Figure 1: Typical Sensorless BLDC Motor System

    Figure 1 shows a typical sensorless BLDC motor system. The components highlighted in blue are usually part of the gate driver integrated circuit (IC), where the power MOSFET is located outside the IC on the circuit board. When the gate driver IC also includes components highlighted in red, the IC is referred to as a motor driver or integrated FET driver. The components highlighted in green are part of the motor controller. We will focus on discussing gate driver and motor driver architectures.

    Gate driver architecture: By selecting different MOSFETs to expand power levels, an external MOSFET based architecture allows system designers to flexibly use the same driver and control design for various applications. Usually, MOSFETs with higher rated currents have larger packaging dimensions to adapt to the lower R (ON) of MOSFETs and provide better thermal performance. System designers can choose different MOSFETs based on system performance requirements and optimize circuit board sizes accordingly. Due to the fact that MOSFETs can be placed in distant locations on circuit boards, gate driver architectures typically provide better thermal performance. One drawback of the gate driver based architecture is that the circuit board design is complex, due to the placement of six MOSFETs on the circuit board (for three-phase BLDC systems). In order to achieve system performance goals such as lower EMI and noise, system designers also need to consider the MOSFET position in the gate driver IC. Due to the large number of components on the circuit board, the gate driver system is much larger than motor driver solutions of the same power and voltage level. An example of a gate driver board is the DRV8304 EVM, which is a 40V BLDC system designed to provide 15A current. The size of the EVM circuit board is 61mm x 56mm (3233 square millimeters). Compared to gate driver ICs, six MOSFETs occupy 2.5 times the area on the circuit board!