LM2638 Datasheet | National Semiconductor

Description The LM2638 provides a prehensive embedded power supply solution for motherboards hosting high performance MPUs such as Pentium™ II, M II™, K6™-2 and other similar high performance MPUs. The LM2638 incorporates a 5-bit programmable, synchronous buck switching controller and two high-speed linear regulator controllers in a 24-pin SO package. In a typical application, the switching controller supplies the MPU core, and the linear regulator controllers supply the GTL+ bus and the clock or graphics chip core. A charge pump pin helps provide the necessary voltage to power the linear sections when 12V is shut off during system standby such as STR mode. Both linear controllers have under voltage latch-off. Features n Provides 3 regulated voltages n Power Good flag and output enable n Charge pump pin Switching Section n Synchronous rectification n 5-bit DAC programmable down to 1.3V n Typical ± 1% DAC tolerance n Switching frequency: 50 k Hz to 1 MHz n Over-voltage protection n Two methods of over-current protection n Adaptive non-overlapping FET gate drives n Soft start without external capacitor Linear Section n N-FET and NPN drive capability n Ultra fast response speed n Under voltage latch-off at 0.63V n Output voltages default to 1.5V and 2.5V yet adjustable Switching Section - The switching regulator controller features an Intel-patible, 5-bit programmable output voltage, over-current and over-voltage protection, a power good signal, and a logic-controlled output enable. There are two user-selectable over-current protection methods. One provides accurate over-current protection with the use of an external sense resistor. The other saves cost by taking advantage of the r DS_ON of the high-side FET. When there is an over voltage, the controller turns off the high side FET and turns on the low side. Linear Section - The two linear regulator controllers feature wide control bandwidth, N-FET and NPN transistor driving capability and an adjustable output. The...