National Semiconductor Introduces Very Small, Highly Efficient Synchronous Step-up DC-DC Converters with True Shutdown Isolation

National Semiconductor Introduces Very Small, Highly Efficient Synchronous Step-up DC-DC Converters with True Shutdown Isolation

National Semiconductor Corporation (NYSE:NSM) today introduced two fixed-frequency step-up DC-DC converters with true shutdown isolation. Packaged in a very small 8-bump micro SMD, the LM3500 and LM3501 are well-suited for driving white LEDs in display backlighting and other lighting applications.

The converters feature a low feedback voltage of 500 mV and fully integrated synchronous switching that requires no external Schottky diode. Power efficiency has been optimized for lighting applications in portable products with single cell Li-Ion or 3-cell NiMH battery supplies. The LM3500 and LM3501 operate with a fixed 1 MHz switching frequency and ceramic input and output capacitors. High switching frequency, very small external ceramic capacitors and the integration of a diode, provides the customer with a small, low-cost solution.

A single external resistor is used to set the maximum LED current in driver applications. The current can easily be adjusted using a pulse-width modulation (PWM) signal on the shutdown pin of the LM3500 or an analog control signal on the CNTRL pin of the LM3501. In shutdown, the converters completely disconnect the input from the output, creating total isolation and preventing any leakage currents from trickling into the LEDs.