Other Parts Discussed in Thread: UCC24612
Team,
I have a customer designing with UCC2897A to build an isolated 2.7V 30A converter working on the bench relatively quickly. He started with the EVM, which outputs 3.3V@30A. The intention was to modify the EVM to function in constant current mode, and then switch to constant voltage when 2.7V was attained at the output. They had no problems designing the crossover circuit.
They then realized that their load might drag the output voltage below 2V at times, and realized that they hadn't considered the gate drive requirements of the synchronous rectifier MOSFETs. (Below 2V, there might be insufficient gate drive for these SR's and since this design features self-driven SR's.)
Their first thought was to swap the SR MOSFETs for low-gate threshold devices, and they tried this, but the converter failed after swapping out the fets, and they then realized that there was probably a simultaneous conduction path (short circuit) on the output.
Question(s):
Do you think it is possible to build a small piggyback board to modify the 2897a EVM's for operation down to 1.5V??? Their thoughts are to design a direct drive circuit as follows. (Two options.):
A.
- Utilize waveforms from the 2897 (either the clock/oscillator or output pins).
- Build a piggyback circuit using a MOS driver chip to drive pulse transformers in order to achieve isolated gate drive signals for the SR MOSFET's.
- Cut the gate pin traces from the board layout, isolating these pins from the original circuit.
- Feed the SR's from the pulse transformers on my piggyback circuit with jumper wires.
- This should acheive operation all the way down to near zero volts on the output, correct?
OR...
B.
The 2897a EVM's were not the right choice from the beginning, and thus it would be prudent / best to scrap the boards altogether and start over with a board that already incorporates direct driven SR's.
