Power Consumption
10.19 Power Consumption
See Section 10.1 for a list of IDD requirements for the 56F8037/56F8027. This section provides additional
detail which can be used to optimize power consumption for a given application.
Power consumption is given by the following equation:
Total power = A: internal [static component]
+B: internal [state-dependent component]
+C: internal [dynamic component]
+D: external [dynamic component]
+E: external [static component]
A, the internal [static component], is comprised of the DC bias currents for the oscillator, leakage currents,
PLL, and voltage references. These sources operate independently of processor state or operating
frequency.
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.
2
C, the internal [dynamic component], is classic C*V *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
2
on the external pins of the chip. This is also commonly described as C*V *F, although simulations on two
of the I/O cell types used on the 56800E reveal that the power-versus-load curve does have a non-zero
Y-intercept.
Table 10-23 I/O Loading Coefficients at 10MHz
Intercept
Slope
8mA drive
4mA drive
1.3
0.11mW / pF
0.11mW / pF
1.15mW
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 10-23 provides coefficients for calculating power dissipated
in the I/O 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
56F8037/56F8027 Data Sheet, Rev. 6
Freescale Semiconductor
165
FREESCALE [ Freescale ]
