Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown
Datasheet
APPLICATION NOTE: Disabling the Watchdog will not automatically set the fan drive. This must be done manually
(or via the Look Up Table).
5.10
Fault Queue
The EMC2104 contains a programmable fault queue on all fault conditions except a FAN_SHORT or
TSD condition (including all temperature high, low, and tcrit limits as well as the hardware set thermal
limit). The fault queue defines how many consecutive out-of-limit conditions must be reported before
the corresponding status bit is set (and the ALERT# pin asserted).
APPLICATION NOTE: With the exception of the Tcrit limit, the fault queue is not applied to the internal diode
measurement.
5.11
Temperature Monitoring
The EMC2104 can monitor the temperature of up to four (4) externally connected diodes as well as
the internal or ambient temperature. Each channel is configured with the following features enabled or
disabled based on user settings and system requirements.
APPLICATION NOTE: When measuring an Intel 45nm CPU, the reported temperature will have an error of
approximately 1.5°C at 100°C. This error is related to a non-perfect ideality factor of the CPU
diode and is proportional to the diode temperature.
5.11.1
Dynamic Averaging
The EMC2104 supports dynamic averaging. When enabled, this feature changes the conversion time
for all channels based on the selected conversion rate. This essentially increases the averaging factor
as shown in Table 5.4. The benefits of Dynamic Averaging are improved noise rejection due to the
longer integration time as well as less random variation on the temperature measurement.
Table 5.4 Dynamic Averaging Behavior
AVERAGING FACTOR (RELATIVE TO 11-BIT CONVERSI0N)
DYNAMIC AVERAGING
ENABLED
DYNAMIC AVERAGING
DISABLED
CONVERSION RATE
1 / sec
2 / sec
4 / sec
8 / sec
8x
4x
2x
1x
1x
1x
1x
1x
5.11.2
Resistance Error Correction
The EMC2104 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
EMC2104 eliminates the need to characterize and compensate for parasitic resistance in the remote
diode path.
SMSC EMC2104
Revision 1.74 (05-08-08)
DATA3S5HEET
SMSC [ SMSC CORPORATION ]
