LTC1771 Datasheet, PDF (1/16 Pages) Linear Technology – Low Quiescent Current High Efficiency Step-Down DC/DC Controller

FEATURES
s _{Very Low Standby Current: 10µA}
s _{Available in Space-Saving 8-Lead MSOP Package}
s _{High Output Currents}
s _{Wide VIN Range: 2.8V to 20V Operation}
s _{VOUT Range: 1.23V to 18V}
s _{High Efficiency: Over 93% Possible}
s _{±2% Output Accuracy}
s _{Very Low Dropout Operation: 100% Duty Cycle}
s _{Current Mode Operation for Excellent Line and}
Load Transient Response
s _{Defeatable Burst Mode}^TM _Operation
s _{Short-Circuit Protected}
s _{Optional Programmable Soft-Start}
s _{Micropower Shutdown: IQ = 2µA}
U
APPLICATIO S
s _{Cellular Telephones and Wireless Modems}
s _{1- to 4-Cell Lithium-Ion-Powered Applications}
s _{Portable Instruments}
s _{Battery-Powered Equipment}
s _{Battery Chargers}
s _Scanners
Final Electrical Specifications
LTC1771
Low Quiescent Current
High Efficiency Step-Down
DC/DC Controller
DESCRIPTIO
February 2000
The LTC^®1771 is a high efficiency current mode step-
down DC/DC controller that draws as little as 10µA DC
supply current to regulate the output at no load while
maintaining high efficiency for loads up to several amps.
The LTC1771 drives an external P-channel power MOSFET
using a current mode, constant off-time architecture. An
external sense resistor is used to program the operating
current level. Current mode control provides short-circuit
protection, excellent transient response and controlled
start-up behavior. Burst Mode operation enables the
LTC1771 to maintain high efficiency down to extremely
low currents. Shutdown mode further reduces the supply
current to a mere 2µA. For low noise applications, Burst
Mode operation can be easily disabled with the MODE pin.
Wide input supply range of 2.8V to 18V (20V maximum)
and 100% duty cycle operation for low dropout make the
LTC1771 ideal for a wide variety of battery-powered appli-
cations where maximizing battery life is important.
The LTC1771’s availability in both 8-lead MSOP and SO
packages provides for a minimum area solution.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
TYPICAL APPLICATIO
C_SS
0.01µF
V_IN
4.5V TO 18V
R_SENSE
0.05Ω
10µF
25V
CER
R_C
10k
C_C
22OpF
V_IN SENSE
RUN/SS PGATE
I_TH LTC1771
V_FB
MODE
GND
M1
Si6447DQ
V_IN
R2
1.64M
1%
R1
1M
1%
5pF
L1
15µH
UPS5817
V_OUT
3.3V
+ C_OUT ^2A
150µF
6.3V
1771 F01
Figure 1. High Efficiency Step-Down Converter
LTC1771 Efficiency
100
V_IN = 5V
90
V_IN = 10V
80
V_IN = 15V
70
60
50
V_OUT = 3.3V
40 ^{RSENSE = 0.05Ω}
0.1
1
10
100 1000
LOAD CURRENT (mA)
10000
1771 F01b
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.
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