LTC3405A
1.5MHz, 300mA
Synchronous Step-Down
Regulator in ThinSOT
FEATURES
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DESCRIPTIO
High Efficiency: Up to 96%
Very Low Quiescent Current: Only 20
µ
A
During Operation
300mA Output Current at V
IN
= 3V
2.5V to 5.5V Input Voltage Range
1.5MHz Constant Frequency Operation
No Schottky Diode Required
Low Dropout Operation: 100% Duty Cycle
Stable with Ceramic Capacitors
0.8V Reference Allows Low Output Voltages
Shutdown Mode Draws < 1µA Supply Current
±2%
Output Voltage Accuracy
Current Mode Operation for Excellent Line and
Load Transient Response
Overtemperature Protected
Low Profile (1mm) ThinSOT
TM
Package
The LTC
®
3405A is a high efficiency monolithic synchro-
nous buck regulator using a constant frequency, current
mode architecture. Supply current during operation is
only 20µA and drops to <1µA in shutdown. The 2.5V to
5.5V input voltage range makes the LTC3405A ideally
suited for single Li-Ion battery-powered applications. 100%
duty cycle provides low dropout operation, extending
battery life in portable systems.
Switching frequency is internally set at 1.5MHz, allowing
the use of small surface mount inductors and capacitors.
The LTC3405A is specifically designed to work well with
ceramic output capacitors, achieving very low output
voltage ripple and a small PCB footprint.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode. Low
output voltages are easily supported with the 0.8V feed-
back reference voltage. The LTC3405A is available in a low
profile (1mm) ThinSOT package.
For fixed 1.5V and 1.8V output versions, refer to the
LTC3405A-1.5/LTC3405A-1.8 data sheet.
, LTC and LT are registered trademarks of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
Protected by U.S. Patents, including 6580258, 5481178.
APPLICATIO S
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Cellular Telephones
Personal Information Appliances
Wireless and DSL Modems
Digital Still Cameras
MP3 Players
Portable Instruments
TYPICAL APPLICATIO
V
IN
2.7V
TO 5.5V
4
C
IN
†
2.2µF
CER
V
IN
RUN
MODE
GND
2
V
FB
5
SW
3
LTC3405A
1
6
100
95
V
IN
= 3.6V
4.7µH**
22pF
EFFICIENCY (%)
V
OUT
*
3.3V
C
OUT
††
4.7µF
CER
90
85
80
75
V
IN
= 5.5V
70
65
60
0.1
V
IN
= 4.2V
887k
280k
3405A F01a
*V
OUT
CONNECTED TO V
IN
FOR 2.7V < V
IN
< 3.3V
**MURATA LQH3C4R7M34
†
TAIYO YUDEN LMK212BJ225MG
††
TAIYO YUDEN JMK212BJ475MG
Figure 1a. High Efficiency Step-Down Converter
Figure 1b. Efficiency vs Load Current
3405afa
U
1
100
10
OUTPUT CURRENT (mA)
1000
3405A F01b
U
U
1
LINER [ LINEAR TECHNOLOGY ]
