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Hi Expert,
The customer would like to run 2pcs UCC28950 in parallel.
They want to know why PMP6712 design locate the UCC28950 at primary side?
Any particular reason here?
Thanks.
Best regards,
Eric Lai
Field Application Engineer
Texas Instruments Taiwan Limited
O: +886-2-2175-2582
M: +886-909-262-582
E-Mail:Eric.Lai@ti.com
Hello Eric
I don't know exactly why the designer decided to use the UCC28950 on the primary side of the system so it's difficult to give an answer.
In general - if the controller is on the primary side then the gate drives to the primary are simplified because the drives do not need to be isolated. Since this design was released in 2012 TI has released several isolated gate driver ICs to the market which simplify the task of bringing the gate drives across the isolation barrier - the UCC21520 for example that were not available when this design was being done. The SR drives are taken across to the secondary through an ISO7420 device.
The main drawback of having the controller on the primary is that the feedback path must include an optocoupler. This will limit the control loop bandwidth and - depending on the application - there may be lifetime concerns about using an Opto.Having the controller on the secondary eliminates the optocoupler so a faster loop response is possible. It is also easier to interface control signals from an external source (Enable, Synchronisation and so on) if the controller is located on the secondary. One of the main disadvantages of a secondary side controller is the need to provide a low power bias supply - sometimes one is needed even for a primary side regulated design like the PMP6712 too.
The UCC28950 controller itself will operate either on the primary side or on the secondary side of the isolation barrier -
Regards
Colin