ASUS designed the P4T around the Intersil reference design for the P4 adaptation of the HIP6301 three phase power supply circuitry, specifically designed for high demand microprocessors. Briefly, a three-phase design distributes the current to the CPU over three channels. All three channels are connected to provide parallel power, meaning that, in case one channel experiences sudden load, the current is distributed equally over all three parallel channels. Regulation and equalization is achieved via an input-sensing resistor, which acts faster than a downstream sensor of output current. Why is the circuitry called 3-phase and not 3-channel? The individual channels are 120 degree phase shifted, and, therefore do not act simultaneously but are offset by 1/3 of the main chip's operating frequency. Thus, effectively, the operating frequency is tripled.
 Current traces of the three individual "shifted" phases and the resulting fluctuations of V core at the leading and falling edge of a response. Note how the voltage ripples of the individual phases cancel each other out. Reprinted with permssion from Intersil white pages
To reduce load and heat dissipation of the main chip, it does not directly drive the switch voltage generators (MOSFETs) but uses separate driver chips as interface. As a summary of the design, the switching currents are accelerated and the phase-induced "ripple currents" are largely eliminated, thus, greatly reducing the need for passive buffering in form of capacitors. Two examples are shown above.
The ASUS ASIC
A consistent feature of all recent ASUS boards has been the presence of an ASUS ASIC chip. It is almost generally known that ASUS uses the ASIC chip for hardware monitoring instead of relying on the integrated solutions from VIA and Intel. Additionally, the ASIC chip serves some other functions as I'll explain below.
A role for IRQ routing
One of the key limitations of the PC platform is the restricted number of IRQs. Most mainboards currently available are capable of IRQ sharing and renegotiating. However, in almost all cases, this is achieved by software emulation (IRQ minirouting drivers). Software emulation, on the other hand is working effectively only if there is no conflict with predetermined rerouting of IRQs by the BIOS which is the main reason to turn off PnP OS Installed in the BIOS.
Most of us have some experience with IRQ conflicts, which, in fully loaded systems, can become a constant source of grief and the desire for more IRQs can be found on basically all bulletin boards throughout the web. One alternative solution is to implement a hardware IRQ distributor or IRQ expansion chip / arbiter. This is exactly what ASUS has done with their ASIC. Keep in mind though, that, in order to enable this function, it is necessary to enable PnP OS Installed in the BIOS which effectively eliminates the IRQ sharing from the main level of the chipset and assigns it to the ASIC chip.
|
