LT3975_15 Datasheet, PDF (1/24 Pages) Linear Technology – 42V, 2.5A, 2MHz Step-Down Switching Regulator with 2.7A Quiescent Current

LT3975
42V, 2.5A, 2MHz Step-Down
Switching Regulator with
2.7µA Quiescent Current
FEATURES
n _{Ultralow Quiescent Current:}
2.7µA I_Q at 12V_IN to 3.3V_OUT
n _{Low Ripple Burst Mode}^® _Operation
Output Ripple < 15mV_P-P
n _{Wide Input Range: Operation from 4.3V to 42V}
n _{2.5A Maximum Output Current}
n _{Excellent Start-Up and Dropout Performance}
n _{Adjustable Switching Frequency: 200kHz to 2MHz}
n _{Synchronizable Between 250kHz to 2MHz}
n _{Accurate Programmable Undervoltage Lockout}
n _{Low Shutdown Current: IQ = 700nA}
n _{Power Good Flag}
n _{Soft-Start Capability}
n _{Thermal Shutdown Protection}
n _{Current Limit Foldback with Soft-Start Override}
n _{Saturating Switch Design: 75mΩ On Resistance}
n _{Small, Thermally Enhanced 16-Lead MSOP Package}
APPLICATIONS
n _{Automotive Battery Regulation}
n _{Portable Products}
n _{Industrial Supplies}
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
DESCRIPTION
The LT^®3975 is an adjustable frequency monolithic buck
switching regulator that accepts a wide input voltage range
up to 42V. Low quiescent current design consumes only
2.7µA of supply current while regulating with no load. Low
ripple Burst Mode operation maintains high efficiency at
low output currents while keeping the output ripple below
15mV in a typical application. The LT3975 can supply up
to 2.5A of load current and has current limit foldback to
limit power dissipation during short circuit. A low dropout
voltage of 500mV is maintained when the input voltage
drops below the programmed output voltage, such as
during automotive cold crank.
An internally compensated current mode topology is used
for fast transient response and good loop stability. A high
efficiency 75mΩ switch is included on the die along with a
boost Schottky diode and the necessary oscillator, control,
and logic circuitry. An accurate 1.02V threshold enable pin
can be driven directly from a microcontroller or used as a
programmable undervoltage lockout. A capacitor on the
SS pin provides a controlled inrush current (soft-start).
A power good flag signals when V_OUT reaches 91.6% of
the programmed output voltage. The LT3975 is available
in a small 16-lead MSOP package with exposed pad for
low thermal resistance.
TYPICAL APPLICATION
V_IN
4.3V TO 42V
3.3V Step-Down Converter
OFF ON
10µF
V_IN
EN
BOOST
PG
SW
LT3975
0.47µF 3.3µH
PDS560
SS
RT
10nF
SYNC
78.7k
OUT
FB
GND
f = 600kHz
1M
10pF
576k
3975 TA01a
V_OUT
3.3V
2.5A
47µF
1210
No-Load Supply Current
4.5
IN REGULATION
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0
5 10 15 20 25 30 35 40 45
INPUT VOLTAGE (V)
3975 TA01b
3975f
1