W83791G Nuvoton Technology Corporation of America, W83791G Datasheet - Page 27

• Manufacturer Part Number: W83791G
• Description: IC MONITOR H/W 48-LQFP
• Manufacturer: Nuvoton Technology Corporation of America

Specifications of W83791G

• Function: Hardware Monitor
• Topology: ADC
• Sensor Type: External
• Sensing Temperature: External Sensor
• Output Type: I²C™
• Output Alarm: Yes
• Output Fan: Yes
• Voltage - Supply: 4.5 V ~ 5.5 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 48-LQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

6.7
6.7.1
W83791D/G support 5 sets of fan counting. Fan inputs are provided for signals from fans equipped
with tachometer outputs. The level of these signals should be set to TTL level, and the maximum input
voltage should not be over +5.5V. If the input signals from the tachometer outputs are over the VCC,
the external trimming circuit should be added to reduce the voltage to meet the input specification. The
normal circuit and trimming circuits are shown as Figure 8.
Determine the fan counter according to:
In other words, if the fan speed counter has been read from register CR [28] or CR [29] or CR [2A] or
CR [BA] or CR [BB] , then the fan speed can be evaluated by the following equation.
The default divisor is 2 and defined at CR47.bit7~4, CR4B.bit7~6, and Bank0 CR5D.bit5~7 which are
three bits for divisor. This provides very low speed fan counter such as power supply fan. The followed
table is an example for the relation of divisor, RPM, and count.
2 (default)
DIVISOR
128
16
32
64
FAN Speed Count and FAN Speed Control
1
4
8
Fan speed count
NOMINAL RPM
8800
4400
2200
1100
550
275
137
68
REVOLUTION
109.08 ms
218.16 ms
436.32 ms
872.64 ms
TIME PER
RPM
Count
13.64 ms
27.27 ms
54.54 ms
6.82 ms
=
=
Count
RPM
Table 2
- 21 -
. 1
. 1
35
35
×
×
×
COUNTS
×
Divisor
Divisor
10
10
153
153
153
153
153
153
153
153
6
6
Publication Release Date: April 14, 2006
70% RPM
6160
3080
1540
770
385
192
96
48
W83791D/G
1246.72 ms
155.84 ms
311.68 ms
623.36 ms
TIME FOR
19.48 ms
38.96 ms
77.92 ms
9.74 ms
Revision 1.1
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