PowerPC 750FL RISC Microprocessor
Preliminary
5.8.3 Minimum Heat Sink Requirements
The worst-case power dissipation (P ) for the 750FL microprocessor is shown in Table 3-5 Power Consump-
D
tion (Low Power) on page 19. A conservative thermal management design provides sufficient cooling to
maintain the junction temperature (T ) of the 750FL microprocessor below 105°C at maximum P and worst-
J
D
case ambient temperature and airflow conditions.
Many factors affect the 750FL power dissipation, including V , T , core frequency, process factors, and the
DD
J
code that is running on the processor. In general, P increases with increases in T , V , Fcore, process
D
J
DD
variables, and the number of instructions executed per second.
For various reasons, analysis of the 750FL microprocessor power dissipation in an application might result in
a value less than the maximum value shown in the datasheet. Assuming a lower PD results in a thermal
management system with less cooling capacity than is required for the maximum datasheet PD. In this case,
the actual maximum 750FL microprocessor PD for the particular application should be determined. Contact
your IBM PowerPC FAE for more information.
In addition to the system factors that must be considered in a cooling system analysis, three things must be
noted. First, 750FL PD rises as T increases. Therefore, it is most useful to measure PD while the 750FL
J
junction temperature is at maximum. Though not specified or guaranteed, this rise in PD with T is typically
J
less than 1W per 10°C. Thus regardless of other factors, the minimum cooling solution must have a maximum
temperature rise of no more than 10°C/W.
This minimum cooling solution is not generally achievable without a heat sink. A heat sink or heat spreader of
some sort must always be used in 750FL applications.
Second, because of process variations, there can be a significant variation in the PD of individual 750FL
devices. In addition, IBM occasionally supplies "downbinned" parts. These are faster parts that are shipped in
lieu of the speed that was ordered. For example, some parts that are marked as 600 MHz might actually run
as fast as 700 MHz. These 700 MHz parts dissipate more power at 600 MHz than the 600 MHz parts. Thus,
power dissipation analysis must be conducted using the fastest parts available.
Finally, regardless of methodology, IBM only supports system designs that successfully maintain the
maximum junction temperature within datasheet limits. IBM also supports designs that rely on the maximum
PD values given in this datasheet, and supply a cooling solution sufficient to dissipate that amount of power
while keeping the maximum junction temperature below the maximum T .
J
System Design Information
Page 60 of 65
750flds60.fm.6.0
April 27, 2007
IBM [ IBM ]
