3 Motor Drive Stage

Motors in HVAC systems are integral to power different HVAC applications, such as fans, compressors, and pumps. These systems typically include different types of motors, such as brushed DC, brushless DC, and stepper. Motor drives are implemented with different degrees of integration, from a standalone gate driver IC to a fully integrated control, gate driver, and FET IC (full integration).

All degrees of integration lessen the components and save space in board layout; however, there are advantages in selecting the standalone gate driver IC. One advantage is better thermal performance during high-power use. Integration has multiple subcomponents in a small package, which can generate more heat when powered; however, a gate driver IC with external FETs can spread heat better, which can benefit high-power HVAC applications. Higher maximum voltage and current specifications can be achieved by using a gate driver IC with external FETs, while ICs with FETs integrated in are typically bottlenecked to the voltage and current capability of the IC. With proper layout, pairing a standalone gate driver IC as close as possible to an external FET also reduces switching loss and EMI.

Motors in HVAC systems are used to power fans, compressors, and valves. Depending on the motor application, key specifications, like voltage and peak current, and driver robustness are important to consider when selecting a gate driver. A gate driver with low peak current works best for a low-power application, while a gate driver with high peak current works best for a high-power application. Interlock can protect against cross-conduction or shoot-through in half-bridge drives, which can occur by parasitic ringing at the input. A gate driver with negative voltage capability adds robustness to the driver, as negative voltages can occur with transients arising from parasitic inductance. Figure 3-1 shows a typical three-phase inverter motor drive topology.

Figure 3-1 Three-Phase Inverter Motor Drive with UCC27712

For half-bridge motor drives, the UCC27710 or UCC27712 can be used to drive low-power applications. Both the UCC27710 and UCC27712 are part of the 620V, sub-3A family, feature interlock to prevent both high and low outputs from being on at the same time, and have negative voltage capability on the input pins for added robustness. The UCC27714 can be used for high-power applications. The UCC27714 is a 600V, 4A driver that also features negative voltage capability on the input pins; however, it has no interlock. In comparison to the UCC27710 and UCC27712, the UCC27714 is available in a larger package to accommodate larger creepage requirements. For low-side motor drives, like the single-switch chopper, the aforementioned UCC44273 can be used.