Final Electrical Specifications
LTC1771
Low Quiescent Current
High Efficiency Step-Down
DC/DC Controller
FEATURES
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DESCRIPTIO
February 2000
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Very Low Standby Current: 10µA
Available in Space-Saving 8-Lead MSOP Package
High Output Currents
Wide V
IN
Range: 2.8V to 20V Operation
V
OUT
Range: 1.23V to 18V
High Efficiency: Over 93% Possible
±2%
Output Accuracy
Very Low Dropout Operation: 100% Duty Cycle
Current Mode Operation for Excellent Line and
Load Transient Response
Defeatable Burst Mode
TM
Operation
Short-Circuit Protected
Optional Programmable Soft-Start
Micropower Shutdown: I
Q
= 2µA
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.
APPLICATIO S
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Cellular Telephones and Wireless Modems
1- to 4-Cell Lithium-Ion-Powered Applications
Portable Instruments
Battery-Powered Equipment
Battery Chargers
Scanners
TYPICAL APPLICATIO
V
IN
4.5V TO 18V
R
SENSE
0.05Ω
V
IN
RUN/SS
C
SS
0.01µF
R
C
10k
C
C
22OpF
SENSE
PGATE
M1
Si6447DQ
10µF
25V
CER
100
V
IN
= 5V
90
EFFICIENCY (%)
I
TH
LTC1771
V
FB
MODE
GND
V
IN
R2
1.64M
1%
L1
15µH
UPS5817
80
70
60
50
40
0.1
V
OUT
= 3.3V
R
SENSE
= 0.05Ω
1
+
C
OUT
150µF
6.3V
V
OUT
3.3V
2A
R1
1M
1%
5pF
1771 F01
Figure 1. High Efficiency Step-Down Converter
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
U
U
LTC1771 Efficiency
V
IN
= 10V
V
IN
= 15V
10
100
1000
LOAD CURRENT (mA)
10000
1771 F01b
1
LINER [ LINEAR TECHNOLOGY ]
