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TPS23731: POE DESIGN || DC ADAPTER PRIORITY REF DESIGN

Hemal Patel
Intellectual 345 points
Part Number: TPS23731
Other Parts Discussed in Thread: PMP22806, , PMP22477

Hii Team,

We want to give priority to DC Adapter when both POE and DC Supply [12V DC Adapter] present as a input supply source. We are using TPS23731 PD Controller in POE design [ref design link:- www.ti.com/.../PMP22806] 

Requirement:- So suppose if a device is running on POE Supply and in this condition 12V Adapter DC supply entered then according to DC Supply as a priority, supply need to switch power from POE  to DC Adapter and switching must be seamlessly so that device able to switch smoothly without Reboot. And now further by taking this scenario continue suppose DC Adapter Power supply removed [POE supply still plugged in] then device supply again get back to POE as input source smoothly without Reboot.

Additionally we have checked oring solution for TPS23753APW [Ref link:- www.ti.com/.../slva306a.pdf] and below option 3 Adapter seems more suitable according to us so please share your feedback.

And Provide ref. design for Oring Solution of TPS23731 PD Controller.

  • 0
    TI__Mastermind 37081 points

    Hi Hemal,

    Thanks for reaching out.

    You can considering using TPS23731's reference circuit (PMP22806) + PMP22477’s secondary oring circuit (PMP22477). It will lower the PoE output voltage when 12-V adapter is added. Please see the heighted circuit in below.

    Best regards,

    Diang

  • 0 in reply to Diang Xing
    Intellectual 345 points

    Hii Diang,

    Thanks for the reply.

    Point 1: This additional connection which you shown here to give adapter priority is for TPS23730RMT but can you please provide full ref. circuit with this adapter priority connection for TPS23731. 

    Point 2: Here you mentioned that below circuit will lower the POE when adapter voltage added but how much lower? Provide value of that lower voltage?

    Point 3: Can you explain how this logic work means if we lower POE then how it give adapter as priority? please explain scenario. 

    Point 4: And if we consider this below logic for adapter priority then please confirm Device [TPS23731] not going to reboot for below two switching case.

    Case 1:- if a device is running on POE Supply and in this condition 12V Adapter DC supply entered then according to DC Supply as a priority, supply need to switch power from POE  to DC Adapter.

    Case 2:- And now further by taking this scenario continue suppose DC Adapter Power supply removed [POE supply still plugged in] then device supply again get back to POE as input source.

    Point 5: For above both case can you please how much time it take to switch power from POE to DC and DC to POE individual case?

     

  • 0 in reply to Hemal Patel
    TI__Mastermind 37081 points

    Hi Hemal,

    Thanks for your reply.

    We will go though your questions and get back to you before Feb/27.

    Best regards,

    Diang

  • 0 in reply to Diang Xing
    TI__Mastermind 37081 points

    Hi Hemal,

    Thanks for your patience. Please see my comments below: 

    Point 1: This additional connection which you shown here to give adapter priority is for TPS23730RMT but can you please provide full ref. circuit with this adapter priority connection for TPS23731. 

    • Sorry we do not have a TPS23731 design with such circuit. But the adapter structure is the same. And PMP22477 is also a flyback converter.

    Point 2: Here you mentioned that below circuit will lower the POE when adapter voltage added but how much lower? Provide value of that lower voltage?

    • The FB voltage is 1.75 V. And the AUX winding voltage to SEC voltage is 1:1 at rectifier on time, which makes the desired AUX voltage = 12 V at rectifier on. Approximately, when Q5 is off, Vout = 1.75V / (4.99k || 35.7k) x (4.99k || 35.7k + 24.9k) = 11.7 V; when Q5 is on, Vout = 1.75V / (4.99k) x (4.99k+ 24.9k) = 10.5 V. You can change Q5 on/off by the opto.

    Point 3: Can you explain how this logic work means if we lower POE then how it give adapter as priority? please explain scenario. 

    • When J14 is short. Q5 is off; when J14 is open, Q5 is on.

    Point 4: And if we consider this below logic for adapter priority then please confirm Device [TPS23731] not going to reboot for below two switching case.

    Case 1:- if a device is running on POE Supply and in this condition 12V Adapter DC supply entered then according to DC Supply as a priority, supply need to switch power from POE  to DC Adapter.

    Case 2:- And now further by taking this scenario continue suppose DC Adapter Power supply removed [POE supply still plugged in] then device supply again get back to POE as input source.

    • Yes, it won’t reboot if the load can work at 10.5-V and 12-V. In a short term the Vout may drop as the below example.

    Point 5: For above both case can you please how much time it take to switch power from POE to DC and DC to POE individual case?

    • You can see the below example waveforms. It is not PMP22477 but with similar secondary side adapter circuit.

    PoE->Adapter Transient (dual-PD, hitless):

     

    Adapter->PoE Transient (dual-PD, hitless):

    Best regards,

    Diang