DSP56366 datasheet(99/110 Pages) FREESCALE

99 / 110 page

DSP56366 Technical Data, Rev. 3.1

Freescale Semiconductor

5-3

•

Take special care to minimize noise levels on the VCCP and GNDP pins.

•

If multiple DSP56366 devices are on the same board, check for cross-talk or excessive spikes on

the supplies due to synchronous operation of the devices.

•RESET must be asserted when the chip is powered up. A stable EXTAL signal must be supplied

while RESET is being asserted.

•

At power-up, ensure that the voltage difference between the 5 V tolerant pins and the chip VCC

never exceeds 3.95 V.

5.3

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 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 following formula:

where:

= node/pin capacitance

= voltage swing

= frequency of node/pin toggle

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, do the following:

•

Set the EBD bit when 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.

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

minimize specific board effects (i.e., 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.

Example 1. Current Consumption

For a Port A address pin loaded with 50 pF capacitance, operating at 3.3 V, and with a 120

MHz clock, toggling at its maximum possible rate (60 MHz), the current consumption is

IC V

I50 10

–

3.3 60 10

9.9mA

DSP56366 Datasheet(PDF) 99 Page - Freescale Semiconductor, Inc

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