A DC motor controller is a device that provides or facilitates accurate control of a DC motor. There are two major types of DC motor - the common DC motor with brushes, and the brushless DC motor. Both types has a non-moving source of magnetic fields, known as a stator, and a rotating source of magnetic fields, known as the rotor.  The interaction of the magnetic fields from the stator and the rotor is what makes the motor shaft turn.

A brushed DC motor, which is operated simply by applying a DC voltage across its terminals, has a 'permanent magnet' stator and an 'electromagnet' rotor. It uses its brushes to deliver commutating current from the motor's external terminals to the moving rotor coils inside. A brushless DC motor, on the other hand, has a 'permanent magnet' rotor and an 'electromagnet' stator. It requires a more complex form of energization to operate - proper sequencing of the delivery of commutating currents to its stator coils.  Brushless DC motors are not subject to the arcing caused by brushes, and therefore have a longer life. 

Brushed DC motors are not widely used in precision motion control application because they are difficult to control. Brushless DC motors are more widely used, which is why many motor controller IC's for DC motors cater to the brushless type.

A typical brushless DC motor controller IC is equipped with a control circuit and a driver circuit.  The control circuit, which is the 'brain' of the controller IC, generates a control output based on some form of input. For instance, it may receive feedback about the state of the motor, usually in the form of input data based on Hall Effect, which it decodes. The logic circuit then applies a built-in commutation logic that interprets the decoded feedback information and outputs the appropriate commutation commands to the driver circuit. 

The driver circuit, which translates the logic circuit commands into motor-useable currents, typically consists of a set of integrated power drivers that supply the correct sequence of currents to the brushless DC motor.  It may also have a built-in pulse width modulation (PWM) circuit that varies the amounts of DC currents delivered to the motor to control its torque and speed.