PC7447AMGH1000LB datasheet(12/44 Pages) ATMEL

12 / 44 page

5387B–HIREL–07/05

PC7447A [Preliminary]

Figure 6-2.

C4 Package with Heat Sink Mounted to a Printed-Circuit Board

Note the internal versus external package resistance.

Heat generated on the active side of the chip is conducted through the silicon, through the heat

sink attach material (or thermal interface material), and finally to the heat sink where it is

removed by forced-air convection.

Because the silicon thermal resistance is quite small, the temperature drop in the silicon may be

neglected for a first-order analysis. Thus, the thermal interface material and the heat sink con-

duction/convective thermal resistances are the dominant terms.

6.4.3

Thermal Management Information

This section provides thermal management information for the high coefficient of the thermal

expansion ceramic ball grid array (HITCE) package for air-cooled applications. Proper thermal

control design is primarily dependent on the system-level design – the heat sink, airflow, and

thermal interface material. The PC7447A implements several features designed to assist with

thermal management, including DFS and the temperature diode. DFS reduces the power con-

sumption of the device by reducing the core frequency; see Table 6-6 on page 19 for specific

information regarding power reduction and DFS. The temperature diode allows an external

device to monitor the die temperature in order to detect excessive temperature conditions and

alert the system; see section ”Temperature Diode” on page 16 for more information.

To reduce the die-junction temperature, heat sinks may be attached to the package by several

methods – spring clips to holes in the printed-circuit board or package, and mounting clips and

screw assembly (see Figure 6-3); however, due to the potentially large mass of the heat sink,

attachment through the printed-circuit board is suggested. If a spring clip is used, the spring

force should not exceed ten pounds.

External Resistance

Internal Resistance

Radiation

Convection

Heat Sink

Thermal Interface Material

Die/Package

Die Junction

Package/Leads

Printed-Circuit Board

Radiation

Convection

PC7447AMGH1000LB Datasheet(PDF) 12 Page - ATMEL Corporation