Threshold voltage instability of p-GaN Gate HEMT in 48-12V Buck Converter & its Impact on Circuit Power Loss Variation

From the circuit perspective, the
$V_{\text{th}}$
instability during circuit operation and its impact on the circuit performance is studied based on a 48–12 V buck converter operates in hard-switching (HS) mode. Unexpectedly, even in the normal circuit operation condition, substantial
$\Delta V_{\text{th}}=+0.2\sim + 0.83$
V at varied frequency (
$f$
) and output current
$(I_{\text{out}})$
were measured in the p-GaN gate HEMTs and the
$\Delta V_{\text{th}}$
exhibits a positive correlation with
$f$
and
$I_{\text{out}}$
. HS double-pulse test as well as on- and off-state stress tests on discrete devices reveal that the hard-switching transient-state is a critical factor causing
$V_{\text{th}}$
instability, while the underlying mechanisms is analyzed in detail. In addition, the impact of
$V_{\text{th}}$
instability on the overall circuit power loss are quantitatively investigated. For instance, at
$f=1.9$
MHz &
$I_{\text{out}}=2\ \mathrm{A}$
, the deadtime power loss significantly increased by 35.35%. The overall power loss consumed by GaN HEMTs increased up to 11.6%.