UCC28950: Dual rail synchronous rectification

Hi,

We have received your post and the investigation will take some time. Thank you for your patience.

Hi

Dual rail output can be challenging using UCC2895x. Can you share your initial design (WEBENCH) how you are planning to get dual rail output. Then only I'll be able to comment on possible SR switching scheme.

Hi 

this is the output side

first it baffled me why two secondary windings, but then i did a digging and clued myself up.

my idea is to duplicate secondary windings and reference one output's ground to the second output( center tap, winding directions taken into account, also SR MOSFETs would be flipped).

if all of this is possible ofc.

Hi

Yes, two secondary winding makes sense for dual rail output. However, needs to be very careful about circulating current and transients on secondary side. Could you please share complete WEBENCH design.  

I've thoroughly checked the datasheet and i highly doubt about SR in such configuration. current flow will be the issue.if i go with conventional way, with diodes , will that affect filtering section at the output? i mean, would i need more capacitance than what's currently advised?

Hi

Yes, UCC28950 is not designed for such requirements. However, for the starting you can go with diode and if two diodes are operating in sync than we can drive all 4 SR using OUTE, OUTF. Have you checked the feasibility of design in simulation? If not, please do simulations and then I'll help adjust the parameters as required. I cannot just directly comment on output capacitor as output caps are not directly in series (center taped). And not just the output caps, compensation, transformer magnetics, clamping etc. all needs to be checked.

Hi

I've considered it ofc. found a thread here suggesting a specific software, but i can no longer find that thread. coud you please recommend applicable software?