Fan Control Device with Hardware Monitoring and Acoustic Noise Reduction Features
Datasheet
Table 6.3 Minimum RPM Detectable Using 3 Edges – No PWM Stretching (continued)
PWM
PULSE WIDTH AT DUTY CYCLE
(PWM ”ON” TIME)
MINIMUM RPM AT DUTY CYCLE (Note 6.4)
(30/TTachPulse
FREQUENCY
)
100%
25%
50%
(MSEC)
(HZ)
(MSEC)
(MSEC)
(Note 6.3)
25%
50%
100%
29.3
21.9
14.6
11
8.53
11.42
17.12
22.73
17.06
22.83
34.25
45.45
34
3554
2648
1761
1325
1768
1319
878
885
661
440
332
45.48
68.23
90.55
661
Note 6.3 100% duty cycle is 255/256.
Note 6.4 RPM=60/TRevolution, TTachPulse= TRevolution/2. Using 3 edges for detection, TTachPulse
=
(PWM ”ON” Time – Guard Time). Minimum RPM values shown use minimum guard time
(88.88usec).
Table 6.4 Minimum RPM Detectable Using 2 Edges – No PWM Stretching
PWM
PULSE WIDTH AT DUTY CYCLE
(PWM ”ON” TIME)
MINIMUM RPM AT DUTY CYCLE (Note 6.6)
(30/TTachPulse
FREQUENCY
)
100%
25%
50%
(MSEC)
(HZ)
(MSEC)
(MSEC)
(Note 6.5)
25%
50%
100%
87.7
58.6
44
2.85
4.27
5.68
7.1
5.7
11.36
17
5433
3588
2683
2139
1777
1324
881
2673
1777
1331
1063
884
1331
887
665
532
442
330
220
166
8.53
11.36
14.2
22.64
28.3
34
35.2
29.3
21.9
14.6
11
8.53
11.42
17.12
22.73
17.06
22.83
34.25
45.45
45.48
68.23
90.55
660
439
663
331
Note 6.5 100% duty cycle is 255/256
Note 6.6 RPM=60/TRevolution, TTachPulse= TRevolution/2. Using 2 edges for detection, TTachPulse
=
2*(PWM ”ON” Time-Guard Time). Minimum RPM values shown use minimum guard time
(88.88usec).
Revision 0.4 (04-05-05)
SMSC EMC6D102
DATA4S2HEET
SMSC [ SMSC CORPORATION ]
