Other Parts Discussed in Thread: TPS23754, , TPS23754EVM-420, TPS23753A, PMP9175, UCC24612
I am in the process of setting the schematic for a 6W PoE design to revise it due to thermal issues. I could use some wisdom from the TI PoE PD/power supply experts.
I have been looking through the reference designs for TPS23753A, TPS23754 (via TPS23754EVM-420 EVM), and TPS23755, trying to choose between the options.
The TPS23754 seems like a fine option, especially since I have already tested it thermally under load on the bench via the EVM.
Unfortunately, that reference schematic has quite a large number of parts, with the driven SR, opto-coupler, etc.
Our design a little size constrained.
The TPS23753A reference design (PMP9175) is interesting because it has an input & output SR's and not too bad a part count.
But this design does use a smaller transformer, and we expect the transformer to be the biggest contributor, so we want to use something like Coilcraft POE300F-12L or CX9642-AL or JA4387-AL, something rated for much higher power than we intend to conduct.
But the TPS23755 is very attractive due to the low part count and no need for an optocoupler.
I am nominally targetting a +5V output, but converting to +12V and then adding another buck converter to 5V and taking the 5-7% efficiency hit may be worth it to reduce the complexity of the control loop running in the flyback converter.
However, the TPS23755 datasheet says specifically that it is tuned for a diode rectifier on the output.
Does that mean that porting the output SR from the PMP9175 design or applying a UCC24612 (or similar) would not work with the TPS23755?
Can the TPS23755 be operated with a lower inductance transformer and still stably accomplish the primary-side regulation?
Do you expect that the TPS23755 would have serious thermal effects due to its 770mOhm internal MOSFET? We could choose a much higher performance & FOM MOSFET with TPS23753A or TPS23754.
If the subject matter experts on the PoE team had any advice here, it would be greatly appreciated.
We are going to go to prototype as soon as we can get this part selection worked out!
