This application note presents the L4978, a 2A monolithic step-down DC-DC converter. It is realized in BCD60 II technology, and it is available in two plastic packages, MINIDIP and SO16L. One direct fixed output voltage at 3.3V ±1% is available, adjustable for higher output voltage values, till 40V, by an external voltage divider. The operating input supply voltage ranges from 8V to 55V, while the absolute value, with no load, is 60V. New internal design solutions and superior technology performance allow to generate a device with improved efficiency in all the operating conditions and with reduced EMI due to an inno- vative internal driving circuit, and reduced external component counts. While internal limiting current and thermal shutdown are today considered standard protection functions, mandatory for a safe load supply, oscillator with voltage feedforward improves line regulation and overall control loop. Soft-start avoids output overvoltages at turn-on, while, shorting this pin to ground, the device is completely disabled, going into zero consumption state.
The document provides an introduction and device description for the L4978, a monolithic step-down DC-DC converter operating in continuous mode. It details the internal architecture, including power supply blocks, oscillator circuits with voltage feedforward, and protection mechanisms like current limiting and thermal shutdown.
Further sections cover specific operational features such as soft-start functionality, inhibit modes, and detailed analysis of current protection levels (pulse-by-pulse and hiccup). The note includes formulas for setting switching frequency and maximum duty cycle based on external components.
The device can generate an adjustable output voltage up to 40V.
The operating input supply voltage ranges from 8V to 55V.
The device provides an internal stabilised power supply of about 12V typ.