Step-down switching regulators released
29 April 2008
For handheld devices and automotive power adapters, National Semiconductor has launched two step-down switching regulators.
The integrated LM34917A and LM34919 are claimed to be the industry’s smallest non-synchronous buck regulators to feature a supply voltage rating up to 50V, 1.25A continuous output current, intelligent current limiting and over-voltage protection.
National’s LM34917A and LM34919 feature programmable switching frequency up to 2MHz and integrated MOSFET switches to reduce system component count. A high switching frequency enables the use of ultra-small inductors and capacitors. Both new products utilise a COT (constant on-time) control scheme, which requires no loop compensation.
The regulators are suitable for use in applications that require high-input voltage regulations such as MP3 players utilising Firewire connectivity (IEEE1394) as well as MP3 players or auxiliary power adapters with direct connection to a 12V automotive power outlet where transient protection requirements can exceed 40V. Also, as the LM34917A and LM34919 feature peak efficiency equal to or greater than 90 per cent, they are in National’s PowerWise family of energy-efficient products.
The LM34917A buck regulator supplies up to 1.25A to the load and contains an N-Channel MOSFET buck switch available in a 12pin 2mm by 2.3mm micro SMD package.
In addition to no loop compensation, the COT feedback regulation scheme also results in fast load transient response and simplified 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 maximum duty cycle limiter. The LM34919 buck regulator supplies up to 0.6A to the load and features the constant on-time feedback regulation scheme of the LM34917A. The LM34919 is offered in a 10pin, 1.5mm by 2mm micro SMD package.
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