LT1576/LT1576-5 1.5A, 200kHz Step-Down Switching Regulator FEATURES DESCRIPTIO n Constant 200kHz Switching Frequency The LT 1576 is a 200kHz monolithic buck mode switching n 1.21V Reference Voltage regulator. A 1.5A switch is included on the die along with n Fixed 5V Output Option all the necessary oscillator, control and logic circuitry. The n Easily Synchronizable topology is current mode for fast transient response and n Uses All Surface Mount Components good loop stability. The LT1576 is a modified version of the n Inductor Size Reduced to 15m H industry standard LT1376 optimized for noise sensitive n Saturating Switch Design: 0.2W applications. n Effective Supply Current: 1.16mA In addition, the reference voltage has been lowered to n Shutdown Current: 20m A allow the device to produce output voltages down to 1.2V. n Cycle-by-Cycle Current Limiting Quiescent current has been reduced by a factor of two. n Fused Lead SO-8 Package Switch on resistance has been reduced by 30%. Switch tran- sition times have been slowed to reduce EMI generation. U The oscillator frequency has been reduced to 200kHz to APPLICATIO S maintain high efficiency over a wide output current range. n Portable Computers The pinout has been changed to improve PC layout by n Battery-Powered Systems allowing the high current high frequency switching cir- n Battery Charger cuitry to be easily isolated from low current noise sensitive n Distributed Power control circuitry. The new SO-8 package includes a fused ground lead which significantly reduces the thermal resis- tance of the device to extend the ambient operating tem- perature range. There is an optional function of shutdown or synchronization. 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 100 5V Buck Converter V = 5V OUT INPUT V = 10V IN 95 6V TO 25V C2 C3* + D2 L = 33H 0.33F 10m F TO 1N914 L1** 50m F 90 V 15m H IN BOOST OUTPUT** V SW 5V, 1.25A LT1576 BIAS 85 SHDN FB OPEN = ON V GND 80 C D1 R1 1N5818 15.8k C1 * RIPPLE CURRENT RATING I /2 OUT + R2 C C 100m F, 10V 75 ** INCREASE L1 TO 30m H FOR LOAD 4.99k 100pF SOLID CURRENTS ABOVE 0.6A AND TO TANTALUM 60m H ABOVE 1A 70 SEE APPLICATIONS INFORMATION 0 0.25 0.50 0.75 1.00 1.25 1.50 1576 TA01 LOAD CURRENT (A) 1576 TA02 1 EFFICIENCY (%) U ULT1576/LT1576-5 ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER INFORMATION (Note 1) ORDER PART NUMBER Input Voltage .......................................................... 25V BOOST Pin Above Input Voltage ............................. 10V LT1576CS8 SHDN Pin Voltage .................................................. 6.5V LT1576CS8-SYNC BIAS Pin Voltage ...................................................... 7V TOP VIEW LT1576IS8 FB Pin Voltage (Adjustable Part) ............................ 3.5V SHDN OR V 1 8 SW LT1576IS8-SYNC SYNC* FB Pin Current (Adjustable Part) ............................ 1mA V 2 7 FB OR SENSE* IN LT1576CS8-5 SYNC Pin Voltage ..................................................... 7V BOOST 3 6 V C LT1576CS8-5 SYNC Operating Junction Temperature Range 4 5 BIAS GND LT1576IS8-5 LT1576C ............................................... 0 C to 125 C S8 PACKAGE LT1576IS8-5 SYNC 8-LEAD PLASTIC SO LT1576I ........................................... 40 C to 125 C q =80 C/ W WITH FUSED GROUND PIN JA Storage Temperature Range ................ 65 C to 150 C S8 PART MARKING CONNECTED TO GROUND PLANE OR LARGE LANDS Lead Temperature (Soldering, 10 sec)................. 300 C 1576 15765 1576SN 5765SN 1576I 1576I5 576ISN 76I5SN *Default is the adjustable output voltage device with FB pin and shutdown function. Option -5 replaces FB with SENSE pin for fixed 5V output applications. -SYNC replaces SHDN with SYNC pin for applications requiring synchronization. Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS The l denotes specifications which apply over the full operating temperature range, otherwise specifications are T , T = 25 C, V = 15V, V = 1.5V, Boost = V + 5V, switch open, unless otherwise noted. A J IN C IN PARAMETER CONDITIONS MIN TYP MAX UNITS Feedback Voltage 1.195 1.21 1.225 V 5V V 25V, V + 0.2V V V 0.2V l 1.18 1.24 V IN OL CC OH Sense Voltage (Fixed 5V) 4.94 5.0 5.06 V All Conditions l 4.90 5.10 V SENSE Pin Resistance 13 18.5 26 kW Reference Voltage Line Regulation 5V V 25V 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) 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 = 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 3.50 A C FB Slope Compensation (Note 9) 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 % 2 U W U U WWW