LTC1878_15 Datasheet, PDF (1/16 Pages) Linear Technology – High Efficiency Monolithic Synchronous Step-Down Regulator

LTC1878
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 = 3.3V}
s _{2.65V to 6V Input Voltage Range}
s _{550kHz Constant Frequency Operation}
s _{Synchronizable from 400kHz to 700kHz}
s _{Selectable Burst Mode}^TM _{Operation or}
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-Lead MSOP Package}
U
APPLICATIO S
s _{Cellular Telephones}
s _{Wireless Modems}
s _{Personal Information Appliances}
s _{Portable Instruments}
s _{Distributed Power Systems}
s _{Battery-Powered Equipment}
DESCRIPTIO
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 (11V 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.
TYPICAL APPLICATIO
High Efficiency Step-Down Converter
V_IN
2.65V
TO 6V _22µF**
CER
220pF
7
SYNC
5
SW
6
V_IN
1
LTC1878
RUN
2
3
I_{TH GND} V_FB
4
10µH*
20pF
887k
280k
*TOKO D62CB A920CY-100M
**TAIYO-YUDEN CERAMIC JMK325BJ226MM
***SANYO POSCAP 6TPA47M
†_{VOUT CONNECTED TO VIN FOR 2.65V < VIN < 3.3V}
V_OUT^†
3.3V
+
47µF***
1878 TA01
Efficiency vs Output Load Current
100
95
V_IN = 3.6V
90
V_IN = 4.2V
85
V_IN = 6V
80
75
70
0.1
Burst Mode OPERATION
V_OUT = 3.3V
L = 10µH
1
10
100
OUTPUT CURRENT (mA)
1000
1878 TA02
1