DSP56166 View Datasheet(PDF) - Motorola => Freescale

Part Name

Description

Manufacturer

DSP56166

16-bit General Purpose Digital Signal Processor

Motorola => Freescale 

PRELIMINARY - 6/15/93

Power Considerations

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

TJ = TA + (PD*ΘJA)

(1)

Where:

TA = Ambient Temperature, °C

ΘJA = Package Thermal Resistance, Junction-to-Ambient, °C/W

PD = PINT + PI/O

PINT = ICC*Vdd, Watts — Chip Internal Power

PI/O = Power Dissipation on Input and Output Pins — User Determined

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

PI/O is neglected) is:

PD = K/(TJ + 273° C)

(2)

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

K = PD*(TA + 273° C) + ΘJA*PD

(3)

Where K is a constant pertaining to the particular part. 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, ΘJA and CA, representing the barrier to heat flow from the semiconductor

junction to the package (case) surface (ΘJC) and from the case to the outside ambient (CA). These terms

are related by the equation:

ΘJA = ΘJC + CA

(4)

ΘJC is device related and cannot be influenced by the user. However, CA is user dependent and can be

minimized by such thermal management techniques as heat sinks, ambient air cooling, and thermal con-

vection. Thus, good thermal management on the part of the user can significantly reduce CA so thatΘJA ap-

proximately equals ΘJC. Substitution of ΘJC for ΘJA in equation (1) will result in a lower semiconductor junc-

tion temperature. 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 mea-

surements are complex and dependent on procedure and setup. User—derived values for thermal resis-

tance may differ.

3

DSP56166 Technical Data Sheet

MOTOROLA

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