AM4961A

Document number: DS36626 Rev. 1 - 2

10 of 17

www.diodes.com

October 2013

© Diodes Incorporated

AM4961A

A Product Line of

Diodes Incorporated

Speed Control

The motor speed is governed by the output PWM duty of the H-Bridge.

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

VMIN Voltage

COSC Output

Low Speed

PWM Variable

High Speed

0V

FG Output

Speed Control and Minimum Speed Setting