Power Consumption Benchmark
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
–12
6
I = 50x10
x3.3x75x10 = 12.375mA
The maximum internal current (ICCImax) 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 (ICCItyp) value reflects the average
switching of the internal buses on typical operating conditions.
For applications that require very low current consumption, do the following:
•
•
Minimize the number of pins that are switching.
Minimize the capacitive load on the pins.
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.
I/MIPS = I/MHz = (ItypF2 - ItypF1)/(F2 - F1)
where :ItypF2
=
=
=
=
current at F2
current at F1
ItypF1
F2
F1
high frequency (any specified operating frequency)
low frequency (any specified operating frequency lower than F2)
NOTE
F1 should be significantly less than F2. For example, F2 could be 66 MHz and F1 could be
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.
21
Power Consumption Benchmark
The following benchmark program permits evaluation of DSP power usage in a test situation.
;***********************************;********************************
;* ;* CHECKS Typical Power Consumption
;********************************************************************
ORG P:$000800
move #$000000,r1
move #$000000,r0
do #1024,ldmem
move r1,p:(r0)
move r1,y:(r0)+
ldmem nop
move #0,b1
;jmp $FF2AE0
;org P:$FF2AE0
move b1,y:>$100
Freescale Semiconductor
DSP56371 Technical Data
63
FREESCALE [ Freescale ]
