RPM-Based Fan Controller with Multiple Temperature Zones & Hardware Thermal Shutdown
Datasheet
Table 7.44 Spin Time
SPINUP_TIME[1:0]
1
0
TOTAL SPIN UP TIME
0
0
1
1
0
1
0
1
250 ms
500 ms (default)
1 sec
2 sec
The Fan Spin Up Configuration Register is software locked.
7.28
Fan Step Register
Table 7.45 Fan Step Register
ADDR
R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT
47h
R/W
Fan Max Step
-
-
32
16
8
4
2
1
10h
The Fan Step Register, along with the Update Time, control the ramp rate of the fan driver response.
The value of the registers represents the maximum step size each fan driver will take between update
times (see Section 7.24, "Fan Configuration 1 Register").
All modes of operation have the options to use the Fan Step Register (and update times) for ramp rate
control based on the Fan Configuration 2 Register settings. The Fan Speed Control Algorithm will
always use the Fan Step Register settings (but see application note below).
The Fan Step Register is software locked.
7.29
Fan Minimum Drive Register
Table 7.46 Minimum Fan Drive Register
ADDR
R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT
Fan Minimum
Drive
66h
(40%)
48h
R/W
128
64
32
16
8
4
2
1
The Fan Minimum Drive Register stores the minimum drive setting for the RPM-based Fan Speed
Control Algorithm. This register is not used if the FSC is not active. The RPM-based Fan Speed Control
Algorithm will not drive the fan at a level lower than the minimum drive unless the target TACH Target
is set at FFh. (See Section 7.32, "TACH Target Register".)
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.
Revision 1.2 (10-08-09)
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