RPM-Based Fan Controller with HW Thermal Shutdown
Datasheet
6.13
Fan Configuration Register
Table 6.17 Fan Control Configuration Register
ADDRESS
REGISTER
B7
EN
B6
B5
B4
B3
B2
B1
B0
DEFAULT
52h
FAN
Configuration
LIMIT2K
-
EDGES[1:0]
UPDATE[2:0]
CBh
The Fan Configuration Register controls the general operation of the RPM based Fan Control
Algorithm used for the High Side Fan Driver.
Bit 7 - EN - enables the RPM based Fan Control Algorithm.
‘0’ - the control circuitry is disabled and the fan driver output is determined by the Fan Driver Setting
Register.
‘1’ (default) - the control circuitry is enabled and the Fan Driver output will be automatically updated
to maintain the programmed fan speed as indicated by the TACH Target Register.
Bit 6 - LIMIT2K - Adjusts the range of reported and programmed TACH count values.
‘0’ - the range of reported and programmable TACH values allows for a minimum speed of
approximately 500 RPM with reduced resolution to report lower speed values.
‘1’ (default) - the range of reported and programmable TACH values allows for a minimum speed
of approximately 2000 RPM with increased resolution to report higher speed values.
Bit 4-3 - EDGES[1:0] - determines the minimum number of edges that must be detected on the TACH
signal to determine a single rotation. A typical fan measured 5 edges (for a 2-pole fan). For more
accurate TACH measurement, the minimum number of poles may be increased, however the TACH
measurement will be artificially higher than expected as denoted in the Effective TACH multiplier.
Additionally, some fans have more than 2-poles and therefore require more edges to be measured as
shown in the Number of Fan Poles
The EDGES[1:0] bits are shown in Table 6.18.
Table 6.18 Minimum Edges for Fan Rotation
EDGES[1:0]
EFFECTIVE TACH
MULTIPLIER (BASED ON 2
POLE FANS)
MINIMUM TACH
EDGES
1
0
NUMBER OF FAN POLES
0
0
1
1
0
1
0
1
3
5
7
9
1 pole
0.6
1
2 poles (default)
3 poles
1.4
1.8
4 poles
Bit 2-0 - UPDATE - determines the base time between fan driver updates. The Update Time, along
with the Fan Step Register, is used to control the ramp rate of the drive response to provide a cleaner
transition of the actual fan operation as the desired fan speed changes. The Update Time is set as
shown in Table 6.19.
SMSC EMC2102
Revision 1.95 (10-19-06)
DATA4S1HEET
SMSC [ SMSC CORPORATION ]
