20.3 A GaN Gate Driver with On-chip Adaptive On-time Controller and Negative Current Slope Detector

Abstract

Monolithic gallium nitride (GaN) solutions are widely used in high power density applications, due to low on-resistance <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\mathrm{R}_{\text{ON}})$</tex> and low parasitic capacitance [1–3]. However, some process defects, such as current collapse, kink effects, and self-heating (top left of Fig. 20.3.1), will degrade the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{I}_{\text{DS}}-\mathrm{V}_{\text{DS}}$</tex> curve of high voltage GaN devices, which can lead to efficiency degradation and power device damage. Current collapse will increase <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{R}_{\text{ON}}$</tex> , which will cause the GaN to heat up causing self-heating, and the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{I}_{\mathrm{D}}$</tex> current drops significantly when GaN enters the saturation region. Furthermore, the kink effect induced by hot electrons trapped by donor-like traps through the GaN buffer will induce a negative slope in the triode region, which may lead to blurred transitions from the triode region to the saturation region. Thus, if the detection of saturation is inaccurate, the sudden change from the kink effect to self-heating will limit the current driving capability. Consequently, in flyback converters, part of the inductor current will leak to the secondary side when the primary side GaN is still turned on, resulting in serious shoot-through effects.