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Datasheet

Thermal Specifications and Design Considerations

5.2.5

TCONTROL and Fan Speed Reduction (Optional)

TCONTROL and Fan Speed Reduction are not requirements for the Celeron D processor on 90 nm

process and in the 478-pin package, but are provided as options for platforms that can use these

features. TCONTROL is part of the temperature specification that defines temperature for system fan

speed management. The BIOS reads the TCONTROL value once and configures the fan control chip

appropriately. The value for TCONTROL will be set during manufacturing and is unique for each

processor. The TCONTROL temperature for a given processor can be obtained by reading the

IA32_TEMPERATURE_TARGET MSR in the processor and is in hexadecimal format.

The value of TCONTROL (read from IA32_TEMPERATURE_TARGET MSR) can vary from 00 h

to 1E h (0 to 30 °C). The TCONTROL read from the IA32_TEMPERATURE_TARGET MSR needs

to be added to a base value of 50 °C to get the final value for comparison with Thermal Diode

temperature (TDIODE). TCONTROL plus the base value of 50 °C is compared to the temperature

reported by TDIODE. When the TDIODE temperature is below TCONTROL, fan speed can be at

minimum. As TDIODE approaches TCONTROL plus the base value of 50 °C, fan speed should be

increased in an effort to maintain TDIODE at/below TCONTROL plus the base value of 50 °C. For

platforms that support this feature, the processor TC-MAX specification must be within guidelines,

as defined by the processor thermal specifications in Table 5-1. For 845G/x chipset platforms that

were not designed to read IA32_TEMPERATURE_TARGET MSR, the processor must be kept

within the TC-MAX specification.

5.2.6

Thermal Diode

The processor incorporates an on-die thermal diode. A thermal sensor located on the system board

may monitor the die temperature of the processor for thermal management/long term die

temperature change purposes. Table 5-2 and Table 5-3 provide the diode parameter and interface

specifications. This thermal diode is separate from the Thermal Monitor’s thermal sensor and

cannot be used to predict the behavior of the Thermal Monitor.

Table 5-2. Thermal Diode Parameters

Symbol

Parameter

Min

Typ

Max

Unit

Notes

IFW

Forward Bias Current

—

187

NOTES:

Intel does not support or recommend operation of the thermal diode under reverse bias.

Diode Ideality Factor

1.0083

1.011

1.0137

—

2,3,4

Characterized at 75 °C.

Not 100% tested. Specified by design characterization.

The ideality factor, n, represents the deviation from ideal diode behavior as exemplified by the diode equation:

IFW = IS * (e

qVD/nkT –1)

where IS = saturation current, q = electronic charge, VD = voltage across the diode, k = Boltzmann Constant,

and T = absolute temperature (Kelvin).

Series Resistance

3.242

3.33

3.594

Ω

2,3,5

The series resistance, RT, is provided to allow for a more accurate measurement of the junction temperature. RT, as defined,

includes the pins of the processor but does not include any socket resistance or board trace resistance between the socket

and the external remote diode thermal sensor. RT can be used by remote diode thermal sensors with automatic series re-

sistance cancellation to calibrate out this error term. Another application is that a temperature offset can be manually calcu-

lated and programmed into an offset register in the remote diode thermal sensors as exemplified by the equation:

Terror = [RT * (N-1) * IFWmin] / [nk/q * ln N]

where Terror = sensor temperature error, N = sensor current ratio, k = Boltzmann Constant, q = electronic

charge.

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