Why would you choose a discrete implementation of components versus an integrated chip approach?
A integrated chip approach combines all areas of the motor signal chain into a single chip, typically including the gate drivers, current sensors and sometimes encoder inputs and power MOSFETs. These chips are very good at optimizing a particular motor control strategy, but do not offer good performance across different motor control strategies and might be limited to a certain size of motor due to the included MOSFETs. For simple commutation schemes, this performance might be enough, but with advanced commutation strategies or advanced power requirements, a discrete solution is needed. One example would be sensorless commutation strategies, where voltage and current sensing is critical. Field Oriented Control also requires precise current sensing and can be helped by advanced current sensors that reject PWM common mode voltages. By having control over the complete signal chain, certain portions can be tweaked to the needs of a particular application, rather than trying to find a one size fits all solution. In heavily cost constrained applications, a single chip will be cheaper, but if performance matters, the discrete option is the way to go. Analog Devices offers a number of discrete motor drive signal chain parts from isolated MOSFET drivers for safety critical applications to rotor position sensors.