LT3971A/LT3971A-5 38V, 1.3A, 2MHz Step-Down Regulator with 2.2A Quiescent Current FEATURES DESCRIPTION n Ultralow Quiescent Current: The LT 3971A is an adjustable frequency monolithic buck 2.8A I Regulating 12V to 3.3V switching regulator that accepts a wide input voltage range Q IN OUT n Fixed Output Voltages: 5V up to 38V. Low quiescent current design consumes only 2.2A I Regulating 12V to 5V 2.8A of supply current while regulating with no load. Low Q IN OUT n Low Ripple Burst Mode Operation: ripple Burst Mode operation maintains high efficiency at Output Ripple < 15mV low output currents while keeping the output ripple below P-P n Wide Input Voltage Range: 4.3V to 38V 15mV in a typical application. An internally compensated n 1.3A Maximum Output Current current mode topology is used for fast transient response n Adjustable Switching Frequency: 200kHz to 2MHz and good loop stability. A high efficiency 0.33 switch n Synchronizable Between 250kHz to 2MHz is included on the die along with a boost Schottky diode n Fast Transient Response and the necessary oscillator, control and logic circuitry. n Accurate 1V Enable Pin Threshold An accurate 1V threshold enable pin can be used to shut n Low Shutdown Current: I = 700nA down the LT3971A, reducing the input supply current to Q n Power Good Flag 700nA. A capacitor on the SS pin provides a controlled n Soft-Start Capability inrush current (soft-start). A power good flag signals when n Internal Compensation V reaches 91% of the programmed output voltage. The OUT n Output Voltage: 1.19V to 30V LT3971A is available in a small 10-lead MSOP package n Small Thermally Enhanced 10-Lead MSOP Package with an exposed pad for low thermal resistance. The LT3971A and LT3971A-5 have a more accurate ref- erence voltage compared to the LT3971 and LT3971-5. APPLICATIONS The LT3971A-5 also has specified V pin current and OUT n USB VBUS Regulation ABSMAX current. These characteristics are important for n Automotive Battery Regulation USB applications. n Power for Portable Products L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks n Industrial Supplies of Linear Technology Corporation. All other trademarks are the property of their respective owners. TYPICAL APPLICATION No Load Supply Current 5.15V Step-Down Converter for USB Applications 3.0 OUTPUT IN REGULATION V IN 6.3V TO 38V 2.5 V IN LT3971A-5 OFF ON EN BOOST 0.47F 10H PG SW 2.0 SS 4.7F LT3971A-5 RT BD 1.5 20k, 1% V OUT 5.15V V OUT 118k SYNC GND 1.3A 715k 47F 1.0 1% f = 400kHz 5 10 15 20 25 30 35 3971 TA01a INPUT VOLTAGE (V) 3971A TA01b 3971af 1 INPUT CURRENT (A)LT3971A/LT3971A-5 ABSOLUTE MAXIMUM RATINGS (Note 1) V , EN Voltage .........................................................38V Operating Junction Temperature Range (Note 2) IN BOOST Pin Voltage ...................................................55V LT3971AI/LT3971AI-5 ........................ 40C to 125C BOOST Pin Above SW Pin .........................................30V Storage Temperature Range .............. 65C to 150C FB, RT, SYNC, SS Voltage ...........................................6V Lead Temperature (Soldering, 10 sec) PG, BD Voltage .........................................................30V (MSE Only) .......................................................300C V Pin Current ....................................................2mA OUT PIN CONFIGURATION LT3971A LT3971A-5 TOP VIEW TOP VIEW BD 1 10 SYNC BD 1 10 SYNC BOOST 2 9 PG BOOST 2 9 PG 11 11 SW 3 8 RT SW 3 8 RT GND GND V 4 7 SS V 4 7 SS IN IN EN 5 6 FB EN 5 6 V OUT MSE PACKAGE MSE PACKAGE 10-LEAD PLASTIC MSOP 10-LEAD PLASTIC MSOP = 45C, = 10C/W = 45C, = 10C/W JA JC JA JC EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LT3971AIMSE PBF LT3971AIMSE TRPBF LTGFQ 10-Lead Plastic MSOP 40C to 125C LT3971AIMSE-5 PBF LT3971AIMSE-5 TRPBF LTGFR 10-Lead Plastic MSOP 40C to 125C 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: