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TPS23753A: TPS23753A circuit discussion

TT_Chin
Expert 2025 points
Part Number: TPS23753A
Other Parts Discussed in Thread: PMP8803, TPS23754, TPS23751, TPS23755, TPS23758

Hi,

I would like to know is there any reason that why two different circuit connections in two piece EVM (PMP8803 and PMP4648)of TPS23753A?

Please see attached. Is it just for EMI consideration?

Thanks!

Sincerely,

Chin

TPS23753A circuit discussion.docx

  • 0
    TI__Mastermind 40100 points
    Hi Chin,

    The diode can be connected to either side (high side or low side) of the transformer. I have seen both implemented equally as much among many flyback designs. What's more important is that the dot convention is correct. In both cases, the dot on the secondary is on the low side.

    Thanks!
  • 0 in reply to Darwin Fernandez
    Expert 2025 points
    Hi Darwin,
    Okay, thanks for your answer!

    Sincerely,
    Chin
  • 0 in reply to Darwin Fernandez
    Expert 2025 points

    Hi Darwin,

    Could you please help to review the attached of TPS23753A PoE circuit and layout file and reply you comment ?

    Thank you for your help!

    PoE_review_0513.zip

    Sincerely,

    Chin

  • 0 in reply to TT_Chin
    TI__Mastermind 40100 points
    Hi Chin,

    C161 should not be installed to stay within the PoE standard spec. Other than this, the schematic looks good.

    The layout may take some time. Please give me this week to have comments regarding the layout. Thanks!
  • 0 in reply to Darwin Fernandez
    Expert 2025 points

    Hi Darwian,

    Thanks for the review and I will wait  for your layout comment, thanks!

    Following questions need you comment.

    1. By the way, for 802.3at Type1 PD , the maximum powr consumption of PD is 13W,

        if the PD consume more than 13W, TPS23753A will disconnet the load ? or PSE will stop applying power to the PD?

    2. Do you have any recommend part of 802.3st Type2 (25W) PD solution? (From technical and product life cycle point of view)

    3. What the definition of minimum input voltage for local power supply ? Please see the word file as attached.

    5148.PoE soultion.docx

    Thanks!

    Sincerely,

    Chin

  • 0 in reply to TT_Chin
    TI__Mastermind 40100 points
    Hi Chin,
    1. It depends on the design. Note the current limit on a PD is higher than a PSE. So if the PD is consuming more than 13W and there is a 100m cable, then the PSE can foldback remove power to the PD. If the PSE is not in a protection mode, then on the PD side it will depend on the whether the current limit of the PD controller is reached (then the PD will go into foldback and inrush if necessary) or the DCDC will protect itself and go into hiccup mode.

    2. I recommend TPS23751 for flyback design and TPS23754 for high efficiency application. I recommend looking at TI's TI Design library for a total system PD solution that meets your power requirements.

    3. Type 2 solutions should be 42.5V minimum while Type 1 should be 37V. This is the PoE voltage at the RJ45.
  • 0 in reply to Darwin Fernandez
    Expert 2025 points
    Hi Darwin,
    Thanks for your answer.
    Is the current limited on PD side of TPS23753A according to the resistor (connect to ground and high side MOSFET) on pin3 (CS)?
    Thanks

    Sincerely,
    Chin
  • 0 in reply to TT_Chin
    TI__Mastermind 40100 points

    Hi Chin,

    The DCDC converter's current limit will be determined by the sense resistor you reference above while the TPS23753A IC itself has a current limit (internally fixed per the datasheet spec).

    Thanks!

    Regards,

    Darwin

  • 0 in reply to Darwin Fernandez
    Expert 2025 points

    Hi Darwin,

    Okay , thanks for your answer!

    By the way, how abput the layout review? Any comment about the layout?

    Thank you!

    Sincerely,

    Chin

  • 0 in reply to TT_Chin
    TI__Mastermind 40100 points
    Hi Chin,

    The primary loop looks too large. This loop has priority over the clamping look (which is pretty good). So make sure C157 to T1 to Q12 back to C157 is tight as possible. Also C170 needs to be closer to the IC. I recommend looking at the below app note that might help with the primary look placement.

    www.ti.com/.../slua469.pdf
  • 0 in reply to Darwin Fernandez
    Expert 2025 points
    Hi Darwin,
    Okay, I will check the loop and the document.
    Thank you!


    Sincerely,
    Chin
  • 0 in reply to Darwin Fernandez
    Expert 2025 points

    Hi Darwin,

    For the schematic I sent to you before. (also see attached), do you think we should add a diode between adapter out anf PoE out?

    See attached for more detail.

    By the way,for the document SLVA306A described follow,what does the meaning of blue text ? do I need extra circuit to the patch?

    Option 3, PoE Priority
    In applications where a regulator is to follow the PoE converter VOUT, an option-3 ORing topology can be
    used as shown in Figure 9. To achieve PoE preference using option-3 ORing, the adapter voltage VADP
    must be less than the PoE output voltage, VOUT, to prevent the PSE from potentially removing power due
    to dc MPS. When used with a secondary-side synchronous rectifier, this circuit needs special attention to
    turn the rectifier off when the adapter takes over. This prevents power from flowing backwards and
    powering the primary side of the converter.

    Thanks!

    Chin

    Adapter current loop.docx

  • 0 in reply to TT_Chin
    TI__Mastermind 40100 points

    Hi Chin,

    You don't need to have a diode since your flyback is non-synch.

    If you had synchronous design then that diode (or a circuit that turns off synch FET like described in blue above) would be necessary.

    Note this design will be PoE priority since the voltage is higher than your adapter. Is this your intention? If adapter priority, I would consider the TPS23755EVM. Note this was designed for this type of application and is a much new IC. Please see below link to the EVM.

    http://www.ti.com/tool/TPS23755EVM-894

  • 0 in reply to Darwin Fernandez
    Expert 2025 points

    Hi Darwin,

    Thank you youre answer, and yes, we want PoE pripoity.Thank you for your suggestion of TPS23755EVM.

    So the flyback has sync and non-sync circuit on PoE TPS23753A design ? how to distinguish that?

    By the way, it seems there is a current loop from output to Pin1(CTL) of TPS23753A when no PoE power source presented, will it happen expected behavior ?(See ther gray trace of attached)

    Thank you

    Sincerely,

    Chin

    Adapter current loop_1.docx

  • 0 in reply to TT_Chin
    TI__Mastermind 40100 points

    Hi Chin,

    Yes TPS23753A has sync and non sync capability.

    Are you asking how to distinguish between the TPS23753A (sync and non sync) and TPS23755 (non sync) and TPS23758 (sync)? If so it's because the other two ICs are PSR controllers while TPS23753A is used for opto feedback. You can do opto feedback with the TPS23755 and then you can do sync or non sync.

    Yes the 12V adapter will drive the secondary component feedback. However, note if there is no PoE connected, then the PWM controller is OFF. Then when PoE is connected, then PD will turn on and PWM controller will start switching. Since the output voltage on PoE is higher in your schematic, PoE will be prioritized.

  • 0 in reply to Darwin Fernandez
    Expert 2025 points

    Hi Darwin,

    Okay, Thanks for your answer!

    Sincerely,

    Chin