LT1506 4.5A, 500kHz Step-Down Switching Regulator FEATURES DESCRIPTIO n Constant 500kHz Switching Frequency The LT 1506 is a 500kHz monolithic buck mode switching n Easily Synchronizable regulator functionally identical to the LT1374 but optimized n Operates with Input as Low as 4V for lower input voltage applications. It will operate over a n Uses All Surface Mount Components 4V to 15V input range compared with 5.5V to 25V for the n Inductor Size Reduced to 1.8m H LT1374. A 4.5A switch is included on the die along with all n Saturating Switch Design: 0.07W the necessary oscillator, control and logic circuitry. High n Shutdown Current: 20m A switching frequency allows a considerable reduction in the n Cycle-by-Cycle Current Limiting size of external components. The topology is current mode for fast transient response and good loop stability. Both U fixed output voltage and adjustable parts are available. APPLICATIO S A special high speed bipolar process and new design tech- n Portable Computers niques achieve high efficiency at high switching frequency. n Battery-Powered Systems Efficiency is maintained over a wide output current range n Battery Charger by keeping quiescent supply current to 4mA and by utiliz- n Distributed Power ing a supply boost capacitor to saturate the power switch. The LT1506 fits into standard 7-pin DD and fused lead SO-8 packages. Full cycle-by-cycle short-circuit protection and thermal shutdown are provided. Standard surface mount external parts are used, including the inductor and capacitors. There is the optional function of shutdown or synchronization. A shutdown signal reduces supply current to 20m 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 APPLICATIO Efficiency vs Load Current 90 V = 3.3V 5V to 3.3V Down Converter OUT V = 5V IN L = 10m H D2 1N914 85 C2 0.68m F 80 L1 BOOST OUTPUT 5m H INPUT V V 3.3V IN SW 5V C3 4A OPEN LT1506-3.3 + 10m F TO 75 OR 50m F SHDN SENSE HIGH CERAMIC GND V C C1 = ON + 100m F, 10V C D1 C SOLID 70 1.5nF MBRS330T3 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 TANTALUM LOAD CURRENT (A) 1506 TA01 1506 TA02 1 EFFICIENCY (%) U ULT1506 ABSOLUTE MAXIMUM RATINGS (Note 1) Input Voltage .......................................................... 16V SYNC Pin Voltage ..................................................... 7V BOOST Pin Above Input Voltage ............................. 15V Operating Junction Temperature Range SHDN Pin Voltage ..................................................... 7V LT1506C ............................................... 0 C to 125 C FB Pin Voltage (Adjustable Part) ............................ 3.5V LT1506I ........................................... 40 C to 125 C FB Pin Current (Adjustable Part) ............................ 1mA Storage Temperature Range ................ 65 C to 150 C Sense Voltage (Fixed 3.3V Part) ............................... 5V Lead Temperature (Soldering, 10 sec)................. 300 C PACKAGE/ORDER INFORMATION ORDER PART ORDER PART FRONT VIEW TOP VIEW NUMBER NUMBER 7 FB OR SENSE* 6 BOOST V 1 8 V IN SW TAB 5 V IN LT1506CS8 LT1506CR IS 4 GND BOOST 2 7 SYNC GND 3 V SW LT1506CR-3.3 FB OR LT1506CS8-3.3 3 6 SHDN 2 SYNC OR SHDN* SENSE* 1 V LT1506CR-SYNC LT1506IS8 C GND** 4 5 V C LT1506IS8-3.3 LT1506CR-3.3 SYNC R PACKAGE 7-LEAD PLASTIC DD PAK S8 PACKAGE LT1506IR 8-LEAD PLASTIC SO T = 125 C, q = 30 C/W JMAX JA S8 PART MARKING LT1506IR-3.3 q = 80 C/ W WITH PACKAGE SOLDERED TO 0.5 SQUARE INCH JA **WITH FUSED (GND) GROUND PIN COPPER AREA OVER BACKSIDE GROUND PLANE OR LT1506IR-SYNC CONNECTED TO GROUND PLANE OR INTERNAL POWER PLANE. q CAN VARY FROM 20 C/W 1506 JA 1506I LT1506IR-3.3 SYNC LARGE LANDS TO > 40 C/W DEPENDING ON MOUNTING TECHNIQUES 150633 506I33 *Default is the adjustable output voltage device with FB pin and shutdown function. Option -3.3 replaces FB with SENSE pin for fixed 3.3V output applications. -SYNC replaces SHDN with SYNC pin for applications requiring synchronization. Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS T = 25 C, V = 5V, V = 1.5V, Boost = V + 5V, switch open, unless otherwise noted. J IN C IN PARAMETER CONDITIONS MIN TYP MAX UNITS Feedback Voltage (Adjustable) 2.39 2.42 2.45 V All Conditions l 2.36 2.48 V Sense Voltage (Fixed 3.3V) 3.25 3.3 3.35 V All Conditions l 3.23 3.37 V SENSE Pin Resistance 4 6.6 9.5 kW Reference Voltage Line Regulation 4.3V V 15V 0.01 0.03 %/V IN Feedback Input Bias Current l 0.5 2 m A Error Amplifier Voltage Gain (Notes 2, 8) 200 400 Error Amplifier Transconductance D I (V ) = 10m A (Note 8) 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 = 2.1V or V = 2.9V l 140 225 320 m A FB SENSE Error Amplifier Sink Current V = 2.7V or V = 3.7V l 140 225 320 m A FB SENSE 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 = 2.1V or V = 2.9V, DC 50% l 4.5 6 8.5 A C FB SENSE Slope Compensation DC = 80% 0.8 A 2 U W U U WWW