AN2323 Freescale Semiconductor / Motorola, AN2323 Datasheet - Page 5

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

Figure 3-5 shows a graphical depiction of the data, and it shows that measured power and power losses both
appear to vary linearly.
The linear relationship for measured power is expected; however, power losses associated with quiescent
and leakage currents should be constant. The variance can be explained by considering the Tsi107 host
bridge and buffer loads pictured in Figure 2-2.
Part IV Determining Maximum I/O Power
Sometimes it is necessary to determine maximum I/O power in order to appropriately provide enough power
supply current. For that reason, this section investigates the derivation of a value for maximum I/O power
on the MPC7455.
4.1
In order to simulate an application that affects the maximum number of I/O signals as frequently as possible,
the routine depicted in Figure 4-6 was used.
MOTOROLA
Initial Theoretical Power
Power Losses
Total Theoretical Power
Measured Power
Value
Measuring Maximum I/O Power
300
200
100
0
Table 2. Power Values at Varying Frequencies (in mW)
Freescale Semiconductor, Inc.
Figure 3-5. Power vs. Frequency Relationship
PowerPC™ MPC7455 I/O Power Evaluation
For More Information On This Product,
66
66 MHz
148
160
163
12
Frequency (MHz)
Go to: www.freescale.com
100
133
100 MHz
163
181
204
18
Measuring Maximum I/O Power
Power
Losses
Measured
Power
133 MHz
177
201
247
24
5