LTC1877_15 Datasheet, PDF (1/18 Pages) Linear Technology – High Effi ciency Monolithic Synchronous Step-Down Regulator

FEATURES
n _{High Efficiency: Up to 95%}
n _{Very Low Quiescent Current: Only 10μA}
During Operation
n _{600mA Output Current at VIN = 5V}
n _{2.65V to 10V Input Voltage Range}
n _{550kHz Constant-Frequency Operation}
n _{No Schottky Diode Required}
n _{Low Dropout Operation: 100% Duty Cycle}
n _{Synchronizable from 400kHz to 700kHz}
n _{Selectable Burst Mode}^® _{Operation or}
Pulse-Skipping Mode
n _{0.8V Reference Allows Low Output Voltages}
n _{Shutdown Mode Draws < 1μA Supply Current}
n _{±2% Output Voltage Accuracy}
n _{Current Mode Control for Excellent Line and Load}
Transient Response
n _{Overcurrent and Overtemperature Protected}
n _{Available in 8-Lead MSOP Package}
APPLICATIONS
n _{Cellular Telephones}
n _{Wireless Modems}
n _{Personal Information Appliances}
n _{Portable Instruments}
n _{Distributed Power Systems}
n _{Battery-Powered Equipment}
LTC1877
High Efficiency
Monolithic Synchronous
Step-Down Regulator
DESCRIPTION
The LTC^®1877 s a high efficiency monolithic synchronous
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 applications. 100%
duty cycle provides low dropout operation, extending bat-
tery 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 exter-
nally 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
feedback 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.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
TYPICAL APPLICATION
High Efficiency Step-Down Converter
V_IN
2.65V
TO 10V
10μF**
CER
220pF
7
SYNC
SW ⁵
6 _{VIN LTC1877}
1
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
1877fb
1