DSP56KFAMUM/AD(1996) View Datasheet(PDF) - Motorola => Freescale

Part Name

Description

Manufacturer

DSP56KFAMUM/AD
(Rev.:1996)

24-BIT DIGITAL SIGNAL PROCESSOR

Motorola => Freescale 

Design Considerations

Power Consumption

POWER CONSUMPTION

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

some factors which affect current consumption. 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

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

V with a 40 MHz clock, toggling at its maximum possible rate (which is 10 MHz), the

current consumption is:

Equation 4: I = 50 × 10–12 × 5.5 × 10 × 106 = 2.75mA

The maximum internal current value (ICCI-max), reflects the maximum ICC expected

when running the code given below. This represents “typical” internal activity, and is

included as a point of reference. Some applications may consume more or less current

depending on the code used. The typical internal current value (ICCI-typ) reflects

what is typically seen when running the given code.

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.

4-4

DSP56002/D, Rev. 3

MOTOROLA

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