Option

Typical Curr ent Options

Reduced Clock Frequency

5.0V operation

610 mA @ 33 MHz, 765 mA @ 50 MHz

3.3V operation

360 mA @ 33 MHz

Remove Clock

150 mA

Suspend Mode clock operating

15 mA

Suspend Mode and Remove Clock

450

µA

Remove Power

0 mA

Table 4 - 1

Power Management Options

Note: Values listed are approximations. Refer to the appropriate SGS-Thomson data book for DC specifications.

ST486DX - SMM POWER MANAGEMENT FEATURES

41

4.

Power Management Features

The SGS-Thomson CPU provides several methods and levels of power management. The fully

static design allows clock stopping. Suspend Mode, SMM and 3.3 volt operation can be used to

achieve optimum CPU and system power management. Table 4-1 summarizes the various power

management options for the SGS-Thomson CPU.

4.1

Reducing the Clock Frequency

The SGS-Thomson CPU is a fully static design meaning the input clock frequency can be reduced

or stopped without a loss of internal CPU data or state. The system designer can make decisions to

reduce the clock frequency by using SGS-Thomson SMM capabilities, Advanced Power Manage-

ment (APM) software API and/or chipset capabilities. When the clock is removed and then reas-

serted, execution will begin with the instruction where the clock was removed from the CPU.

4.2

Lowering the CPU Supply Voltage

SGS-Thomson CPUs are available that operate at either 3.3 or 5.0 volts. Parts rated at 3.3 volts

have the letter ’V’ included in the part number (Refer the appropriate SGS-Thomson data book for

duced by approximately 50% when operating at 3.3 instead of 5.0 volts. Operating the CPU at 3.3

volts can reduce CPU power consumption by over 70%, as the power consumption increases as the

square of the power supply voltage (P-=-V