Freescale Semiconductor 56F8122 - Manual (Page 126)

56F8322 Techncial Data, Rev. 10.0
126 Freescale Semiconductor
Preliminary
B, the internal [state-dependent component], reflects the supply current required by certain on-chip
resources only when those resources are in use. These include RAM, Flash memory and the ADCs.
C, the internal [dynamic component], is classic C*V
2
*F CMOS power dissipation corresponding to the
56800E core and standard cell logic.
D, the external [dynamic component], reflects power dissipated on-chip as a result of capacitive loading
on the external pins of the chip. This is also commonly described as C*V
2
*F, although simulations on two
of the IO cell types used on the 56800E reveal that the power-versus-load curve does have a non-zero
Y-intercept.
Note: V
REFH
is tied to V
DDA
and V
REFLO
is tied to V
SSA
inside this package.
Power due to capacitive loading on output pins is (first order) a function of the capacitive load and
frequency at which the outputs change.
Table 10-25 provides coefficients for calculating power dissipated
in the IO cells as a function of capacitive load. In these cases:
TotalPower =
Σ
((Intercept + Slope*Cload)*frequency/10MHz)
where:
• Summation is performed over all output pins with capacitive loads
• TotalPower is expressed in mW
• Cload is expressed in pF
Because of the low duty cycle on most device pins, power dissipation due to capacitive loads was found
to be fairly low when averaged over a period of time.
E, the external [static component], reflects the effects of placing resistive loads on the outputs of the
device. Sum the total of all V
2
/R or IV to arrive at the resistive load contribution to power. Assume V =
0.5 for the purposes of these rough calculations. For instance, if there is a total of eight PWM outputs
driving 10mA into LEDs, then P = 8*.5*.01 = 40mW.
In previous discussions, power consumption due to parasitics associated with pure input pins is ignored,
as it is assumed to be negligible.
Table 10-25 IO Loading Coefficients at 10MHz
Intercept Slope
PDU08DGZ_ME 1.3 0.11mW / pF
PDU04DGZ_ME 1.15mW 0.11mW / pF