LTC1707 Datasheet, PDF (1/16 Pages) Linear Technology – High Efficiency Monolithic Synchronous Step-Down Switching Regulator

FEATURES
s _{600mA Output Current (VIN ≥ 4V)}
s _{High Efficiency: Up to 96%}
s _{Constant Frequency: 350kHz Synchronizable}
to 550kHz
s _{2.85V to 8.5V VIN Range}
s _{0.8V Feedback Reference Allows Low Voltage}
Outputs: 0.8V ≤ V_OUT ≤ V_IN
s _{No Schottky Diode Required}
s _{1.19V ±1% Reference Output Pin}
s _{Selectable Burst Mode}^TM _{Operation/Pulse}
Skipping Mode
s _{Low Dropout Operation: 100% Duty Cycle}
s _{Precision 2.7V Undervoltage Lockout}
s _{Current Mode Control for Excellent Line and}
Load Transient Response
s _{Low Quiescent Current: 200µA}
s _{Shutdown Mode Draws Only 15µA Supply Current}
s _{Available in 8-Lead SO Package}
U
APPLICATIO S
s _{Cellular Telephones}
s _{Portable Instruments}
s _{Wireless Modems}
s _{RF Communications}
s _{Distributed Power Systems}
s _{Single and Dual Cell Lithium}
Final Electrical Specifications
LTC1707
High Efficiency Monolithic
Synchronous Step-Down
Switching Regulator
DESCRIPTIO
December 1999
The LTC^®1707 is a high efficiency monolithic current
mode synchronous buck regulator using a fixed frequency
architecture. The operating supply range is from 8.5V
down to 2.85V, making it suitable for both single and dual
lithium-ion battery-powered applications. Burst Mode op-
eration provides high efficiency at low load currents.
100% duty cycle provides low dropout operation, extend-
ing operating time in battery-powered systems.
The switching frequency is internally set at 350kHz,
allowing the use of small surface mount inductors. For
noise sensitive applications it can be externally synchro-
nized up to 550kHz. Burst Mode operation is inhibited
during synchronization or when the SYNC/MODE pin is
pulled low preventing low frequency ripple from interfer-
ing with audio circuitry. Soft-start is provided by an
external capacitor.
The internal synchronous MOSFET switch increases effi-
ciency and eliminates the need for an external Schottky
diode, saving components and board space. Low output
voltages down to 0.8V are easily achieved due to the 0.8V
internal reference. The LTC1707 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 APPLICATIO
V_IN*
3V TO
8.5V
+
22µF
16V
6
V_IN
5
SW
2
RUN
8
V_REF
LTC1707
7
3
SYNC/MODE V_FB
1
I_TH
GND
47pF
4
15µH
+
249k
80.6k
*V_OUT FOLLOWS V_IN FOR
3V < VIN < 3.3V
V_OUT
3.3V
100µF
6.3V
1707 F01a
Figure 1a. High Efficiency Low Dropout Step-Down Converter
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)
1707 F01b
Figure 1b. Efficiency vs Output Load Current
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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