National Semiconductor Introduces High-Power-Density, Self-Synchronizing Buck Regulators

Part of National’s PowerWise® energy-efficient product family, the highly integrated regulators feature a variety of input voltages and output currents, and offer a combination of power sequencing, adjustable switching frequency and clock synchronization options.

The new line of LM201xx and LM202xx synchronous buck regulators includes 2A, 3A, 4A and 5A output current devices. Each regulator integrates two switching MOSFETs and utilizes an externally compensated peak current-mode control loop, providing superior load transient response in low duty cycle applications. The external compensation allows the performance to be optimized for the output capacitor and inductor. With current-mode control, just two external components are needed for compensation. The ability of the 3A and 4A clock synchronization devices to self-synchronize when in out-of-phase operation reduces input capacitance and voltage ripple in power supply designs.

National offers a downloadable power supply design tool for the new low voltage synchronous buck regulators that eliminates the need for tedious hand calculations. The tool, in a Microsoft Excel spreadsheet format, calculates component values based on user-specified design parameters to quickly create a complete power supply design. The design tool allows the design engineer to quickly analyze the control loop response, thermal performance and efficiency of the design.

Technical Features of the New Low-Voltage Buck Regulators
Offered in a 16-pin thermally enhanced TSSOP package, the nine low-voltage buck regulators operate with an input voltage range from 2.95V to 5.5V and deliver up to 5A of continuous output current. Both fixed and adjustable switching frequency versions are available.

Each buck regulator has a precise internal voltage of 1.5 percent accuracy from -40 degrees C to 125 degrees C while providing excellent line and load regulation. They include a precision enable pin that allows accurate setting of the turn-on threshold and sequencing of the turn-on of multiple devices, eliminating the need for an external voltage supervisor chip. Also included is a power good indicator that regulates the output voltage within tolerance and can sequence loads that have an enable input.

A tracking and soft-start feature allows the design engineer to set the output to accurately track an external supply, as well as provide a controlled voltage ramp to protect loads against in-rush current that could cause latch-up. The monotonic start-up into pre-biased load feature prevents the possibility of latch-up in field programmable gate array (FPGA) and application-specific integrated circuit (ASIC) applications.

The buck regulators enhance system reliability by using an accurate current limit to provide robust protection for long-term hard shorts while minimizing the inductor size. Over-voltage and under-voltage events are monitored at the output voltage.-National Semiconductor