LT1959 4.5A, 500kHz Step-Down Switching Regulator FEATURES DESCRIPTIO n Operates with Input as Low as 4V The LT 1959 is a 500kHz monolithic buck mode switching n Output Range Down to 1.21V regulator functionally identical to the LT1506 but optimized n Constant 500kHz Switching Frequency for lower output voltage applications. It will operate down n Uses All Surface Mount Components to 1.21V output compared to 2.42V for the LT1506. A 4.5A n Inductor Size Reduced to 1.8m H switch is included on the die along with all the necessary n Saturating Switch Design: 0.07W oscillator, control and logic circuitry. High switching fre- n Shutdown Current: 15m A quency allows a considerable reduction in the size of ex- n Easily Synchronizable ternal components. The topology is current mode for fast n Cycle-by-Cycle Current Limiting transient response and good loop stability. n 4.5A Switch A special high speed bipolar process and new design tech- n Current Mode Control niques achieve high efficiency at high switching frequency. Efficiency is maintained over a wide output current range U APPLICATIO S by keeping quiescent supply current to 3.8mA and by uti- lizing a supply boost capacitor to saturate the power switch. n Portable Computers n The LT1959 fits into standard 7-pin DD and fused lead Battery-Powered Systems n SO-8 packages. Full cycle-by-cycle short-circuit protection Battery Chargers n and thermal shutdown are provided. Standard surface Distributed Power n mount external parts are used, including the inductor and 5V to 3.3V Conversion n capacitors. There is the optional function of shutdown or 5V to 2.5V Conversion n synchronization. A shutdown signal reduces supply current 5V to 1.8V Conversion to 15m A. Synchronization allows an external logic level sig- nal to increase the internal oscillator from 580kHz to 1MHz. , LTC and LT are registered trademarks of Linear Technology Corporation. TYPICAL APPLICATION Efficiency vs Load Current 5V to 1.8V Down Converter 90 V = 3.3V OUT D2 V = 5V IN 1N914 L = 10m H 85 C2 0.68m F L1 5m H BOOST OUTPUT 80 INPUT V V 1.8V IN SW 5V C3 4A R1 OPEN LT1959 + 10m F TO 1.21k OR 50m F SHDN FB HIGH 75 CERAMIC GND V C C1 = ON + R2 100m F, 10V C D1 C 2.49k SOLID 1.5nF MBRS330T3 TANTALUM 70 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 1959 TA01 LOAD CURRENT (A) 1959 TA02 1 EFFICIENCY (%) U ULT1959 ABSOLUTE MAXIMUM RATINGS (Note 1) Input Voltage .......................................................... 16V SYNC Pin Voltage ..................................................... 7V BOOST Voltage ........................................................ 30V Operating Junction Temperature Range BOOST Pin Above Input Voltage ............................. 15V LT1959C ................................................ 0 C to 125 C SHDN Pin Voltage ..................................................... 7V LT1959I ........................................... 40 C to 125 C FB Pin Voltage ....................................................... 3.5V Storage Temperature Range ................ 65 C to 150 C FB Pin Current ....................................................... 1mA Lead Temperature (Soldering, 10 sec)................. 300 C PACKAGE/ORDER INFORMATION ORDER PART ORDER PART FRONT VIEW TOP VIEW NUMBER NUMBER 7 FB 6 BOOST V 1 8 V IN SW 5 V TAB IN LT1959CR 4 GND LT1959CS8 IS BOOST 2 7 SYNC 3 V GND SW LT1959IR LT1959IS8 2 FB 3 6 SHDN SHDN 1 V C GND** 4 5 V C R PACKAGE 7-LEAD PLASTIC DD S8 PACKAGE 8-LEAD PLASTIC SO T = 150 C, q = 30 C/W S8 PART MARKING JMAX JA WITH PACKAGE SOLDERED TO 0.5 SQUARE INCH T = 150 C, q = 80 C/W JMAX JA COPPER AREA OVER BACKSIDE GROUND PLANE OR **WITH (FUSED GND) GROUND PIN 1959 INTERNAL POWER PLANE. q CAN VARY FROM 20 C/W JA CONNECTED TO GROUND PLANE OR TO >40 C/W DEPENDING ON MOUNTING TECHNIQUES LARGE LANDS 1959I ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T = 25 C, T = 25 C, V = 5V, V = 1.5V, Boost = V + 5V, switch open, unless A J IN C IN otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Feedback Voltage (Adjustable) All Conditions l 1.19 1.21 1.23 V Reference Voltage Line Regulation 4.3V V 15V 0.01 0.03 %/V IN Feedback Input Bias Current l 0.5 0 0.5 m A Error Amplifier Voltage Gain (Note 2) 200 400 Error Amplifier Transconductance D I (V ) = 10m A 1500 2000 2700 m Mho C l 1000 3100 m Mho V Pin to Switch Current Transconductance 5.3 A/ V C Error Amplifier Source Current V = 1.05V l 140 225 320 m A FB Error Amplifier Sink Current V = 1.35V l 140 225 320 m A FB V Pin Switching Threshold Duty Cycle = 0 0.9 V C V Pin High Clamp 2.1 V C Switch Current Limit V Open, V = 1.05V, DC 50% l 4.5 6 8.5 A C FB Slope Compensation DC = 80% 0.8 A 2 U W U U WWW