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Features
Provides 3 regulated voltages
Power Good flag and output enable
Charge pump pinSwitching Section
Synchronous rectification
5-bit DAC programmable down to 1.3V
Typical ±1% DAC tolerance
Switching frequency: 50 kHz to 1 MHz
Over-voltage protection
Two methods of over-current protection
Adaptive non-overlapping FET gate drives
Soft start without external capacitorLinear Section
N-FET and NPN drive capability
Ultra fast response speed
Under voltage latch-off at 0.63V
Output voltages default to 1.5V and 2.5V yet adjustable
Description The LM2638 provides a comprehensive 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.
Switching Section - The switching regulator controller features an Intel-compatible, 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 rDS[lowbar]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 wide control bandwidth makes meeting the GTL+ bus transient response requirement an easy job. In minimum configuration, the two controllers default to 1.5V and 1.25V respectively.
Both linear controllers have under voltage latch-off.
Applications
Embedded power supplies for motherboards
Triple DC/DC power supplies
Programmable high current DC/DC power supply
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