LT1578IS8#PBF Analog Devices

LT1578/LT1578-2.5 1.5A, 200kHz Step-Down Switching Regulator FEATURES DESCRIPTIO n 1.5A Switch Current The LT 1578 is a 200kHz monolithic buck mode switching n High EfficiencyLow Loss 0.2W Switch regulator. A 1.5A switch is included on the die along with n Constant 200kHz Switching Frequency all the necessary oscillator, control and logic circuitry. The n 4V to 15V Input VoltageRange topology is current mode for fast transient response and n Minimum Output: 1.21V good loop stability. The LT1578 is a modified version of the n Low Supply Current: 1.9mA LT1507 that has been optimized for noise sensitive appli- n Low Shutdown Current: 20m A cations. It will operate over a 4V to 15V input range. n Easily Synchronizable Up to 400kHz In addition, the reference voltage has been lowered to al- n Cycle-by-Cycle Current Limit low the device to produce output voltages down to 1.2V. n Reduced EMI Generation Quiescent current has been reduced by a factor of two. n Low Thermal Resistance SO-8 Package Switch on resistance has been reduced by 30%. Switch tran- n Uses Small Low Value Inductors sition times have been slowed to reduce EMI generation. The oscillator frequency has been reduced to 200kHz to U maintain high efficiency over a wide output current range. APPLICATIO S The pinout has been changed to improve PC layout by al- n Portable Computers lowing the high current, high frequency switching circuitry n Battery-Powered Systems to be easily isolated from low current, noise sensitive con- n Battery Chargers trol circuitry. The new SO-8 package includes a fused n Distributed Power Systems ground lead that significantly reduces the thermal resistance of the device to extend the ambient operating temperature range. Standard surface mount external parts can be used including the inductor and capacitors. , LTC and LT are registered trademarks of Linear Technology Corporation. TYPICAL APPLICATION Efficiency vs Load Current 90 3.3V Buck Converter INPUT 85 5V TO 15V + C2 C3* D2 0.33F 10m F TO 1N914 80 L1** 50m F V 15m H BOOST IN OUTPUT** V 75 SW 3.3V, 1.25A LT1578 70 OPEN = ON SHDN FB 65 GND V R1 C 8.66k 60 C1 * RIPPLE CURRENT RATING I /2 OUT + C D1 R2 100m F, 10V V = 3.3V C OUT ** INCREASE L1 TO 30m H FOR LOAD 100pF 1N5818 4.99k SOLID 55 V = 5V IN CURRENTS ABOVE 0.6A AND TO TANTALUM L = 25H 60m H ABOVE 1A 50 SEE APPLICATIONS INFORMATION 1578 TA01 0 0.25 0.50 0.75 1.00 1.25 1.50 LOAD CURRENT (A) 1578 TA02 1 EFFICIENCY (%) U ULT1578/LT1578-2.5 ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION (Note 1) ORDER PART TOP VIEW Input Voltage .......................................................... 16V NUMBER BOOST Pin Above Input Voltage ............................. 10V V 1 8 SYNC SW SHDN Pin Voltage ..................................................... 7V SHDN LT1578CS8 V 2 7 IN SENSE Pin Voltage .................................................... 4V FB/SENSE LT1578IS8 BOOST 3 6 FB Pin Voltage (Adjustable Part) ............................ 3.5V V LT1578CS8-2.5 GND 4 5 C FB Pin Current (Adjustable Part) ............................ 1mA LT1578IS8-2.5 S8 PACKAGE SYNC Pin Voltage ..................................................... 7V 8-LEAD PLASTIC SO Operating Junction Temperature Range S8 PART MARKING q =80 C/ W WITH FUSED GROUND PIN JA LT1578C ............................................... 0 C to 125 C CONNECTED TO GROUND PLANE OR LARGE LANDS 1578 157825 LT1578I ........................................... 40 C to 125 C 1578I 578I25 Storage Temperature Range ................ 65 C to 150 C Lead Temperature (Soldering, 10 sec)................. 300 C Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS The l denotes specifications which apply over the full operating tempera- ture range, otherwise specifications are at 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 1.195 1.21 1.225 V All Conditions l 1.18 1.24 V Sense Voltage (Fixed 2.5) 2.46 2.5 2.54 V All Conditions l 2.44 2.56 V Sense Pin Resistance 5.7 9.5 13.7 kW Reference Voltage Line Regulation 4.3V V 15V l 0.01 0.03 %/V IN Feedback Input Bias Current l 0.5 2 m A Error Amplifier Voltage Gain (Notes 2, 10) 200 400 Error Amplifier Transconductance (Note 10) D I (V ) = 10m A 800 1050 1300 m Mho C l 400 1700 m Mho V Pin to Switch Current Transconductance 1.5 A/V C Error Amplifier Source Current V = 1.1V l 40 110 190 m A FB Error Amplifier Sink Current V = 1.4V l 50 130 200 m A FB V Pin Switching Threshold Duty Cycle = 0 0.8 V C V Pin High Clamp 2.1 V C Switch Current Limit V Open, V = 1.1V, DC 50% l 1.5 2 3.5 A C FB Slope Compensation (Note 8) DC = 80% 0.3 A Switch On Resistance (Note 7) I = 1.5A 0.2 0.35 W SW l 0.45 W Maximum Switch Duty Cycle V = 1.1V 90 94 % FB l 86 94 % Minimum Switch Duty Cycle (Note 9) 8% Switch Frequency V Set to Give 50% Duty Cycle 180 200 220 kHz C l 160 240 kHz Switch Frequency Line Regulation 4.3V V 15V l 0 0.15 %/V IN Frequency Shifting Threshold on FB Pin D f = 10kHz l 0.4 0.74 1.0 V Minimum Input Voltage (Note 3) l 4.0 4.3 V Minimum Boost Voltage (Note 4) I 1.5A l 2.3 3.0 V SW 2 U W U U WWW