Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown
Datasheet
Appendix C RPM to Tachometer Count Look Up Table
C.1
1k RPM Range
The Look Up Table is an example based on the assumption that the fan being measured has 2-poles
and is measuring 5 edges using the 1k RPM range settings. The data presented in the reading is only
the high byte data and the decimal count value only represents high byte data.
Table C.1 Tachometer Count to RPM Look Up Table (Range = 1000 RPM)
REGISTER
TACH COUNT
(DECIMAL)
REGISTER
FAN SPEED
TACH COUNT
(DECIMAL)
READING
(HEX)
FAN SPEED
(RPM)
READING (HEX)
(RPM)
0
00
01
02
03
04
05
06
07
08
09
0A
0B
0C
0D
0E
0F
10
11
Disabled
245760
122880
81920
61440
49152
40960
35109
30720
27307
24576
22342
20480
18905
17554
16384
15360
14456
13653
12935
12288
11703
11171
10685
10240
4096
4128
4160
4192
4224
4256
4288
4320
4352
4384
4416
4448
4480
4512
4544
4576
4608
4640
4672
4704
4736
4768
4800
4832
4864
80
81
82
83
84
85
86
87
88
89
8A
8B
8C
8D
8E
8F
90
91
92
93
94
95
96
97
98
1920
1905
1890
1876
1862
1848
1834
1820
1807
1794
1781
1768
1755
1743
1731
1719
1707
1695
1683
1672
1661
1649
1638
1628
1617
32
64
96
128
160
192
224
256
288
320
352
384
416
448
480
512
544
576
608
640
672
704
736
768
12
13
14
15
16
17
18
SMSC EMC2104
Revision 1.74 (05-08-08)
DATA9S7HEET
SMSC [ SMSC CORPORATION ]
