LTC3772B Datasheet, PDF (1/20 Pages) Linear Technology – Micropower No RSENSE Constant Frequency Step-Down DC/DC Controller

LTC3772B
Micropower No R_SENSE
Constant Frequency Step-Down
DC/DC Controller
FEATURES
■ _{No Current Sense Resistor Required}
■ _{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 Pulse Skipping 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
U
APPLICATIO S
■ _{1- or 2-Cell Li-Ion Battery-Powered Applications}
■ _{Wireless Devices}
■ _{Portable Computers}
■ _{Distributed Power Systems}
DESCRIPTIO
The LTC^®3772B 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 LTC3772B automatically switches into pulse skipping
operation at light loads. It consumes only 200µA of quies-
cent current under a no-load condition.
The LTC3772B 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.
, LT, LTC and LTM are registered trademarks 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. Protected by
U.S. Patents including 5731694, 6127815.
TYPICAL APPLICATIO
550kHz Micropower Step-Down DC/DC Converter
680pF
20k
82.5k
I_TH/RUN V_IN
LTC3772B
GND PGATE
V_FB
SW
22pF 174k
3.3µH
V_IN
2.75V TO 9.8V
10µF
47µF
V_OUT
2.5V
2A
3772B TA01
Efficiency and Power Loss vs Load Current
(Figure 5 Circuit)
100
10
90
80
EFFICIENCY
1
70
60
50
0.1
40
POWER LOSS
30
0.01
20
10
V_IN = 3.3V
V_IN = 5V
0
0.001
1
10
100
1000 10000
LOAD CURRENT (mA)
3772B TA01b
3772bfa
1