AM9789 Datasheet, PDF (12/18 Pages) Diodes Incorporated – Single Phase Full-wave Motor Driver for Silent Fan Motor

Data Sheet
Single Phase Full-wave Motor Driver for Silent Fan Motor AM9789
Application Information
the heat to the ambient air.
1. Reverse Connection of Power Supply
Connector
Reverse connection of power supply connector may
break IC. Some methods such as inserting a diode
between power supply and VCC terminal can be
taken to avoid the reverse connection destruction.
2. Power Supply Line
Back electromotive force (EMF) causes regenerated
current to the power supply line, so insert a capacitor
(recommended value: 1µF or larger) as close as
possible to the space between the power supply pin
(VCC pin) and ground pin (GND pin) for routing
regenerated current.
3. GND Potential and External Components
Ensure that the potential of GND terminal is the
minimum potential in any operating condition.
External components connected to the ground must
be connected with lines that are as short as possible
and external components connected between IC pins
must be placed as close to the pins as possible.
4. Mounting Failures
In the process of attaching IC to the printed board,
more attention must be paid to the direction and
location of the IC, since mounting failures may also
break IC. In addition, destruction is also possible
when the circuit is shorted by foreign substance
between outputs or between output and power supply
or between output and GND.
5. Thermal Consideration
Refer to Figure 7 “Power Dissipation vs. Ambient
Temperature (MSOP-10/MSOP-8)”, the IC is safe to
operate below the curve and the thermal protection
will be caused if the operating area is above the line.
For example, when T_A=75°C, the maximum power
dissipation is about 0.35W.
The power dissipation can be calculated by the
following equation:
P_D=V_SAT(H+L)×I_OUT+V_CC×I_CC
For example, V_CC=5V, I_CC=2mA, I_OUT=250mA,
V_SAT(H+L)=0.5V, then P_D=0.135W.
The GND pin provides an electrical connection to the
ground and channeling heat away. The printed circuit
board (PCB) forms a heat sink and dissipates most of
6. Thermal Shutdown Circuit
Considering the power dissipation under actual
operating condition, the thermal design must be
applied with sufficient margin.
AM9789 features thermal shutdown (TSD) circuit
(operation temperature is 165°C typical and
hysteresis width is 30°C typical). When the chip
temperature reaches the TSD circuit temperature, the
output terminal becomes an open state. TSD circuit is
designed simply for the purpose of intercepting IC
from overheating. Make sure that the IC should not
be used again after this circuit operating. Figure 10
shows a fan rotates normally first and then enters into
OTP mode since the chip temperature reaches 165°C.
Finally the chip temperature decreases below 135°C,
then OTP mode is canceled and the fan rotates
normally again.
V_OUT1
5V/div
V_OUT2
5V/div
V_FG
5V/div
Time 1s/div
Figure 10. OTP Function
7. Over Current Protection
The driver current is detected by AM9789 internal
circuit. When the output current is over 1A or larger,
AM9789 will close the output driver. After that if the
output current decreases, AM9789 will enable the fan
to rotate again. Figure 11 shows the detailed process.
V_OUT1
5V/div
V_OUT2
5V/div
V_FG
5V/div
Time 1s/div
Figure 11. OCP Function
8. PWM Mode
The output transistor is on when a high-level voltage
is input to the PWM pin, and is off when a low-level
voltage is input. PWM controls the speed of the
motor by inputting the pulse in accordance with the
duty cycle to the PWM pin. When the motor is
Oct. 2012 Rev. 1. 1
BCD Semiconductor Manufacturing Limited
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