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UCD3138 vs UCD30xx (eg UCD3020)

Other Parts Discussed in Thread: UCD3138, UCD3020

Can someone give me a brief overview of what logic I would use to select between the UCD3138 and the UCD3020 .

My target application is an off-line Resonant LLC stepping 400VDC down to 24V with output power around 1.5kW. So probably full bridge drive and synchronous rectifiers on the output. I am also looking for some more advanced options like constant power limiting that are difficult with the analog only controllers.

I see there is a nice LLC EVAL board on the UCD3138. So that alone make the UCD3138 slightly more attractive.

The biggest difference I see is the feedback compensator - 2p/2z PID for the UCD3138 verses 3p/3z for the UCD30xx. I would expect a greater range of phase compensation with the latter but are there down sides to that scheme?

  • The DPWM on the UCD3020 has a resonant mode, but it doesn't provide a way to do a practical LLC circuit.  You pretty much have to go with the UCD3138 family. 

  • Ian,

    thanks for that. Are you able to elaborate on why LLC is not practical on the UCD3020? Just reading the datasheets gives the impression it should be suitable.  The UCD3138 appear to be a more modern part  and seems to have more control options so I wonder is there a few key functions that make the difference.

    Finally are you able to comment on the differences in compensation networks.