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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Datasheets

Title		Size	Date	Other Language
	LM2638 Motherboard Power Supply Solution with a 5-Bit Programmable Switching Controller and Two Linear Regulator Controllers	165 Kbytes	26-Jun-99	日本語

More Application Notes

Title		Size	Date	Other Language
	AN-1146: Application Note 1146 Designing a Multi-phase Asynchronous Buck Regulator Using the LM2639	127 Kbytes	10-May-04
	AN-1208: Application Note 1208 LM2633 Evaluation Board	700 Kbytes	10-May-04

Reliability Metrics

Part Number	Process	EFR Reject	EFR Sample Size	PPM	LTA Rejects	LTA Device Hours	FITS	MTTF (Hours)
LM2638M	ABCD150	0	34175	0	0	4234000	1	1201409060

Note: The Early Failure Rates (EFR) were calculated as point estimate PPM based on rejects and sample size for EFR. The Long Term Failure Rates were calculated at 60% confidence using the Arrhenius equation at 0.7eV activation energy and derating the assumed stress temperature of 150°C to an application temperature of 55°C.

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Obsolete Versions

Obsolete Part	Alternate Part or Supplier	Source	Last Time Buy Date
LM2638M	NONE	NATIONAL SEMICONDUCTOR	01 Dec 2009