AN2323 Freescale Semiconductor / Motorola, AN2323 Datasheet - Page 4

• Manufacturer Part Number: AN2323
• Description: PowerPC MPC7455 I/O Power Evaluation
• Manufacturer: Freescale Semiconductor / Motorola

Measured Power for all EEMBC Benchmarks
Measured Power for all EEMBC Benchmarks
again as Figure 2-2 depicts, the Tsi107 host bridge and buffer have an effect on the current measurement but
their effect is small. This theory was tested by tracking memory signals with the logic analyzer and in fact,
less than a handful of signals were driven during the routine and they transitioned at a very low frequency.
While running this routine on the MPC7455 the following measurement was taken:
After adding this result with the initial theoretical power from Part I, a final theoretical power value of 180.3
mW is attained which is very close to the measured value of 204 mW. The close relationship of the two
values proves the validity of the measured value.
2.3
The same procedure, including having the caches off, for measuring actual I/O power for the JPEG
compression benchmark was used for the 46 other EEMBC benchmarks and the results are summarized in
Figure 2-4.
The average current measured for all 47 benchmarks was 81.2 mA corresponding to an average power of
203.1 mW. These benchmarks were created to simulate a variety of real world applications so these results
can represent typical I/O power values for the MPC7455. From Figure 2-4, one can see that typical I/O
power is not only low at around 200 mW, but also does not vary much at all.
Part III Varying Bus Frequency and
Power
The equation shown in Figure 1-1 implies that power is linearly related to bus frequency. This section
investigates that assumption.
3.1
Using the same setup pictured in Figure 2-2, current measurements were taken at bus frequencies of 66, 100,
and 133 MHz for the JPEG compression benchmark. Power losses and initial theoretical power were also
re-evaluated for the same varying frequencies. The results are summarized in Table 2 below.
4
Measured Power for all EEMBC Benchmarks
Varying Bus Frequency Measurements
I
250.0
200.0
150.0
100.0
LOSSES
50.0
0.0
Freescale Semiconductor, Inc.
Figure 2-4. Power for all EEMBC Benchmarks
PowerPC™ MPC7455 I/O Power Evaluation
For More Information On This Product,
= 65 mA -> P
1
5
Go to: www.freescale.com
9
13
LOSSES
17
Benchmark
= 162.5 mW
21
25
29
33
37
41
45
MOTOROLA