emc2105 Standard Microsystems Corp., emc2105 Datasheet - Page 64

• Manufacturer Part Number: emc2105
• Description: Emc2105 Rpm-based High Side Fan Controller With Hardware Thermal Shutdown
• Manufacturer: Standard Microsystems Corp.

ADDR
48h
APPLICATION NOTE: The UPDATE bits and Fan Step Register settings operate independently of the RPM based
APPLICATION NOTE: If the Fan Speed Control Algorithm is used, the default settings in the Fan Configuration 2
Revision 1.74 (05-08-08)
6.24
6.25
ADDR
49h
R/W
R/W
R/W
R/W
When the FSC algorithm is enabled, Ramp Rate control is automatically used. When the FSC is not
active, then Ramp Rate control can be enabled by asserting the EN_RRC bit (see
The Fan Step Registers are software locked.
The Fan Minimum Drive Register stores the minimum drive setting for each RPM based Fan Speed
Control Algorithm. The RPM based Fan Speed Control Algorithm will not drive the fan at a level lower
than the minimum drive unless the target Fan Speed is set at FFh (see
During normal operation, if the fan stops for any reason (including low drive), the RPM based Fan
Speed Control Algorithm will attempt to restart the fan. Setting the Fan Minimum Drive Registers to a
setting that will maintain fan operation is a useful way to avoid potential fan oscillations as the control
circuitry attempts to drive it at a level that cannot support fan operation.
The Fan Minimum Drive Register is software locked.
The Valid TACH Count Register stores the maximum TACH Reading Register value to indicate that
the each fan is spinning properly. The value is referenced at the end of the Spin Up Routine to
determine if the fan has started operating and decide if the device needs to retry. See
translating the count to an RPM. This register is only used when the FSC is active.
If the TACH Reading Register value exceeds the Valid TACH Count Register (indicating that the Fan
RPM is below the threshold set by this count), then a stalled fan is detected. In this condition, the
algorithm will automatically begin its Spin Up Routine.
If a TACH Target setting is set above the Valid TACH Count setting, then that setting will be ignored
and the algorithm will use the current fan drive setting.
Fan Minimum Drive Register
Valid TACH Count Register
Fan Minimum
REGISTER
Valid TACH
REGISTER
Drive
Count
Fan Speed Control Algorithm and will always limit the fan drive setting. That is, if the
programmed fan drive setting (either in determined by the RPM based Fan Speed Control
Algorithm, the Look Up Table, or by manual settings) exceeds the current fan drive setting
by greater than the Fan Step Register setting, the EMC2105 will limit the fan drive change
to the value of the Fan Step Register. It will use the Update Time to determine how often to
update the drive settings.
Register will cause the maximum fan step settings to be ignored.
128
4096
B7
Table 6.38 Minimum Fan Drive Register
B7
Table 6.39 Valid TACH Count Register
2048
B6
B6
64
DATASHEET
RPM-Based High Side Fan Controller with Hardware Thermal Shutdown
1024
B5
B5
32
64
512
B4
B4
16
256
B3
B3
8
128
B2
B2
4
Section
B1
64
B1
2
6.27)
B0
32
Section
B0
Equation [3]
SMSC EMC2105
1
DEFAULT
6.20)
Datasheet
F5h
DEFAULT
(40%)
66h
for