LT3685_15 Datasheet, PDF (1/24 Pages) Linear Technology – 36V, 2A, 2.4MHz Step-Down Switching Regulator

LT3685
36V, 2A, 2.4MHz Step-Down
Switching Regulator
FEATURES
■ _{Wide Input Range:}
Operation From 3.6V to 36V
Overvoltage Lockout Protects Circuit through
60V Transients
■ _{2A Maximum Output Current}
■ _{Adjustable Switching Frequency: 200kHz to 2.4MHz}
■ _{Low Shutdown Current: IQ < 1μA}
■ _{Integrated Boost Diode}
■ _{Synchronizable Between 250kHz to 2MHz}
■ _{Power Good Flag}
■ _{Saturating Switch Design: 0.25 On-Resistance}
■ _{0.790V Feedback Reference Voltage}
■ _{Output Voltage: 0.79V to 20V}
■ _{Soft-Start Capability}
■ _{Small 10-Pin Thermally Enhanced MSOP and}
(3mm × 3mm) DFN Packages
APPLICATIONS
■ _{Automotive Battery Regulation}
■ _{Set Top Box}
■ _{Distributed Supply Regulation}
■ _{Industrial Supplies}
■ _{Wall Transformer Regulation}
DESCRIPTION
The LT^®3685 is an adjustable frequency (200kHz to 2.4MHz)
monolithic step-down switching regulator that accepts
input voltages up to 38V operating and 60V maximum. An
internal overvoltage protection circuit turns off the power
switch when V_IN is above 38V typical (36V minimum) which
then allows the part to safely withstand 60V transients. A
high efficiency 0.25 switch is included on the die along
with a boost Schottky diode and the necessary oscillator,
control, and logic circuitry. Current mode topology is
used for fast transient response and good loop stability.
The LT3685’s high operating frequency allows the use of
small, low cost inductors and ceramic capacitors result-
ing in low output ripple while keeping total solution size
to a minimum. The low current shutdown mode 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 89% of the programmed output voltage. The
LT3685 is available in 10-Pin MSOP and 3mm × 3mm DFN
packages 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 APPLICATION
3.3V Step-Down Converter
V_IN
4.5V TO 36V
TRANSIENT
TO 60V
OFF ON
14k
4.7μF
470pF
40.2k
V_IN
RUN/SS
BD
BOOST
V_C
LT3685
SW
R_T
PG
SYNC
GND
FB
V_OUT
3.3V
2A
0.47μF _4.7μH
316k
100k
22μF
3685 TA01
Efficiency
100
V_OUT = 5V
90
80
V_OUT = 3.3V
70
60
V_IN = 12V
L = 5.6μH
50
F = 800 kHz
0 0.5
1.0
1.5
2
LOAD CURRENT (A)
3685 TA01b
3685fb
1