Kingbor Technology Co.,Ltd
TEL:(86)0755-26508846 FAX:(86)0755-26509052
KB3408
1.5MHz,
350mA
Synchronous Step-Down
Regulator in
SOT23-5
FEATURES
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DESCRIPTION
The KB3408 is a high efficiency monolithic synchro-
nous buck regulator using a constant frequency, current
mode architecture. The device is available in an adjustable
version and fixed output voltages of 1.8V and 3.3V. Supply
current during operation is only 20µA and drops to 1µA
in shutdown. The 2.5V to 7.4V input voltage range makes
the KB3408 ideally suited for single Li-Ion battery-pow-
ered applications. 100% duty cycle provides low dropout
operation, extending battery life in portable systems.
Automatic Burst Mode operation increases efficiency at
light loads, further extending battery life.
Switching frequency is internally set at 1.5MHz, allowing
the use of small surface mount inductors and capacitors.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode. Low
output voltages are easily supported with the 0.6V feed-
back reference voltage. The KB3408 is available in a low
profile (1mm) SOT23-5 package.
High Efficiency: Up to 96%
Very Low Quiescent Current: Only 20
µ
A
During Operation
350mA Output Current
2.5V to 7.4V Input Voltage Range
1.5MHz Constant Frequency Operation
No Schottky Diode Required
Low Dropout Operation: 100% Duty Cycle
0.6V Reference Allows Low Output Voltages
Shutdown Mode Draws
1µA
Supply Current
Current Mode Operation for Excellent Line and
Load Transient Response
Overtemperature Protected
Low Profile (1mm) SOT23-5 Package
APPLICATIONS
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Cellular Telephones
Personal Information Appliances
Wireless and DSL Modems
Digital Still Cameras
MP3 Players
Portable Instruments
TYPICAL APPLICATION
95
90
V
IN
2.7V
TO 7.4V
4.7µH
C
OUT
10µF
CER
5
V
OUT
1.8V
350mA
V
IN
= 2.7V
85
EFFICIENCY (%)
4
+
C
IN
4.7µF
Tan
1
V
IN
SW
3
V
IN
= 3.6V
80
V
IN
= 4.2V
75
70
65
60
0.1
V
OUT
= 1.8V
1
10
100
OUTPUT CURRENT (mA)
500
KB3408-1.8
RUN
V
OUT
2
GND
Figure 1a. High Efficiency Step-Down Converter
Figure 1b. Efficiency vs Load Current
March 2007
1
KB3408
KINGBOR [ KINGBOR TECHNOLOGY CO ]
