W83L786NR Datasheet, PDF (20/50 Pages) Winbond – H/W Monitoring IC

W83L786NR/ W83L786NG
+12V
+5V
R1
R2
G
PWM Clock Input
D
NMOS
S
PNP Transistor
+
C
-
FAN
R1
R2
G
PWM Clock Input
D
NMOS
S
PNP Transis
+
C
-
FAN
Figure 9
7.6.2.3. DC Mode
W83L786NR/NG has a 4-bit DAC, which produces 0 to 3.3 voltages DC output that provides
maximum 2 sets for fan speed control. The analog output can be programmed in the CR 81, and CR
87 (manual mode). The expression of output voltage can be represented as follows,
OUTPUT Voltage = VCC × ^{Programmed 4 - bit Register Value}
16
The application circuit is shown as follows,
IO+12V
R1
FANOUT
0
IO+12V
4 ^LM358
3
+
1
2
C1
-
0.1U
11
R3
IO-12V
R4
47K
33K
Q1
NPN
Tachometer ou
3
2
1
FAN
Figure 10
Be careful 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
- 15 -
Publication Release Date: March 31, 2006
Revision 0.9