33.3 An Automotive-Use 2MHz 100VOUT Flicker-Free Frequency-Modulated GaN-Based Buck-Boost LED Driver Achieving Bootstrap Charge Balancing and 16.8dBμV Radiated EMI Noise Reduction

Automotive headlamp and/or taillamp tend to integrate a high number of LEDs (up to 30 LEDs in series) for sequential turn signal light. As the LEDs are turned on/off sequentially, the output voltage across the LED string $(V_{{OUT}})$ can be below, equal to, or above the input battery voltage $(V_{{IN}})$ which also experiences a large transient from 4 to 60V. To achieve accurate and stable LED current regulation over such a wide operation voltage range, high-voltage buck-boost converters are desperately demanded [1] –[4]. Although high- switching-frequency $(f_{sw})$ solutions have been explored as in [4], [5], the stringent thermal and size limitations imposed by automotive applications have made it increasingly challenging to continue using silicon-FET-based converters. Gallium-Nitride (GaN) FET, which offers a $5\times$ lower capacitance and nearly zero reverse recovery to enable an efficient high-voltage operation at high $f_{SW}(\gt 2MHz)$, has been proven to be a very promising device in this scenario [5]. However, severe electromagnetic interference (EMI) due to high f sw operation and complicated bootstrap GaN gate driving become very challenging for GaN buck-boost LED drivers in automotive applications.