LT3971A_15 Datasheet, PDF (1/24 Pages) Linear Technology – 38V, 1.3A, 2MHz Step-Down Regulator with 2.2A Quiescent Current

FEATURES
n _{Ultralow Quiescent Current:}
2.8μA I_Q Regulating 12V_IN to 3.3V_OUT
n _{Fixed Output Voltages: 5V}
2.2μA I_Q Regulating 12V_IN to 5V_OUT
n _{Low Ripple Burst Mode}^® _Operation:
Output Ripple < 15mV_P-P
n _{Wide Input Voltage Range: 4.3V to 38V}
n _{1.3A Maximum Output Current}
n _{Adjustable Switching Frequency: 200kHz to 2MHz}
n _{Synchronizable Between 250kHz to 2MHz}
n _{Fast Transient Response}
n _{Accurate 1V Enable Pin Threshold}
n _{Low Shutdown Current: IQ = 700nA}
n _{Power Good Flag}
n _{Soft-Start Capability}
n _{Internal Compensation}
n _{Output Voltage: 1.19V to 30V}
n _{Small Thermally Enhanced 10-Lead MSOP Package}
APPLICATIONS
n _{USB VBUS Regulation}
n _{Automotive Battery Regulation}
n _{Power for Portable Products}
n _{Industrial Supplies}
LT3971A/LT3971A-5
38V, 1.3A, 2MHz
Step-Down Regulator with
2.2µA Quiescent Current
DESCRIPTION
The LT^®3971A is an adjustable frequency monolithic buck
switching regulator that accepts a wide input voltage range
up to 38V. Low quiescent current design consumes only
2.8μA 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. An internally compensated
current mode topology is used for fast transient response
and good loop stability. A high efficiency 0.33Ω switch
is included on the die along with a boost Schottky diode
and the necessary oscillator, control and logic circuitry.
An accurate 1V threshold enable pin can be used to shut
down the LT3971A, reducing the input supply current to
700nA. A capacitor on the SS pin provides a controlled
inrush current (soft-start). A power good flag signals when
V_OUT reaches 91% of the programmed output voltage. The
LT3971A is available in a small 10-lead MSOP package
with an exposed pad for low thermal resistance.
The LT3971A and LT3971A-5 have a more accurate ref-
erence voltage compared to the LT3971 and LT3971-5.
The LT3971A-5 also has specified V_OUT pin current and
ABSMAX current. These characteristics are important for
USB applications.
L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
TYPICAL APPLICATION
5.15V Step-Down Converter for USB Applications
V_IN
6.3V TO 38V
OFF ON EN
V_{IN BOOST}
4.7μF
PG
SW
SS _LT3971A-5
RT
BD
118k
SYNC GND ^VOUT
f = 400kHz
0.47μF _10μH
20k, 1%
715k
47μF
1%
3971 TA01a
V_OUT
5.15V
1.3A
No Load Supply Current
3.0
OUTPUT IN REGULATION
2.5
LT3971A-5
2.0
1.5
1.0
5
10 15 20 25 30 35
INPUT VOLTAGE (V)
3971A TA01b
3971af
1