LTC1772B
Constant Frequency
Current Mode Step-Down
DC/DC Controller in SOT-23
FEATURES
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DESCRIPTION
The LTC
®
1772B 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
LTC1772B when the input voltage falls below 2.0V.
The LTC1772B provides a ± 2.5% output voltage accuracy
and consumes only 270μA of quiescent current. In shut-
down, the device draws a mere 8μA.
To further maximize the life of a battery source, the
external P-channel MOSFET is turned on continuously
in dropout (100% duty cycle). High constant operating
frequency of 550kHz allows the use of a small external
inductor.
The LTC1772B is available in a small footprint 6-lead
TSOT-23.
For a Burst Mode operation enabled version of the
LTC1772B, please refer to the LTC1772 data sheet.
L,
LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Burst Mode
®
Operation Disabled for Lower Output
Ripple at Light Loads
High Efficiency: Up to 94%
High Output Currents Easily Achieved
Wide V
IN
Range: 2.5V to 9.8V
Constant Frequency 550kHz Operation
Low Dropout: 100% Duty Cycle
Output Voltage Down to 0.8V
Current Mode Operation for Excellent Line and Load
Transient Response
Shutdown Mode Draws Only 8µA Supply Current
Tiny 6-Lead TSOT-23 Package
APPLICATIONS
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One or Two Lithium-Ion-Powered Applications
Cellular Telephones
Wireless Devices
Portable Computers
Distributed 3.3V, 2.5V or 1.8V Power Systems
TYPICAL APPLICATION
R1
0.03Ω
1
10k
220pF
I
TH
/RUN PGATE
LTC1772B
2
3
GND
V
FB
V
IN
SENSE
–
5
4
D1
6
L1
M1 4.7μH
C1
10μF
10V
V
IN
2.5V
TO 9.8V
100
95
90
EFFICIENCY (%)
V
OUT
2.5V
2A
174k
85
80
75
70
C1: TAIYO YUDEN LMK325BJ106K-T
C2A: SANYO 6TPA47M
C2B: AVX 0805ZC105KAT1A
D1: MOTOROLA MBRM120T3
L1: MURATA LQN6C-4R7
M1: FAIRCHILD FDC638P
R1: IRC LRC-LR1206-01-R030F
80.6k
65
60
1772 F01a
Efficiency vs Load Current*
LTC1772
Burst Mode
OPERATION
+
C2A
47μF
6V
C2B
1μF
10V
LTC1772B
NON-Burst Mode
OPERATION
V
IN
= 3.6V
V
OUT
= 2.5V
10
100
1000
10000
LOAD CURRENT (mA)
*OUTPUT RIPPLE WAVEFORMS FOR THE CIRCUIT
OF FIGURE 1 APPEAR IN FIGURE 2.
1772 F01b
Figure 1. High Efficiency, High Output Current 2.5V/2A Regulator
1772bfa
1
LINER [ LINEAR TECHNOLOGY ]
