DSP56321 datasheet(64/84 Pages) FREESCALE

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DSP56321 Technical Data, Rev. 11

4-4

Freescale Semiconductor

Design Considerations

Equation 4:

The maximum internal current (ICCImax) value reflects the typical possible switching of the internal buses on best-

case operation conditions—not necessarily a real application case. The typical internal current (ICCItyp) value

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

Perform the following steps for applications that require very low current consumption:

Set the EBD bit when you are not accessing external memory.

Minimize external memory accesses, and use internal memory accesses.

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 (for example, CLKOUT, XTAL).

One way to evaluate power consumption is to use a current-per-MIPS measurement methodology to minimize

specific board effects (that is, to compensate for measured board current not caused by the DSP). A benchmark

power consumption test algorithm is listed in Appendix A. Use the test algorithm, specific test current

measurements, and the following equation to derive the current-per-MIPS value.

Equation 5:

Where:

ItypF2

current at F2

ItypF1

current at F1

high frequency (any specified operating frequency)

low frequency (any specified operating frequency lower than F2)

Note:

F1 should be significantly less than F2. For example, F2 could be 66 MHz and F1 could be 33 MHz. The

degree of difference between F1 and F2 determines the amount of precision with which the current rating

can be determined for an application.

4.4 Input (EXTAL) Jitter Requirements

The allowed jitter on the frequency of EXTAL is 0.5 percent. If the rate of change of the frequency of EXTAL is slow

(that is, it does not jump between the minimum and maximum values in one cycle) or the frequency of the jitter is

fast (that is, it does not stay at an extreme value for a long time), then the allowed jitter can be 2 percent. The phase

and frequency jitter performance results are valid only if the input jitter is less than the prescribed values.

–

3.3

5.48 mA

MIPS

⁄

MHz

⁄

typF2

typF1

–

()

–

()

⁄

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