dsp56004 Freescale Semiconductor, Inc, dsp56004 Datasheet - Page 78

• Manufacturer Part Number: dsp56004
• Description: Symphonytm Audio Dsp Family 24-bit Digital Signal Processors
• Manufacturer: Freescale Semiconductor, Inc

Design Considerations
Power Consumption Considerations
POWER CONSUMPTION CONSIDERATIONS
4-4
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 3:
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 formula:
where:
The Maximum Internal Current (I
switching of the internal buses on best-case operation conditions, which is not
necessarily a real application case. The Typical Internal Current (I
reflects the average switching of the internal buses on typical operating conditions.
For applications that require very low current consumption:
Equation 4:
•
•
•
•
•
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.
C = node/pin capacitance
V = voltage swing
f = frequency of node/pin toggle
I
=
C V f
I
=
Freescale Semiconductor, Inc.
Example 4-1 Current Consumption
50 10
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12
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5.5 20 10
CCI
max) value reflects the typical possible
6
=
5.5mA
CCItyp
MOTOROLA
) value