LT3975
42V, 2.5A, 2MHz Step-Down
Switching Regulator with
2.7µA Quiescent Current
FEATURES
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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.
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Ultralow Quiescent Current:
2.7µA I
Q
at 12V
IN
to 3.3V
OUT
Low Ripple Burst Mode
®
Operation
Output Ripple < 15mV
P-P
Wide Input Range: Operation from 4.3V to 42V
2.5A Maximum Output Current
Excellent Start-Up and Dropout Performance
Adjustable Switching Frequency: 200kHz to 2MHz
Synchronizable Between 250kHz to 2MHz
Accurate Programmable Undervoltage Lockout
Low Shutdown Current: I
Q
= 700nA
Power Good Flag
Soft-Start Capability
Thermal Shutdown Protection
Current Limit Foldback with Soft-Start Override
Saturating Switch Design: 75mΩ On Resistance
Small, Thermally Enhanced 16-Lead MSOP Package
APPLICATIONS
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Automotive Battery Regulation
Portable Products
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.
TYPICAL APPLICATION
3.3V Step-Down Converter
V
IN
4.3V TO 42V
OFF ON
EN
PG
10µF
SS
RT
SYNC
78.7k
f = 600kHz
LT3975
OUT
FB
GND
BOOST
SW
V
IN
0.47µF 3.3µH
PDS560
No-Load Supply Current
4.5
4.0
INPUT CURRENT (µA)
3.5
3.0
2.5
2.0
1.5
1.0
0
15 20 25 30 35
INPUT VOLTAGE (V)
45
IN REGULATION
1M
10pF
576k
3975 TA01a
10nF
V
OUT
3.3V
2.5A
47µF
1210
5
10
40
3975 TA01b
3975f
1
LINER [ LINEAR TECHNOLOGY ]
