LT3975 42V, 2.5A, 2MHz Step-Down Switching Regulator with 2.7A Quiescent Current FEATURES DESCRIPTION n Ultralow Quiescent Current: The LT 3975 is an adjustable frequency monolithic buck 2.7A I at 12V to 3.3V switching regulator that accepts a wide input voltage range Q IN OUT n Low Ripple Burst Mode Operation up to 42V. Low quiescent current design consumes only Output Ripple < 15mV 2.7A of supply current while regulating with no load. Low P-P n Wide Input Range: Operation from 4.3V to 42V ripple Burst Mode operation maintains high efficiency at n 2.5A Maximum Output Current low output currents while keeping the output ripple below n Excellent Start-Up and Dropout Performance 15mV in a typical application. The LT3975 can supply up n Adjustable Switching Frequency: 200kHz to 2MHz to 2.5A of load current and has current limit foldback to n Synchronizable Between 250kHz to 2MHz limit power dissipation during short circuit. A low dropout n Accurate Programmable Undervoltage Lockout voltage of 500mV is maintained when the input voltage n Low Shutdown Current: I = 700nA drops below the programmed output voltage, such as Q n Power Good Flag during automotive cold crank. n Soft-Start Capability An internally compensated current mode topology is used n Thermal Shutdown Protection for fast transient response and good loop stability. A high n Current Limit Foldback with Soft-Start Override efficiency 75m switch is included on the die along with a n Saturating Switch Design: 75m On Resistance boost Schottky diode and the necessary oscillator, control, n Small, Thermally Enhanced 16-Lead MSOP Package and logic circuitry. An accurate 1.02V threshold enable pin can be driven directly from a microcontroller or used as a APPLICATIONS programmable undervoltage lockout. A capacitor on the n Automotive Battery Regulation SS pin provides a controlled inrush current (soft-start). n Portable Products A power good flag signals when V reaches 91.6% of OUT n Industrial Supplies the programmed output voltage. The LT3975 is available L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks in a small 16-lead MSOP package with exposed pad for of Linear Technology Corporation. All other trademarks are the property of their respective low thermal resistance. owners. TYPICAL APPLICATION No-Load Supply Current 4.5 3.3V Step-Down Converter IN REGULATION V IN 4.0 4.3V TO 42V V IN 3.5 OFF ON EN BOOST 0.47F 3.3H 3.0 PG SW 10F PDS560 LT3975 2.5 SS OUT 2.0 1M V OUT 3.3V RT FB 1.5 10pF 2.5A SYNC GND 10nF 47F 78.7k 576k 1.0 1210 0 5 10 15 20 25 30 35 40 45 3975 TA01a INPUT VOLTAGE (V) f = 600kHz 3975 TA01b 3975f 1 INPUT CURRENT (A)LT3975 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) TOP VIEW V , EN Voltage (Note 3) ...........................................42V IN FB 1 16 SYNC 2 BOOST Pin Voltage ...................................................55V SS 15 PG OUT 3 14 RT BOOST Pin Above SW Pin .........................................30V 4 17 BOOST 13 EN SW 5 GND 12 V IN FB, RT, SYNC, SS Voltage ...........................................6V 6 SW 11 V IN SW 7 10 V IN PG Voltage ................................................................30V 8 NC 9 NC OUT Voltage ..............................................................16V MSE PACKAGE 16-LEAD PLASTIC MSOP Operating Junction Temperature Range (Note 2) = 40C/W JA EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB LT3975E ............................................. 40C to 125C LT3975I.............................................. 40C to 125C LT3975H ............................................ 40C to 150C Storage Temperature Range .................. 65C to 150C Lead Temperature (Soldering, 10 sec) ...................300C ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3975EMSE PBF LT3975EMSE TRPBF 3975 16-Lead Plastic MSOP 40C to 125C LT3975IMSE PBF LT3975IMSE TRPBF 3975 16-Lead Plastic MSOP 40C to 125C LT3975HMSE PBF LT3975HMSE TRPBF 3975 16-Lead Plastic MSOP 40C to 150C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: