PowerPC 602 RISC Microprocessor Hardware Specifications

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1.7.3 Decoupling Recommendations

Due to the 602’s dynamic power management feature, large address and data buses, and high operating

frequencies, the 602 can generate transient power surges and high frequency noise in its power supply,

especially while driving large capacitive loads. This noise must be prevented from reaching other

components in the 602 system, and the 602 itself requires a clean, tightly regulated source of power.

Therefore, it is recommended that the system designer place a decoupling capacitor with a low ESR

(effective series resistance) rating at every other Vdd and OVdd pin of the 602.

These capacitors should range in value from 220 pF to 10

µF to provide both high and low frequency

filtering, and should be placed as close as possible to their associated Vdd pin. Surface-mount tantulum or

ceramic devices are preferred. It is also recommended that these decoupling capacitors receive their power

from Vdd and GND power planes in the PCB, utilizing short traces to minimize inductance. Power or

ground connections must be made to all external Vdd and GND pins of the 602.

1.7.4 Connection Recommendations

To ensure reliable operation, it is highly recommended to connect unused inputs to an appropriate signal

level. Unused active-low inputs should be connected to Vdd. Unused active-high inputs should be

connected to GND.

1.7.5 Thermal Management Information for the Motorola Package

This section provides a thermal management example for the 602; this example is based on a typical desktop

configuration using a 144 lead, 28 mm x 28 mm, Motorola wire-bond PQFP package.

1.7.5.1 Thermal Characteristics for the Motorola Wire-Bond PQFP Package

The thermal characteristics for a wire-bond PQFP package are as follows:

Thermal resistance (junction-to-case) = Rθjc or θjc = 2.8°C/Watt (junction-to-case)

1.7.5.2 Thermal Management Example

The junction temperature can be calculated from the junction-to-ambient thermal resistance, as follows:

Junction temperature: Tj = Ta + Rθja * P

or

Tj = Ta + (Rθjc + Rcs + Rsa) * P

Where:

Ta is the ambient temperature in the vicinity of the device

Rθja is the junction-to-ambient thermal resistance

Rθjc is the junction-to-case thermal resistance of the device

Rcs is the case-to-heat sink thermal resistance of the interface material

Rsa is the heat sink-to-ambient thermal resistance

P is the power dissipated by the device

In this environment, it can be assumed that all the heat is dissipated to the ambient through the heat sink, so

the junction-to-ambient thermal resistance is the sum of the resistances from the junction to the case, from

the case to the heat sink, and from the heat sink to the ambient.

Note that verification of external thermal resistance and case temperature should be performed for each

application. Thermal resistance can vary considerably due to many factors including degree of air

turbulence.

For a power dissipation of 2.5 Watts in an ambient temperature of 40

°C at 1 m/sec with the heat sink

Freescale Semiconductor, Inc.

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