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MC9S12KT256 Datasheet, PDF (558/594 Pages) Freescale Semiconductor, Inc – Microcontrollers | |||
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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 (TJ) in °C can be
obtained from:
TJ = TA + (PD ⢠ÎJA)
TJ = Junction Temperature, [°C ]
TA = Ambient Temperature, [°C ]
PD = Total Chip Power Dissipation, [W]
ÎJA = 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 â
VDD + IDDPLL â
VDDPLL + IDDA â
VDDA
â PIO = i RDSON â
IIOi2
PIO is the sum of all output currents on I/O ports associated with VDDX and VDDR.
For RDSON is valid:
RDSON = V--I--O-O----L-L--;for outputs driven low
respectively
RDSON = V-----D----D----I-5-O----â-H---V-----O-----H-- ;for outputs driven high
2. Internal voltage regulator enabled
PINT = IDDR â
VDDR + IDDA â
VDDA
IDDR is the current shown in Table A-8 and not the overall current ï¬owing into VDDR, which
additionally contains the current ï¬owing into the external loads with output high.
â PIO = i RDSON â
IIOi2
PIO is the sum of all output currents on I/O ports associated with VDDX and VDDR.
MC9S12KT256 Data Sheet, Rev 1.15
558
Freescale Semiconductor
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