LTC1772B Datasheet, PDF (1/12 Pages) Linear Technology – Constant Frequency Current Mode Step-Down DC/DC Controller in SOT-23

LTC1772B
Constant Frequency
Current Mode Step-Down
DC/DC Controller in SOT-23
FEATURES
s _{Burst Mode}^TM _{Operation Disabled for Lower Output}
Ripple at Light Loads
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 _{Low Dropout: 100% Duty Cycle}
s _{Output Voltage down to 0.8V}
s _{Current Mode Operation for Excellent Line and Load}
Transient Response
s _{Shutdown Mode Draws Only 8µA Supply Current}
s _{Tiny 6-Lead SOT-23 Package}
U
APPLICATIO S
s _{One or Two Lithium-Ion-Powered Applications}
s _{Cellular Telephones}
s _{Wireless Devices}
s _{Portable Computers}
s _{Distributed 3.3V, 2.5V or 1.8V Power Systems}
DESCRIPTIO
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
SOT-23.
For a Burst Mode operation enabled version of the
LTC1772B, please refer to the LTC1772 data sheet.
, 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
LTC1772B
2
GND
3
V_FB
5
V_IN
SENSE^{– 4}
R1
0.03Ω
C1
10µF
10V
L1
M1 _4.7µH
+ C2A
D1
47µF
6V
V_IN
2.5V
TO 9.8V
V_OUT
2.5V
C2B
2A
1µF
10V 174k
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
1772 F01a
Figure 1. High Efficiency, High Output Current 2.5V/2A Regulator
Efficiency vs Load Current*
100
LTC1772
95 _{BURST MODE}
OPERATION
90
85
80
LTC1772B
NON-BURST MODE
75
OPERATION
70
65
V_IN = 3.6V
V_OUT = 2.5V
60
10
100
1000 10000
LOAD CURRENT (mA)
*OUTPUT RIPPLE WAVEFORMS FOR THE CIRCUIT
OF FIGURE 1 APPEAR IN FIGURE 2.
1772 F01b
1