MSC8112 Dual Core Digital Signal Processor Data Sheet, Rev. 0

Hardware Design Considerations

Freescale Semiconductor

40

3.4

External SDRAM Selection

The external bus speed implemented in a system determines the speed of the SDRAM used on that bus. However, because of

differences in timing characteristics among various SDRAM manufacturers, you may have use a faster speed rated SDRAM to

assure efficient data transfer across the bus. For example, for 133 MHz operation, you may have to use 133 or 166 MHz

SDRAM. Always perform a detailed timing analysis using the MSC8112 bus timing values and the manufacturer specifications

for the SDRAM to ensure correct operation within your system design. The output delay listed in SDRAM specifications is

usually given for a load of 30 pF. Scale the number to your specific board load using the typical scaling number provided by

the SDRAM manufacturer.

3.5

Thermal Considerations

Eqn. 1

where

R

The power dissipation values for the MSC8112 are listed in Table 2-3. 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

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

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 that is painted

black. The MSC8112 device case surface is too shiny (low emissivity) to yield an accurate infrared temperature measurement.

Eqn. 2

where

θ

Note:

See MSC8102, MSC8122, and MSC8126 Thermal Management Design Guidelines (AN2601/D).