National Semiconductor Corporation has introduced a line of buck switching regulators (LM201xx and LM202xx) that it said are among the first to feature high-power density and self-synchronization. The synchronous devices are designed to provide high-efficiency dc-dc power conversion for point-of-load power supply designs in automotive and other applications.
The buck regulators, in National's PowerWise product family, feature a variety of input voltages and output currents and offer a combination of power sequencing, adjustable switching frequency and clock synchronization options.
Offered in a 16-pin thermally enhanced TSSOP package, the low-voltage buck regulators operate with an input voltage range from 2.95 V to 5.5 V. Both fixed and adjustable switching frequency versions are available.
The line includes 2 A, 3 A, 4 A and 5 A output current devices. 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 5 A for enabling the smallest solution size. The low-voltage LM20143, LM20144 and LM20145 buck regulators feature adjustable frequencies for maximum design flexibility.
Each regulator integrates two switching MOSFETs and uses an externally compensated peak current-mode control loop that is said to provide superior load transient response in low duty cycle applications. The external compensation allows 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, according to National.
Each buck regulator has a precise internal voltage of 1.5% accuracy from -40 °C to 125 °C while providing excellent line and load regulation. A precision enable pin 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 design engineerd 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. Overvoltage and undervoltage events are monitored at the output voltage.
National offers a downloadable power supply design tool for the new synchronous buck regulators that eliminates the need for 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.