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Power Supply for Processor+Cache Modules

How do I supply power to an processor/cache module (interposer)? Do I have to use

the VRM?

The MPC750-based processor/cache module (often called the “interposer”) presents a 5-

bit voltage encoding pattern which can be used to control the inputs of an industry-stan-

dard Voltage Regulator Module (VRM), available from numerous manufacturers (Ray-

theon, Cherry, and others). The output of the VRM is used to supply the core voltage of

the processor (IVDD), while the I/O pins are driven by the +3.3V power supply

(OVDD).

The use of a VRM is optional, however. As long as the correct power is supplied, the

voltage settings can be ignored. Thus, some systems may wish to place a +2.6V power

supply directly on the board to supply the IVDD power, ignoring the VRM settings. For

systems in which the end-user cannot change the interposer, the power supply can be

ﬁxed to whatever processor will be used in the system, with no risk of inadvertently

damaging parts.

Alternately, the components for the VRM can be placed on the motherboard to supply

the VRM function without the cost of the socket. This may reduce cost slightly at the

expense of additional board space.