RPM-Based Fan Controller with HW Thermal Shutdown
Datasheet
condition (0%, 60% or 75% drive). If a value of FFh is written, then the fan driver will be disabled
until a valid setting is written.
2. Disabling the RPM based Fan Control Algorithm by clearing the EN bit will disable the Watchdog
Timer. The fan driver will be set to the programmed setting written in the Fan Driver Setting
Register.
Writing any other configuration registers will not disable the Watchdog Timer. If the VDD_5V supply
drops below the reset threshold, then the Watchdog Timer will be stopped but not reset.
5.5
High Side Fan Driver
The EMC2102’s fan controller integrates a 5V, 600mA, linear high side fan driver to directly drive a 5V
fan. By fully integrating the linear fan driver, the typical requirement for the discrete pass device and
other external linearization circuitry is completely eliminated. The linear fan driver is driven by an 8-bit
DAC providing better than 20mV resolution between steps.
5.5.1
Overcurrent Limit
The High Side Fan Driver contains circuitry to allow for significant overcurrent levels to accommodate
transient conditions on the FAN pins. The overcurrent limit is dependent upon the output voltage with
the limit dropping as the voltage nears 0V.
If the fan driver current detects a short-circuit condition for longer than 2 seconds, then the I_SHORT
status bit is set and an interrupt generated. Additionally, the fan driver will be disabled (by setting the
drive level to 00h).
In both Manual Mode and when using the RPM based Fan Control Algorithm, the device will attempt
to restart the fan after a time equal to the spin-up time programmed in the Fan Spin Up Configuration
Register (see Section 6.14). If the High Side Fan Driver is configured to operate in Manual Mode, when
it attempts to restart the fan after a overcurrent condition, it will set the Fan Drive Setting Register to
the most recently written value (prior to the overcurrent condition). If the High Side Fan Driver is
configured to use the RPM based Fan Control Algorithm, it will invoke the Spin Up Routine described
in Section 5.3.3.
If the overcurrent condition persists, the fan driver will continue to attempt to restart the fan until the
overcurrent condition is removed or the High Side Fan Driver is disabled by setting the TACH Target
to FFh (when using the RPM based Fan Control Algorithm) or by writing the Fan Setting Register to
a value of 00h (when operating in Manual Mode)
5.6
Internal Thermal Shutdown (TSD)
The EMC2102 contains an internal thermal shutdown circuit that monitors the internal die temperature.
If the die temperature exceeds the Thermal Shutdown Threshold (see Table 3.2), then the following
will occur:
1. The High Side Fan Driver is disabled. It will remain disabled until the internal temperature drops
below the threshold temperature minus 50°C.
2. The TSD Status bit will be set and the ALERT pin asserted. This signal cannot be masked.
3. The SYS_SHDN pin is asserted.
5.7
Critical/Thermal Shutdown
The EMC2102 provides a hardware Critical/Thermal Shutdown function for systems. Figure 5.4 is a
block diagram of this Critical/Thermal Shutdown function. The Critical/Thermal Shutdown function in
the EMC2102 consists of both analog and digital functions. It accepts digital inputs from the CPU
Revision 1.95 (10-19-06)
SMSC EMC2102
DATA2S6HEET
SMSC [ SMSC CORPORATION ]
