FAN8460MPX FAIRCHILD [Fairchild Semiconductor], FAN8460MPX Datasheet - Page 9

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

Application Information
1 Direct output PWM for FAN Motor Speed Control
Direct output PWM method is used to control driving power to a fan motor and thus fan motor speed. A motor current, and
thus fan motor speed is proportional to duty-cycle of output PWM signal in FAN8460MTC/FAN8460MP. The internal PWM
signal is driven by comparing a triangle wave (PWM oscillator output, V
illustrates the relationships among oscillator output (V
duty.
.
As shown in figure2, the output PWM duty-cycle can be decreased as V
trol voltage (V
V
2 H-bridge motor driver (OUTA, OUTB)
Using an H-bridge to drive a single-phase BLDC motor provides several advantages for DC fans over a two phase motor com-
monly driven by two commutated low-side switches. A single phase motor has only two connections; hence, the H-bridge
topology requires only two output terminals and two traces are needed on the fan PCB. Generally, this H-bridge method with
single phase motor increases fan motor torque density over a typical unipolar drive method. In addition, the H-bridge topology
eliminates the number of external component for snubbing and allows recirculation of winding current to maintain energy in a
VCON
is 1.3V, the output PWM duty becomes 50%.
VCON
Figure 2. The Relationship Between Speed Control Voltage and Output PWM Duty
) is 0.8 ~1.8V(typical) which represents a duty-cycle range of 0% to 100% on PWM signal.When
Output PWM(Duty)
1.8V
0.8V
V
V
100%
VCON
i
50%
M
CT
0
High Speed
Figure 1. Basic Speed Control Concept
PWM
Speed Control Voltage(V
i
M(avg)
0.8V
V
VCON
CT
), speed control voltage (V
Mid Speed
1.3V
i
V
M
t
CT
OFF
t
PWM
t
ON
VCON
CT
1.8V
Low Speed
) and a control DC voltage V
VCON
i
is increased. The effective range of speed con-
freewheeling
)
VCON
2V
), motor current, and output PWM
FAN8460MTC/FAN8460MP
VCON
). Figure.1
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