AM9800 Datasheet, PDF (9/11 Pages) Diodes Incorporated – Three Phase Direct PWM Sensorless Motor Driver

Data Sheet
Three Phase Direct PWM Sensorless Motor Driver
AM9800
Application Information (Continued)
11．Position Detector Comparator Circuit
V_UO
5V/div
for Rotor
The position detector comparator circuit for the rotor
V_VO
5V/div
V_WO
5V/div
-I_WO
100mA/div
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
Time 5ms/div
capacitor (between 1000 and 10000pF) must be
connected between COMIN pin (pin 5) and the FIL
Figure 11. Rotation Mode Waveform (PWM Mode)
pin (pin 6) to prevent any motor startup misoperation
(f=25kHz, V_H=5V, V_L=0V, Duty Cycle=50%)
that is caused by the comparator input noise.
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.
V_UO
5V/div
V_VO
5V/div
V_WO
5V/div
-I_WO
200mA/div
Time 200µs/div
Figure 12. Soft Switching Waveform
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.
V_UO
5V/div
V_VO
5V/div
V_FG
5V/div
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
a level determined by the equation I=V_RF/R_F
(V_RF=0.25V typical).
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.
Time 5ms/div
Figure 14. FG Output Signal
13. Lock Shutdown and Auto Restart
This IC detects the rotation of the motor by internal
circuit block, and adjusts lock detection ON time (t_ON)
and lock detection OFF time (t_OFF) by internal counter.
t_ON and t_OFF are shown as below:
V_UO
5V/div
V_VO
5V/div
V_OSC
100mV/div
V_WO
5V/div
Time 1s/div
Time 500µs/div
Figure 13. OSC Waveform (C_OSC=2200pF)
Sep. 2012 Rev. 1. 0
Figure 15. Lock Mode
BCD Semiconductor Manufacturing Limited
9