FAN8460MPX FAIRCHILD [Fairchild Semiconductor], FAN8460MPX Datasheet - Page 11

• Manufacturer Part Number: FAN8460MPX
• Description: Single Phase Full Wave BLDC Motor Driver with Variable Speed Control
• Manufacturer: FAIRCHILD [Fairchild Semiconductor]

4.2 PWM Speed Control using Internal Oscillator(Scheme 2)
A digital PWM input applied to VPWM pin is converted to analog DC voltage by PWM decoder and external RC filter. The
external filter capacitor, C
V
frequency. The lower frequency of digital PWM input needs the larger value of C
define the V
For example, R
200uA. For some design margin, under the 8% duty of digital PWM input, fan motor stops because the output PWM duty is 0.
If the duty of digital PWM input is lager than 0.92, then output PWM duty is 100%. It means fan motor is operated in full
speed. Figure5.a shows the relationship between digital PWM input and active filter out (V
VCON has
0.72V
4 0
3 6
3 2
2 8
2 4
2 0
1 6
1 2
8
4
0
1.9V
0.8V
1.8V
V
0
VCON
0
VCON
10 20 30 40 50 60 70 80 90 100
smaller value of AC component (ripple), but larger time delay can be occurred in V
(V)
PWM
8%
Digital VPWM Input Duty
Figure 5. The Relationship Digital PWM Input Duty VS V VCON and Output PWM Duty
1 0 K ohm N T C
range as follow;
=6.2K and R
tem p era ture[°C ]
PWM
V
50%
, eliminates high frequency AC component in V
VCON ON
Figure 4. Sensed temperature and speed control voltage
OPT
V
VCON OFF
=120K, V
VC O N volta g e
=
92%
V
VCON
REF
=
V
100%
–
VREF
become between 0.72V and 1.9V, because V
2
1 .8
1 .6
1 .4
1 .2
1
0 .8
0 .6
0 .4
0 .2
0
R
PWM
R
100%
50%
OPT
0%
I
Output PWM(Duty)
VCON
40
36
32
28
24
20
16
12
8
4
0
0
10K NTC
R
PWM
8%
Digital VPWM Input Duty
VCON
------------------------------- -
R
+
PWM
OPT
R
R
OPT
. If a large value of C
Equivalent Resistance
. External resistor R
+
OPT
tem p erature[°C ]
R
VCON
50%
PWM
VCON
) and figure5.b illustrates the
VREF
FAN8460MTC/FAN8460MP
with some fixed input
88%
=2V, I
PWM,
PWM
V C ON voltage
VOCN
is used,
R
100%
PWM
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
=
11