LT3991 - 55V, 1.2A Step-Down Regulator with 2.8μA Quiescent Current

Features

  • Ultralow Quiescent Current: 2.8μA IQ Regulating 12VIN to 3.3VOUT
  • Fixed Output Voltages: 3.3V, 5V 2.1μA IQ Regulating 12VIN
  • Low Ripple Burst Mode® Operation: Output Ripple < 15mVP-P
  • Wide Input Voltage Range: 4.3V to 55V
  • 1.2A Maximum Output Current
  • Adjustable Switching Frequency: 200kHz to 2MHz
  • Synchronizable Between 250kHz to 2MHz
  • Fast Transient Response
  • Accurate 1V Enable Pin Threshold
  • Low Shutdown Current: IQ = 700nA
  • Power Good Flag
  • Soft-Start CapabilityV
  • Internal Compensation
  • Saturating Switch Design: 0.44Ω On-Resistance
  • Output Voltage: 1.19V to 30V
  • Small Thermally Enhanced 10-Pin MSOP Package and (3mm × 3mm) DFN Packages
Designed for Automotive and Transportation Applications
AEC-Q100 data available for specific packages


Typical Application

LT3991 Typical Application
LT3991 Typical Application

Description

The LT3991 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.

Packaging

CAD Symbols and Footprints: The downloadable Zip file below contains the schematic symbol and PCB footprints.

For complete and up to date package information and drawings, please refer to our packaging page

Part Number Package Code Temp Package
Drawing
RoHS
LT3991EDD#PBF 3x3 DFN-10 DD E 05-08-1699 Yes
LT3991EDD#TRPBF 3x3 DFN-10 DD E 05-08-1699 Yes
LT3991EMSE-3.3#PBF MS-10E MSE E 05-08-1664 Yes
LT3991EMSE-3.3#TRPBF MS-10E MSE E 05-08-1664 Yes
LT3991EMSE-5#PBF MS-10E MSE E 05-08-1664 Yes
LT3991EMSE-5#TRPBF MS-10E MSE E 05-08-1664 Yes
LT3991EMSE#PBF MS-10E MSE E 05-08-1664 Yes
LT3991EMSE#TRPBF MS-10E MSE E 05-08-1664 Yes
LT3991IDD#PBF 3x3 DFN-10 DD I 05-08-1699 Yes
LT3991IDD#TRPBF 3x3 DFN-10 DD I 05-08-1699 Yes
LT3991IMSE-3.3#PBF MS-10E MSE I 05-08-1664 Yes
LT3991IMSE-3.3#TRPBF MS-10E MSE I 05-08-1664 Yes
LT3991IMSE-5#PBF MS-10E MSE I 05-08-1664 Yes
LT3991IMSE-5#TRPBF MS-10E MSE I 05-08-1664 Yes
LT3991IMSE#PBF MS-10E MSE I 05-08-1664 Yes
LT3991IMSE#TRPBF MS-10E MSE I 05-08-1664 Yes


LT3991 Package Drawing
LT3991 Package Drawing
LT3991 Package Drawing

Order Info

  • Part numbers ending in PBF are lead free. Solder plated terminal finish (SnPb) versions are non-standard and special terms and conditions and pricing applies if available. Please contact LTC marketing for information.
  • Part numbers containing TR or TRM are shipped in tape and reel or 500 unit mini tape and reel, respectively
  • Please refer to our general ordering information or the product datasheet for more details

