Fan Control Device with High Frequency PWM and Temperature Monitors
Datasheet
Table 8.27 Register Setting vs. Temperature Range (continued)
RAN[3:0]
RANGE (°C)
0111
1000
1001
1010
1011
1100
1101
1110
1111
10
13.33
16
20
26.67
32
40
53.33
80
Note: The range numbers will be used to calculate the slope of the PWM ramp up. For the fractional
entries, the PWM will go on full when the temp reaches the next integer value e.g., for 3.33,
PWM will be full on at (min. temp + 4).
8.2.15
Register 62h, 63h: PWM Ramp Rate Control
Table 8.28 Register 62h, 63h: Min/Off, PWM Ramp Rate Control
Register
Address
Read/
Write
Bit 7
(MSb)
Bit 0
(LSb)
Default
Value
Register Name
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
62h
63h
R/W
R/W
PWM 1 Ramp Rate Control
RES
RES
RES
RES
RR1E
RR3E
RR1-2
RR3-2
RR1-1
RR3-1
RR1-0
RR3-0
E0h
00h
PWM 2, PWM 3 Ramp
Rate Control
RR2E
RR2-2
RR2-1
RR2-0
These registers become read only when the Lock bit is set. Any further attempts to write to these
registers shall have no effect.
The duty cycle will be set to the Minimum Fan Duty Cycle when the measured temperature falls below
the Temperature LIMIT register setting for the corresponding PWM.
Description of Ramp Rate Control bits:
If the Remote1 or Remote2 pins are connected to a processor or chipset, instantaneous temperature
spikes may be sampled by the part. The auto fan control logic calculates the PWM duty cycle for all
temperature readings. If Ramp Rate Control is disabled, the PWM output will jump or oscillate
between different PWM duty cycles causing the fan to suddenly change speeds, which creates
unwanted fan noise. If enabled, the PWM Ramp Rate Control logic will prevent the PWM output from
jumping, instead the PWM will ramp up/down towards the new duty cycle at a pre-determined ramp
rate.
Ramp Rate Control
The Ramp Rate Control logic limits the amount of change to the PWM duty cycle over a period of time.
This period of time is programmable via the Ramp Rate Control bits. For a detailed description of the
Ramp Rate Control bits see Table 8.29. For a description of the Ramp Rate Control logic see Ramp
Rate Control Logic on page 35.
Note:
RR1E, RR2E, and RR3E enable PWM Ramp Rate Control for PWM 1, 2, and 3 respectively.
RR1-2, RR1-1, and RR1-0 control ramp rate time for PWM 1
RR2-2, RR2-1, and RR2-0 control ramp rate time for PWM 2
RR3-2, RR3-1, and RR3-0 control ramp rate time for PWM 3
SMSC EMC2300
Revision 0.2 (06-14-06)
DATA6S3HEET
SMSC [ SMSC CORPORATION ]
