1°C Triple Temperature Sensor with Beta Compensation and Hotter of Two Zones
Datasheet
When monitoring the thermal diode of an AMD K8 processor, the Resistance Error Correction must be
disabled for accurate temperature measurements. This is accomplished by clearing the REC bit in the
configuration 2 register (see Section 4.5). Please see Application note “13.16 - Using the EMC1043
with AMD Processors” for more details.
3.7
Beta Compensation
The Beta Compensation function automatically eliminates temperature errors caused by beta variation
in modern, low beta transistors used for monitoring processor temperatures. Changes in beta as
differing currents are applied to temperature transistors can cause significant temperature errors in
monitoring devices. As modern processor geometries shrink the trend is for transistor betas to
decrease, which exacerbates temperature errors.
Discrete transistors, with collector connected to base to form a diode, are generally immune to these
temperature errors because of high (>100) betas. A beta variation of 10% from low current to high
current, when beta equals 100, induces approximately 0.12° error at 100°C. However for a low beta
(1.0) substrate transistor used for processor temperature measurement, a beta variation of 10% from
low to high current induces approximately 6.12° error at 100°C.
Because the Beta Compensation function is designed to be used with substrate PNP transistors only,
this function should be disabled when using a diode-connected transistor (such as the 2N3904) or
CPUs that implement the thermal diode as a two-terminal device. The Beta Compensation function is
disabled by writing 07h to the Beta Configuration register
When measuring an AMD K8 processor, the Beta Compensation circuitry must be disabled. See
Section 4.8. Please see SMSC Application note “13.16 - Using the EMC1043 with AMD Processors”
for more details.
3.8
Programmable Ideality Factor
The EMC1043 default is for a diode ideality factor of 1.008 which is common for a 2N3904 diode and
for many processor transistors. When a diode or transistor is used that has a different ideality factor
value than 1.008 a temperature error is induced that is a linear function of temperature. Previous
solutions for this mismatch in ideality factor has been to supply a programmable offset to the
temperature reading which corrects the error at a single temperature but causes a residual error at all
other temperatures. The EMC1043 ideality factor register corrects this mismatch error at all
temperatures (see Section 4.7).
APPLICATION NOTE: When monitoring a substrate transistor or CPU diode and beta compensation is enabled, the
Ideality Factor should not be adjusted. Beta Compensation automatically corrects for most
ideality errors.
3.9
Diode Faults
The EMC1043 detects a fault if the DP pin is left floating or is shorted to VDD. In the case of a diode
fault, the corresponding status bit will be set and the output data will be set at 400h.
Revision 1.37 (09-05-06)
SMSC EMC1043
DATA1S6HEET
SMSC [ SMSC CORPORATION ]
