LTC3772_15 Datasheet, PDF (1/20 Pages) Linear Technology – Micropower No RSENSE Constant Frequency Step-Down DC/DC Controller

LTC3772
Micropower No R_SENSE
Constant Frequency Step-Down
DC/DC Controller
FEATURES
■ _{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
U
(0.75mm)
Packages
APPLICATIO S
■ _{1- or 2-Cell Li-Ion Battery-Powered Applications}
■ _{Wireless Devices}
■ _{Portable Computers}
■ _{Distributed Power Systems}
DESCRIPTIO
The LTC^®3772 is a constant frequency current mode
step-down DC/DC controller in a low profile 8-lead SOT-23
(ThinSOT^TM) and a 3mm × 2mm DFN package. The No
R_SENSE^TM architecture eliminates the need for a current
sense resistor, improving efficiency and saving board
space.
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 fea-
ture 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 switch-
ing 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.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
ThinSOT and No R_SENSE are trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATIO
550kHz Micropower Step-Down DC/DC Converter
680pF
20k
82.5k
I_TH/RUN V_IN
LTC3772
GND PGATE
V_FB
SW
22pF 174k
3.3µH
V_IN
2.75V TO 9.8V
10µF
47µF
V_OUT
2.5V
2A
3772 TA01
Efficiency and Power Loss vs Load Current
100
10
V_IN = 3.3V
90
V_IN = 5V
1
80
70
0.1
V_IN = 5V
V_IN = 3.3V
60
0.01
50
40
1
FIGURE 5 CIRCUIT _0.001
10
100
1000 10000
LOAD CURRENT (mA)
3772 TA01b
3772f
1