LTC1879 Datasheet, PDF (1/20 Pages) Linear Technology – 1.2A Synchronous Step-Down Regulator with 15mA Quiescent Current

LTC1879
1.2A Synchronous
Step-Down Regulator with
15µA Quiescent Current
FEATURES
s _{High Efficiency: Up to 95%}
s _{Low Quiescent Current: Only 15µA with No Load}
s _{550kHz Constant Frequency Operation}
s _{2.65V to 10V Input Voltage Range}
s _{VOUT from 0.8V to VIN, IOUT to 1.2A}
s _{True PLL Frequency Locking from 350kHz to 750kHz}
s _{Power Good Output Voltage Monitor}
s _{Low Dropout Operation: 100% Duty Cycle}
s _{Burst Mode}^® _{or Pulse Skipping Operation}
s _{Current Mode Operation for Excellent Line and Load}
Transient Response
s _{Shutdown Mode Draws < 1µA Supply Current}
s _{±2% Output Voltage Accuracy}
s _{Overcurrent and Overtemperature Protected}
s _{Available in 16-Lead SSOP Package}
U
APPLICATIO S
s _{Cellular Telephones}
s _{Portable Computers}
s _{Wireless Modems}
DESCRIPTIO
The LTC^®1879 is a high efficiency monolithic synchro-
nous buck regulator using a constant frequency, current
mode architecture. Operating supply current is only 15µA
with no load and drops to < 1µA in shutdown. The input
supply voltage range of 2.65V to 10V makes the LTC1879
ideally suited for both single and dual Li-Ion battery-pow-
ered applications. 100% duty cycle provides low dropout
operation, extending battery life in portable systems.
The switching frequency is internally set to 550kHz, allow-
ing the use of small surface mount inductors and capaci-
tors. For noise sensitive applications, the LTC1879 can be
externally synchronized from 350kHz to 750kHz. Burst
Mode operation is inhibited during synchronization or
when the SYNC/MODE pin is pulled low.
The internal synchronous rectifier switch increases effi-
ciency and eliminates the need for an external Schottky
diode. Low output voltages are easily supported with a
0.8V feedback reference voltage. The LTC1879 is available
in a 16-lead SSOP package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
High Efficiency Step-Down Converter
V_IN
2.65V TO 10V
C_IN
10µF
150k
13
SV_IN
2
RUN/SS
8, 9
PV_IN
15
5, 12
SYNC/MODE SWP
14
LTC1879
6, 11
PGOOD
SWN
4
I_TH
7, 10
PGND
L1
6.2µH
V_OUT*
3.1V
C_OUT
47µF
47pF
220pF
SGND
1
3
V_FB
80.6k
28.0k
1879 TA01a
C_IN: TAIYO YUDEN CERAMIC LMK325BJ106MN
C_OUT: TDK CERAMIC C4532X5ROJ476M
L1: TOKO A921CY6R2M
*V_OUT CONNECTED TO V_IN (MINUS SWITCH AND L1 VOLTAGE DROP) FOR 2.65V < V_IN < 3.1V
Efficiency vs Output Load Current
100
V_IN = 3.6V
90
80
V_IN = 7.2V
70
V_IN = 10V
60
50
40
30
0.1
Burst Mode OPERATION
V_OUT = 3.1V
L = 6.2µH
1
10
100
OUPUT CURRENT (mA)
1000
1879 TA01b
1879f
1