LM2639

The LM2639 provides an attractive solution for power supplies of high power microprocessors (such as Pentium II™, M II™, K6™-2, K6™-3, etc.) exhibiting ultra fast load transients. Compared to a conventional single-phase supply, an LM2639 based multi-phase supply distributes the thermal and electrical loading among components in multiple phases and greatly reduces the corresponding stress in each component. The LM2639 can be programmed to control either a 3-phase converter or a 4-phase converter. Phase shift among the phases is 120° in the case of three phase and 90° with four-phase. Because the power channels are out of phase, there can be significant ripple cancellation for both the input and output current, resulting in reduced input and output capacitor size. Due to the nominal operating frequency of 2 MHz per phase, the size of the output inductors can be greatly reduced which results in a much faster load transient response and a dramatically shrunk output capacitor bank. Microprocessor power supplies with all surface mount components can be easily built.

The internal high speed transconductance amplifier guarantees good dynamic performance. The output drive voltages can be adjusted through a resistor divider to control switching loss in the external FETs.

The internal master clock frequency of up to 8 MHz is set by an external reference resistor. An external clock of 10 MHz can also be used to drive the chip to achieve frequency control and multi-chip operation.