National Semiconductor Corp. has introduced two step-down switching regulators for use in automotive power adapters as well as handheld devices.

The PowerWise LM34917A and LM34919 are said to include all of the functions needed to implement a low-cost, efficient buck bias regulator. They integrate MOSFET switches to reduce system component count, and they feature programmable switching frequency up to 2 MHz, which enables the use of ultra-small inductors and capacitors, according to the company. The combination ranks them among the smallest non-synchronous buck regulators that feature a supply voltage rating up to 50V, 1.25A continuous output current, intelligent current limiting, and over-voltage protection.

The LM34917A and LM34919 feature peak efficiency of 90% or better. A constant on-time (COT) control scheme requires no loop compensation, supports fast load transient response, and simplifies circuit implementation. The operating frequency remains constant with line and load variations due 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 a maximum duty cycle limiter.

The LM34917A buck regulator supplies up to 1.25 A to the load. It contains an N-Channel MOSFET buck switch and is available in a 12-pin, 2 mm by 2.3 mm micro SMD package. The LM34919 buck regulator supplies up to 0.6 A to the load and features the constant on-time feedback regulation scheme of the LM34917A. The LM34919 is offered in a 10-pin, 1.5 mm by 2 mm micro SMD package.

Available now, the LM34917A is priced at $1.35 and the LM34919 at $1.05 in 1,000-unit quantities.