Intel 848P, Thermal Design Manual

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Thermal Metrology
R
18 Intel
®
848P Chipset Thermal Design Guide
3.2.2.1 Recommended Test Parameters
The following example describes how to determine the voltage required to operate at the
recommended MCH Thermal Design Power (TDP) listed in Table 2. The voltage to be applied to
each heater can be easily calculated. The heater resistance must be measured on each TMTV unit to
set the correct power dissipation. The typical resistance of the heater is 70
Ω
. The maximum
allowable power for the TMTV is 30 W so as not to exceed the temperature limit of the package.
Example
TDP = 8.1 W
R
= 70
Ω
(measured resistance across heater)
V = SQRT (Power x Resistance) = SQRT (8.1 W * 70 Ω ) = 23.8 V
Solving for voltage, the calculated value of V = 23.8 V. Hence, if a nominal 23.8 V is applied to the
die heater, the TMTV will operate at the 8.1 W thermal design power.
3.2.2.2 TMTV Correction Factors
Due to changes in die size between the TMTV and the planned production die size, a correction
factor is required for any heatsink thermal performance measurements made with the TMTV.
Thermal performance of a MCH heatsink is determined using the case-to-ambient thermal
characterization parameter,
Ψ
CA
(Psi). Refer to Section 3.1 for instructions on measuring
T
C
(package case temperature). Figure 7 shows recommended ambient temperature measurement
locations for a board in a JEDEC test configuration.
Ψ
CA
is analogous to thermal resistance but is
defined using total package power instead of the actual power dissipated between the package case
and local ambient. The TMTV die size is 8.153 mm x 8.153 mm [0.321 in x 0.321 in]. The
correction factors listed in Table 5 are for a currently assumed die size of 9.73 mm x 9.73 mm
[0.383 in x 0.383 in] for the MCH.
Table 5. TMTV Correction Factor
Parameter Correction Factor
Ψ
CA
0.935
NOTE: The TMTV correction factor was calculated assuming an airflow velocity of 0.76 m/s [150 lfm] and a TIM
comprised of phase change material. The correction factor may not apply to configurations that deviate
from these assumptions.
Any case-to-ambient thermal characterization parameters based on data collected from a TMTV
should be multiplied by the correction factor in Table 5 to account for changes in die size. The
correction factor calculation is as follows:
{MCH
Ψ
CA
} = {TMTV
Ψ
CA
} x Correction factor
Example Calculation
T
C
= 90 °C
T
A
= 50 °C
Total Package Power = 11.7 W
Ψ
CA, MEASURED
= (T
C
– T
A
) / Total Package Power = (90 – 50) / 11.7 = 3.4 °C/W
Applying the correction factor, we get:
Ψ
CA, CORRECTED
= Correction Factor x
Ψ
CA, MEASURED
= 0.968 x 3.4 = 3.3 °C/W