PowerPC 740 and PowerPC 750 Microprocessor
CMOS 0.20 µm Copper Technology, PID-8p, PPC740L and PPC750L, dd3.2
System Design Information
Thermal Assist Unit Specifications
Num
Characteristic
Minimum
Maximum
Unit
°C
Notes
1
2
3
Temperature range
Comparator settling time
Resolution
0
20
4
128
—
1
2
3
ms
°C
—
Note:
1. The temperature is the junction temperature of the die. The thermal assist unit's (TAU) raw output does not indicate an absolute temperature, but it must
be interpreted by software to derive the absolute junction temperature. For information on how to use and calibrate the TAU, contact ppc-
supp@us.ibm.com. This specification reflects the temperature span supported by the design.
2. The comparator settling time value must be converted into the number of CPU clocks that need to be written into the THRM3 SPR. For parts with nom-
inal operating frequencies (speed sort) above 266 MHz, the settling time = 20 µs × (266/nominal frequency). For example: for 500 MHz parts, settling
time = 20 µs × (266/500) = 10.6 µs. It is recommended that the maximum value be set in THRM3 under all conditions.
3. This value is guaranteed by design and is not tested.
Thermal Assist Unit Accuracy
Some previous versions of this Datasheet incorrectly specified the accuracy of the Thermal Assist Unit (TAU).
See the PowerPC 750-PID8p Microprocessor Errata List, Version 4.4 for details.
A Design Margin has been issued, which describes a fault in the TAU of certain dd3.2 parts, which prevents
them from attaining the accuracy specified in this Datasheet. See Design Margin, PPC750L dd3.2 TAU False
High Reading Fault for more details.
The TAU is an analog device whose accuracy can be affected by various error sources. The cumulative
effects of these error sources is shown in the table sin this section. IBM strongly recommends that at least a
single-point calibration be performed on the TAU before use. More information on calibrating and improving
the accuracy of the TAU is provided in the IBM Application Note, Calibrating the Thermal Assist Unit in the
IBM25PPC750L Processors.
The table “Selected Worst Case Maximum and Minimum Readings” shows, for selected actual junction tem-
peratures, the highest and lowest TAU reading at which an exception could be signalled by the TAU. This
table applies only to uncalibrated units. Readings for temperatures not shown can be extrapolated from the
points in the table.
Selected Worst Case Maximum and Minimum Readings
Actual
22
Highest TAU Reading
Lowest TAU Reading
32
46
2
35
13
21
29
37
45
53
61
69
45
56
55
67
65
77
75
88
85
98
95
109
119
105
9/6/2002
Version 2.0
Page38
IBM [ IBM ]
