4-4
DSP56367
MOTOROLA
Design Considerations
Power Consumption Considerations
•
RESET must be asserted when the chip is powered up. A stable EXTAL signal must
be supplied before deassertion of RESET.
•
At power-up, ensure that the voltage difference between the 3.3 V tolerant pins and the
chip V
CC
never exceeds a TBD voltage.
4.3
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
C = node/pin capacitance
V = voltage swing
f = frequency of node/pin toggle
The maximum internal current (I
CCI
max) 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 (I
CCItyp
) 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.
Example 4-1 Current Consumption
For a Port A address pin loaded with 50 pF capacitance, operating at 3.3 V, and with a 100 MHz clock, toggling at its maximum possible
rate (50 MHz), the current consumption is
I
C
V
f
×
×
=
I
50
10
12
–
×
3.3
×
50
×
10
6
×
8.25mA
=
=
Summary of Contents for DSP56367
Page 16: ...xvi MOTOROLA CONTENTS Paragraph Number Title Page Number ...
Page 22: ...xxii MOTOROLA List of Figures Figure Number Title Page Number ...
Page 26: ...xxvi MOTOROLA List of Tables Table Number Title Page Number ...
Page 148: ...4 6 DSP56367 MOTOROLA Design Considerations PLL Performance Issues ...
Page 248: ...9 30 DSP56367 MOTOROLA Serial Host Interface SHI Programming Considerations ...
Page 306: ...10 58 DSP56367 MOTOROLA Enhanced Serial Audio Interface ESAI ESAI Initialization Examples ...
Page 389: ...Bootstrap ROM Contents MOTOROLA DSP56367 A 15 end ...
Page 390: ...A 16 DSP56367 MOTOROLA Bootstrap ROM Contents ...
Page 432: ...C 8 DSP56367 MOTOROLA JTAG BSDL ...
Page 484: ...D 52 DSP56367 MOTOROLA Programmer s Reference ...
Page 490: ...E 6 DSP56367 MOTOROLA Power Consumption Benchmark ...
Page 516: ...F 26 DSP56367 MOTOROLA IBIS Model ...
Page 522: ...Index 6 MOTOROLA Index ...
Page 523: ......