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Is there a high efficiency reference design from TI using the TPS23753A?
We want to get the maximum output power out of standard PoE - class 0/3.
Also, we are using the Wurth transformer 749 119 350 because of height restrictions.
Michael, My apologies...I now see you have the output description in the title...5V @ 3A...is 15W...so we need to move up to Class 4, correct?
Thomas, thanks for your attending to my request.
1. transformer: yes, we are open to other transformers, but we must not exceed 9mm height restriction on the PCB.
2. Power output: yes, we need 12.95W, the class 0 or class 3 maximum.
3. Isolation: we have a shielded RJ45 jack with GbE, so to my knowledge, yes, we need isolation.
4. Number of outputs: we need a single output with +5V
5. Efficiency: no goal, as high as possible, because what we do not dissipate in the power supply is available power for the circuit.
Hi Michael,
I had checked with coilcraft and wurth to see if there was a similar transformer spec as PMP9175 in an EFD15 core (much thinner) however I didn’t find one.
For the transformer you want to use, you can get away with using it if you pair it with the UCC24630 as you suggested in our email offline. In this case you can use the TPS23753A.
Or you can use it in a driven flyback approach (with an external gave drive transformer). In this case, you can consider the TPS23757 since it has a second gate drive. Its EVM has pretty good efficiency for the DCDC converter (~91-92% efficiency) and uses an EFD core.
www.ti.com/.../slvu318b.pdf
Regards,
Darwin
Hi Darwin,
thanks for your answer. Do you have a reference schematic for the UCC24630 replacing D3 in slvu315a or a similar EVM?
BR
Michael
Hi Michael,
Unfortunately, we have yet to use this synch gate controller in our TI designs or EVMs for PoE. I've seen it used mostly in offline applications at greater than 30W converters and not yet for 13W. It may be difficult to modify an PoE EVM with this controller as well. It might be that you must prototype it first with a new board.
How about the TPS23757 board I recommended? It would be higher efficiency performance than using UCC24630 since TPS23757 design is a driven approach.
Hi Darwin,
I have 2 last questions, before we close this thread:
1. There are 1 or 2 (in case of aux power) diodes B1100 in the power flow. This causes app. 0.2W of loss for each diode, i.e. 0.4W in case of aux power. Is there a better way?
2. Would you be willing to do a design review of our schematic in order to spot any mistakes?
BR
Michael
Hi Michael,
1. Yes we have an in-between bridge (FET-diode bridge) that is not as bad as a diode bridge but not as good as a FET bridge. Please see the bridge we use in TPS2372-3EVM-757. For this design, note the det resistor on the EVM. Be sure it is increased when using this bridge.
2. Absolutely! Let us know and we can check it.
Thanks!
Regards,
Darwin
Hi Michael,
Ah I see what you're asking now. Yes I have seen designs in the past that use a PFET as the pass element instead of the diode and a divider from the input to the gate. I have not tried this myself though.
Regards,
Darwin
Hi Darwin,
do you have a sample schematic and part recommendation for such a PFET ORing diode?
Best regards,
Michael
Hi Darwin,
I have followed you recommendation and used EVM slvu318b in our design. Could you please check my schematics for correctness? According to the documentation this design delivers 11W. Other products, like the Silvertel Ag92015-S (www.silvertel.com/.../160-ag9200.html), advertise their modules as being able to deliver 13W with standard bridges. What makes the difference of 2 Watts?
Best regards,
Michael
Hi Darwin,
the TPS23757EVM uses the Pulse PA0184 gate drive transformer. This transformer is rather large. Can we replace it with B82804A0354A110 ( en.tdk-electronics.tdk.com/.../b82804a.pdf ). I suppose it has similar parameters, but a bit smaller that current transformer.
Best regards,
Michael