Package Variations and Pricing

Part Number Package Temp Price
(1-99)
Price
(1k)*
RoHS
LT3991EDD#PBF 3x3 DFN-10 E $4.22 $2.95 Yes
LT3991EDD#TRPBF 3x3 DFN-10 E $3.01 Yes
LT3991EMSE-3.3#PBF MS-10E E $4.22 $2.95 Yes
LT3991EMSE-3.3#TRPBF MS-10E E $3.01 Yes
LT3991EMSE-5#PBF MS-10E E $4.22 $2.95 Yes
LT3991EMSE-5#TRPBF MS-10E E $3.01 Yes
LT3991EMSE#PBF MS-10E E $4.22 $2.95 Yes
LT3991EMSE#TRPBF MS-10E E $3.01 Yes
LT3991IDD#PBF 3x3 DFN-10 I $4.69 $3.28 Yes
LT3991IDD#TRPBF 3x3 DFN-10 I $3.34 Yes
LT3991IMSE-3.3#PBF MS-10E I $4.69 $3.28 Yes
LT3991IMSE-3.3#TRPBF MS-10E I $3.34 Yes
LT3991IMSE-5#PBF MS-10E I $4.69 $3.28 Yes
LT3991IMSE-5#TRPBF MS-10E I $3.34 Yes
LT3991IMSE#PBF MS-10E I $4.69 $3.28 Yes
LT3991IMSE#TRPBF MS-10E I $3.34 Yes
Buy NowRequest Samples
* The USA list pricing shown is for BUDGETARY USE ONLY, shown in United States dollars (FOB USA per unit for the stated volume), and is subject to change. International prices may differ due to local duties, taxes, fees and exchange rates. For volume-specific price or delivery quotes, please contact your local Linear Technology sales office or authorized distributor.

Demo Boards

Linear Technology offers many demo boards free of charge to qualified customers. Contact your local sales office or distributor to inquire about a demo board. Certain demo boards are also available for sale via credit card on this website. Demo boards are for evaluation purposes only. It remains the customer’s responsibility to verify proper and reliable operation in the actual end application.

Part Number Description Price Documentation
DC1526A LT3991EMSE Demo Board | 55V, 1.2A, Step-Down Regulator with 2.8uA Quiescent Current $125.00
Buy Now
Click here to view our complete list of demo boards

Designed for Automotive and Transportation Applications

AEC-Q100 data is available for these specific part numbers. Please contact your local sales representative for more information regarding reliability reports or to inquire about parts that are not included. For more information, view our Automotive and Transportation page

Part Number Package Temp Price
(1-99)
Price
(1k)*
RoHS
LT3991IDD#PBF 3x3 DFN-10 I $4.69 $3.28 Yes
LT3991IDD#TRPBF 3x3 DFN-10 I $3.34 Yes
LT3991IMSE-3.3#PBF MS-10E I $4.69 $3.28 Yes
LT3991IMSE-3.3#TRPBF MS-10E I $3.34 Yes
LT3991IMSE-5#PBF MS-10E I $4.69 $3.28 Yes
LT3991IMSE-5#TRPBF MS-10E I $3.34 Yes
LT3991IMSE#PBF MS-10E I $4.69 $3.28 Yes
LT3991IMSE#TRPBF MS-10E I $3.34 Yes
Buy NowRequest Samples
* The USA list pricing shown is for BUDGETARY USE ONLY, shown in United States dollars (FOB USA per unit for the stated volume), and is subject to change. International prices may differ due to local duties, taxes, fees and exchange rates. For volume-specific price or delivery quotes, please contact your local Linear Technology sales office or authorized distributor.

Applications

  • Automotive Battery Regulation
  • Power for Portable Products
  • Industrial Supplies

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Design Tools

LTspice

LTspice® software is a powerful, fast and free simulation tool, schematic capture and waveform viewer with enhancements and models for improving the simulation of switching regulators. Click here to download LTspice

To launch a ready to run LTspice demonstration circuit for this part:

  • Step 1: If you have not installed LTspice on this computer, download and install LTspice
  • Step 2: Once LTspice is installed, click on the link(s) below to launch the simulation
  • Step 3: If LTspice does not automatically open after clicking the link above, you can instead run the simulation by right clicking on the link and selecting "Save Target As." After saving the file to your computer, start LTspice and open the demonstration circuit by selecting 'Open' from the 'File' menu

To explore other ready to run LTspice demonstration circuits, please visit our Demo Circuits Collection.

Models for the following parts are available in LTspice:
LT3991

LTpowerCAD

The LTpowerCAD design tool is a complete power supply design tool program that can significantly ease the tasks of power supply design. It guides users to a solution, selects power stage components, provides detailed power efficiency, shows quick loop bode plot stability and load transient analysis, and can export a final design to LTspice for simulation. Click here to download LTpowerCAD

Design tools for the following parts are available in LTpowerCAD:
LT3991

Technical Support