NCT6627UD Nuvoton Technology Corporation of America, NCT6627UD Datasheet - Page 51

• Manufacturer Part Number: NCT6627UD
• Manufacturer: Nuvoton Technology Corporation of America

Specifications of NCT6627UD

• Lead Free Status / Rohs Status: Supplier Unconfirmed

7.6
This section is divided into two parts, one to measure the speed and the other to control the speed.
The W83627UHG can measure fan speed for fans equipped with tachometer outputs. The tachometer signals
should be set to TTL-level, and the maximum input voltage cannot exceed +5 V. If the tachometer signal exceeds
+5 V, an external trimming circuit should be added to reduce the voltage accordingly.
The fan speed counter is read from Bank0 Index 28h, and 29h. The fan speed can then be evaluated by the
following equation:
The default divisor is 2 and is specified at Bank0 Index 47h, bits 7 ~ 4; and Index 5Dh, bits 6 ~ 5. There are three
bits for each divisor, and the corresponding divisor is listed in the table below.
The following table provides some examples of the relationship between divisor, RPM, and count.
7.6.1 Fan Speed Measurement
Fan Speed Measurement and Control
BIT 2
2 (default)
DIVISOR
0
0
0
0
16
1
4
8
BIT 1
0
0
1
1
NOMINAL
8800
4400
2200
1100
RPM
BIT 0
550
0
1
0
1
Table 7-5 Divisor, RPM, and Count Relation
FAN DIVISOR
REVOLUTION
Table 7-4 Fan Divisor Definition
109.08 ms
TIME PER
13.64 ms
27.27 ms
54.54 ms
6.82 ms
RPM
1
2
4
8
=
Count
. 1
35
COUNTS
BIT 2
×
×
-42-
Divisor
1
1
1
1
153
153
153
153
153
10
W83627UHG/NCT6627UD
6
BIT 1
0
0
1
1
Publication Release Date: October 26, 2010
70% RPM
6160
3080
1540
770
385
BIT 0
0
1
0
1
FAN DIVISOR
TIME FOR 70%
155.84 ms
19.48 ms
38.96 ms
77.92 ms
9.84 ms
128
16
32
64
Revision 1.7