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




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