LT1946A 2.7MHz Boost DC/DC Converter with 1.5A Switch and Soft-Start FEATURES DESCRIPTIO n 1.5A, 36V Internal Switch The LT 1946A is a fixed frequency step-up DC/DC con- n 2.7MHz Switching Frequency verter containing an internal 1.5A, 36V switch. Capable of n Integrated Soft-Start Function generating 12V at 430mA from a 5V input, the LT1946A is n Adjustable Output from V to 35V ideal for powering large TFT-LCD panels. The LT1946A IN n Low V Switch: 300mV at 1.5A (Typical) switches at 2.7MHz, allowing the use of tiny, low profile CESAT n 12V at 430mA from a 5V Input inductors and low value ceramic capacitors. Loop com- n Small Thermally Enhanced 8-Lead MSOP Package pensation can be either internal or external, giving the user flexibility in setting loop compensation and allowing opti- U mized transient response with low ESR ceramic output APPLICATIO S capacitors. Soft-start is controlled with an external capaci- tor which determines the input current ramp rate during n TFT-LCD Bias Supplies start up. The 8-lead MSOP package and high switching n GPS Receivers frequency ensure a low profile overall solution less than n DSL Modems 1.1mm high. n Local Power Supply , LTC and LT are registered trademarks of Linear Technology Corporation. TYPICAL APPLICATIO L1 D1 Efficiency 2.2H V OUT V IN 12V 90 5V 430mA 65 R1 85 V SW IN 182k 3 OFF ON SHDN 80 2 C1 LT1946A FB 1 7 2.2F C2 75 V COMP C 2.2F R C SS GND* 70 27.4k R2 8 4 21k C C C SS 65 270pF 100nF 60 1946A TA01 C1: 2.2F, X5R or X7R, 6.3V C2: 2.2F, X5R or X7R, 16V 55 D1: MICROSEMI UPS120 OR EQUIVALENT L1: SUMIDA CR43-2R2 50 * EXPOSED PAD MUST ALSO BE GROUNDED 0 100 200 300 400 500 LOAD CURRENT (mA) Figure 1. 5V to 12V, 430mA Step-Up DC/DC Converter 1946A TA01 sn1946a 1946afs 1 EFFICIENCY (%) U ULT1946A UUW ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO (Note 1) ORDER PART V Voltage .............................................................. 16V IN TOP VIEW NUMBER SW Voltage ................................................0.4V to 36V V 1 8 SS C FB 2 7 COMP FB Voltage .............................................................. 2.5V LT1946AEMS8E SHDN 3 6 V IN Current into FB Pin ............................................... 1mA GND 4 5 SW SHDN Voltage .......................................................... 16V MS8E PACKAGE MS8E PART 8-LEAD PLASTIC MSOP Maximum Junction Temperature .......................... 125 C EXPOSED PAD IS GROUND MARKING (MUST BE SOLDERED TO PCB) Operating Temperature LTYZ Range (Note 2) ....................................... 40 C to 85 C T = 125 C, q = 40 C/W, JMAX JA q = 10 C/W JC Storage Temperature Range ................. 65 C to 150 C Lead Temperature (Soldering, 10 sec).................. 300 C Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T = 25 C. V = 3V, V = V unless otherwise noted. (Note 2) A IN SHDN IN PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum Operating Voltage 2.45 2.6 V Maximum Operating Voltage 16 V Feedback Voltage 1.23 1.25 1.27 V l 1.22 1.27 V FB Pin Bias Current V = 1.25V (Note 3) l 20 120 nA FB Error Amp Transconductance D I = 2mA40 m mhos Error Amp Voltage Gain 300 V/V Quiescent Current V = 2.5V, Not Switching 3.6 5 mA SHDN Quiescent Current in Shutdown V = 0V, V = 3V 0 1 m A SHDN IN Reference Line Regulation 2.6V V 16V 0.01 0.05 %/V IN Switching Frequency 2.4 2.7 3 MHz l 2.3 3.1 MHz Switching Frequency in Foldback V = 0V 0.85 MHz FB Maximum Duty Cycle l 73 80 % Switch Current Limit (Note 4) l 1.5 2.1 3.1 A Switch V I = 1A 240 340 mV CESAT SW Switch Leakage Current V = 5V 0.01 1 m A SW Soft-Start Charging Current V = 0.5V 2.5 4 6 m A SS SHDN Input Voltage High 2.4 V SHDN Input Voltage Low 0.5 V SHDN Pin Bias Current V = 3V 16 32 m A SHDN V = 0V 0 0.1 m A SHDN Note 1: Absolute Maximum Ratings are those values beyond which the life temperature range are assured by design, characterization and correlation of a device may be impaired. with statistical process controls. Note 2: The LT1946AE is guaranteed to meet performance specifications Note 3: Current flows out of the FB pin. from 0 C to 70 C. Specifications over the 40 C to 85 C operating Note 4: Current limit guaranteed by design and/or correlation to static test. Current limit is independent of duty cycle and is guaranteed by design. sn1946a 1946afs 2 U WWW