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Electrical characteristics
MPC5607B Microcontroller Data Sheet, Rev. 5
Freescale Semiconductor
37
4.5.3
Power considerations
The average chip-junction temperature, TJ, in degrees Celsius, may be calculated using Equation 1:
TJ = TA + (PD x RJA)
Eqn. 1
Where:
TA is the ambient temperature in °C.
RJA is the package junction-to-ambient thermal resistance, in °C/W.
PD is the sum of PINT and PI/O (PD = PINT + PI/O).
PINT is the product of IDD and VDD, expressed in watts. This is the chip internal power.
PI/O represents the power dissipation on input and output pins; user determined.
Most of the time for the applications, PI/O< PINT and may be neglected. On the other hand, PI/O may be significant, if the device
is configured to continuously drive external modules and/or memories.
An approximate relationship between PD and TJ (if PI/O is neglected) is given by:
RJB CC
Thermal resistance,
junction-to-board4
Single-layer board — 1s
100
—
36
°C/W
144
—
38
176
—
38
Four-layer board — 2s2p
100
—
33.6
144
—
33.4
176
—
33.4
RJC CC
Thermal resistance,
junction-to-case5
Single-layer board — 1s
100
—
23
°C/W
144
—
23
176
—
23
Four-layer board — 2s2p
100
—
19.8
144
—
19.2
176
—
18.8
1 Thermal characteristics are targets based on simulation.
2 V
DD = 3.3 V ± 10% / 5.0 V ± 10%, TA = 40 to 125 °C.
3 Junction-to-ambient thermal resistance determined per JEDEC JESD51-3 and JESD51-6. Thermal test board
meets JEDEC specification for this package. When Greek letters are not available, the symbols are typed as RthJA
and RthJMA.
4 Junction-to-board thermal resistance determined per JEDEC JESD51-8. Thermal test board meets JEDEC
specification for the specified package. When Greek letters are not available, the symbols are typed as RthJB.
5 Junction-to-case at the top of the package determined using MIL-STD 883 Method 1012.1. The cold plate
temperature is used for the case temperature. Reported value includes the thermal resistance of the interface
layer. When Greek letters are not available, the symbols are typed as RthJC.
Table 10. LQFP thermal characteristics1 (continued)
Symbol
C
Parameter
Conditions2
Pin count
Value
Unit
Min Typ Max