Intel Celeron Processors 540 BX80537540 Data Sheet

65

The Intel

 

Celeron M processor incorporates two methods of monitoring die temperature, the Intel 

Thermal Monitor and the thermal diode. The Intel Thermal Monitor (detailed in 

) must 

be used to determine when the maximum specified processor junction temperature has been 

reached. The second method, the thermal diode, can be read by an off-die analog/digital converter 

(a thermal sensor) located on the motherboard, or a standalone measurement kit. The thermal diode 

may be used to monitor the die temperature of the processor for thermal management or 

instrumentation purposes but cannot be used to indicate that the maximum T

J

 of the processor has 

been reached. Please see 

 for thermal diode usage recommendation when the 

PROCHOT# signal is not asserted.

 provide the diode interface and specifications.

The reading of the external thermal sensor (on the motherboard) connected to the processor 

thermal diode signals, will not necessarily reflect the temperature of the hottest location on the die. 

This is due to inaccuracies in the external thermal sensor, on-die temperature gradients between the 

location of the thermal diode and the hottest location on the die, and time based variations in the die 

temperature measurement. Time based variations can occur when the sampling rate of the thermal 

diode (by the thermal sensor) is slower than the rate at which the T

J

 temperature can change. 

The offset between the thermal diode based temperature reading and the Intel Thermal Monitor 

reading may be characterized using the Intel Thermal Monitor’s automatic mode activation of 

thermal control circuit. This temperature offset must be taken into account when using the 

processor thermal diode to implement power management events.

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

support or recommend operation of the thermal diode when the processor power supplies are not within their 
specified tolerance range.

2. Characterized at 100 °C.
3. Not 100% tested. Specified by design/characterization.
4. The ideality factor, n, represents the deviation from ideal diode behavior as exemplified by the diode 

equation: 

THERMDA

B18

Thermal diode anode

THERMDC

A18

Thermal diode cathode

I

FW

Forward Bias Current

5

300

µA

1

n

Diode Ideality Factor

1.00151

1.00220

1.00289

2, 3, 4

R

T

Series Resistance

3.06

ohms

2, 3, 5