Intel Celeron M 520 1.60 GHz BX80537520 Data Sheet

66

I

FW

=I

s

 

x 

(e

(qV

D

/nkT)

 -1)                                                                                                                                                                         

Where I

S

 = saturation current, q = electronic charge, V

D 

= voltage across the diode, k = Boltzmann Constant, 

and T = absolute temperature (Kelvin).

5. The series resistance, R

T

, is provided to allow for a more accurate measurement of the diode junction 

temperature. R

T

 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. R

T

 can be used by 

remote diode thermal sensors with automatic series resistance cancellation to calibrate out this error term. 
Another application is that a temperature offset can be manually calculated and programmed into an offset 
register in the remote diode thermal sensors as exemplified by the equation:                                                                          
T

error

 = [R

T

 

x 

(N-1) 

x 

I

FWmin

]/[(no/q) 

x 

ln N]

The Intel Thermal Monitor helps control the processor temperature by activating the TCC when the 

processor silicon reaches its maximum operating temperature. The temperature at which the Intel 

Thermal Monitor activates the thermal control circuit (TCC) is not user configurable and is not 

software visible. Bus traffic is snooped in the normal manner, and interrupt requests are latched 

(and serviced during the time that the clocks are on) while the TCC is active.

With a properly designed and characterized thermal solution, it is anticipated that the TCC would 

only be activated for very short periods of time when running the most power intensive 

applications. The processor performance impact due to these brief periods of TCC activation is 

expected to be so minor that it would not be detectable. An under-designed thermal solution that is 

not able to prevent excessive activation of the TCC in the anticipated ambient environment may 

cause a noticeable performance loss, and may affect the long-term reliability of the processor. In 

addition, a thermal solution that is significantly underdesigned may not be capable of cooling the 

processor even when the TCC is active continuously.

The Intel Thermal Monitor controls the processor temperature by modulating (starting and 

stopping) the processor core clocks when the processor silicon reaches its maximum operating 

temperature. The Intel Thermal Monitor uses two modes to activate the TCC: Automatic mode and 

On-Demand mode. If both modes are activated, automatic mode takes precedence. The Intel 

Thermal Monitor Automatic Mode must be enabled via BIOS for the processor to be operating 

within specifications.This mode is selected by writing values to the Model Specific Registers 

(MSRs) of the processor. After the automatic mode is enabled, the TCC will activate only when the 

internal die temperature reaches the maximum allowed value for operation. 

When Intel Thermal Monitor is enabled, and a high temperature situation exists, the clocks will be 

modulated by alternately turning the clocks off and on at a 50% duty cycle. Cycle times are 

processor speed dependent and will decrease linearly as processor core frequencies increase. After 

the temperature has returned to a non-critical level, modulation ceases and the TCC goes inactive. 

A small amount of hysteresis has been included to prevent rapid active/inactive transitions of the 

TCC when the processor temperature is near the trip point. The duty cycle is factory configured 

and cannot be modified. Also, the automatic mode does not require any additional hardware, 

software drivers or interrupt handling routines. Processor performance will be decreased by the 

same amount as the duty cycle when the TCC is active, however, with a properly designed and 

characterized thermal solution the TCC most likely will never be activated, or will be activated 

only briefly during the most power intensive applications. 

The TCC may also be activated using On-Demand mode. If bit 4 of the ACPI Intel Thermal 

Monitor Control register is written to a "1", the TCC will be activated immediately, independent of 

the processor temperature. When using On-Demand mode to activate the TCC, the duty cycle of 

the clock modulation is programmable via bits 3:1 of the same ACPI Intel Thermal Monitor 

Control Register. In automatic mode, the duty cycle is fixed at 50% on, 50% off, in On-Demand 

mode, the duty cycle can be programmed from 12.5% on/ 87.5% off, to 87.5% on/12.5% off in