AM9789 datasheet(12/18 Pages) DIODES

12 / 18 page

Data Sheet

Single Phase Full-wave Motor Driver for Silent Fan Motor

AM9789

Oct. 2012

Rev. 1. 1

BCD Semiconductor Manufacturing Limited

Application Information

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: 1

µF 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 TA=75°C, the maximum power

dissipation is about 0.35W.

The power dissipation can be calculated by the

following equation:

PD=VSAT(H+L)×IOUT+VCC×ICC

For example, VCC=5V, ICC=2mA, IOUT=250mA,

VSAT(H+L)=0.5V, then PD=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

the heat to the ambient air.

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

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.

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.

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

VOUT1

5V/div

VOUT2

5V/div

VFG

5V/div

Time

1s/div

VOUT1

5V/div

VOUT2

5V/div

VFG

5V/div

Time

1s/div

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