Data Sheet

Three Phase Direct PWM Sensorless Motor Driver

AM9800

Sep. 2012 Rev. 1. 0

BCD Semiconductor Manufacturing Limited

8

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 (SGND 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 Shutdown Circuit

Considering the power dissipation under actual

operating condition, the thermal design must be

applied with sufficient margin.

AM9800 features thermal shutdown (TSD) circuit

(protection temperature is 175

°C typical and

hysteresis width is 25

°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 9

shows a fan rotates normally first and then enter into

OTP mode since the chip temperature reaches 175

°C.

Finally the chip temperature decreases below 150

°C,

then OTP mode is canceled and the fan rotates

normally again.

Figure 9. OTP Function

6. F/R Function

A high level input causes the current to flow into the

motor in the order of U, V, and W and a low level

input in the order of U, W, and V. When the motor is

used with the F/R pin open, the built-in resistor

enables the F/R pin to GND. Changing the order of

current application turns the motor to rotate in the

opposite direction. Switching H/L of F/R (pin 9)

terminal should not be done during the motor rotation.

It should be done once the motor stops. F/R terminal

should be connected to VCC or GND for reducing

PWM noise. Figure 10 shows a rotating fan’s

waveform at forward mode (F/R pin is connected to

SGND pin).

Figure 10. Rotation Mode Waveform (Forward Mode)

7. PWM Mode

The output transistor is on when a high-level voltage

is input to the PWM pin (pin 11), 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 operated with the PWM pin open, the built-in

resistor enables the PWM pin to change to high-level

voltage and the motor speed rises to full speed. When

the PWM pin is fixed at low-level voltage, the motor

decelerates, and after the motor stops, it enters

“Power Saving Mode”. Figure 11 shows a rotating

fan’s waveform at PWM Mode.

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