Final Electrical Specifications
LTC1878
High Efficiency
Monolithic Synchronous
Step-Down Regulator
FEATURES
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DESCRIPTIO
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
= 3.3V
2.65V to 6V 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
®
1878 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
6V input voltage range makes the LTC1878 ideally suited
for single Li-Ion battery-powered applications. 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 LTC1878 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 LTC1878 is available in a
space saving 8-lead MSOP package.
For higher input voltage (12V abs max) applications, refer
to the LTC1877 data sheet.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
APPLICATIO S
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Cellular Telephones
Wireless Modems
Personal Information Appliances
Portable Instruments
Distributed Power Systems
Battery-Powered Equipment
TYPICAL APPLICATIO
V
IN
2.65V
TO 6V
22µF**
CER
7
6
1
2
220pF
5
Efficiency vs Output Load Current
100
95
EFFICIENCY (%)
90
V
IN
= 4.2V
85
V
IN
= 6V
80
75
1878 TA01
High Efficiency Step-Down Converter
10µH*
20pF
SYNC
V
IN
RUN
I
TH
GND V
FB
4
3
SW
V
OUT
†
3.3V
LTC1878
887k
280k
+
47µF***
*TOKO D62CB A920CY-100M
**TAIYO-YUDEN CERAMIC JMK325BJ226MM
***SANYO POSCAP 6TPA47M
†
V
OUT
CONNECTED TO V
IN
FOR 2.65V < V
IN
< 3.3V
70
0.1
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
V
IN
= 3.6V
Burst Mode OPERATION
V
OUT
= 3.3V
L = 10µH
1
10
100
OUTPUT CURRENT (mA)
U
U
1000
1878 TA02
1
LINER [ LINEAR TECHNOLOGY ]
