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Thermal Specifications and Design Considerations

Datasheet

accomplished using the equations listed under Table 30. In most temperature sensing

devices, an expected value for the diode ideality is designed-in to the temperature

calculation equation. If the designer of the temperature sensing device assumes a

perfect diode the ideality value (also called ntrim) will be 1.000. Given that most diodes

are not perfect, the designers usually select an ntrim value that more closely matches

the behavior of the diodes in the processor. If the processors diode ideality deviates

from that of ntrim, each calculated temperature will be offset by a fixed amount. This

temperature offset can be calculated with the equation:

Terror(nf) = Tmeasured X (1 – nactual/ntrim)

Where Terror(nf) is the offset in degrees C, Tmeasured is in Kelvin, nactual is the measured

ideality of the diode, and ntrim is the diode ideality assumed by the temperature

sensing device.

To improve the accuracy of diode based temperature measurements, a new register

(Tdiode_Offset) has been added to processor that will contain thermal diode

characterization data. During manufacturing each processors thermal diode will be

evaluated for its behavior relative to a theoretical diode. Using the equation above, the

temperature error created by the difference between ntrim and the actual ideality of the

particular processor will be calculated. This value (Tdiode_Offset) will be programmed in

to the new diode correction MSR and when added to the Tdiode_Base value can be used

to correct temperatures read by diode based temperature sensing devices.

If the ntrim value used to calculate Tdiode_Offset differs from the ntrim value used in a

temperature sensing device, the Terror(nf) may not be accurate. If desired, the

Tdiode_Offset can be adjusted by calculating nactual and then recalculating the offset using

the actual ntrim as defined in the temperature sensor manufacturers' datasheet.

The Diode_Base value and ntrim used to calculate the Diode_Correction_Offset are

listed in Table 32.

§ §

Table 32.

Thermal “Diode” ntrim and Diode_Correction_Offset

Symbol

Parameter

Unit

ntrim

Diode ideality used to calculate Diode_Offset

1.008

—

Diode_Base

°C

Table 33.

Thermal Diode Interface

Signal Name

Land Number

Signal

Description

THERMDA

AL1

diode anode

THERMDC

AK1

diode cathode

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