RPM-Based Fan Controller with HW Thermal Shutdown
Datasheet
Set TACH Target
Count
Measure Fan Speed
Spin Up
Required
?
Yes
Perform Spin Up
Routine
No
TACH
Reading =
TACH
Yes
Maintain Fan Drive
Target?
No
TACH
Reading <
TACH
Ramp Rate Control
No
Yes
Target?
Reduce Fan Drive
Increase Fan Drive
Figure 5.4 RPM based Fan Speed Control Algorithm
5.5.1
Programming the RPM Based Fan Speed Control Algorithm
The RPM based Fan Speed Control Algorithm powers-up disabled. The following registers control the
algorithm. The EMC2103 fan control registers are pre-loaded with defaults that will work for a wide
variety of fans so only the TACH Target Register is required to set a fan speed. The other fan control
registers can be used to fine-tune the algorithm behavior based on application requirements.
Note that steps 1 - 7 are optional and need only be performed if the default settings do not provide
the desired fan response.
1. Set the Valid TACH Count Register to maximum number of tach counts to indicate the fan is
spinning.
2. Set the Spin Up Configuration Register to the Spin Up Level and Spin Time desired.
Revision 0.85 (01-29-08)
SMSC EMC2103
DATA2S8HEET
SMSC [ SMSC CORPORATION ]
