Ah5795 – Diodes AH5795 User Manual
Page 7
AH5795
SINGLE PHASE HALL EFFECT LATCH SMART
FAN MOTOR CONTROLLER
AH5795
Document number: DS35277 Rev. 1 - 2
7 of 13
August 2011
© Diodes Incorporated
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Application Note
DC Supply voltage speed control
Motor speed can be controlled by varying the Vdd supply voltage while PWM pin is tied to Vdd pin.
For example, with 5V nominal motor, changing supply voltage between 5V to 1.8V, speed can be reduced from 100% to 36%
typically.
PWM speed control
Motor speed can also be adjusted by applying a PWM speed control signal into the PWM pin while keeping the Vdd pin at
nominal motor voltage. The motor speed is proportional to the PWM signal duty. For example, with 5V nominal motor, Vdd
pin is maintained at 5V typical while varying the PWM control signal duty to adjust the motor speed linearly. Figure below
shows the output O1 and O2 in relation to PWM speed control signal at PWM pin.
Frequency of PWM speed control signal can be between 15Hz to 50kHz. Recommended typical PWM signal frequency is
25kHz to keep switching frequency away from audible band. If PWM signal level at PWM pin stays low for longer than 65ms
typical, the outputs are disabled.
Depending on the motor design and its inertia, minimum start-up PWM duty required can be typically between 30% - 40%
while minimum running PWM duty can be down to 20%-25% typical. If voltage at Vdd is lower than the nominal motor
voltage, both start-up PWM duty and minimum running PWM duty required will be higher.