25.2 A 10MHz 3-to-40V VIN tri-slope gate driving GaN DC-DC converter with 40.5dBµV spurious noise compression and 79.3 ringing suppression for automotive applications

摘要

As power efficiency becomes essential in automotive applications, DC-DC converters are widely employed [1]. However, size and thermal limits have made it challenging to continue using standard CMOS-based converters. Gallium Nitride (GaN) FETs, on the other hand, have a much higher conductivity with small size/capacitance in comparison to silicon FETs, enabling a highly efficient power conversion at high switching frequency (fSW). However, there are several issues that must be resolved before using GaN in automotive. High fSW incurs larger di/dt and dv/dt transitions which injects high frequency electromagnetic interference (EMI) noise into the input bus. This creates unwanted noise or even a malfunction in a safety-critical system. A bulky input filter can reduce EMI, but it greatly increases size and cost. Several techniques [2–5] are reported to mitigate EMI. Frequency hopping using discrete frequencies is proposed in [2], but cannot spread the frequency evenly to lower the peak noise effectively. Alternatively, a series resistor is typically added at the gate of the GaN FET to slow down the transition [3–4]. However, the switching loss is dramatically increased. To mitigate this, adjustable driving strength is proposed in [5]. Unfortunately, the sensing and driver delays confine its use in low fSW applications, where the switch node rising time is several tens or hundreds of ns. Another issue of high fSW operation is that it causes significant current and voltage spikes due to the parasitics at the drain/source of the high side GaN FET (MH), which could lead to GaN VDS breakdown or damage on logic-level FETs. Thus, EMI noise suppression and reliable operation of GaN FETs remain as major challenges in realizing high fSW power converters for automotive-use.