IDT79RC4640

IDT79RC4640™

If the conditions are not correct when the WAIT instruction finishes the

W pipe-stage (i.e. the SysAd bus is not idle), the WAIT is treated as a

NOP.

Once the CPU is in Standby Mode, any interrupt, including the internally generated timer interrupt, will cause the CPU to exit Standby

Mode.

Thermal Considerations

The RC4640 utilizes special packaging techniques to improve the thermal properties of high-speed processors. The RV4640 is packaged using cavity-up packaging in a 128-pin thermally enhanced PQFP package (“DU”) with a drop-in heat spreader, for devices with low peak power. The R4640 utilizes the PQFP package for higher power consumption devices (the “DZ” package), which is an all-aluminum package with the die attached to a normal copper lead frame mounted to the aluminum casing.

Due to the heat-spreading effect of the aluminum, the PQFP package allows for an efficient thermal transfer between the die and the case. The aluminum offers less internal resistance from one end of the package to the other, reducing the temperature gradient across the package and therefore presenting a greater area for convection and conduction to the PCB for a given temperature. Even nominal amounts of air flow will dramatically reduce the junction temperature of the die, resulting in cooler operation. The PQFP package is pin and socket compatible with the 128-pin QFP package.

The R4640 and the RV4640 are guaranteed in a case temperature range of 0

°C to +85°C for commercial temperature parts and the

RV4640 in a case temperature range of -40

°C to +85°C for industrial temperature parts. The type of package, speed (power) of the device, and air flow conditions affect the equivalent ambient temperature conditions that will meet this specification.

The equivalent allowable ambient temperature, T

A

, can be calculated using the thermal resistance from case to ambient (

∅

CA

) of the given package. The following equation relates ambient and case temperatures:

T

A

= T

C

- P *

∅

CA where P is the maximum power consumption at hot temperature, calculated by using the maximum I

CC

specification for the device.

Typical values for

∅

CA

at various air flows are shown in Table 5.

∅

CA

Airflow (ft/min) 0 200 400 600 800 1000

128 PQFP (DU)

128 PQFP (DZ)

17

20

9

12

7

9.5

5

8

4

7

Table 5 Thermal Resistance (

∅CA) at Various Airflows

3

6.5

Note that the RC4640 implements advanced power management to substantially reduce the average power dissipation of the device. This operation is described in the IDT79RC4640/ IDT79RC4650 RISC

Processor Hardware User’s Manual.

MasterClock

SysAD

SysCmd

ValidOut

ValidIn

RdRdy

WrRdy

Release

Addr

Read

Data0 Data1

CData

CData

Data6 Data7

CData CEOD

Figure 3 RC4640 Block Read Request

8 of 23 December 5, 2008