W83627THF_06 Datasheet, PDF (35/142 Pages) Winbond – Winbond LPC I/O

W83627THF/W83627THG
5.4.2 Fan speed control
The W83627THF has a 4 bit DAC which produces 0 to 5 volts DC output that provides maximum 3
sets for fan speed control. The analog output can be programmed in the Bank0 Index 01h, Index 03h
and Index 11h. The default value is 0xFY,Y is reserved nibble, that is default output value is 5 V. The
expression of output voltage can be represented as follow ,
OUTPUT Voltage = AVCC × ^{Programmed 4 - bit Register Value}
16
The application circuit is shown as follow,
R1
FANOUT
0
IO+12V
C1
0.1U
4
3₊
2_-
LM358
1
11
IO-12V
R4
20K
R3
28K
IO+12V
Q1
NPN
3
2
1
FAN
Tachometer output
Figure 5-8
Must be take care when choosing the OP-AMP and the transistor. The OP-AMP is used for amplify the
5V range of the DC output up to 12V . The transistor should has a suitable β value to avoid its base
current pulling down the OP-AMP ’s output and gain the common current to operate the fan at fully
speed.
5.5 SmartFan^TM Control
SmartFan^TM Control provides two mechanisms. One is Thermal Cruise mode and the other is Fan
Speed Cruise mode. No matter which mode you use, the FAN will full speed run at beginning.
- 28 -