LT1938 25V, 2.2A, 2.8MHz Step-Down Switching Regulator FEATURES DESCRIPTION Wide Input Voltage Range: 3.6V to 25V The LT 1938 is an adjustable frequency (300kHz to 2.2A Maximum Output Current 2.8MHz) monolithic buck switching regulator that accepts Adjustable Switching Frequency: 300kHz to 2.8MHz input voltages up to 25V. A high efficiency 0.18 switch Low Shutdown Current: I < 1A is included on the die along with a boost Schottky diode Q Integrated Boost Diode and the necessary oscillator, control and logic circuitry. Power Good Flag Current mode topology is used for fast transient response Saturating Switch Design: 0.18 On-Resistance and good loop stability. The LT1938s high operating fre- 1.265V Feedback Reference Voltage quency allows the use of small, low cost inductors and Output Voltage: 1.265V to 20V ceramic capacitors resulting in low output ripple while Soft-Start Capability keeping total solution size to a minimum. The low current Small 10-Pin Thermally Enhanced (3mm 3mm) shutdown mode reduces input supply current to less than DFN Package 1A while a resistor and capacitor on the RUN/SS pin provide a controlled output voltage ramp (soft-start). A APPLICATIONS power good flag signals when V reaches 90% of the OUT programmed output voltage. The LT1938 is available in Automotive Battery Regulation a 3mm 3mm DFN package with Exposed Pad for low Power for Portable Products thermal resistance. Distributed Supply Regulation , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. Industrial Supplies All other trademarks are the property of their respective owners. Wall Transformer Regulation TYPICAL APPLICATION 3.3V Step-Down Converter Efficiency (V = 3.3V) OUT V V IN OUT 3.3V 90 4.5V TO V = 7V 2.2A IN 25V 85 V BD IN RUN/SS BOOST OFF ON 80 V = 24V 0.47F 4.7H V = 12V IN IN 16.2k V SW 75 C 4.7F LT1938 RT 70 680pF PG BIAS 65 324k FB 60.4k 60 GND 200k 22F 55 L: NEC PLC-0745-4R7 f = 800kHz 50 1938 TA01 0 0.2 0.4 0.6 1.2 1.4 1.6 1.8 2.0 2.2 0.8 1.0 LOAD CURRENT (A) 1938 G02 1938fa 1 EFFICIENCY (%)LT1938 PIN CONFIg URATION Ab SOLUTE MAx IMUM RATINg S (Note 1) V , RUN/SS Voltage .................................................25V TOP VIEW IN BOOST Pin Voltage ...................................................50V BD 1 10 RT BOOST Pin Above SW Pin .........................................25V BOOST 9 V 2 C FB, RT, V Voltage .......................................................5V 11 3 SW 8 FB C V 4 7 BIAS BIAS, PG, BD Voltage ................................................25V IN RUN/SS 5 6 PG Operating Junction Temperature Range (Note 2) LT1938E ............................................. 40C to 125C DD PACKAGE 10-LEAD (3mm 3mm) PLASTIC DFN LT1938I .............................................. 40C to 125C T = 125C, = 45C/W, = 10C/W JMAX JA JC Storage Temperature Range ................... 65C to 150C 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 LT1938EDD PBF LT1938EDD TRPBF LDFT 10-Lead (3mm 3mm) Plastic DFN 40C to 125C LT1938IDD PBF LT1938IDD TRPBF LDFT 10-Lead (3mm 3mm) Plastic DFN 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: