LT1533 Ultralow Noise 1A Switching Regulator UFEATURESDESCRIPTION ■ Greatly Reduced Conducted and Radiated EMI The LT®1533 is a new class of switching regulator designed (<100 µ VP-P in Typical Application) to reduce conducted and radiated electromagnetic interfer- ■ Low Switching Harmonic Content ence (EMI). Ultralow noise and EMI are achieved by providing ■ Independent Control of Switch Voltage and user control of the output switch slew rates. Voltage and Current Slew Rates current slew rates can be independently programmed to ■ Two 1A Current Limited Power Switches optimize switcher harmonic content versus efficiency. The ■ Regulates Positive and Negative Voltages LT1533 can reduce high frequency harmonic power by as ■ 20kHz to 250kHz Oscillator Frequency much as 40dB with only minor losses in efficiency. ■ Easily Synchronized to External Clock The LT1533 utilizes a dual output switch current mode ■ Wide Input Voltage Range: 2.7V to 23V architecture optimized for low noise topologies. The IC ■ Low Shutdown Current: 12µA Typical includes two 1A power switches along with all necessary ■ Easier Layout than with Conventional Switchers oscillator, control and protection circuitry. Unique error amp ■ Outputs Can Be Forced to 50% Duty Cycle for circuitry can regulate both positive and negative voltages. Unregulated Applications The internal oscillator may be synchronized to an external U clock for more accurate placement of switching harmonics. APPLICATIONS Protection features include cycle by cycle current limit pro- ■ tection, undervoltage lockout and thermal shutdown. Precision Instrumentation Systems ■ Isolated Supplies for Industrial Automation Low minimum supply voltage and low supply current during ■ Medical Instruments shutdown make the LT1533 well suited for portable applica- ■ Wireless Communications tions. The part may also be forced into a 50% duty cycle mode ■ Single Board Data Acquisition Systems for unregulated applications. The LT1533 is available in the 16-pin narrow SO package. , LTC and LT are registered trademarks of Linear Technology Corporation. UTYPICAL APPLICATIONLow Noise 5V to 12V Forward Push-Pull DC/DC Converter 5V L1 L2 1N4148 + 300µH B 33µH A 12V Output Noise (BW = 100MHz) 14 T1 12V 33µF VIN 11 2 150mA SHDN COL A 1N4148 + C1 + C2 3 DUTY 15 47µF 33µF COL B 4 16V 20V 820pF SYNC Note 1 A 16 5 <100µVP-P PGND C 100µV/DIV T LT1533 13 15k 16.9k 6 RVSL RT B 12 15k R 2mV/DIV CSL 15k 10 7 21.5k, 1% V FB 1533 TA01 C GND NFB 2.49k C1: SANYO OS-CON 0.015µF 1000pF 9 8 1% C2: AVX TPS TANTALUM L1: COILTRONICS CTX300-2 2µs/DIV L2: COILCRAFT DT1608C-333 1533 TA02 T1: COILTRONICS CTX02-13834 NOTE 1: 25nH TRACE INDUCTANCE OR COILCRAFT B07T 1
