Part Number:TPS23753A
I have a design where we are presently using a PoE module with a TPS23753A onboard.
This design is suffering from thermal issues, even at relatively low load, 10W or less delivered power.
I am investigating the possibility of moving away from the module and implementing our own TPS23753A or TPS23755 circuit on our board, where some of the components can be controlled.
While TPS23755 looks like the easiest circuit to implement, I have a major concern that the internal MOSFET will limit the ability to solve dissipation issues or make them worse.
The goal is to deliver ~10W of output power. The final output should be 5v, but a second stage DC/DC, buck or boost, after the isolation stage would be acceptable if advantageous (reduce current in the flyback output stage?)
I'll also note that I am not a hardcore EE by any means, and I am searching for a resolution based on what I can glean from the datasheets and app notes.
The attraction to use TPS23753A is that we could choose the transformer, switching FET, and output diode.
Following slva305c, the MBRS540T3 seems to be about the best choice I can find for the output rectifier, in terms of forward current drop.
Use of a very high-performance MOSFET like BSZ900N15NS3GATMA1 seems like it could reduce both switching loss and resistive loss.
But given the relatively low primary current, maybe it would be better to select a part primarily to minimize switching losses and diode drop first?
Has the internal MOSFET for TPS23755 already been optimized for all 3 parameters?
The loss in Rcs seems like it may be as high as 330 mW based on the primary currents calculated in slva305c. However, think there is nothing that can be done about that, without the use of a very expensive isolation amplifier? That solution is probably not within scope.
Are there any SPICE simulations ( or any other package ... matlab maybe? Mathematica notebook of equations?) available for the reference designs for TPS23755 or TPS23753A?
There are some transformers with very low winding resistance and inductance (e.g. Moatel EP13) that would require a complete recalculation of the circuit, so having that simulation coded up could be helpful.
Any recommendations you have on how to implement a PoE PD and isolated converter in the ~10W range where every effort can be made to reduce thermal impact would be very helpful.