LTC1627
Monolithic Synchronous
Step-Down Switching Regulator
FEATURES
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DESCRIPTION
The LTC
®
1627 is a monolithic current mode synchronous
buck regulator using a fixed frequency architecture. The
operating supply range is from 8.5V down to 2.65V, making
it suitable for one or two lithium-ion battery-powered appli-
cations. Burst Mode operation provides high efficiency at
low load currents. 100% duty cycle provides low dropout
operation, which extends operating time in battery-operated
systems.
The operating frequency is internally set at 350kHz, allowing
the use of small surface mount inductors. For switching noise
sensitive applications it can be externally synchronized up to
525kHz. The SYNC/FCB control pin guarantees regulation of
secondary windings regardless of load on the main output by
forcing continuous operation. Burst Mode operation is inhib-
ited during synchronization or when the SYNC/FCB pin is
pulled low to reduce noise and RF interference. Soft-start is
provided by an external capacitor.
Optional bootstrapping enhances the internal switch drive for
single lithium-ion cell applications. The internal synchronous
switch increases efficiency and eliminates the need for an
external Schottky diode, saving components and board
space. The LTC1627 comes in an 8-lead SO package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
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High Efficiency: Up to 96%
Constant Frequency 350kHz Operation
2.65V to 8.5V V
IN
Range
V
OUT
from 0.8V to V
IN
, I
OUT
to 500mA
No Schottky Diode Required
Synchronizable Up to 525kHz
Selectable Burst Mode
TM
Operation
Low Dropout Operation: 100% Duty Cycle
Precision 2.5V Undervoltage Lockout
Secondary Winding Regulation
Current Mode Operation for Excellent Line and
Load Transient Response
Low Quiescent Current: 200µA
Shutdown Mode Draws Only 15µA Supply Current
±1.5%
Reference Accuracy
Available in 8-Lead SO Package
APPLICATIONS
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Cellular Telephones
Portable Instruments
Wireless Modems
RF Communications
Distributed Power Systems
Scanners
Single and Dual Cell Lithium
TYPICAL APPLICATION
1
47pF
C
SS
0.1µF
2
3
4
I
TH
SYNC/FCB
8
7
6
5
L1 15µH
C
OUT
+
100µF
6.3V
V
OUT
3.3V
249k
V
IN
2.8V*
TO 8.5V
C
IN
22µF
16V
EFFICIENCY (%)
100
V
OUT
= 3.3V
95
V
IN
= 6V
90
85
80
75
70
V
IN
= 8.4V
V
IN
= 3.6V
RUN/SS
V
DR
LTC1627
V
FB
GND
V
IN
SW
+
*V
OUT
CONNECTED TO V
IN
FOR 2.8V < V
IN
< 3.3V
80.6k
1627 F01a
1
Figure 1a. High Efficiency Step-Down Converter
Figure 1b. Efficiency vs Output Load Current
U
U
U
10
100
OUTPUT CURRENT (mA)
1000
1627 F01b
1
LINER [ LINEAR TECHNOLOGY ]
