Final Electrical Specifications
LTC1772
Constant Frequency
Current Mode Step-Down
DC/DC Controller in SOT-23
September 1999
FEATURES
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DESCRIPTION
The LTC
®
1772 is a constant frequency current mode step-
down DC/DC controller providing excellent AC and DC load
and line regulation. The device incorporates an accurate
undervoltage lockout feature that shuts down the LTC1772
when the input voltage falls below 2.0V.
The LTC1772 boasts a
±2.5%
output voltage accuracy and
consumes only 270µA of quiescent current. For applica-
tions where efficiency is a prime consideration, the LTC1772
is configured for Burst Mode operation, which enhances
efficiency at low output current.
To further maximize the life of a battery source, the
external P-channel MOSFET is turned on continuously in
dropout (100% duty cycle). In shutdown, the device draws
a mere 8µA. High constant operating frequency of 550kHz
allows the use of a small external inductor.
The LTC1772 is available in a small footprint 6-lead
SOT-23.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
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High Efficiency: Up to 94%
High Output Currents Easily Achieved
Wide V
IN
Range: 2.5V to 9.8V
Constant Frequency 550kHz Operation
Burst Mode
TM
Operation at Light Load
Low Dropout: 100% Duty Cycle
0.8V Reference Allows Low Output Voltages
Current Mode Operation for Excellent Line and Load
Transient Response
Low Quiescent Current: 270µA
Shutdown Mode Draws Only 8µA Supply Current
±2.5%
Reference Accuracy
Tiny 6-Lead SOT-23 Package
APPLICATIONS
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One or Two Lithium-Ion-Powered Applications
Cellular Telephones
Wireless Modems
Portable Computers
Distributed 3.3V, 2.5V or 1.8V Power Systems
Scanners
TYPICAL APPLICATION
R1
0.03Ω
1
10k
220pF
I
TH
/RUN PGATE
LTC1772
2
3
GND
V
FB
V
IN
SENSE
–
5
4
D1
6
L1
M1 4.7µH
C1
10µF
16V
V
IN
2.5V
TO 9.8V
EFFICIENCY (%)
100
90
80
+
C2
47µF
6V
169k
V
OUT
2.5V
2A
70
60
50
40
1
78.7k
C1: TAIYO YUDEN CERAMIC EMK325BJ106MNT
C2: SANYO POSCAP 6TPA47M
D1: IR10BQ015
L1: MURATA LQN6C-4R7
M1: Si3443DV
R1: DALE 0.25W
V
OUT
= 2.5V
R
SENSE
= 0.03Ω
100
1000
10
LOAD CURRENT (mA)
10000
1772 F01b
1772 F01a
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.
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Efficiency vs Load Current
V
IN
= 3.3V
V
IN
= 4.2V
V
IN
= 6V
V
IN
= 9.8V
V
IN
= 8.4V
1
LINER [ LINEAR TECHNOLOGY ]
