UCC28250: Switch Node Pulse Ringing – How to rectify it.

Hi,

Where is T2 pin 2 connected to? Please provide full power stage circuit.

Is your design a current mode control or a voltage mode control?

Please provide your UCC28250 related circuit along with its full power stage circuit.

Hi,

It looks this is a typical symmetrical hard switching half--bridge converter. This topology cannot use current mode control which will make flux walking and saturating the transformer. It looks this is the reason. Please use only voltage mode control for this topology.   

Hi,

What is this waveform? Can you show switch node, top and bottom gate, and also ILIM waveforms in one picture?

Also please resend your schematics - the current one you sent is not readable in detail. I need to these to find where to adjust to resolve the issue.

Hi,

The ringing at switch node is due to the transformer leakage inductance and PCB trace parasitic parameters. The ringing can be reduced by lower transfomer leakage inductance and smaller PCB layout loop on this switch node to get lower trace inductance.

Adding snubber (R-C) on switch node can help reduce this ringing. 

The front ringing is due to L-pulse off, and the back ringing is due to H-pulse off. The ringing depends on current level, a higher current can cause higher ringing. Also the ringing depends on voltage level from Vin usually higher Vin can cause higher ringing. Higher leakage inductance causing higher ringing.

Hi,

ok