DSP56371D Motorola Inc, DSP56371D Datasheet - Page 36

• Manufacturer Part Number: DSP56371D
• Description: high density CMOS device
• Manufacturer: Motorola Inc

Design Considerations
18.3
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 following formula:
The maximum internal current (I
on best-case operation conditions, which is not necessarily a real application case. The typical internal
current (I
For applications that require very low current consumption, do the following:
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).
Use the test algorithm, specific test current measurements, and the following equation to derive the current
per MIPS value.
36
Power Consumption Example
For a GPIO address pin loaded with 50 pF capacitance, operating at 3.3 V, and with a 150 MHz clock,
toggling at its maximum possible rate (75 MHz), the current consumption is
where
•
•
where : I
NOTE: F1 should be significantly less than F2. For example, F2 could be 66 MHz and F1 could be
Minimize the number of pins that are switching.
Minimize the capacitive load on the pins.
CCItyp
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.
Power Consumption Considerations
I
I MIPS
C
V
f
I
F2
F1
⁄
typF2
typF1
=
) value reflects the average switching of the internal buses on typical operating conditions.
C
×
= node/pin capacitance
= voltage swing
= frequency of node/pin toggle
= current at F2
= current at F1
= high frequency (any specified operating frequency)
= low frequency (any specified operating frequency lower than F2)
V
=
×
I MHz
f
⁄
Freescale Semiconductor, Inc.
I
=
For More Information On This Product,
=
50
CCI
(
I typF2 I typF1
×
max) value reflects the typical possible switching of the internal buses
10 12
DSP56371 Technical Data
Go to: www.freescale.com
–
–
×
3.3
×
)
75
⁄
(
F2 F1
×
10 6
–
=
)
12.375mA
MOTOROLA