Called EPC9195, it is a synchronous buck converter built around a pair of 2.5 x 1.5mm EPC2619 GaN hemts, and an LTC7891 controller IC from Analogue Devices.
“48V input is getting popular due to USB PD 3.1 efforts to increase power and to reduce cabling for up to 240W,” according to EPC. The board is “96.4% efficiency at 48V to 13.5V and 16A continuous current”.
Bottom view
“ADI’s LTC7890, LTC7891, LT8418, and LT8390A are designed to pair with GaN fets for high power density solutions,” said ADI applications director Keith Szolusha. “They offer higher switching frequency and optimised deadtime while operating in low power consumption.”
Dead-time at 750kHz
The demo board has a half-bridge topology running at 750kHz, and offers all of the control IC’s dead-time options through two three-way jumpers:
- Adaptive, where a gate is not turned on before the other transistor is off, which results, said ADI, in approximately 20ns between one gate falling and the other rising.
- Smart, which reduces the delay between the rising edge of the half-bridge mid-point to the falling edge of the bottom gate, or the falling edge of the mid-point to the rising edge of the bottom gate “to near zero”, said ADI. .
- Resistor-programmable, which adds programmable delays of between 7 and 60ns into either of the two ‘near zero’ delays of the ‘smart’ option.
Three light-load operating modes jumper selectable: forced continuous inductor current, pulse skipping and burst mode.
A GaN-specific feature of the control IC is a smart switch – instead of a simple diode – in the bootstrap circuit for the upper transistor, which is included to prevent the gate of the upper transistor from being over-driven – GaN hemt gates are damaged by voltages only slightly above the correct drive value.
Heat-sinking, over the marked central area of the PCB, is required in certain operation conditions.
EPC9195 demo board data sheet and user guide
LTC7891 controller IC for GaN data sheet