LTC1877 Datasheet, PDF (1/16 Pages) Linear Technology – High Efficiency Monolithic Synchronous Step-Down Regulator

FEATURES
s _{High Efficiency: Up to 95%}
s _{Very Low Quiescent Current: Only 10µA}
During Operation
s _{600mA Output Current at VIN = 5V}
s _{2.65V to 10V Input Voltage Range}
s _{550kHz Constant Frequency Operation}
s _{Synchronizable from 400kHz to 700kHz}
s _{Selectable Burst Mode}^TM _Operation/
Pulse Skipping Mode
s _{No Schottky Diode Required}
s _{Low Dropout Operation: 100% Duty Cycle}
s _{0.8V Reference Allows Low Output Voltages}
s _{Shutdown Mode Draws < 1µA Supply Current}
s _{±2% Output Voltage Accuracy}
s _{Current Mode Control for Excellent Line and}
Load Transient Response
s _{Overcurrent and Overtemperature Protected}
s _{Available in 8-LeaUd MSOP Package}
APPLICATIONS
s _{Cellular Telephones}
s _{Wireless Modems}
s _{Personal Information Appliances}
s _{Portable Instruments}
s _{Distributed Power Systems}
s _{Battery-Powered Equipment}
Final Electrical Specifications
LTC1877
High Efficiency
Monolithic Synchronous
Step-Down Regulator
DESCRIPTION
May 2000
The LTC^®1877 is a high efficiency monolithic synchro-
nous buck regulator using a constant frequency, current
mode architecture. Supply current during operation is
only 10µA and drops to < 1µA in shutdown. The 2.65V to
10V input voltage range makes the LTC1877 ideally suited
for both single and dual Li-Ion battery-powered applica-
tions. 100% duty cycle provides low dropout operation,
extending battery life in portable systems.
Switching frequency is internally set at 550kHz, allowing
the use of small surface mount inductors and capacitors.
For noise sensitive applications the LTC1877 can be
externally synchronized from 400kHz to 700kHz. Burst
Mode operation is inhibited during synchronization or
when the SYNC/MODE pin is pulled low, preventing low
frequency ripple from interfering with audio circuitry.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode. Low
output voltages are easily supported with the 0.8V feed-
back reference voltage. The LTC1877 is available in a
space saving 8-lead MSOP package. Lower input voltage
applications (less than 7V abs max) should refer to the
LTC1878 data sheet.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
TYPICAL APPLICATION
V_IN
2.65V
TO 10V
High Efficiency Step-Down Converter
10µF**
CER
220pF
7
SYNC
5
SW
6
V_IN
1
LTC1877
RUN
2
I_TH
GND
V_FB ³
4
10µH*
20pF
887k
280k
VOUT^†
3.3V
+
47µF***
*TOKO D62CB A920CY-100M
**TAIYO-YUDEN CERAMIC LMK325BJ106MN
***SANYO POSCAP 6TPA47M
†_{VOUT CONNECTED TO VIN FOR 2.65V < VIN < 3.3V}
1877 TA01
Efficiency vs Output Current
100
95 ^{VIN = 3.6V}
90
85
V_IN = 10V
80
V_IN = 7.2V
75
V_IN = 5V
70
65
60
55
50
0.1
V_OUT = 3.3V
L = 10µH
Burst Mode OPERATION
1.0
10
100
OUTPUT CURRENT (mA)
1000
1877 • TA02
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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