Conducted and radiated emission considerations

Conducted and radiated emissions depend on the switching frequency, dv/dt, di/dt, switching voltage oscillations and reflections, and the switching current loop area.

The DRV7308 incorporates these multiple design techniques and printed circuit board (PCB) layout options to address EMI and electromagnetic compatibility concerns:

• PWM switching frequency. The higher the switching frequency, the greater the impact on the EMI frequency spectrum. A higher switching frequency helps reduce current ripple and capacitor requirements to meet the conducted emissions. The DRV7308 offers a wide range of switching frequencies, from very low values up to 60kHz. Designers can choose the optimum frequency based on the system performance and EMI requirements.
• The dv/dt. The DRV7308 predriver can control the phase-node switching slew rate to meet EMI requirements.
• The di/dt. With zero reverse recovery and low parasitics, GaN can offer better switching performance without creating voltage overshoot and oscillations at the phase node during switching. Figure 4 and Figure 5show the clean switching of the DRV7308, which translates to lower EMI.
• A small switching current loop area. Local decoupling capacitors will provide pulse currents during switching. The DRV7308 is designed such that the switching current loop area to the DC voltage decoupling capacitor (C_VM) is very minimal, as shown in Figure 8.