National Semiconductor’s 65V Dual-Channel, Dual-Phase Synchronous Buck Controller Saves PCB Space in High Voltage Applications

Today’s telecommunication, automotive and industrial control applications must regulate low output voltages at increasing load currents from a high input voltage that can change widely while still meeting stringent PCB space and efficiency requirements. Traditional approaches require two DC-DC conversion stages: one to regulate an intermediate bus voltage of approximately 9V to 12V and a second to regulate the specific load voltages that can be as low as 1V and can require currents in excess of 20 amperes. National’s LM5119 enables direct regulation of two output voltages from an input, eliminating the need for an intermediate bus conversion stage that limits efficiency and requires up to twice the number of components.

National’s proprietary ECM control technology enables precise control of very small duty cycles necessary in high voltage applications, which allows accurate regulation of DC output voltages with excellent transient response. For high-current output requirements, the two outputs can be connected in parallel to power loads up to 40A with interleaved switching that minimizes input and output capacitance.

Technical Features of the LM5119 Buck Controller
National’s LM5119 features a wide operating voltage range of 5.5V to 65V and a 0.8V, 1.5 percent reference enables accurate regulation of load voltages from 0.8V up to 90 percent of the input voltage. The operating frequency is user-programmable from 50 kHz up to 750 kHz and can be synchronized to an external clock signal. Diode emulation mode (DEM) enables discontinuous inductor current operation at light load conditions for improved efficiency. This mode allows controlled start-up into a pre-biased load by preventing current flow into the synchronous MOSFET. A high voltage bias regulator with automatic switch-over to external bias further improves efficiency. Additional features include thermal shutdown, cycle-by-cycle and hiccup mode current limit and adjustable line under-voltage lockout. The wide Vin range, multi-phase operation, programmable soft-start, input UVLO and diode emulation mode together enhance the system designer’s flexibility and control of all applications.