emc2106 Standard Microsystems Corp., emc2106 Datasheet - Page 39

• Manufacturer Part Number: emc2106
• Description: Emc2106 Dual Rpm-based Linear Fan Controller With Hardware Thermal Shutdown
• Manufacturer: Standard Microsystems Corp.

Dual RPM-Based Linear Fan Controller with Hardware Thermal Shutdown
Datasheet
SMSC EMC2106
5.14.2
5.14.3
5.14.4
5.15
CONVERSION RATE
Resistance Error Correction
The EMC2106 includes active Resistance Error Correction to remove the effect of up to 100 ohms of
series resistance. Without this automatic feature, voltage developed across the parasitic resistance in
the remote diode path causes the temperature to read higher than the true temperature is. The error
induced by parasitic resistance is approximately +0.7°C per ohm. Sources of parasitic resistance
include bulk resistance in the remote temperature transistor junctions, series resistance in the CPU,
and resistance in the printed circuit board traces and package leads. Resistance error correction in the
EMC2106 eliminates the need to characterize and compensate for parasitic resistance in the remote
diode path.
Beta Compensation
The forward current gain, or beta, of a transistor is not constant as emitter currents change. As well,
it is not constant over changes in temperature. The variation in beta causes an error in temperature
reading that is proportional to absolute temperature. This correction is done by implementing the BJT
or transistor model for temperature measurement.
For discrete transistors configured with the collector and base shorted together, the beta is generally
sufficiently high such that the percent change in beta variation is very small. For example, a 10%
variation in beta for two forced emitter currents with a transistor whose ideal beta is 50 would contribute
approximately 0.25°C error at 100°C. However for substrate transistors where the base-emitter junction
is used for temperature measurement and the collector is tied to the substrate, the proportional beta
variation will cause large error. For example, a 10% variation in beta for two forced emitter currents
with a transistor whose ideal beta is 0.5 would contribute approximately 8.25°C error at 100°C.
The Beta Compensation circuitry in the EMC2106 corrects for this beta variation to eliminate any error
which would normally be induced. It automatically detects the appropriate beta setting to use.
Digital Averaging
The External Diode 1 channel support a 4x digital averaging filter. Every cycle, this filter updates the
temperature data based an a running average of the last 4 measured temperature values. The digital
averaging reduces temperature flickering and increases temperature measurement stability.
The digital averaging can be disabled by setting the DIS_AVG bit in the Configuration 2 Register (see
Section
The External Diode 1, External Diode 2, and External Diode 3 channels can be configured to monitor
a thermistor. When this function is enabled, the data on the VIN1, VIN2, or VIN3 channels can be
configured to measure a simple voltage input or a ground-connected thermistor circuit (see
A
The External Diode 1 channel can only be configured as a voltage input if the SHDN_SEL pin is set
to a logic ‘1’.
Thermistor Support
for more information).
4 / sec
8 / sec
6.10).
Table 5.4 Dynamic Averaging Behavior
DATASHEET
AVERAGING FACTOR (RELATIVE TO 11-BIT CONVERSI0N)
DYNAMIC AVERAGING
39
ENABLED
2x
1x
DYNAMIC AVERAGING
Revision 1.74 (05-08-08)
DISABLED
1x
1x
Appendix