Family of High-Efficiency, Full-Featured PowerWise® Synchronous Buck Regulators

National Semiconductor has introduced a new line of buck switching regulators that are the first in the industry to feature high power density and self-synchronisation.  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 synchronisation 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 synchronisation devices to self-synchronize when in out-of-phase operation reduces input capacitance and voltage ripple in power supply designs.

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.

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 synchronisation for synchronisation to an external clock source.
The low-voltage LM20154 buck regulator features out-of-phase clock output for current sharing or out-of-phase operation.

Technical Features of the New High Voltage Buck Regulator

The high-voltage LM20242 buck regulator, offered in a 20-pin TSSOP package with exposed pad, operates with an input voltage range from 4.5V to 36V and delivers up to 2A of continuous output current.  The LM20242 features adjustable frequency from 250 kHz to 1 MHz for maximum design flexibility

Features & benefits:

• Precision enable can be used to turn the device on at a precise input voltage for sequencing of multiple devices.
• Power good indicates that the output voltage is regulated within tolerance, and it can be used to sequence devices that have an enable input.
• Tracking sets the output to accurately track an external supply for sequencing of multiple devices.
• Soft-start provides a controlled voltage ramp to protect loads against in-rush current that could cause latch-up.
• Sync-in allows synchronisation of the device to an external clock source.
• Sync-out provides 180 degree out-of-phase clock output that can be used for current sharing or multi-phase operation.
• Frequency adjust allows optimization of the power solution for efficiency or solution size.
• Synchronous operation with low RDS_ON integrated FETs provide high efficiency at high load currents and diode emulation mode for high efficiency at light loads.
• External compensation allows the performance to be optimized for the desired output capacitor and inductor.
• Start-up into pre-biased loads prevents the possibility of latch up in FPGA and ASIC applications.
• High-accuracy current limit, over-voltage and under-voltage protection provides enhanced system reliability.
• Start-up into pre-biased loads prevents the possibility of latch up in FPGA and ASIC applications.
• High-accuracy current limit, over-voltage and under-voltage protection provides enhanced system reliability.

Application information:

Ideal for powering FPGAs, DSPs, and microprocessors
in servers, networking equipment, optical networks, and
industrial power supplies.

Product information table: