LTC3440
1
3440fd
For more information www.linear.com/LTC3440
Description
Micropower Synchronous
Buck-Boost DC/DC Converter
Features
applications
n
Single Inductor
n
Fixed Frequency Operation with Battery Voltages
Above, Below or Equal to the Output
n
Synchronous Rectification: Up to 96% Efficiency
n
25µA Quiescent Current in Burst Mode
®
Operation
n
Up to 600mA Continuous Output Current
n
No Schottky Diodes Required (V
OUT
< 4.3V)
n
V
OUT
Disconnected from V
IN
During Shutdown
n
2.5V to 5.5V Input and Output Range
n
Programmable Oscillator Frequency
from 300kHz to 2MHz
n
Synchronizable Oscillator
n
Burst Mode Enable Control
n
<1µA Shutdown Current
n
Small Thermally Enhanced 10-Pin MSOP and
(3mm
×
3mm) DFN Packages
n
Palmtop Computers
n
Handheld Instruments
n
MP3 Players
n
Digital Cameras
The LT C
®
3440 is a high efficiency, fixed frequency, Buck-
Boost DC/DC converter that operates from input voltages
above, below or equal to the output voltage. The topology
incorporated in the IC provides a continuous transfer
function through all operating modes, making the prod-
uct ideal for single lithium-ion, multicell alkaline or NiMH
applications where the output voltage is within the battery
voltage range.
The device includes two 0.19Ω N-channel MOSFET
switches and two 0.22Ω P-channel switches. Switch-
ing frequencies up to 2MHz are programmed with an
external resistor and the oscillator can be synchronized
to an external clock. Quiescent current is only 25µA in
Burst Mode operation, maximizing battery life in portable
applications. Burst Mode operation is user controlled and
can be enabled by driving the MODE/SYNC pin high. If the
MODE/SYNC pin has either a clock or is driven low, then
fixed frequency switching is enabled.
Other features include a 1µA shutdown, soft-start con-
trol, thermal shutdown and current limit. The LTC3440
is available in the 10-pin thermally enhanced MSOP and
(3mm × 3mm) DFN packages.
Efficiency vs V
IN
SW1
V
IN
SHDN/SS
MODE/SYNC
R
T
SW2
V
OUT
FB
V
C
GND
3
7
8
2
1
4
6
9
10
5
LTC3440
L1
10µH
R1
340k
R2
200k
R3
15k
3440 TA01
R
T
60.4k
C1: TAIYO YUDEN JMK212BJ106MG
C2: TAIYO YUDEN JMK325BJ226MM
L1: SUMIDA CDRH6D38-100
*1 = Burst Mode OPERATION
0 = FIXED FREQUENCY
C1
10µF
Li-Ion
V
IN
=
2.7V TO 4.2V
*
+
C5 1.5nF
C2
22µF
V
OUT
3.3V
600mA
V
IN
(V)
2.5
EFFICIENCY (%)
3.0
3.5
4.0 4.5
3440 TA02
5.0
100
98
96
94
92
90
88
86
84
82
80
5.5
V
OUT
= 3.3V
I
OUT
= 100mA
f
OSC
= 1MHz
typical application
Li-Ion to 3.3V at 600mA Buck-Boost Converter
L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks
and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.