AN1001

Application Note 1001
How to Control Motor Fan Speed of AM4961
Prepared by Dong Xiang Lian
System Engineering Dept.
1. Operating Diagram
VPWM Voltage
(VCC 28%)
Lowest speed setting voltage
Open Thermistor
fCP=25kHz (CCP=100pF)
VCPH (VCC 30%)
VMIN Voltage
COSC Output
VCPL(VCC 16%)
Low Speed
0V
Full Speed
Low Temperature
PWM Variable
High Temperature
VCC
0V
FG Output
Figure 1. Operating Diagram of AM4961
2. Typical Application
L
D2
D3
OUT2
OUT1
VCC
GND
VMIN
AM4961
D1
VPWM
R1
18k
R1
30k
PWM
R6
91k
R16
39k
COSC
FG
C2
1 µF
R4
18k
R13
6.2k
R2
18k
Q1
D4
RD
C8
0.33 µF
R7
56k
VREF
HINHB
C11
100pF
R10
18k
C4 0.47µ F
CT
HALL
HIN+
PGND
Note: D2 and D3 are recommended to be used when the average current in coil L1 is higher
than 300mA.
Figure 2. Typical Application 1
BCD Semiconductor Manufacturing Limited
Mar. 2011 Rev. 1. 1
1
Application Note 1001
When VPWM voltage is higher than VMIN pin voltage, fan
speed is settable by VMIN pin voltage. The minimum duty
cycle is settable by comparing COSC oscillating voltage and
VMIN pin voltage. When VPWM voltage is lower than
VMIN pin voltage, PWM control system works by
comparing VMIN voltage and COSC oscillating voltage. If
VMIN voltage is higher than COSC oscillating voltage, the
ON duty cycle of the upper side transistor will be minimized
and fan speed becomes lower. Vice versa.
100
Speed / Full Speed (%)
80
Please refer to Figure 3.
60
40
20
0
100
100
80
60
40
20
0
Output Duty Cycle (%)
Figure 4. Speed/Full Speed vs. Output Duty Cycle
Output Duty Cycle (%)
80
Therefore, if you wish to adjust speed, it is necessary to
change VPWM voltage.
60
Please refer to Figure 5.
40
100
20
80
0
1
1.8 2
3 3.2
4
Output Duty Cycle (%)
0
VPWM Voltage (V)
Figure 3. Output Duty Cycle vs. VPWM Voltage
When VPWM voltage is lower than about 1.8V (the low
side of COSC oscillating voltage), output duty cycle is
100%. When VPWM voltage is higher than about 3.2V
(VMIN pin voltage), output duty cycle is about 18% which
is the minimum duty cycle on the condition that VCC=12V.
Within the range of 1.8V to 3.2V, output duty cycle will be
reduced gradually, and fan speed becomes lower and lower.
60
40
20
0
0
1
2
3
4
VPWM Voltage (V)
Please refer to Figure 4.
Figure 5. Speed/Full Speed vs. VPWM Voltage
BCD Semiconductor Manufacturing Limited
Mar. 2011 Rev. 1. 1
2
Application Note 1001
2. Typical Application (Continued)
D1
VCC
L1
R1
27k
C1
0.1µ F
D2
C2 R2
1µF 10k
1
OUT2
OUT1
VCC
GND
2
3
R4 39k
PWM
VMIN
4 VPWM
R6 330k
R3 7.5k
CT
VREF
14
13
12
11
5
COSC
6
HB 9 HALL
FG
RD PGND HIN+ 8
7
R7
100k
D3
AM4961
HIN- 10
C5
0.47µF
C4
100pF
C3
0.33µF
R8 68k
R5 100k
Note: D2 and D3 are recommended to be used when the average current in coil L1 is higher than 300mA.
Figure 6. Typical Application 2
100
The VPWM voltage is changed with the input duty cycle of
PWM (refer to Figure 7), therefore, the fan speed is
changeable with input (refer to Figure 8).
Speed / Full Speed (%)
80
3.2
VPWM Voltage (V)
2.8
2.4
60
40
20
2.0
0
100
80
60
40
20
0
1.6
PWM Duty Cycle (%)
Figure 8. Speed / Full Speed vs. PWM Duty Cycle
1.2
100
80
60
40
20
0
PWM Duty Cycle (%)
Figure 7. VPWM Voltage vs. PWM Duty Cycle
BCD Semiconductor Manufacturing Limited
Mar. 2011 Rev. 1. 1
3
Similar pages