National Semiconductor Introduces the New LM3477, LM3478 and LM3488 Switching Controllers
National Semiconductor Corp. (Santa Clara, CA) introduced three new switching controllers for general-purpose power supplies, which are intended to address the need for greater flexibility in high-efficiency switching power-supply design. The LM3477, LM3478 and LM3488 are claimed to be small, versatile solutions with a wide range of input voltages as well as high operating frequencies. They are designed for use in custom power supplies in high-volume systems such as DSL and cable modems, set-top boxes, desktop and notebook PCs, distributed-power systems, and a variety of battery-powered portable products.
The new controllers can be used in traditional switching-regulator topologies such as buck, boost and flyback, as well as other topologies, including CUK, inverting and SEPIC. National Semiconductor claims that the new chips, which contain evaluation boards, a cookbook of common circuits and WebSim, have the flexibility to satisfy most high-performance power-supply requirements. All of the new controllers feature a current-mode control scheme.
The LM3477 controller is meant for topologies requiring high-side N-FETs, while the LM3478 and LM3488 controllers are suitable for regulator topologies requiring low-side N-FETs. The LM3488 can also be synchronized to an external clock, and includes a 1.5-percent internal reference. The input voltage range for the LM3478 and LM3488 is 2.95V to 40V and the switching-frequency for both parts can be adjusted between 100kHz and 1MHz with a single external resistor. The LM3477 step-down controller operates from 2.95V to 35V with a fixed-clock frequency of 500kHz.
Both the LM3477 and LM3488 have a shutdown mode intended to extend battery life by reducing quiescent current to 5mA. Other protection features include thermal shutdown, under-voltage and over-voltage protection, short-circuit protection, cycle-by-cycle current limit, and an adjustable current limit.
"National's versatile use-anywhere controllers provide the perfect balance of size, efficiency, current handling and cost," said John Perzon, National's manager of strategic marketing for switching-regulator products.
The LM3477MM and LM3478MM controllers are available now in eight-lead mini-S08 packages, and are priced at $1.65 each in quantities of 1,000. Also available immediately, the LM3488MM parts are $1.95 each in 1,000-piece quantities.
