LTC3447_15 Datasheet, PDF (1/16 Pages) Linear Technology – I2C Controllable Buck Regulator

LTC3447
I²C Controllable Buck
Regulator in 3mm × 3mm DFN
FEATURES
■ _I²_{C 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) I}²_C
■ _{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
V_IN
2.5V TO 5.5V
C2
4.7µF
CERAMIC
I²C _VCCD
10k 10k
SDA
SCL
PWREN
C3
4.7µF
* 600mA AT V_IN = 3V
V_IN
RUN
PGOOD
LTC3447
V_CCD
SW
SDA
V_OUT
SCL
FB
GND
EXPOSED PADDLE
TO GROUND
V_IN
RPU1
20k
L1
3.3µH
C1
10µF
V_OUT
0.69V
TO 2.05V
AT 600mA*
R1
100k
R2
49.9k
3447 TA01
Efficiency and Power Loss vs
Load Current (V_IN = 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