Sensor Based Thermal Specification Design Guidance

8.4.1DTS 1.1 A New Fan Speed Control Algorithm without

TAMBIENT Data

In most system designs incorporating processor ambient inlet data in fan speed control adds design and validation complexity with a possible BOM cost impact to the system. A new fan speed control methodology is introduced to improve system acoustics without needing the processor inlet ambient information.

The DTS 1.1 implementation consists of two parts, a ΨCA requirement at TCONTROL and a ΨCA point at DTS = -1.

The ΨCA point at DTS = -1 defines the minimum ΨCA required at TDP considering the worst case system design Tambient design point:

ΨCA = (TCASE_max - TAmbient target) / TDP

For example, for a 95 TDP part, the Tcase max is 72.6C and at a worst case design point of 40C local ambient this will result in

ΨCA = (72.6 - 40) / 95 = 0.34 C/W

Similarly for a system with a design target of 45 C ambient the ΨCA at DTS = -1needed will be 0.29 C/W.

The second point defines the thermal solution performance (ΨCA) at TCONTROL. Figure 8-1lists the required ΨCA for various TDP processors.

These two points define the operational limits for the processor for DTS 1.1

implementation. At TCONTROL the fan speed must be programed such that the resulting ΨCAis better than or equivalent to the required ΨCA listed in Table 8-1. Similarly the fan

speed should be set at DTS = -1 such that the thermal solution performance is better than or equivalent to the ΨCArequirements at Tambient_Max. Based on the processor temperature, the fan speed controller must linearly change the fan speed from DTS =

TCONTROL to DTS = -1 between these points. Figure 8-3gives a visual description on DTS 1.1.

Thermal/Mechanical Specifications and Design Guidelines

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