LT3991 Datasheet, PDF (1/24 Pages) Linear Technology – 55V, 1.2A Step-Down Regulator with 2.8 Quiescent Current

FEATURES
n _{Ultralow Quiescent Current:}
2.8μA I_Q Regulating 12V_IN to 3.3V_OUT
n _{Low Ripple Burst Mode}^® _Operation:
Output Ripple < 15mV_P-P
n _{Wide Input Voltage Range: 4.3V to 55V}
n _{1.2A 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 _{Saturating Switch Design: 0.44Ω On-Resistance}
n _{Output Voltage: 1.19V to 30V}
n _{Small Thermally Enhanced 10-Pin MSOP Package}
and (3mm × 3mm) DFN Packages
APPLICATIONS
n _{Automotive Battery Regulation}
n _{Power for Portable Products}
n _{Industrial Supplies}
LT3991
55V, 1.2A Step-Down
Regulator with 2.8µA
Quiescent Current
DESCRIPTION
The LT^®3991 is an adjustable frequency monolithic buck
switching regulator that accepts a wide input voltage range
up to 55V. 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 0.44Ω 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 LT3991, 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 volt-
age. The LT3991 is available in small 10-pin MSOP and
3mm × 3mm DFN packages with exposed pads for low
thermal resistance.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode 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 55V
OFF ON
4.7μF
V_IN
EN
BOOST
PG
SW
SS _LT3991
RT
BD
0.47μF _10μH
V_OUT
3.3V
1.2A
10pF
1.78M
118k
SYNC GND ^FB
1M
47μF
3991 TA01
No Load Supply Current
4.0
3.5
3.0
2.5
2.0
1.5
1.0
5
15
25
35
45
55
INPUT VOLTAGE (V)
3991 TA01b
3991f
1