F81867
DAC Fan Control
The range of DC output is 0~VCC, controlled by 8-bit register. 1 LSB is about 0.013V
(VCC=3.3V). The output DC voltage is amplified by external OP circuit, thus to reach maximum FAN
OPERATION VOLTAGE, 12V. The output voltage will be given as followed:
Programmed 8bit Register Value
Output_voltage (V) = VCC ×
256
And the suggested application circuit for linear fan control would be:
+12V
R
4.7K
PMOS
U1A
Q1
3
2
D1
1N4148
+
-
1
DC OUTPUT VOLTAGE
R
LM358
R
4.7K
JP1
R
27K
3
2
1
FANIN MONITOR
10K
C
47u
C
0.1u
R
10K
CON3
R
3.6K
Fig 7-5
PWM duty Fan Control
The duty cycle of PWM can be programmed by a 8-bit register. The default duty cycle is set to
100%, that is, the default 8-bit registers is set to FFh. The expression of duty can be represented as
follows.
Programmed 8bit Register Value
Duty_cycle(%) =
×100%
255
+12V
R2
R1
PNP Transistor
G
D
NMOS
S
+
-
C
FAN
Fig 7-6
37
Dec, 2011
V0.12P
FINTEK [ FEATURE INTEGRATION TECHNOLOGY INC. ]
