LT3681
36V, 2A, 2.8MHz Step-Down
Switching Regulator with
Integrated Power Schottky Diode
FEATURES
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DESCRIPTIO
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Wide Input Voltage Range: 3.6V to 34V Operating,
36V Maximum
2A Maximum Output Current
Low Ripple Burst Mode
®
Operation
50µA I
Q
at 12V
IN
to 3.3V
OUT
Output Ripple < 15mV
P-P
Adjustable Switching Frequency: 300kHz to 2.8MHz
Low Shutdown Current: I
Q
< 1µA
Integrated Boost Diode
Integrated Power Schottky Diode
Power Good Flag
Saturating Switch Design: 0.18Ω On-Resistance
1.265V Feedback Reference Voltage
Output Voltage: 1.265V to 20V
Soft-Start Capability
Small 14-Pin Thermally Enhanced
(4mm x 3mm) DFN Package
APPLICATIO S
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Automotive Battery Regulation
Power for Portable Products
Distributed Supply Regulation
Industrial Supplies
Wall Transformer Regulation
The LT
®
3681 is an adjustable frequency (300kHz to 2.8MHz)
monolithic buck switching regulator that accepts input
voltages up to 34V (36V maximum). A high efficiency
0.18Ω switch is included on the die along with a boost
Schottky diode and the necessary oscillator, control, and
logic circuitry. An undedicated power Schottky diode is
integrated into the LT3681 to minimize the solution size.
Current mode topology is used for fast transient response
and good loop stability. Low ripple Burst Mode operation
maintains high efficiency at low output currents while
keeping output ripple below 15mV in a typical application.
In addition, the LT3681 can further enhance low output
current efficiency by drawing bias current from the output
when V
OUT
is above 3V. Shutdown reduces input supply
current to less than 1µA while a resistor and capacitor on
the RUN/SS pin provide a controlled output voltage ramp
(soft-start). A power good flag signals when V
OUT
reaches
90% of the programmed output voltage. The LT3681
is available in 14-Pin 4mm x 3mm DFN package with
exposed pads for low thermal resistance.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
TYPICAL APPLICATIO
V
IN
6.3V TO
34V
OFF ON
20k
4.7
m
F
V
C
RT
330pF
PG
60.4k
V
IN
RUN/SS
5V Step-Down Converter
BD
BOOST
0.47
m
F
L
6.8
m
H
V
OUT
5V
2A
100
90
80
70
EFFICIENCY (%)
60
50
40
30
20
590k
GND
FB
200k
22
m
F
10
0
0.0001
0.001
LT3681
SW
DC
DA
BIAS
L: NEC PLC-0745-6R8
3681 TA01
U
Efficiency
10.0000
1.0000
POWER LOSS (W)
0.1000
0.0100
V
IN
= 12V
V
OUT
= 3.3V
L = 4.7
m
H
F = 800 kHz
0.01
0.1
I
LOAD
(A)
1
10
3681 TA01b
U
U
0.0010
0.0001
3681f
1
LINER [ LINEAR TECHNOLOGY ]
