• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 2 answers
  • Subscribers 38 subscribers
  • Views 633 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

PMP22301: TPS23754

Francois Godreau
Prodigy 30 points

Part Number: PMP22301
Other Parts Discussed in Thread: TPS23730

Tool/software:

We are referring to the PMP22301 reference design to develop a 30W (24V/1.25A) PD based on the guidelines outlined in SLVA305C, using the POE300F-24L_ transformer.

According to these guidelines, a minimum primary inductance of 135µH is required for PoE+ input without an adapter. However, the POE300F-24L_ has a primary inductance of 37µH, which results in significantly higher peak currents.

Based on the transformer characteristics provided in the datasheet, the calculated primary currents are as follows:

  • Low-line average DC input current: 0.9A
  • On-state step current: 1.7A
  • Ramp current: 1.9A
  • Peak current: 2.7A

Since the peak current rating of the POE300F-24L_ is 2.6A, I am concerned about its suitability for this design.

Would it be possible to achieve a stable 24V/1A output using this transformer? I would appreciate your feedback on whether the POE300F-24L_ can be used in this configuration or if you have any recommendations for alternative solutions.

Here are the component changes required to use the POE300F-24L_.

Thank you for your insights!

Best regards,

Francois

  • 0
    TI__Mastermind 41800 points

    Hi Francois, the transformer used in the reference design has a different turns ratio and primary inductance and higher current rating. I recommend using the same transformer used in the reference design as it's a proven solution as shown by the test report. 

    With that said, your main concern was the peak current rating. Are you using 42V as the minimum input voltage? For the .at standard (PoE+) it is 42V and not 37V (.af standard). 

  • 0 in reply to Darwin Fernandez
    Prodigy 30 points

    Hi Darwin,

    Thank you for your feedback—I really appreciate it.

    I would like to change the transformer due to availability constraints. The required quantity is not available, so we are considering using a "standard" transformer instead.

    You're right that the turn ratio and primary inductance are quite different. However, it is still suitable for our input voltage range (42V to 57V), compared to the reference design, which ranges from 18V to 57V. I believe this is why the turn ratio is particularly important, as well as the peak current.

    Yes, I am using 42V as the minimum voltage.

    I would appreciate your feedback on any alternative solutions or considerations to keep in mind when selecting this new transformer.

    Thanks again for your input!

  • 0 in reply to Francois Godreau
    TI__Mastermind 41800 points

    Hi Francois, after looking at your power requirements if you're targeting 1.25A on the output, per the standard, this puts your design greater than Class 4 and you should be looking at the Type 3 (Class 5-6) controller like TPS23730.

    Here is a reference design that would be more compliant to your specs. 

    https://www.ti.com/tool/PMP23287

    It uses a wurth transformer. They usually are quick to get samples to customers.

  • 0 in reply to Darwin Fernandez
    Prodigy 30 points

    Hi Darwing,

    Thank you for your feedback, and I apologize for any confusion. I am working to ensure compliance with PSE PD 30W. The expected output power is 25W with a minimum input voltage of 42V.

    According to the guidelines provided in SLVA305C, the primary inductance should be around 100µH, with a peak current of 2.7A, and Nps = 3.7, Npb = 7. I have found a transformer that closely meets these requirements: the LDT1069-50R from LinkCom. However, its output voltage is 12V at 2.1A, which differs from my application, which requires a 24V output.

    Has anyone used this transformer, or a similar part, in a design with a 24V output? Do you believe it could be adapted for this voltage?

    Thank you in advance for your help.

  • 0 in reply to Francois Godreau
    TI__Mastermind 41800 points

    Hi Francois,

    Thanks for clarifying the PSE spec. This means to be compliant, the PD needs to have max input power of 25.5W. This means your 24V output has to be around 0.9A. I don't think you'll have an issue with the peak input current if that is the case using the POE300F-24L. If you stay at Class 4 power levels on the PD. This transformer should be okay. Please see below example schematic we have implemented in the past.

    HPA420C_24V_sch.pdf

    I don't recommend the linkcom transformer because the primary to secondary and primary to bias has the same turns ratio. If you set the output voltage 24V, the bias will also be 24V and would damage the IC. 

  • 0 in reply to Darwin Fernandez
    Prodigy 30 points

    Hi Darwing,

    Thank you so much for your response!

    The schematic you shared as an example implements the same component changes as the first schematic I provided in my initial post—this is great.

    I have one more question about the example schematic you shared: Is it necessary to keep the gate drive output connected? It seems that Q3 is no longer connected to the secondary side.

    Thanks again for your support—I really appreciate it.

    Best regards,

  • 0 in reply to Francois Godreau
    TI__Mastermind 41800 points

    Hi Francois, that's correct, since this is a diode rectified flyback, you no longer need that driving circuitry. Thanks!