LTC1772 Datasheet, PDF (1/16 Pages) Linear Technology – Constant Frequency Current Mode Step-Down DC/DC Controller in SOT-23

Final Electrical Specifications
LTC1772
Constant Frequency
Current Mode Step-Down
DC/DC Controller in SOT-23
September 1999
FEATURES
s _{High Efficiency: Up to 94%}
s _{High Output Currents Easily Achieved}
s _{Wide VIN Range: 2.5V to 9.8V}
s _{Constant Frequency 550kHz Operation}
s _{Burst Mode}^TM _{Operation at Light Load}
s _{Low Dropout: 100% Duty Cycle}
s _{0.8V Reference Allows Low Output Voltages}
s _{Current Mode Operation for Excellent Line and Load}
Transient Response
s _{Low Quiescent Current: 270µA}
s _{Shutdown Mode Draws Only 8µA Supply Current}
s _{±2.5% Reference Accuracy}
s _{Tiny 6-Lead SOT-23 Package}
U
APPLICATIONS
s _{One or Two Lithium-Ion-Powered Applications}
s _{Cellular Telephones}
s _{Wireless Modems}
s _{Portable Computers}
s _{Distributed 3.3V, 2.5V or 1.8V Power Systems}
s _Scanners
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.
TYPICAL APPLICATION
10k
220pF
1
6
I_TH/RUN PGATE
LTC1772
2
GND
3
V_FB
5
V_IN
SENSE^{– 4}
C1: TAIYO YUDEN CERAMIC EMK325BJ106MNT
C2: SANYO POSCAP 6TPA47M
D1: IR10BQ015
R1
0.03Ω
L1
M1 _4.7µH
+
D1
C1
10µF
16V
V_IN
2.5V
TO 9.8V
C2
47µF
6V
V_OUT
2.5V
169k ^2A
78.7k
L1: MURATA LQN6C-4R7
M1: Si3443DV
R1: DALE 0.25W
1772 F01a
Figure 1. High Efficiency Step-Down Converter
Efficiency vs Load Current
100
V_IN = 4.2V
V_IN = 3.3V
90
80
V_IN = 6V
70
V_IN = 9.8V ^{VIN = 8.4V}
60
50
40
1
V_OUT = 2.5V
R_SENSE = 0.03Ω
10
100
1000
LOAD CURRENT (mA)
10000
1772 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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