DSP56011 Просмотр технического описания (PDF) - Motorola => Freescale

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DSP56011

24-BIT DVD DIGITAL SIGNAL PROCESSOR

Motorola => Freescale 

Design Considerations

Power Consumption Considerations

POWER CONSUMPTION CONSIDERATIONS

Power dissipation is a key issue in portable DSP applications. Some of the factors

which affect current consumption are described in this section. Most of the current

P R E L I M I N A R Y consumed by CMOS devices is Alternating Current (AC), which is charging and

discharging the capacitances of the pins and internal nodes.

Current consumption is described by the formula:

Equation 3: I = C × V × f

where:

C = node/pin capacitance

V = voltage swing

f = frequency of node/pin toggle

Example 4-1 Current Consumption

For an I/O pin loaded with 50 pF capacitance, operating at 5.5 V, and with a 81 MHz clock, toggling

at its maximum possible rate (20 MHz), the current consumption is:

Equation 4: I = 50 × 10–12 × 5.5 × 20 × 106 = 5.5mA

The Maximum Internal Current (ICCImax) value reflects the typical possible

switching of the internal buses on best-case operation conditions, which is not

necessarily a real application case. The Typical Internal Current (ICCItyp) value

reflects the average switching of the internal buses on typical operating conditions.

For applications that require very low current consumption:

• Minimize the number of pins that are switching.

• Minimize the capacitive load on the pins.

• Connect the unused inputs to pull-up or pull-down resistors.

• Disable unused peripherals.

• Disable unused pin activity.

Preliminary Information

4-4

DSP56011 Technical Data Sheet, Rev. 1

MOTOROLA

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