LTC3772
Micropower No RSENSE
Constant Frequency Step-Down
DC/DC Controller
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FEATURES
DESCRIPTIO
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The LTC®3772 is a constant frequency current mode
step-down DC/DC controller in a low profile 8-lead SOT-23
(ThinSOTTM) and a 3mm × 2mm DFN package. The No
RSENSETM architecture eliminates the need for a current
sense resistor, improving efficiency and saving board
space.
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No Current Sense Resistor Required
40µA No-Load Quiescent Current
High Output Currents Easily Achieved
Internal Soft-Start Ramps VOUT
Wide VIN Range: 2.75V to 9.8V
Low Dropout: 100% Duty Cycle
Constant Frequency 550kHz Operation
Low Ripple Burst Mode® Operation at Light Load
Output Voltage as Low as 0.8V
±1.5% Voltage Reference Accuracy
Current Mode Operation for Excellent Line and Load
Transient Response
Only 8µA Supply Current in Shutdown
Low Profile 8-Lead SOT-23 (1mm) and
(3mm × 2mm) DFN (0.75mm) Packages
The LTC3772 automatically switches into Burst Mode
operation at light loads to increase efficiency at low output
current. It consumes only 40µA of quiescent current
under a no-load condition.
The LTC3772 incorporates an undervoltage lockout feature that shuts down the device when the input voltage
falls below 2V. To maximize the runtime from a battery
source, the external P-channel MOSFET is turned on
continuously in dropout (100% duty cycle). High switching frequency of 550kHz allows the use of a small inductor
and capacitors. An internal soft-start smoothly ramps the
output voltage from zero to its regulation point.
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APPLICATIO S
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1- or 2-Cell Li-Ion Battery-Powered Applications
Wireless Devices
Portable Computers
Distributed Power Systems
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
ThinSOT and No RSENSE are trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
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TYPICAL APPLICATIO
Efficiency and Power Loss vs Load Current
550kHz Micropower Step-Down DC/DC Converter
10
100
20k
LTC3772
3.3µH
SW
47µF
22pF
VIN = 5V
10µF
PGATE
82.5k
VFB
90
VOUT
2.5V
2A
1
80
0.1
70
VIN = 5V
VIN = 3.3V
60
174k
POWER LOSS (W)
GND
VIN = 3.3V
VIN
2.75V TO 9.8V
VIN
ITH/RUN
EFFICIENCY (%)
680pF
0.01
3772 TA01
50
FIGURE 5 CIRCUIT
40
1
100
1000
10
LOAD CURRENT (mA)
0.001
10000
3772 TA01b
3772f
1
LTC3772
U
W W
W
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Supply Voltage (VIN)........................ – 0.3V to 10V
IPRG, PGATE Voltages ................ – 0.3V to (VIN + 0.3V)
VFB, ITH/RUN Voltages ............................. – 0.3V to 2.4V
SW Voltage ........... – 2V to (VIN + 1V) or 10V Maximum
PGATE Peak Output Current (
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