Help!! Help to design Brushless DC motor driver!!!

Thread Starter


Joined Jan 13, 2015
Hi everyone,

I have designed a BLDC driver for 24V, 300W BLDC hub motor using Allegro's A3931kjpt IC. my digital inputs are,
PWM freq=20KHz
internal current control with Vref=3.5V

With this setup my motor runs from 0% to 100% duty cycle. But it is not able to provide the torque. Even at 100% duty cycle if I try to stop the motor, it stops.

Can someone suggest me the solution?

From my understanding a BLDC will generate more torque when there is a larger amount of current applied.

Heat loss (such as described in the link below), as well as physical size, play a role in the torque capabilities of a BLDC. Here's an informative link I found that may help you go in the right direction:

Sorry if this isn't what you're looking for, I hope the math on that page helps though!

Thread Starter


Joined Jan 13, 2015
Thanks for reply. Voltage is not at all dropping. and current limit what I set is much grater than actual current motor is drawing from the supply.
In my board I put Vref=4.5 which is current limit value. and my Rsense=10mOhm

Thanks, but yeah I knw this math, but i want help specific to this IC A3931.