EMC2102 Standard Microsystems Corporation, EMC2102 Datasheet - Page 26

• Manufacturer Part Number: EMC2102
• Description: Rpm-based Fan Controller with HW Thermal Shutdown
• Manufacturer: Standard Microsystems Corporation

Revision 1.95 (10-19-06)
5.5
5.5.1
5.6
5.7
2. Disabling the RPM based Fan Control Algorithm by clearing the EN bit will disable the Watchdog
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.
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.
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
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
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)
The EMC2102 contains an internal thermal shutdown circuit that monitors the internal die temperature.
If the die temperature exceeds the Thermal Shutdown Threshold (see
will occur:
1. The High Side Fan Driver is disabled. It will remain disabled until the internal temperature drops
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.
The EMC2102 provides a hardware Critical/Thermal Shutdown function for systems.
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
High Side Fan Driver
Internal Thermal Shutdown (TSD)
Critical/Thermal Shutdown
Section
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.
Timer. The fan driver will be set to the programmed setting written in the Fan Driver Setting
Register.
below the threshold temperature minus 50°C.
5.3.3.
Section
6.14). If the High Side Fan Driver is configured to operate in Manual Mode, when
DATASHEET
26
RPM-Based Fan Controller with HW Thermal Shutdown
Table
3.2), then the following
SMSC EMC2102
Figure 5.4
Datasheet
is a