Diodes AM4961 - Manual (Page 10)

SINGLE PHASE FULL WAVE DIRECT PWM MOTOR DRIVER AM4961
Data Sheet
10
May. 2011 Rev. 2. 4 BCD Semiconductor Manufacturing Limited
Operating Diagram
Note 5:
1. Low Speed Setting Mode
When VPWM voltage is higher than VMIN pin voltage,
motor speed is settable by VMIN pin voltage. The mini-
mum drive duty cycle is settable by comparing COSC
oscillating voltage and VMIN pin voltage.
VPWM voltage is decided by variation of PWM duty.
2. Variable Speed Setting Mode
When VPWM voltage is lower than VMIN pin voltage,
PWM control system works by comparing VPWM voltage
and COSC voltage. If VPWM voltage is higher, the ON
duty cycle of the upper side transistors will be minimized
and motor speed becomes lower. Vice versa.
3. Full Speed Rotation Mode
At a certain PWN duty, when VPWM voltage is lower than
the low side of COSC output voltage, the motor will run at
full speed.
Figure 10. Operating Diagram of AM4961 (Note 5)
M
Lowest speed setting voltage
VPWM adjustable Voltage
f
OSC
=25kHz (C
OSC
=100pF)
VMIN Voltage
COSC Output
Low Speed PWM Variable High Speed
V
CC
0V
FG Output
V
osc
V
osc