MC9S12XD256MAL Datasheet, PDF (1242/1348 Pages) Freescale Semiconductor, Inc – Freescale’s Scalable Controller Area Network

Appendix A Electrical Characteristics
A.1.8 Power Dissipation and Thermal Characteristics
Power dissipation and thermal characteristics are closely related. The user must assure that the maximum
operating junction temperature is not exceeded. The average chip-junction temperature (T_J) in °C can be
obtained from:
TJ = TA + (PD • Θ_JA)
TJ = Junction Temperature, [°C ]
TA = Ambient Temperature, [°C ]
PD = Total Chip Power Dissipation, [W]
Θ_JA = Package Thermal Resistance, [°C/W]
The total power dissipation can be calculated from:
PD = PINT + PIO
PINT = Chip Internal Power Dissipation, [W]
Two cases with internal voltage regulator enabled and disabled must be considered:
1. Internal voltage regulator disabled
PINT = IDD ⋅ VDD + IDDPLL ⋅ VDDPLL + IDDA ⋅ VDDA
∑ ^{PIO =} _i ^{RDSON ⋅ IIOi2}
P_IO is the sum of all output currents on I/O ports associated with V_DDX and V_DDR.
For R_DSON is valid:
respectively
RDSON = ^{V--I--O-O----L-L--;for} outputs driven low
RDSON = ^{V-----D----D----I-5-O----–}-H---V-----O-----H-- ;for outputs driven high
2. Internal voltage regulator enabled
PINT = IDDR ⋅ VDDR + IDDA ⋅ VDDA
I_DDR is the current shown in Table A-10. and not the overall current flowing into V_DDR, which
additionally contains the current flowing into the external loads with output high.
∑ ^{PIO =} _i ^{RDSON ⋅ IIOi2}
P_IO is the sum of all output currents on I/O ports associated with V_DDX and V_DDR.
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MC9S12XDP512 Data Sheet, Rev. 2.21
Freescale Semiconductor