Ultralow Noise 1A Switching Regulator

The LT1533 is a new class of switching regulator designed to reduce conducted and radiated electromagnetic interference (EMI). Ultralow noise and EMI are achieved by providing user control of the output switch slew rates. Voltage and current slew rates can be independently programmed to optimize switcher harmonic content versus efficiency. The LT1533 can reduce high frequency harmonic power by as much as 40dB with only minor losses in efficiency.

The LT1533 utilizes a dual output switch current mode architecture optimized for low noise topologies. The IC includes two 1A power switches along with all necessary oscillator, control and protection circuitry. Unique error amp circuitry can regulate both positive and negative voltages. The internal oscillator may be synchronized to an external clock for more accurate placement of switching harmonics. Protection features include cycle by cycle current limit protection, undervoltage lockout and thermal shutdown.

Low minimum supply voltage and low supply current during shutdown make the LT1533 well suited for portable applications. The part may also be forced into a 50% duty cycle mode for unregulated applications. The LT1533 is available in the 16-pin narrow SO package.

Applications

* Precision Instrumentation Systems

* Isolated Supplies for Industrial Automation

* Medical Instruments

* Wireless Communications

* Single Board Data Acquisition Systems

* Greatly Reduced Conducted and Radiated EMI (<100µVP-P in Typical Application)

* Low Switching Harmonic Content

* Independent Control of Switch Voltage and Current Slew Rates

* Two 1A Current Limited Power Switches

* Regulates Positive and Negative Voltages

* 20kHz to 250kHz Oscillator Frequency

* Easily Synchronized to External Clock

* Wide Input Voltage Range: 2.7V to 23V

* Low Shutdown Current: 12µA Typical

* Easier Layout than with Conventional Switchers

* Outputs Can Be Forced to 50% Duty Cycle for Unregulated Applications