The new LM557x and LM2557x family of switching regulators from National Semiconductor

The LM557x and LM2557x family of switching regulators feature all of the functions necessary to implement efficient, high voltage buck regulators using a minimum of external components.

This easy to use regulator family offers either a 42V (LM2557x) or 75V (LM557x) integrated N-channel MOSFET, with output current capabilities of 0.5Amps, 1.5Amps or 3Amps. The regulator control method is based upon current mode control utilizing an emulated current ramp. Current mode control provides inherent line voltage feed-forward, cycle-by-cycle current limiting and ease of loop compensation. The use of an emulated control ramp reduces noise sensitivity of the pulse-width modulation circuit, allowing reliable control of very small duty cycles necessary in high input voltage applications. The operating frequency is programmable from 50kHz to 1MHz and the adjustable output voltage can go down to 1.225V with 1.5% feedback reference accuracy. An oscillator synchronization pin allows multiples of regulators to self-synchronize or to be synchronized to an external clock. Additional protection features include a wide bandwidth error amplifier, programmable soft-start, current limit, thermal shutdown and remote shutdown capability. The devices are available in TSSOP-16 and TSSOP-20 package options as shown below:

Features & benefits:

• Fast, reliable switching power supply solution
• Extremely Broad, Adjustable Switching Frequency
• Frequency Synchronization (Input and Output)
• Excellent Transient Response + Ultra-Short Duty Cycle
• Higher, Programmable Switching Frequency
• External or Self Clock Synchronization
• Emulated Peak Current Mode Architecture
• Cycle-by-cycle current limiting
• Thermal Shutdown and Remote Shutdown
• Ease of loop compensation

Applications:

• Broad range of applications with wide VIN
• Most commonly, the family will be used to drive digital loads that need support for great transients

Product information table: