SMBus Fan Control with 1°C Accurate Temperature Monitoring
Datasheet
Table 6.19 TACH Modes
TACH_M[1]
TACH_M[0]
TACH MODE
False readings when under minimum
detectable RPM (TACH Limit).
0
0
(Default condition - See Note 6.2)
0
1
1
1
0
1
FFFFh reading when under minimum
detectable RPM.
Note 6.2 When the PWM base clock is set at 360kHz mode 00b is used regardless of the setting
of the TACH_M[1:0] bits.
6.17
Fan Spin Up Configuration Register
Table 6.20 Fan Spin Up Configuration Register
ADDR.
R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT
Fan Spin Up
Config
FAST_
TACH
4Bh
R/W
-
-
SPIN_DRIVE[1:0]
SPIN_TIME[2:0]
3Fh
The Fan Spin Up Configuration register controls the spin-up behavior of the device. The Fan driver
enters its spin-up routine any time it transitions from a minimum fan setting (00h) to a higher fan setting
(but does not invoke the spin-up routine upon power up). Once the spin-up time has been met, the
fan driver is reduced to the programmed setting.
Bit 5 - FAST_TACH - Determines whether the Spin-Up routine aborts when the measured TACH is less
than the TACH Limit.
‘0’ - The Spin-Up routine uses the duty cycle and spin-up time independently of the TACH reading.
‘1’ (default) - The Spin-Up routine will abort when the TACH measurement is less than the TACH
Limit or the programmed Spin-Up time is met, whichever is less. In this case, the SPIN_DRIVE[1:0]
bits are ignored and the drive will always be at 100%.
APPLICATION NOTE: This bit will be ignored if the ALT_TCH bit in the Configuration Register (see Section 6.5) is
set to ‘0’.
APPLICATION NOTE: If the SPIN_TIME[2:0] bits are set at 000b, then the Spin-Up Routine is bypassed regardless
of the status of this bit.
Bit 4 - 3 SPIN_DRIVE[1:0] - Determines the setting of the drive circuit during the Spin-Up routine
according to Table 6.21.
Table 6.21 Spin-Up Drive
SPIN_DRIVE[1:0]
1
0
SPIN UP DRIVE
0
0
0 - Spin-Up Cycle bypassed
SMSC EMC2101
Revision 2.53 (03-13-07)
DATA4S1HEET
SMSC [ SMSC CORPORATION ]
