TPS2373: Reference design ( TPS2373-3EVM-024 ) Application note for designing discrete parts

Anand Krishnan M1

Part Number: TPS2373

Hi Team,

I am designing a Power over ethernet PD controller with TPS2373-3, LM51551QDSSRQ1, TL431LIAIDBZR. My output power requirement is 12V@3A. I got exact reference design ( TPS2373-3EVM-024 ) frotidrxx2.pdfm TI. Same attached for reference. Is there any suitable application note for designing the following sections in the reference schematics ?

1. Flyback transformer input and output filter circuit.

2. Shunt regulator RC network.

3. Optocoupler RC network.

over 5 years ago

0 Brett Colteaux over 5 years ago

TI__Expert 3700 points

Hello,

The PoE applications engineering team is currently out of the office and will respond by end of day Monday, 7/13.

Best Regards,

Brett Colteaux

PoE Product Marketing Engineer

0 Michael Pahl over 5 years ago

TI__Mastermind 21320 points

Hello,

The following paper walks through a flyback design with all the parts you mentioned:

https://www.ti.com/lit/an/slva305c/slva305c.pdf

If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

Regards,

Michael P.

Applications Engineer

Texas Instruments

0 Anand Krishnan M1 over 5 years ago in reply to Michael Pahl

Prodigy 140 points

Hi Michael,

Thanks for your reply.

Please see the image below. This is bridge rectifier section of the PoE reference design.

May I know why the common anode pin of P1 diode is left floating ? How the transistor Q3 turns ON without any bias ? Please help to clear my doubt.

0 Michael Pahl over 5 years ago in reply to Anand Krishnan M1

TI__Mastermind 21320 points

Hello,

What reference design is this?

The one you mentioned earlier has the front end:

This is what I would recommend if you are moving forward with this design.

If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

Regards,

Michael P.

Applications Engineer

Texas Instruments

0 Anand Krishnan M1 over 5 years ago in reply to Michael Pahl

Prodigy 140 points

Hi Michael,

I got this bridge rectifier part number from the TI reference design TPS2373-4EVM-758.

We have space constraints in our board, so I selected this integrated bridge rectifier FDMQ8205A.

May I know if you need any other information ?

0 Michael Pahl over 5 years ago in reply to Anand Krishnan M1

TI__Mastermind 21320 points

Hello,

I am not seeing the diode with three pins in the input rectifier in the TPS2373-4EVM-758.

Now you are using an integrated FET bridge which is fine, but I am not seeing where this 3 pin diode fits into any of our designs?

Please simply copy our front end designs. Since these affect the PoE Compliance by changing the capacitance and resistance of overall system, I highly recommend completely copying one of our tested designs. Thank you.

If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

Regards,

Michael P.

Applications Engineer

Texas Instruments

0 Anand Krishnan M1 over 5 years ago in reply to Michael Pahl

Prodigy 140 points

Hi Michael

Ok I will implement the front as per the reference design.

In the flyback controller section, is the Optocoupler U3 acting as just simple switch or in the active region when the shunt regulator U4 is conducting ?

Also in the application note the compensation value Rcomp is common for both shunt and optcoupler sections. But in the reference schematics it is different. May I know how to calculate it differently ?

0 Michael Pahl over 5 years ago in reply to Anand Krishnan M1

TI__Mastermind 21320 points

Hello,

The optocoupler is in the active region, that is how the feedback is adjusted.

The calculation involved is in section 2.8 Feedback Control. Another paper on feedback: https://www.onsemi.com/pub/Collateral/TND352-D.PDF

Additionally, most compensation components are determined in the lab with testing. Even if you calculate your own I'd recommend verifying it in the lab.

If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

Regards,

Michael P.

Applications Engineer

Texas Instruments

0 Anand Krishnan M1 over 5 years ago in reply to Michael Pahl

Prodigy 140 points

Hi Michael

Ok I will check the application note.

For the PoE isolated flyback design we were following this reference design TPS2373-3EVM-024 ( Class 6 Low Cost Flyback for PoE PD ). In this design Class 6 upto 50W is mentioned. But in our case the power requirement is around 30W. As I mentioned earlier we found spacing issues in PCB due to the size of Flyback transformer 750317065. So is it possible to design this circuit for 30W thereby reducing the size of the flyback transformer. Can you please suggest a smaller flyback transformer for this design ?

0 Michael Pahl over 5 years ago in reply to Anand Krishnan M1

TI__Mastermind 21320 points

Hello,

We have multiple 30W PoE PD reference designs. Either copy one of them, or use the transformer from their designs.

Here's an exmaple:

https://www.ti.com/tool/PMP21103

You can find our reference designs by searching "TI Reference Designs PoE"

https://www.ti.com/power-management/reference-designs.html?DCMP=pmp-reference-designs&HQS=powerlab#search?DCMP=pmp-reference-designs&HQS=powerlab&famid=64

If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

Regards,

Michael P.

Applications Engineer

Texas Instruments

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TPS2373: Reference design ( TPS2373-3EVM-024 ) Application note for designing discrete parts