First high-reliability, high-power-density, synchronous buck regulators

National Semiconductor Corporation has introduced a new line of buck switching regulators that are said to be the first in the industry to feature high reliability, high power density. These 10 full-featured, synchronous buck regulators provide high-efficiency DC-DC power conversion for point-of-load power supply designs in applications such as communication, data storage, industrial and automotive. 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 output voltage 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 high reliability 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
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. Fixed, adjustable and external synchronous switching frequency versions are available.

The key advantage offers by the nine buck regulators is system reliability. With industry leading +/-10% precision current limit threshold over temperature, LM201xx prevents output inductor from saturating more reliably than peers in the industry, provides robust protection for long-term hard shorts while minimizing the inductor saturation current and thus size. Over-voltage and under-voltage events are monitored at the output voltage. System load safety is guaranteed without latch-up and filtering capacitor over discharge.

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 low-voltage LM20123, LM20124 and LM20125 buck regulators feature fixed frequencies of 1.5 MHz at 3A, 1 MHz at 4A or 500 KHz at 5A for enabling the smallest solution size.

The low-voltage LM20143, LM20144 and LM20145 buck regulators feature adjustable frequencies for maximum design flexibility.

The low-voltage LM20133 and LM20134 buck regulators provide clock synchronization for synchronization to an external clock source.

National Semiconductor