APR7SLASHD datasheet(81/101 Pages) NXP

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DSP56001A

Power Consumption

MOTOROLA

DSP56001A/D, Rev. 1

4-7

POWER CONSUMPTION

Power dissipation is a key issue in portable DSP applications. The following describes some

factors that affect current consumption. Current consumption is described by the formula:

Equation 5: I = C

× V × f

where :

C =

node/pin capacitance

V =

voltage swing

frequency of node/pin toggle

For example, for an address pin loaded with a 50 pF capacitance and operating at 5.5V with a 33

MHz clock, toggling at its maximum possible rate (which is 8.25 MHz), the current consumption

is:

Equation 6: I = 50

× 10–12× 5.5×8.25 × 106= 227 mA

The maximum internal current value (ICCI – max), reflects the maximum possible switching of

the internal buses, which is not necessarily a real application case. The typical internal current

value (ICCI – typ) reflects the average switching of the internal buses.

The following steps are recommended for applications requiring very low current consumption:

1. Minimize external memory accesses; use internal memory accesses instead.

2. Minimize the number of pins that are switching.

3. Minimize the capacitive load on the pins.

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

HOST PORT CONSIDERATIONS

Careful synchronization is required when reading multi-bit registers that are written by another

asynchronous system. This is a common problem when two asynchronous systems are

connected. The situation exists in the Host Interface. The following paragraphs present

considerations for proper operation.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

APR7/D Datasheet(PDF) 81 Page - NXP Semiconductors