Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown
Datasheet
The PWM 1 and 2 Divide Registers determine the final frequency of the PWM 1and PWM 2 drivers.
Each driver base frequency is divided by the value of the respective PWM Divide Register to determine
the final frequency. The duty cycle settings are not affected by these settings, only the final frequency
of the PWM driver. A value of 00h will be decoded as 01h.
6.22
Fan Configuration 1 Registers
Table 6.28 Fan Configuration 1 Registers
ADDR
R/W
REGISTER
B7
B6
B5
B4
B3
B2
B1
B0
DEFAULT
Fan 1
Configuration
1
EN_
ALGO
42h
R/W
RANGE[1:0]
RANGE[1:0]
EDGES[1:0]
EDGES[1:0]
UPDATE[2:0]
2Bh
Fan 2
Configuration
1
EN_
ALGO
82h
R/W
UPDATE[2:0]
2Bh
The Fan Configuration 1 Register controls the general operation of the RPM based Fan Speed Control
Algorithm used for the Fan 1 driver.
Bit 7 - EN_ALGO - enables the RPM based Fan Speed Control Algorithm. This bit is set and cleared
automatically when the LUT_LOCK bit is set based on the setting of the TACH / DRIVE bit (see
Section 6.32). When the LUT_LOCK bit is cleared, then setting this bit will enable the FSC without
using the Look Up Table.
‘0’ - (default) the control circuitry is disabled and the fan driver output is determined by the Fan
Driver Setting Register.
‘1’ - 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.
Bits 6- 5 - RANGE[1:0] - Adjusts the range of reported and programmed tachometer reading values.
The RANGE bits determine the weighting of all TACH values (including the Valid TACH Count, TACH
Target, and TACH reading) as shown in Table 6.29.
Table 6.29 Range Decode
RANGE[1:0]
REPORTED MINIMUM
RPM
TACH COUNT
MULTIPLIER
1
0
0
0
1
1
0
1
0
1
500
1000 (default)
2000
1
2
4
8
4000
Bits 4-3 - EDGES[1:0] - determines the minimum number of edges that must be detected on the
TACHx signal to determine a single rotation. A typical fan measured 5 edges (for a 2-pole fan). For
more accurate tachometer measurement, the minimum number of edges measured may be increased.
Increasing the number of edges measured with respect to the number of poles of the fan will cause
the TACH Reading registers to indicate a fan speed that is higher or lower than the actual speed. In
order for the FSC Algorithm to operate correctly, the TACH Target must be updated by the user to
accommodate this shift. The Effective Tach Multiplier shown in Table 6.30 is used as a direct multiplier
SMSC EMC2104
Revision 1.74 (05-08-08)
DATA6S5HEET
SMSC [ SMSC CORPORATION ]
