Published at the OCP Global Summit in San Jose, PI’s white paper proposes its 1,250V and 1,700V GaN transistors as the main power switches in first stage of down-conversion.
These are high voltages for GaN technology, where transistors tend to peak at a nominal 650V.
To hit the higher voltages, Power Integrations uses a cascode-connected transistor pair where a low-voltage silicon mosfet switches a co-packaged high voltage depletion-mode (normally-on) GaN hemt. The mosfet is mounted directly onto the GaN die to minimise connection parasitics.
“Depletion-mode GaN devices are regarded as highly reliable since they do not require a p-type GaN gate layer,” said PI. “As a result, they avoid threshold voltage drift and related instability concerns, ensuring long-term stability.”
PI is proposing direct conversion from 800V to a 12.5V bus in a single stage using an isolated LLC converter that includes a 32:1 transformer – actually 32:1+1 because the output rectifier is a half-wave (see diagram).
It sees 1,250V GaN power transistors rather than Si mosfets as essential, exploiting the higher maximum operating frequency to shrink the convert sufficiently to be practical.
In its design example it predicts a 1MHz zero-voltage switched converter with and transition dead time of <100ns and >98% efficiency.
For auxiliary power within the rack, PI is proposing its 1,700V-rated GaN-based IMX2353F ‘InnoMux2-EP’ IC, which can directly derive up to three power rails in one stage – including 48V for a fan and 12V for electronics, it said, from an input of up to 1,000V.
The company’s white paper on 800V data centre proposals is detailed and well worth a look.
Nvidia has recruited many of the big names in power electronics for its 800Vdc data centre initiative
