LT3991/LT3991-3.3/LT3991-5

1

3991fa

Typical applicaTion

DescripTion

55V, 1.2A Step-Down

Regulator with 2.8µA

Quiescent Current

switchingregulatorthatacceptsawideinputvoltagerange

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

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, 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.

3.3V Step Down Converter

FeaTures

applicaTions

n

Ultralow Quiescent Current:

n

Fixed Output Voltages: 3.3V, 5V

n

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

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

n

Automotive Battery Regulation

n

Power for Portable Products

n

Industrial Supplies

No Load Supply Current

SW

SS

RT

4.3V TO 55V

3.3V

1.2A

4.7µF

0.47µF

47µF

118k

f = 400kHz

12µH

GND

BD

SYNC

OFF ON

LT3991-3.3

3991 TA01a

EN./UVLO

BOOST

PG

INPUT VOLTAGE (V)

5

2.0

2.5

45

3991 G06

1.5

1.0

15

25 30

55

3.0

35

10

20

50

40

LT3991-5

LT3991-3.3

OUTPUT IN REGULATION