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.
Documentation & Resources
R530 Reliability Data3/26/2018
DC1526A - Demo Manual3/12/2010
Tools & Simulations
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Models for the following parts are available in LTspice:
LT3991 Companion Parts
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Pricing displayed is based on 1-piece. The USA list pricing shown is for budgetary use only, shown in United States dollars (FOB USA per unit), and is subject to change. International prices may vary due to local duties, taxes, fees and exchange rates.