MSC7119 Freescale Semiconductor / Motorola, MSC7119 Datasheet - Page 41

• Manufacturer Part Number: MSC7119
• Description: Low-Cost 16-bit DSP with DDR Controller and 10/100 Mbps Ethernet MAC
• Manufacturer: Freescale Semiconductor / Motorola

3
This section described various areas to consider when incorporating the MSC7119 device into a system design.
3.1
An estimation of the chip-junction temperature
The power dissipation values for the MSC7119 are listed in Table 4. The ambient temperature for the device is the air
temperature in the immediate vicinity that would cool the device. The junction-to-ambient thermal resistances are JEDEC
standard values that provide a quick and easy estimation of thermal performance. There are two values in common usage: the
value determined on a single layer board and the value obtained on a board with two planes. The value that more closely
approximates a specific application depends on the power dissipated by other components on the printed circuit board (PCB).
The value obtained using a single layer board is appropriate for tightly packed PCB configurations. The value obtained using a
board with internal planes is more appropriate for boards with low power dissipation (less than 0.02 W/cm
convection) and well separated components. Based on an estimation of junction temperature using this technique, determine
whether a more detailed thermal analysis is required. Standard thermal management techniques can be used to maintain the
device thermal junction temperature below its maximum. If T
the power dissipation of the chip.
You can verify the junction temperature by measuring the case temperature using a small diameter thermocouple (40 gauge is
recommended) or an infrared temperature sensor on a spot on the device case. Use the following equation to determine T
Freescale Semiconductor
where
T
R
P
P
P
where
T
Ψ
P
A
D
INT
I/O
D
T
θ
JT
Hardware Design Considerations
JA
= ambient temperature near the package (°C)
= P
= thermocouple (or infrared) temperature on top of the package (°C)
= power dissipation in the package (W)
Thermal Design Considerations
= power dissipated from device on output pins (W)
= thermal characterization parameter (°C/W)
= I
= junction-to-ambient thermal resistance (°C/W)
INT
DD
+ P
× V
I/O
DD
= power dissipation in the package (W)
= internal power dissipation (W)
MSC7119 10/100 Mbps Ethernet MAC Data Sheet, Rev. 6
,
T
T
T
J
J
J
,
= T
= T
in °C can be obtained from the following:
A
T
+ (R
+ (
Ψ
θ
J
JT
JA
appears to be too high, either lower the ambient temperature or
× P
× P
D
D
)
)
Hardware Design Considerations
2
with natural
Eqn. 1
Eqn. 2
J
:
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