Santa Clara, Calif.—National Semiconductor says its two new step-down switching regulators for handheld devices and automotive power adapters, the LM34917A and LM34919, are the industry's smallest non-synchronous buck regulators to feature a supply voltage rating up to 50 volts, 1.25-amp continuous output, intelligent current-limiting, and over-voltage protection. These chips, in the company's PowerWise family, are suited to applications that require high-input voltage regulation such as MP3 players utilizing Firewire connectivity (IEEE1394), and MP3 players and auxiliary power adapters with direct connection to a 12-volt (universal) automotive power outlet where transient protection requirements can exceed 40 volts.
The chips include all of the functions needed to implement a low-cost, efficient buck bias regulator. The LM34917A (12-bump, 1.97-by-2.3 mm micro SMD package) features programmable switching up to 2 MHz, thus facilitating the use of ultra-small inductors and capacitors for very small solution size. The chip utilizes a constant on-time (COT) control scheme, which requires no loop compensation. It has a peak efficiency of at least 90 percent.
The chip's COT feedback regulation scheme results in fast load transient response and simplifies circuit implementation. The operating frequency remains constant with line and load variation, owing to the inverse relationship between the input voltage and the on-time. The valley current-limit results in a smooth transition from constant-voltage to constant-current mode without foldback when the output is overloaded. Additional features include VCC under-voltage lockout, thermal shutdown, gate drive under-voltage lockout, and maximum duty-cycle limiting. The LM34917A can deliver up to 1.25 amps to the load.
The LM34919 (10-bump, 1.51-by-1.97 mm package) can deliver up to 600 mA. It features the same COT feedback regulation scheme used in the LM34917A.
Pricing : Available now, the LM34917A is priced at $1.35 each and the LM34919 is priced at $1.05 each, both for 1k quantities.
National Semiconductor , 1-800-272-9959, www.national.com