 21.6mV Resolution
■ Overtemperature Protected
■ High Efficiency: Up to 93%
■ Very Low Quiescent Current: Only 33µA
■ 600mA Output Current at VIN = 3V
■ 2.5V to 5.5V Input Voltage Range
■ 1MHz Constant Frequency Operation
■ No Schottky Diode Required
■ Low Dropout Operation: 100% Duty Cycle
■ Stable with Ceramic Capacitors
■ Shutdown Mode Draws <1µA Supply Current
■ ±2% Output Voltage Accuracy
■ Standard (100kHz) or Fast Mode (400kHz) I2C
■ 6-Bit Voltage DAC (0.69V to 2.05V)
■ Disable Burst Mode Operation
■ Enable Power Good Blanking
■ Optional External Start-Up Resistors
■ Soft-Start
■ 10 Lead, 3mm × 3mm DFN Package
U
APPLICATIO S
■ Distributed Power Supplies
■ Notebook Computers
■ PDAs and Other Handheld Devices
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 5481178, 6580258, 6304066, 6127815,
6498466, 6611131.
DESCRIPTIO
The LTC®3447 is a high efficiency monolithic synchronous
current mode buck regulator. Using an I2C interface, the
output voltage can be set between 0.69V and 2.05V using
an internal 6-bit DAC.
The buck regulator has optional external feedback resis-
tors that can be used for setting the initial start up voltage.
The feedback voltage reference for this start-up option
is 0.6V. Once the voltage DAC is updated via the I2C, the
buck regulator switches from external to internal feedback
resistors. When there are no external resistors, the default
start-up voltage is 1.38V.
The switching frequency is internally set at 1MHz, al-
lowing the use of small surface mount inductors and
capacitors.
In Burst Mode® operation, supply current is only 33µA,
dropping to <1µA in shutdown. The 2.5V to 5.5V input
voltage range makes the LTC3447 ideally suited for single
cell Li-Ion battery-powered applications. 100% duty cycle
capability provides low dropout operation, extending
battery life in portable systems. Automatic Burst Mode
operation increases efficiency at light loads, further ex-
tending battery life.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode.
TYPICAL APPLICATIO
VIN
2.5V TO 5.5V
C2
4.7µF
CERAMIC
I2C VCCD
10k 10k
SDA
SCL
PWREN
C3
4.7µF
* 600mA AT VIN = 3V
VIN
RUN
PGOOD
LTC3447
VCCD
SW
SDA
VOUT
SCL
FB
GND
EXPOSED PADDLE
TO GROUND
VIN
RPU1
20k
L1
3.3µH
C1
10µF
VOUT
0.69V
TO 2.05V
AT 600mA*
R1
100k
R2
49.9k
3447 TA01
Efficiency and Power Loss vs
Load Current (VIN = 3.6V)
100
1000
90
80
70
100
60
50
40
10
30
20
PULSE SKIP EFFICIENCY
10
Burst Mode EFFICIENCY
LOSS
0
1
1
10
100
1000
LOAD CURRENT (mA)
3447 TA01b
3447f
1
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