Power
Transient modelling and loop stability in spaceborne eGaN HEMT low-dropout regulators under total ionizing dose
A rigorous analytical model demonstrates how spaceborne eGaN HEMT-based LDO regulators stabilize the control loop and eliminate radiation-induced drift under TID environments, explains Diego de Azcuénaga from EPC Space
T
he architecture of power management systems for spaceborne platforms demands semiconductor devices capable of operating deterministically
under continuous ionizing radiation fluxes. In traditional space-grade LDO linear regulators, silicon MOSFETs serve as the primary pass element. However, prolonged exposure to TID induces the generation of electron-hole pairs within the gate dielectric of these devices. Holes trapped at the oxide interface shift the threshold voltage (Vth
)
and irreversibly degrade transconductance (gm
), typically by magnitudes exceeding 20 per cent. This parametric degradation introduces severe non-linearities into the analogue feedback loop, forcing designers to incorporate over-dimensioned design margins or complex dynamic compensation networks to prevent control loop oscillation or voltage hunting over the mission lifespan. To mitigate these constraints without incurring critical mass penalties from localized physical shielding, eGaN HEMTs emerge as a viable architectural alternative. Due to their wide bandgap nature, the lateral AlGaN/GaN heterostructure inherently lacks a physical gate oxide, thereby eliminating the primary mechanism of low-dose charge trapping. Experimental evaluations demonstrate that the transconductance of eGaN devices experiences variations of less than 3 per cent under harsh exposure profiles up to 500 kRad. This structural resilience guarantees the consistency of the control loop’s dynamic parameters. Nevertheless, implementing these N-channel devices in linear topologies introduces specific analytical challenges, such as the requirement for a bias voltage higher than the combined magnitude of the output voltage and the maximum gate-
34 September 2026
source potential at full load, alongside susceptibility to high-frequency oscillations induced by gate parasitic inductances. This paper examines the mathematical modelling of these variables and validates the transient stability of the system under load steps in the time domain.
Analytical modelling and methods The implementation of eGaN HEMTs as pass elements in linear topologies introduces specific biasing constraints due
Components in Electronics
to their exclusive availability as N-channel polarity devices. To operate within the linear region and maintain continuous regulation, the control loop must provide a gate bias potential (Vbias
) strictly
higher than the combined magnitude of the regulated output voltage and the maximum gate-source voltage required at full load current: Vbias
> Vout + Vgs (Id(max) )
The exceptional stability of the GaN threshold voltage (Vth) against cumulative
radiation effects (< 3 per cent variation up to 500 kRad) allows designers to parameterize this conduction boundary with a minimal safety margin. This tight tolerance window minimizes voltage stress on the error amplifier stage and reduces power overhead within the control loop. Figure 1 illustrates the robust operational envelope of a representative eGaN HEMT device (such as the FBG04N30 platform) under continuous exposure up to 500 kRad.
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