Features and Benefits
- 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
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.
- Automotive Battery Regulation
- Power for Portable Products
- Industrial Supplies
Product Lifecycle Production
At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.
Evaluation Kits (1)
Demonstration circuit 1526 is a monolithic step-down DC/DC switching regulator featuring the LT3991. The switching frequency is adjustable up to 2MHz. The demo circuit is designed for 3.3V, 1.2A output from a 4.5V to 55V input. The wide input range of the LT3991 allows a variety of input sources including automotive batteries and 24V industrial supplies. Low ripple Burst Mode increases the efficiency at the light load while keeping the output ripple below 15mV. The part is in shutdown when the EN pin is low and active when the pin is high. The threshold of the EN pin is accurate at 1.01V with 30mV of hysteresis. When VIN is above 6V, adding a resistor divider from VIN to EN can program the LT3991 to regulate the output only when VIN is above a desired voltage. The circuit consumes only 2.8μA of quiescent current. The boost diode, control and logic circuit are integrated to reduce the components count and solution size. The current mode control scheme creates fast transient response and good loop stability.
Tools & Simulations
LTspice® is a powerful, fast and free simulation software, schematic capture and waveform viewer with enhancements and models for improving the simulation of analog circuits.
To launch ready-to-run LTspice demonstration circuits for this part:
Step 1: Download and install LTspice on your computer.
Step 2: Click on the link in the section below to download a demonstration circuit.
Step 3: If LTspice does not automatically open after clicking the link below, 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.
Models for the following parts are available in LTspice:
LTpowerCAD® is a power supply design program which selects power stage components, provides detailed power efficiency, shows quick loop Bode plot stability and load transient analysis, and can export to LTspice for simulation.
Design tools for the following parts are available in LTpowerCAD:
ADI has always placed the highest emphasis on delivering products that meet the maximum levels of quality and reliability. We achieve this by incorporating quality and reliability checks in every scope of product and process design, and in the manufacturing process as well. "Zero defects" for shipped products is always our goal.
Sample & Buy
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 Analog Devices, Inc. sales office or authorized distributor. Pricing displayed for Evaluation Boards and Kits is based on 1-piece pricing.