RPM-Based Fan Controller with HW Thermal Shutdown
Datasheet
where:
1
-
(
n
–
1
)
-
RPM
= -------------------
×
---------------------------------
×
1,966,080
(
poles
)
1
-
COUNT
×
----
m
poles = number of poles of the fan
(typically 2)
n = number of edges measured
(typically 5)
m = the multiplier defined by the
RANGE bits
[4]
COUNT = TACH Reading Register
value (in decimal)
[3]
3,932,160
×
m
-
RPM
= -------------------------------------
COUNT
6.32
Look Up Table Configuration Register
Table 6.48 Look Up Table Configuration Register
ADDR
50h
R/W
R/W
REGISTER
LUT
Configuration
B7
USE_D
TS_F1
B6
USE_D
TS_F2
B5
LUT_L
OCK
B4
RPM /
PWM
B3
-
B2
TEMP3
_CFG
B1
-
B0
TEMP4
_CFG
DEFAULT
00h
The Look Up Table Configuration Register controls the setup information for the temperature to fan
drive look up table.
Bit 7 - USE_DTS_F1 - This bit determines whether the Pushed Temperature 1 Register is using DTS
data.
‘0’ (default) - The Pushed Temperature 1 Register is not using DTS data. The contents of the
Pushed Temperature 1 registers is standard temperature data.
‘1’ - The Pushed Temperature 1 Register is loaded with DTS data. The contents of this register is
automatically subtracted from a fixed value of 100°C before being compared to the Look Up Table
threshold levels.
Bit 6 - USE_DTS_F2 - This bit determines whether the Pushed Temperature 2 Register is using DTS
data.
‘0’ (default) - The Pushed Temperature 2 Register is not using DTS data. The contents of this
register is standard 2’s complement temperature data.
‘1’ - The Pushed Temperature 2 Register is loaded with DTS data. The contents of this register is
automatically subtracted from a fixed value of 100°C before being compared to the Look Up Table
threshold levels.
Bit 5 - LUT_LOCK - This bit locks updating the Look Up Table entries and determines whether the look
up table is being used.
‘0’ (default) - The Look Up Table entries can be updated normally. The Look Up Table will not be
used while the Look Up Table entries are unlocked. During this condition, the PWM output will not
change states regardless of temperature or tachometer variation.
‘1’ - The Look Up Table entries are locked and cannot be updated. The Look Up Table is fully active
and will be used based on the loaded values. The PWM output will be updated depending on the
temperature and / or TACH variations.
APPLICATION NOTE:
When the LUT_LOCK bit is set at a logic ‘0’, the PWM drive setting will be set at whatever
value was last used by the RPM based Fan Speed Control Algorithm or the Look Up Table.
SMSC EMC2103
63
Revision 0.85 (01-29-08)
DATASHEET
SMSC [ SMSC CORPORATION ]
