Data Sheet

Three Phase Direct PWM Sensorless Motor Driver

AM9800

Sep. 2012 Rev. 1. 0

BCD Semiconductor Manufacturing Limited

9

Application Information (Continued)

Figure 11. Rotation Mode Waveform (PWM Mode)

8. Soft Switching Circuit

AM9800 adopts variable duty soft switching to

minimize the motor drive noise. Figure 12 shows

how soft switching circuit works during the fan

rotation.

Figure 12. Soft Switching Waveform

9. Current Limiter Circuit

The driver current is detected by connecting a resistor

between RF pin (pin 15) and ground. The current

limiter circuit limits the output current peak value to

10. OSC Circuit

A capacitor must be connected between OSC pin (Pin

7) and ground. When a capacitor is connected, the

OSC pin starts self-oscillation, and its frequency

becomes the startup frequency. Figure 13 shows a fan

system’s OSC Waveform.

11．Position Detector Comparator Circuit

for Rotor

The position detector comparator circuit for the rotor

is a comparator for detecting rotor positional

information with the back EMF signal generated

when the motor rotates. The IC determines the timing

at which the output block applies current to the motor

based on the position information obtained here. A

capacitor (between 1000 and 10000pF) must be

connected between COMIN pin (pin 5) and the FIL

pin (pin 6) to prevent any motor startup misoperation

that is caused by the comparator input noise.

12．FG Output Circuit

FG output pin (pin 10) provides a pulse signal

equivalent to what provided by systems using a

Hall-effect sensor. A pull-up resistor (10kΩ is

recommended) must be connected between FG pin

and the power supply. Figure 14 shows the FG output

signal when the fan rotates.

Figure 14. FG Output Signal

13. Lock Shutdown and Auto Restart

This IC detects the rotation of the motor by internal

Figure 15. Lock Mode

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