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TPS23756: schematic review support

Bruce li
Genius 5580 points
Part Number: TPS23756
Other Parts Discussed in Thread: TPS23754EVM-383

Dear TI Experts,

Attached is my customer's first version of TPS23756 design, could you kindly help to review and give some advices?

Besides, there are other concerns from customer, could you kindly help to advise? thanks a lot.

1) customer use 100M phy, the power from POE is from 1,2,3,6 pin or 4,5,7,8 pin of RJ45?

2) customer refered TPS23754EVM-383's guide(attached slvu304) , there are some key components such as T1, J3, D9,D10, are these devices mandatory from slvu304 or customer can change these devices from other brand? 

2772.slvu304c.pdf

PX30 POE 0708.pdf

  • 0
    TI__Mastermind 40100 points

    Hi Bruce,

    This is currently being looked into and an answer will be given when available. Is a review by end of Wednesday okay? Thanks!

  • 0 in reply to Darwin Fernandez
    Genius 5580 points

    Dear Darwin,

    Thanks a lot for your support, I'd appreciate if it'll be reviewed earier. 

  • 0 in reply to Bruce li
    TI__Mastermind 40100 points

    Hi Bruce,

    1) I recommend looking at the white paper below that goes into this is great detail. But yes for Type 2 applications it will be 2 pair power so either 12/36 or 45/78 will be powered.

    https://ethernetalliance.org/wp-content/uploads/2018/04/WP_EA_Overview8023bt_FINAL.pdf

    2) It is recommended to use all the same components (or similar spec components) as the EVM since this is a validated design. If component spec and values change, then the operation may not be guaranteed.

    Please see comments below regarding your schematic:

    • C389 should not be 0.1uF. The standard has a max input cap spec and C2053 meets the requirement. C389 should be 1nF.
    • D213 is a 40V schottky. This needs to be a TVS for protection. Please use at least SMAJ58A
    • I see that T2P is not being used. I recommend looking at the below FAQ that discusses why T2P should be used. 

    https://e2e.ti.com/support/power-management/f/196/p/723192/2668066?tisearch=e2e-sitesearch&keymatch=t2p%20darwin%20faq#2668066

    • pin 17 of IC should NOT be floating. I recommend at least putting a zero ohm resistor to RTN
    • Since you are not using an external adapter, D215 C2054 can be a short
    • U2003 is not connected correctly, it needs to connect to CTL and not VB
    • PQ53 needs to be a PMOS
    • For the power transformer I have not used the PA3342 in the past or typically see a dual output forward topology in the past. As such, I cannot comment if you have the secondary windings connected correctly. But it does not look correct on the schematic after looking at the transformer datasheet. Why not use what we recommend on the EVM?
    • The output inductor is too small for a 12V output. It needs to be at least 22uH like in the EVM. Note for the forward, the energy is stored in the output inductor. The consideration is different on the output inductor than it is for a flyback (which is used for filtering)
    • D206 TVS and D207 is overrated. This is for the bias winding which isn't high power. You can use a lower current rated diode here.
  • 0 in reply to Darwin Fernandez
    Genius 5580 points

    Dear Darwin,

    Thank you so much for your detailed suggestion