EMC2103 Standard Microsystems Corporation, EMC2103 Datasheet - Page 55

• Manufacturer Part Number: EMC2103
• Description: Rpm-based Fan Controller with HW Thermal Shutdown
• Manufacturer: Standard Microsystems Corporation

RPM-Based Fan Controller with HW Thermal Shutdown
Datasheet
SMSC EMC2103
6.22
ADDR
42h
R/W
R/W
The PWM Divide Register determines the final frequency of the PWM driver. The driver base frequency
is divided by the value of the 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.
The final PWM frequency is derived as the base frequency divided by the value of this register as
shown in
The Fan Configuration 1 Register controls the general operation of the RPM based Fan Speed Control
Algorithm used on the PWM pin.
Bit 7 - EN_ALGO - enables the RPM based Fan Speed Control Algorithm. Based on the setting of the
RPM / PWM bit, this bit is automatically set or cleared when the LUT_LOCK bit is set (see
Section
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
Bits 4-3 - EDGES[1:0] - determines the minimum number of edges that must be detected on the TACH
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
Fan Configuration 1 Register
1
0
0
1
1
‘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.
Configuration 1
REGISTER
6.32).
Equation
RANGE[1:0]
Fan
[2].
f
Table 6.29 Fan Configuration 1 Register
PWM
ALGO
EN_
B7
=
Table 6.30 Range Decode
PWM base freqeuncy
-------------------------------------------------------------- -
PWM Divide Setting
0
0
1
0
1
RANGE[1:0]
DATASHEET
B6
Table
55
B5
6.30.
EDGES[1:0]
B4
REPORTED MINIMUM
1000 (default)
B3
RPM
2000
4000
500
Table 6.31
B2
UPDATE[2:0]
is used as a direct multiplier
B1
[2]
Revision 0.85 (01-29-08)
B0
TACH COUNT
MULTIPLIER
1
2
4
8
DEFAULT
2Bh