Am4961a – Diodes AM4961A User Manual
Page 10
AM4961A
Document number: DS36626 Rev. 1 - 2
10 of 17
October 2013
© Diodes Incorporated
AM4961A
A Product Line of
Diodes Incorporated
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Applications Note
(cont.)
Speed Control
The motor speed is governed by the output PWM duty of the H-Bridge.
M
The voltage on the VPWM, VMIN pin and COSC pin controls the output PWM duty and therefore the speed of the motor. When the VPWM
voltage is smaller than VMIN voltage, the output PWM duty is generated by comparing the triangular voltage at COSC pin with VPWM. If the
VPWM pin voltage is higher than the VMIN pin, the speed is controlled by comparing COSC voltage with VMIN voltage. When the VPWM
voltage is lower than the low side of the COSC voltage, the motor will run at full speed. See “Speed Control and Minimum Speed Setting” figure.
An input DC voltage from 3.6V to 1.9V (for 12V supply) on the VPWM pin controls the output PWM duty form 0% to 100% thus allowing speed
control from 0% to 100% of the full speed. If variable speed control is not required the pin should be tied to an external voltage through a
potential divider for a fixed speed or tied to ground for full speed (i.e. 100% output duty PWM drive). The potential divider for a fixed voltage can
be supplied by the supply voltage (as shown in typical application circuit) or by the VREF provided the maximum current drawn out form the
VREF pin is below 5mA.
For speed control based on ambient temperature, a thermistor can be used as one of the resistors in the potential divider.
If an external input PWM signal is used to control the motor speed, the input PWM signal can be converted to a DC level with transistor Q1,
resistors R1 to R and an integrating capacitor C2. See typical application circuit.
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
Speed Control and Minimum Speed Setting