LT3991/LT3991-3.3/LT3991-5
55V, 1.2A Step-Down
Regulator with 2.8µA
Quiescent Current
Features
Description
Ultralow Quiescent Current:
2.8µA IQ Regulating 12VIN to 3.3VOUT
n Fixed Output Voltages: 3.3V, 5V
2.1µA IQ Regulating 12VIN
n Low Ripple Burst Mode® Operation:
Output Ripple < 15mVP-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: I = 700nA
Q
n Power Good Flag
n Soft-Start CapabilityV
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
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 VOUT reaches 91% of the programmed output voltage. The LT3991 is available in small 10-pin MSOP and
3mm × 3mm DFN packages with exposed pads for low
thermal resistance.
n
Applications
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.
Automotive Battery Regulation
Power for Portable Products
n Industrial Supplies
n
n
Typical Application
No Load Supply Current
3.0
3.3V Step Down Converter
OFF ON
EN./UVLO
VIN
BOOST
0.47µF
PG
SS
4.7µF
INPUT CURRENT (µA)
VIN
4.3V TO 55V
LT3991-3.3
12µH
SW
RT
BD
118k
f = 400kHz
SYNC
GND
VOUT
47µF
3991 TA01a
VOUT
3.3V
1.2A
OUTPUT IN REGULATION
2.5
LT3991-5
2.0
LT3991-3.3
1.5
1.0
5
10 15 20 25 30 35 40 45 50 55
INPUT VOLTAGE (V)
3991 G06
3991fa
1
