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

Abstract

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 (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SW</sub> ). However, there are several issues that must be resolved before using GaN in automotive. High f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SW</sub> 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 f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SW</sub> applications, where the switch node rising time is several tens or hundreds of ns. Another issue of high f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SW</sub> operation is that it causes significant current and voltage spikes due to the parasitics at the drain/source of the high side GaN FET (M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> ), 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 f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SW</sub> power converters for automotive-use.