Max Vds for Capacitive Tuning Bank

Designing with GaN FETs and ICs
1

I’m designing a switched capacitor network to tune a coil antenna for optimal resonance. The capacitor network has a few capacitors in parallel, each with their own MOSFET to enable or disable the associated capacitor from contributing to the series resonance with the coil antenna. LTSPICE simulations show that at peak resonance there are some fairly high AC voltages involved and the capacitor branches that are disabled/OFF will be exposed to AC voltages as great as 215Vpk. Enabled branches experience lower peak voltages. Resonance will occur at 129 kHz.

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TUNING NETWORK SCHEMATIC

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VDS Applied to EPC2054 in OFF State

Can a 200V EPC2054 tolerate these peak voltages or should I move up to the more expensive 350V EPC2050? I’m trying to avoid the extra expense if I can, but I don’t understand how the VDSmax continuous relates to a non-continuous voltage.

2

Hello,
thank you for your interest in GaN FETs.
As you noticed, the devices behave OK even above the max rating: that is because the max rating is a reliability rating, rather than based on a specific breakdown voltage like in Si MOSFET. Some EPC GaN devices have actually an overvoltage specification (typically 20%): sometimes as a limited number of pulses, and in the latest ones as a repetitive pulse for the lifetime of the device. Unfortunately, none of the 200V devices have this rating, so we cannot guarantee that this will be OK. And if you consider that you might have some variation in component values and this peak might also change between systems, I think you will need to move to a higher voltage rated part.

3

Hi Andrea,

Thank you very much for your guidance. I will follow your recommendations.

Todd.