APR9SLASHD datasheet(79/101 Pages) NXP

79 / 101 page

DSP56001A

Heat Dissipation

MOTOROLA

DSP56001A/D, Rev. 1

4-5

HEAT DISSIPATION

The average chip junction temperature, TJ, in °C, can be obtained from:

Equation 1: T

J = TA + (PD × ΘJA)

Where:

TA = ambient temperature, °C

JA =

package thermal resistance, junction-to-ambient,

°C/W

PD = PINT + PI/O

PINT = ICC × VCC watt—chip internal power

PI/O = power dissipation on input and output pins—user determined

For most applications PI/O < PINT and PI/O can be neglected. An appropriate relationship between

PD and TJ (if PI/O is neglected) is:

Equation 2: P

D = K / (TJ + 273)

Solving equations (1) and (2) for K gives:

Equation 3: K = P

D × (TA + 273) + PD × ΘJA

Where:

K is a constant pertaining to the particular package

K can be determined from equation (2) by measuring PD (at equilibrium) for a known TA. Using

this value of K, the values of PD and TJ can be obtained by solving equations (1) and (2) iteratively

for any value of TA. The total thermal resistance of a package (ΘJA) can be separated into two

components,

JC and ΘCA, representing the barrier to heat flow from the semiconductor junction to

the package (case) surface (

JC) and from the case to the outside ambient (ΘCA). These terms are

related by the equation:

Equation 4:

JA = ΘJC + ΘCA

JC is device-related and cannot be influenced by the user. However, ΘCA is user-dependent and

can be minimized by thermal management techniques such as heat sinks, ambient air cooling,

and thermal convection. Thus, good thermal management can significantly reduce

CA so that

JA approximately equals ΘJC. Values for thermal resistance presented in this document, unless

estimated, were derived using the procedure described in Motorola Reliability Report 7843,

“Thermal Resistance Measurement Method for MC68XX Microcomponent Devices”, and are

provided for design purposes only. Thermal measurements are complex and dependent on

procedure and setup. User-derived values for thermal resistance may differ.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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