A motor driver IC with auto calibration function is provided, the motor driver IC utilizes a Hall sensor of a switched sensor circuit to detect the changes in an external magnetic field. By using the compensation current which is generated by the automatic calibration circuit to correct the unexpected offset existed in the Hall sensor of the sensing unit itself to zero so that the sensing unit can sense the changes in the external magnetic field accurately and can point out the rotor position correctly, and the motor can be further driven to commutate relatively to reduce the motor rotation noise to achieve good output performance of the motor rotation and the better motor driving system stability.