Final Electrical Specifications
LTC1877
High Efficiency
Monolithic Synchronous
Step-Down Regulator
FEATURES
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DESCRIPTION
May 2000
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High Efficiency: Up to 95%
Very Low Quiescent Current: Only 10
µ
A
During Operation
600mA Output Current at V
IN
= 5V
2.65V to 10V Input Voltage Range
550kHz Constant Frequency Operation
Synchronizable from 400kHz to 700kHz
Selectable Burst Mode
TM
Operation/
Pulse Skipping Mode
No Schottky Diode Required
Low Dropout Operation: 100% Duty Cycle
0.8V Reference Allows Low Output Voltages
Shutdown Mode Draws < 1µA Supply Current
±2%
Output Voltage Accuracy
Current Mode Control for Excellent Line and
Load Transient Response
Overcurrent and Overtemperature Protected
Available in 8-Lead MSOP Package
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.
APPLICATIONS
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Cellular Telephones
Wireless Modems
Personal Information Appliances
Portable Instruments
Distributed Power Systems
Battery-Powered Equipment
TYPICAL APPLICATION
High Efficiency Step-Down Converter
20pF
LTC1877
GND
4
*TOKO
D62CB A920CY-100M
**TAIYO-YUDEN
CERAMIC LMK325BJ106MN
***SANYO
POSCAP 6TPA47M
†
V
OUT
CONNECTED TO V
IN
FOR 2.65V < V
IN
< 3.3V
V
FB
3
887k
280k
V
IN
2.65V
TO 10V
7
10µF**
CER
6
1
2
220pF
SYNC
V
IN
RUN
I
TH
SW
5
10µH*
VOUT
3.3V
†
Efficiency vs Output Current
100
95
90
85
V
IN
= 10V
V
IN
= 7.2V
V
IN
= 5V
V
IN
= 3.6V
+
EFFICIENCY (%)
80
75
70
65
60
55
50
0.1
47µF***
1877 TA01
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.
U
U
U
V
OUT
= 3.3V
L = 10µH
Burst Mode OPERATION
1.0
100
10
OUTPUT CURRENT (mA)
1000
1877 • TA02
1
LINER [ LINEAR TECHNOLOGY ]
