LTC1627 Datasheet, PDF (1/16 Pages) Linear Technology – Monolithic Synchronous Step-Down Switching Regulator

LTC1627
Monolithic Synchronous
Step-Down Switching Regulator
FEATURES
s _{High Efficiency: Up to 96%}
s _{Constant Frequency 350kHz Operation}
s _{2.65V to 8.5V VIN Range}
s _{VOUT from 0.8V to VIN, IOUT to 500mA}
s _{No Schottky Diode Required}
s _{Synchronizable Up to 525kHz}
s _{Selectable Burst Mode}^TM _Operation
s _{Low Dropout Operation: 100% Duty Cycle}
s _{Precision 2.5V Undervoltage Lockout}
s _{Secondary Winding Regulation}
s _{Current Mode Operation for Excellent Line and}
Load Transient Response
s _{Low Quiescent Current: 200µA}
s _{Shutdown Mode Draws Only 15µA Supply Current}
s _{±1.5% Reference Accuracy}
s _{Available in 8-Lead SO Package}
U
APPLICATIONS
s _{Cellular Telephones}
s _{Portable Instruments}
s _{Wireless Modems}
s _{RF Communications}
s _{Distributed Power Systems}
s _Scanners
s _{Single and Dual Cell Lithium}
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.
TYPICAL APPLICATION
47pF
C_SS
0.1µF
1
I_TH
8
SYNC/FCB
2
RUN/SS
7
V_DR
LTC1627
3
6
V_FB
V_IN
4
GND
5 ^{L1 15µH}
SW
C_OUT +
100µF
6.3V
V_OUT ⁺
3.3V
249k
V_IN
2.8V*
TO 8.5V
C_IN
22µF
16V
*V_OUT CONNECTED TO V_IN FOR 2.8V < V_IN < 3.3V
80.6k
Figure 1a. High Efficiency Step-Down Converter
1627 F01a
100
V_OUT = 3.3V
95
90
V_IN = 3.6V
V_IN = 6V
85
V_IN = 8.4V
80
75
70
1
10
100
1000
OUTPUT CURRENT (mA)
1627 F01b
Figure 1b. Efficiency vs Output Load Current
1